Nervous system

 

Nervous system

Objectives

At the end of this lecture, student will be able to

• List the structures of nervous system

• Explain various functions of nervous system

• Describe the basic histology of nervous tissue

• Differentiate between various types of neurons

• Explain the neurohumoral transmission of nervous system

• Describe the role of neurotransmitter in the neurohumoral transmission

• Explain the organisation of nervous system

• Distinguish the physiology of various nervous systems

• List the various parts of brain

• Describe the protective coverings of brain

• Explain the importance of blood brain barrier

• Describe the role of cerebrospinal fluid

• List the various parts of brain stem

• Describe the anatomy of brain stem

• Explain the physiology and functions of various parts of brain stem

• Describe the anatomy of cerebellum

• Explain the functions of cerebellum

• List the various components of diencephalon

• Describe the physiology and functions of components of diencephalon

• Describe the role of hypothalamus

• Describe the functions of circumventricular organs

• Explain the structure and function of cerebrum

• List and locate the lobes of the cerebrum

• Describe the nuclei that comprise the basal ganglia

• List the structures of the limbic system

• Describe the functions of limbic system

• Explain the locations and functions of various areas of cerebral cortex

• Define “brain waves”

• Indicate the significance of brain waves

• List various cranial nerves

• Identify the cranial nerves by name, number and type

• Describe the location and functions of cranial nerves

• Describe the protective structures of spinal cord

• Describe the gross anatomical features of the spinal cord

• Explain spinal nerves connected to the spinal cord

• Describe the functions of the major sensory and motor tracts of the spinal cord

• Describe the functional components of a reflex arc and the ways reflexes maintain homeostasis

• Describe pre ganglionic and post ganglionic neurons of the autonomic nervous system

• Compare the anatomical components of the sympathetic and parasympathetic divisions of the autonomic nervous system

• Describe the components of an autonomic reflex

• Explain the relationship of the hypothalamus to the ANS

Content

−Structures of nervous system

−Functions of nervous system

−Histology of nervous tissue

−Types of neurons

•Neurohumoral transmission

•Organization of nervous system

•Physiology of nervous systems

•Parts of brain

•Protective coverings of brain

•Blood brain barrier

•Cerebrospinal fluid

Anatomy and Physiology of

– Brain stem

– Cerebellum

– Diencephalon

– Hypothalamus

– Circumventricular organs

– Cerebrum

– Basal ganglia

– Limbic system

• Physiology of cerebral cortex

• Brain waves

Cranial nerves

– Types

– Location

– Functions

• Spinal cord

– Protective structures

– Anatomical features

– Sesory and motor tract

• Spinal nerves

• Reflex arc

• Autonomic nervous system

– Sympathetic

– Parasympathetic

• Autonomic reflex

• Hypothalamus and ANS

Nervous System

• Mass of 2 kg, 3% of total body

• One of the smallest and yet the most complex systems

• The structures include:

– Brain

– Cranial nerves and their branches

– Spinal cord

– Spinal nerves and their branches

– Ganglia

– Enteric plexuses

– Sensory receptors

• The skull encloses the brain – contains about 100 billion neurons

• 12 pairs cranial nerves, numbered I - XII

• Emerge from the base of the brain

• Nerve:

– Bundle of axons + associated connective tissue & blood vessels

– Lies outside the brain and spinal cord

– Follows a defined path

– Serves a specific region of the body

Cranial Nerves

Name of cranial nerves

      0lfactory nerve

      Optic nerve

       Oculomotor nerve

      Trochlear nerve

      Trigeminal nerve

     Abducent nerve

      Facial nerve

      Vestibulocochlear nerve

      Glossopharyngeal nerve

      Vagus nerve

     Accessory nerve

      Hypoglossal nerve

• The Spinal Cord

– Connects to the brain through the foramen magnum of the skull

– Encircled by the bones of the vertebral column

– Contains about 100 million neurons

– 31 pairs of spinal nerves emerge from the spinal cord

Spinal Nerve

• 31 pairs

• Spinal nerve follows the name of corresponding vertebra column.

• Consists cervical spinal nerve, thoracic spinal nerve, lumbar spinal nerve, sacral spinal nerve and coccyx spinal nerve.

• Emerge from spinal cord and through the intervertebral foramina of vertebra.

• Spinal nerves:

1.      8 pairs of cervical spinal nerves

2.      12 pairs of thoracic spinal nerves

3.      5 pairs of lumbar spinal nerves.

4.      5 pairs of sacral spinal nerves

5.      1 pairs of coccyx spinal nerves.

• Ganglia

– Consisting primarily of neuron cell bodies

– Located outside the brain and spinal cord

Functions of Nervous System

• Carries out a complex array of tasks

• Allows us to sense various smells

• Produce speech

• Remember past events

• Provides signals that control body movements

• Regulates the operation of internal organs

• These diverse activities can be grouped into three basic functions:

– Sensory

– Integrative

– Motor

Sensory function

• Sensory receptors detect internal or external stimuli

• Carried into the brain and spinal cord through cranial and spinal nerves

 • Sensory receptor

– Dendrites of sensory neurons

– Specialized cells that monitor changes in the internal or external environment

Integrative function

• Processes sensory information by analyzing and storing some of it and by making decisions

• Perception - the conscious awareness of sensory stimuli

Motor function

• Elicit an appropriate motor response by activating effectors through cranial and spinal nerves

• Causes muscles to contract and glands to secrete

Histology of Nervous Tissue

• Neurons:

– Provide most of the unique functions of the nervous system

• Neuroglia:

– Support, nourish, protect the neurons and maintain homeostasis

– Smaller than neurons, 5 to 50 times more numerous

– Do not generate or propagate action potentials

The cell body (Perikaryon or soma)

• Contains a nucleus & typical cellular organelles: lysosomes, mitochondria, and a golgi complex and free ribosomes

• Prominent clusters of rough ER (nissl bodies)

• The cytoskeleton: Neurofibrils & microtubules

• Lipofuscin - Product of neuronal lysosomes

Nerve Fiber

• Neuronal process (extension) emerges from the cell body of a neuron

• 2 kinds of processes: multiple dendrites and a single axon

• Dendrites (little trees)

– The receiving or input portions of a neuron

– Short, tapering, and highly branched

– Cytoplasm contains Nissl bodies, mitochondria, and other organelles

• Axon

– Propagates nerve impulses toward another neuron, a muscle fiber, or a gland cell

– Long, thin, cylindrical projection that often joins the cell body

– At a cone-shaped elevation called the axon hillock

– Closest to the axon hillock is the initial segment

• The cytoplasm of an axon, called axoplasm

• Surrounded by a plasma membrane known as the axolemma

• Side branches - axon collaterals

• The axon and its collaterals end by dividing into many fine processes called axon terminals

Structural Classification of Neurons

Functional classification of Neurons

• Motor or efferent neurons

• Sensory or afferent neurons

• Interneuron or association neurons

Neuroglial Cells

Astrocytes – Cover capillaries of brain to form BBB and help regulate passage of molecules from blood to brain

Oligodendrocytes – Form myelin sheath around central axons producing the white matter of CNS

• Microglia – Phagocytic amoeboid cells in CNS, remove foreign and degenerated material from brain

• Ependymal cells - Line the ventricles or brain cavities and central canal of spinal cord

• Schwann cells - Surround axons of all peripheral nerve fibres, form the myelin sheath

• Satellite cells - Supply nutrients to the surrounding neurons and also have some structural function, protective, cushioning cells

Myelination

• Multilayered lipid and protein covering

• Electrically insulates the axon

• Increases the speed of nerve impulse conduction

• Two types of neuroglia produce myelin sheaths:

– Schwann cells (in the PNS)

– Oligodendrocytes (in the CNS)

