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Biology 2nd Baccalaureate

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7.2.1. Neuron


The neuron is the anatomical and physiological unit of the nervous system. Although they can have different shapes, the typical neuron is a star-shaped cell in which it is distinguished:

  • The neuronal bodysoma or perikaryon. It contains the cell nucleus.
  • Two types of branches:
    • A long branch, the axon. At its end he has the synaptic knobsa small vesicles containing neurotransmitters that will drop to transmit the nerve impulse and detect the dendrites of the next neuron. The axon may be surrounded by a sheath of myelin, a cover formed by the Schwann cells covering the axon leaving a small space between sheath uncovered and sheath, called nodes of Ranvier.
    • Numerous, short and branched extensions, called dendrites. They are responsible for receiving the nerve impulse.
Neurona en la que se señala el cuerpo celular y su núcleo, las dendritas, el axón, la mielina, los nódulos de Ranvier, etc.
300px-Neurona.svg.png (imagen PNG, 300 × 161 píxeles) - Escalado (0%). (s. f.). Recuperado a partir de

Activity: Parts of the neuron .

Do it yourself: Model of a neuron 

Neuron characteristics

The neurons are the main cells of the nervous system and are responsible for the transmission of the nerve impulse. They are the most differentiated cells, which has made them lose the ability to divide and reproduce, so when they die they are not replaced.

Neurons, like other cells, have a common structure. They are surrounded by a plasma membrane, which separates the interior of the neuron from the external environment that surrounds it. Furthermore, as has been seen, three parts are distinguished: the cell body, the dendrites and the axon.

Neurona en la que se aprecia su estructura interna
By LadyofHats (English original); Josell7 (Spanish translation) [Public domain], via Wikimedia Commons

Classification of neurons

There are several different types of neurons, so it can be classified according to the number and arrangement of their processes:

  • Multipolar (starry). It is the most typical form, with an axon and several dendrites emerging from the soma.
  • Bipolar. It has two processes (an axon and a dendrite) that come out of opposite places in the cell body.
  • Monopolar. It only has an extension that comes out of the soma. In some cases, this extension is divided into a dendritic and an axonal portion, calling this type pseudomonopolar.

Tipos de neuronas: multipolar, unipolar y bipolar

By Artwork by Holly Fischer [CC BY 3.0], via Wikimedia Commons

Neurons can also be classified according to their function:

  • Sensory or afferent neurons: carry information from sensory receptors (sense organs) to the Central Nervous System.
  • Motor or efferent neurons: they transmit information from the Central Nervous System to the effector organs (muscles or glands), in the opposite direction to the sensory ones.
  • Association neurons or interneurons: they connect sensory neurons with motor neurons, are the largest group of neurons and are found in the Central Nervous System.

The axons of many neurons group together to form nerves . Some nerves, such as the sciatic nerve, can measure up to a meter in length.

Imagen de la médula espinal donde las neuronas intercalares conectan neuronas sensitivas con neuronas motoras
By By Ruth Lawson Otago Polytechnic [CC BY 3.0], via Wikimedia Commons


Activity: Neurons and nerves.

Answer in your notebook

7.3.- Describe what a typical neuron looks like.

Answer in your notebook

7.4.- What type of neuron can a person have damaged who does not feel anything in his right hand? What if you can't move your left hand?


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