Sensory visual processing

action potential

electrical signals that travel along neuronal axons to conduct information to the brain

where are action potentials generated?

the axon hillock — the point where the neuronal cell body narrows to form the axon

what is depolarisation?

depolarisation occurs when a neural cell undergoes a shift in electrical charge across its cell membrane that results in a less negative charge inside the cell compared to the outside

what is hyperpolarisation?

• the reverse of depolarisation

• it is a shift in electrical charge across a neuronal cell membrane that results in more negative charge inside the cell compared to outside the cell

what is repolarisation?

• this occurs after depolarisation, as the negative charge inside the cell progressively increases, shifting the electrical charge across the cell membrane towards equilibrium

what happens when an appropriate stimulus is placed in a neural cell’s receptive field?

an increased rate of action potentials occurs (+)

what happens when an inappropriate stimulus is placed in the cell’s receptive field?

it will have no or little effect, or can even suppress the rate of action potentials (-)

parvocellular cells (small)

• small RGC with small spread of dendrites

• small receptive fields

• they can discriminate fine detail

• are colour sensitive

• dominate in the fovea

magnocellular cells (large)

• large RGC with a large spread of dendrites

• large receptive field and average signals from many bipolar cells

• relatively insensitive to detail & not colour sensitive

• are motion sensitive

• mainly found in the peripheral retina