IGCSE Biology chapter 13 -nervous system summary

1. B Y :
A D E L I N E L A U R E N
C L A R I S S A
G E R A L V I N M N O R A L I M
J A S O N J A Y A L I E
O W E N J O N G
R U I Z O R L A N D O
Biology
Chapter 13 : The Nervous System

2. Sensitivity
A living organism is able to react to
changes in the surrounding.
The change in the environment that
cause an organism to react is called a
stimulus.
An organism’s reaction to a stimulus is
called a response.
The ability to respond to a stimulus is
known as sensitivity or irritability.

3. An organism usually responds to a stimulus by moving in a way
that benefits itself. For example:
Plant needs light for photosynthesis, so they
grow towards the light. This response occurs
over time.
Euglena, a single-celled organism, makes food
by photosynthesis. Euglena swims towards the
light.
Cockroaches, move away from the light. They
hide in dark areas during the day.

4. What is the role of the nervous system in
humans?
The nervous system in humans controls the activities of the body and
how it reacts to the surroundings.
The nervous system consist of a brain, spinal cord, spinal nerves and
highly specialized sense organs.
Sense organs:
• help the body to adjust to any
changes in the environment
• Enable the various parts of the
body to coordinate with one
another

5. In humans, many activities such as the heartbeat, peristalsis
and breathing movements are automatic and are not
controlled consciously. They are called involuntary actions.
Activities that are controlled consciously are called voluntary
actions.
Voluntary and involuntary actions

6. Thoughtless action
Sea anemone are some of the simplest animals under the sea, they do
not even have brains.
When a prey such as small fish brush against a sea anemone’s
tentacles, stinging cells in the tentacles are stimulated. The sea anemone
responds by stinging the prey. This is called as involuntary action.

7. Human nervous system
Component of the human nervous system:
-The central nervous system (CNS) consisting of the brain and
the spinal cord
-The peripheral nervous system (PNS) consisting of the cranial
nerves (nerves from the brain) and spinal nerves (nerves from
the spinal cord) and the sense organs.

8. -Sense organs are used to detect stimuli, they are also called receptors.
They inform the central nervous system about changes in the
surroundings, by producing electrical messages called nerve impulses.
These nerve impulses are transmitted through the peripheral nervous
system to the central nervous system.

9. Nervous tissue

10. Motor end plate
Dendron
Cell body contains a
nucleus, cytoplasm, cell
surface membrane and
organelles.
The nerve fibers
that transmit
nerve impulses
towards the cell
body are called
dendrons.
The dendrites of
a dendron of a
motor neuron
receives nerve
impulses from
other neurons
The nerve fibers
that transmit
nerve impulses
away from the
cell body are
called axons
The layer of
fatty
substances
enclosing
many nerve
fibers is the
myelin
sheath.
The region where the
myelin sheath is
absent are called
nodes of ranvier.
The axon
terminals of a
motor neuron
transmit nerve
impulses to the
effector.
The junction between the axon
terminal and the muscle fiber
is the motor end plate.

11. Structure of sensory neurone
Direction of nerve impulse

12. What is a
synapse?
Definition of synapse:
A synapse is a junction between 2 neurones, or a
junction between a neurone and an effector such
as a muscle or a gland
At a synapse, impulses are
transmitted from the
axon of one neurone to
the dendron of another
neuron ( or the cells of
the effector) across the
tiny space
Nerve impulse are
transmitted across the
synapse by certain
chemicals released by
the neurone. These
chemicals are called
neurotransmitters

13. What are nerves?
A nerve is a bundle of
nerve fibres enclosed in a
sheath of connective
tissue.
Nerve may emerge from the brain (cranial
nerve) or spinal cord (spinal nerve). They may
contain:
• Sensory nerve only – conduct nerve
impulses from sense organs.
• Motor nerve fibres only – conduct nerve
impulses from effectors.
• Mixed fibres (both sensory and motor nerve
fibres) – located in spinal nerves.

