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The Human Nervous System
The Human Nervous
Our bodies have over ten million million (1013) living cells
Nerve Impulse
which must work in co-operation for us to live and grow. To
co-operate they must communicate. The brain, spinal cord,
nerves, sense organs and receptors are the vital parts of
Synaptic knob
the human nervous system that facilitate communication
13
Our
bodies
have
over
ten
million
million
(10
)
living
cells
between our cells. In this lesson we will look at the formation
and
function
of the
nervous
system.
which
must
work
in co-operation
for us to live and grow. To
co-operate
they mustsystem
communicate.
The brain, spinal cord,
How
is our nervous
formed?
Release of
nerves,
sense
organs
are
of
The
central nervous
system
(CNS) and
beginsreceptors
to form halfway
intothe
the vital parts
transmitter
embryonic
period,
28
days
after
conception.
The
development
of
substance
the human nervous system that facilitate communication
the central nervous system is the first major event in the formation of
between
our cells.
In this
we will
lookfrom
at the formation
organs
in the developing
embryo.
The lesson
nervous system
develops
the ectoderm, the outer of the three germ layers. The skeletal system
and
function
of
the
nervous
system.
develops from the mesoderm, the middle of the germ layers, with the
cranium and vertebrae forming a protective cover around the brain and
spinal cord.
How is our nervous system formed?
The membranes of the cell body and its d
onto which a signalling chemical from
stimulate it into activity.
Terminal dendrite
The axon is the long extension from th
the signal to the target site. Axons can
transfer time over one long axon is mu
to travel dendrite
over many cells. If the nerve c
Terminal
other cells, then, for example, a signal
have to travel along about 200,000 ce
minutes.We could not survive if there
to dangers
Synaptic vesicle
Synaptic vesicle
Transmitter
substance
Nerve Impulse
Presynaptic
membrane
Synaptic
cleft
Synaptic knob
Receptor
molecule
The numerous terminal dendrites ensur
Transmitter
many of the cells of the target tissue. Sy
substance
to the target cell.
Postsynaptic
membrane
What is the role of neuro
Fig.2 The synaptic cleft
Although nerve signals are electric in n
strictly like an electric circuit. Due to th
the ‘electrical
signal’ cannot run direct
Presynaptic
Sensory neurons transfer
signals
Release
of from the stimulated sense organs to
halfwaytheinto
thenervous system
central
(CNS). Motor neurons transfer signals from
transmitter
the CNS to
and glands initiating a response to a stimulus.
development
ofthe muscles
substance
Interneurons relay signals between the motor and sensory neurons.
The central nervous system (CNS) begins to form
membrane
The arrival of a signal, called an impuls
embryonic period, 28 days after conception. The
chemicals into Synaptic
the gap. These chem
the central nervous system is the first major event in the formation of
cleft
across the gap locking into the recep
The motor
organs in the developing embryo. The nervous system develops
fromand sensory neurons are specialised for rapid, long distance,
membrane, causing it to ‘switch on’.
direct
communication. They have three major
functions – to receive
the ectoderm, the outer of the three germ layers. The skeletal
system
Receptor
neurotransmitters
Postsynaptic are released and tho
signals, transmit signals quickly over a long distance
and transfer signals
Brain
molecule
develops from the mesoderm, the middle of the germ layers,towith
the cell.
have
been broken down by an enzym
membrane
the target
neurotransmitters are then reabsorbed
cranium and vertebrae forming a protective cover around the brain and
Fig.2 The synaptic cleft
Fig.3 The sensory and motor neuron
spinal cord.
Because the transmission between ne
it is possible
to alter
signalling
Sensory
neurons transfer
sense
organs
to betwee
Neurotransmitter
swelling
Dendrites signals from the stimulated
Spinal cord
substances.
The
most common
the central nervous system (CNS). Motor neurons
transfer
signals
from are
substances can be used for pain-relie
the CNS to the muscles and glands initiating ahealth,
response
to a stimulus.
Axon
while others, if abused or misterminals
Interneurons relay signalsCell
between
the
motor
and
sensory
neurons.
health
consequences.
body
Nucleus
Fig.1 The central nervous system – brain and spinal cord
Spinal cord
How are messages transferred?
The brain is the main command centre sending and receiving signals
to and from all parts of the body, storing information and giving us the
amazing ability of self-awareness, i.e. consciousness.
