Noadswood Science, 2011

The Nervous System

To know how the body responds to the outside environment

Tuesday, April 18, 2023

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?

Sense Organs

Each organ has receptors sensitive to particular kinds of stimulus…

Skin Tongue Nose Eyes Ears

What stimuli do these sense organs detect?

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)

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!

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

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

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

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

Conscious Response ExampleStimulus Receptor Coordinator Effector Response

What are the stimulus, receptor, coordinator, effector and response in the following example?

Oh No!

Conscious Response Example

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

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

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)

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

Conscious Response

1. Receptors in your skin detect a stimulus

2. The impulse is carried by sensory neurones to the spinal chord

3. Here relay neurones carry signals to and from the brain

4. The brain ‘decides’ to move away the hand

5. This impulse is sent by motor neurones to the hand muscles (the effectors) via the spinal chord…

6. Which then moves the hand away

Conscious Responses

Stimulus Receptor Sensory neurone Relay neurone

Coordinator Motor neurone Effector Response

Sensory neurone

Relay neurone

Motor neurone

Stimulus & receptor

Co-ordinator

(CNS)

Effector & response

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

Reflex Responses

Reflex Responses

Stimulus Receptor Sensory neurone Relay neurone

Motor neurone Effector Response

Reflex Arcs

1. Receptor detects a stimulus - change in the environment

2. Sensory neurone sends signal to relay neurone

3. Motor neurone sends signal to effector

4. Effector produces a response

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

Conflict

Look at the following and say the COLOUR, not the word!

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!

YELLOW

BLACKINDIGO

WHITE

BLUE

PURPLEORANGE

REDGREEN

LILAC