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Neurons are specialized cells in the central nervous system (CNS). They are classified according to structure, form and function. Each type of neuron has a specific role for the proper functioning of the brain and spinal cord.
We can classify neurons according to different criteria: according to their morphology and according to their function.
Classification according to morphology
There are four main types of neurons depending on their shape: unipolar, bipolar, pseudounipolar and multipolar.
The Unipolar neurons are the most common in invertebrates. These neurons are characterized by a primary projection that serves as the axon and dendrites.
From the soma comes a single extension that can be branched into many branches. One of these serves as an axon, and the others function as dendritic reception structures. They have no dendrites that leave the soma.
Another type of neurons are the bipolar neurons, each with an axon that transmits signals from the cell body that goes to the brain and spinal cord, and with dendrites that send signals from the body's organs to the cell body. These bipolar neurons are usually found in sensory organs, such as the eyes, nose and ears.
Sometimes, it is difficult to know which of the extensions is the axon and what the dendrites are. But from a functional point of view these dendrites are specialized in receiving information from other neurons, and the axon to conduct this information in the form of nerve impulses to the terminal buttons.
The pseudounipolar neurons they resemble unipolar neurons because each one has an axon, but no true dendrites. However, pseudounipolar neurons are actually variants of bipolar neurons. The reason for this is that the single axon attached to the cell body proceeds to two "poles" or opposite directions: one towards the muscle, joints and skin, and the other towards the spinal cord. Pseudounipolar neurons they are responsible for the sense of touch, pain and pressure.
The multipolar neurons they are the dominant neurons in vertebrates in terms of number. Each of them has a cellular body, a long axon and short dendrites.
Depending on the length of the axon, we can divide them into multipolars, type Golgi I and type Golgi II.
Type Golgi I: are multipolar long axon neurons.
They are multipolar neurons Golgi I type the pyramidal cells of the cerebral cortex and the purkinje cells of the cerebellum
Type Golgi II: they are multipolar short axon neurons and, therefore, establish contacts with nearby neurons.
According to its function
Neurons can also be classified according to their specific function. We can distinguish between sensory, motor and interneuron neurons.
Sensory neurons are those that collect information from different sensory organs, such as eyes, nose, ears, tongue and skin.
They are usually pseudomonopolar neurons.
Motor neurons transmit signals from the brain to the spinal cord to the muscles to initiate action or response to stimuli.
They are generally Golgi I multipolar neurons.
It is the most abundant type of neurons; they are all other neurons that are neither sensory nor motor.
The interneurons connect one neuron with another: the long axons of the projection interconnects connect distant regions of the brain; The shorter axons of the local interneurons form smaller circuits between the neighboring cells.
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