Neurons and Action Potentials: Key Concepts in Neurophysiology

What are the two primary types of cytoplasmic extensions found in a neuron?

Dendrites, which receive information, and axons, which send signals.

What is the function of the axon hillock?

It is the base of the axon where electrical signals are generated.

Define a nerve in the context of neuron anatomy.

A nerve consists of the axons of many neurons held together by connective tissue.

What are the three functional types of neurons and their roles?

Sensory (afferent) neurons carry signals to the nervous system; interneurons integrate information; motor (efferent) neurons carry signals to effectors.

What does it mean for a cell membrane to be polarized?

It means there is a difference in electrical charge on either side of the membrane, with the outside being more positive than the inside.

What is an excitable cell?

A cell that can rapidly change its membrane potential, such as neurons and muscle cells.

What two mechanisms primarily maintain the resting membrane potential?

The sodium-potassium pump and leaky potassium channels.

How does the sodium-potassium pump function?

It uses active transport to pump 3 Na+ ions out of the cell and 2 K+ ions into the cell per cycle.

What is the role of leaky potassium channels in resting potential?

They are always open, allowing K+ that was pumped in to diffuse back out, contributing to the negative membrane potential.

Define hyperpolarization and depolarization.

Hyperpolarization is when the membrane potential moves further from zero (more negative); depolarization is when it moves closer to zero (less negative).

What is the threshold potential for most neurons?

-55 mV.

What triggers the opening of voltage-gated ion channels?

They open in response to specific changes in membrane potential.

What happens during the rising phase of an action potential?

Voltage-gated Na+ channels open at the threshold, causing rapid depolarization as Na+ enters the cell.

What occurs during the falling phase of an action potential?

Voltage-gated Na+ channels close and voltage-gated K+ channels open, allowing K+ to diffuse out and the membrane potential to fall.

What is the cause of the undershoot phase?

K+ channels remain open after the falling phase, causing the membrane potential to become more negative than the resting potential (hyperpolarization).

What does the 'all-or-nothing' principle of action potentials mean?

An action potential either occurs fully once the threshold is reached or does not occur at all; the strength of the action potential is always the same.

How does the nervous system communicate the intensity of a sensation?

Intensity is communicated through the frequency of action potentials and the number of neurons involved, not the strength of individual action potentials.

Why is the propagation of an action potential unidirectional?

Because the area behind the action potential is in a refractory period, preventing the signal from traveling backward.

What is continuous conduction?

The propagation of an action potential in unmyelinated axons, characterized by a smooth wave of depolarization along the entire length of the axon.

What is saltatory conduction?

The propagation of an action potential in myelinated axons, where the signal 'jumps' from one Node of Ranvier to the next.

What are the Nodes of Ranvier?

Gaps in the myelin sheath where Na+ and K+ channels are concentrated, allowing for depolarization.

What are the advantages of saltatory conduction over continuous conduction?

It is significantly faster (up to 50x) and more energy-efficient.