In Class Notes (2/12/25)

Question 1

Electrostatic Pressure – What does it do and how does it affect ion movement?

Answer 1

Opposite charges attract; similar charges repel. Shapes how ions move across the membrane. K+ diffuses out but is attracted back in by the neuron’s negative charge. Na+ diffuses in, attracted to the negative charge, but has limited leak channels, creating pressure for entry.

Question 2

What happens when ions enter or leave?

Answer 2

The membrane potential changes locally. At rest, the neuron is polarized, with a more negative charge inside.

Question 3

EPSPs (Excitatory Post-Synaptic Potential) – What is their effect on the neuron?

Answer 3

Depolarization that creates an excitatory effect. If enough depolarization occurs, an action potential (AP) is triggered. Many ways to depolarize a neuron, but APs are always the same.

Question 4

IPSPs (Inhibitory Post-Synaptic Potential) – What is their effect on the neuron?

Answer 4

Hyperpolarization that creates an inhibitory effect. The summation of EPSPs and IPSPs determines if there is enough depolarization to fire an AP.

Question 5

Action Potential – Where does it occur, and what happens when the threshold is reached?

Answer 5

Occurs at the axon hillock, where a high concentration of Na+ and K+ voltage-gated ion channels exist. When the threshold is reached, the gates open immediately for ~1 ms before becoming refractory. They cannot reopen until the membrane potential returns to a negative value near the threshold.