Cortex

Question 1

How many layers are there in the cortex?

Answer 1

6 layers (labelled counting from out to in)

Question 2

Which layer is the major output layer? (The working layer)

Answer 2

Layer 4 (counting out to in) made up of pyramidal cell bodies.

They received information from the outermost layers (1/2) where their dendrites extend to.

They transmit their output from axons that extend down in to the deeper layers (5/6).

Question 3

How are the pyramidal cells output modulated? (I.e. their excitations that they receive from their dendrites aren’t just always propagated to their axons?)

Answer 3

1. Feed-forwards inhibition:
   The same excitation that hits their dendrites also directly hits the dendrites of a bipolar cell.
   (Inhibits via the connecting basket cell)
2. Feed-back inhibition:
   The bipolar cell is also receiving the propagated signal after it has been propagated by the pyramidal cell body. (Inhibits via the connecting basket cell)

Question 4

What are the basic components of a cortical synapse?

Answer 4

Presynaptic nerve terminals

Synaptic cleft

Postsynaptic neurone: receptors (GABA, AMPA, NMDA)

Supporting glial cells

Question 5

What are the steps of transmission across a synapse?

Answer 5

Presynaptic nerve:

1. Sodium channels open causing influx of sodium
2. Potassium channels open causing efflux of Potassium
   - AP produced by this depolarisation and repolarisation-

Presynaptic nerve terminal:

3. AP reaches end of nerve terminal and opened VGCa channels, calcium influx occurs
4. Binding of vesicles by calcium and vesicles fuse with synapse releasing its neurotransmitter contents

Post synaptic membrane:
5. Neurotransmitters bind at receptors and cause:
GABA = chloride influx and inhibition
Glutamate = sodium or calcium influx and excitation

6. Then the glutamate and GABA are reuptaken by the glial cell (degraded by enzymes) or by the presynaptic membrane (degraded by enzymes or repackaged in vesicles)