Lecture 5: Vision Flashcards
Special Senses of the body include:
1)Vision
2)Chemical Senses
- Taste
- Smell
3) Hearing
4) Equilibrium
All special sensory receptors are distinct receptor cells localized in the: _____ region
head
The Function of the Accessory Structures of the Eye is to:
Protect the eye and aid eye function
What is Conjunctiva?
transparent mucous membrane that produces lubricating secretions
Palebral Conjunctiva:
membrane that lines the underside of the eye
What is the Bulbar Conjunctiva:
membrane that covers the white of the eyes (not the cornea)
What is the Conjunctival Sac:
space between palpebral and bulbar conjunctiva (area where contact lens sit)
There are ___ straplike extrinsic eye muscles
6
The extrinsic eye muscles originate from the: _____ ____
bony orbit
THe extrinsic muscles of the eye originate from the bony structure and insert on the ________
eyeball
Name three motor inputs of the eye
1: CN III - Oculomotor
2. CN IV - Trochlear
3. CN VI - Abducens
The walls of the eyeball contain 3 layers. What are they?
- Fibrous Layer
- Vascular Layer
- Inner Layer
The internal cavity of the eye is filled with fluid called:
humors
The internal cavity of the eye is separated. by the _____
lens
The eye is separated by the lens into the ____ and ____ segments
anterior and psoterior
Pupil constriction is controlled by the ______ nervous system
parasympathetic
The iris consists of two muscles
Sphincter pupillae
Dilator pupillae
Pupil dilation is controlled by the ______ nervous system
sympathetic
Focus on Distance requires 3 simultaneous Processes. What are they?
- Accommodations of lenses
- Constriction of pupils
- Convergence of the eyeball
What is Presbyopia?
loss of lens accommodation over the age of 50
To focus on distance the lens of the eyeball will
flatten
When focusing on distance, the ______ muscle is relaxed. Which causes a pull on ciliary zonule
Ciliary
Myopia is a problem of
Refraction
Myopia (nearsightedness) is a result of the eyeball being:
too long - the focal point is in front of the retina
To correct for Myopia, corrected lens need to be:
concave
Hyperopia is a problem of
Refraction
Hyperopia (farsightedness) results from the eyeball being:
too short - the focal point is behind the retina
Hyperopia is corrected with _____ lens
convex
What is the optic disc?
Site where the optic nerve leaves the eye
Why is the optic disc also known as the blind spot?
it lacks photoreceptors
What is the function of the pigmented layer of the Retina? (3)
- Absorbs light and prevents scattering
- Phagoctyizes photoreceptor cell fragments
- Stores vitamin A
The Neural layer of the retina contains ___ and ____
rods
cones
The three main types of neurons in the neural layer of the retina are:
- Photoreceptors
- Bipolar cells
- Ganglion cells
Rods are required to see colours.
True or False
False.
Rods do not produce colour vision or sharp images.
The greatest number of rods are found at the _____
periphery
Rods are more sensitive to light than cones.
True or False
True
Photoreceptor are modified neurons of rods and cones that consist of a _____, _____ and 2 ______
Cell body
synaptic terminal
segements:
The outer segment of the photoreceptor are the ____ receiving photopigment
light
The outer segment of the photoreceptor change ____ as they absorb light
shape
The inner segment of the photoreceptor ____ cell body and is connected via cilium to the outer segment.
joins
Retinal is the key ___ -absorbing molecule that combines with 1 or 4 proteins
light-absorbing
The protein that retinal combines with are called: ____
opsins
4 opsins are called ____ and found in the rods
Rhodopsin
3 opsins are found in the cones:
Green
Blue
Red
How do people see different hues?
Cone wavelengths overlap and trigger more than one cone enabling us to see hues
Retinal isomer are different 3d forms. Retinal is in ___ form in the dark.
bent
When the retinal isomer pigment absorbs light it will
straighten out
11-cis-retinal is the ___ form retinal isomer
bent
all-trans-retinal is the ___ form of retinal isomer
straight
Conervsion of bent to straight retinal initiates electrical impulses along the ____ nerve
optic
What are the three steps to converting a bent retinal (11-cis-retinal) to a straight (all-trans-retinal) (3)
- Pigment synthesis
- Pigment Bleaching
- Pigment Regeneration
What occurs during Pigment Synthesis?
11-cis-retinal is combined with opsin to form rhodopsin
What occurs during Pigment Bleaching?
light absorption by rhodopsin triggers a rapis series of steps in which retinal changes shape (11-cis to all-trans) and eventually release from opsin
What occurs during Pigment Regeneration?
Enzymes slowly convert all-trans-retinal to its 11-cis-retinal from cells of the pigmented layer. Requires ATP
When moving from darkness to light we see a glare because:
both rods and cones are strongly stimulated
Light adaptation occurs in 5-10 minutes as:
rod system turns off
transducin moves to inner segment
retinal sensitivity decreases
Dark adaptation occurs when moving from bright light into darkness. Blackness is seen because:
cones stop functioning in low intensity light
Bright light bleached rod pigments are still off
Rhodopsin accumulates in the dark so retinal sensitivity starts in increase and transducins return to the outer segment and occur in 20-30 minutes. This results in
Dark Adaptation
What occurs at stage 1 of information processing in the retina?
cGMP-gated channels open, allowing cation influx and photoreceptors depolarize
What occurs at stage 2 of information processing in the retina?
Voltage-gated Ca+ channels open in synaptic terminals
What occurs at stage 3 of information processing in the retina?
Neurotransmitter is release continuously
What occurs at stage 4 of information processing in the retina?
Neurotransmitter causes IPSP in bipolar cells causing hyperpolarization
What occurs at stage 5 of information processing in the retina?
Hyperpolarization closes voltage gated Ca+ channels, inhibiting neurotransmitters
What occurs at stage 6 of information processing in the retina?
No EPSP occur in glanglion cell
Action potentials are generated in the _____ cells
ganglion
Rods:
Noncolour Vision
High sensitivity (functions in dim light )
Low acuity (many rods converge on one ganglion)
More numerous
Mostly in peripheral
Cones:
Colour vision
low sensitivity (function in bright)
High acuity 1 cone:1ganglion
less numerous
mostly in central retina