The spinal cord is a complex dual carriageway. Information passes
rapidly between the brain and almost all the organs of the body.
Schwann cell
Myelin sheath
Dendrites or
nerve endings
Receptors or
sense organs
Axon
terminals
Axon
Node of
Ranwier
The spinal cord is a complex dual carriageway. Information passes
rapidly between the brain and almost all the organs of the body.
Signals are conducted along specialised cells called neurons. There are
three types of neuron; sensory neurons, motor neurons and interneurons.
The neurons do not connect directly with one another; there is a small
gap between them, called the synaptic cleft.
called the reflex arc provides a shorter
of impulses.
Parkinson’s disease
Cell body
Neurotransmitter swelling
All nerve cells have a similar basic structure: a cell body, extensions from
the cell body called dendrites, and an axon.
The brain is the main command centre sending and receiving signals
to and from all parts of the body, storing information and giving us the
amazing ability of self-awareness, i.e. consciousness.
the greater is the chance of avoiding inj
Dendrites
Axon
terminals
Interneurons transfer signals from the sensory neurons to the motor neurons;
they do not have a myelin sheath and
so do not operate as quickly.
Nucleus
How are messages transferred?
The faster the response to potentially
Neurotransmitter swelling
Cell body
Fig.1 The central nervous system – brain and spinal cord
can be compared with a thick telephon
wires (axons) in separate bundles.
Axon
Fig.3 The sensory and motor neuron
Dendrite
Schwann cell
Myelin sheath
DIRECTION OF IMPULSE
Signals are conducted along specialised cells called neurons. There are
three types of neuron; sensory neurons, motor neurons and interneurons.
The neurons do not connect directly with one another; there is a small
gap between them, called the synaptic cleft.
Dendrite
DIRECTION OF IMPULSE
Cell body
It for
is essential
that the
lines of commu
The motor and sensory neurons
rapid, long
distance,
Nucleusare specialised
muscle tissue remain intact to permit m
direct communication. They have three major
functions – to receive
Nerve impulses
pass to
and from the
signals, transmit signals quickly over a long distance
and transfer
signals
sensory and motor neurons in the 31 p
to the target cell.
DIRECTION OF IMPULSE
Brain
Node of
Ranwier
DIRECTION OF IMPULSE
Axon
Parkinson’s disease is a progressive n
with the build
up of protein inclusions i
Nucleus
the brain, causing degeneration of the
reduced production of dopamine, a neur
in the number of connections between
ganglia are responsible for controllin
body. Where there is a malfunction of
in Parkinson’s disease, aspects of mov
slowness Axon
of movement, stiffness and
limbs and tremors – characteristic feat
Axon
terminals
Dendrites or
nerve endings
Receptors or
sense organs
Neurotransmitter swelling
Interneurons transfer signals from the sensory neurons to the motor neurons;
they do not have a myelin sheath and so do not operate as quickly.
All nerve cells have a similar basic structure: a cell body, extensions from
the cell body called dendrites, and an axon.
The Human Nervous System
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us System
Our bodies have over ten million million (1013) living cells
Nerve Impulse
which must work in co-operation for us to live and grow. To
co-operate they must communicate. The brain, spinal cord,
nerves, sense organs and receptors are the vital parts of
Synaptic knob
the human nervous system that facilitate communication
The
membranes
of
the
cell
body
and
its
dendrites
have
special
chemicals
between our cells. In this lesson we will look at the formation
onto
which aof signalling
and function
the nervouschemical
system. from another neuron can lock and
The membranes of the cell body and its d
onto which a signalling chemical from
stimulate it into activity.
Terminal dendrite
The axon is the long extension from th
the signal to the target site. Axons can
transfer time over one long axon is mu
to travel over many cells. If the nerve c
otheron
cells,
then, for
example, a signal
Imagine you are
a boat
in the
to travel
about 200,000 ce
middle of thehave
ocean
withalong
no sail,
minutes.We could not survive if there
no compass and
no
rudder.
How
to dangers
Synaptic vesicle
Transmitter
substance
stimulate it into activity.
How is our nervous system formed?
The axon is the long extension from the nerve cell body that transfers
Release of
Presynaptic
The central nervous system (CNS) begins to form halfway into the
transmitter
long do you think it would take to
membrane
the
signalperiod,
to the 28
target
can be
updevelopment
to one metre
the
The numerous terminal dendrites ensur
embryonic
dayssite.
afterAxons
conception.
