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The Nervous System
As the most complex system, the nervous system serves as the body control centre and
communications electrical-chemical wiring network. As a key homeostatic regulatory and
coordinating system, it detects, interprets, and responds to changes in internal and
external conditions. The nervous system integrates countless bits of information and
generates appropriate reactions by sending electrochemical impulses through nerves to
effector organs such as muscles and glands. The nervous system allows the animal to quickly
detect, communicate and co-ordinate information about its external and internal
environment so it can make efficient appropriate responses for survival and/or
reproduction.
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 spinal nerves are nerves that connect to the spinal cord. The
cranial and spinal nerves contain the axons (fibres) of sensory and motor nerve cells. The
peripheral nervous system carries the messages from the sensory organs to the CNS and
carries messages from the CNS along motor nerves out to the muscles and glands.
The PNS has two parts: the somatic nervous system and the autonomic nervous system.
The somatic nervous system, or voluntary nervous system, enables humans to react
consciously to environmental changes. It includes 31 pairs of spinal nerves and 12 pairs of
cranial nerves. This system controls movements of skeletal (voluntary) muscles.
The involuntary nervous system (autonomic nervous system) maintains homeostasis. As
its name implies, this system works automatically and without voluntary input. The effectors
in this system are smooth muscle, cardiac muscle and glands, all structures that function
without conscious control. An example of autonomic control is movement of food through
the digestive tract during sleep.
Special sense receptors provide for taste, smell, sight, hearing, and balance. Nerves
carry all messages exchanged between the CNS and the rest of the body
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The Nervous System
On the diagram below colour in a label the:

Brain

Spinal Cord

Peripheral Nervous System
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The Brain
The brain has billions of neurons that receive, analyse, and store information about internal
and external conditions. It is also the source of conscious and unconscious thoughts, moods,
and emotions. Four major brain divisions govern its main functions: the cerebrum, the
diencephalon, the cerebellum, and the brain stem.
The cerebrum is the large rounded area that divides into left and right hemispheres.
Surprisingly, each hemisphere controls muscles and glands on the opposite side of the body.
Comprising 85 percent of total brain weight, the cerebrum controls language, conscious
thought, hearing, somatosensory functions (sense of touch), memory, personality
development, and vision.
Gray matter (unmyelinated nerve cell bodies) composes the cerebral cortex (outer portion of
the cerebrum). Beneath the cortex lies the white matter (myelinated axons). During
embryonic development, the cortex folds upon itself to form gyri (folds) and sulci (shallow
grooves) so that more gray matter can reside within the skull cavity.
The diencephalon forms the central part of the brain. It consists of three bilaterally
symmetrical structures: the hypothalamus, thalamus, and epithalamus.
The hypothalamus is the main neural control centre (brain part that controls endocrine
glands). The pituitary gland lies just below the hypothalamus. The pituitary gland is a small
endocrine gland that secretes a variety of hormones.
The hypothalamus also regulates visceral (organ-related) activities, food and fluid intake,
sleep and wake patterns, sex drive, emotional states, and production of antidiuretic hormone
(ADH) and oxytocin.
At the rear of the brain is the cerebellum. The cerebellum is similar to the cerebrum: each
has hemispheres that control the opposite side of the body and are covered by gray matter
and surface folds. The cerebellum controls balance, posture, and coordination.
The brain stem connects the cerebrum and cerebellum to the spinal cord. Its superior
portion, the midbrain, is the centre for visual and auditory reflexes; examples of these include
blinking and adjusting the ear to sound volume. The middle section, the pons, bridges the
cerebellum hemispheres and higher brain centres with the spinal cord. Below the pons lies
the medulla oblongata; it contains the control centres for swallowing, breathing, digestion, and
heartbeat.
The reticular formation extends throughout the midbrain. This network of nerves has
widespread connections in the brain and is essential for consciousness, awareness, and
sleep. It also filters sensory input, which allows a person to ignore repetitive noises such as
traffic, yet awaken instantly to a baby's cry.
The spinal cord is a continuation of the brain stem. It is long, cylindrical, and passes through
a tunnel in the vertebrae called the vertebral canal. Like the cerebrum and cerebellum, the
spinal cord has gray and white matter, although here the white matter is on the outside. The
spinal cord carries messages between the CNS and the rest of the body, and mediates
numerous spinal reflexes such as the knee-jerk reflex.
