Equipping People To Make Sense Of What They Are Told
Although the entire nervous system is extremely complex it has only three functions:
Sensory Input (sensory neurons) - provides information to the central nervous system
and assists organs to adjust to the surrounding environment, both inside and outside
the body.
Integration - it has to make sense of the input it is receiving. Interneurons integrate
input from sensory nerves into the central nervous system.
Motor Output (motor neurons) - respond to information received by the sensory neurons.
The Nervous System is divided into two parts:
The Central Nervous System (CNS)
The brain, spinal cord and the optic nerves. The part of the nervous system that
functions to coordinate the activity of all parts of the bodies. The CNS is contained
within the dorsal cavity, with the brain in the cranial cavity and the spinal cord
in the spinal cavity. The brain is protected by the skull the spinal cord is protected
by the vertebrae. The brain together with the spinal cord coordinates most voluntary
movement and regulates non-conscious processes.
Spinal Cord - The nerve fibres of the spinal cord link the brain with the arms, legs
and torso, however the spinal cord is not only a passive conduit for nerve signals
it is able to bypass the brain - reflex actions
The spinal cord is a bundle of axons (nerve fibres) about 35 to 45 cm long (15 to
18 inch’s) tapering to a thread like tail at the lower (lumberoscral).
The spinal cord is located and protected within the spinal canal, a long tunnel within
the vertebrae (aligned column of backbones) which protects the spinal cord from knocks
and blows, the circulating cerebrospinal fluid acts as a shock absorber and the layer
of fat and connective tissue in the epidural space acts as a cushion.
The spinal cord -contains the nerves that come from the brain, and is protected
by the spine. Nerves from the spinal cord come out from between the vertebrae to
convey messages to and from various parts of the body.
The spine is made up of many bones called vertebrae. The vertebrae are roughly circular
and between each vertebra is a 'disc'. The discs are made of strong rubber-like tissue
which allows the spine to be fairly flexible. Strong ligaments also attach between
adjacent vertebrae to give extra support and strength to the spine.
There are also various muscles that are attached to the spine which enable the spine
to bend and move in various ways.
There are small facet joints that help to attach vertebrae to each other.
The Peripheral Nervous System (PNS)
All of the nerves that run to and from the brain and spinal cord linking up with
muscles, skin and joints. Information flows from muscles and sensory organs back
through the PNS to the CNS controlling coordination and movement (voluntary and involuntary).
The peripheral nervous system relay’s information to and from the central nervous
system. The peripheral nerves transmit voluntary and involuntary actions.
The peripheral nervous system consists of:
12 pairs of cranial nerves, these emerge from the brain and mainly serve the head
and neck.
31 pairs of spinal nerves, these branch off from the spinal cord and supply the rest
of the body.
The Somatic System - A division of the peripheral nervous system associated with
the voluntary control of body movements through the action of skeletal muscles (with
the exception of reflex arcs) and with reception of external stimuli helps keep the
body in touch with its surroundings such as:
Hearing.
Sight.
Touch.
The system includes all the neurons connected with:
Skeletal muscles.
Skin.
Sense organs.
The somatic nervous system consists of efferent nerves responsible for sending brain
signals for muscle contraction.
Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna
Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood
Cliffs, New Jersey, USA: Prentice Hall. pp. 132–144.
Autonomic System - A division of the peripheral nervous system that acts as a control
system functioning largely below the level of consciousness, and controls visceral
functions.
It is classically divided into two subsystems: the parasympathetic nervous system
and sympathetic nervous system. Both supply essentially the same organs but cause
opposite effects. This is because their activating chemicals, or neurotransmitters,
are different
The systems are associated with:
Diameter of the pupils.
Digestion.
Heart rate.
Maintaining homeostasis in the body.
Perspiration.
Respiration rate.
Salivation.
Sexual arousal.
Urination.
Most of the actions are involuntary, however some such as breathing work in tandem
with the conscious mind. Although the autonomic nervous system is considered to be
involuntary, this is not entirely true. A certain amount of conscious control can
be exerted over it as demonstrated by practitioners of Yoga and Zen Buddhism. During
periods of meditation, these people are clearly able to alter a number of autonomic
functions including heart rate and the rate of oxygen consumption.
The Sympathetic Nervous System usually prepares the organism to deal more effectively
with a situation of strife or emergency and controls systems associated with internal
organ functions that are involuntary and happen subconsciously. Often referred to
as the 'fight-or-flight' system the sympathetic nervous system prepares the body
for emergencies by:
Shunting blood to essential muscles.
Increasing blood pressure.
Increasing heart rate.
Increasing breathing rate.
These actions enables the body to combat stressful situations.
Some effects created by sympathetic nervous system stimulus are:
Blood to the gut is stopped.
Dilation of the air passages in lung.
Dilatation pf the pupils.
Increased blood glucose levels.
Increased heart rate.
Raised hair and goosebumps.
Reduction of gut motility
Reduced urine output.
Shunting of blood to vital organs (blood goes to the; brain, heart, necessary muscles).
Sweating.
The Parasympathetic Nervous System restores body functions to normal after they have
been stimulated by the sympathetic nervous system. In times of danger, the sympathetic
nervous system prepares the body for violent activity. The parasympathetic system
reverses these changes when the danger is over.
Rest and digest. The parasympathetic nervous system restores and maintains at a low
level.
Energy.
Blood pressure.
Heart rate.
Breathing rate.
It also directs blood to the digestive tract to encourage active digestion of food
This is why it is sometimes called the 'rest and digest' system.
Some effects created by parasympathetic nervous system stimulus:
