The eye Flashcards
Where does the optic nerve take action potentials?
To the visual cortex
Where do the optic nerves develop from?
Optic cups of the embryonic diencephalon
What are the 3 layers of the eye?
Fibrous
Vascular
Neural
Where is the aqueous humour located?
Anterior segment
Which nerve controls movement of the eyelids?
Facial nerve - VII
Where is the lipid component of the tear film produced?
Tarsal gland of the eyelid
What is the conjunctiva?
Mucous membrane covering the eyelids and front of the eye, except the cornea
What do goblet cells in the conjunctiva produce?
Mucin component of the tear film
What are the 7 muscles surrounding the eyeball?
- Dorsal rectus
- Lateral rectus
- Ventral rectus
- Medial rectus
- Ventral oblique
- Dorsal oblique
- Retractor bulbi/oculi
Where is the aqueous component of the tear film produced from?
3rd eyelid and an extra gland called the lacrimal gland
What is the fucnction of the Descemets membrane in the fibrous tunic?
Last defence in the eyeball
What happens when the endothelium of the eye is damaged?
Cells don’t replicate so they get increasingly thinner and spread
Where is the vascular tunic located?
Sits between the fibrous tunic and neural layer in the caudal part of the eye.
What makes up the anterior and posterior uvea?
Anterior = iris and ciliary body Posterior = choroid
What is the function of the iris?
Iris is a sphincter with constrictor and dilator muscles which alter the size of the pupil to vary the amount of light entering the eye
What is the term for:
1) Constriction of the eye?
2) Dilation of the eye?
What control are they under?
1 = miosis = parasympathetic
2 = mydriasis = sympathetic
What is the function of the choroid?
Provides blood supply to deep layers of retina
Name the structure that reflects light back to the retina to give improved night vision?
Tapetum lucidum
What is the function of the lens?
Refracts light, and can change depth of focus by accommodation (limited in veterinary species)
What are the 4 main cell types that make up the retina?
- Retinal pigment epithelium (RPE)
- Photoreceptor cells (rods & cones)
- Bipolar ganglion cells
- Multipolar ganglion cells
Describe the field of view in prey species?
Very wide vision
Blind spot at the front
What determines the shape of the pupil?
Shape of constrictor muscles
What is the name of the corners of the eyelids?
Canthi
What are the 2 types of photo receptors? What do each allow you to see?
Rods = black and white Cones = colour
What is the name of the photopigment that rods and cones contain?
Rhodopsin
What makes up the photo-pigment rhodopsin?
opsin (protein) + retinal (vitamin A)
Which species cannot convert B-carotene into vitamin A?
Cats
What % of a cat/dogs photo-receptors are rods/cones?
95% rods
5% cones
Which molecule keeps sodium channels open meaning the photoreceptors stay active and release glutamate?
Cyclic GMP
When is cyclic GMP released?
In the darkness
What are the 5 steps in signal transduction?
- Light energy is “trapped” by cis-retinal and the molecule changes conformation
- This causes the large opsin molecule to loose its “retinal” and become active
- Active opsin causes the alpha subunit of transducin (a G-protein) to activate cGMP phosphodiesterase
- Results in an elevation of GMP but a reduction of cGMP
- Sodium channels close and the cell hyperpolarises
What is released when photoreceptors are active?
Glutamate
What are the effects of glutamate being excitatory or inhibitory?
There are on and off bipolar cells
What are the 2 other types of retinal neurons, what are they involved in?
Horizontal cells and Amacrine cells
- involved in visual processing
How does the monocular and binocular vision vary in carnivores vs herbivores?
Carnivores = restricted monocular, large central binocular Herbivores = wide monocular lateral field, narrow binocular area
What is the name of the visual cortex in the brain, in which species is this large?
Tectum
- in birds
What process is the thalamus involved in?
Sensory processing
Through which part of the thalamus does the optic nerve pass?
lateral geniculate nucleus
