What are Neurons?

The human body is consist of more than hundred billion cells. And there are many different types of cells. Among these cells, some cells perform specialized tasks in the body system. In the human nervous system, the cells specialized for receiving, transmitting and processing of nerve impulses to and from the brain are known as neurons. They are the basic structural and functional units of the brain.
Structure of Neuron
Each neuron processes and transmits information in both chemical and electrical forms. Actually, neurons are the core component of the communication system in the human body. 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 of the body, a neuron is also consists of a nucleus, mitochondria, golgi bodies, cytoplasm and cell membrane.

Usually, 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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