Page 48 - Human anatomy COMPLETELY DONE1

NERVOUS SYSTEM
The functions of the nervous system are to ensure the regulation of all body
systems and to provide reactions to changes in the external and internal environment
that are significant for the body. Also, the nervous system (NS) is able to store
information.
The human nervous system, like many animals, is divided into central and
peripheral (figure 32). In the central nervous system (CNS), the spinal cord and brain
are isolated. The peripheral nervous system (PNS) consists mainly of nerves and nerve
nodes. Nerves are bundles of axons of neurons and the surrounding shell of neuroglia
cells.
The PNS consists of 12 pairs of cranial nerves and 31 pairs of spinal nerves.
Sensitive nerves conduct impulses from receptors towards the central nervous system.
Motor nerves conduct impulses from the central nervous system to the performing
organ, that is, the effector. The effectors are often muscles. There are also mixed nerves
consisting of their different axons, both motor and sensory.
In the peripheral nervous system, nerve plexuses are isolated, which are
localizations of nerve fibers of various nerves in one place. Nerve plexuses innervate
the skin, muscles, and internal organs. The solar plexus is located in the abdominal
cavity.
The nervous system consists of nervous tissue, the main cells of which – neurons
– have short processes – dendrites and one long process – axon. The bodies of nerve
cells are closer to gray color, axons – to white. In addition to neurons, the nervous tissue
consists of glial cells (neuroglia), they are diverse in structure and function.
Neurons have conductivity. The signal inside the cells is transmitted electrically,
between the cells – chemically. The nervous system reacts to certain stimuli of the
environment, converting their energy into a transmitted nerve impulse.

According to the functional principle, the nervous system is divided into somatic
and vegetative. The first regulates the work of skeletal muscles, with its help a person
can arbitrarily control his body. The autonomic nervous system is also called
autonomous. It regulates the work of internal organs, maintains the constancy of the
internal environment and defies conscious control.
The nervous system, mainly vegetative, is divided into sympathetic and
parasympathetic. With some exceptions, the sympathetic NS (digestive system) is
responsible for arousal, the parasympathetic for inhibition.
The work of the nervous system is reflex in nature. Reflexes are controlled by
nerve centers – certain areas of the nervous system.

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