Chapter 15: Special Senses

Special Senses

a. taste, smell, balance, hearing, sight

most of the body's sensory receptors

70% are in the eye

visual processing requires

half of cerebral cortex function

eye accessories

a. Eyebrows
Sun and sweat protection
b. Eyelids
c. Conjunctiva
Mucous membrane
Areas
1. Palpebral
2. Bulbur
3. Conjunctival sac
Conjunctivitis (pink eye)
d. Lacrimal apparatus
Tears and tear ducts
e. Extrinsic eye muscles
6 total

conjunctivitis

inflammation of conjunctiva (pink eye)

strabismus

cross eye syndrome

layers of the eye

fibrous layer
vascular layer
neural layer

fibrous layer

i. Sclera- white covering
ii. Cornea- anterior 1/6 of fibrous layer

vascular layer

i. Choroid region (posterior)
ii. Ciliary body
iii. Iris

neural layer

i. Photoreceptors
ii. Bipolar cells
iii. Ganglion cells
iv. Optic disc

Iris

divides the eye into anterior and posterior segments

When light hits the photoreceptor cells, the signal then spreads to what other cells

spreads to the nerves

rods

i. Better in dim light
ii. More numerous
iii. No sharp images

cones

i. High resolution
ii. Color
iii. Better in bright light
iv. Macula lutea
Lateral to blind spot
Fovea centralis
All cones
Best vision

retinal detachment

a. Where the retina gets displaced, often caused by glaucoma

vitreous humor

- liquid in the posterior chamber

aqueous humor

liquid in the anterior chamber

glaucoma

a. Damage in the optic nerve

lens structure

a. A biconvex flexible clear structure

refreaction

a. Bending of light through transparent medium
b. Entering the cornea, entering the lens and exiting
the lens

light passes through these structures

a. Passes through the cornea, humor, lens, vitreous humor, neural layer, and then the receptors

distance vision

a. The lens is flat because the ciliary muscles are completely relaxed

3 adjustments to see close

a. Accommodation of the lens
b. Constriction of the pupils
c. Convergence of the eyeballs

myopia

a. Eye is too long, prevents eye from seeing far

hyperopia

a. Eye is short, convex lens, cannot see close

astigmatism

a. Blurry vision at any distance

phototransduction

a. The process of converting photons to an action potential

steps of phototransduction

1. The outer segment absorbs light and changes
shape when that light hit the cell
2. It then moves into the inner segment where an AP is
formed
3. In the dark, retinal is in the bent form (11-cis-retinal)
4. When retinal absorbs light, it straightens out (all-
trans-retinal)
5. all-trans-retinal is then released from opsin
6. all-trans-retinal is then converted back to 11-cis-
retinal by enzymes
7. 11-cis-retinal then combines with opsin again

photoreceptors segments

a. Outer segment
Light receiving
Visual pigments
Renewed every 24 hours
b. Inner segment
Contains connectors

colorblindness

a. Color deficiency caused by faulty cones

retinal

a. Retinal
Pigment made from vit A
Associated with opsins

rhodospin

rod retinal

photpsin

cone retinal

dark vision process

i. Retinal bent
ii. Na+ and Ca++ channels are open; both ions move
into photoreceptor
iii. Photoreceptor depolarizes releasing inhibitory
glutamate
iv. This hyperpolarizes bipolar cell
v. No signal sent to ganglion cell, no AP down optic
nerve

light vision process

i. Retinal straightens
ii. Na+ and Ca++ channels close
iii. Photoreceptor hyperpolarizes; no inhibitory
glutamate is released
iv. This depolarizes the bipolar cell
v. Ganglion cell depolarizes, AP sent down optic nerve

the key to vision

hyperpolarization

light adaptation

i. Rods and cones are both active
ii. Retinal is released

dark adaptation

cones shut off

nyctalopia

a. Rods are dysfunctional due to a lack of vitamin A
b. Retinitis pigmentosa- degenerative retinal disease

optic pathway

a. Photoreceptors stimulate bipolar cells which
stimulate ganglion cells
b. The axons of the ganglion cells form the optic nerve
which exits the back of the eye
c. Ganglion axons from the medial part of the eye
cross over to the opposite side at the optic
chiasma and axons from the lateral side stay at the
same side.

