Download Reflex arc ppt - bananateachersworld

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
STARTER
Name the hormones – Using Figure 2 on page 24 of
the Student Book, write down the 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 continued
Name the hormones – Have you thought of any
others?
Time: 10 seconds to add them to your list
STARTER
answers
Pituitary gland – FSH, LH (stimulates the release and maturity
of follicles during menstruation)
Thyroid gland – Thyroxine (regulates the rate of metabolism)
Adrenal gland - corticosteroids and catecholamines including
cortisol and adrenaline and small amounts of testosterone
(regulates stress levels)
Pancreas – peptides (regulates the production of shorter active
digestive enzymes)
Ovary – oestrogen, progesterone and small amounts of
testosterone (regulates the growth of eggs and stabilises the
growing foetus during pregnancy)
Testis – testosterone (plays a key role in the health and wellbeing of the man)
LEARNING OBJECTIVES
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 glands and are transported to their target
organs by the bloodstream.
I CAN
Explain how the body control’s its functions and responses through hormones
(chemicals) and nerves (electrical impulses)
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?
CONTROL SYSTEMS
There are two main control systems in your body.
1. Nervous system – which has two main sections


central or CNS that is made up of the spinal cord and brain and
functions to coordinate all actions of the body
peripheral or PNS that is made up of the bodies nerves and functions
to connect the CNS to the rest of the body through neurones. PNS is
further divided into


2.
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 body
movements 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 fast response (fight or fight response)

Sympathetic nervous system works in actions that do require a fast
response (rest and digest response)
Endocrine system – which is a system of glands that
release a number of signalling chemicals known as
hormones.
Say what?
NERVOUS SYSTEM
CNS
Nervous
system
releases
electrical impulses that are quick
but the effects are short lived and
it involves the CNS (either just
spinal cord or both spinal cord
and brain) messages are carried
by neurones
PNS
ANS
Parasympatheti
c
SNS
Sympatheti
c
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.
Parts of the nervous system
The nervous system is made up of three main parts;
 The brain
 The spinal cord
 Nerve fibres
It detects stimuli such as light, sounds, temperature,
pressure, pain and co-ordinates the bodies
response.
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
 Your brain then sends a message to move your
body away or to put out the fire!
SIMPLES RIGHT!
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.
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
NERVE FIBRES
 Nerve fibres are bundles of nerve cells (neurones) that pass
on electrical signals (impulses) to the brain.
 From the brain, nerve fibres send impulses to effectors
(muscles).
NEURONES
There are three types of neurones
1. Sensory neurone – carries impulses from the receptors to the
spinal cord.
2. Relay Neurone – carries impulses to and from the spinal cord
and the brain
3. Motor Neurone – carries impulses from the brain to the
effector
Multiple-choice quiz
SYNAPSES
Where two neurones meet, there is a tiny gap called a
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/aqa/human/th
enervoussystemrev2.shtml
Watch this video on synapses then draw a flow chart of the process
What is a synapse?
A synapse is a junction between two neurones across which electrical signals
pass. The human body contains up to 500 trillion synapses.
presynaptic cell
postsynaptic cell
The release of neurotransmitters
When a nerve impulse arrives at the end of one neurone it triggers the release
of neurotransmitter molecules from synaptic vesicles.
synaptic
vesicle
neurotransmitter
molecules
Continuing the impulse
The neurotransmitters diffuse across the synaptic cleft and bind with receptors on
the next neurone, triggering another impulse.
synaptic
cleft
nerve
impulse
receptor
The stick drop test!
METHOD:
1. Working in pairs, one student holds a metre rule vertically at the zero end,
between the thumb and forefinger of another student, so that the 50 cm mark is
level with the top of the forefinger.
2. Without warning, the first student drops the rule and the second student
attempts to catch it between the thumb and forefinger, noting the distance on
the ruler just above the 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
control of variables?
Identify the parts of the body involved. What senses are being used? Can we train
ourselves to react more quickly? Does practice make perfect?
Can we alter reflex actions? – think of a situations where it is possible to alter
the automatic response (not dropping a hot object, deliberately breathing more
slowly, etc.). Are there some reflex actions over which we have no control?
REFLEX ARC

When your body needs to react to something very quickly
(to protect itself) it uses a reflex arc (spinal reflex).
 Instead of sending impulses from the receptor
Spinal cord
brain
spinal cord
effector

It sends impulses from the receptor
spinal cord
effector…Yup it bypasses the brain!
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/human/th
enervoussystemrev3.shtml
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 motor neurone.
 Glands or muscle that produce the
effect or make a response.
The sequence of a reflex arc
REFLEX ACTION
The way the iris in our
eye adjusts the size
of the pupil in
response to bright
or dim light is also
a reflex 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.
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/human/th
enervoussystemrev3.shtml
The iris reflex
Inside the eye
cornea
protects eye surface and focuses
light rays
suspensory ligaments
retina
hold lens in place
senses light
lens
focuses light
on retina
iris
regulates amount
of light entering eye
ciliary muscles
change shape of the lens
optic nerve
transmits impulses to the
brain
REFLEX ACTION
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 the impulse (zap)
gets passed to them.
NERVE PATHWAY… Have a go at completing this worksheet
effector
Sense organ/
receptor
NERVE PATHWAY… answers
SENSE ORGAN/
RECEPTOR
Senses stimuli
from our
surroundings.
SENSORY NEURONE
Takes impulses from
the sense organ to the
relay neurone.
SPINAL CORD
Where the
relay neurones
are found.
BRAIN
Receives impulses
from the spinal
cord and sends out
new impulses.
RELAY NEURONE
Takes impulses to
the brain and from
the brain.
MOTOR NEURONE
Takes impulses from
the relay neurone to
the effector.
EFFECTOR
The muscle that
receives the
impulse from
motor neurone.
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 eye – sensory neurone – relay neurone brain – motor neurone - effector
4d) i) brain, ii) takes too long
iii) Stimulus
sensory neurone
relay neurone
motor neurone
effector
Glossary (1/2)
 accommodation – The reflex reaction that keeps the
lens the right shape to focus light on the retina.
 CNS – The central nervous system, consisting of the brain
and spinal cord.
 iris – The part of the eye that limits the amount of light
entering the eye.
 lens – The part of the eye that focuses light on the retina.
 motor neurone – A neurone that carries electrical
impulses from the CNS to muscles and glands.
 neurone – A specialized cell that carries electrical
impulses.
Glossary (2/2)
 neurotransmitter – A chemical that diffuses across
synapses 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 that carries electrical
impulses from sense organs to the CNS.
 synapse – The gap between two connecting neurones.
LEARNING OBJECTIVES
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 glands and are transported to their target
organs by the bloodstream.
I CAN
Explain how the body control’s its functions and responses through hormones
(chemicals) and nerves (electrical impulses)