Week 4 - Study Guide - Vision Flashcards
What is the percentage of receptors in the body has to do with the eye?
70% receptors is they eye
AND
1/2 the cerebral cortex
Eyeball wall contains three tunics
Fibrous - outer
Vascular (Uvea)
Sensory - innermost
Additional separation in the eye by the leans creates two cavities with humors
Aqueous humor - water - anterior
Vitreous - posterior
maintains pressure and shape
Outer membrane on eye
Conjunctiva
Another name for eyelids
palpabrae
What part of the eye produces tears?
Lacrimal apparatus
What are Extrinsic eye muscles?
-Muscles - not of lens or iris
-But attach to outer surface of the eye
^ have individual innervation and can be diagnostic
What drains the humors?
Venous sinus drains
Outermost layer of the eye - Fibrous Tunic
Sclera - white part
Cornea - transparent
Sclera sinus drainage
Middle layer of the eye -
Vascular Tunic
AKA - Uvea
has vascularity and nutritive purposes
- Choroid
- Ciliary bodies
- Ciliar ligaments
- Iris
Choroid
POSTERIOR
1. covers the inside of the sclera
2. Pigment helps absorb additional light rays
3. Helps supply blood to the structures of the eye
Ciliary Bodies
ring surrounding the lens
Helps control the shape of the lens by altering - that is the ciliary muscle
Ciliary Zonal Ligaments
Attach to the lens
Controls the shape pf the lens
Can focus light
Iris
color surrounding pupil
where light enters
AKA - diaphragm
Dilates and constricts
Innermost layer of the eye - Sensory Layer
Retina
Photoreceptors
Optic Disc
(pigmented & Neural)
Where sensors exist
Photoreceptors
Rods
Cones
Rods
- Peripheral
- Dim light
- monochromatic
- Indistinct
- Broad image - no detail
Vitreous Humor
- Main body of the eye
- Posterior
- Watery solutes
Humor
Fluid sitting in the eye
Move humor through the posterior chamber and move towards the anterior chamber
Aqueous Humor
- Anterior
- Produced by cells anterior to the ciliary body
Sclera
White, tough, collagenous
posterior
Collagen fibers run in all directions
Cornea
Anterior
clear
collagen in parallel to keep transparent
What gives clarity?
- collagen fibers run parallel
- dehydrating the eye by -moving Na+ out
-creating a concentration gradient
Water will follow by osmosis
What is accomodation in the eye?
allows for vision up close and far away
Iris
color surrounding the pupil where light enters and hits the retina
Dark - dilate - gather light - sympathetic
Light - constrict - reduce bright light
-parasympathetic
Cones
- In front of the fovea centralis
- Bright light
- High acuity - lots of detail
- Color vision
When light hits rods or cones –
Goes from:
1. Photoreceptor
2. Bipolar Neurons
3. Ganglion cells
4. Opti Nerve
- Light enters and hits rods or cones
- Move forward to eye
- Bipolar neurons which will
- send signal even more forward to
- ganglion cells
- Which will create the axon that
- makes up the optic nerve
Optic Disc
Blind spot
Where the optic nerve and blood vessels enter and exit the eye
Area at the back of the retina that does not have receptors
Nerve is exiting the eye
Pupillary Reflex
Parasympathetic
causing pupil constriction
consensual= response in both eyes
Ciliospinal reflex
Sympathetic
Causing pupil dilation
ipsilateral and not consensual
Salivary reflex
parasympathetic
Which has more specific control, sympathetic or parasympathetic?
Parasympathetic
Has a pathway to a specific neuron for a specific response
Not sympathetic because:
Adrenal Gland messes everything up
E/NE one shot at survival
not specific
survival mode - dump resources
Terminal Ganglia
Parasympathetic
end or near target organ
long pre-ganglionic axon
Cholinergic features
Ach
N/M
Nico- gate opens - depolarization
M- 2nd messenger system
inhibitory or excitatory
Adrenergic features
NE
Alpha/Beta
B1 - heart
B2 - BV of lungs, brain, heart
Alpha - BV of periphery, excitatory
Alpha
Constricts blood vessels of Periphery
Excitatory to smooth muscle - constriction
Remember that not all cranial nerves cross
Not all cranial nerves cross
Adrenergic
fiber type releases NE
Cholinergic
fiber type that releases Ach
Muscarinic
Ach receptor that involves a 2nd messenger
Nicotinic
Ach receptor that is always excitatory
Alpha
Sympathetic receptor on skin, mucosa, viscera
Beta
Sympathetic receptor on heart - B1
B2= airways, blood vessels of heart, brain and lungs
We have cones that are
Blue, Green, Red
Blood to Retina and Photoreceptor Distribution
Where the blood is coming from that feeds either the:
1. internal eye
2. External surface of the eye
Feeding the outer layer of the eye
Choroid -outer third (photoreceptors)
Central artery (inner 2/3)
(ganglion & bipolar cells)
Visual Acuity defined
Ability of a subject to discern details
Flat lens =
Distance vision
What actions flatten the lens
- Ciliary muscles relax
- Zonular ligaments pulled tight
- Causing lens to flatten
to increase distance vision
What action rounds the lens?
