The Nervous System

The Nervous System is the body’s information gatherer, storage

centre and control system. Its overall function is to collect information about the external conditions in relation to the

body’s internal state, to analyse this information, and to initiateappropriate responses to satisfy certain needs, i.e. maintainhomeostasis.

Homeostasis is the maintaining of constant internal balance.

Control & CoordinationKey Words

Control & CoordinationRevision

1. Which two systems maintain control of our bodies?2. What makes up the central nervous system?3. Draw a labelled diagram of the human brain.4. What is the function of each of these labelled parts?5. Draw a labelled diagram of a nerve cell.6. What is the function of each of these labelled parts?7. What is a reflex action?8. What are hormones? Give some examples.9. Name some examples of endocrine glands. Which gland

controls other glands?10. What are the main types of drugs? Give some examples

of each type.

1. What is the nervous system made up of?2. Name the parts of the nervous system.3. What is a reflex?4. What is homeostatis?5. Outline the difference between a receptor and an effector.6. What is a reflex action? Give an example.7. Explain why brain damage is usually permanent.8. List 2 things each of the following brain parts are

responsbible for: cerebrum, cerebellum, medulla.9. What is the funciton of the folds in the cerebrum?10. What do the following words mean – synapse and

neurotransmitter?11. What are psychoactive drugs?12. Name 4 dangers of drug abuse.13. Name a drug that belongs to each of the following groups

– opiate, stimulants and hallucinogens.

14. Name the chemical messengers in our body.15. Describe the endocrine system.16. Why is the pituitary gland so important?17. What do we need glucose for?18. How is the concentration of glucose controlled?19. How can we treat diabetes.20. Outline the task of the kidneys.21. Draw and label a diagram of a kidney.22. Outline 5 ways we maintain a constant body temperature?23. Name the hormones excreted by the thyroid, pancrease,

hypothalamus and pituitary.24. What is the function of adrenaline in the body?25. How is heat gained by the body? How is it lost?

Nervous system

Central nervous system Peripheral nervous system

Motor nerves Sensory nerves

Somatic nervous system Autonomic nervous system

Sympathetic nervous system Parasympathetic nervous system

Central nervous system

The Central Nervous System (CNS) consist of the brain and the spinal cord. The spinal cord carries messages from the body to the brain, where they are analyzed

and interpreted. Response messages are then passed from

the brain through the spinal cord and to the rest of the

body.

Functions of the Nervous System

• Gathers information both from the outside world and from inside the body.

• Transmits the information to the processing area of the brain and spinal cord

• Process the information to determine the best response.• Sends information to muscles, glands and organs (effectors) so

they can respond correctly.

The Peripheral Nervous System (PNS)

The Peripheral Nervous System (PNS) consists of the neurons NOT

included in the brain and spinal cord. Some peripheral neurons collect information from the body and transmit it toward the

CNS. These are called afferent neurons. Other Peripheral Neurons transmit information away from the CNS. These are called efferent neurons.

The PNS is responsible for the body functions which are NOT under conscious control – like the heartbeat or the digestive system.

Our Our

SensesSenses

The Eye

Part of eye

Description Function

Corneafront part of the tough outer coat, the sclera. It is convex and transparent.

Protects front of eye and bends light to form an image on the retina.

Conjunctiva

membrane covering the exposed front part of the eye, and lining the eyelids. It is kept moist by antiseptic secretions from the tear glands.

Protects the cornea

ScleraThe opaque 'white of the eye' - also called the sclerotic. A tough and fibrous outer layer covering whole of eye except cornea.

Protection

Iris

Pigmented (decides the colour of your eyes) so light cannot pass through. Its muscles contract and relax to alter the size of its central hole or pupil

Protects the photoreceptors in the retina from being damaged by too much light

PupilA black hole in the centre of the iris. It is the dark pigmented layer inside the eye - the choroid - which makes the pupil appear black.

