Neuronal Communication

Question 1

How are electrical potentials measured, and what is the resting membrane potential?

Answer 1

Extracellular recording: Measures potentials outside the cell; lacks detail on individual neurons.
• Intracellular recording: Measures potentials inside the cell; provides specific details.
• Resting membrane potential (Vm) is about -70mV, determined by ion distribution (mainly Na⁺ and K⁺)

Question 2

How is the electrochemical gradient established?

Answer 2

Na⁺/K⁺ ATPase pump moves 3 Na⁺ out and 2 K⁺ in using ATP.

2. The impermeable membrane restricts ion movement to specialized channels, maintaining charge separation.
3. Ion movement depends on:

• Negative inside: Stops K⁺ from leaving.

• Positive inside: Stops Na⁺ from entering.

Question 3

How is the membrane potential calculated, and why is Vm closer to E(K)?

Answer 3

Use the Nernst equation for single ions or the Goldman-Hodgkin-Katz (GHK) equation for multiple ions.

• Simplified formula: Vm ≈ 58mV × log [C(out)/C(in)].

• Vm is closer to E(K) (-90mV) than E(Na) (+60mV) because the membrane is ~50x more permeable to K⁺.

Question 4

What are the principles of an action potential?

Answer 4

Depolarizing stimulus must reach a threshold.

2. Action potentials are all-or-nothing and propagate without losing size.
3. During the refractory period, the membrane is inexcitable.
4. At its peak, Vm approaches E(Na).

Question 5

How do voltage-gated ion channels function during an action potential?

Answer 5

Na⁺ channels: Closed → Open → Refractory (3 states).

• K⁺ channels: Closed → Open (no inactivation state but slower to open).

• During the refractory period, K⁺ overshoots, causing hyperpolarization. Leak channels help reset Vm.

Question 6

How does myelination affect conduction speed?

Answer 6

Myelinated axons: Faster conduction as Na⁺/K⁺ channels are localized at nodes of Ranvier. The signal travels internally in compact, fast signals.

• Non-myelinated axons: Slower conduction due to lack of insulation, signal loss, and continuous propagation along the entire axon.

Question 7

What is optogenetics, and how does it relate to ion distribution?

Answer 7

Optogenetics uses light to control neurons. For example, blue light can depolarize the membrane by altering ion distribution.

Question 8

What are the two types of refractory period?

Answer 8

Absolute - inactivation of Na+ channels, lasts until membrane potential is restored
Relative - results from hyperpolarization phase, when a greater stimuli is needed to reach threshold