Meninges, three connective tissue layers, protect the brain and spinal cord. The outermost
dura layer forms partitions in the skull that prevents excessive brain movement. The
arachnoid middle layer forms a loose covering beneath the dura. The innermost pia layer
clings to the brain and spinal cord; it contains many tiny blood vessels that supply these
organs.
Another protective substance, cerebrospinal fluid, surrounds the brain and spinal cord. The
brain floats within the cerebrospinal fluid, which prevents against crushing under its own
weight and cushions against shocks from walking, jumping, and running.
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The Nervous System
Questions:
1. Complete the following Table
Central Nervous System
Brain
Spinal Cord
Peripheral Nervous System
Cranial Nerves
Structure
Function
2. Outline the function of the nervous system
3. Identify the components on the CNS
4. Identify the components of the PNS
5. Describe what the PNS is and how it works
6. Compare and Contrast the autonomic nervous system and the somatic
nervous system
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Spinal Nerves
7. Explain how the CNS is protected within the body
8. Define neuron
9. How is a neuron different to a nerve?
10. In the table below, tabulate the function of the different parts of the
brain
Structure
Function
Research
1. Find a diagram of the human brain. Draw/print out. Ensure that it is
labelled
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Experiment: Sheep Brain Dissection
Aim: To dissect and observe a sheep’s brain.
Apparatus:




lambs brain
Dissecting kit
Gloves
newspaper
Risk Assessment:
Method:
1. Draw a scaled, labelled diagram of the sheep brain. Label the front of the
brain, the cerebrum. Cerebellum, brain stem and the spinal cord.
2. Pull away the membrane of the brain. What is this membrane called?
3. Observe the folds in the brain. Divide the brain into the right and left
hemispheres.
4. Locate the parts shown in the diagram. Label on your diagram and record
the colour, size and appearance of the cerebrum, cerebellum and spinal
cord.
Results:
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Discussion:
1. Describe the texture of the brain.
2. The brain is a very soft and easily damaged organ. How does our body
protect it?
3. Research and find the names of the folds and groves of the brain. Explain
what they are for.
4. Explain the role of the brain. In your answer include some of its specific
structures and functions.
5. Compare and contrast the role of the brain to that of the peripheral
nervous system.
Conclusion:
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What are sense organs?
Humans have 5 senses: touch, taste, smell, sight, and hearing. The senses are
based on receptor cells or groups of receptor cells called sense organs.
Receptors respond to stimuli and send nerve impulses along sensory neurons. The
brain interprets the nerve impulse and, thus, we perceive the impulse as one of
our senses.
Activity:
In groups you will be allocated an experiment that you need to design, request
equipment for, write up a worksheet for and conduct in class.
Sense
Experiment
Taste
Tasty Buds – a map of
the tongue
Taste
Identifying – what
taste is that?
Touch
Two Point
Discrimination
Smell
Expose Your Nose
Sight
Depth Perception
Sight
Blind Spot
Group
The websites below will have all of the information that you need.
Taste Experiments
http://faculty.washington.edu/chudler/chtaste.html
Smell Experiments
http://faculty.washington.edu/chudler/chsmell.html
Touch Experiments
http://faculty.washington.edu/chudler/twopti.html
Sight Experiments
http://faculty.washington.edu/chudler/chvision.html
The Senses
http://leavingbio.net/THE%20SENSES_files/THE%20SENSES.htm
Discussion:What are some of the advantages and disadvantages of
working in groups?
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Neurons
The human body is made up of trillions of cells. Cells of the nervous system,
called nerve cells or neurons, are specialised to carry "messages" through an
electrochemical process. The human brain has approximately 100 billion neurons.
Neurons come in many different shapes and sizes. Some of the smallest neurons
have cell bodies that are only 4 microns wide. Some of the biggest neurons have
cell bodies that are 100 microns wide. (Remember that 1 micron is equal to one
thousandth of a millimetre!).
A Neuron consists of three main parts:
1.
CELL BODY - The largest part, contains the nucleus and much of the
cytoplasm (area between the nucleus and the cell membrane), most of the
metabolic activity of the cell, including the generation of ATP (Adenine
Triphosphate Compound that Stores Energy) and synthesis of protein.
2. DENDRITES - Short branch extensions spreading out from the cell
body. Dendrites Receive STIMULUS (Action Potentials) and carry
IMPULSES from the ENVIRONMENT or from other NEURONS AND
CARRY THEM TOWARD THE CELL BODY.
3. AXON - A Long Fibre that CARRIES IMPULSES AWAY FROM THE CELL
BODY. Each neuron has only ONE AXON. The Axon Ends in a series of
small swellings called AXON TERMINALS.
