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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 Peripheral Nervous System

Brain Spinal Cord Cranial Nerves Spinal 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

7. Explain how the CNS is protected within the body

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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:

Discussion:

1. Describe the texture of the brain.

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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:

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:

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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 Group

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

The websites below will have all of the information that you need.

Taste Experimentshttp://faculty.washington.edu/chudler/chtaste.html

Smell Experimentshttp://faculty.washington.edu/chudler/chsmell.html

Touch Experimentshttp://faculty.washington.edu/chudler/twopti.html

Sight Experimentshttp://faculty.washington.edu/chudler/chvision.html

The Senseshttp://leavingbio.net/THE%20SENSES_files/THE%20SENSES.htm

Discussion:What are some of the advantages and disadvantages of working in groups?

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

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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. Neurons are surrounded by a cell membrane.2. Neurons have a nucleus that contains genes.3. Neurons contain cytoplasm, mitochondria and other organelles.4. 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)

dendrites - the branching structure of a neuron that receives messages (attached to the cell body)

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

Schwann's cells - cells that produce myelin - they are located within the myelin sheath.

There are 3 types of neurons:

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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).

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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

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 water2. Mix all of the ingredients together3. Allow to cool

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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 synapse2. 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.swf1. 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 vesicle3. The neurotransmitters move across the synaptic cleft from the axon terminal of the

presynaptic neuron to the dendrite of the postsynaptic neuron4. The neurotransmitters bind to the receptor sires on the ion channels

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5. Ions cross the membrane through the open ion channels6. The influx of ions produces an action potential on the postsynaptic neuron

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 effectors3. What is the name of the system that

produces hormones?4. Identify 5 examples of endocrine

glands and the hormones that they secrete

Reflex Arc

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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 reflexes4. 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 arc6. 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

Exercise. Exercise can affect reaction time. Physically fit subjects have faster reaction times.

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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 apart3. 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 results5. 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

Response to

Light (cm)

Speed of

Response to

Light (sec)

Distance of

Response to

Sound (cm)

Speed of

Response to

Sound (sec)

Distance of

Response to

Touch (cm)

1

2

3

4

5

6

7

8

9

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Average

Table 2: Class Average Times

Name Average Speed

of response to

Light (sec)

Average Speed

of response to

Sound (sec)

Average Speed

of response to

Touch (sec)

Average Time

for class (sec)

Distance in cm Time in seconds Distance in cm Time in seconds1 0.045 21 0.2072 0.064 22 0.212

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3 0.078 23 0.2174 0.090 24 0.2215 0.101 25 0.2266 0.111 26 0.2307 0.120 27 0.2358 0.128 28 0.2399 0.136 29 0.243

10 0.143 30 0.24711 0.150 31 0.25212 0.156 32 0.25613 0.163 33 0.26014 0.169 34 0.26315 0.175 35 0.26716 0.181 36 0.27117 0.186 37 0.27518 0.192 38 0.27819 0.197 39 0.28220 0.202 40 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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