Question

Describe the differences and similarities between graded and action potentials;

Describe the processes involved in the movement of an action potential along the axon of a neurone; explain how voltage changes with action potential propagation

Answer 1

Differences:

Origin: Action potential arises at trigger zones and propagates along axon while graded potential arises mainly on dendrites and cell body.

Types of channels Action potential involves voltage-gated channels for Na+ and K+ while graded potential involves ligand-gated or mechanically-gated ion channels.

Conduction: Action potential propagates and permits communication over long distances while graded potential do not propagated and permits communication over short distances only.

Amplitude: Action potential is typically about 100 mV while graded potential depends on the strength of stimulus and varies from <1 mV to >50 mV.

Duration: Action potential has shorter duration which ranges from 0.5 to 2 milliseconds while graded potential has typically longer which ranges from few milliseconds to few minutes.

Polarity: Action potential always consists of depolarizing phase followed by repolarizing phase and return to resting membrane potential while graded potential may be hyperpolarizing or depolarizing.

Refractory period: In action potential, refractory period is present and summation cannot occur while in graded potential, it is not present and summation can occur.

Similarities:

Both graded are membrane depolarizations of the nerve cells.

Both are generated as a result of transmission of signals.

Both involves Na+ and K+ ions.

The movement of action potential along axon of a neuron involve Depolarization and Repolarization.

A stimulus causes cell membrane to depolarized towards the threshold potential, causing all Na+ channels to open. This forms action potential. At the peak of the action potential, K+ channels open and K+ begins to leave the cell while Na+ channels close. This results in hyperpolarization of membrane. This state of membrane cannot fire as it is in refractory period. Then, K+ channels close and the resting potential is restored.