Neurons may have Dozens or even Hundreds of DENDRITES but usually ONLY
ONE AXON.
Neurons are similar to other cells in the body because:
1.
2.
3.
4.
Neurons are surrounded by a cell membrane.
Neurons have a nucleus that contains genes.
Neurons contain cytoplasm, mitochondria and other organelles.
Neurons carry out basic cellular processes such as protein synthesis and
energy production.
However, neurons differ from other cells in the body because:
1. Neurons have specialized extensions called dendrites and axons.
Dendrites bring information to the cell body and axons take information
away from the cell body.
2. Neurons communicate with each other through an electrochemical
process.
3. Neurons contain some specialized structures (for example, synapses) and
chemicals (for example, neurotransmitters).
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Read the definitions, and then label the neuron diagram below.
Axon - the long extension of a neuron that
carries nerve impulses away from the body
of the cell.
axon terminals - the hair-like ends of the
axon. At these Terminals the neuron may
make contact with the DENDRITES of
another neuron, with a RECEPTOR, or with
an EFFECTOR.
cell body - the cell body of the neuron; it
contains the nucleus (also called the soma)
myelin sheath - the fatty substance that
surrounds, insulates and Speeds Up
transmission of Action Potentials through the
Axon.
node of Ranvier - one of the many gaps in the
myelin sheath - this is where the action
potential occurs, allows the impulses to travel
faster than if they travelled along the entire
length of the neuron
nucleus - the organelle in the cell body of the
neuron that contains the genetic material of the
cell
dendrites - the branching structure of a
neuron that receives messages (attached to
the cell body)
Schwann's cells - cells that produce myelin they are located within the myelin sheath.
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There are 3 types of neurons:
Sensory Neurons- Sensory neurons carry electrical signals (impulses) from
receptors or sense organs to the CNS.
Motor Neurons- Motor neurons carry impulses from the CNS to effector organs
(muscles and organs).
Interneuron’s- These are also called intermediate, relay, or associative neurons.
They carry information between sensory and motor neurons. They are found in
the CNS
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Experiment: Making Models of Nerve Cells
Scientific Models:
Aim: To make models of nerve cells out of play-doh and pipe cleaners
Hypothesis: If model nerve cells are made then the similarities and differences
between the different types of neurons will be easier to understand
Equipment:
Part A: Making the play doh






½ cup salt
1 cup plain flour
2 tablespoons cream of tartar
1 cup boiling water
1 tablespoon vegetable oil
Food colouring
Part B: Making the Models



Pipe cleaners
Cardboard
Pens and paper for labels
Method:
Part A
1. Add the desired food colouring to the hot water
2. Mix all of the ingredients together
3. Allow to cool
Part B
1. Using the play doh and pipe cleaners make a model of each of the three
types of neurons, motor neurons, interneurons and sensory neurons.
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How do neurons talk to each other?
Neurons carry nerve impulses. Nerve impulses travel along neurons in only one
direction and must travel from one neuron to the next. Between the end of one
neuron and the beginning of the next is a tiny gap called a synapse. Nerve
impulses must ‘jump’ across this gap if the signal is to be transmitted from one
nerve to the next.
The nerve impulse arrives at the axon terminal of the presynaptic neuron. This
triggers the release of chemical messengers called neurotransmitters into the
synaptic gap. The neurotransmitters travel across the synaptic gap and
stimulate a nervous impulse in the dendrite of the next neuron. The message
continues along through this nerve until the next until it reaches an effector. An
effector is an organ that produces an effect in response to nerve stimulation.
Muscles and glands are effectors.
Questions:
1. Draw a synapse
2. What are the chemical messengers?
3. How does the nerve impulse get from one neuron to the next?
4. What is an effector?
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Go to: http://www.mind.ilstu.edu/flash/synapse_1.swf
1. On the diagram below label:
Mitochondria, Vesicle containing neurotransmitters, Neurotransmitters, Receptor sites, Ion
Channel, Ions, Synaptic cleft, Extracellular Fluid, Membrane, Axon terminal, Dendrite
2. Define the following words
Word
Definition
Action Potential
Synaptic Cleft
Ions
Neurotransmitters
Mitochondria
Postsynaptic Neuron
Presynaptic neuron
3. Cut out the pictures of the events that occur at the synapse. Place them in order and label
with the descriptions below.
