Steps in neurotransmission/action potential and vocabulary

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Three main areas involved in synaptic transmission

Presynaptic cell, synaptic cleft, postsynaptic cell.

Step 1 (What arrives at the axon terminal?)

Action Potential (AP) arrives at terminal

Step 2 (What allows chemicals to release?)

Voltage-gated calcium channels open, causing calcium influx into the synapse.

Step 3 (What does the Ca⁺ do?)

Calcium makes vesicles fuse to the membrane to release signals for neurotransmitters to be released

Step 4 (What do the released chemicals do?)

The NTs release and diffuse across cleft

Step 5 (What do these chemicals bind to?)

NTs bind to receptor molecules on the postsynaptic cell

Step 6 (What do these receptors do?)

Receptor allows ions to flow into the cell causing (Excitatory postsynaptic potential) EPSP or (Inhibitory postsynaptic potential) IPSP

Step 7 (Once the NTs have done their job, what next?)

NTs are inactivated somehow (e.g, taken up by reuptake transporters)

Step 8 (What can NTs also do after reception?)

NTs can also bind to autoreceptors to give feedback to presynaptic cell

Excitatory postsynaptic potential (EPSP)

Na+ channels open > influx of Na+. Happens during AP firing (rest (right before) + depolarization)
* Change in the membrane potential of the postsynaptic cell in response to the NT.

Inhibitory postsynaptic potential (IPSP)

Cl- channels open > influx of Cl-. Happens after Na channels close (absolute refractory, relative refractory, at rest)
* Change in the membrane potential of the postsynaptic cell in response to the NT.

Action Potential

Rapid change in membrane potential in response to threshold stimulus followed by return to RMP

At Rest

~-65mV. Sometimes different because of movement.

Depolarization

-50mV. Voltage-gated sodium channels open; sodium floods into the cell.

Absolute refractory/Repolarization

Potassium floods out, downward as channels close, preventing sodium from entering further. Cannot fire again during this time.

Relative refractory/Hyperpolarization

More negative, below, resting to recharge. Need a larger stimulus to trigger another AP compared to rest (~70)

Saltatory Conduction

Propagation at nodes of ranvier as it ‘recreates’ the AP at each node. (openings between myelin sheaths) propagation can become faster via Myelin.