1. The Nervous System
Noadswood Science, 2011

2. Saturday, April 15, 2017
The Nervous System
To know how the body responds to the outside environment

3. The Nervous System
The nervous system allows us to react to the surroundings and respond to the changes – it carries electrical impulses up to 120m/sec
Receptors are groups of specialised cells which detect stimuli (changes in the environment)
These stimuli detections are then converted into electrical impulses
Receptors are often located in the sense organs, with each sense organ having receptors sensitive to particular kinds of stimuli – what sense organs does the human body have?

4. Sense Organs
Each organ has receptors sensitive to particular kinds of stimulus…
Skin
Tongue
Nose
Eyes
Ears
What stimuli do these sense organs detect?

5. Receptor Sensitive To…
Sense Organs
Each organ has receptors sensitive to particular kinds of stimulus…
Sense Organ
Receptor Sensitive To…
Skin
Touch, pain, pressure, temperature
Tongue
Chemicals in food (taste)
Nose
Chemicals in air (smell)
Eyes
Light
Ears
Sound (and position of head)

6. Receptors
In groups test your senses on one another – have someone blindfolded within the group and investigate their different senses (taking this in turns)
Try and keep the equipment secret so those being tested cannot just guess from what they have already seen!

7. Coordinator
The central nervous system (CNS) in humans consists of the brain and spinal cord
When a receptor is stimulated, it sends a signal along the nerve cells (neurones) to the brain
The brain then co-ordinates the response

8. Effectors
An effector is any part of the body that produces the response
Some examples of effectors in the human body include: -
A muscle contracting to move the arm
A muscle squeezing saliva from the salivary gland
A gland releasing a hormone into the blood

9. Stimulus  Receptor  Coordinator  Effector  Response
Conscious Responses
The nervous system enables us to react to our surroundings
It consists mainly of the brain, the spinal chord, nerve cells (neurones) and receptors…
When we react to a stimulus our bodies use the following pattern: -
Stimulus  Receptor  Coordinator  Effector  Response

10. Stimulus  Receptor  Coordinator  Effector  Response
Conscious Responses
Stimulus  Receptor  Coordinator  Effector  Response
Stimulus – a change in the environment
Receptor – a specialised cell which detects the stimulus
Coordinator – part of the body which coordinates a response
Effector – part of the body which produces a response
Response – the change in the body

11. Conscious Response Example
Stimulus  Receptor  Coordinator  Effector  Response
What are the stimulus, receptor, coordinator, effector and response in the following example?
Oh No!

12. Conscious Response Example
Stimulus – shark swims close; receptor – eyes detect shark; coordinator – brain determines what to do; effector – muscles respond; response – individual swims quickly!

13. Neurones
Neurones are nerve cells – they carry information as tiny electrical signals
There are three different types of neurones, each with a slightly different function: -
Motor neurones carry signals from the central nervous system to effectors
Sensory neurones carry signals from receptors to the spinal cord and brain
Relay neurones carry messages from one part of the central nervous system to the another
Motor neurone
Sensory neurone
Relay neurone

14. Neurone A typical neurone consists of the: -
Cell body – containing the nucleus, cell membrane, cytoplasm and many dendrites (highly branched to convey nerve impulses towards the cell body)
Axon – long extension from the neurone to carry the impulse)
Nerve endings – where the synapses are located (connection between two neurones)

15. Synapses Where two neurones meet, there is a tiny gap called a synapse
Signals cross this gap using chemicals – one neurone releases the chemical into the gap and the chemical diffuses across resulting in the next neurone transmitting an electrical signal

16. Conscious Response Receptors in your skin detect a stimulus
The impulse is carried by sensory neurones to the spinal chord
Here relay neurones carry signals to and from the brain
The brain ‘decides’ to move away the hand
This impulse is sent by motor neurones to the hand muscles (the effectors) via the spinal chord…
Which then moves the hand away

17. Conscious Responses
Stimulus  Receptor  Sensory neurone  Relay neurone  Coordinator  Motor neurone  Effector  Response
Co-ordinator (CNS)
Motor neurone
Relay neurone
Effector & response
Sensory neurone
Stimulus & receptor

18. Reflex Responses
When a receptor is stimulated, it sends a signal to the central nervous system, where the brain co-ordinates the response
Sometimes a very quick response is needed, one that does not need the involvement of the brain – this is a reflex action
Reflex actions are rapid and happen without us thinking, e.g. you would pull your hand away from a hot flame without thinking about it

19. Reflex Responses

20. Reflex Responses
Stimulus  Receptor  Sensory neurone  Relay neurone  Motor neurone  Effector  Response

21. Reflex Arcs Receptor detects a stimulus - change in the environment
Sensory neurone sends signal to relay neurone
Motor neurone sends signal to effector
Effector produces a response

22. Reflex Arcs
The way the iris in our eye adjusts the size of the pupil in response to bright or dim light is also a reflex action
In bright light – radial muscles of the iris relax and circular muscles of the iris contract resulting in less light entering through the eye via the contracted pupil
In dim light – radial muscles of the iris contract and circular muscles of the iris relax resulting in more light entering through the eye via the dilated pupil

23. Conflict YELLOW GREEN RED BLACK BLUE INDIGO ORANGE PURPLE WHITE LILAC
Look at the following and say the COLOUR, not the word!
YELLOW
GREEN
RED
BLACK
BLUE
INDIGO
ORANGE
PURPLE
WHITE
LILAC
Left / right side brain conflict – the right side of your brain is trying to say the colour, whilst the left side is trying to read the word!