Lecture Objectives for: Impulse Conduction and Synaptic Transmission

Question 1

Describe the action potential propagation and explain how this affects the coding of information by action potentials

Answer 1

The action potential is propagated in a all-or-nothing fashion because of the voltage at the voltage threshold being strong enough to initiate the opening of voltage-gated sodium channels in the adjacent tissue; Due to the all-or-nothing nature of the action potential, the coding of information is determined by the frequency, which is dependent on the action potential duration and the refractory periods.

Question 2

Explain how the presence of a myelin sheath around axons of neurons produces saltatory conductance and why action potentials are conducted faster along myelinated axons

Answer 2

Myelin sheaths reduce the capacitance of the membrane, meaning a lower amount of ions is required to move the voltage along the membrane- making it easier for the charge to move of the charge because the lipid acts as an insulator, and so the action potential reinitiates in between the myelinated areas, creating areas for saltatory conductance. The action potential velocity is proportional to the fraction (1/R_a*C_m) thus, the reduction of the capacitance increases the velocity of the AP.

Question 3

Describe the effect of axon diameter on conduction velocity

Answer 3

In the same fashion as the example with the capacitance, the reduction of the axial resistance, which is affected by the axon’s diameter, will increase the conduction velocity.

Question 4

Compare and contrast electrical and chemical synapses

Answer 4

• Electrical synapses: bidirectional, initiates the opening of gates along the membrane through conductance
• Chemical synapses: unidirectional, releases and binds neurotransmitters

Question 5

List the steps of synaptic transmission by chemical synapses

Answer 5

1st: The action potential reaches terminal
2nd: Voltage-gated Ca2+ channels open
3rd: Calcium enters axon terminal
4th: Neurotransmitter releases and diffusion
5th: Neurotransmitter binds to postsynaptic receptors
6th: Neurotransmitter removed from the synaptic cleft

Question 6

Explain the significance of voltage-gated calcium channels to synaptic transmission

Answer 6

The calcium channels are critical for the release of the chemicals (neurotransmitters) in the synaptic vesicles into the synaptic cleft.

Question 7

Provide definition and mechanism explaining the phenomena of facilitation

Answer 7

Definition: Postsynaptic Potentials evoked by an impulse are increase when that impulse closely follows a prior impulse.

Mechanism: Action potentials close together at the pre-synaptic membrane (opening the voltage-gated calcium channels).. The calcium influx enables the synaptic vesicles to fuse to the presynaptic membrane, using SNARE, and release their neurotransmitter into the synaptic cleft.

Question 8

Provide definition and mechanism explaining the phenomena of post-tetanic potentiation

Answer 8

Definition: High-frequency sequence of action potentials which causes an increase in neurotransmitters

Mechanism: A large accumalation of Ca

Question 9

Provide definition and mechanism explaining the phenomena of long-term potentiation

Answer 9

The cell is rapidly stimulated and this results in a stronger response

Question 10

What is synaptic plasticity?

Answer 10

the ability of synapses to strengthen or weaken over time in response to increases or decreases in their activity