Neuron Structure and Types in the Nervous System

Overview of the Nervous System

The nervous system is composed of structural and functional units called neurons. Neuroglial cells are tightly packed spirals that cover most long fibers, servicing and supporting neurons, and making up as much as half of the nervous system.

Structure of a Neuron

A typical neuron consists of three parts: cell body, axon, and dendrites. The cell body contains the nucleus, cytoplasm, and other organelles. The axon conducts nerve impulses away from the cell body, and its end is subdivided into axon filaments. The dendrites or dendron, on the other hand, conduct impulses towards the cell body. Schwann cells, which wrap themselves around the axon and form a myelin sheath, are neuroglial cells found in the peripheral nervous system, leaving gaps called the nodes of Ranvier.

Types of Neurons

Neurons are classified according to their function and shapes into three types:

Sensory Neuron

Sensory neurons carry sensory information to the brain and spinal cord from different parts of the body. They have a structure that is typically unipolar, with a process that extends from the cell body dividing into a branch that extends to the periphery and another that extends to the central nervous system.

Interneuron

Interneurons occur within the central nervous system and are typically multipolar. They convey messages between various parts of the CNS, including those between sensory neurons and motor neurons or those from the brain to the cord vice versa. They also form complex pathways in the brain.

Motor Neuron

Motor neurons take messages from the central nervous system to muscle fibers or glands. They are said to be multipolar because they have many dendrites and a single axon.

Components of a Neuron

Nissl's granules, which are groups of ribosomes associated with rough ER and Golgi apparatus, are present in the cell body. Microtubules, neurofibrils, rough endoplasmic reticulum, and mitochondria are present throughout the axoplasm of the neuron. Dendrites and axons are collectively called neuron fibers.