• Axons without such a covering – unmyelinated

Collections of nervous tissue

• Nerve

– Bundle of axons

– Located in the PNS

– Cranial nerves connect the brain to the periphery

– Spinal nerves connect the spinal cord to the periphery

• Tract

– A bundle of axons

– Located in the CNS

– Interconnect neurons in the spinal cord and brain

• White matter

– Composed primarily of myelinated axons

– Appear whitish

• Gray matter

– Neuronal cell bodies, dendrites, unmyelinated axons, axon terminals & neuroglia

– Appears grayish; Nissl bodies impart a gray color



Neurohumoral Transmission

Plasma membranes of presynaptic and postsynaptic neurons - separated by the synaptic cleft

Nerve impulses cannot conduct across the synaptic cleft

In response to a nerve impulse, the presynaptic neuron releases a neurotransmitter

Diffuses through the fluid in the synaptic cleft binds to receptors in the plasma membrane of the postsynaptic neuron

The postsynaptic neuron receives the chemical signal produces a postsynaptic potential

Synapse

Role of Pre and Post synaptic Neurons

Thus, the presynaptic neuron converts an lectrical signal (nerve impulse) into a chemical signal (released neurotransmitter)

The postsynaptic neuron receives the chemical signal and in turn generates an electrical signal (postsynaptic potential)

Neurohumoral Transmission

A nerve impulse arrives at a synaptic end bulb of a presynaptic axon

The depolarizing phase of the nerve impulse opens voltage gated ca channels

Calcium ions are more concentrated in the EC fluid - flows inward through the opened channels

Increase in the concentration of ca - triggers exocytosis of the synaptic vesicles

As vesicle membranes merge with the plasma membrane, neurotransmitter released into the synaptic cleft

Each synaptic vesicle contains several thousand molecules of neurotransmitter

Diffuse across the synaptic cleft and bind to neurotransmitter receptors in the postsynaptic neuron’s plasma membrane

Binding of neurotransmitter – opens the channels and allows particular ions to flow across the membrane

As ions flow through the opened channels, the voltage across the membrane changes

This change in membrane voltage is a postsynaptic potential

Postsynaptic potential may be a depolarization or a hyperpolarization

When a depolarizing postsynaptic potential reaches threshold, it triggers an action potential in the axon of the postsynaptic neuron

Excitatory Postsynaptic Potentials

 • A neurotransmitter that depolarizes the postsynaptic membrane is excitatory

• A depolarizing postsynaptic potential - Excitatory postsynaptic potential (EPSP)

• Although a single EPSP normally does not initiate a nerve impulse, the postsynaptic cell does become more excitable

Inhibitory Postsynaptic Potentials

• A neurotransmitter that causes hyperpolarization of the postsynaptic membrane is inhibitory

• During hyperpolarization, generation of an action potential is more difficult

• Membrane potential becomes inside more negative

• Even farther from threshold than in its resting state

• A hyperpolarizing postsynaptic potential - an inhibitory post synaptic potential (IPSP)

Neurotransmitter Receptors

• Ionotropic receptor

• Metabotropic Receptor

Removal of the Neurotransmitter

Diffusion

• Some diffuse away from the synaptic cleft

Enzymatic degradation

• Inactivated through enzymatic degradation

• Example - the enzyme acetylcholinesterase breaks down acetylcholine in the synaptic cleft

Uptake by cells

• Many neurotransmitters are actively transported back into the neuron that released them (reuptake)

• Others are transported into neighboring neuroglia (uptake)

Neurotransmitters

• Neurotransmitters can be divided into two classes based on size: small-molecule neurotransmitters and neuropeptides

• The small-molecule neurotransmitters include:

– Acetylcholine, amino acids, biogenic amines, ATP and other purines, and nitric oxide

• Neuropeptides:

– Substance P, encephalin, endorphin and dynorphin

Organisation of Nervous system

Organisation of the CNS

• Consists of the brain and spinal cord

• Processes many different kinds of incoming sensory information

• The source of thoughts, emotions, and memories

• Most nerve impulses that stimulate muscles to contract and glands to secrete originate in the CNS

Organization of the PNS 

• Includes all nervous tissue outside the CNS

• Components of the PNS include:

– Cranial nerves and their branches

– Spinal nerves and their branches

– Ganglia

– Sensory receptors

• Subdivided into SNS, ANS & ENS

Somatic Nervous System

Consists of:

Sensory neurons

• Convey information from somatic receptors in the head, body wall, and limbs

• From receptors for the special senses of vision, hearing, taste, and smell to the CNS

Motor neurons

• Conduct impulses from the CNS to skeletal muscles only

• Motor responses - voluntary

Autonomic Nervous System

Sensory neurons

Motor neurons

• Convey information from autonomic sensory receptors

• Convey information from autonomic sensory receptors

 

• Located primarily in visceral organs to the CNS

• Conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands

• Involuntary

• Motor part - two branches

• Parasympathetic division - “rest-and-digest” activities

• Sympathetic division - “fight-or-flight” responses

Enteric Nervous System

• “Brain of the gut,” involuntary

• Sensory neurons

– Monitor chemical changes and stretching within GIT

• Motor neurons

– Govern:

               • Contraction of GI tract smooth muscle to propel food

               • Secretions of the GI tract organs such as gastric acid

               • Activity of GIT endocrine cells - secrete hormones

Action potential

• An action potential (AP) or impulse is a sequence of rapidly occurring events that decrease and reverse the membrane potential and then eventually restore it to the resting state

• Two main phases:

– A depolarizing phase

– A repolarizing phase

Brain

• The adult brain consists of four major parts:

– Brain stem

– Cerebellum

– Diencephalon

– Cerebrum

• Brain stem

– Continuous with the spinal cord

– Consists of the medulla oblongata, pons, and midbrain

• Cerebellum

– Posterior to the brain stem

• Diencephalon

– Superior to the brain stem

– Consists of the thalamus, hypothalamus, and epithalamus

• Cerebrum

– Largest part of the brain

– Supported on the diencephalon and brain stem

Protective Coverings of the Brain

• The cranium and the cranial meninges surround and protect the brain

• The cranial meninges

– Continuous with spinal meninges

– Outer dura mater

– Middle arachnoid mater

– Inner pia mater

Cranial meninges

Extensions of the dura mater

• Separate parts of the brain:

• Falx cerebri

– Separates the two hemispheres (sides) of the cerebrum

• Falx cerebelli

– Separates the two hemispheres of the cerebellum

• Tentorium cerebelli

– Separates the cerebrum from the cerebellum






Blood flow to Brain

• Blood flows to the brain - via the internal carotid and vertebral arteries

• Internal jugular veins return blood from head to heart

• Consumes about 20% of oxygen & glucose used even at rest

• Neurons synthesize ATP from glucose using oxygen

• When increases in a region of the brain, blood flow to that area also increases

• Virtually no glucose is stored in the brain (supply of glucose must be continuous)

Blood Brain Barrier

• Protects brain cells from harmful substances and pathogens

• Prevents passage of many substances from blood into brain tissue

• Consists mainly of tight junctions - seal together the endothelial cells of brain capillaries

• Along with a thick basement membrane around the capillaries

• The processes of many astrocytes, press up against the capillaries

• Secrete chemicals - maintain the permeability characteristics of the tight junctions

• A few water-soluble substances (glucose) cross BBB by Active transport

• Others - creatinine, urea, and most ions, cross the BBB very slowly

• Proteins and most antibiotic drugs—do not pass at all

• However, lipid-soluble substances, such as oxygen, carbon dioxide, alcohol, and most anesthetic agents, easily cross

Cerebrospinal Fluid

• Clear, colorless liquid

• Protects the brain and spinal cord from chemical and physical injuries

• Carries oxygen, glucose, and other needed chemicals from the blood to neurons and neuroglia