- Ciliary muscles contracted
- Zonular ligaments slacken
- Causing lens to round to increase close up vision
Refraction
Bending of light rays
Rods & Cones Similarities
- Photoreceptor cells
- Found in retina
- Absorb light
- Converts light into signals that result in phototransduction
- Assist in vision in presence of light
- Synapse with Bipolar cells
- Chemical process that supports phototransduction is similar
Differences in Rods
- Found at the periphery of the retina
- Low light vision
- More rod cells than cone cells (120 million)
- Rod cells triggered by a single photon of light
- one type of protein pigment in rod cells - Rhodospin
- Sensitive to scattered light and direct light
- Absent in fovea
- Loss of rod cells cause night blindness
Differences in Cones
- Cones found in the front of the fovea of the retina
- Vision in bright light
- Color vision
- Number of cones are less than rods (6 million)
- Large number of protons required to trigger cone cells
- 3 different types of photopsin - red, blue, green
- cones only sensitive to direct light
- Concentrated in fovea
Loss of cone cells causes legal blindness
Photoreceptor does
A specialized nerve that:
1. takes in light
2. converts it into a neural impulse
Photoreceptors send
only IPSPs
Bipolar cells send
only EPSPs
Ganglion cells send
only Action Potentials
Pure Dark
Signal transmission in the retina
Darkness:
1. Rods will be firing IPSPs
2. You see nothing
3. Photoreceptors are saying there is nothing to see
4. Going to inhibit Bipolar cells from sending any signals because there is nothing to see
Darkness to some light - what does the light do?
- It hyperpolarizes photoreceptors
- Turns photoreceptors off
- If photoreceptors are off - they stop sending inhibitory signals
- NOW Bipolar cells start to depolarize with an EPSP
- When they send EPSPs to the ganglion cells
- It will lead to an action potential
- Send signal to optic nerve
- To the brain
- Now instead of being in total darkness - see nothing- you are in low light - see something
Rhodospin
Visual (chemical) pigment in rods made of protein
Rhodospin comes in two isomer forms
11-cis-retinal = In Dark
All-trans-retinal = In Low Light
In the dark, Rhodospin
Forms and accumulates
All-trans-retinal –> 11-cis-retinal
In the light, Rhodospin
Breaks down
11-cis=retinal –> all-trans isomer
Retinal and opsin separate (bleaching pigment)
When light hits rods
Rods will turn off and stop sending IPSPs
CIS =
kinked
trans =
straight
PHOTOTRANSDUCTION
in light
- Rhodospin = cis –> trans
- G protein transducin is activated
- transducin activates PDE (enzyme catalyzes a reaction)
- PDE converts cGMP –> GMP
- Drop in cGMP –> channel closes - rod stops sending IPSPs to Bipolar cells
- Hyperpolarization
PHOTOTRANSDUCTION
in Dark
- cGMP build up over time
- cGMP binds and opens channel of the rod
- Na+ and Ca2+ influx depolarizes!!!
- Rod sends its specific type of signal - IPSPs
Visual Adaption
- Light Adaption is quicker
dark to light
-Visual acuity improves over 5-10 minutes - Dark Adaption slower
Light - Dark
-Retinal sensitivity increases 20-30 minutes
Hemifield
Visual field in front of you
Hemiretina
Lateral/Temporal
Lateral Hemiretina of left eye is perceiving visual information from right region of the hemifield
Hemiretina
Medial/Nasal
Medial Hemiretina of left eye is perceiving visual information from Left side of visual field
Visual Pathways:
Different parts of the visual field go to different locations
Contralateral projections
Result of optic chiasm and the hemifields
Some will cross over and some will stay on the same side
Ipsilateral and contralateral organization
Left Hemifield
will eventually end up on Right Optic tract
crossover at optic chiasm
Right Hemifield
will eventually end up on Left Optic tract
crossover at optic chiasm
Temporal views crossover
Nasal views stay in same side
Temporal views crossover
Nasal views stay in same side
Scotoma
Portions of the visual field that are non-functional
There has been damage somewhere in the visual pathway causing very specific losses of what the L and R eye can actually see
Right eye blind
Damage to R optic Nerve
Tunnel Vision
(temporal hemifield blind)
Take out optic chiasm
- each eye losing most peripheral field of vision
- See in only the medial region
Think horse and blinders
Left Hemifield Blind
Take out an Optic Tract
(After the Optic chiasm)
- Loss of vision on right nasal field
- Loss of vision on left hemifield
Hemifield
Half of visual field
Damage to Right Optic Cord
Loss L half visual field in both eyes
Hemiretina
Half of the posterior of the eye
Damage to the L optic Nerve
Loss of vision in L eye
Damage to optic chiasm
Loss of peripheral vision
Damage to R nasal hemiretina
loss of peripheral vision of R eye
Give two differences & similarities between a stretch & a withdrawal reflex:
- Stretch - direct connection of sensory & motor neuron (monosynaptic), painful stimuli VS muscle spindle initiates.
- Both are automatic; go through spinal cord & are ipsilateral
Somatic VS ANS
- Both are motor pathways, leading to effectors
- effectors are different
- Differ in # of motor neurons
- Voluntary/Involuntary
Para VS Sympa
- Same # of motor neurons
- Fiber types differ
- Myelination same pattern
- Effectors overlap
Which receptor converge to bipolar cells?
rods (600 to 1)
Large receptive field
excellent motion detection
not detail
Which receptor is non-converging
cones. (1:1:1)
cone –> bipolar cell –> ganglion
detailed, high resolution small receptive fields
Photoreceptors only send
IPSPs
Bipolar cells send only
EPSPs
Ganglion cells send only
APs
Light Adaptation
Dark –> Light
1. pigment broken down
2. pupils constrict
3. rod function stops
4. cones & neurons rapidly adapt
5. Visual acuity in 5-10 minutes
Dark Adaptation
Light –> Dark
1. Reverse light adaptation
2. Cones stop functioning
3. Pupils dilate
4. 11-cis retinal builds up
Retinal sensitivity increases over 20-30 minutes