The
of in length;
substance
Synaptic
find land?
transfer
oversystem
one long
is much
than ifofthe signal had
many of the cells of the target tissue. Sy
the centraltime
nervous
is the axon
first major
event shorter
in the formation
cleft
to the target cell.
organs
in the
developing
embryo.
Thenerve
nervous
system
develops
from size as most
to
travel
over
many cells.
If the
cells
were
the same
Health
care
systems
can be just
the ectoderm,
the outer
the three germ
layers.
The the
skeletal
Receptor
Postsynaptic
other
cells, then,
forofexample,
a signal
from
footsystem
to the brain would
like
that
boat
at sea. Without
new of neuro
molecule
What
is the role
develops from the mesoderm, the middle of the germ layers, with the
membrane
have
toand
travel
along
about
200,000cover
cellsaround
and would
seven
medicines
to
tackle
disease,
cranium
vertebrae
forming
a protective
the braintake
and aboutFig.2
The synaptic cleft
Although nerve signals are electric in n
minutes.We
could not survive if there were such delays in responding
spinal cord.
without new
equipment
strictly
like an electric to
circuit. Due to th
Sensory neurons transfer signals from the stimulated sense organs to
to dangers
perform operations, and perhaps most importantly
of all,signal’
without
the ‘electrical
cannot run direct
the central nervous system (CNS). Motor neurons transfer signals from
researchers
totocome
up with new
breakthroughs,
the CNS
and glands initiating
a response
a stimulus.
The numerous terminal dendrites ensure extensive communication
withto the musclesexperienced
The arrival
of a signal, called an impuls
motor
and sensory
ourbetween
healththe
care
system
couldneurons.
just drift aimlessly
and never
reach
chemicals
into the
gap. These chem
many of the cells of the target tissue. Synaptic knobs transfer the Interneurons
signals relay signals
across the gap locking into the recep
ground.
The motor and sensory new
neurons
are specialised for rapid, long distance,
to the target cell.
What is the role of neurotransmitters?
Brain
membrane, causing it to ‘switch on’.
direct communication. They have three major functions – to receive
neurotransmitters
are released and tho
Health
Board
(HRB)signals
provides direction
and funding
signals, transmit signalsThe
quickly
over aResearch
long distance
and transfer
have been
down by an enzym
to support health research in Ireland. By doing
so,broken
the HRB
to the target cell.
neurotransmitters are then reabsorbed
underpins the delivery of, and the continued improvement of, our
Although nerve signals are electric in nature, the nervous systemFig.3
is not
The sensory and motor neuron
Because the transmission between ne
health care system.
strictly like an electric circuit. Due to the presence of the synaptic cleft,
it is possible to alter signalling betwee
Neurotransmitter swelling
Dendrites
Spinal
the ‘electrical signal’ cannot run directly
intocord
the target cell.
most common are
The HRB funds research into a wide range ofsubstances.
areas. OurThe
funded
The brain is the main command centre sending and receiving signals
Myelin sheath
Itto is
thatof the
linesstoring
of communication
between
andessential
from all parts
the body,
information and giving
us the the brain and
Dendrites or
amazing ability
of remain
self-awareness,
muscle
tissue
intact i.e.
to consciousness.
permit many important body functions.
nerve endings
The spinal cord is a complex dual carriageway. Information passes
DIRECTION OF IMPULSE
Nucleus
Because the transmission between neurons is by a chemical process,
it is possible to alter signalling between nerve cells by using chemical
substances.
The most common are known as anaesthetics; suchDendrite
Fig.1 The central nervous system – brain and spinal cord
substances can be used for pain-relief and the restoration of mental
Schwann cell
health, while others, if abused or mis-administered, can have serious
How are
messages transferred?
health
consequences.
substances can be used for pain-relie
researchers study diseases like diabetes, cancer
and Parkinson’s
health, while others, if abused or misdisease. In Parkinson’s Cell
disease
we
are
studying
ways to grow
health consequences.
body
nerve cells outside the body which could then be transplanted
It is essential that the lines of commu
Nucleus
back into the body. This is
just one of our projects
theremain
central
muscleon
tissue
intact to permit m
nervous system.
Nerve impulses pass to and from the
sensory out
and motor
In addition to funding research, we also carry
our neurons
own in the 31 p
can be compared with a thick telephon
research in areas such as mental health, child
health
and
drug
wires (axons) in separate bundles.
