Nerve tissue basically comprises two types of cell: neurons and glial cells.
Neuron: It is the structural and functional unit of the nervous system that specializes for rapid communication. It has the basic function of receiving, processing and sending information.
Glias cells: comprises the cells that occupy the spaces between the neurons and its function is support, coating or isolation and modulation of neural activity.
Neurons: are highly cells excitable cells that communicate with each other or with other effector cells, using basically electrical language. Most neurons have three regions responsible for specialized functions: cell body, dendrites, and axons.
The Cellular Body: It is the metabolic center of the neuron, responsible for the synthesis of all neuronal proteins. The shape and size of the cell body are extremely variable, depending on the type of neuron. The cell body is also, along with the dendrites, a stimulus reception site through synaptic contacts.
Dendrites: they are usually short and branch profusely, like tree branches, at sharp angles, resulting in smaller diameter dendrites. These are the processes or projections that transmit impulses to the cell bodies of neurons or axons.
In general, dendrites are unmyelinated. A neuron can have thousands of dendrites. Therefore, dendrites specialize in receiving stimuli.
Axons: The vast majority of neurons have an axon, a long, thin extension that originates from the cell body or a major dendrite. The axon has a very variable length, and may be a few millimeters as more than one meter. It is the processes that transmit impulses that leave the cell bodies of neurons, or dendrites. The terminal portion of the axon undergoes several branches to form hundreds to thousands of axon terminals, within which chemical neurotransmitters are stored. Therefore, the axon specializes in generating and driving the action potential.
There are three types of neurons: Sensitive, Motor and Interneuron.
a Sensory neuron conducts information from the periphery towards the CNS, also being called afferent neuron.
a Motor neuron It conducts CNS information towards the periphery and is known as the efferent neuron. Sensory and motor neurons are found in both CNS and PNS.
Interneuron neuron they are those that connect one neuron to another, being found in the CNS.
So the nervous system has three basic functions.
Sensitive Function: Sensory nerves capture information from the internal and external environment of the body and carry it to the CNS;
Integrating Function: Sensitive information brought to the CNS is processed or interpreted;
Motor Function: The motor nerves carry CNS information toward the muscles and glands of the body, carrying CNS information.
Neuron classification for its extensions: Most neurons have several dendrites and one axon, so they are called multipolar. But there are also bipolar and pseudo unipolar neurons.
In bipolar neurons, two extensions leave the cell body, one dendrite and one axon.
In pseudo unipolar neurons, only one extension leaves the cell body.
Synapses: Neurons, mainly through their axon endings, come into contact with other neurons, passing them information. The locations of such contacts are called synapses. That is, neurons communicate with each other at synapses - points of contact between neurons, where we find synaptic vesicles, where neurotransmitters are stored. Communication occurs through neurotransmitters - chemical agents released or secreted by a neuron. The most common neurotransmitters are acetylcholine and norepinephrine. Other CNS neurotransmitters include epinephrine, serotonin, GABA, and endorphins.
Nervous Fibers: A nerve fiber comprises an axon and, when present, its wrap of glial origin. The main envelope of nerve fibers is the myelin sheath (layers of lipid and protein substances), which acts as electrical insulation. When surrounded by myelin sheath, axons are called myelinic nerve fibers. In the absence of myelin the fibers are called myelinic. Both types occur in the central nervous system and peripheral nervous system, with the myelin sheath formed by Schwann cells, in the peripheral and central by oligodendrocytes. The myelin sheath allows faster conduction of the nerve impulse and, along the axons, conduction is saltatory, ie, the action potential only occurs in structures called Ranvier nodules.
Nerves: After exiting the brainstem, spinal cord or sensory ganglia, the motor and sensory nerve fibers assemble into bundles that associate with conjunctive structures, constituting spinal and cranial nerves.
Curiosities about the Peripheral Nervous System
In the peripheral nervous system, the axon is surrounded by special cells called Schwann cells, which form the axon myelin sheath. The Schwann cell nucleus and cytoplasm lie outside the myelin sheath and constitute the neurilema. This structure is important in cases where the nerve is severed, as it is partly responsible for its regeneration. Thus, surgically reconstituted nerves may eventually reestablish their connections, allowing for recovery of sensation and movement.
The brain weight of an adult male is 1,300 grams and in woman 1,200 grams. It is assumed that in the adult male of medium height the smallest brain compatible with normal intelligence would be 900 grams. Above this limit, attempts to correlate brain weight with degree of intelligence run into numerous exceptions (this refers to body weight rather than degree of intelligence, since it has not yet been proved at all which of the two sexes is more smart). Intelligence refers not only to the amount of gray matter, but to the ability of human beings to understand, reason, interpret and relate knowledge about lived and un lived experiences and the adaptive capacity of human beings to new situations.