This document provides information about the nervous system and reflex actions. It defines key terms like stimulus, receptors, central nervous system, effector, and the three types of neurons. It explains that the nervous system coordinates and regulates bodily functions through sensory neurons that detect stimuli, relay neurons that transmit signals within the central nervous system, and motor neurons that activate effectors. It describes reflex arcs and gives examples of spinal and cranial reflexes like the knee jerk reaction and pupil reflex. Finally, it outlines the sequence of events that occur in a reflex action from stimulus detection to response.

1. Coordination &
Responses
Chapter 13.1:
The Nervous System
Prepared By, Mrs Yap-Wong Fui Yen 2014Prepared By, Mrs Yap-Wong Fui Yen 2014

2. Learning Outcomes:
 state the relationship between receptors, the
central nervous system and the effectors.
 state that the nervous system - brain, spinal cord
and nerves, serves to co-ordinate and regulate
bodily functions.
 outline the functions of sensory neurons, relay
neurones and motor neurons.
 discuss the function of the brain and spinal cord in
producing a co-ordinated response as a result of
a specific stimulus in a reflex action.
13.1

3. Prepared By, Ms Wong
What do these celebrities have in common?
 Muhammad Ali & Michael
J.Fox suffered from
Parkinson’s disease,
which affected their CNS
 Christopher Reeve
suffered from spinal
cord injury when he fell
off from a horse.
13.1

4. NERVOUS SYSTEM
Central Nervous System
(CNS)
Peripheral Nervous System
(PNS)
Cranial Nerves
(from brain)
Spinal nerves
(from spinal cord)
Sense organs
with receptors
( receive stimuli)
Brain Spinal Cord
13.1

5. Prepared By, Ms Wong
Terms: Functions:
Central Nervous System Consists of the brain and the spinal cord.
Stimulus : A sudden change in the environment.
Receptor : Sense organ which receive stimulus and produce nerve
impulses to be transmitted to the CNS.
Nerve impulse : Electrical messages transmitted by nerves.
Types of neurones
(a) Sensory neurone
(b) Relay
(intermediate) neurone
(c) Motor neurone
: Transmits nerve impulses from receptor to CNS
: Transmits nerve impulses from sensory neurons to the
motor neurons across junctions called synapse
: Transmits nerve impulses from CNS to effector
Effector : The effect of a response (e.g muscles , glands)
Reflex action : Immediate response to a specific stimulus without
conscious control
13.1

6. What is “receptor”?
 Sudden changes in the environment is
known as stimulus.
 Sense organs (e.g eyes, nose, skin) has
receptors sensitive to particular kinds of
stimulus.
 Receptors help to detect the stimulus
and turn them into nerve impulses.
13.1

7. Sense organs with receptors to detect Stimulus
skin
tongue
nose
touch,
pressure,
pain,
temperature
chemicals in
food
chemicals in
air
13.1

8. Sense organs with receptors to detect Stimulus
eye
ear
light
sound
13.1

9.  Sensory (receptor) neurons:
Transmit nerve impulses from receptors towards the central
nervous system.
 Relay (Intermediate) neurons:
Transmit nerve impulses between sensory neurons and motor
neurons.
 Motor (or effector) neurons:
Transmit nerve impulses away from the central nervous system to
the effectors (muscles or glands).
1
2
3
1
2
3
13.1

10.  Nerve cell is known as neurone.
 They transmit information as
nerve impulses (signals).
 There are three different types of
neurones, each with a slightly
different function.
 (a) Sensory (receptor) neurone

 (b) Relay (intermediate) neurone
 (c) Motor (effector) neurone
Nerve Cell
13.1

11. Nervous System Pathway:
Receptors
(in sense
organs)
Stimulus
Central Nervous
System
(e.g brain or spinal cord)
Effector
(e.g muscles,
glands)
detected by
13.1

12. Nervous System Pathway:
Receptors
(in sense
organs)
Stimulus
Central Nervous
System
(e.g brain or spinal cord)
Effector
(e.g muscles,
glands)
detected by
(i) Sensory neurone
(ii) Relay neurone
(iii) Motor neurone

13. Involuntary actions:
 automatic actions
 Not under control of
the will
 E.g. heartbeat,
peristalsis, breathing,
blinking
13.1

