Upload
sureshthevan
View
215
Download
0
Embed Size (px)
Citation preview
7/27/2019 07 the Nervous System
1/6
- GCSE Bitesize - The nervous system
//www.bbc.co.uk/schools/gcsebitesize/science/edexcel/responses_to_environment/thenervoussystemrev_print.shtml[10/21/2013 8:13:52 PM]
Science
The nervous system
The nervous system allows the body to respond, through
effectors, to changes in the environment detected by
receptors. The process involves neurones and is usuallycoordinated by the brain. A reflex action is an extra-rapid
response to a stimulus: this process also involves the
nervous system but i t bypasses the brain.
Receptors and effectors
Receptors
Receptors are groups of specialised cells. They can detect
changes in the environment, which are called stimuli, and turn
them into electrical impulses. Receptors are often located in the
sense organs , such as the ear, eye and skin. Each organ has
receptors sensitive to particular kinds of stimulus.
Different receptors
sense organs receptors sensitive to
touch, pressure, pain and
temperature
chemicals in food
Skin
7/27/2019 07 the Nervous System
2/6
- GCSE Bitesize - The nervous system
//www.bbc.co.uk/schools/gcsebitesize/science/edexcel/responses_to_environment/thenervoussystemrev_print.shtml[10/21/2013 8:13:52 PM]
chemicals in the air
light
sound and position of the head
Tongue
Nose
Eyes
7/27/2019 07 the Nervous System
3/6
- GCSE Bitesize - The nervous system
//www.bbc.co.uk/schools/gcsebitesize/science/edexcel/responses_to_environment/thenervoussystemrev_print.shtml[10/21/2013 8:13:52 PM]
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 brainthen co-ordinates the response.
Effectors
An effector is any part of the body that produces the response.
Here are some examples of effectors:
a muscle contracting to move the arm
a muscle squeezing saliva from the salivary glanda gland releasing a hormonehormone: chemical
messengers produced in glands and carried by the blood
to specific organs in the body into the blood.
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:
1. sensory neurones carry signals from receptorsreceptor:
organ which recognizes and responds to stimuli to the
spinal cord and brain.
2. relay neurones carry messages from one part of the
CNSCNS: Central Nervous System (brain and spinal
cord). to another.
Ears
7/27/2019 07 the Nervous System
4/6
- GCSE Bitesize - The nervous system
//www.bbc.co.uk/schools/gcsebitesize/science/edexcel/responses_to_environment/thenervoussystemrev_print.shtml[10/21/2013 8:13:52 PM]
3. motor neurones carry signals from the CNS to
effectorseffector: organ which has an effect when
stimulated (eg muscles or glands).
The diagram below shows a typical neurone: in this case, a
motor neurone. It has tiny branches at each end (the dendron)
and a long fibre carries the signals (the axon).
The axon is surrounded by a fatty layer known as the myelin
sheath . This helps to protect the neurone and allow impulses to
travel faster.
Synapses
Where two neurones meet, there is a tiny gap called a synapse.
Signals cross this gap using chemicals released by a neurone.
The chemical diffuses across the gap makes the next neurone
transmit an electrical signal.
A motor neurone
7/27/2019 07 the Nervous System
5/6
- GCSE Bitesize - The nervous system
//www.bbc.co.uk/schools/gcsebitesize/science/edexcel/responses_to_environment/thenervoussystemrev_print.shtml[10/21/2013 8:13:52 PM]
1. An electrical impulse travels along an axon.
2. This triggers the nerve-ending of a neuron to release
chemical messengers called neurotransmitters.
3. These chemicals diffuse across the synapse (the gap)
and bind with receptor molecules on the membrane of
the next neuron.
4. The receptor molecules on the second neuron bind only
to the specific chemicals released from the first neuron.
This stimulates the second neuron to transmit the
electrical impulse
The animation below shows a synapse between two neurons:
Reflex actions
When a receptor is stimulated, it sends a signal to the central
nervous system, where the brain co-ordinates the response.
But 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. For
example, you would pull your hand away from a hot flame
without thinking about it. The animation below allows you to step
through each stage of the reflex arc.
This is what happens:
7/27/2019 07 the Nervous System
6/6
- GCSE Bitesize - The nervous system
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
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.
n bright light:
Radial muscles of the iris relax.
Circular muscles of the iris contract.
Less light enters the eye through the contracted pupil.
n dim light:
Radial muscles of the iris contract.Circular muscles of the iris relax.
More light enters the eye through the dilated pupil.
Now try a Test Bite.
Back to Revision Bite
http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/responses_to_environment/thenervoussystem/quiz/q97170197/http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/responses_to_environment/thenervoussystemrev1.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/responses_to_environment/thenervoussystemrev1.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/responses_to_environment/thenervoussystem/quiz/q97170197/