Neuron is the fundamental building block of the nervous system. It is a cell capable of communicating with other neurons and various other compatible cells in the human body. Unlike most of the other cells it can generate an action potential, so neurons are called excitable tissues. Neurons can be classified according to their function and the structure.
Functional classification
Sensory neurons
Sensory neurons are responsible for the sensations we are getting. They detect and transmit sensory data from our sense organs into the central nervous system.
Motor neurons
Motor neurons are responsible for our day to day activities. They send commands from our brain’s motor cortex into the skeletal muscles.
Autonomic nerves
Autonomic nerves are responsible for our automatic functions such as salivation, lacrimation, intestinal motility and control of heart rate.
Various interneurons
Interneurons are responsible for the data processing inside the brain and spinal cord grey matter. They connect sensory neurons to motor neurons via complex pathways. Complexity of the interneurons makes us what we are.
Structural (morphological) classification of neurons
Basic structure of neurons
Neurons have a cell body, axon, and dendrites. Axon is a relatively large projection from the neuron. Dendrites are relatively small projections. Usually neurons have only one axon and many dendrites. Some neurons have only one axon and others have only dendrites.
Usually axons are covered with a myelin sheath. There are several gaps in the myelin sheath called nodes of ranvier. Myelinated nerves conduct impulses much faster than non myelinated cells.
Unipolar neurons
Unipolar neurons have only one projection, and it is usually divided into two. Examples are neurons in the posterior root ganglion of the spinal cord.
Bipolar neurons
They have only two projections in the opposite direction. Examples can be found in retina of the eye.
Multipolar neurons
They have one axon and many dendrites.
Another structural classification is the golgi classification
Golgi type 1
Golgi type 1 neurons have very long axons. Some of them are travelling from the brain in to the tip of the big toe. Examples are purkinge cells of the cerebellum and the cerebral cortical pyramidal cells.
Golgi type 11
Golgi type 11 neurons have a short axon and they terminate near the parent cell. They are much more numerous than other types. Gogi type 11 neurons are the most common neurons in grey matter of the human brain.
Amacrine cells
Some neurons do not have any projections at all. They are rare.