Allows light to enter eye

Lens

Transparent, bi-convex, flexible disc behind the iris attached by the suspensory ligaments to the ciliary muscles

Brings the light entering through the pupil to a focus on the retina. The ciliary muscles control the lens' thickness and curvature

Ciliary muscle

Ring of muscle fibres around lens Controls lens thickness and curvature

Suspensory ligaments

Ligament between lens and ciliary muscle

Supports lens and connects it to the ciliary muscle

Retina

The lining of the back of eye containing two types of photoreceptor cells - rods (sensitive to dim light and black and white) and cones (sensitive to colour). A small area called the fovea in the middle of the retina has many more cones than rods.

Screen on which images are formed as a result of light being focused onto it by the cornea and lens. The fovea is the point of maximum visual sharpness.

Optic nerve

Bundle of sensory neurones at back of eye.

Carries signals from the photoreceptors of the retina to the brain. At the point where the sensory neurones leave the retina to form the optic nerve - the so-called 'blind spot' - there are no rods and cones, and no image can therefore be seen.

The eye: adjusting for light and focusingThe eye needs to be able to control the amount of light entering in different light conditions.

In dim conditions, more light is allowed to enter so that a clear image can be formed on the retina.

In bright conditions less light is allowed to enter so that the retina is not damaged.

This adjustment is done by two sets of muscles in the iris: its circular muscles contract to close up the iris, making the pupil smaller - while its radial muscles contract to open up the iris, making the pupil larger.

FocusingLight from an object is reflected in all directions. Some of it enters the front of the eye - the transparent cornea - and is refracted as it meets its curved surface. It then goes through the pupil, and enters the lens.

At the lens it is refracted again - this time with fine adjustments to ensure the image focused onto the retina is sharp. From the retina the impulses are taken by the optic nerve to the brain for processing. (The image projected onto the retina is actually upside down, but the brain takes care of this so that we 'see' it the right way up.)

When light travels to the eye from a distant object, the rays are almost parallel and need to be bent very little to be brought to a focus. So when viewing a distant object, the lens must be made thinner and less convex.

This is done by:• relaxing the ciliary muscles • stretching the suspensory ligaments, and • increasing the muscular tension on the lens.

When light travels from a near object the rays are going away from each other and need to bend a lot more to be brought to a focus. So when viewing a near object the lens needs to be made fatter and more convex.

This is done by: • contracting the ciliary muscles • slackening the suspensory ligaments, and • reducing the muscular tension on the lens.

The lens's ability to change its shape to focus near and distant objects is called accommodation.

Science Fact

Some eye diseases include:

1. Glaucoma occurs when there is too much vitreous humour and it squashes and kills the light-sensitive cells.

2. Cataracts occur when the lens turns milky and stops light from entering the eye. As you become older the lens does not move freely?

How can cataracts be treated?

Dissection of a Mammalian Eye

Aim: To dissect a sheep’s eye, which is similar to the eyes of humans and gain an understanding of the structure and function of the parts of the eye.

The human Ear

Why two ears?Two ears help us determine the direction of a sound. If a sound reaches both ears at the same time, our brain interprets this to tell us that the source of the sound is directly in front of, behind or above us. If a sound reaches, say, the left ear before the right ear, the brain tells us that the source of the sound is to our left.

Bionic EarAn Australian invention known as the cochlear implant or bionic ear can restore a degree of hearing to some people. The bionic ear replaces a nonfunctioning inner ear. It consists of a microphone that sends information to a small speech processor worn behind the ear or attached to a belt. The speech processor sorts out which information is important for understanding speech, transmitting it to a receiver–stimulator implanted in the mastoid bone. The receiver–stimulator then produces electrical signals in probes embedded near the cochlea. These are detected by the nerves and transmitted to the brain.

Use this chart to work out which sounds will harm your hearing.

Science FactDeafness can result from injuries to the head or from prolongedexposure to loud noises. Hearing loss is gradual and you do not notice it. Most hearing loss cannot be restored.

There are two main kinds of deafness:• conduction deafness occurs when sound waves cannot be

conducted properly through the ear. This is usually due to congenital defects, repeated middle ear infections or when ossicles fuse together.

• Nerve deafness occurs when the cilia on the sense receptor on the cochlear wear away. This could occur due to ageing and also through someone listening to loud music amplified to 130 decibels or more.

