learning objectives
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Learning Objectives. 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 ? - PowerPoint PPT PresentationTRANSCRIPT
Learning Objectives• 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?
Responding to change• 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 STIMULI.
Sense organs and receptors• Receptor cells are special cells adapted to
detect stimuli. • They are found in our sense organs.
Light
Chemical
ChemicalPressure/heat
Movement of sound waves
Impulses• Information from these receptors passes as
electrical impulses 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.
The structure of the nervous system
• 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• Neurones transmit impulses around the body.• Impulses travel at speeds of between 10 and
100 m/s• Sensory neurones carry impulses from the
receptor to the brain.• Motor neurones carry impulses from the
brain to the effector.
Sensory neurone• Stimuli are picked up by sensory receptors and
passed into the neurone.
Sensory neurone• Stimuli are picked up by sensory receptors and
passed into the neurone.
• This generates an impulse which travels along the neurone.
Sensory neurone• Stimuli are picked up by sensory receptors and
passed into the neurone.
• This generates an impulse which travels along the neurone.
Direction of impulse
Sensory 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.
Direction of impulse
Sensory neurone• The neurone is surrounded by cells made of a
substance called myelin. • This insulates the neurone.
Myelin sheath
Sensory neurone• The dendron carries the impulse up to the cell body,
it then becomes the axon.
• The cell body contains the nucleus and all the other components that a cell needs to function.
Cell body
Axon
Dendron
Sensory neurone
Direction of impulse
Cell body
AxonMyelin sheathDendron
Junction with sensory receptor Junction
with CNS
Motor neurone• A message is sent out from the brain down the
dendrites. • The impulse travels down the axon.
Cell body
Dendron
Axon
Myelin sheath
Dendrites
Muscle
Motor neurone• The impulse arrives at a muscle (effector)
causing it to contract.
Direction of impulse
Cell body
Dendron
Axon
Myelin sheath
Dendrites
Muscle
Reflex Action• 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.
Reflex Action• 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.
Iris constricting in bright
For example
Reflex Action• 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.
Iris constricting in bright Touching something very hot
For example
Reflex arcSensory neurone
Relay neurone
Motor neurone
Spinal cord
Reflex arc
The signal does not go up to the brain, but is processed in the spinal cord via a relay neurone.
Sensory neurone
Relay neurone
Motor neurone
Spinal cord
Reflex arc
Stimulus
Reflex arc
Stimulus
Receptor
Reflex arc
Stimulus
Receptor
Coordinator
Reflex arc
Stimulus
Receptor
Coordinator
Effector
Reflex arc
Stimulus
Receptor
Coordinator
Effector
Response
Reflex arcStimulus
Receptor
Coordinator
Effector
Response
Sensory neurone
Motor neurone
Reflex arcStimulus
Receptor
Coordinator
Effector
Response
Sensory neurone
Motor neurone
The candle
Reflex arcStimulus
Receptor
Coordinator
Effector
Response
Sensory neurone
Motor neurone
The candle
Temperature receptor in finger
Reflex arcStimulus
Receptor
Coordinator
Effector
Response
Sensory neurone
Motor neurone
The candle
Temperature receptor in finger
Relay neurone in spinal cord
Sensory neurone
Reflex arcStimulus
Receptor
Coordinator
Effector
Response
Sensory neurone
Motor neurone
The candle
Temperature receptor in finger
Relay neurone in spinal cord
Muscle in arm
Sensory neurone
Motor neurone
Reflex arcStimulus
Receptor
Coordinator
Effector
Response
Sensory neurone
Motor neurone
The candle
Temperature receptor in finger
Relay neurone in spinal cord
Muscle in arm
Arm moves away from candle
Sensory neurone
Motor neurone
Coordinated response• A reflex is an example of an automatic
coordinated response. • In a voluntary response the brain would be
the coordinator not the spinal cord.