Neuron Structure & Classification

What is a neuron and what is its main function?

A neuron is the functional unit of the nervous system that conducts impulses and carries information, mainly in the form of electrical signals.

Why can neurons create extensive networks of connections?

Their three-dimensional cell shapes allow them to form an extensive network of connections.

How does information normally travel through the main parts of a neuron?

Information is received by the dendrites, collected by the cell body, the signal is first generated at the axon hillock, and the impulse travels down the axon toward the synaptic terminal.

What is the role of dendrites in a neuron?

Dendrites receive input from other neurons or cells, functioning somewhat like antennae.

What is the cell body, and what does it do?

The cell body, or soma, is the main part of the neuron containing the cytoplasm and nucleus. It collects information from the dendrites and passes it onward.

What is the axon hillock and why is it important?

The axon hillock is where the cell body connects to the axon and is the site where nerve signals are first generated.

What is the function of an axon?

The axon conducts an electrical impulse away from the neuron's cell body and is also called a nerve fiber.

What is the axon or synaptic terminal?

It is the branched end of an axon that leads to the synaptic knob.

What does the synaptic knob do?

The synaptic knob is a small enlargement at the end of an axon that makes, holds, and secretes neurotransmitters.

What are Schwann cells and where are they found?

Schwann cells are cells in the PNS that surround a nerve fiber and form the neurilemmal sheath and myelin.

What is the function of the myelin sheath?

The myelin sheath consists of layers of lipid proteins surrounding the axon and provides insulation.

What is the neurilemma?

The neurilemma is the sheath formed from Schwann cells that surrounds the myelin sheath on the axon.

What are the Nodes of Ranvier?

They are gaps in the myelin sheath between Schwann cells located along the axon.

What is a synapse?

A synapse is the junction where a neuron meets another cell and exchanges chemical or electrical impulses.

What characteristics can differ between neurons when they are structurally classified?

Neurons can differ in structure, size, cell-body shape, axon and dendrite length and size, and the number of connections they make.

What are the three major structural classifications of neurons?

Multipolar, bipolar, and unipolar neurons.

How are multipolar neurons structurally organized?

They have many processes extending from the cell body. One process is an axon and the rest are dendrites.

Where are multipolar neurons mostly found?

They are mostly found in the brain or spinal cord.

How are bipolar neurons structurally organized?

They have two processes, one extending from each end of the cell body. One is an axon and the other is a dendrite.

Where are bipolar neurons found?

They are found in the eyes, nose, and ears.

How are unipolar neurons structurally organized?

They have one process extending from the cell body that divides into two branches, which function as a single axon.

What are the two branches of a unipolar neuron associated with?

The peripheral branch is associated with dendrites near a peripheral body part, while the central branch enters the brain or spinal cord.

What is a ganglion?

A ganglion is a mass of neuron cell bodies outside of the CNS.

What are the three major functional classifications of neurons?

Afferent (sensory) neurons, interneurons, and efferent (motor) neurons.

How are neurons classified functionally?

They are classified according to whether they conduct impulses into the CNS, within the CNS, or out of the CNS.

What do afferent neurons do?

Afferent, or sensory, neurons conduct impulses from peripheral body parts into the brain or spinal cord.

Why are afferent neurons called sensory neurons?

They receive sensory information from peripheral body parts and carry the resulting impulses into the CNS.

How can afferent neurons detect sensory information?

They may have specialized receptor endings at the tips of their dendrites or dendrites associated with receptor cells, such as skin receptor cells.

What happens when an afferent neuron is stimulated?

An impulse travels along its axon to the brain or spinal cord, where other neurons can process the impulse.

What structural type are most sensory neurons?

Most sensory neurons are unipolar, although some are bipolar.

What do interneurons do?

Interneurons conduct impulses from one part of the brain or spinal cord to another and help process and interpret incoming sensory information.

Where are interneurons located?

They lie entirely within the brain or spinal cord.

What are other names for interneurons?

Association neurons or relay neurons.

How do interneurons connect sensory information to motor responses?

They direct incoming sensory impulses to other parts of the CNS for processing and interpretation or transfer the impulse to efferent motor neurons.

What structural type are interneurons?

Interneurons are multipolar neurons.

What are nuclei?

Nuclei are masses of neuron cell bodies located inside the CNS.

What do efferent neurons do?

Efferent, or motor, neurons conduct impulses out of the brain or spinal cord to effectors.

What do motor impulses control?

Motor impulses control muscle contraction and secretion by glands.

What structural type are efferent neurons?

Efferent neurons are multipolar neurons.

What is the easiest way to distinguish afferent, interneuron, and efferent neurons?

Afferent carries information into the CNS, interneurons carry information within the CNS, and efferent carries information out of the CNS.

How does the functional pathway connect sensory and motor neurons?

Sensory information enters through afferent neurons, is processed or relayed by interneurons within the CNS, and leaves through efferent motor neurons to reach effectors.

What is the difference between a ganglion and a nucleus?

A ganglion is a mass of neuron cell bodies outside the CNS, while a nucleus is a mass of neuron cell bodies inside the CNS.

What is the difference between structural and functional classification?

Structural classification describes how a neuron is built, such as multipolar, bipolar, or unipolar. Functional classification describes what the neuron does, such as afferent, interneuron, or efferent.