olfactory epithelium

a. Smell reception are at the top of the nose
b. Cell types
Olfactory Sensory neurons
Supporting cells
Olfactory stem cells

olfactory activation

a. Odorants bind to the receptors
b. Na/ca channels open depolarizing the cell
c. Action potential occurs

olfactory adaptation

a. Decreased response to stimuli

taste bud location

surface of the tongue

3 types of papillae

a. Fungiform- mushroom-like
b. Foliate- located on the side walls
c. Vallate- largest, form a V at the back of the tongue

tongue epithelial cells

Gustatory- gustatory hair cell
Basal- dynamic stem cells that are replaced every 7-10 days

taste activation

Triggered by hairs, releases a transmitter, AP occurs in cranial nerves VII and IX

primary taste sensations

a. Sweet
b. Sour
c. Salty
d. Bitter
e. Umami
f. Possible sixth having to do with fatty acids

3 major areas of the ears

a. Outer ear
b. Middle ear
c. Inner ear (hearing and balance)

functions of the outer ear

a. To funnel sound into the ear
b. Auricle
c. Helix
d. lobule

tympanic membrane

a. The ear drum
b. Vibrates in response to sound
c. Boundary between external and middle ear
d. Transfers energy to the bones in the middle ear

tympanic cavities and structures

a. The cavity that hold the middle ear, in between the
ear drum and the oval window
b. Pharyngotymantic tube
Connects the ear to the throat
Regulates pressure
c. Auditory ossicles (synovially jointed)
Malleus (hammer)
Incus (anvil)
Stapes (stirrups)
d. Skeletal muscles
Tensor tympani
stapedius

otitis media

a. Middle ear inflammation
b. Can cause hearing loss
c. Treated with antibiotics or ear tubes

parts and divisions of the inner ear

a. 3 regions
Cochlea
Vestibule
Semicircular canals
b. 2 divisions
Bony labyrinth
Membranous labyrinth

inner ear fluids

a. Endolymph fluid- internal (high k+ concentration)
b. Perilymph fluid- between labyrinths (high na+)

vestibule

a. Helps with balance (maculae)
b. Sacs
Saccule- cochlear duct
Utricle- semicircular canals

semicircular canals

a. houses equilibrium receptors in a region called the
crista ampullaris located in an enlarged area of
each canal (ampulla)
b. Crista ampullaris (rotational movement)

Auditory ossicles

i. Malleus (hammer)
ii. Incus (anvil)
iii. Stapes (stirrups)

cochlea

Contains the spiral organ
center of the inner ear

3 chambers of the cochlea

a. Scala vestibuli
b. Scala media- endolymph fluid
c. Scala tympani- perilymph fluid

cochlear structures

a. Vestibular membrane- roof of the cochlea
b. Strata vascularis- outside wall
c. Basilar membrane- floor
d. Spiral organ- center of the cochlea
e. Tectorial membrane- roof of the spiral organ
covering

spiral organ

a. Located between the tectorial and basilar
membrane
b. 1 row of inner hairs, 3 rows of outer
c. Hairs are moved which transmits to a nerve

sound wave process

a. The sound waves enter your auricle, travel down the external auditory meatus, causing your tympanic membrane to vibrate; results in vibration of the auditory ossicles

physiology of sound transduction

a. Sound waves vibrate the tympanic membrane
b. Auditory ossicles vibrate with pressure’
c. Pressure waves created by stapes vibrates fluid in
scala vestibuli
d. Sounds with frequencies below hearing travel
through the cochlea and do not excite hair cells.
e. Sounds in the hearing range go through the
cochlear duct, vibrating the basilar membrane and
deflecting hairs on inner hair cells.

deafness

a. Conduction
Blocked conduction
b. Sensorineural
Damage to the neural tract at any point
Usually at the hairs

tinnitus

a. Ringing or buzzing in the ears

equilibrium

a. Response to movements in the head
b. Static
No movement relative to gravity
Maculae
c. Dynamic
Head moves
Crista ampularis

maculae

a. It helps with posture by monitoring static
equilibrium
b. Hair cells
c. One in the saccule and one in the utricle in the
vestibule of the inner ear
d. Monitors position of head in space
e. Plays a key role in posture
f. Responds to linear acceleration

cristae ampullaris

a. sensory receptor organ that monitors dynamic
equilibrium
b. Located in the ampulla in each semicircular canal; 3
canals for all three planes of motion
c. Excited by acceleration and deceleration of the
head (especially by rotational or angular
movements)

vestibular nystagmus

a. Strange eye movements during or immediately after
rotation
b. Can occur because semicircular canal impulses are
linked to reflexive movements of the eye