1. An action potential (electrical impulse) arrives at the axon terminal
2. The action potential triggers the release of neurotransmitters from a vesicle
3. The neurotransmitters move across the synaptic cleft from the axon terminal of the
presynaptic neuron to the dendrite of the postsynaptic neuron
4. The neurotransmitters bind to the receptor sires on the ion channels
5. Ions cross the membrane through the open ion channels
6. The influx of ions produces an action potential on the postsynaptic neuron
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Neurotransmitters, drugs, and mental diseases
Neurones do not touch each other. If they did, then it would be like turning on one switch in
your house and having all lights and appliances come on. Obviously we need to control which
nerves ‘fire’ at a certain time. There are microscopic gaps between neurones called synapses.
Impulses are sent across these gaps by substances called transmitter chemicals, or
neurotransmitters. About 50 different neurotransmitters have been found. Acetylcholine was
the first of these to be discovered. A lack of acetylcholine in the brain has been associated
with Alzheimer’s disease, the symptoms of which are memory loss, confusion, loss of reasoning
ability and illogical behaviour.
Noradrenaline is involved in our state of alertness. Dopamine is another neurotransmitter; it is
associated with emotional behaviour and movement. Amphetamine drugs increase the amount of
these two transmitters, and so earn the name ‘speed’. Lack of dopamine causes the shaking and
impaired movements seen in Parkinson’s disease. Another neurotransmitter is serotonin. A lack
of serotonin is associated with depression, and it is affected by LSD. The brain even has its own
pain deadening transmitters, called enkephalins and endorphins. Morphine, heroin, pethidine and
codeine act in much the same way. Once a neurotransmitter has passed the impulse on to the
next neurone, enzymes may quickly break it down, so that a new message can be passed along.
(Compare this to wiping a blackboard between notes.) Some toxins, including nerve gases, snake
venom, bacterial toxins (e.g. tetanus toxin) and insecticides, interfere with these enzymes, with
disastrous results for the organism.
Questions:
1. Some neurotransmitters cause neurones to become more active, while others do the opposite.
What role do you think noradrenaline and dopamine have?
2. Flies sprayed with flyspray often go into a frenzy. Try to explain this in terms of effects of
the spray on neurotransmitters.
3. Outline the role of neurotransmitters in nerve impulses
4. Describe the structure of a synapse and how a nerve impulse (message) is transmitted from
one neuron to another
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Responses of Muscles and Glands – effectors
Definitions for effectors:



Any muscle, organ etc. that can respond to a stimulus from a nerve
a nerve fibre that terminates on a muscle or gland and stimulates contraction or secretion
fifth step in a reflex - a muscle or gland that responds to the impulses
Muscles and glands carry out commands from the nervous system. They are effectors.
Muscles receive and respond to the chemical messengers (neurotransmitters) secreted directly
from the end of the motor neuron. These neurotransmitters do not have to travel in the
bloodstream. Muscles therefore react almost immediately to the nerve impulse but the
contraction (shortening) of the muscle lasts only a short time.
In contrast, when the neurotransmitter reaches a gland, it stimulates the gland to secrete a
substance such as a hormone. These hormones travel in the bloodstream and as a result take
longer to reach the target cells. Glands may take minutes or even days to produce a response.
Homework Research
1. How are hormones transported in the
body?
2. Compare the responses of muscles and
glands as effectors
3. What is the name of the system that
produces hormones?
4. Identify 5 examples of endocrine glands
and the hormones that they secrete
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Reflex Arc
Research: Research the following questions
1. Draw a labelled picture of a reflex arc including an effector, motor
neuron, receptor, sensory neuron, interneuron and spinal cord.
2. What is a reflex arc?
3. Identify some examples of reflexes
4. Explain why a reflex is necessary. What advantage does it have over
normal responses to our environment?
5. Where is the interneuron located in a reflex arc
6. How is a stimulus detected?
7. What is a receptor? Give an example.
8. What is an effector? Give an example.
9. How does the message travel from the receptor to the effector?
10. If you put your finger on a hot stove, what is the stimulus? What is the
response?
11. Are reflexes voluntary or involuntary?
12. How is the brain involved in a reflex?
13. Complete a flow chart with the following terms:
Effector, stimulus, interneurons (in spinal cord), sensory neurons, motor
neurons, sense organ (e.g. skin receptors)
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Reaction Times
Your reaction time is the time between when you were presented with a stimulus (something you see,
hear, smell, taste or feel) and when your respond to it. This could be you moving away from the stimulus,
jumping back or just slamming on the brakes in the car.
