visual system: from the retina to the cortex (I)

Question 1

How does information from the retina reach the cortex?

Answer 1

The axons of retinal ganglion cells project as the optic NERVES to the lateral geniculate nuclei. The fibers partially cross at the optic chiasm and continue as the optic TRACTS.

Question 2

Optic chiasm

Answer 2

The part of the brain where the optic nerves cross and is therefore of primary importance to the visual pathway.

Question 3

Left eye projections to the LGN + Draw it

Answer 3

1. Nasal → project on opposite side (right)
2. Temporal → project on same side (left)

Question 4

Right eye projections to the LGN + Draw it

Answer 4

1. Nasal → project on opposite side (left)
2. Temporal → project on same side (right)

Question 5

Where do midget and parasol project to in the LGN?

Answer 5

Midget and parasol cells project to six distinct layers in the LGN

Question 6

How are inputs arranged in the LGN?

Answer 6

Inputs from the two eyes and from the midget and parasol cells are segregated in distinct layers of the lateral geniculate nucleus.

→different eyes project to different layers
→M pathway & P pathway stay separate despite receiving mixed information from the different eyes

Question 7

Projections to the LGN: ipsilateral eye

Answer 7

Projects to layers II, III, V

Question 8

Projections to the LGN: contralateral eye

Answer 8

Projects to layers I, IV, VI

Question 9

Projections leaving the LGN: M-pathway

Answer 9

Projections from layers I, II

Question 10

Projections leaving the LGN: P-pathway

Answer 10

Projections from layers III, IV, V, VI

Question 11

Where do bistratified retinal ganglion cells project to in the LGN?

Answer 11

Bistratified retinal ganglion cells project to LGN layers in between the prominent magnocellular and parvocellular layers.

→referred to as koniocellular layers

Question 12

Koniocellular layers

Answer 12

Regions of the LGN, sparsely populated with small neurons, in between the prominent magnocellular and parvocellular layers where the bistratified retinal ganglion cells project to.

Question 13

T or F: a lot of convergence/divergence occurs at the level of the lateral geniculate nucleus to the primary visual cortex.

Answer 13

False!

Lateral geniculate neurons faithfully relay inputs from retinal ganglion cells to primary visual cortex, without significant change in the receptive fields