Neurophysiology Part 1: Neurons, Nerves, and Action Potentials

Question-and-answer flashcards covering core concepts from Part 1 of the neuro material (neuron structure, CNS/PNS, synapses, ion channels, membrane potentials, and the action potential).

What is the difference between a neuron and a nerve?

A neuron is a single nerve cell; a nerve is an organ that contains many neurons along with blood vessels and connective tissue.

What are the two main divisions of the nervous system?

Central nervous system (CNS) and Peripheral nervous system (PNS).

What are the two divisions of the PNS?

Sensory (afferent) and motor (efferent) divisions.

What are the two subdivisions of the motor division, and what does each control?

Somatic nervous system (voluntary control of skeletal muscle) and Autonomic nervous system (involuntary control of organs; subdivides into sympathetic and parasympathetic).

What is the somatic nervous system primarily associated with?

Voluntary control of skeletal muscles.

What does the autonomic nervous system regulate, and what are its main divisions?

Involuntary functions of visceral organs; divided into sympathetic (fight/flight) and parasympathetic (rest/digest).

How many cranial nerves are there, and which numerals should you know?

There are 12 cranial nerves; you should know Roman numerals I through XII.

What are dendrites, the soma, and the axon?

Dendrites are the primary receptive regions that receive signals; the soma (cell body) is the biosynthetic center; the axon is the impulse-generating/conducting region.

Where is the axon hillock located and what is its significance?

At the axon’s origin (between soma and axon); the site where the action potential is typically initiated if threshold is reached.

What are axon terminals responsible for?

They are the secretory region that releases neurotransmitters into the synaptic cleft.

What is myelin and which cells form it in the PNS and CNS?

Myelin is an insulating sheath around axons; formed by Schwann cells in the PNS and oligodendrocytes in the CNS.

What are nodes of Ranvier?

Gaps in the myelin sheath along a myelinated axon.

What is the functional difference between myelinated and unmyelinated axons?

Myelinated axons conduct impulses rapidly via saltatory conduction; unmyelinated axons conduct more slowly.

Where are ion channels located and what are the main types?

Voltage-gated channels are on the axon and nodes; chemically gated channels are on dendrites and soma; passive (leakage) channels are widespread.

Which ion channels are involved in generating and propagating the action potential?

Voltage-gated channels (primarily for Na+ and K+).

What is resting membrane potential (RMP) and its value?

The baseline membrane potential when the neuron is at rest; typically about -70 millivolts (mV).

Which ion is the primary extracellular ion and which is the primary intracellular ion?

Sodium (Na+) is the primary extracellular ion; potassium (K+) is the primary intracellular ion.

What is an electrochemical gradient?

A combined effect of concentration gradients and electrical gradients that drives ion movement across the membrane.

What is diffusion in the context of neurotransmitter signaling?

Movement of neurotransmitter molecules from a region of high concentration (presynaptic) to low concentration (postsynaptic) across the synaptic cleft.

What is a synapse and what is the synaptic cleft?

A synapse is the junction between two neurons; the synaptic cleft is the gap between the presynaptic axon terminal and the postsynaptic dendrite/soma.

What does presynaptic mean and what does postsynaptic mean?

Presynaptic refers to the neuron sending the signal before the synapse; postsynaptic refers to the neuron receiving the signal after the synapse.

What are axodendritic and axosomatic synapses?

Axodendritic: axon of one neuron to dendrite of another; axosomatic: axon of one neuron to the soma (cell body) of another.

What is a synaptic cleft, and why is it important for neurotransmission?

The space across which neurotransmitters diffuse to pass the signal from the presynaptic to the postsynaptic neuron.

What is the difference between a nerve and a neuron when it comes to tissue organization?

A neuron is a single cell; a nerve is an organ composed of many neurons plus connective tissue and blood vessels.

What is the resting membrane potential driven by in part by?

Passive ion channels (leak channels) that help maintain the -70 mV resting potential.

What is the action potential and why is it important?

A rapid, short-lasting electrical impulse that travels along the axon; it is the nerve signal that triggers communication with other neurons or effectors.

What are the three phases of the action potential and what happens in each?

Depolarization (Na+ influx makes inside more positive), Repolarization (Na+ channels inactivate; K+ channels open; inside becomes more negative), Hyperpolarization (membrane becomes more negative than rest before returning to rest).

What is threshold and its typical value?

The membrane potential (-55 mV) that must be reached to trigger an action potential.

What is the difference between an absolute and a relative refractory period?

Absolute refractory period: no second action potential can be generated regardless of stimulus strength; Relative refractory period: a second AP can occur but only with a stronger-than-normal stimulus.

What is the role of the Na+/K+ pump?

To restore ion gradients after an action potential by moving Na+ out and K+ in, returning the cell to its resting state.