Cellular level of the organization of the nervous system
The simplest elements of the brain (the brain and spinal cord) are neurons and glial cells. The total number of neurons in the central nervous system (CNS) is about 50 billion, and they are distributed unevenly in different brain structures.The structure of the neuron in the elementary form can be imagined as a body with a nucleus and two kinds of processes - one long (axon) and many short (dendrites). Sprouts perform the transfer of information from the neuron to the neuron for short and long distances.
The junction points (contacts) between neurons are called synapses (S. Ramon-i-Kahal, 1911), and the process of transmitting information in these places is Synoptic transmission. In the interaction of neurons, the presynaptic cell secretes a certain substance (neurotransmitter) on the receptor surface of the postsynaptic neuron. The neurotransmitter closes the chain, carrying out the chemical transfer of information through the synoptic gap - the structural gap between the transmitting and receiving cells at the site of the synapse.
A single neuron with a divergent structure can send signals to a thousand and even a larger number of other neurons. But more often one such neuron is connected with only a few specific neurons. Similarly, a neuron can receive input information from other neurons via one, several, or many input links, if convergent paths converge on it.
According to the generally accepted view, the transfer of information is always anterograde, ie. from a presynaptic to a postsynaptic cell. Recently, there have been reports of reverse, retrograde transmission with a variety of substances - from small mobile nitrogen oxide molecules to large polypeptides, such as nerve growth factor. It is believed that the reverse transfer in the synapse provides a greater plasticity of the synapses during brain development and learning (preservation or potentiation of active synapses in neural networks).
The space between nerve cells and their processes is filled with supporting cells - glia. Glial cells are 5-10 times larger than neurons. The most common among the glial cells are astrocytes, named for their star shape. It is believed that they purify the extracellular spaces from the excess of mediators and ions, deliver glucose to neurons and cells. Glial cells of another type (oligodendrocytes) provide "electrical insulation" conductors, because they contain myelin in the form of a dense shell.
Structural organization of the nervous system
In the structural plan, the central (CNS) and peripheral nervous system is distinguished. The CNS includes the brain, brain stem and spinal cord. All the rest refers to the peripheral nervous system, which is usually divided into somatic and vegetative (autonomous). The somatic system consists of the nerves that go to the sensory organs and from the motor organs. The vegetative system is also called visceral, since it controls the internal organs of the body (lat viscera - internal). The somatic nervous system activates an arbitrary musculature (also called a transversal band because of the transverse depletion of its fibers). The autonomic nervous system innervates the so-called involuntary (smooth) muscles.
The central nervous system consists of the brain, brainstem and spinal cord. The spinal cord - is a nerve fiber cord that goes in the middle of the body and is protected by a bone structure. It serves as a link between the brain and the peripheral nervous system. The spinal cord itself carries out only a number of very simple reflexes (for example, the knee-jerk reflex). Under normal conditions, all reactions control the brain.
The brain can be divided into anterior, middle and posterior brain. The forebrain includes mainly the cortex of the two hemispheres of the brain, as well as four relatively small formations: the amygdala, the hippocampus, the basal ganglia (the striatum, pallid sphere, subthalamic nucleus, black substance) and a septum forming a wall between the ventricles of the brain. The middle brain includes the thalamus and the hypothalamus. The hindbrain is made up of the variolium bridge, medulla oblongata, brainstem and cerebellum.
During the evolution of the brain, his hemispheres acquired an ever increasing specialization, which manifested itself in the preferred use of the human right arm (90% of people), the location of speech centers in the left hemisphere (in 92% of people), the polarity of emotional states (the right hemisphere is negative emotional states, and the left ones - positive) and a number of other features.
There are also some morphological and functional differences of the brain in men and women.
In particular, women in a certain area of the corpus callosum have more nerve fibers than men. This may mean that the nerve connections between the hemispheres are more numerous, which contributes to a better interaction of the hemispheres. Perhaps, this explains a number of sexual differences in the behavior and features of mental functions in men and women.
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