• CSF continuously circulates through cavities in the brain and spinal cord and in the subarachnoid space

• The total volume of CSF is 80 to 150 ml

• CSF contains glucose, proteins, lactic acid, urea, cations (na, K, ca2, mg2), and anions (cl and HCO3)

• Also contains some WBC

Role of CSF

• The CSF contributes to homeostasis in three main ways:

Mechanical protection

• Shock-absorbing medium; protects the delicate tissues from jolts; buoys the brain so that it “floats” in the cranial cavity

Chemical protection

• Provides an optimal chemical environment for accurate neuronal signaling

• Even slight changes - seriously disrupt production AP

Circulation

• CSF allows exchange of nutrients and waste products between the blood and nervous tissue

Ventricles

• CSF - filled cavities within the brain

A lateral ventricle

• Located in each hemisphere of the cerebrum

• Anteriorly, the lateral ventricles are separated by a thin membrane - Septum pellucidum

The third ventricle

• Narrow cavity along the midline

• Superior to the hypothalamus

• Between the right and left halves of the thalamus

The fourth ventricle

• Lies between the brain stem and the cerebellum

• Contains some white blood cells

Ventricles of Brain

Formation of CSF in the Ventricles

• The sites of CSF production are the choroid plexuses - networks of blood capillaries in the walls of the ventricles

• Ependymal cells covering the capillaries form CSF from blood plasma by filtration and secretion

• Ependymal cells are joined by tight junctions

• This blood–CSF barrier permits certain substances to enter the CSF but excludes others

• Thus, protects the brain and spinal cord from potentially harmful blood borne substances

Circulation of CSF

• The CSF formed in the choroid plexuses of each lateral ventricle

• Flows into the third ventricle through two narrow, oval openings, the interventricular foramina

• The fluid then flows through the aqueduct of the midbrain (cerebral aqueduct)

• Passes through the midbrain, into the fourth ventricle

• The choroid plexus of the fourth ventricle contributes more fluid

• CSF enters the subarachnoid space through three openings in the roof of the fourth ventricle: a median aperture and the paired lateral apertures, one on each side

• CSF then circulates in the central canal of the spinal cord and in the subarachnoid space around the surface of the brain and spinal cord

CSF Flow

Choroid plexus

Ventricles of brain and flow of CSF

Brain Stem

• Part of the brain between the spinal cord and the diencephalon

• It consists of three structures:

– Medulla oblongata

– Pons

– Midbrain

Reticular formation

• Extends through the brain stem Netlike region of interspersed gray and white matter

Medulla oblongata (Medulla)

• Continuous with spinal cord

• Forms the inferior part of brain stem

• Begins at the foramen magnum

• Extends to the inferior border of the po

• The medulla’s white matter contains all sensory (ascending) tracts and motor (descending)

• Anterior aspect of the medulla has - pyramids

Medulla oblongata - Pyramids

• Pyramids - Large corticospinal tracts, pass from the cerebrum to the spinal cord

• Control voluntary movements of the limbs and trunk

• Just superior to the junction of the medulla with the spinal cord – decussation of pyramids

Medullary nuclei

• The medulla also contains several nuclei

• Some of these nuclei control vital body functions

• Cardiovascular center

– Regulates the rate and force of the heartbeat and the diameter of blood vessels

• The medullary rhythmicity area - respiratory center

– Adjusts the basic rhythm of breathing

Medulla also control reflexes for:

• The vomiting center

• The deglutition center

• Sneezing

• Coughing

• Hiccupping

Olive

• Just lateral to each pyramid is an oval-shaped swelling called an olive

Inferior olivary nucleus

• Receives input from the cerebral cortex red nucleus of the midbrain, and spinal cord

• Regulate the activity of cerebellar neurons

• Provides instructions that the cerebellum uses to make adjustments to muscle activity as you learn new motor skills

Left gracile nucleus and cuneate nucleus

• Nuclei associated with sensations of touch, pressure, vibration, and conscious proprioception

• Located in the posterior part of the medulla

Nuclei of sensory pathways

Medulla also contains nuclei - components of sensory pathways for: gustation (taste), audition (hearing) & equilibrium (balance)

The gustatory nucleus

• Part of the gustatory pathway from the tongue to the brain

The cochlear nuclei

• Part of the auditory pathway from the inner ear to the brain

The vestibular nuclei

• Components of the equilibrium pathway from the inner ear to the brain

Medullary nuclei – Associated to Cranial Nerves

• Medulla contains nuclei associated with five pairs of cranial nerves:

– Vestibulocochlear (VIII) nerves

– Glossopharyngeal (IX) nerves

– Vagus (X) nerves

– Accessory (XI) nerves (cranial portion)

– Hypoglossal (XII) nerves

Pons

• Lies superior to the medulla and anterior to the cerebellum

• Is a bridge that connects different parts of the brain with one another

• Connections are provided by bundles of axons

• Consists of nuclei, sensory tracts, and motor tracts

• Along with the medulla, the pons contains vestibular nuclei that are components of the equilibrium pathway

• Other nuclei in the pons: The pneumotaxic area and the apneustic area of the respiratory center

• Contains nuclei associated with the following four pairs of cranial nerves:

– Trigeminal (V) nerves

– Abducens (VI) nerves


– Facial (VII) nerves– Vestibulocochlear (VIII) nerves  

Midbrain (Mesencephalon)

• Extends from the pons to the diencephalon

• The midbrain contains both nuclei and tracts

• The anterior part contains paired bundles of axons – cerebral peduncles

• The cerebral peduncles consist of axons of:

– Corticospinal

– Corticopontine

– Corticobulbar tracts

• Conduct nerve impulses from motor areas in the cerebral cortex to the spinal cord, pons and medulla

Tectum

• The posterior part of the midbrain; Contains four rounded elevations

Superior colliculi (two superior elevations)

• Reflex centers for certain visual activities

• Visual stimuli elicit eye movements for tracking moving images & scanning stationary images

• Reflexes for movements of the head, eyes, and trunk in response to visual stimuli

Inferior colliculi (two inferior elevations)

• Part of the auditory pathway

• Relay impulses from the receptors for hearing in the inner ear to the brain

• Reflex centers for the startle reflex, sudden movements of the head, eyes, and trunk

Reticular Formation

• Brain stem consists of small clusters of neuronal cell bodies (gray matter)

• Interspersed among small bundles of myelinated axons (white matter)

• Exhibit a netlike arrangement is known as the reticular formation

• Extends from the upper part of the spinal cord, throughout the brain stem, and into the lower part of the diencephalon

• Neurons within the reticular formation have both ascending (sensory) and descending (motor) functions

Reticular activating system (RAS)

• Part of the reticular formation

• Consists of sensory axons that project to cerebral cortex

• Helps maintain consciousness and is active during awakening from sleep

• Descending functions are to help regulate posture and muscle tone, the slight degree of contraction in normal resting muscles

Cerebellum

• Occupies the inferior and posterior aspects of the cranial cavity

• Has highly folded surface – greatly increases the surface area

• Posterior to the medulla and pons

• Inferior to the posterior portion of the cerebrum

• A deep groove known as the transverse fissure, along with the tentorium cerebelli

• Supports the posterior part of the cerebrum, separate the cerebellum from the cerebrum

Cerebellum – Superior or inferior view

• In superior or inferior views - shape of cerebellum resembles a butterfly

• Central constricted area - vermis (Worm)

• The lateral “wings” or lobes - cerebellar hemispheres

• Each hemisphere consists of lobes separated by deep and distinct fissures

Cerebellum lobes

• The anterior lobe and posterior lobe govern subconscious aspects of skeletal muscle movements

• The flocculonodular lobe on the inferior surface contributes to equilibrium and balance

Cerebellar cortex

• The superficial layer of the cerebellum

• Consists of gray matter in a series of slender

• Parallel folds called folia (leaves)

