What are Neurons?

The human body is made up of around 30 trillion cells, with over 200 different cell types. Each type of cells have their own structure and function. Of these, some perform distinctly specialized tasks in the body system.

In the human nervous system, cells specialized in receiving, transmitting and processing nerve impulses to and from the brain are known as neurons. They are the basic structural and functional units of the brain and serve as the core component of the communication system in the human body

Structure of Neuron Each neuron processes and transmits information in both chemical and electrical forms. They receive electric signals from all parts of the body and translate these signals into specific neurotransmitters and deliver these neurotransmitters to target cells.

Structurally, similar to other cells in the body, a neuron generally consists of a nucleus, mitochondria, golgi bodies, cytoplasm and cell membrane.

However, most neurons have three distinct parts:
  1. A cell body
  2. An axon
  3. Multiple dendrites

Classification of Neurons

Neurons are classified by many different criteria.

According to their functions, they can be classified into two types:
  1. Sensory or Afferent Neurons. They carry sensory information from tissues and organs to the nervous system.
  2. Motor or efferent Neurons. They transmit nerve impulses from the nervous system to the effector cells in the body.
Based on the number and arrangements of processes attached to the cell body, they can be classified into three types. These include:
  1. Unipolar Neurons. They have a single, short process that includes both the axon and dendrite (e.g. dorsal root ganglion neurons). They are exclusively sensory neurons and serve to transmit general sensation.
  2. Bipolar Neurons. They have two processes, the axon and a single dendrite. They are not very common in the human body, and found mostly in the olfactory epithelium and inner nuclear layer of retina.
  3. Multipolar Neurons. They have more than two processes, a single axon and two or more dendrites (e.g. pyramidal cell of cerebral cortex). They are common and have an extensive dendrite tree.

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