Outline-4, BIO 2310, Special Senses



A. Receptors in upper nasal mucosa

B. Olfactory nerve

C. Olfactory bulb

D. Olfactory tract

E. Temporal lobe of cerebral cortex


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



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


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


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


A. Outer ear

1. Function

Gathers and resonates sound

2. Pinna

3. External auditory meatus [canal]

-ceruminous glands


4. Tympanic membrane


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]

Hearing Pathway Animation

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…