Module 5: Special Senses

What are the three tunic layers in the eye

fibrous, vascular, sensorineural

What is the superficial layer in the eye

fibrous layer

What is the deep layer in the eye

sensorineural

What is the sclera

dense C.T. that helps give the eye shape

What is the cornea

continuous with sclera, only present on the anterior surface of the eye; allows light to pass through but upon hitting the light waves are refracted

What makes up the vascular tunic

choroid, ciliary body, iris

What is the fibrous tunic made up of

sclera and cornea

What is the retina made up of

pigmented and neural layer

What does the choroid do

highly pigmented area that lies against the sclera. highly vascularized and supplies nutrients to retina

What does stray light lead to

"noise" and causes a blurred image

What is a ciliary body

continuous with choroid, smooth muscle, connected to suspensory ligaments that connect to lens.

What does changing the lens do

changes the degree of refraction

What is the iris

continuous with ciliary body and is muscle tissue found between cornea and lens. Hole in middle (pupil).

contraction of circular smooth muscle =pupil decreasing in size

contraction of radial muscle: results in pupil increasing in size

What does the size of the pupil control

how much light enters the eye

When the lens becomes more bulbous...

the iris blocks stray light from hitting the retina

What is the retina

deepest tunic and contains nervous tissue; continuous with optic nerve through axon projections

What is a focal point

where the lens converges as a single point

What is the lens

made up of rings of protein, biconvex, shape of lens is controlled by ciliary body and suspensory ligaments

For a closer object you want the lens to be

bulbous

For an object further away, you want the lens to be

elongated

Vision physiology: what is vision controlled by

light and it's reflection off an object

What do the light rays come into contact with first

cornea which refracts light towards the lens

Process of vision physiology

1. light hits object and is reflected

2. light reaches cornea which refracts the light towards the lens

3. light hits lens and is refracted again to converge on a single point on the retina

4. light converges at focal point via exiting the lens through the posterior side

Ideally, where is the focal point

on the retina

If an object moves closer, where does the focal point go

behind/posterior to the retina

If an object moves further away, where does the focal point go

in front of the retina

What happens when light hits the retina without passing through the lens

light would be unrefracted and does not converge with other light rays. This creates "noise" and the image is blurred.

When does the iris contract

the same time the lens changes shape in order to block the light ways that won't converge

When don't light rays need to be refracted as much

if object moves further away because the light rays are more parallel. this allows the curvature of the biconvex lens to decrease and light is refracted less

In the lens, objects in the superior visual field are focused on

the inferior portion of the retina

In the lens, objects in the inferior visual field are focused on

superior portion of the retina

Projection of the image is

inverted

Where are photoreceptors

located in the retina

What are the other neurons in the retina called

Bipolar cells and ganglion cells

Which retina neuron is tertiary

ganglion

Which retina neuron is secondary

bipolar

Which cell axons group together to form the optic nerve

ganglion cells; transmits signals to the brain

What are the layers in the retina

inner plexiform, inner nuclear, outer plexiform, outer nuclear, and rod/con layer

What does the deepest layer of the retina contain

rods/cones

What are rods/cones stimulated by

light

What are the two types of photoreceptors

cones/rods

Rods

extremely sensitive to light, insensitive to the wavelength

Cones

not as sensitive to light, very sensitive to wavelngths

Which photoreceptor are responsible for color vision

cones

Why don't you see color at night

b/c cones require much more light to be stimulated

Multiple rods synapse with

a single bipolar cell

a single cone synapses with

a single bipolar cell

Why are cones better at resolving detail

because multiple rods synapse with a single bipolar cell while a single cone synapses with a single bipolar cell

What are the three types of cones

red, green, blue

What cones does yellow light stimulate

green and red

What cones does cyan light stimulate

blue and green

What happens when light hits rhodopsin

rhodophsin changes shape by alterining retinal.