Mean Reaction Times
For about 120 years, the accepted figures for mean simple reaction times for college-age individuals
have been about 190 milliseconds (msec) (0.19 sec) for light stimuli and about 160 msec for sound
stimuli. Reaction time to touch is intermediate, at 155 msec
Factors that affect reaction time
Type of Stimuli Many researchers have confirmed that reaction to sound is faster than reaction to
light, with mean auditory reaction times being 140-160 msec and visual reaction times being 180-200
msec. Perhaps this is because an auditory stimulus only takes 8-10 msec to reach the brain but a visual
stimulus takes 20-40 msec. Reaction time to touch is intermediate, at 155 msec.
Age Simple reaction time shortens from infancy into the late 20s, then increases slowly until the 50s
and 60s, and then lengthens faster as the person gets into his 70s and beyond
Gender. At the risk of being politically incorrect, in almost every age group, males have faster reaction
times than females, and female disadvantage is not reduced by practice.
Fatigue Reaction time gets slower when the subject is fatigued
Distraction Distractions increase reaction time. Background noise lengthens reaction time by inhibiting
parts of the cerebral cortex.
Alcohol Slows reaction time
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Exercise. Exercise can affect reaction time. Physically fit subjects have faster reaction times.
Learning Disorders. Miller and Poll (2009) found that college students with a history of language and/or
reading difficulties had slower reaction times. Within the affected group of students, better language
skills were associated with faster reaction times.
Brain Injury. As might be expected, brain injury slows reaction time, but different types of responses
are slowed to different degrees
Experiment: Voluntary Actions and Reaction times
Aim: To compare the speed of your reaction times when two different receptors (the eye and the ear)
are used.
Hypothesis: If different receptors are tested then the reaction times will be different
Materials


metre ruler
table
Method:
PART A: The eye as the receptor – Speed of response to sight
1. Sits sideways at a bench with your forearm resting flat on the bench and your hand over the edge
2. Hold your thumb and fingers about 5-7 cm apart
3. Your partner will place the ruler in the space between your thumb and fingers so that the zero of the
ruler is level with the top of your hand.
4. When your partner lets the ruler go, catch it as quickly as you can. Record the distance the ruler
falls. Repeat this a ten times to find the average distance. Record the results
5. Use the table to calculate your reaction time
PART B: The ear as the receptor – speed of response to sound
1. Repeat steps 1 to 3 of part A.
2. Listen for when your partners lets the ruler go. They will say ‘now’ as they drop the ruler. Catch the
ruler as quickly as you can.
3. Record your results. Repeat this ten times and calculate the average distance.
PART C: Touch as the receptor – speed of response to touch
1. Repeat steps 1 to 3 of part A.
2. Close your eyes. When your partner lets the ruler go, they will tap you on the thumb as they drop the
ruler. Catch the ruler as quickly as you can.
3. Record your results. Repeat this ten times and calculate the average distance.
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Results: Distance and Speed of Responses to Different Stimuli
Trial
Distance of
Speed of
Distance of
Speed of
Distance of
Speed of
Response to
Response to
Response to
Response to
Response to
Response to
Light (sec)
Sound (cm)
Sound (sec)
Touch (cm)
Sound (sec)
Light (cm)
1
2
u
3
4
5
6
7
8
9
10
Average
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Table 2: Class Average Times
Name
Average Speed
Average Speed
Average Speed
of response to
of response to
of response to
Light (sec)
Sound (sec)
Touch (sec)
Average Time
for class (sec)
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Distance in cm
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Time in seconds
0.045
0.064
0.078
0.090
0.101
0.111
0.120
0.128
0.136
0.143
0.150
0.156
0.163
0.169
0.175
0.181
0.186
0.192
0.197
0.202
Distance in cm
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22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Time in seconds
0.207
0.212
0.217
0.221
0.226
0.230
0.235
0.239
0.243
0.247
0.252
0.256
0.260
0.263
0.267
0.271
0.275
0.278
0.282
0.286
Discussion:
1. Identify the:
a. Controlled Variables
b. Independent Variable
c. Dependant Variable
2. How did your reaction time compare with the average reaction times of the class?
3. Did your reflexes improve with practice?
4. How might these factors affect your reactions time: fatigue; alcohol; alertness; distractions?
5. Explain why it is necessary to keep the variables controlled during an experiment.
6. Give examples of where a fast reaction time is necessary
Conclusion:
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