Human Physiology/The Nervous System
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Human Physiology/The Nervous System
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The
central nervous system
includes the
brain
and
spinal cord
. The brain and spinal cord are protected by bony
structures, membranes, and fluid. The brain is held in the cranial cavity of the skull and it consists of the
cerebrum
,
cerebellum
, and the
brain stem
. The nerves involved are cranial nerves and spinal nerves.
Nervous system
Overview of the entire nervous system
The nervous system has three main functions: sensory input,
integration of data and motor output. Sensory input is when the body
gathers information or data, by way of neurons, glia and synapses. The
nervous system is composed of excitable nerve cells (neurons) and
synapses that form between the neurons and connect them to centers
throughout the body or to other neurons. These neurons operate on
excitation or inhibition, and although nerve cells can vary in size and
location, their communication with one another determines their
function. These nerves conduct impulses from sensory receptors to the
brain and spinal cord. The data is then processed by way of integration
of data, which occurs only in the brain. After the brain has processed
the information, impulses are then conducted from the brain and spinal
cord to muscles and glands, which is called motor output. Glia cells are
found within tissues and are not excitable but help with myelination,
ionic regulation and extracellular fluid.
The nervous system is comprised of two major parts, or subdivisions,
the central nervous system (CNS) and the peripheral nervous system
(PNS). The CNS includes the brain and spinal cord. The brain is the
body's "control center". The CNS has various centers located within it
that carry out the sensory, motor and integration of data. These centers can be subdivided to Lower Centers
(including the spinal cord and brain stem) and Higher centers communicating with the brain via effectors. The PNS
is a vast network of spinal and cranial nerves that are linked to the brain and the spinal cord. It contains sensory
receptors which help in processing changes in the internal and external environment. This information is sent to the
CNS via afferent sensory nerves. The PNS is then subdivided into the autonomic nervous system and the somatic
nervous system. The autonomic has involuntary control of internal organs, blood vessels, smooth and cardiac
muscles. The somatic has voluntary control of skin, bones, joints, and skeletal muscle. The two systems function
together, by way of nerves from the PNS entering and becoming part of the CNS, and vice versa.