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.

–        Exteroceptors

–        Interoceptors

–        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

External

•         Cornea (transparent) and Sclera (white).

Middle

•         Anterior

–        Iris: radial smooth muscle (III ocoulomotor)

–        Uvea: vasculariazed.

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

–        Cilliary processes: secrete aqueous humor.

•         Posterior

–        Choroid: dark pigment.

Inner

•         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

•         Ganglion

•         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

–        Osicles

»        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

–        Vestible

•         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