• How and why do organisms respond to
changes in their environment?
• Can you list what is required for a coordinated
response?
• What makes up the CNS?
• Can you explain that receptors are used to
generate impulses in neurones, resulting in a
rapid response?
• What is a reflex arc?
• In order for living organisms to find food, avoid
danger, find a mate they need to be able to
respond to changes in their environment.
• These changes are called
.
• Receptor cells are special cells adapted to
detect stimuli.
• They are found in our sense organs.
Movement of
sound waves
Light
Pressure/heat
Chemical
Chemical
• Information from these receptors passes as
along nerve cells
(neurones) to the brain.
• The brain then coordinates the response.
• Some responses are voluntary, some are
automatic.
• Some responses bypass the brain altogether,
these are called reflex actions.
• There are two parts:
– The Central Nervous System (CNS)
which consists of the brain and
spinal cord.
– The Peripheral Nervous System
which is all the nerves that take
information from our sense
organs into the CNS and from the
CNS out to effectors (muscles or
glands).
• Neurones transmit impulses around the body.
• Impulses travel at speeds of between 10 and
100 m/s
carry impulses from the
receptor to the brain.
carry impulses from the
brain to the effector.
• Stimuli are picked up by sensory receptors and
passed into the neurone.
• Stimuli are picked up by sensory receptors and
passed into the neurone.
• This generates an impulse which travels along
the neurone.
• Stimuli are picked up by sensory receptors and
passed into the neurone.
• This generates an impulse which travels along
the neurone.
• Stimuli are picked up by sensory receptors and
passed into the neurone.
• This is then passed to the spinal cord or the
brain to interpret the initial stimuli.
• The neurone is surrounded by cells made of a
substance called myelin.
• This insulates the neurone.
Myelin sheath
• The dendron carries the impulse up to the cell
body, it then becomes the axon.
Cell body
Dendron
Axon all the other
• The cell body contains the nucleus and
components that a cell needs to function.
Cell body
Junction with
sensory receptor
Dendron
Myelin sheath
Axon
Junction
with CNS
• A message is sent out from the brain down
the dendrites.
• The impulse travels down the axon.
Dendron
Dendrites
Axon
Muscle
Cell body
Myelin sheath
• The impulse arrives at a muscle (effector)
causing it to contract.
Dendron
Dendrites
Axon
Muscle
Cell body
Myelin sheath
• A reflex is a rapid, automatic response to a
stimulus.
• The action often protects the body.
• The nerve pathway of a reflex is called the
reflex arc.
• A reflex is a rapid, automatic response to a
stimulus.
• The action often protects the body.
• The nerve pathway of a reflex is called the
reflex arc.
For example
Iris constricting in bright
• A reflex is a rapid, automatic response to a
stimulus.
• The action often protects the body.
• The nerve pathway of a reflex is called the
reflex arc.
For example
Iris constricting in bright
Touching something very hot
Spinal cord
Sensory neurone
Relay neurone
Motor neurone
Spinal cord
Sensory neurone
Relay neurone
Motor neurone
The signal does not go up to the
brain, but is processed in the
spinal cord via a relay neurone.
Stimulus
Receptor
Stimulus
Coordinator
Receptor
Stimulus
Coordinator
Receptor
Effector
Stimulus
Response
Coordinator
Receptor
Effector
Stimulus
Stimulus
Receptor
Sensory neurone
Coordinator
Motor neurone
Effector
Response
Stimulus
Receptor
Sensory neurone
Coordinator
Motor neurone
Effector
Response
The candle
Stimulus
The candle
Receptor
Temperature receptor in finger
Sensory neurone
Coordinator
Motor neurone
Effector
Response
Stimulus
The candle
Receptor
Temperature receptor in finger
Sensory neurone
Coordinator
Motor neurone
Effector
Response
Sensory neurone
Relay neurone in spinal cord
Stimulus
The candle
Receptor
Temperature receptor in finger
Sensory neurone
Coordinator
Motor neurone
Effector
Response
Sensory neurone
Relay neurone in spinal cord
Motor neurone
Muscle in arm
Stimulus
The candle
Receptor
Temperature receptor in finger
Sensory neurone
Coordinator
Motor neurone
Sensory neurone
Relay neurone in spinal cord
Motor neurone
Effector
Muscle in arm
Response
Arm moves away from candle
• A reflex is an example of an automatic
coordinated response.
• In a voluntary response the brain would be
the coordinator not the spinal cord.