III. SPECIAL SENSES
OLFACTION
A. Receptors in upper nasal mucosa
B. Olfactory nerve
C. Olfactory bulb
D. Olfactory tract
E. Temporal lobe of cerebral cortex
GUSTATION
A. Taste buds – receptors
1. Taste pore
2. Dissolved in liquid
B. Sensory nerve fibers
1. Facial [ant. 2/3]
2. Glossopharyngeal [post.1/3]
3. Vagus [pharynx]
C. Brain stem
D. Thalamus
E. Parietal lobe of cerebral cortex
VISION
A. Anatomy of eye
1. Fibrous tunic– Outer layer
a. Sclera
b. Cornea
2. Vascular tunic = uvea– Middle layer
a. Choroid
b. Ciliary body
c. Iris; Pupil
3. Nervous tunic =Retina– Inner layer
a. Outer pigmented layer
Pigment decreases reflection of light
b. Nervous layer
c. Photoreceptors [rods & cones]
1. Macula
Yellow region on retina
2. Fovea centralis
Depression in macula
d. Optic nerve
1. Optic disc
Where optic nerve leaves eye
2. Blind spot
No rods and cones here
4. Misc.
a. Lens
Changes shape to allow focusing
b. Anterior cavity– aqueous humor
c. Posterior cavity– vitreous humor
5. Accessory eye structures
a. Eyelids = palpebrae
1. Tarsal plate
Dense connective tissue
2. Meibomian glands
Oil
3. Palpebral fissure
4. Lateral commissure
5. Medial commissure
6. Caruncle
7. Sebaceous ciliary glands
b. Conjunctiva
1. Palpebral
2. Bulbar
c. Lacrimal apparatus
1. Function
Tears to lubricate, moisten eye, cleanse eye of foreign material
2. Lacrimal gland
Superior and lateral margin
3. Lacrimal puncta
4. Lacrimal canal
5. Nasolacrimal duct
B. Vision
1. Light, Refraction
Bending of light rays
2. Emmetropia
Normal vision, light rays come to focus on a single point behind the lens called the focal point
3. Accommodation
Focusing for close vision
a. Pupils constrict
b. Convergence of eyeballs
c. Near point of vision
Distance from eye to nearest point whose image can be clearly focused on the retina
4. Eye movement controls
a. Voluntary fixation movement – premotor/frontal
b. Involuntary fixation movement – occip. lobe
5. Binocular vision
Each eye views a part of the world that overlaps considerable with the view from the other eye. The disparity between eyes allows a person to judge distances and have depth perception.
a. Diplopia
Double vision
b. Strabismus
Eye movement is not coordinated.
6. Photoreceptors
a. Rods
1. Rhodopsin
Photopigment
2. 120 million
Very sensitive to light, relative lack of color, peripheral in location, work well for night vision, poor detail, convergence
b. Cones
1. 400 nm blue
2. 500 nm green
3. 600 nm red
Operate in high levels of illumination, color, excellent precise detail, located mostly in center of retina, little convergence
7. Neural components
a. Bipolar neurons
b. Ganglion neurons
c. Lateral inhibition
1. Horizontal cells
2. Amacrine cells
8. Visual acuity
20/20 Snellen eye chart
9. Light/Dark adaptation
a. Photopigment concentration
Even a small change in rhodopsin concentration in rods can greatly influence light sensitivity
b. Pupillary light reflex
1. PNS
Constricts pupils
2. Direct, Indirect
Direct is ipsilateral, indirect is consensual or contralateral
c. Neural adaptation
{cones inhibit rods in brt.. lt.}
10. Visual pathway
a. Optic nerve
b. Optic chiasma
About 1/2 of the axons cross
c. Optic tracts
d. Lateral geniculate body – thalamus
e. Occipital lobe of cerebrum
EAR
A. Outer ear
1. Function
Gathers and resonates sound
2. Pinna
3. External auditory meatus [canal]
-ceruminous glands
Wax
4. Tympanic membrane
Eardrum
B. Middle ear
1. Auditory = Eustachian tube
Equalizes air pressure in middle ear
2. Malleus, incus, stapes
Ossicles – lateral to medial
3. Oval window
Separates middle and inner ear, vibrated by stapes
4. Round window
Separates middle and inner ear, can bulge back into middle ear to keep inner ear pressure stabilized
C. Inner ear
1. Osseous labyrinth [perilymph]
2. Membranous labyrinth [endolymph]
3. Vestibule
a. Utricle
b. Saccule
4. Semicircular canals/ducts
5. Cochlea
a. Vestibular membrane
b. Basilar membrane
c. Cochlear duct[endolymph]
d. Scala tympani [perilymph]
Outer cochlear tunnel
e. Scala vestibuli [perilymph]
Inner cochlear tunnel
f. Spiral organ = organ of Corti
Contains receptors for hearing, hair cells located on basilar membrane
D. Hearing
1. Transmission of sound
a. Tympanic reflex
Muscles dampen ossicle vibrations in response to loud sounds
2. High frequency [base]
At the base of the cochlea (near the windows) the hairs are short and thick and vibrate and higher frequencies
3. Low frequency [apex]
At the apex of the cochlea the hairs are long and thin and vibrate at lower frequencies
4. Auditory pathway
Cranial nerve VIII
5. Pitch determination[20-20000 cps; best 1000-4000]
6. Loudness determination [amp. 1-120db]
7. Localization of sound [time-loudness]
E. Equilibrium
1. Utricle & Saccule
a. Macula
b. Otolith
c. Linear acceleration,
Linear deceleration,
Head position.
2. Semicircular ducts
a. Crista
Group of hair cells
b. Cupula
Gelatinous mass
c Rotational acceleration/deceleration
d. Vestibular nystagmus
Characteristic eye movement to allow eyes to stay fixed on object while moving
3. Dynamic equilibrium
Whole body equilibrium involves receptors in eyes, ears, skin, muscles, joints…