• Deep to the gray matter are tracts of white matter called arbor vitae (tree of life) resemble branches of a tree

Cerebellar nuclei:

• Regions of gray matter; Deeper within the white matter

• Give rise to axons carrying impulses from the cerebellum to other brain centers

Functions of Cerebellum

Primary Function

• Evaluate how well movements initiated by motor areas in the cerebrum are actually being carried out

• Detects the discrepancies in movements

• Sends feedback signals to motor areas of the cerebral cortex, via thalamus

• Thus help correct the errors

• Smooth the movements

• Coordinate complex sequences of skeletal muscle contractions

• Main brain region that regulates posture and balance

• Make possible all skilled muscular activities, from catching a baseball to dancing to speaking

• May also have non motor functions such as cognition (acquisition of knowledge) and language processing

Diencephalon

• Extends from the brain stem to the cerebrum

• Surrounds the third ventricle

• Includes: Thalamus, hypothalamus and epithalamus

 

Thalamus

• Consists of paired oval masses of gray matter organized into nuclei with interspersed tracts of white matter

• Axons that connect thalamus and cerebral cortex pass through internal capsule - thick band of white matter Lateral to thalamus

Internal Capsule

• Intermediate mass

Thalamus (Interthalamic adhesion)

– A bridge of gray matter

– Joins the right and left halves of the thalamus

• Internal medullary lamina

– A vertical y-shaped sheet of white matter

– Divides the gray matter of the right and left sides of the thalamus

– Consists of myelinated axons - enter and leave the various thalamic nuclei

Importance of Thalamus

• Major relay station

– For most sensory impulses that reach the primary sensory areas of the cerebral cortex from the spinal cord and brain stem

• Contributes to motor functions

– By transmitting information from the cerebellum and basal ganglia to the primary motor area of the cerebral cortex

• Role - maintenance of consciousness

Thalamic Nuclei

• Based on positions and functions

Anterior nucleus

• Input from the hypothalamus & sends output to the limbic system

• Functions in emotions and memory

Medial nuclei

• Input from the limbic system and basal ganglia & send output to the cerebral cortex

• Function in emotions, learning, memory, and cognition

Nuclei in the lateral group

• Receive input from the limbic system, superior colliculi, and cerebral cortex & send output to the cerebral cortex

• Dorsal nucleus functions in the expression of emotions

• Posterior nucleus and pulvinar nucleus help integrate sensory information

Intralaminar nuclei

• Lie within the internal medullary lamina

• Make connections with the reticular formation, cerebellum, basal ganglia & wide areas of the cerebral cortex

• Function in arousal (activation of the cerebral cortex) and integration of sensory and motor information

Midline nucleus

• Forms a thin band adjacent to the third ventricle

• Function in memory and olfaction

Reticular nucleus

• Surrounds the lateral aspect of the thalamus, next to the internal capsule

• Monitors, filters and integrates activities of other thalamic nuclei

Ventral group

• Five nuclei are part of the ventral group

• Ventral anterior nucleus, ventral lateral nucleus, ventral posterior nucleus, lateral geniculate nucleus, medial geniculate nucleus

Ventral Group Nuclei

Ventral anterior nucleus

• Receives input from the basal ganglia

• Sends output to motor areas of the cerebral cortex

• Plays a role in movement control

Ventral lateral nucleus

• Receives input from the cerebellum and basal ganglia

• Sends output to motor areas of the cerebral cortex

• Plays a role in movement control

Lateral geniculate nucleus

• Relays visual impulses for sight from the retina to the primary visual area of the cerebral cortex

Medial geniculate nucleus

• Relays auditory impulses for hearing from the ear to the primary auditory area of the cerebral cortex

Ventral posterior nucleus

• Relays impulses for somatic sensations from the face and body to the cerebral cortex.

• Somatic sensations - touch, pressure, vibration, itch, tickle temperature, pain & proprioception

Hypothalamus

• Small part of the diencephalon

• Located inferior to the thalamus

• Composed of a dozen or so nuclei in four major regions: – Mamillary, Tuberal, Supraoptic & Preoptic

Hypothalamic Regions

Mammillary region

• Adjacent to the midbrain

• Includes the mammillary bodies & posterior hypothalamic nuclei

• Mammillary bodies - two, small, rounded projections that serve as relay stations for reflexes related to the sense of smell

Tuberal region

• Widest part of the hypothalamus

• Includes dorsomedial, ventromedial & arcuate nucleus

• Stalk like infundibulum - connects the pituitary gland to hypothalamus

• Median eminence - slightly raised region, encircles the infundibulum

Supraoptic region

• Lies superior to the optic chiasm

• Contains paraventricular, supraoptic, anterior hypothalamic & suprachiasmatic nucleus

Preoptic region

• Anterior to the supraoptic region

• Considered part of hypothalamus (regulates certain autonomic activities)

• Contains the medial and lateral preoptic nuclei

Role of Hypothalamus

• Controls many body activities

• Major regulators of homeostasis

• Monitor osmotic pressure, glucose level, certain hormone concentrations & temperature of blood

• Has several very important connections with the pituitary gland

• Produces a variety of hormones

• Some functions can be attributed to specific hypothalamic nuclei

Functions of Hypothalamus

Control of the ANS

• Controls and integrates activities of the ANS

• Example: Regulation of HR, movement of food through the GIT & contraction of the urinary bladder

Regulation of emotional and behavioral patterns

• Together with the limbic system

• Participates in expressions of:

– Rage, aggression, pain, pleasure & behavioral patterns related to sexual arousal

Production of hormones

• Releasing hormones and inhibiting hormones

• Released into capillary networks in the median eminence

• Bloodstream carries these hormones to anterior lobe of the pituitary

• Cell bodies secretes two hormones (oxytocin, ADH)

• Transported to the posterior pituitary and release

Regulation of eating and drinking

• Through feeding center, satiety center and thirst center

Control of body temperature

• As body’s thermostat

• Directs the ANS to stimulate activities that promote heat loss or production and retention

Regulation of circadian rhythms

• Suprachiasmatic nucleus serves as the body’s internal biological clock

• Establishes the circadian rhythms

• Receives input from the eyes (retina)

• Sends output to other hypothalamic nuclei, the reticular formation, & pineal gland

Epithalamus

• Small region superior and posterior to the thalamus

• Consists of:

– Pineal gland

– Habenular nuclei

Pineal gland

• Size of a small pea

• Secretes the hormone melatonin

• Contribute to the setting of the body’s biological clock

• Controlled by the supra chiasmatic nucleus of hypothalamus

• Promote sleepiness

Habenular nuclei

• Involved in olfaction

• Emotional responses to odors

Circumventricular organs (CVOs)

• Parts of the diencephalon

• Can monitor chemical changes in the blood (lack BBB)

• Include part of:

Hypothalamus, pineal gland, pituitary gland, and few other nearby structures

• Functionally:

– These regions coordinate homeostatic activities of the endocrine and nervous systems

– Regulation of BP, fluid balance, hunger, and thirst

Cerebrum- Seat of Intelligence

• Provides us with the ability to read, write & speak

• Make calculations and compose music

• To remember the past, plan for the future & imagine things

• The cerebrum consists of:

– Outer cerebral cortex

– An internal region of cerebral white matter

– Gray matter nuclei deep within the white matter

Cerebral cortex

• Region of gray matter

• Forms the outer rim of the cerebrum

• Contains billions of neurons

Gyri or convolutions - folds

Fissures - deepest grooves between folds

Sulci - shallower grooves between folds are

Longitudinal fissure - separates the cerebrum into cerebral hemispheres

Corpus callosum

• Cerebral hemispheres are connected internally by the corpus callosum

• A broad band of white matter containing axons that extend between the hemispheres