What is the change in retinal

cis-retinal to trans-retinal

When rhodopsin changes shape what does it communicate with

G-protein called transducin

What is activated when rhodopsin joins with transducin

cyclic GMP phosphodiesterase

What does cyclic GMP phosodiesterase do

breaks down cyclic GMP

What do the Na+ channels on the rod cell membranes have

cyclic GMP ligand

Does a photoreceptor generate a "true" action potential

since the cell cannot depolarize it can no longer release the neurotransmitter. The neurotransmitter in rods is glutamate which acts as an inhibitor and inhibits the bipolar cell from generating an action potential

essentialy: if glutamate is present in the synapse, biopolar cell is essentially inactive

If glutamate is not present in the synapse what can happen

the biopolar cell generates an action potential

How does glutamate work

by binding to the dendrite of the bipolar cell and creating an enzyme cascade that closes the Na+ channels on a bipolar cell. This causes Na+ channels on the bipolar cell to close and bipolar cell is unable to depolarize

What do the cones use as a signaling chemical

opsin (red, green, blue_

What is a visual field

everything that is seen by one eye

Binocular visual field

the overlap of each eye's individual field

How is the retina divided

four visual quadrants: temporal, nasal, superior, inferior

What is located at the center of the four retina quadrants

fovea centralis of the macula

Where is the sharpest focus located at

fovea centralis of the macula

how does the inversion of an image work

works along the y-axis

how does reversal of the image work

along the x-axis

Where would the reversal of an image in the temporal region be

the nasal portion

Where would the reversal of an image in the inferior region be

the superior region

Picture of the 4 quadrants in retina

What is a nerve pathway

nerve tract to optic nerve to optic chiasm, crossing of nerve tracts

Where do nerve tracts from the temporal retina cross

nasal field of view, do not cross

What does the brain look for when putting together images

regions of overlap from the right and left field of view

Where do nerve cells in the corpus callosum communicate

with the nuclei of the visual cortex

Where are images in the nasal field of view projected

from the right and onto the temporal portion of the retina

Where are images from the temporal view of the left eye projected

onto the nasal portion of the retina

Which tracts cross at optic chiasm

nasal tracts

Crossing the fibers provides the left side of the brain with

all visual info on the right visual field

vice versa for right side of brain

What is the optic tract

where nerve fibers merge again

travels to lateral geniculate body of thalamus and then to visual core

Where does partial decussation occur

when optic nerve fibers exit the eye at the optic disk and project into the optic chiasm

Steropsis

the process by which the visual cortex combines the differing neural signals caused by binocular disparity, resulting in the perception of depth

What are the three major cell types in the olfactory epithelium

olfactory receptor neurons

sustentacular cells

basal cells

What are bowman's glands

responsible for producing mucus with antibodies to protect against bacteria and viruses

What is the protein complex located on the olfaction's plasma membrane

GOLF

G-protein of OLFaction

What the are units of the G-protein complex

alpha, beta, gamma

What else is located on the plasma membrane of the olfactory

Adenylyl cyclase and cation channels (transmembrane), closed chlorine channels

Generation of Olfactory Action Potential

1. odorant binds to receptor

2. binding of the odorant causes alpha subunit of the G-protein complex dissociates

3. G-protein interacts with adenylyl cyclase

4. GTP binds to alpha G-protein-adenyly cyclase compound

5. binding of GTP causes adenylyl cyclase to produce cyclic AMP (cAMP)

6. cAMP binds with cation channel and allows Na+ and Ca2+ to enter cell

7. Ca2+ ions enter the cell and bind to closed Cl- channel

8. Cl- channel opens and theres an efflux of Cl- ions

9. Cell becomes more positive (depolarizes)

10. sensory neuron is depolarized and action potential propagates down the sensory neuron

Where are the axon terminals that the sensory receptors respond to located

glomerulus

Give the pathway of what happens after A.P. is generated

1. odorants binds to sensory neurons

2. depolarization of sensory neuron and action potential is generated

3. multiple sensory neurons have the same reaction (many are responsive to same neuron)

4. action potentials propagates down each axon to axon terminal (group at glomerulus)

5. signal is transferred from sensory to secondary neuron (either mitral or tufted cell)

6. Activation of mitral/tufted cell causes activation of interneuron (periglomerular cell)

7. causes inhibition of mitral/tufted cells associated with axon terminal of other chemoreceptors

8. A.P. is sent to olfactory cortex via olfactory tract

9. signal from olfactory cortex is transmitted back through olfactory bulb through centrifugal fibers

10. granular cells are activated

11. granule cells release gamma aminobutryic acid (GABA; inhibitory neurotransmittor)

12. chemoreceptors are inhibited

What are the four types of papillae

Filiform, foliate, fungiform, vallate

What is gustation

sense of taste

Filiform

filament shaped

Fungiform

mushroom shaped

Vallate

surrounded by wall

Foliate

leaf shaped

What does the epithelium of the tongue consist of

taste cells, sustentacular cells, basal cells

Taste cells are...

chemical sensory neurons

Sustentacular cells are...

support cells

Basal cells are...

stem cells