O nervous tissue it is sensitive to various types of stimuli that originate from outside or inside the organism. When stimulated, this tissue becomes capable of conducting the nerve impulses quickly and sometimes over relatively large distances. It is one of the most specialized tissues in the animal organism. such fabric is composed byneurons and gliocytes (or glial cells).
Read too: Muscle tissue - tissue that guarantees our movements and heartbeats
neurons
neurons are cells responsible for nerve impulses, highly specialized, endowed with a cell body and numerous cytoplasmic processes, called neurofibers or nerve fibers.
The cell body of the neuron contains a large rounded core. At mitochondria they are numerous, and ergastoplasm is well developed. Neuron prolongations can be of two types:
dendrites (from the greek dendron: tree): branches that have the function of capturing stimuli,
axon (from the greek axon: axis): the longest extension of the nerve cell (ranging from fractions of a millimeter to about 1 meter), transmits nerve impulses.
To learn more about these important nerve tissue cells, read: neurons.
Glyocytes
You gliocyteshave the function of involving and nourishing neurons, keeping them together. The main types of cells of this nature are:
astrocytes,
oligodendrocytes,
microglia,
Schwann cells.
The extensions of some of these cells wrap themselves around the axons and form, around them, the myelin sheath, which acts as an electrical insulator and contributes to increasing the speed of propagation of the nerve impulse along the axon.
The myelin sheath, however, is not continuous. Between one Schwann cell and another there is a region of discontinuity in the sheath, which causes the existence of a constriction (strangulation) called ranvier's nodule.
There are axons where Schwann cells do not form the myelin sheath. That is why, there are two varieties of axons: myelinated and unmyelinated. In a myelinated fiber, we have three sheaths surrounding the axon: myelin sheath (lipidic in nature), Schwann sheath and the endoneurium.
nerves
Nerve fibers organize themselves into bundles. Each bundle, in turn, is surrounded by a conjunctival sheath called the perineurium. Several bundles grouped in parallel form a nerve. The nerve is also surrounded by a sheath of connective tissue called epineurium.
the nerves do not contain the cell bodies of neurons; these cell bodies are located in the central nervous system or in the nerve ganglia, which can be seen near the spinal cord.
When they depart from brain, are called cranials; when they leave the spinal cord, are called spinals.
Nerves allow the communication of the nerve centers with the receptor organs (sensory) or even with the effector organs (muscles and glands). According to the direction of transmission of the nerve impulse, the nerves can be:
sensitive or afferent: when transmitting nerve impulses from the receptor organs to the central nervous system;
motors or efferents: when transmitting nerve impulses from the central nervous system to effector organs;
mixed: when they have both sensory and motor fibers. They are the most common in the body.
Synapses
synapses are chemical connection regions established:
between one neuron and another (interneural synapses);
between a neuron and a muscle fiber (neuromuscular synapses);
or between a neuron and a glandular cell (neuroglandular synapses).
A neuron does not physically communicate with another neuron or muscle fiber or gland cell. There is between them a microspace, called synaptic space, in which one neuron transmits the nerve impulse to another through the action of chemical mediators or neurohormones.
See too: Bone tissue - tissue related to the support, locomotion and protection of organs
Performance of neurohormones
The neurohormones are contained in microvesicles present at the ends of the axon. When the nerve impulse reaches these extremities, the microvesicles release the chemical mediator into the synaptic space. The neurohormone then combines with molecular receptors present on the neuron that is to be stimulated (either on the muscle fiber or on the gland cell).
From this combination results the change in receptor cell membrane permeability, a fact that triggers an entry of ions into the interior of the cell and the consequent inversion of the membrane's polarity. An action potential then arises that generates a nerve impulse in the receiving cell.
By Mariana Araguaia
Graduated in Biology
Source: Brazil School - https://brasilescola.uol.com.br/biologia/tecido-nervoso.htm