14. Brain
Forebrain:
• Concerned with
intelligence,
memory, learning
sensations and
overall control of
all voluntary
actions in human
• Concerned with the
regulation of body
temperature and
water potential of
blood, appetite,
sleep and emotions
• Produces and
relase many
important
The human brain can be divided into 3 parts: the
forebrain, the midbrain, and the hindbrain
Midbrain:
•Concerne
d with
sight and
visual
reflexes,
e.g.
movement
of the
eyeballs
Forebrain:
• Controls
muscular
coordination,
especially
maintaining
balance
• Controls
involuntary
actions, e.g.
the heartbeat,
peristalsis, the
rate of
respiratory

15. Distribution of the grey matter and white matter
in the central nervous system
Grey matter
The grey matter consist of mainly of the
cell bodies of the neurones .
It forms the outer layers of the brain and
the central parts of spinal cord
White matter
The white matter consist of mainly of
nerve fibres .
It forms the central parts of the brain,
and the outer layers of the spinal
cord.
Central canal
The central canal contains
a fluid called cerebrospinal
fluid that brings nutrients
to spinal cord

16. As the spinal nerves leave the spinal cord, it
branches itself into nerve fibres which is supplied
to different parts of our body
• Before the spinal nerve joins the spinal cord, it
is divided into two roots :
a) Dorsal root ( towards the back )
b) Ventral root ( towards the front )

17. 1. Sensory neuron in the spinal cord
transmit impulses to the relay neuron in
the brain
2. Relay neuron in the brain transmit
impulses back to the motor neuron in
the spinal cord
Remember !
The relay neurons
synapse with the
sensory and motor
neurons to enable the
transmission of nerve
impulses from the
sensory to motor
neurons

18. Dorsal root ganglion
• A small swelling in the
dorsal root containing cell
bodies of sensory neurons
Dorsal root
• Joints the back part
of the spinal cord
• It contains nerve
fibres of sensory
neurons that
transmit impulses to
the spinal cord
Ventral root
• Joins the front part of
the spinal cord
• It contains only nerve
fibres of motor
neurons that transmit
impulses from the
spinal cord
Spinal nerve
(mixed nerve)
• Form by the joining
of dorsal and ventral
root
• Contains both
sensory and motor
neurons

19. Sensation
When you touch a piece of ice, you can feel its coldness. This is because the
temperature receptor in in your skin is stimulated. Impulses are produced.
Impulses are transmitted to the forebrain. The brain interprets the impulses,
and you have a sensation of coldness.
The pathway of impulses is as follows:
Receptor in skin  sensory neurone relay neurone in spinal cord 
forebrain

20. voluntary actions
Voluntary action is a deliberate action, for example, you decide to raise
your hand to answer a question in class.
The pathway of impulses is as follow:
Forebrain  relay neurone in spinal cord  motor neurone  effector

21. Reflex Action
Reflex action is an immediate response to a specific
stimulus without conscious control
It is an involuntary action
Classified into :
- Cranial reflexes
- Spinal reflexes
 The spinal cord and the brain are reflex centres

22. Knee Jerk Reflex

24. Reflex arc
 A reflex arc is the shortest pathway by which nerve impulses travel from the
receptor to the effector in a reflex action

25. Conditioned Reflex

26. The nervous system
Central nervous system
(CNS)
Peripheral nervous system
(PNS)
Brain Spinal cord Receptors Nerves
- Controls
voluntary
actions by
generating
nerve
- Controls
cranial
reflexes
e.g.
salivation
- transmit
nerve
impulses
to and
from brain
- controls
spinal
reflexes .e.g.
knee-jerk
reflex
Receive
stimuli from
the
environment
Cranial nerves
-sensory nerves
transmit impulses
from receptors to the
brain.
-Motor nerves
transmit impulses
from brain to
effectors
Spinal nerves
-sensory nerves
transmit impulses
from receptors to
spinal cords .
- Motor nerves
transmit impulses
from spinal cord to
effectors

27. Nervous Tissues
Neurons
Sensory (receptor)
neuron
-Transmits nerve
impulses from
receptors to CNS
Relay (intermediate)
neurons
-found within CNS
-Transmits nerve
impulses from sensory
neurons to motor
neurons
Motor (effectors)
neuron
-transmits nerve
impulses from CNS to
effectors
Components of reflex arc
A sense
organ
(receptor)
A sensory
neuron
A relay
neuron in a
reflex center
(brain or
spinal cord)
A motor
neuron
An
effector