Lobes of the Cerebrum

• Each cerebral hemisphere subdivided into 4 lobes

• Named after the bones covering them:

– Frontal, Parietal, Temporal and Occipital lobes

• Central sulcus

– Separates the frontal lobe from the parietal lobe

• Lateral cerebral sulcus (fissure)

– Separates the frontal lobe from the temporal lobe

• Parieto- occipital sulcus

– Separates the parietal lobe from the occipital lobe

Cerebral Lobes and Sulci

Cerebral White Matter

• Consists primarily of myelinated axons in three types of tracts

1.  Association tracts

– Contain axons that conduct nerve impulses

– Between gyri in the same hemisphere

2. Commissural tracts

– Contain axons - conduct nerve impulses from gyri to other (b/w hemisphere)

– Corpus callosum

– Anterior commissure

– Posterior commissure

3. Projection tracts

• Contain axons that conduct nerve impulses from the cerebrum to lower parts of the CNS (vice versa)

• Example internal capsule contains both ascending and descending axons

Basal Ganglia

• Deep within each cerebral hemisphere are three nuclei (masses of gray matter)

• Two are side-by-side, just lateral to the thalamus

Corpus striatum

• Refers to the striated (striped) appearance. It includes:

• Lentiform nuclei

– Globus pallidus - closer to the thalamus

– Putamen - closer to the cerebral cortex

• Caudate nucleus

– Large head connected to smaller tail by long comma-shaped body

• Substantia nigra of midbrain and subthalamic nuclei linked functionally

Basal Ganglia

• Receive input from the cerebral cortex

• Output back to motor areas of the cerebral cortex via thalamus

• Nuclei of the basal ganglia are interconnected

• Axons from the substantia nigra terminate in the caudate nucleus and putamen

• Subthalamic nuclei interconnect with the globus pallidus

Functions of basal ganglia

• Help initiate and terminate movements of the body

• Suppress unwanted movements & regulate muscle tone

• Influence many aspects of cortical function (sensory, limbic, cognitive, and linguistic functions)

Basal Ganglia & Associated Structures

Limbic System

• Ring structures on the inner border of the cerebrum and floor of the diencephalon

• Encircles the upper part of the brain stem and the corpus callosum

Main Components of the Limbic System

• Limbic lobe

– Rim of cerebral cortex on the medial surface of each hemisphere

Cingulate gyrus - Lies above the corpus callosum

Parahippocampal gyrus - Temporal lobe below

Hippocampus - Portion of the parahippocampal gyrus that extends into the floor of the lateral ventricle

• Dentate gyrus

– Lies between the hippocampus and parahippocampal gyrus

• Amygdala

– Composed of several groups of neurons located close to the tail of the caudate nucleus

• Septal nuclei

– Located within the septal area

– Formed by regions under corpus callosum & paraterminal gyrus

• Mammillary bodies of the hypothalamus

– Two round masses close to midline near cerebral peduncles

• Anterior nucleus & medial nucleus

– Participate in limbic circuits

• Olfactory bulbs

– Flattened bodies of the olfactory

• Fornix, stria terminalis, stria medullaris, medial forebrain bundle, and mammillothalamic tract

– Linked by bundles of interconnecting myelinated axons

Role of Limbic System

• Emotional brain - primary role in a range of emotions

• Pleasure, pain, docility, affection, fear, and anger

• Involved in olfaction and memory

• Amygdala – Rage

• Hippocampus - Together with other parts of the cerebrum, functions in memory

 Functional Organization of Cerebral Cortex

Sensory areas

• Receive sensory information

• Involved in perception

• Conscious awareness of sensation

Motor areas

• Control the execution of voluntary movements

Association areas

• Deal with more complex integrative functions

• Such as memory, emotions, reasoning, will, judgment, personality traits & intelligence

Sensory Areas

• Sensory information arrives mainly in the posterior half of cerebral hemispheres, in regions behind the central sulci.

• Primary sensory areas of cerebral cortex receive sensory information (relayed from peripheral sensory receptors through lower regions of the brain)

• Sensory association areas receive input both from the primary areas and from other brain regions

• Integrate sensory experiences to generate meaningful patterns of recognition and awareness

Primary somatosensory area

• Located directly posterior to central sulcus of each cerebral hemisphere

• In the postcentral gyrus of each parietal lobe

• Receives nerve impulses for: Touch, pressure, vibration, itch, tickle, temperature, pain, and proprioception

Primary visual area

• Located at the posterior tip of the occipital lobe mainly on the medial surface

• Receives visual information

• Involves in visual perception

Primary auditory area

• Located in the superior part of the temporal lobe

• Receives information for sound

• Involves in auditory perception

Primary gustatory area

• Located at the base of the post central gyrus

• Receives impulses for taste

• Involves in gustatory perception and taste discrimination

Primary olfactory area

• Located in the temporal lobe on the medial aspect

• Receives impulses for smell and is involved in olfactory perception

Motor Areas

• Motor output from the cerebral cortex flows mainly from the anterior part of each hemisphere

Primary motor area

• Located in the precentral gyrus of the frontal lobe

• Each region in the primary motor area controls voluntary contractions of specific muscles or groups of muscles

• More cortical area is devoted to those muscles involved in skilled, complex, or delicate movement

Broca’s speech area

• Located in the frontal lobe close to the lateral cerebral sulcus

• Involves in the articulation of speech

• In most people, localized in the left cerebral hemisphere

• Neural circuits - broca’s speech area, the premotor area, and primary motor area activate muscles of the larynx, pharynx, and mouth and breathing muscles

• Coordinated contractions of speech and breathing muscles enable us to speak your thoughts

Association Areas

• Consist of large areas

• Anterior to the motor areas

• Connected with one another by association tracts

– Somatosensory association area

– Visual association area

– Facial recognition area

– Auditory association area

– Orbitofrontal cortex

– Wernicke’s area

– Commo integrative area

– Prefrontal cortex

– Premotor area

– Frontal eyefield area

Somatosensory association area

• Posterior to primary somatosensory area

• Receives input from the primary somatosensory area + thalamus + other parts of the brain

• Permits to feel object

• Store memories of past somatic sensory experiences, enabling to compare

• For example recognize objects such as a pencil and a paperclip simply by touching them

Visual association area

• Located in the occipital lobe

• Receives sensory impulses from the primary visual area + thalamus

• Relates present and past visual experiences (essential for recognizing and evaluating)

• For example recognize an object (spoon) simply by looking

Facial recognition area

• Located in inferior temporal lobe

• Receives nerve impulses from the visual association area

• Stores information about faces & allows to recognize people

• Dominant in right hemisphere

Auditory association area

• Located inferior and posterior to the primary auditory area in the temporal cortex

• Allows to recognize a particular sound as speech, music or noise

Orbitofrontal cortex

• Along the lateral part of the frontal lobe

• Receives sensory impulses from the primary olfactory area

• Allows to identify and discriminate odors

• Right hemisphere exhibits greater activity

Wernicke’s (posterior language) area

• Broad region in the left temporal and parietal lobes

– Interprets the meaning of speech by recognizing spoken words

– Active as we translate words into thoughts

• Regions in right hemisphere

– correspond to Broca’s and Wernicke’s areas in the left hemisphere

– contribute to verbal communication by adding emotional content, such as anger or joy, to spoken words

Prefrontal Cortex (Frontal Association Area)

• In the anterior portion of the frontal lobe

• Numerous connections with: Thalamus, hypothalamus, Cerebellum, limbic system

• Concerned with the makeup of a person’s:

– Personality, intellect, complex learning abilities

– Recall of information, initiative, judgment, foresight, reasoning,

– Conscience, intuition, mood, planning for the future

– Development of abstract ideas

Common integrative area

• Bordered by somatosensory, visual, and auditory association areas

• Receives nerve impulses from primary gustatory area, primary olfactory area, the thalamus, and parts of the brain stem

