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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 ?

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Learning objectives
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
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
Sense organs and receptors

  • 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


Impulses
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
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

  • 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
Sensory neurone

  • Stimuli are picked up by sensory receptors and passed into the neurone.


Sensory neurone1
Sensory neurone

  • Stimuli are picked up by sensory receptors and passed into the neurone.

  • This generates an impulse which travels along the neurone.


Sensory neurone2
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 neurone3
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 neurone4
Sensory neurone

  • The neurone is surrounded by cells made of a substance called myelin.

  • This insulates the neurone.

Myelin sheath


Sensory neurone5
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

Dendron

Axon


Sensory neurone6
Sensory neurone

Direction of impulse

Cell body

Dendron

Junction with sensory receptor

Myelin sheath

Junction with CNS

Axon


Motor neurone
Motor neurone

  • A message is sent out from the brain down the dendrites.

  • The impulse travels down the axon.

Dendron

Dendrites

Axon

Muscle

Myelin sheath

Cell body


Motor neurone1
Motor neurone

  • The impulse arrives at a muscle (effector) causing it to contract.

Direction of impulse

Dendron

Dendrites

Axon

Muscle

Myelin sheath

Cell body


Reflex action
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 action1
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.

For example

Iris constricting in bright


Reflex action2
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.

For example

Iris constricting in bright

Touching something very hot


Reflex arc
Reflex arc

Spinal cord

Sensory neurone

Relay neurone

Motor neurone


Reflex arc1
Reflex arc

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.


Reflex arc2
Reflex arc

Stimulus


Reflex arc3
Reflex arc

Receptor

Stimulus


Reflex arc4
Reflex arc

Coordinator

Receptor

Stimulus


Reflex arc5
Reflex arc

Coordinator

Receptor

Effector

Stimulus


Reflex arc6
Reflex arc

Response

Coordinator

Receptor

Effector

Stimulus



Reflex arc8
Reflex arc

Stimulus

Receptor

Sensory neurone

Coordinator

Motor neurone

Effector

Response


Reflex arc9
Reflex arc

Stimulus

The candle

Receptor

Sensory neurone

Coordinator

Motor neurone

Effector

Response


Reflex arc10
Reflex arc

Stimulus

The candle

Temperature receptor in finger

Receptor

Sensory neurone

Coordinator

Motor neurone

Effector

Response


Reflex arc11
Reflex arc

Stimulus

The candle

Temperature receptor in finger

Receptor

Sensory neurone

Sensory neurone

Coordinator

Relay neurone in spinal cord

Motor neurone

Effector

Response


Reflex arc12
Reflex arc

Stimulus

The candle

Temperature receptor in finger

Receptor

Sensory neurone

Sensory neurone

Coordinator

Relay neurone in spinal cord

Motor neurone

Motor neurone

Effector

Muscle in arm

Response


Reflex arc13
Reflex arc

Stimulus

The candle

Temperature receptor in finger

Receptor

Sensory neurone

Sensory neurone

Coordinator

Relay neurone in spinal cord

Motor neurone

Motor neurone

Effector

Muscle in arm

Response

Arm moves away from candle


Coordinated response
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.


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