Action Potential: Definition, Steps, Facts, Phases, FAQs

Definition Of Action Potential

The action potential is the brief fluctuation in the electrical potential that occurs in the membrane of a nerve cell (neuron) or muscle cell during the transmission of a nerve impulse or the contraction of a muscle fibre.

Action potentials are the main way the cells of the nervous system communicate over long distances and underlie nearly all higher brain functions like perception, action, and thought.

Cellular Basis Of Action Potential

The action potential is generated in the following step-by-step process initialised by the neuron membrane and ion channels:

Structure Of Neuron

• The cell body, dendrites, axon

• It depolarises due to the opening of sodium channels and repolarises due to the

Latest: NEET 2024 Paper Analysis and Answer Key 

Don't Miss: Most scoring concepts for NEET | NEET papers with solutions

New: NEET Syllabus 2025 for Physics, Chemistry, Biology

NEET Important PYQ & Solutions: Physics | Chemistry | Biology | NEET PYQ's (2015-24)

This Story also Contains

1. Definition Of Action Potential
2. Cellular Basis Of Action Potential
3. Generation of Action Potential
4. Propagation Of The Action Potential
5. Factors Determining Action Potential
6. Action Potential And Transmission Of Nerve Impulse
7. Disorders Related To Action Potential
8. Significance In Neurological Research
9. Recommended Video On ‘Action Potential’

opening of potassium channels.

Resting Membrane Potential

Normally −70 mV because of ion concentration gradients, the sodium-potassium pump creates.

Generation of Action Potential

Action potential occurs in several phases:

Threshold Potential

• Lowest membrane potential that can be used to initiate an action potential.

Depolarisation Phase

• Open sodium channels, allow sodium ions to enter, the membrane is thus depolarised.

Repolarisation Phase

• Open potassium channels, allowing potassium ions to exit, hence repolarising the membrane.

Hyperpolarisation Phase

• At this point, the membrane potential becomes slightly more negative than at rest.

Propagation Of The Action Potential

Conduction down the axon:

Saltatory Conduction Vs. Continuous Conduction

• Saltatory conduction occurs in myelinated axons.

• Here, the action potentials jump between the nodes of Ranvier.

Role Of Myelin Sheath

• The myelin sheath insulates and speeds up the conduction by reducing ion leakage across the membrane.

Nodes Of Ranvier

• They are small gaps in the myelin sheath, where action potentials are regenerated

Factors Determining Action Potential

There are several factors determining action potential kinetics.

Temperature

• Higher temperatures increase the conduction velocity.

Axon Diameter

• The greater the diameter the less resistance, so conduction takes more rapidly.

Myelinisation

• Myelinated axons conduct impulses faster than unmyelinated axons because of the saltatory conduction in myelinated axons.

Action Potential And Transmission Of Nerve Impulse

Action potentials transmit messages through synapses:

Synaptic Transmission

Neurotransmitters are stored in the synaptic vesicles of axon terminals. When an action potential reaches the axon terminals, calcium ions enter the cell, the neurotransmitter gets released into the synapse between the neuron and muscle fibre through which the action potential produces muscle contraction.

Disorders Related To Action Potential

• Multiple Sclerosis, where myelin is damaged and the signal does not travel properly.

• Medications are used in diseases associated with the modulation of the ion channels or neurotransmitter release in neurological disorders.

Significance In Neurological Research

Action potential research methodologies, and trends:

• Techniques within electrophysiology in recording an action potential.

Current Trends In Research

• Studying synaptic plasticity, ion channel mutations, and neural circuitry.

Conclusion

Understanding action potential is fundamental to comprehending nervous system function, and ongoing research holds promise for advancing treatments for neurological disorders.

Recommended Video On ‘Action Potential’