Classification of Neurons

Neurons can be classified in two primary ways: structural classification and functional classification.

Structural Classification of Neurons

Neurons are differentiated based on the number of processes attached to the cell body:

1. Unipolar Neurons

• Have a single process projecting from the cell body.
• Also called pseudo-unipolar when the single process branches.

2. Bipolar Neurons

• Have two processes extending from the cell body.
• Rare in the body, typically found in special senses (e.g., retina of the eye).

3. Multipolar Neurons

• Have more than two processes emerging from the cell body.
• Most common type of neuron.

Common Features

• Regardless of structural differences, all neurons have regions to receive information, generate and conduct action potential, and convey action potential to the next cell.
• Utilize color coding for illustrating different regions and parts.

Functional Classification of Neurons

Functional classification is based on the direction of information flow:

1. Sensory Neurons

• Carry information into the central nervous system (CNS).
• Typically unipolar neurons.

2. Interneurons

• Completely contained within the CNS.
• Do not project in or out of the CNS, act as internal wiring.
• Most numerous type, involved in internal connections in the brain and spinal cord.

3. Motor Neurons

• Carry information from the CNS out to the body.
• Typically multipolar neurons.

Key Points

• Unipolar neurons are generally associated with sensory functions, whereas multipolar neurons are associated with motor functions.
• Interneurons are numerous and essential for internal connectivity in the CNS but do not fit neatly into the structural categories.
• Bipolar neurons are rare and primarily associated with special senses.