• Integrates sensory interpretations from the association areas and impulses from other areas

• Allows the formation of thoughts based on a variety of sensory inputs

Premotor area

• Motor association area - immediately anterior to the primary motor area

• Deals with learned motor activities of a complex and sequential nature (writing your name)

• Also serves as a memory bank for such movements

Frontal eye field area

• In the frontal cortex (sometimes included in the premotor area)

• Controls voluntary scanning movements of the eyes (just like reading this sentence)

Brain waves 

• Brain neurons generate millions of nerve impulses (action potentials), taken together, these electrical signals are called brain waves

• A record of such waves is called an electroencephalogram or EEG Pattern of activation of brain neurons produces four types of brain waves

– Alpha waves

– Beta waves

– Theta waves

– Delta waves

Alpha wave

• Rhythmic waves occur at a frequency of about 8–13 cycles per second

• Present in the EEGs of normal individuals when awake and resting with their eyes closed

• These waves disappear entirely during sleep

Beta waves

• Frequency - between 14 and 30 Hz

• Appear when the nervous system is active— during periods of sensory inpu and mental activity

Theta waves

• Frequencies of 4–7 Hz

• Occur in children and adults experiencing emotional stress

• Also occur in many disorders of the brain

Delta waves

• Frequency of these waves is 1–5 Hz

• Occur during deep sleep in adults

• They are normal in awake infants

• If produced by an awake adult, they indicate brain damage

Significance of brain waves

• To study normal brain functions - changes that occur during sleep

• Diagnosing brain disorders - Epilepsy, tumors, trauma, hematomas, metabolic abnormalities, sites of trauma, & degenerative diseases

• To establish or confirm brain death

Cranial Nerves

• 12 pairs of cranial nerves

• Arise from the brain inside the cranial cavity

• Pass through various foramina in the bones of the cranium

• Part of PNS

Olfactory (I) Nerve (Sensory)

• Arises in olfactory mucosa

• Passes through foramina in the cribriform plate of the ethmoid bone

• Ends in the olfactory bulb

• The olfactory tract extends via two pathways to olfactory areas of cerebral cortex

• Function: Smell

Optic (II) Nerve (Sensory)

• Arises in retina of eye

• Passes through the optic foramen

• Forms the optic chiasm and then the optic tracts

• Terminates in the lateral geniculate nuclei of the thalamus

• From thalamus, axons extend to primary visual area of cerebral cortex

Function: vision

Oculomotor Nerve (III) (Motor)

• Originates in the midbrain

• Passes through the superior orbital fissure

• Axons of somatic motor neurons innervate:

– Levator palpebrae superioris muscle of the upper eyelid

– Four extrinsic eyeball muscles

• Parasympathetic axons innervate:

– Ciliary muscle of the eyeball

– Circular muscles (sphincter pupillae) of the iris

Somatic motor function: Movement of upper eyelid and eyeball

Autonomic motor function (parasympathetic): Accommodation of lens for near vision and constriction of pupil

Trochlear (IV) Nerve (Motor)

• Originates in the midbrain

• Passes through the superior orbital fissure

• Innervates superior oblique muscle (an extrinsic eyeball muscle)

• Somatic motor function: movement of the eyeball

Trigeminal (V) Nerve (Mixed)

• Sensory Portion: consists of three branches, all end in the pons

         

Ophthalmic nerve

• Contains axons from the skin over the upper eyelid, eyeball, lacrimal glands, nasal cavity, side of nose, forehead, and anterior half of scalp that pass through superior orbital fissure

Maxillary nerve

• Contains axons from the mucosa of the nose, palate, parts of the pharynx, upper teeth, upper lip, and lower eyelid that pass through the foramen rotundum

Mandibular nerve

• Contains axons from the anterior two-thirds of the tongue, the lower teeth, skin over mandible, cheek and mucosa deep to it, and side of head in front of ear that pass through the foramen ovale.

• Motor portion:

– Part of the mandibular branch

– Originates in the pons

– Passes through the foramen ovale

– Innervates muscles of mastication

• Sensory function: conveys impulses for touch, pain & temperature sensations and proprioception

• Somatic motor function: chewing

Abducens (VI) Nerve (Motor)

• Originates in the pons

• Passes through the superior orbital fissure

• Innervates the lateral rectus muscle - an extrinsic eyeball muscle

• Function: movement of the eyeball

Oculomotor, Trochlear & Abducens Nerve

Facial (VII) Nerve (Mixed)

Sensory Portion:

• Arises from taste buds on the anterior two-thirds of the tongue

• Passes through the stylo mastoid foramen and geniculate ganglion

• Ends in the pons

• Extend to thalamus & then to gustatory areas of the cerebral cortex

• Also contains axons from proprioceptors in muscles of face & scalp

       

• Motor Portion

– originates in the pons and passes through the stylo mastoid foramen

– Axons of somatic motor neurons innervate facial, scalp, and neck muscles

– Parasympathetic axons innervate lacrimal, sublingual submandibular, nasal, and palatine glands

Sensory function: Touch, pain, and temperature sensations, proprioception & taste

Somatic motor function: Facial expression

Autonomic motor function: Secretion of saliva and tears

Vestibulocochlear (VIII) Nerve (Sensory)

Vestibular Branch

• Arises in the semicircular canals, saccule & utricle

• Forms the vestibular ganglion

• Axons end in the pons and cerebellum

• Conveys impulses related to equilibrium

Cochlear Branch

• Arises in the spiral organ (organ of corti)

• Forms the spiral ganglion

• Passes through nuclei in the medulla

• Ends in the thalamus

• Relay impulses to the primary auditory area of the cerebral cortex

Glossopharyngeal (IX) Nerve (Mixed)

Sensory portion:

• Consists of axons from taste buds and somatic sensory receptors on posterior one-third of the tongue

• From proprioceptors in swallowing muscles supplied by the motor portion

• From baroreceptors in carotid sinus and chemoreceptors in carotid body near the carotid arteries

• Axons pass through the jugular foramen and end in the medulla

Motor portion:

• Originates in the medulla and passes through the jugular foramen

• Axons of somatic motor neurons innervate the stylo pharyngeus muscle

• Parasympathetic axons innervate the parotid salivary gland

Glossopharyngeal (IX) Nerve - Functions

Sensory Function

• Taste and somatic sensations (touch, pain, temperature) from posterior third of tongue

• Proprioception in swallowing muscles; monitoring of blood pressure

• Monitoring of O2 and CO2 in blood for regulation of breathing rate and depth

Somatic Motor Function

• Elevates the pharynx during swallowing and speech

Autonomic Motor Function (Parasympathetic)

• Stimulates secretion of saliva

Vagus (X) Nerve (Mixed)

Sensory portion:

• Consists of axons from:

– Small number of taste buds in the epiglottis and pharynx

– Proprioceptors in muscles of the neck and throat

– Baroreceptors in the arch of the aorta

– Chemoreceptors in the aortic bodies near the arch of the aorta

– Visceral sensory receptors in most organs of the thoracic and abdominal cavities

Motor portion:

• Originates in medulla and passes through the jugular foramen

• Axons of somatic motor neurons innervate skeletal muscles in the throat and neck

• Parasympathetic axons innervate:

– Smooth muscle in the airways

– Esophagus, stomach, small intestine, most of large intestine,

– Gallbladder

– Cardiac muscle in the heart

– Glands of GIT

Vagus Nerve

Vagus (X) Nerve - Functions

Sensory function

• Taste and somatic sensations from epiglottis and pharynx

• Monitoring of blood pressure

• Regulates of breathing rate and depth

Somatic motor function

• Swallowing, coughing, and voice production

Autonomic motor function (parasympathetic)

