visual pathway

PATHWAY

Visual pathway relays signal in the following way:

1. Receptors receive signals 

2. They synapse with bipolar cells 

3. Bipolar cells synapse with ganglion cells 

4. Ganglion cells from the optic nerve 

5. Fibres of the optic nerve cross over each other partially at the optic chiasma 

6. The nasal half of the retina crosses over at optic chiasma (retinal half stays intact)

7.  After crossing over the optic track is formed 

8. The optic track reaches the lateral geniculate body

9. From the lateral geniculate body, it proceeds as optic fibres

10. Optic fibres end in the primary visual cortex 

Note: the optic track is formed by optic tracks from the opposite side and the temporal track of the same side 

In short :

1. Optic nerve

 2. Optic chiasma

 3. Optic tract

 4. Lateral geniculate body

 5. Optic radiation 

6. Visual cortex.

Optic nerve 

• The optic nerve is formed by axons of ganglionic cells 

• Leaves eye through optic disk 

• The temporal part of the optic nerve carries impulse from the nasal half 

• The nasal part of optic nerve carries impulse form temporal half 

Optic chiasma 

• Medial fibres of each optic nerve cross the midline and join the uncrossed lateral fibres of the opposite side, to form optic track 

• The cross over area is called optic chiasma 

Optic tract 

LATERAL GENICULATE BODY

The optic track brings signals from eyes and ends in the lateral geniculate body 

From the lateral geniculate body the neurons process as optic fibres and end in the visual cortex 

The lateral geniculate body has 6 layers named from 1 to 6.

• Layers 1, 4 and 6 receive inputs from the medial half of the eye 

• Layers 2, 3 and 5 receive inputs from the lateral half of the eye 

MAGNOCELLULAR LAYER

• Layers 1 and 2 contain large neurons called magnocellular layers 

• These cells are called M cells (Y type retinal ganglion cell)

• They project to the magnocellular layer of LGB 

• They transmit black and white visual signals 

PARVOCELLULAR LAYER

• Layers 3 to 6 have small to medium-sized nerves called the parvocellular layer 

•  X type cells and P-type cells of retinal ganglion project to this layer 

• The velocity of transmission is slow