Physio Ex Exercise 3 Activity 5 (2025)

FAQs

What is inactivation as it applies to a voltage gated sodium channel? ›

1. Define inactivation as it applies to a voltage-gated sodium channel. Voltage-gated sodium channels are inactivated when they no longer allow sodium to diffuse through.

Most often, the threshold potential is a membrane potential value between –50 and –55 mV, but can vary based upon several factors. A neuron's resting membrane potential (–70 mV) can be altered to either increase or decrease likelihood of reaching threshold via sodium and potassium ions.

The value of the membrane potential at which an action potential is initiated is called the threshold value. Threshold is usually about 20 mV above the resting potential.

You correctly answered: The threshold for the first action potential is lower than the threshold for the second action potential.

Voltage-gated Na(+) channels (VGSCs) initiate action potentials thereby giving rise to rapid transmission of electrical signals along cell membranes and between cells. Depolarization of the cell membrane causes VGSCs to open but also gives rise to a nonconducting state termed inactivation.

Abstract. Voltage-gated sodium channels open (activate) when the membrane is depolarized and close on repolarization (deactivate) but also on continuing depolarization by a process termed inactivation, which leaves the channel refractory, i.e., unable to open again for a period of time.

A voltage change that reaches threshold will cause voltage-gated sodium channels to open in the axonal membrane. The influx of sodium causes the rising phase of the action potential, but the ion flow also depolarizes nearby axon regions. As the depolarization reaches threshold, the action potential moves down the axon.

Depolarization also opens voltage-gated K⁺ channels, allowing K⁺ efflux, which, together with rapid Na⁺ channel inactivation, quickly repolarizes the membrane during the falling phase of the action potential. This enables the cell to propagate electrical signals quickly and with high efficiency.

When the depolarization reaches about -55 mV a neuron will fire an action potential. This is the threshold. If the neuron does not reach this critical threshold level, then no action potential will fire.

The cell membrane must reach threshold before voltage-gated Na⁺ channels open. If threshold is not reached, those channels do not open, and the depolarizing phase of the action potential does not occur, the cell membrane will just go back to its resting state.

What is the refractory period of a neuron? ›

The refractory period is a state of recovery that occurs after a neuron has fired an action potential. During this period, another action potential cannot be easily produced. This encourages unidirectional flow of action potentials because they cannot travel backwards to inactive neurons.

Acetylcholine. This excitatory neurotransmitter does a number of functions in your central nervous system (CNS [brain and spinal cord]) and in your peripheral nervous system (nerves that branch from the CNS).

So, an action potential is generated when a stimulus changes the membrane potential to the values of threshold potential. The threshold potential is usually around -50 to -55 mV.

In its wake, the action potential leaves the Na⁺ channels inactivated and K⁺ channels activated for a brief time. These transitory changes make it harder for the axon to produce subsequent action potentials during this interval, which is called the refractory period.

Process in a typical neuron

A stimulus is applied at time = 1 ms, which raises the membrane potential above −55 mV (the threshold potential). After the stimulus is applied, the membrane potential rapidly rises to a peak potential of +40 mV at time = 2 ms.

Voltage-gated ion channel in its closed, open, and inactivated states. The inactivated channel is still in its open state, but the ball domain blocks ion permeation. The ball and chain model, also known as N-type inactivation or hinged lid inactivation, is a gating mechanism for some voltage-gated ion channels.

1. Define inactivation as it applies to voltage-gated sodium channel. Voltage-gated sodium channels are. inactivated when they no longer allow sodium to diffuse through.

Voltage-dependent inactivation of Na⁺ channels is a consequence of voltage-dependent activation (Aldrich et al., 1983), and inactivation is characterized by at least two distinguishable kinetic components: an initial rapid component (fast inactivation) and a slower component (slow inactivation).

Each Na+ channel has two voltage-sensitive gates, an activation gate, and an inactivation gate. The activation gate opens and closes the channel. The inactivation gate plugs the channel when the cell activation gate is open. Sodium can only pass through the channel in the open state.