Special Senses PPT/PDF


Special Senses 

         Composed of sensory receptors throughout the body.

        General senses

         Touch, pressure, pain, heat, cold, stretch, vibration.

        Special senses

         Vision, hearing, equilibrium, olfaction, taste.

         Relative to the source of the stimuli.



        Propioceptors (sketetal muscle). Conscious.

         General structure

        Modified dendrites.

         Free nerve endings

         Merkel discs in epidermis

         Hair follicle receptors

         Meissner corpuscles: light touch

         Ruffini corpuscles: deep pressure and stretching.

         Pacinian corpuscles: pressure receptor.

         Muscle spindles

         Golgi tendon organs

         Receptor physiology

        Act as signal transducers. Direct relationship between importance and number of clustering of the receptors; punctuate distribution.

Special Senses

  1. Vision
  2. Olfaction
  3. Taste
  4. Hearing and equilibrium

1.                       Vision

·         70 percent of all sensory receptors are in the eyes

·         Each eye has over a million nerve fibers

·         Protection for the eye

1.      Most of the eye is enclosed in a bony orbit made up of the lacrimal (medial), ethmoid (posterior), sphenoid (lateral), frontal (superior), and zygomatic and maxilla (inferior)

2.      A cushion of fat surrounds most of the eye


Organ: Eye ball

Accessory structures


·         Lacrimal apparatus.

§  Lacrimal gland: secretes tears; solution of salts and lyzozyme.

§  Lacrimal canals: drains lacrimal fluid from eyes

§  Nasolacrimal canal: empties lacrimal fluid into the nasal cavity

·         Eyelids (papebrae) - brush particles out of eye or cover eye

·         Medial and lateral canthus

·         Caruncle

·         Conjunctiva - Mucus membrane that lines inner surface of eyelids. Stratified squamous and stratified cilindrical epithelium.

·         Eyelashes - trap particles and keep them out of the eye

·         Ciliary glands - lubricate eyeball, modified sweat glands between the eyelashes- secrete acidic sweat to kill bacteria, lubricate eyelashes

·         Tarsal glands: lubricate eyeball

·         6 extrinsic eye muscles


Internal structure of the eye

Composed of 3 layers or tunics


         Cornea (transparent) and Sclera (white).



        Iris: radial smooth muscle (III ocoulomotor)

        Uvea: vasculariazed.

        Cilliar body(muscles) : control the curvature of the lens (cristaline).

        Cilliary processes: secrete aqueous humor.


        Choroid: dark pigment.


         Retina: sensory region

Additional internal structures

·         Humor vitreous

·         Macula lutea (yellow spot): high cone density

·         Fovea centralis: area of maximum (very high amount of cones) sight acuity.

·         Sclera venous sins( Schlemm canal)

·         Ciliary zonule



Histology of the retina


         Sensory tunic

        Outer pigmented epithelial layer

        Inner neural layer.

         Photoreceptors: cones or rods.

         Bipolar neurons


         Axons of ganglions

2. Olfaction

·         Olfactory receptors are in the roof of the nasal cavity

§  Neurons with long cilia

§  Chemicals must be dissolved in mucus for detection

·         Impulses are transmitted via the olfactory nerve

·         Interpretation of smells is made in the cortex (olfactory area of temporal lobe)

Sensory structure:

Olfactory epithelium. Chemoreceptor.

§  Olfactory receptor cell: bipolar neuron (I)

§  Support cells: pseudo stratified ciliated epithelium.

§  Basal cells.

3.   Taste

·         Taste buds house the receptor organs

·         Location of taste buds

§  Most are on the tongue

§  Soft palate

§  Cheeks

The Tongue and Taste

·         The tongue is covered with projections called papillae

§  Filiform papillae – sharp with no taste buds

§  Fungifiorm papillae – rounded with taste buds

§  Circumvallate papillae – large papillae with taste buds

·         Taste buds are found on the sides of papillae

Structure of Taste Buds

·         Gustatory cells are the receptors

§  Have gustatory hairs (long microvilli)

§  Hairs are stimulated by chemicals dissolved in saliva

·         Impulses are carried to the gustatory complex (pareital lobe) by several cranial nerves because taste buds are found in different areas

§  Facial nerve

§  Glossopharyngeal nerve

§  Vagus nerve

Taste Sensations

  • Sweet receptors
    • Sugars
    • Saccharine
    • Some amino acids
  • Sour receptors
    • Acids
  • Bitter receptors
    • Alkaloids
  • Salty receptors
    • Metal ions
  • Umami
    • Glutamate, aspartate (MSG, meats)

Sensory structure

a.      Taste bud. Chemoreceptor. Mechanoreceptor. Thermo receptor.

                                                                                                  i.      Basic tastes: sweet, sour, salt, bitter.

                                                                                                ii.      Types (location in figure)

1.      Fungiform papillae (mushrooms)

2.      Circunvallate papilla (globes)

3.      Filiform papilla

                                                                                              iii.      Cell types

1.      Gustatory (taste) cells: bipolar neurons.

2.      Support cells

4. Hearing and balance

Eye Reflexes

·         Internal muscles are controlled by the autonomic nervous system

·         Bright light causes pupils to constrict through action of radial (iris) and ciliary muscles

·         Viewing close objects causes accommodation

·         External muscles control eye movement to follow objects- voluntary, controlled at the frontal eye field

·         Viewing close objects causes convergence (eyes moving medially)

The Ear

·         Houses two senses

·         Hearing (interpreted in the auditory cortex of the temporal lobe)

·         Equilibrium (balance) (interpreted in the cerebellum)

·         Receptors are mechanoreceptors

·         Different organs house receptors for each sense


Organ: Ear (sensory receptor for hearing and equilibrium).

·         The ear is divided into three areas

§  Outer (external) ear

§  Middle ear

§  Inner ear

·         Involved in hearing only

·         Structures of the external ear

§  Auricle

§  External acoustic meatus

§  Tympanic membrane

§  Ceruminous glands

·         Structures of the Middle ear

         Tympanic cavity


»        Malleus (hammer)

»        Incus (anvil)

»        Staples (stirrup). Connects with the oval window.

         Pharingotimpanic tube. Pressure equalization of middle ear and environment.

·         Structures of the Inner ear

         Bony and membranous labyrinth

        Cochlea: hearing

        Vestible: equilibrium

        3 perpendicular semicircular canals: equilibrium

Hearing physiology

         Sound waves travel from the outer ear (timpanic membrane)à middle ear (Malleus,Incus, staples, oval window)à inner ear (scala tympani)/scala vestibulià stimulates the stereocillia of the organ of cortià VIII

         The round window serves as a pressure relief valve.

Equilibrium physiology

         Located in the vestibular apparatus


         Utricle and saccule (sacs) within vesitble.

        Receptor: Macculae (static equilibrium)

»        Hair cells (stereocillia) are embedded in the otholitic membrane which contain CaCO3 (otoliths). Respond to vertical acceleration.

        Membranous semicircular ducts

         Ampulla (located at the base of each perpendicular duct). Mechism of dynamic equilibrium (angular acceleration).

        Receptor: Crista ampullaris. Stereocilia covered by a gelatinous cupula. Endolymph stimulates the recptor.


Special Senses PDF

Special Senses PPT

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