Visual System - Optic Nerves and Visual pathways 17.02.23

Question 1

What does the outer segment of the rods and cones contain?

Answer 1

Contains discs containing light sensitive photopigment

Question 2

What is the inner segment of rods and cones made up of?

Answer 2

Cell body, axon and synaptic terminals

Question 3

What is phototransduction?

Answer 3

This is the process of absorbing light and sending an electrical signal

Question 4

What is the photopigment called in rods and cones?

Answer 4

Rods: Rhodopsin
Cones: Opsin

Question 5

What are opsins?

Answer 5

Transmembrane proteins which contain the light sensitive molecule retinal

Question 6

Describe the photo transduction pathway?

Answer 6

• Rhodopsin absorbs a photon
• This triggers a conformational change to all-trans form
• This change also triggers changes in the opsin structure
  -This in turn triggers a cascade within the cell: closure of cation channel, and hyperpolarization of the photoreceptor cell.

Question 7

How is an action potential created from a signal in the retina?

Answer 7

• Photoreceptor signals bipolar cell which in turn activates retinal ganglion cell
• The horizontal and apocrine cells modulate this signal
• The retinal ganglion cell doesn’t have a graded response so creates an action potential

Question 8

How to the RGCs create an action potential?

Answer 8

Retinal ganglion cells (RGC) bear the sole responsibility of propagating visual stimuli to the brain. Their axons, which make up the optic nerve, project from the retina to the brain

Question 9

What are the 2 retinas involved in the visual pathway?

Answer 9

The temporal retina and the nasal retina

Question 10

Describe the extracranial pathway from getting sensory information to the primary visual cortex?

Answer 10

• Optic nerve formed by convergence of axons from retinal ganglion cells (RGCs)
• RGCs receive impulses from rods and cones
• Optic nerve leaves via optic canal through sphenoid bone
• enters cranial cavity and runs along middle cranial fossa

Question 11

Describe the intracranial pathway from getting sensory information to the primary visual cortex?

Answer 11

• The optic nerves join to form the optic chiasm
• At this chiasm, fibres from medial halves cross the contralateral optic tract
• Fibres from the lateral halves remain ipsilateral
• optic tracts then travel to lateral geniculate nucleus (LGN) in the thalamus and fibres synapse

Question 12

What is in the upper optic radiation?

Answer 12

• Carries fibres from superior retinal quadrants (Baumans loop)
• Travels through parietal lobe to visual cortex

Question 13

What is in the lower optic radiation?

Answer 13

• Carries fibres from the inferior retinal quadrants
• travels through the temporal lobe (via Meyer’s loop) to visual cortex

Question 14

What is the Meyer’s loop?

Answer 14

This is the inferior optic radiation loop and corresponds to the superior quadrant visual aspect

Question 15

What is the Bauman’s loop?

Answer 15

this is the superior optic radiation loop and corresponds to the inferior quadrant visual aspect

Question 16

What happens to our vision when we have damage to the left optic nerve?

Answer 16

No vision in the left eye

Question 17

What happens to our vision when we have damage to the optic chiasma?

Answer 17

Loss of vision of the temporal visual fields

Question 18

What happens to our vision when we have damage to the left optic tract?

Answer 18

Loss of vision to the:
Left eye nasal field
Right eye temporal field

Question 19

What happens to our vision when we have damage to the left Myer’s loop?

Answer 19

(inferior)
so loss of vision in right eye superior temporal and left eye superior nasal field

Question 20

What happens to our vision when we have damage to the left Baum’s loop?

Answer 20

loss of vision in right eye inferior temporal and left eye inferior nasal field