the nervous system and reflex arc

7/27/2019 The Nervous System and Reflex Arc

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GCSE Biology 1A Human Biology

KEYWORDS(Write these into your journal book and find the definition as part of your weeks homework)

Gland, Hormone, Impulse, Nervous system, Effector, Stimulus,

Receptor, Neurone, Synapse


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Name the hormonesUsing Figure 2 on

page 24 of the Student Book, write downthe names of the hormones secreted by the

glands shown on the diagram.

Time: 10 minutes

Working Groups: Your choice of 1, 2 or 3

STARTER


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STARTER continued

Name the hormones Have you thought of

any others?

Time: 10 seconds to add them to your list


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STARTER answersPituitary glandFSH, LH (stimulates the release and maturity of

follicles during menstruation)

Thyroid glandThyroxine(regulates the rate of metabolism)

Adrenal gland - corticosteroids and catecholamines includingcortisol and adrenaline and small amounts of testosterone(regulates stress levels)

Pancreaspeptides (regulates the production of shorter activedigestive enzymes)

Ovaryoestrogen, progesterone and small amounts oftestosterone (regulates the growth of eggs and stabilises the

growing foetus during pregnancy)

Testistestosterone (plays a key role in the health and well-beingof the man)


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I AM LEARNING TO understand how the body is controlled

I WILL LEARN THAT

The nervous system enables humans to react to their

surroundings and coordinate their behaviour.

Receptors detect stimuli which include light, sound, changes in

position, chemicals, touch, pressure, pain and temperature. Information from receptors passes along cells (neurones) in

nerves to the brain. The brain coordinates the response.

Many processes in the body are coordinated by chemical

substances called hormones. Hormones are secreted by glandsand are transported to their target organs by the bloodstream.

I CAN

Explain how the body controls its functions and responses

through hormones (chemicals) and nerves (electrical impulses)

LEARNING OBJECTIVES


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Identification of the density of nerve endings

AIM: To investigate the sensitivity of different areas of the skin.Method:

1. Working in pairs, one student looks in a different direction,

while another student touches them on the back of the hand

with either one or two pieces of blunt pencil about 1 cm apart.2. The blindfolded student has to say whether it was one point or

two points that touched them.

3. Place a cross on the hand for each point felt.

Results:

Map the density of sensory receptors by drawing it into your book.

Conclusion:

Are the receptors in groups? Or randomly placed? What can you

say about the density of the receptors identified?


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CONTROL SYSTEMS

There are two main control systems in your body.1. Nervous systemwhich has two main sections

central or CNS that is made up of the spinal cord and brain and functions tocoordinate all actions of the body

peripheral or PNS that is made up of the bodies nerves and functions toconnect the CNS to the rest of the body through neurones. PNS is further

divided into somatic or SNS which is associated with the voluntary control of body

movements and is made up of all neurones, sense organs, skin, skeletal muscles

Autonomic or ANS which is associated with the involuntary control of bodymovements such as reflex and controls such things as heart rate, body temperature,digestion etc. The ANS is further divided into

Parasympathetic nervous system works in actions that do not require a fastresponse (fight or fight response)

Sympathetic nervous system works in actions that do require a fastresponse (rest and digest response)

2. Endocrine systemwhich is a system of glands that release anumber of signalling chemicals known as hormones.


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Say what? NERVOUS SYSTEM

CNS PNS

ANSSNS

Parasympathetic Sympathetic

Nervous system releases electrical

impulses that are quick but the

effects are short lived and it involves

the CNS (either just spinal cord orboth spinal cord and brain) messages

are carried by neurones

Endocrine system releases chemical signals that are slow to

react but the effects are long lasting. This does not involve the

CNS. Messages are carried by the blood.


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Parts of the nervous system

The nervous system is made up of three mainparts;

The brain The spinal cord

Nerve fibres

It detects stimuli such as light, sounds,temperature, pressure, pain and co-ordinates

the bodies response.


