Lecture 11

Question 1

What are the key differences between rods and cones?

Answer 1

• Rods: Dim light, high sensitivity, low acuity, no colour
• Cones: Bright light, low sensitivity, high acuity, colour-specific (RGB)

Question 2

What is the fovea and why is it important?

Answer 2

• Central pit in retina with displaced ganglion cells
• High density of cones, no rods or blood vessels
• Specialised for high-acuity, colour vision

Question 3

What is the optic disc and what is its significance?

Answer 3

• Exit point for retinal ganglion cell axons
• Entry/exit for retinal blood vessels
• No photoreceptors → physiological blind spot

Question 4

What is the general anatomical layout of the retina?

Answer 4

• The retina is a laminated structure
• Light must pass through the RGCs to reach the photoreceptors
• Information travels through the axons of the RGCs which form the optic nerve

Question 5

What is the flow of information through the retina?

Answer 5

Photoreceptors → Bipolar cells → Retinal Ganglion Cells (RGCs) → Brain

Question 6

What is a receptive field in the retina?

Answer 6

The area of photoreceptors that converge onto a single RGC, determining its sensitivity and spatial resolution

Question 7

How does convergence affect visual acuity and sensitivity?

Answer 7

• Fovea: 1:1 cone to RGC → high acuity, low sensitivity
• Peripheral retina: Many rods to one RGC → high sensitivity, low acuity

Question 8

What is the conscious visual pathway?

Answer 8

RGC → Optic nerve → Optic chiasm → Lateral Geniculate Nucleus (LGN) → Optic radiations → Primary visual cortex (V1)

Question 9

What is the function of the optic chiasm?

Answer 9

• Nasal retinal axons decussate
• Temporal retinal axons remain ipsilateral
• Ensures left visual field projects to right hemisphere and vice versa

Question 10

What is the stria of Gennari and where is it found?

Answer 10

• A dense band of myelinated fibres in V1
• Visible in histological sections
• Defines the striate cortex (V1)

Question 11

What are the dorsal and ventral visual streams?

Answer 11

• Dorsal stream (“Where”): V1 → V2/V3 → V5 → Parietal cortex → Spatial awareness, motion
• Ventral stream (“What”): V1 → V2/V4 → Temporal cortex → Object recognition, colour, faces

Question 12

What are the unconscious visual pathways from RGCs?

Answer 12

• Superior colliculus: Reflexive gaze shifts
• Pretectal nucleus: Pupillary light reflex
• Pulvinar: Spatial attention
• Suprachiasmatic nucleus: Circadian rhythm

Question 13

What is the pupillary light reflex pathway?

Answer 13

Light → Retina → RGC → Optic nerve → Optic chiasm → Pretectal nucleus → Bilateral Edinger-Westphal nuclei → CN III → Ciliary ganglion → Iris sphincter → Pupil constriction

Question 14

What is the difference between the direct and consensual pupillary light reflex?

Answer 14

• Direct: Pupil constriction in the eye receiving light
• Consensual: Pupil constriction in the opposite eye due to bilateral projection from pretectal nucleus