Nerve Impulse in Biology

Study Notes

Signal Strength and Nerve Impulses

Signal strength varies based on the number of neurons stimulated and the frequency of action potentials (APs).
The strength of an individual AP remains constant.

Action Potential Propagation

Nerve impulses consist of a series of action potentials.
At a node of Ranvier, sodium ions (Na+) flow into the axon, causing depolarization.
After Na+ influx, Na+ pumps close, and Na+ diffuses along the axon in both directions.
The next node becomes depolarized due to the increased positive charge, triggering another AP.
Impulses cannot reverse direction due to the refractory period at previous nodes.

Saltatory Conduction

Myelinated cells exhibit saltatory conduction, where action potentials jump between nodes of Ranvier.
This allows for significantly faster impulse transmission compared to non-myelinated fibers.
A larger axon diameter enhances impulse speed; myelination effectively increases the axon's diameter.

Synapses

A synapse is the connection between two neurons or a neuron and an effector.
Nerve impulses travel to synaptic terminals, where a synaptic cleft exists between neurons.

Neurotransmitter Function

Neurotransmitters are chemical messengers that facilitate signal transmission across the synaptic cleft.
Sequence of events at the synapse:
- AP reaches the presynaptic neuron's end.
- Synaptic vesicles containing neurotransmitters undergo exocytosis, fusing with the axon membrane.
- Neurotransmitters are released into the synaptic cleft.
- They bind to receptor proteins on the postsynaptic membrane, opening ion channels.
- If depolarization reaches the threshold, an AP is initiated in the next neuron.

Description

Test your understanding of nerve impulses, focusing on action potentials and their transmission. Explore how the strength of signals is affected by neuron stimulation and frequency, and the role of nodes of Ranvier in the conduction process.