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Parts of the nervous system

For example;

If you smell something burning

Your nose (receptor) detects the stimulus

(smell)

Nerve fibres send the message to the brain

Yourbrain then sends a message to move

your body away or to put out the fire!

SIMPLES RIGHT!


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Lets look at some bits more closely

RECEPTORS Receptors are sensors on the body that detect stimuli

They convert stimuli into electrical signals (messages) called

impulses.


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EFFECTORS

An effector is any part of the body that produces the response.

Here are some examples of effectors:

a muscle contracting to move the arm

a muscle squeezing saliva from the salivary gland

a gland releasing a hormone into the blood


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NERVE FIBRES

Nerve fibres are bundles of nerve cells (neurones)that pass on electrical signals (impulses) to thebrain.

From the brain, nerve fibres send impulses toeffectors (muscles).


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NEURONES

There are three types of neurones1. Sensory neuronecarries impulses from the

receptors to the spinal cord.

2. Relay Neuronecarries impulses to and fromthe spinal cord and the brain

3. Motor Neuronecarries impulses from the brainto the effector


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Multiple-choice quiz


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SYNAPSES

Where two neurones meet, there is a tiny gap calleda synapse.

Signals cross this gap using chemicals.

One neurone releases the chemical into the gap.The chemical diffuses across the gap and makes the

next neurone transmit an electrical signal.

http://www.bbc.co.uk/schools/gcsebitesize/science/aq

a/human/thenervoussystemrev2.shtml

Watch this video on synapses then draw a flow chart of the process
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/human/thenervoussystemrev2.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/aqa/human/thenervoussystemrev2.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/aqa/human/thenervoussystemrev2.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/aqa/human/thenervoussystemrev2.shtml


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What is a synapse?A synapse is a junction between two neurones across

which electrical signals pass. The human body contains upto 500 trillion synapses.

presynaptic

cell

postsynaptic

cell

GCSE Bi l 1A H Bi l


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The release of neurotransmittersWhen a nerve impulse arrives at the end of one neurone it

triggers the release ofneurotransmittermolecules fromsynaptic vesicles.

synaptic

vesicle

neurotransmitter

molecules

GCSE Bi l 1A H Bi l


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Continuing the impulseThe neurotransmitters diffuse across the synaptic cleft and

bind with receptors on the next neurone, triggering anotherimpulse.

nerveimpulse

receptor

synaptic

cleft

GCSE Bi l 1A H Bi l


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The stick drop test!METHOD:

1. Working in pairs, one student holds a metre rule vertically at the zero end, betweenthe thumb and forefinger of another student, so that the 50 cm mark is level with thetop of the forefinger.

2. Without warning, the first student drops the rule and the second student attempts tocatch it between the thumb and forefinger, noting the distance on the ruler just abovethe forefinger.

3. Repeat several times, so that a mean can be calculated.

4. Then change around so that everyone gets a turn. Write a report of the experiment.

CONCLUSION AND DISCUSSION:

What was the accuracy of the measurements, the calculation of means and the controlof variables?

Identify the parts of the body involved. What senses are being used? Can we trainourselves to react more quickly? Does practice make perfect?

Can we alter reflex actions?think of a situations where it is possible to alter theautomatic response (not dropping a hot object, deliberately breathing more slowly,

etc.). Are there some reflex actions over which we have no control?

GCSE Bi l 1A H Bi l


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REFLEX ARC

When your body needs to react to something veryquickly (to protect itself) it uses a reflex arc(spinal reflex).

Instead of sending impulses from the receptorSpinal cord brain spinal cord effector

It sends impulses from the receptorspinal cord effectorYup it bypasses the brain!



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ANSWERS

Electrical impulses along neurones, chemical(neurotransmitters) across the synapse.

The microscopic gap between two neurones.

By chemicals called neurotransmitters.