Axon
misuse. The HRB keeps databases on drug misuse, disability and
The faster the response to potentially
mental health. By examining this data we can
spot trends, and
the greater is the chance of avoiding inj
help others plan relevant services where they called
are needed
the reflexaround
arc provides a shorter
the country.
of impulses.
DIRECTION OF IMPULSE
The arrival of a signal, called an impulse, triggers the release of special Axon
terminals
chemicals into the gap. These chemicals, neurotransmitters, diffuse
across the gap locking into the receptor molecules in the target cell Axon
membrane, causing it to ‘switch on’. It switches off when no more
Node of
neurotransmitters are released and those that were previously releasedRanwier
have been broken down by an enzyme in the gap. The broken down
Cell body
neurotransmitters are then reabsorbed into the synaptic knob.
Health research can provide a rich, varied
and stimulating
Parkinson’s
disease
Axon
career. Health researchers
can have a background
nursing,
terminals
Parkinson’sindisease
is a progressive n
social science, maths, medicine, computers,with
chemistry,
physics
the build up
of protein inclusions i
the brain, causing degeneration of the
or biology.
reduced production of dopamine, a neur
Receptors or
in the number of connections between
Nerve
impulses pass to and from the spinal cord along the axons
of
sense organs
rapidly between the brain and almost all the organs of the body.
ganglia are responsible for controllin
Neurotransmitter swelling
sensory and motor neurons in the 31 pairs of spinal nerves; each nerve
Where there
is a malfunction of
More information about the HRB can body.
be found
at our
Signals are conducted along specialised cells called neurons. There are
can be compared with a thick telephone cable with many thousands
of transfer signals from the sensory neurons to the motor neurons;
in Parkinson’s disease, aspects of mov
Interneurons
three types of neuron; sensory neurons, motor neurons and interneurons.
website
www.hrb.ie
or
www.sta.ie.
slowness of movement, stiffness and
wires
(axons)
in separate
bundles.
they do not have a myelin sheath and so do not operate as quickly.
The neurons
do not
connect directly
with one another; there is a small
gap between them, called the synaptic cleft.
limbs and tremors – characteristic feat
nerve cells have a similar basic structure: a cell body, extensions from
The faster the response to potentially dangerous, unforeseen All
stimuli,
the cell body called dendrites, and an axon.
the greater is the chance of avoiding injury. A special signalling pathway
called the reflex arc provides a shorter, faster pathway for the transfer
Is there a specific cause of Parkinson’s disease?
of impulses.
Parkinson’s disease affects one in 250 people over the age of 40, and
one in 100 people over 65. Unfortunately there are few if any real clues
Parkinson’s disease
as to the cause of Parkinson’s disease in the vast majority of patients.
Parkinson’s disease is a progressive neurological disorder that begins
The fact that the level of this condition is the same worldwide, indicates
with the build up of protein inclusions in neurons in the basal ganglia of
that an environmental agent is not responsible. There is no clear genetic
the brain, causing degeneration of the neurons. As a result there is a
cause for the disease although many genes may be responsible for
reduced production of dopamine, a neurotransmitter, and a major decline
the condition. Some gene variations have been shown to increase
in the number of connections between the surviving neurons. The basal
susceptibility to the disease.
ganglia are responsible for controlling automatic movements of the
body. Where there is a malfunction of the basal ganglia, as happens
How can Parkinson’s disease be treated?
in Parkinson’s disease, aspects of movement are impaired, resulting in
Treatments of Parkinson’s disease include drugs that mimic the action of
slowness of movement, stiffness and increased effort in movement of
dopamine and the transplanting of dopamine secreting cells to the site
limbs and tremors – characteristic features of the disease.
of degeneration. Recently deep brain stimulation using electrodes has
proven to reduce hyperactivity in movement control centres.
The Human Nervous System
The Human Nervous
Our bodies have over ten million million (1013) living cells
which must work in co-operation for us to live and grow. To
co-operate they must communicate. The brain, spinal cord,
nerves, sense organs and receptors are the vital parts of
the human nervous system that facilitate communication
Syllabus
Reference
between
our cells.
In this lesson we will look at the formation
and function of the nervous system.
Synaptic vesicle
Synaptic knob
Leaving Certificate Biology
How is our nervous system formed?
