The nervous system coordinates the activity of the muscles, monitors the organs’
activity, initiates body actions and receives information about the external environment.
Prominent participants in a nervous system include nerves, which play roles in
such coordination. All parts of the nervous system are made of nervous tissue.
The basic structural unit of the nervous system is the neuron and its function is
transmission of impulses. Each neuron is composed of the cell body (with cytoplasm
and a nucleus), dendrites (branched projections conducting impulses to the cell
body), and an axon (long, single projection conducting impulses away from the cell
body). Each nerve can be described as a bundle of axons of many neurons.
The nervous system is divided into three main parts: the central nervous system, the
peripheral nervous system, and the autonomic nervous system.
The central nervous system consists of the brain and the spinal cord. The brain is
located in the cranial cavity and is surrounded by the skull. There are three main
parts of the brain: the cerebrum, the cerebellum and the brain stem. The cerebrum is
divided into two hemispheres by the longitudinal fissure. The outer portion of the
cerebrum, called the gray matter, is composed of cell bodies. The inner portion, the
white matter, is composed of myelinated nerve fibres. The brain is the site of reason
and intelligence, which include such components as cognition, perception, attention,
memory and emotion. The brain is also responsible for control of posture and movement.
Moreover, it can perform a variety of functions automatically, without the need
for conscious awareness, such as coordination of senses, walking, and body functions
such as heart rate, blood pressure, fluid balance, and body temperature.
The peripheral nervous system contains only nerves and connects the brain and spinal
cord (CNS) to the rest of the body. It includes e.g. the nerves that branch off the
brain (12 pairs of cerebral nerves) and the spinal cord (31 pairs of spinal nerves).
The autonomic nervous system controls the involuntary actions of internal organs. It
controls muscles in the heart, the smooth muscles in internal organs such as the intestine,
bladder, and uterus. The autonomic system has two subsystems. The sympathetic
nervous system and parasympathetic nervous system work in opposition to
each other. For example: when you are scared the sympathetic system causes your
heart to beat faster; the parasympathetic system slows it down.
There are various types of diseases affecting the nervous system: infectious (meningitis),
congenital (hydrocephalus), traumatic (injuries), degenerative (multiple sclerosis).
The symptom of disorders connected with the nervous system are for example:
acute headaches, paresis, hemiparesis, speech and visual disturbances, vomiting,
drowsiness, dizziness.