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The Nervous System
Lesson objectives
By the end of this lesson you should know:
• The difference between the CNS and the
PNS
• The function of the nervous system
• Distinguish between sensory, motor and
interneurons in terms of structure and
function
Introduction
In animals there are 2 systems of
communication allowing the animal to respond
to internal and external stimuli
• Nervous system (Rapid responses)
• Endocrine system (Slower responses)
There are 2 parts to the nervous system:
In order to make the correct response to
a stimulus 4 processes are involved:
• Reception
• Transmission
• Integration
• Response
NS ----- Co-ordination & Response
Neurones
•
•
•
•
Neurones are the basic
units of nerve cells
Are specialised to carry
information as electrical
impulses from 1 place
to another
Neurons not only vary
in type but differ in size
– in the brain they are
tiny but the spine and
feet can be up to 1m
long
There are 3 main types:
Sensory neurons
• Sensory (afferent)
neurones – sends
messages from sense
organs to CNS
Motor neurons
• Motor (efferent)
Neurones – send
messages from CNS
to muscles and
glands
Interneurons
• Interneurons carry
information between
sensory and motor
neurons – found only
in CNS
Structure of neurons
Functions of the
parts of neurons
Relationship between nerve
fibres and neurones
• Many axons often
combine to form
nerve fibres (nerve)
• Axons can be up to
1m in length
What do you know?
Can you....
• Distinguish between the CNS and the
PNS?
• Describe function of the nervous system?
• Distinguish between sensory, motor and
interneurons in terms of structure and
function?
Lesson objectives
By the end of this lesson you should know:
• How nerve impulses move along the axon
• Activation and inactivation of the
neurotransmitter at the synapse
Transmission of nerve impulses
• A neuron has to receive a
stimulus of sufficient
strength
• The movement of the
electrical impulse
involves the movement of
ions (charged particles)
Features of nerve impulses
Resting neuron
• When a neuron is not carrying an impulse ions are
pumped in and out of the axon – this results in the inside
of the axon being negative and the outside positive
Threshold
• The threshold is the minimum stimulus needed to cause
an impulse to be carried
• A stimulus below the threshold has no effect but one that
is at or above the threshold causes an electrical impulse
to travel along the axon
Features of nerve impulses
The all or nothing law
• The all or nothing law states that if the
threshold is reached an impulse is carried
but if the threshold is not reached no
impulse is carried
• Simply the impulse is either carried or not
Transmission
of nerve
impulses
Transmission of nerve impulses
Refractory period
• The refractory period is a
short time span after a
neuron has carried an
impulse during which a
stimulus fails to cause a
response
• While ions are moving in
and out of each section of
the neuron the region
affected cannot carry
another impulse
• There has to be a slight
delay of 5ms between
any 2 impulses - the
refractory period
Transmission of nerve impulses
•
•
•
•
Speed of impulse
Depends on myelin
sheath
If myelin is absent speed
is reduced to 2m/s
In a myelinated neuron
the changes can only
move in and out of the
gaps in the myelin - the
impulse jumps from gap
to gap and is transmitted
more rapidly- 120m/s
Also the larger the
diameter of the axon the
faster transmission
Synapse
• A synapse is a region
where 2 neurons
come into close
contact – commonly
found between the
axon terminals of 1
neuron and the
dendrites of another
• A synaptic cleft is the
tiny gap between the
neurons at a synapse
– 20nm
Activation and inactivation of
neurotransmitters
Transmission Across a
Synapse 1
Transmission Across a Synapse 2
Functions of synapses
1. They transmit impulses
from 1 neurone to
another or effector
(muscle or glands)
2. They control the
direction of the nerve
impulse
3. They prevent over
stimulation of effectors
4. The impulse can be
blocked by certain
chemicals (drugs) –
important in controlling
pain and certain
psychiatric disorders
What have you learned?
Can you explain....
• How nerve impulses move along the
axon?
• Activation and inactivation of
neurotransmitters at the synapse?
Lesson objectives
By the end of this lesson you should know:
• The structure and function of the following
parts of the brain: cerebrum, cerebellum,
medulla oblongata, thalamus and
hypothalamus
• 1 nervous system disorder
The central nervous system
(CNS)
Brain
• The senses and
individual sensory
neurones act as
receptors for incoming
stimuli
• Electrical impulses are
passed along sensory
neurons to the CNS
particularly the brain
• The brain acts as the
interpreting centre to sort
and process the incoming
impulses and decide on a
response
Structure of the brain
Functions of the cerebrum
Functions of the cerebellum
• Controls muscular co
– ordination
• Allows smooth refined
muscular action
• Controls balance
• The responses of the
cerebellum are
involuntary once they
have been learned
Functions of the medulla
oblongata
• Connects the spinal
cord with the rest of
the brain
• Controls involuntary
actions like breathing,
blood pressure,
swallowing, coughing,
salivation, sneezing
and vomiting
Functions of the Thalamus
• Acts as a sorting
centre for the brain
and relays all
incoming messages
to the relevant part of
the brain
Functions of the
Hypothalamus
• It regulates the
internal environment
of the body
(homeostasis) by
monitoring blood
temperature, appetite,
thirst, osmoregulation
and blood pressure
• It is thought to be a
link between the mind
and the body
Nervous system disorder –
Parkinson’s disease
•
•
•
•
Cause
Symptoms include:
Prevention
Treatment
What have you learned?
Can you discuss...
• The structure and function of the following
parts of the brain: cerebrum, cerebellum,
medulla oblongata, thalamus and
hypothalamus?
• 1 nervous system disorder?
Lesson objectives
By the end of this lesson you should know:
• The structure and function of the parts of
the spinal cord
• The structure and function of the PNS
• Discuss the simplest form of activity in the
nervous system-the reflex action
The Spinal Cord
TS of spine
The Peripheral Nervous
System
• Consists of nerve
fibres outside the
spinal cord
• Made up of long
dendrites or axons
taking impulses to
and from the CNS
Reflex action/Reflex Arc
• The simplest form of
activity in the nervous
system is a reflex action
• It is an automatic,
involuntary and
unthinking response
to a stimulus
• The neurons forming the
pathway taken by the
nerve impulses in a
reflex action make up a
reflex arc
Reflex response
Reflex Arcs
What have you learned?
Can you discuss...
• The structure and function of the parts of
the spinal cord?
• The structure and function of the PNS?
• The simplest form of activity in the nervous
system-the reflex action?