Image of a nerve cell (enlarged under a microscope)
The nerve is an anatomical structure formed by multiple neuronal axons and dendrites, responsible for the transmission of the electrical nerve impulse.
Simply put, we can understand that each nerve is surrounded by a connective tissue tube (called epineurium) and that it has several nerve fascicles that are surrounded by another layer of connective tissue (perineurium) that is lined with a third layer of tissue. connective tissue called endoneurium.
The nerve fibers are formed by an axon and its sheaths wrap. Nerve fibers are divided into two types: myelinic (small axons that have only one myelin fold) and myelinic (large-caliber axons that have many myelin sheath folds). The region without myelin is known as the Ranvier nodule, and it is through this region that the nerve impulse is propagated.
Sensory nerves transmit a pulse generated by a sensory receptor of the central nervous system. As an example, we can mention the motor nerves, which transmit an impulse from the central nervous system to a peripheral muscle or viscera.
The cranial nerves or pairs are those that come directly out of the brain (brain), moving towards the face (motor and sensory innervation), the sense organs, viscera and proximal trunk muscles.
The spinal nerves are those that depart from the spinal cord. They are formed by two roots: the anterior spinal (motor) and the posterior spinal (sensory). The other nerves are the peripheral ones.