Can your hearing be affected by listening to too loud music in disk-players,

loud rock bands at concerts or in nightclubs or even the sound of Formula 1

racing cars when spectators don’t wear earplugs?

Hearing testsAim To examine the directional ability of our ears in detecting

sounds

MethodSeat one of your group and blindfold them. Ensure they are facing straight ahead. Develop a test that will indicate how well they can detect a sound coming from various directions. Test what effect changing distance and blocking one ear have on your results.

Questions1. Describe how the distance of the sound source affects

results.2. Describe what happens if the person covers one ear.3. Evaluate the need for two ears.

Reading decibelsAim To measure the sound level of various sounds around

the school

EquipmentSound level meter

Method1. Use the meter to measure at least five different sounds

around the school. For example, you might measure the sound levels of two people chatting and then arguing, a noisy classroom, and traffic on the road outside the school.

2. For each measurement, estimate your distance from the subject.

Questions1. Use a table to record your sound level measurements.2. Use the table and Figure 8.2.6 to classify each of thesounds as harmful, dangerous, loud, normal or quiet.

TouchSkin contains millions of nerve endings that send information about touch, pain, pressure and temperature to the brain. Inhumans, the touch receptors are more concentrated in the face,tongue, lips, fingertips and toes.

Body hair also plays an important role in our ability to sense touch. A large number of receptors are found in the skin at the base of hair follicles.

SKIN SENSITIVITY

Aim: To examine whether your touch receptors are evenly

distributed in your skin.

Materials:1. Two toothpicks2. A cork3. A ruler

Method:1. Push two toothpicks through a cork so that the points are 2

mm apart.

Caution:Be sure not to press too hard with the toothpicks.

2. Work in pairs to test different surfaces of the body. One person is to gently touch the skin of the other person. Test the upper and lower surface of the hand, fingertips, upper arm and back of the neck. When the toothpicks are touched on the skin the student should indicate and record whether he/she can feel two points or one.

3. Record your results in the table.

Area Tested # of toothpicks felt by student 1

# of toothpicks felt by student 2

sensitivity

Upper surface of the hand

Lower surface of the hand

Fingertips

Upper arm

Back of the neck

Conclusion:What can you conclude about the distribution of touch

receptors in your skin?

Science Fact

Some animals have senses that people do not have.

1. A platypus can detect the electrical messages of prawns in a river.

2. Pigeons find their way using the magnetic field of the Earth.

3. The sense of smell of some dogs is one thousand times more sensitive than that of people.

SmellYou detect a smell because a few tiny chemical particles enter your nose and dissolve in its moist lining. The dissolved substance triggers nearby nerve cells in the upper part of the nasal cavity, called olfactorycells. Impulses in the olfractory nerve send messages to the brain so we can smell the substance.

The typical human nose can detect around 2000 smells, and may be trained to detect up to 10 000.

Smell fatigueAim To investigate the phenomenon of smell fatigue

Equipment1. A safe, strong-smelling substance;2. a watch;3. a small container (e.g. a film canister and lid)

Note: Check with the class for students who may beallergic to any of the substances to be used in the experiment.

Method1. Obtain a sample of a safe, strong-smelling substance in a

container that can be sealed.2. Carefully take a small whiff of the substance. Do not breathe in

too deeply. Avoid taking your breath away.3. Re-seal the container and wait 30 seconds before taking a similar

whiff. Rate the strength of the smell from 0 (no smell) to 5 (the strength of your first smell).

4. Continue to take a whiff every 30 seconds, giving the strength of the smell a rating each time until you have about six ratings.

Questions1. Describe what happens to the strength of what you smell after several whiffs.2. Construct a graph to display your ratings.

TasteThe surface of the tongue is covered with thousands of bumps, called papillae. More than 10 000 taste buds are embedded between the papillae.

Humans can detect five primary taste sensations: sweet, sour,salty, bitter and umami.

Umami is distinctly different from the other basic tastes and is believed to activate a separate set of taste receptors. It is the savoury taste of glutamate found in processed meats, cheeses andmonosodium glutamate (MSG).