Unit 3.5.3: Responses in Humans
The central nervous system (CNS) begins to form halfway into the
embryonic
period, 28
daysScience
after conception. The development of
Junior Certifi
cate
the central nervous system is the first major event in the formation of
Section
1B3:
Sensoryembryo.
System
organs
in the
developing
The nervous system develops from
the ectoderm, the outer of the three germ layers. The skeletal system
develops from the mesoderm, the middle of the germ layers, with the
cranium and vertebrae forming a protective cover around the brain and
spinal cord.
Learning Objectives
Brain
The membranes of the cell body and its d
onto which a signalling chemical from
stimulate it into activity.
Terminal dendrite
Nerve Impulse
Transmitter
substance
Activities
Investigative Activities
The axon is the long extension from th
the signal to the target site. Axons can
transfer time over one long axon is mu
to travel over many cells. If the nerve c
other cells, then, for example, a signal
have to travel along about 200,000 ce
minutes.We could not survive if there
to dangers
effect.
Have a friend hold
Reaction time measurement
and the training
Presynaptic
membrane
a 30 cm ruler vertically at
the 30 cm mark. Place
your
thumb
and index
The
numerous
terminal
dendrites ensur
Synaptic
many ofthe
the0cells
the target
finger at the front and back of thecleft
ruler and just outside
cmofmark,
but tissue. Sy
to the
cell.the next six
not holding the ruler. Tell your friend to let the ruler
falltarget
within
Receptor
Postsynaptic
seconds. When the ruler
falls, catch it between your
thumb
and firole
nger of
as neuro
molecule
What
is the
membrane
quickly as you can. Record the position at which you caught the ruler. This
Fig.2 The synaptic cleft
nerve signals are electric in n
is the distance the ruler fell before being caught; Although
the shorter
the distance
strictly like an electric circuit. Due to th
Sensory neurons transfer
signalsyour
from reaction
the stimulated
sense
organs
to
the faster
time.
Repeat
twice
more
and
take
the average
the
‘electrical
signal’
cannot run direct
the central nervous system (CNS). Motor neurons transfer signals from
distance.
Then
to
see
if
practice
has
any
infl
uence
on
reaction
time, repeat
the CNS to the muscles and glands initiating a response to a stimulus.
The arrival of a signal, called an impuls
the procedure
each
day for a school
week.into
Compare
Interneurons relay signals
between the several
motor andtimes
sensory
neurons.
chemicals
the gap. the
These chem
results
on
the
fi
fth
day
with
the
original
result.
Is
it
a
waste
of timeinto
forthe recep
across
the
gap
locking
The motor and sensory neurons are specialised for rapid, long distance,
membrane, causing it to ‘switch on’.
sprinters
or Formula
1 drivers
to –practise
their starts?
direct communication.
They have
three major
functions
to receive
Release of
transmitter
substance
neurotransmitters are released and tho
signals, transmit signals quickly over a long distance and transfer signals
have
down
by an enzym
Knee jerk reflex. The person being tested sits on
a been
chairbroken
with his
or her
neurotransmitters
are then
reabsorbed
legs crossed at the knees, such that the lower part
of one leg can
swing
The sensory and motor neuron
transmission
between ne
freely. Hit the knee firmly just below the kneecapBecause
(on thethe
patella
tendon)
is possible to swings
alter signalling
Neurotransmitter
with theswelling
outside edgeDendrites
of your open hand. The leg itimmediately
out. betwee
substances. The most common are
Then ask them to try not to jerk their knee on the substances
next trial. can be used for pain-relie
On completing this lesson the student should be able
to:
to the
target cell.
Give an outline description of the central nervous system
•
Relate the structure of a motor neuron
its function
Spinaltocord
•
Describe the structure of a synapse
•
Explain how nerve signals are transferred across a synapse
•
Show how the spinal cord is protected by the vertebrae
•
Fig.3
Axon
terminals
Axon
Node of
Ranwier
Describe the nerve pathway of a spinal reflex action.
Nucleus
Dendrite
Fig.1 The central nervous system – brain and spinal cord
Schwann cell
How are messages transferred?
General Learning Points
The brain is the main command centre sending and receiving signals
to and from all parts of the body, storing information and giving us the
amazing ability of self-awareness, i.e. consciousness.
Myelin sheath
rapidly between the brain and almost all the organs of the body.
sense organs
Communication between cells is essential to co-ordinate the activity
nerve endings
The spinal
cord is a complex
dual carriageway. Information passes
Receptors or
of a multicellular
organism.
