Download Nervous System

The Nervous System
The function of the nervous system is to allow the
animal to quickly detect, communicate and coordinate information about its external and internal
environment.
 The two major parts of our nervous system are the
central nervous system (CNS) and peripheral
nervous system (PNS).
 The CNS is made of the brain and spinal cord.
 The cranial nerves, spinal nerves and ganglia make
up the PNS.
 The cranial nerves connect to the brain.
 The cranial and spinal nerves contain the axons
(fibres) of sensory and motor nerve cells.
 Nerve cells are also known as neurons.

Sensory Neurons
 Sensory neurons carry electrical signals
(impulses) from receptors or sense organs to the
CNS.
 Sensory neurons are also called afferent neurons.
 The cell body of sensory neurons is outside the
CNS in ganglia.
Motor Neurons
 Motor neurons carry impulses from the CNS to
effector organs.
 Motor neurons are also called efferent neurons.
 The cell bodies of motor neurons are inside the
CNS.

A synapse is a specialised junction between a
neuron and its target cell.
 Cerebrum:
centre for sensory and motor
control, language, memory, intelligence, and
consciousness.
 Cerebellum: muscle co-ordination, movement
and balance.
 Medulla Oblongata: controls breathing and
heart rate.
 Hypothalamus: osmoregulation and
temperature control.
 Pituitary Gland: secretes a wide variety of
hormones – a major endocrine gland.
A
reflex action is a very fast unconscious
response to an unexpected and potentially
dangerous stimulus.
 Examples of reflex action: knee jerk, eye blink,
pupil size alteration, closure of the glottis on
swallowing.
 A reflex arc is a specific nerve pathway involved
in a fast, unconscious response to an unexpected
stimulus.
 E.g. Spinal Reflex Action - the withdrawal of
hand when finger jabbed unexpectedly with a
pin.
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Pain and pressure receptors in the skin are stimulated.
Sensory neurons carry the impulses to the spinal cord
by way of the dorsal root.
An interneuron picks up the impulse from the sensory
and transmits it to the motor neuron.
At the same time the impulse is also transmitted
to the brain.
The motor neuron stimulates the specific effector organ
to make the appropriate response, muscles in the arm
are stimulated to contract pulling the hand away from the
pin.
The response is very fact – occur before the brain is
aware of the situation.
The brain, having received the information, may transmit
impulses to other muscles to modify the response.