Saliva in our mouths must first dissolve samples of food so that the taste buds can detect them and send messages to the brain. A single taste bud contains fifty to one hundred taste cells, which can detect all five taste sensations. Our taste buds also provide information on the intensity and pleasantness or unpleasantness of taste.Although all areas of the tongue are able to detect all taste sensations, some areas may be more sensitive to certain tastes.

Tongue

Taste regionsAim To determine

whether some areas of the tongue are more receptive to certain tastes.

Equipment1. Clean cotton buds;2. samples of the following

solutions in new plastic cups;

• Sugar;• Salt;• vinegar or lemon juice;• Coffee

Method1. Dip a cotton bud in one of

the solutions and touch it to each area of your tongue (shown as A, B, C and D below).

2. Do not share cotton buds with others in the class. Use a new end for each sample.

3. Record whether each area is sensitive to the solution (e.g. sweet).

4. Repeat for the other three solutions.

Questions1. Record your results on a copy of tongue diagram but without

the marked zones.2. Compare your results with those of your classmates.3. Compare your own map to this.4. Using your own and class results evaluate the accuracy of the

map below.

The Human Nervous System

The Neuron

• The cells that carry messages throughout the Nervous System are called neurons.

• The Neuron is the basic functional unit of the nervous system.• All neurons have the same physical parts: The Cell Body, Dendrites

and Axon.

Neuron Structures and Functions

Cell Structure

Function

Dendrites Receives chemical messages from the axon of the neuron before it.

Myelin Insulates the electrical impulse that travels through the neuron when the dendrites receive the chemical messages.

axon Sends chemical messages across the synapse when stimulated by an electrical impulse.

Types of Neurons

1. Sensory (receptor) Neurons (afferent)Carry impulses from the SENSE ORGANS (receptors) to the brain and spinal cord. Receptors detect external or internal changes and send the information to the central nervous system in the form of impulses by way of the afferent neurons.

2. Motor Neurons (efferent)Carry impulses from the brain and spinal cord to muscles or glands. Muscles and glands are two types of effectors. In response to impulses, muscles contract and glands secrete.

Two types of neurons

Impulse Transmission

1. An outside stimulus causes an electrical impulse in a sensory neuron.

2. This electrical impulse moves to the axon end of the neuron, causing the axon to dump chemicals into the synapses.

3. When these chemicals touch the dendrites of neurons across the synapse, they cause electrical impulses in those neurons.

Science Fact

Damage to neurons can lead to serious handicaps. Neurons in the

body do not grow back or repair themselves.

• Paralegia results from a broken nerve, usually in the neck or back.

• The pain from a pinched nerve in the back may be felt in the leg or hand.

• Multiple sclerosis (MS) is a disease in which the nerve impulse leaks out. It is caused when the myelin sheath breaks down.

How Fast is a Nerve Impulse?

Aim: To measure the speed of a nerve impulse.

Materials:1. Stopwatch2. Calculator3. Tape measure4. Ruler

Method:1. Students should stand in a large circle around the room,

loosely holding hands. The first person squeezes the hand of the student next to them, who then squeezes the next hand, and so on.

2. Record the time for a squeeze of a hand to travel round the class, with a stopwatch.

3. Select a student of average size in your class. Measure the distance that the nerve impulse travelled, from one hand, up the arm into the brain, and back down the second arm and hand. Multiply this distance by the number of students in the chain.

4. The speed of the nerve is the distance it travelled divided by the time taken. Record your results.

5. Repeat the above method twice and record your results.

Results:1. Time taken for the squeeze of the hand to travel round

the class is __________ minutes.2. Total distance the impulse travelled

distance from one hand to the other hand _______ cms x________ number of students in class = _____ cms.

3. The speed of the nerve impulse = total distance / time taken

= _____ / _______= _____ sec.

Discussion:1. What was the average time taken for the nerve impulse

to travel round the class?

Conclusion:What happens if this experiment is repeated a few time.

Science Fact

Anaesthetics are drugs that stop your nerve neurons from sending messages around your body. They prevent impulses from travelling along the neurons.

A local anaesthetic is given when you want to prevent nerves from working in one area of your body. For example, an injection of a

local anaesthetic in the gum area allows a dentist to work on your tooth without any pain.

