Lecture 27: Action Potentials: Generation and Transmission

Flashcards about Action Potentials: Generation and Transmission. The flashcards have been generated based on the provided lecture notes.

Action Potential

A brief fluctuation in membrane potential caused by a transient opening of voltage-gated ion channels which spreads, like a wave, along an axon.

Information

The frequency of action potentials encodes __

Signal transmission

Action potentials are a key element of __ along (often very long) axons.

Stimulus

A slow depolarisation evoked by a stimulus

Threshold

Membrane potential reaches __, followed by fast depolarisation to ~ +30 mV (‘overshoot’)

Absolute refractory

__ period = 1 + 2 (fast depolarisation to ~ +30 mV (‘overshoot’) + repolarization)

Relative refractory

__ period = 3 (After-hyperpolarisation)

voltage-gated Na+

When MP reaches the threshold there is a sudden activation (opening) of __ channels

Action potential

Each __ is an all- or-none event

Constant

The amplitude of action potentials is usually __ (~ 100 mV) and does not depend on the ‘stimulus’ intensity as long as the stimulus is ‘suprathreshold’.

Externally

Under experimental situations, you can provide electrical stimulation via a battery

Internally

Under physiological situations, post-synaptic potentials build up

Least resistance

Current follows the path of __!

axon initial segment (‘axon hillock’)

APs are first generated in the __, which has the lowest threshold, and thus serves as the ‘trigger zone’ for APs.

excitatory postsynaptic potentials (EPSPs)

Depolarisation to threshold is evoked by __ which spread mainly passively from dendrites.

actively

Once generated, APs are transmitted __ along the axon, away from the cell body

Myelination Action potential Transmission in Myelinated Axons

increase AP speed by increasing the efficiency of passive spread.

Ranvier

APs are generated only at nodes of __, and current flows passively between nodes. This process is known as saltatory conduction.

Receptor potential

First, it evokes a graded depolarisation in the sensory endings, known as the __

trigger

The receptor potential spreads passively to the nearby located __ zone, where APs are generated.