• Smooth muscle contraction and relaxation in organs of GIT

• Slowing of the heart rate

• Secretion of digestive fluids

Accessory (XI) Nerve (Motor)

• Originates in the anterior gray horn of the first 5 cervical segments of the spinal cord

• Emerges laterally from the cord and then ascends through the foramen magnum into the cranial cavity

• It then arches inferiorly to leave the jugular foramen

• Function: mediates movement of head and pectoral girdle

Hypoglossal (XII) Nerve (Motor)

• Originates in the medulla

• passes through the hypoglossal canal, and supplies muscles of the tongue

• Function: Movement of tongue during speech and swallowing

Spinal Cord

• Contribute to homeostasis by providing quick, reflexive responses to many stimuli

• Pathway for sensory input to the brain and motor output from the brain

Protective Structures of Spinal Cord

• Two types of connective tissue coverings

• Bony vertebrae

• Tough, connective tissue meninges—plus a cushion of CSF

• Surround and protect the delicate nervous tissue of the spinal cord

Protective Structures - Vertebral Column

• Spinal cord is located within the vertebral canal of the vertebral column

• Vertebral foramina of all the vertebrae, stacked one on top of the other, form the vertebral canal

• The surrounding vertebrae provide a sturdy shelter for the enclosed spinal cord

Meninges

• Three connective tissue coverings encircle the spinal cord and brain

• Continuous with the cranial meninges

Dura mater

• Superficial spinal meninges

• Composed of dense, irregular connective tissue

• Epidural space - Between dura mater & wall of vertebral canal

Arachnoid mater

• Middle a vascular covering

• Continuous with arachnoid mater of the brain

• Subdural space – Between dura mater and the arachnoid

Pia mater

• Innermost meninge - Thin transparent connective tissue

• Blood vessels – Supply oxygen and nutrients

• Subarachnoid space: Between arachanoid and pia mater (CSF)

External Anatomy of Spinal Cord

• Roughly cylindrical (flattened slightly anteriorly & posteriorly)

• Extends from the medulla oblongata to the superior border of the second lumbar vertebra

• In newborn, extends to the third or fourth lumbar vertebra

• Two conspicuous of spinal cord

– Superior enlargement – cervical enlargement C4 - T1

– Inferior enlargement – lumbar enlargement T9 - T12

• Inferior to the lumbar enlargement, the spinal cord terminates as a tapering, conical structure - conus medullaris

• Ends at the level of the intervertebral disc between L1-L2

Filum terminale

– Arise from the conus medullaris

– Extension of pia mater that extends inferiorly

– Blends with the arachnoid mater and dura mater

– Anchors the spinal cord to the coccyx

Spinal Nerves

• Paths of communication between the spinal cord and specific regions of the body

• 31 pairs of spinal nerves emerge at regular intervals from intervertebral foramina

• Each pair of spinal nerves arise from a spinal segment

• Roots of these spinal nerves angle inferiorly in the vertebral canal from the end of the spinal cord

• Branched nerves connect the CNS to the sensory receptors, muscles, and glands in all parts of the body

There are:

•   8 pairs cervical nerves (C1–C8)

•   12 pairs of thoracic nerves (T1–T12)

•   5 pairs of lumbar nerves (L1–L5)

•   5 pairs of sacral nerves (S1–S5)

•   1 pair of coccygeal nerves (co1)

• Roots -Two bundles of axons

• Rootlets - connect each spinal nerve to a segment of the cord by even smaller bundles of axons

Posterior (dorsal) root and rootlets

• Contain only sensory axons

• Conduct nerve impulses from sensory receptors in the skin, muscles, and internal organs into the CNS

• Each posterior root has a swelling - posterior (dorsal) root ganglion

Anterior (ventral) root and rootlets

• Contain axons of motor neurons

• Conduct nerve impulses from the CNS to effectors (muscles and glands)

Internal Anatomy of Spinal Cord

• Spinal cord reveals regions of white matter that surround an inner core of gray matter

• Two grooves penetrate the white matter

• Divide spinal cord into right and left sides

• Anterior median fissure

• Posterior median sulcus

• Gray matter of the spinal cord is shaped like the letter H or a butterfly

• Gray commissure forms the crossbar of the H

• Small space in the center of the gray commissure - Central canal

• Extends the entire length of spinal cord (filled with CSF)

Gray Matter of Spinal Cord

• Gray matter on each side of the spinal cord is subdivided into regions called horns

Posterior (dorsal) gray horns

• Contain cell bodies and axons of interneurons as well as axons of incoming sensory neurons

Anterior (ventral) gray horns

• Contain somatic motor nuclei

• Provide nerve impulses for contraction of skeletal muscles

Lateral gray horns

• Present only in thoracic & upper lumbar segments of spinal cord

• Contain autonomic motor nuclei

White matter of Spinal Cord

• Organized into regions

• The anterior and posterior gray horns divide the white matter on each side into three broad areas:

– Anterior (ventral) white columns

– Posterior (dorsal) white columns

– Lateral white columns

• Each columns – bundles of axons

Processing of sensory input and motor output by the spinal cord

Physiology of Spinal Cord

• The spinal cord has two principal functions in maintaining homeostasis:

– Nerve impulse propagation

– Integration of information

• White matter tracts are highways for nerve impulse propagation

• Sensory input travels along these tracts toward the brain

• Motor output travels from the brain along these tracts toward skeletal muscles and other effector tissues

• Gray matter of the spinal cord receives and integrates incoming and outgoing information

Reflexes and Reflex Arc

• Spinal cord promotes homeostasis is by serving as an integrating center for some reflexes

• Reflex is a fast, automatic, unplanned sequence of actions that occurs in response to a particular stimulus

• Some reflexes – inborn: pulling hand away from a hot surface feel

• Other reflexes are learned or acquired: driving

Reflex Arc



• The pathway followed by nerve impulses that produce a reflex is a reflex arc

• Five functional components

– Sensory receptor

– Sensory neuron

– Integrating center

– Motor neuron

– Effector

Reflexes Types and Examples

• Reflexes may be spinal or cranial and somatic or autonomic

• Somatic spinal reflexes include the stretch reflex, the tendon reflex, the flexor (withdrawal) reflex & crossed extensor reflex

• All exhibit reciprocal innervation

• Monosynaptic reflex arc: Consists of one sensory & one motor neuron (stretch reflex – patellar reflex, is an example)

• Polysynaptic reflex arc: Contains sensory neurons, interneurons, and motor neurons

Stretch Reflex

Tendon Reflex

 Autonomic Nervous System

• Contributes to homeostasis by responding to subconscious visceral sensations

• Operates without conscious control

• Peripheral nervous system (PNS) includes:

– Cranial and spinal nerves

– Divided into: SNS, ANS & ENS

• Structurally, ANS includes:

– Autonomic sensory neurons

– Integrating centers in the CNS

– Autonomic motor neurons

Division of ANS

The output (motor) part of the ANS has two divisions:

   Sympathetic

   Parasympathetic

ANS & Visceral Activities

• Autonomic motor neurons regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities in their effector tissues (cardiac muscle, smooth muscle, and glands)

Motor Neuron Pathways

Anatomical Components of ANS

Preganglionic Neurons

Autonomic Ganglia

Sympathetic ganglia

• Sympathetic trunk ganglia: superior, middle, and inferior cervical ganglia

• Prevertebral ganglia: celiac, superior mesenteric, inferior mesenteric, aorticorenal, renal ganglion

Parasympathetic ganglia

• Terminal ganglia (intramural ganglia): Ciliary ganglion, pterygopalatine ganglion, submandibular ganglion, and otic ganglion