•
Rapid direct information transmission is carried out by the
signals to and from other cells.
terminals
Dendrites or
•
Signals are conducted along specialised cells called neurons. There are
system.
threenervous
types of neuron;
sensory neurons, motor neurons and interneurons.
The neurons do not connect directly with one another; there is a small
•
Neurons
are
the
cells that pick up, transfer and
gap between them, calledspecialised
the synaptic cleft.
muscle tissue remain intact to permit m
Confusing image. Roll a page into a long tubeNerve
about
as wide
astoyour
impulses
pass
and from the
sensoryup
and
in the 31 p
thumb. Place one end of the paper tube horizontally
tomotor
one neurons
eye and
can
be compared
thick telephon
look though it. Place your other hand beside the
tube
– aboutwith
halfa way
wires (axons) in separate bundles.
Axon
along it – with the palm directly
facing the other eye. One eye is then
response
to potentially
looking down the tube and the other is looking at The
the faster
palm the
of your
hand.
It
greater is the chance of avoiding inj
will appear that you are looking through a hole inthe
your
hand. Now put the
called the reflex arc provides a shorter
tube at the back of a friend’s head. Look down the
tube with one eye and
of impulses.
at the ear with the other eye. It appears to be a hole directly through the
Parkinson’s disease
head from ear to ear – ‘in oneAxon
ear and out the other’!
DIRECTION OF IMPULSE
Cell body
health, while others, if abused or mis-
Eye blink. Hold a pane of clear plastic in front of health
your face.
Get a friend to
consequences.
Cell body
throw a small ball at the pane. Consciously try not to blink. Bet you cannot
is essential that the lines of commu
Nucleus
do so! You cannot consciously
stop this eye blinkIt refl
ex.
DIRECTION OF IMPULSE
•
True or False
Neurotransmitter swelling
Indicate whether each of the following
Interneurons transfer signals from the sensory neurons to the motor neurons;
they do not have a myelin
and soa
docircle
not operate
as quickly.the T or F.
by sheath
drawing
around
transmit
All nerve cells have a similar basic structure: a cell body, extensions from
(a) The brain and spinal cord form the central
the cell body called dendrites, and an axon.
Parkinson’s disease is a progressive n
with the build up of protein inclusions i
the brain, causing degeneration of the
reduced production of dopamine, a neur
in the number of connections between
ganglia are responsible for controllin
body. Where there is a malfunction of
is
true (T) disease,
or false
(F) of mov
in Parkinson’s
aspects
slowness of movement, stiffness and
limbs and tremors – characteristic feat
nervous system.
T
F
•
The long axon is the major time saving feature of neurons – some of
these are over a metre long.
(b) The spinal cord connects the brain to all the sense organs.
T
F
(c) Neurons are specialised cells to transfer information signals.
T
F
•
The signal is transferred chemically to the ‘target cell’ at the synapse.
(d) Motor neurons carry signals to the central nervous system.
T
F
•
The chemical transmission at the synapse can be modified by
specific medicines.
(e) Interneurons carry signals from the central nervous system.
T
F
•
The reflex arc is a rapid response pathway for reflex action.
(f) Signals are transferred to target cells by diffusion of chemicals. T
F
•
The spinal cord is the ‘go between’ for the brain, sense organs
and effectors and damage to the spinal cord inhibits normal
communication between them.
(g) Some motor and sensory neurons may be about a metre
in length.
T
F
(h) The axon is the time-saving feature for rapid information transfer.T
F
(i) A reflex arc is a long signal pathway involved in slow responses. T
F
(j) There are 33 vertebrae and 33 pairs of spinal nerves.
T
F
(k) All organs below the head connect to the brain by the spinal cord. T
F
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The Human Nervous System
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us System
Our bodies have over ten million million (1013) living cells
which must work in co-operation for us to live and grow. To
co-operate they must communicate. The brain, spinal cord,
nerves, sense organs and receptors are the vital parts of
the human nervous system that facilitate communication
Examination
between our cells. In Questions
this lesson we will look at the formation
and function of the nervous system.
Synaptic vesicle
Synaptic knob
2006 Leaving Certificate Higher Level
How is our nervous system formed?
Release of
(i)
What is a neuron?
The central nervous system (CNS) begins to form halfway into the
transmitter
embryonic
period,between
28 days sensory,
after conception.