14. Voluntary actions:
 under conscious control
(may or may not involve sensory neurone)
 Intelligent responses
 Involve processing of information and
conscious decisions
 E.g. get up in morning, have breakfast, go
out or stay indoors etc......
13.1

15. Coordination &
Responses
Chapter 13.2:
Reflex Action
Prepared By, Mrs Yap-Wong Fui Yen 2014Prepared By, Mrs Yap-Wong Fui Yen 2014

16.  A direct and immediate response to a
specific stimulus without conscious
control.
 Inherited, do not need to learn; protect
body from harm. Simplest form of
response
 Reflex arc – shortest pathway by which
nerve impulses travel from receptor to
effector during a reflex action.
What is a Reflex Action?
13.2

17. What is a Reflex
Action?
S : Specific stimulus
I : Immediate response
S : Shortest path
I : Involuntary action
13.2

18. Prepared By, Ms Wong
“ Stimulus “
(sudden
tapping)
CNS
(spinal cord)
Effectors
(muscles)
(i) sensory
neurone
(iii) motor
neurone
(ii) relay
neurone
Receptors
(stretch receptors)
13.2

19.  2 types :
 Spinal reflex - nerve impulses pass through spinal cord
and do not involve the brain
Examples:
 knee-jerk,
 sudden withdrawal of hand touching a hot object, sharp
pain
 Cranial reflex - nerve impulses pass through the brain
Examples:
 pupil reflex,
 sudden blinking of eyes when object moves past them
yawning
 secretion of saliva,
 tearing , sneezing, coughing, breathing
13.2

20. Knee Jerk
 Type - Spinal reflex
 Stimulus - Extension of knee tendon
e.g. knee bends; knock on knee cap.
 Response - Contraction of thigh muscle
causing leg to straighten
 Survival value - Ensure leg will support
body when standing or walking
13.2

21. Pupil Reflex
 Type - Cranial reflex
 Stimulus - Bright light falling on eyes
 Response - Contraction of circular muscles
of iris to reduce pupil size
 Survival Value - To protect eyes from
damage due to excessive exposure to light
13.2

22. microQuestion
 1.Describe the similarities and
differences between a voluntary action
and a reflex action.
Prepared By, Mrs Yap
13.2

23. Coordination &
Responses
Chapter 13.3:
Nervous Pathway in
Reflex Action
Prepared By, Mrs Yap-Wong Fui Yen 2014Prepared By, Mrs Yap-Wong Fui Yen 2014

25. Prepared By, Ms Wong
What are the sequence of events
which take place during a reflex action?
13.3

26. Sequence of events :
1. The heat on the object stimulates the nerve
endings (receptor) in the skin.
2. Impulses are produced and travel along the
sensory neurone to the spinal cord.
3. In the spinal cord, the impulses are transmitted
first across a synapse to a relay neurone, and
then across another synapse to the motor
neurone.
4. Nerve impulses leave the spinal cord along the
motor neurone to the effector.
5. The effector (the muscles) then contracts,
causing a sudden withdrawal of the hand.
13.3

27. Prepared By, Ms Wong
Prepared By, Ms Wong
What happens when your eye is suddenly exposed
to a bright surrounding?
13.3

28. Sequence of events :
1. Light stimulates the nerve endings of the light-
sensitive cells in the eye retina.
2. Nerve impulses stimulated and travel along
sensory neurone in optic nerve.
3. The nerve impulse transmit from sensory neurone
to the relay neurone in the brain.
4. Nerve impulses then transmit across the synapse
from relay neurone to the motor neurone.
5. Effector ( iris muscle) contract to control to the
pupil size.
13.3

29.  Have you ever felt dazed after
bumping your arm, leg or after
smashing a finger or toe?
 Would you like to know what causes
these types of sudden feelings in your
body?

31. microQuestion
 2. The diagram shows a nerve pathway
involved in a reflex action
13.3
Which structure is a motor neurone?

32. microQuestion
 3. A finger that touches a hot object is quickly taken
away from the source of heat.
 What is the role of relay neurones in this response?
 A) To carry nerve impulses within the spinal cord.
 B) To generate impulses in the receptors of the finger.
 C) To link the sense organs to the sensory neurones.
 D) To pass nerve impulses out to the neurones.
Prepared By, Mrs Yap
13.3
Answer :