A general anaesthetic is used in hospitals for long opeations that require patients to be immobilised.

REFLEXES

A reflex is a way of sending a nerve message quickly before injury

results.

Reflex actions are automatic responses, which you cannot control.

A REFLEX PATHWAY1. Stimulus detected by heat receptors in skin.2. Sensory neuron carries impulses.3. Spinal column relays impulse.4. Motor neuron carries impulse.5. Effector organ (biceps muscle) pulls hand away.

A reflex arc

INVESTIGATION INTO SIMPLE REFLEXES

Aim:

THE BRAINThe brain is soft, wrinkly tissue with a mass of around 1.4 kg.

The brain has three main structural parts: thecerebrum, cerebellum andmedulla.

The cerebellumcontrols complex muscularmovements like cycling,walking and running.

The medulla controls vitalactivities you do not haveto think about, likebreathing and heartbeat.

The cerebrum makes up90% of the brain’s volume.It is divided into right andleft hemispheres.

The surface has many folds, creating a large surface area with billions of neurons. These are a grey colour (grey matter).

The cerebrum is responsible for complex thoughts.

The right side is responsible for artistic, musical, intuitive and perceptual abilities.

The left takes care of language, learning mathematics and logical thinking.

Some regions (the sensory areas) are concerned with receiving and interpreting impulses from sense organs.

The motor areas control muscles.

The association areas are concerned with memory and thinking.

The cerebrum controls many functions.

Dissection of a sheep’s brain

Aim: To observe different parts of the brain.

Materials:1. sheep’s brain2. Scalpel 3. Dissecting board4. Newspaper

Method:1. Place the brain on a dissecting board with newspaper

underneath. Examine it and look for the white and grey matter. Note the cerebrum, cerebellum and brain stem.

2. Peel away the membrane covering the brain. Observe the folds. Cut the brain into the right and left hemispheres.

3. Locate the parts of the brain. Record the colour, size and appearance of the cerebrum, cerebellum and brain stem.

4. Compare the sheep’s brain with the model of a human brain.

Results:Draw the top view of the brain and label the parts.

Discussion:1. What was the colour and size of the brain?2. How did the cerebrum differ from the cerebellum?3. What is the function of the brain stem?

Conclusion:How is the sheep’s brain similar and different from a human

brain?

Science Fact

The avearage human brain weighs 1.3 kg, an elephant’s brain weighs

5 kg and a whale’s is 10 kg.

Hormones

Hormones are produced by the endocrine glands,which are scattered throughout your body.

Although they may work together, they are not controlled from one central location like the nervous system is.

Hormones regulate functions like growth anddevelopment, water balance, sexual reproduction and the rate of chemical reactions in cells.

Major human endocrine glands

Name of gland

Hormones produced Functions controlled by the hormone

Adrenals Adrenalin Readiness or flight or fight

Pituitary Growth hormone (HGH)Antidiuretic hormone (ADH)Stimulating hormone

Cell growth and developmentWater balanceDirect other glands to release hormone

Pancreas InsulinGlucagons

Blood glucose level

thyroid Thyroxin Rate of chemical reactions in cell

Ovaries OestrogenProgesterone

Female sexual development and the control of ovary and uterus in pregnancy

Testes testosterone Male sexual development and sexual activity

The pituitary is the ‘master’ gland.

Thyroxin released from the thyroid gland influences growth.

GoitreIodine is an essential component of thyroxin. A deficiency of iodine can cause enlargement of the thyroid gland (a goitre). Goitres were once common in areas where the soil lacked iodine, but use of iodised salt has large lysolved this problem.

Control of blood glucose level

Too much or too little?Insulin-dependent diabetics must obtain a regular supply of insulin. They must also eat regularly.

If a diabetic injects a dose of insulin (which lowers blood glucose levels) but then does not eat later, their blood glucose will fall too far. The brain will be affected, resulting in a hypo glycaemic (low sugar) episode or ‘hypo’, and possible unconsciousness.

To avoid this problem, many diabetics wear an identifying label and carry a sugar source (like jelly beans) that can be taken if signs of a‘hypo’ appear.