Theinterneurons
development of
substance
(ii)
Distinguish
motor and
(association
the neurones).
central nervous system is the first major event in the formation of
organs in the developing embryo. The nervous system develops from
(iii)
y explain
theofrole
neurotransmitter
the Briefl
ectoderm,
the outer
the of
three
germ layers. The substances.
skeletal system
spinal
1. cord.
Schwann
Cells,
2. Myelin sheath.
(v) In relation to Parkinson’s disease or paralysis give,
1. a possible cause,
2. a method of treatment.
Brain
2005 Leaving Certificate Higher Level
Transmitter
substance
The membranes of the cell body and its d
onto which a signalling chemical from
stimulate it into activity.
The axon is the long extension from th
the signal to the target site. Axons can
transfer time over one long axon is mu
to travel over many cells. If the nerve c
other cells, then, for example, a signal
same
size
as a along
tennis
ball,200,000 ce
have
to travel
about
minutes.We could not survive if there
to dangers
•
If the cell body of a motor neuron was the
the axon would be about 10 km long.
•
Presynaptic
Your spinal cord is about
a thick as your little finger.
membrane
•
Synaptic in the first month of embryological
The brain and spinal cord are formed
many of the cells of the target tissue. Sy
cleft
to the target cell.
development.
The numerous terminal dendrites ensur
Receptor
develops from the mesoderm, the middle of the germ layers, with the
(iv)
State a function for
cranium and vertebrae forming a protective cover around the brain and
Terminal dendrite
Nerve Impulse
Fig.2
Postsynaptic
•
Smoking by a pregnant
woman can lead toWhat
brain is
damage
in the
molecule
the role
of
membrane
developing
baby
–
as
a
result
of
a
decrease
in
the
oxygen
supply.
The synaptic cleft
Sensory neurons transfer signals from the stimulated sense organs to
the central nervous system (CNS). Motor neurons transfer signals from
the CNS to the muscles and glands initiating a response to a stimulus.
Interneurons relay signals between the motor and sensory neurons.
Biographical Notes
neuro
Although nerve signals are electric in n
strictly like an electric circuit. Due to th
the ‘electrical signal’ cannot run direct
The arrival of a signal, called an impuls
chemicals into the gap. These chem
across the gap locking into the recep
The motor and sensory
neurons
are specialised
long distance,
Luigi
Galvani
(1737for–rapid,
1798)
membrane, causing it to ‘switch on’.
direct communication. They have three major functions – to receive
Was a physician and physicist who was born, worked
and died in Bologna,
neurotransmitters
are released and tho
signals, transmit signals quickly over a long distance and transfer signals
have
been
down by an enzym
Italy.
It
was
he
who
discovered
that
muscle
and
nerve
cellsbroken
can produce
to the target cell.
are then reabsorbed
electricity. Dissecting a frog at a table where heneurotransmitters
had been conducting
Ranwier
Cell body
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Dendrite
Fig.1 The central nervous system – brain and spinal cord
Schwann cell
How You
are messages
Did
Know? transferred?
The brain is the main command centre sending and receiving signals
Nucleus
three types of neuron; sensory neurons, motor neurons and interneurons.
•The There
are at least 1012 other supporting cells in the brain.
neurons do not connect directly with one another; there is a small
between
them, called
the brain
synaptic
cleft.be in contact with 200,000
•gapAn
interneuron
in the
may
other interneurons.
of impulses.
In addition, he studied the life cycle of Plasmodium falciparum and related
Parkinson’s
disease
the timing of fevers seen in malaria
with the life cycle
of this organism.
Axon
Parkinson’s disease is a progressive n
with the build up of protein inclusions i
brain,
degeneration
of the
Was a German physiologist. He recognised thethecell
as causing
the basic
unit
reduced production of dopamine, a neur
of animal structure and is regarded as the founder
of
histology.
While
in the number of connections between
investigating digestive
processes, he isolated a ganglia
substance
responsible
are responsible
for controllin
Neurotransmitter swelling
Where
is a malfunction
of
for digestion in the stomach, which he named body.
pepsin.
Hethere
coined
the
Parkinson’s disease,
Interneurons transferterm
signalsmetabolism,
from the sensoryidentifi
neuronsed
to the
motor
neurons;
the
role
played by in
microorganisms
in aspects
the of mov
slowness of movement, stiffness and
they do not have a myelin
sheath and so do
operate as
quickly.and formulated
decomposition
ofnot
organic
matter,
the basic principles
limbs and tremors – characteristic feat
All nerve cells have a
basic structure:
a cell body, extensions
from is a single cell that eventually
ofsimilar
embryology
by observing
that the egg
the cell body calleddevelops
dendrites, and
anaaxon.
into
complete organism.