Parasympathetic Division

• Axons of sympathetic preganglionic neurons pass to sympathetic trunk ganglia

• They may connect with postganglionic neurons in different ways

Sympathetic Division

Autonomic Plexuses

• Tangled networks of axons of both sympathetic and parasympathetic neurons

• Many lie along major arteries

• They are:

– Cardiac plexus

– Pulmonary plexus

– Celiac plexus

– Superior mesenteric plexus

– Inferior mesenteric plexus

– Hypogastric plexus

– Renal plexus

ANS - Neurotransmission

Physiology of ANS

Autonomic Reflex

• Response that occur when nerve impulses pass through an autonomic reflux arc

Regulate controlled conditions in the body like

Blood pressure – by adjusting - heart rate, contraction of ventricles, diameter of blood vessels

Digestion – by adjusting motility and muscle tone of GIT

Defecation and Urination – by regulating opening and closing of sphincters

Components of autonomic reflex

Receptor

• In the distal end of sensory neuron

• Responds to stimulus and produce nerve impulse

• Associated with interoceptor

Sensory neurons

• Conduct nerve impulse from receptor to CNS

Integrating centre

• Interneurons in CNS relay signals from sensory to motor neuron

• Located in hypothalamus and brain stem

Motor neurons

• Carry impulse out of CNS

• Preganglionic neuron and post ganglionic neuron

Effector

• Smooth muscles, cardiac muscles, and glands

Autonomic Control by Higher Centers

Hypothalamus

• Major control and integration center of the ANS

• Receives sensory input related to visceral functions, olfaction, gustation, changes in temperature, osmolarity & levels of various substances in blood

• Also receives input related to emotions from the limbic system

• Output from the hypothalamus influences autonomic centers in both:

– Brain stem (such as the cardiovascular, salivation swallowing, and vomiting centers)

– Spinal cord (such as the defecation and urination reflex centers in the sacral spinal cord)

• The posterior and lateral parts of the hypothalamus control the sympathetic division

• The anterior and medial parts of the hypothalamus control the parasympathetic division

Summary

• Structures of nervous system - the brain, cranial nerves (12 pairs) and their branches, the spinal cord, spinal nerves (31 pairs) and their branches, ganglia, enteric plexuses, and sensory receptors

• Functions- Homeostasis and integrates all body activities by sensing changes, interpreting them and reacting to them

• Nervous tissue consists of neuron and neuroglia

• Parts of neuron – Dendrite, Axon & cell body

• Neuroglia support, nurture, and protect neurons and maintain the interstitial fluid

• White matter - aggregates of myelinated axons

• Gray matter - cell bodies, dendrites, and axon terminals of neurons, unmyelinated axons, and neuroglia

• Plasma membranes of presynaptic and postsynaptic neurons - separated by the synaptic cleft

• Release of neurotransmitter, postsynaptic neuron receives the chemical signal, produces a postsynaptic potential

• Postsynaptic potential may be a depolarization or a hyperpolarization, depends on the neurotransmitter released

• CNS consists of the brain and spinal cord

• PNS consists of somatic nervous system (SNS), autonomic nervous system (ANS), and enteric nervous system (ENS)

• SNS - Sensory neurons, conduct impulses from somatic and special sense receptors to the CNS; motor neurons from the CNS to skeletal muscles

• ANS - Sensory neurons from visceral organs and motor neurons; convey impulses from the CNS to smooth muscle tissue, cardiac muscle tissue, and glands

• ENS consists of neurons in enteric plexuses in the gastrointestinal (GI) tract

• Major parts of the brain are the brain stem, cerebellum, diencephalon, and cerebrum

• Brain is protected by cranial bones and the cranial meninges

• Blood flow to the brain is mainly via the internal carotid and vertebral arteries

• Blood–brain barrier (BBB) causes different substances to move between the blood and the brain tissue

• Cerebrospinal fluid (CSF) is formed in the choroid plexuses and circulates through various ventricles

• CSF provides mechanical protection, chemical protection, and circulation of nutrients

• Brain stem consists of medulla oblongata, pons and mid brain

• Medulla oblongata- continuous with spinal cord, has vital center like respiratory, cardiovascular, vomiting, deglutition

• Pons - lies superior to the medulla and anterior to the cerebellum; Signals for voluntary movements from motor areas of the cerebral cortex are relayed

• Mid brain - Extends from the pons to the diencephalon; has centers for various reflexes

• Reticular formation-Netlike region of interspersed gray and white matter; extends through the brain stem

• Cerebellum - occupies the inferior and posterior aspects of the cranial cavity

• The anterior lobe and posterior lobe govern subconscious aspects of skeletal muscle movements

• Flocculonodular lobe on the inferior surface contributes to equilibrium and balance

• Diencephalon surrounds the third ventricle and consists of the thalamus, hypothalamus, and epithalamus

• Thalamus is superior to the midbrain and contains nuclei

• Thalamus serve as relay stations for most sensory input to the cereberal cortex

• Hypothalamus is inferior to the thalamus

• It controls the ANS, produces hormones, and regulates emotional and behavioral patterns; controls body temperature by serving as the body’s thermostat

• Circumventricular organs (CVOs) can monitor chemical changes in the blood because they lack the blood–brain barrier

• Cerebrum is the largest part of the brain

• Its cortex contains gyri (convolutions), fissures, and Sulci

• Cerebral hemispheres are divided into four lobes: frontal, parietal, temporal, and occipital

• White matter of the cerebrum is deep to the cortex

• It consists primarily of myelinated axons extending to other regions as               association,commissural, and projection fibers

• Basal ganglia are several groups of nuclei in each cerebral hemisphere

• Help initiate and terminate movements, suppress unwanted movements, and regulate muscle tone

• Limbic system encircles the upper part of the brain stem and the corpus callosum

• It functions in emotional aspects of behavior and memory

• Sensory areas of the cerebral cortex allow perception of sensory information

• The motor areas control the execution of voluntary movements

• The association areas are concerned with more complex integrative functions such as memory, personality traits, and intelligence

• Brain waves generated by the cerebral cortex are recorded from the surface of the head in an electroencephalogram (EEG)

• EEG may be used to diagnose epilepsy, infections, and tumors

• Twelve pairs of cranial nerves originate from the nose, eyes, inner ear, brain stem, and spinal cord

• Three cranial nerves (I, II, and VIII) carry axons of sensory neurons - sensory nerves

• Five cranial nerves (III, IV, VI, XI, and XII) contain only axons of motor neurons as they leave the brain stem - motor nerves

• Four cranial nerves (V, VII, IX, and X) are mixed nerves because they contain axons of both sensory and motor neurons

• The spinal cord is protected by the vertebral column, the meninges, cerebrospinal fluid, and denticulate ligaments

• 3 meninges (dura mater, arachnoid mater, and pia mater) are coverings that run continuously around the spinal cord and brain

• 31 pair of spinal nerves connect to each segment of the spinal cord by two roots

• There are 8 pairs of cervical, 12 pairs of thoracic, 5 pairs of lumbar, 5 pairs of sacral, and 1 pair of coccygeal nerves

• A reflex is a fast, predictable sequence of involuntary actions, such as muscle contractions or glandular secretions, which occurs in response to certain changes in the environment

• The pathway followed by nerve impulses that produce a reflex is a reflex arc

• Components of a reflex arc - sensory receptor, sensory neuron, integrating center, motor

• ANS comprises of sympathetic and parasympathetic division

• Sympathetic division favors body functions that can support vigorous physical activity and rapid production of ATP (fight-or flight response)

• The parasympathetic division regulates activities that conserve and restore body energy

• Autonomic ganglia comprises of sympathetic and parasympathetic ganglia

• Sympathetic ganglia include sympathetic trunk ganglia and pre vertebral ganglia

• Parasympathetic ganglia are known as terminal ganglia

• Hypothalamus is the major control and integration center of the ANS

• It is connected to both the sympathetic and the parasympathetic divisions

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