To pass the impulse onto the correct motorneurone.

Glands or muscle that produce the

effect or make a response.

GCSE Bi l 1A H Bi l


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The sequence of a reflex arc

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REFLEX ACTION

The way the iris in oureye adjusts the sizeof the pupil in

response to bright ordim light is also areflex action.



In bright

light

In dim light

Radial muscles of

the iris relax.

Circular muscles of

the iris contract.

Less light enters the

eye through the

contracted pupil.

Radial muscles of

the iris contract.

Circular muscles of

the iris relax.

More light enters

the eye through the

dilated pupil.



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The iris reflex



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Inside the eye

lensfocuses light

on retina

iris

regulates amountof light entering eye

ciliary muscleschange shape of the lens

optic nervetransmits impulses to

the brain

corneaprotects eye surface and

focuses light rays

retinasenses lighthold lens in place

suspensory ligaments



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REFLEX ACTION



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PASS THE ZAP Some volunteers get an A4 sheets on which

the names of parts of the reflex pathway are to

be written.

The students should then arrange themselves

in the correct order.

Using a lightning-shaped zap, each student is

to talk through their bit of the process as theimpulse (zap) gets passed to them.



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NERVE PATHWAY Have a go at completing this worksheet



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NERVE PATHWAY answers

SENSORY NEURONETakes impulses from

the sense organ to the

relay neurone.

RELAY NEURONE

Takes impulses to

the brain and from

the brain.

MOTOR NEURONE

Takes impulses from

the relay neurone to

the effector.

BRAIN

Receives impulses

from the spinal

cord and sends out

new impulses.

SENSE ORGAN/RECEPTOR

Senses stimuli

from our

surroundings.

EFFECTOR

The muscle that

receives the

impulse from

motor neurone.

SPINAL CORD

Where the

relay neurones

are found.



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NERVOUS SYSTEM answers

REFLEX PROTECTION GIVEN

BLINKING To eye

COUGHING Stops us choking

SNEEZING Removes blockages from the

nose

PUPILS CHANGE SIZE Protects the retina

4a) 37m

55m/s

= 0.67s

4b) RT = d

s

= 20m

40m/s

= 0.5s

4c) sensory receptor in eyesensory neurone

relay neurone - brainmotor neurone - effector

4d) i) brain, ii) takes too long

iii) Stimulus sensory neurone

relay neurone motor neurone

effector



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Glossary (1/2)

accommodation

The reflex reaction that keeps thelens the right shape to focus light on the retina.

CNS The central nervous system, consisting of the brainand spinal cord.

iris

The part of the eye that limits the amount of lightentering the eye.

lens The part of the eye that focuses light on the retina.

motor neurone

A neurone that carries electricalimpulses from the CNS to muscles and glands.

neurone A specialized cell that carries electricalimpulses.



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Glossary (2/2)

neurotransmitterA chemical that diffuses acrosssynapses to continue an impulse in a connecting neurone.

reaction time The time taken to respond to a stimulus.

reflex A fast, automatic protective response.

retina The part of the eye that contains light receptors.

sensory neurone

A neurone thatcarries electricalimpulses from sense organs to the CNS.

synapse The gap between two connecting neurones.

GCSE Biology 1A Human BiologyLEARNING OBJECTIVES


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I AM LEARNING TO understand how the body is controlled

I WILL LEARN THATThe nervous system enables humans to react to their

surroundings and coordinate their behaviour.

Receptors detect stimuli which include light, sound, changes in

position, chemicals, touch, pressure, pain and temperature. Information from receptors passes along cells (neurones) in

nerves to the brain. The brain coordinates the response.

Many processes in the body are coordinated by chemical

substances called hormones. Hormones are secreted by glands

and are transported to their target organs by the bloodstream.

I CAN

Explain how the body controls its functions and responses

through hormones (chemicals) and nerves (electrical impulses)

the nervous system and reflex arc

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