Nervous System Overview & Neurophysiology

A comprehensive set of question-and-answer flashcards covering nervous system organization, neuron structure and function, electrophysiology, signal conduction, and synaptic transmission.

Which two organ systems coordinate internal functions, and how does each communicate?

The endocrine system (via hormones in the blood) and the nervous system (via electrical and chemical signals from cell to cell).

What are the three basic steps by which the nervous system carries out its task?

1) Sensory organs detect changes and send information to the CNS; 2) The CNS processes the information and decides what to do; 3) The CNS issues commands to muscles or glands (effectors).

What structures constitute the central nervous system (CNS)?

The brain and spinal cord, enclosed by the cranium and vertebral column.

What makes up the peripheral nervous system (PNS)?

All nervous tissue outside the CNS—nerves and ganglia.

Define a nerve.

A bundle of nerve fibers (axons) wrapped in fibrous connective tissue.

Define a ganglion.

A knot-like swelling in a nerve where neuron cell bodies are concentrated.

Into which two functional divisions is the PNS separated?

The sensory (afferent) division and the motor (efferent) division.

What information does the somatic sensory division carry?

Signals from receptors in skin, muscles, bones, and joints to the CNS.

What information does the visceral sensory division carry?

Signals from the viscera (heart, lungs, stomach, urinary bladder) to the CNS.

What does the somatic motor division control, and what kinds of responses can it produce?

It carries signals to skeletal muscles, producing voluntary movement and somatic reflexes (involuntary contractions).

What tissues are controlled by the autonomic (visceral motor) nervous system?

Cardiac muscle, smooth muscle, and glands.

What general effect does the sympathetic division have?

It tends to arouse the body for action—accelerates heart rate and respiration, inhibits digestion and urination.

What general effect does the parasympathetic division have?

It calms the body—slows heart rate and breathing, stimulates digestion and urination.

Name the three universal properties of neurons.

Excitability, conductivity, and secretion.

List the three functional classes of neurons.

Sensory (afferent) neurons, interneurons, and motor (efferent) neurons.

What primary role do interneurons play?

They lie entirely within the CNS and perform integrative functions—processing and decision-making.

What is the control center of a neuron called?

The neurosoma (cell body or soma).

What is the axon hillock?

A mound on the neurosoma from which the axon originates; often called the trigger zone.

Which structures receive signals from other neurons?

Dendrites.

What is an axon terminal?

The swollen distal end of an axon that forms a synapse with the next cell and contains neurotransmitter-filled vesicles.

Describe a multipolar neuron.

It has one axon and multiple dendrites; it is the most common neuron type in the CNS.

Where are bipolar neurons typically found?

In the olfactory epithelium, retina, and inner ear.

Which neuron type has a single process leaving the soma and functions mainly as a sensory neuron?

A unipolar (pseudounipolar) neuron.

Which neuron type has many dendrites but no true axon?

An anaxonic neuron, found in the retina, brain, and adrenal gland.

Approximately what is the resting membrane potential (RMP) of a typical neuron?

About −70 millivolts (mV).

Which ion has the greatest influence on the RMP, and why?

Potassium (K+) because the membrane is more permeable to K+ than to any other ion.

How does the Na+/K+ pump maintain ion gradients (numbers and direction)?

It moves 3 Na+ ions out of the cell for every 2 K+ ions it brings in, using one ATP.

What is a local potential?

A small, graded change in membrane potential that occurs near the site of stimulation on a neuron.

Give four properties that distinguish local potentials from action potentials.

Local potentials are graded, decremental, reversible, and can be excitatory or inhibitory.

What membrane voltage threshold must be reached for most neurons to fire an action potential?

About −55 mV.

During the depolarization phase of an action potential, which channels open and what ion enters the cell?

Voltage-gated Na+ channels open, and Na+ rushes into the cell.

Why is an action potential said to follow an all-or-none law?

If threshold is reached, the neuron fires at full amplitude; if threshold is not reached, it does not fire at all.

Name the two phases of the refractory period.

The absolute refractory period and the relative refractory period.

During which refractory phase can no stimulus, no matter how strong, trigger another action potential?

The absolute refractory period.

How do unmyelinated fibers propagate action potentials down the axon?

By continuous conduction—sequential opening of voltage-gated channels along the entire length.

What is continuous conduction?

A step-by-step depolarization and repolarization of each adjacent membrane segment in an unmyelinated fiber.

How do myelinated fibers propagate electrical signals?

By saltatory conduction—action potentials jump from one node of Ranvier to the next.

Define saltatory conduction.

The rapid, node-to-node leap of action potentials along a myelinated axon.

Why does myelin speed nerve conduction?

It reduces ion leakage and increases the distance over which local currents can travel inside the axon.

What happens at a node of Ranvier during signal conduction?

High concentrations of voltage-gated channels open, regenerating a full-strength action potential.

In a chemical synapse, which neuron releases neurotransmitter?

The presynaptic neuron.

What is the neuron that responds to neurotransmitter called?

The postsynaptic neuron.

Name three anatomical relationships possible between two communicating neurons.

Axodendritic, axosomatic, and axoaxonic synapses.

Approximately how many synaptic inputs can a typical spinal motor neuron receive?

About 10,000 synapses (≈8,000 on dendrites and ≈2,000 on the soma).

Roughly how many synapses can a single neuron in the cerebellum possess?

Up to about 100,000 synapses.