Transcript Functions of the Nervous System

Introduction to the Nervous System
The Nervous System consists of the
brain, spinal cord and thousands of
nerves.
The Brain and Spinal Cord are
collectively known as the Central
Nervous System.
The Peripheral Nervous System is the
collective term for all nerves outside the
brain and spinal cord.
Functions of the Nervous System
The general function of the nervous system is
to allow the organism to respond to stimuli.
A Stimulus is any change in the environment
of the organism. The nervous system will then
induce a response, which may be movement,
speech, blinking etc.
Advanced organisms have specialised sense
organs, which are designed to react to
stimuli.These are often called receptors and
are sensitive to one stimuli (e.g. Skin to touch,
eyes to light patterns)
Reacting to Stimuli
When a receptor is exposed to a stimulus,
an electronic impulse is sent to the central
nervous system via nerves.The brain then
analyses the message and based on
experiences / memory, the brain sends out
a suitable response back to an effector
(muscle) via nerve fibres. When the nerve
impulse reaches the effector muscle it
contracts accordingly.
Neurons or Nerve Cells
There are three types of nerve cells of which two are
important to us.
Sensory Neurons move from the receptor to the
Central Nervous System.
Motor Neurons move from the Central Nervous
System to the effector muscle.
Movement of the message in neurons is based on
Electro-chemical conduction. This is similar to
electricity in wires but much slower.
Inside nerve cells the impulse moves quite fast but
the message must also move out of one cell and into
another. This is slow and is based on charged ions
(Atoms with extra or missing electrons).
This is why elements like Chlorine,
Magnesium, Sodium and Potassium are
important in the diet of animals. When these
elements are not available, the effector
muscles will not react as required and will
cramp.
For example, low Mg with cause muscle
spasms.
The Reflex Arc
A reflex is the simplest form of response to a
stimulus. The most common reflex is the knee jerk. In
a reflex reaction, the response occurs before the
message reaches the brain, or the message may not
reach the brain at all.
This is because of the reflex arc!
The receptor cell sends an impulse through a
sensory neuron to the spinal cord. The message
doesn’t go directly to the brain but to the cell body of
a motor neuron and then to the muscle. The muscle
contracts.
The brain may get the message soon after. In
reflexes, the impulse is not related to stored
information in the brain before the response.