Myelin sheath
•to and
It was
Parkinson,
a London
doctor,
fromin
all1817
parts that
of theJames
body, storing
information
and giving
us thefirst described
Dendrites or
amazing
of self-awareness,
i.e. consciousness.
The ability
Shaking
Palsy, a slowly
progressive degeneration of the nervous
nerve endings
system
distinguished
by
shaking
when
at
rest,
slowness
in
starting
The spinal cord is a complex dual carriageway. Information passes
Receptors or
sense organs
movement
and
muscle
rigidity.
rapidly
between the
brain
and almost
all the organs of the body.
11
•Signals
There
100,000,000,000
(10cells
) neurons
in theThere
brain.
are are
conducted
along specialised
called neurons.
are
Nerve impulses pass to and from the
Was an Italian physician and scientist. He studiedsensory
medicine
at University
and motor neurons in the 31 p
of Pavia, from which he graduated in 1865. He spent
much
of his
career
can be
compared
with
a thick telephon
wires (axons)
in separate
bundles.
studying the central nervousAxon
system. Tissue staining
techniques
in the
latter half of the 19th century were inadequate for studying
tissue.
The fasternervous
the response
to potentially
He devised a method of staining nervous tissuethe
which
enabled
himoftoavoiding inj
greater
is the chance
called the reflex arc provides a shorter
view the paths of nerve cells in the brain.
DIRECTION OF IMPULSE
(iii) Suggest a possible role for a drug in relation to the events that you
have outlined in (ii).
DIRECTION OF IMPULSE
Fig.3 The
and motor neuron
Name a disorder of the nervous system, other than cancer, and indicate
a sensory experiments
with static electricity, Galvani’s Because
assistant
touched an
the transmission
between ne
possible cause and a means of treatment.
it is possible
alterpicked
signalling betwee
exposedswelling
sciatic nerveDendrites
of the frog with a metal scalpel,
whichtohad
Neurotransmitter
Spinal cord
most common are
up a charge. This caused the dead frog’s leg to substances.
kick, as if itThe
were
alive.
substances can be used for pain-relie
2004 Leaving Certificate Higher Level
to
appreciate
the or misAxon The observation made Galvani the first investigator
health, while others, if abused
terminals
relationship between electricity
and animation —health
or life.
He is generally
consequences.
Cell body
(i) Draw and label sufficient of two neurons to show a synaptic cleft.
Axon credited with the discovery of bioelectricity.
It is essential that the lines of commu
Nucleus
(ii) Describe the sequence of events that allows an impulse to be
muscle tissue remain intact to permit m
transmitted across a synapse from one neuron to the next.
Node of Camillo Golgi (1843 – 1926)
terminals
Theodor Schwann, (1810 – 1882)
•
Signals (impulses) pass along ‘myelinated’ axons at about 100 metres
per second, so taking about one hundredth of a second to pass
between any two parts of the body.
•
Unmyelinated axons conduct impulses at only one metre per second.
•
It takes about one thousandth of a second for the signal to pass across
a chemical synapse to the next neuron.
•
A single neuron may have from 1000 to 10,000 synapses with
target cells.
Can you recall the meaning of these terms? Reviewing
terminology is a powerful aid to recall and retention.
•
The synaptic cleft is about 0.00002 mm (20 nm) wide, too small to be
seen with a light microscope.
•
Thousands of synaptic vesicles are present in a synaptic knob.
•
One impulse may stimulate the release of a neurotransmitter from
hundreds to thousands of synaptic vesicles.
•
It takes only one minute to regenerate synaptic vesicles with recycled
neurotransmitter.
Histology, ectoderm; germ layers; mesoderm; neurons; sensory
neurons; motor neurons; interneurons; synaptic cleft; receive
signals; transmit signals; transfer signals; dendrites; axon; cell;
body; axon; membranes; terminal dendrites; target tissue; synaptic
knobs; target cell; impulse; neurotransmitters; spinal nerves;
reflex arc; basal ganglia; dopamine; deep brain stimulation.
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Revise the Terms
Check the Glossary of Terms for this lesson at www.sta.ie