Nervous System

Type of psychology: Biological bases of behavior; language; learning;
memory; sensation and perception
Fields of study: Auditory, chemical, cutaneous, and body senses;
biological treatments; endocrine system; nervous system; organic
disorders; schizophrenias; thought; vision
The nervous system represents the interconnections of cells that recognize and coordinate
the senses of the body. The nervous system is divided into two major components:
the central nervous system, which includes the brain and spinal cord, and the peripheral
nervous system, which communicates impulses to and from the regions of the body.

Key concepts
• central nervous system
• endocrine system
• endorphins and enkephalins
• limbic system
• neuron
• neurotransmitters
• peripheral nervous system

The functions of the human nervous system are in many ways analogous to
that of a computer. The brain receives information in the form of stimuli
from the senses open to the outside world. Within the brain are specific regions,
analogous to programs, that interpret the stimuli and allow for a response.
More specifically, such responses take the form of physiological or
behavioral changes. Some of these stimuli result from activation of tissues or
organs within the endocrine system, a network of glands which secrete hormones
directly into the bloodstream for regulation of target organs.
The functional unit of the nervous system is the neuron, a cell which receives
or sends information in the form of electrical impulses. The major
component of the neuron is the cell body, the portion which contains the
nucleus and most of the internal organelles. Two major forms of neurons
are found within the nervous system: sensory neurons, which transmit the
impulse toward the central nervous system (brain and spinal cord), and motor
neurons, which receive impulses from the brain or spinal cord and transmit
the impulse to muscles or other tissues.

Depending upon the type of neuron, a variety of processes may emanate
from the cell body. Axons transmit the impulse away from the cell body and
toward the target cell or tissue. Dendrites receive the impulse from other
neurons or other sources of stimuli. The actual nerve consists of bundles of
thousands of axons wrapped within a form of connective tissue.
The surface of a resting, or unstimulated, neuron has a measurable electrical
potential across the membrane. When the nerve is stimulated, whether
mechanically such as by pressure or electrically as in the sense of sight, an influx of electrically charged ions such as sodium occurs; the result is referred
to as an action potential. The electrical discharge flows along the axon until
it reaches the end of the neuron. Eventually the resting potential is restored,
and the neuron may again undergo stimulation.
At its tip, the axon divides into numerous terminal branches, each with a
structure called a synaptic bulb on the end. Within the bulb are vessels containing
chemicals called neurotransmitters, molecules which transmit the
electrical signal from one neuron to another, or to target tissues such as
those in the endocrine system.

There exist within the nervous system a large number of different forms
of neurons, many of which respond to different types of neurotransmitters.
Alterations in production of these chemicals, or in the ability of nerves to respond
to their stimuli, formthe physiological basis for a variety of psychological
problems. 567