Coordination & Control – the Nervous System (OCR GCSE Combined Science A (Gateway): Biology): Flashcards
Exam code: J250
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What is the function of the nervous system?
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What is the function of the nervous system?
It allows an organism to react to its surroundings and to coordinate its behaviour.
Define stimulus.
A detectable change in the internal or external environment, such as light, sound or temperature.
Define receptor.
A cell or organ that detects a stimulus.
Define effector.
A cell, tissue or organ that carries out the response — usually a muscle or a gland.
Define neurone.
A nerve cell, adapted to carry electrical impulses from one part of the body to another.
Which two organs make up the central nervous system?
The brain and the spinal cord.
What is the role of the central nervous system?
It coordinates the response, directing the impulse to the correct effector.
What does a sensory neurone do?
Carries impulses from receptors to the CNS.
What does a motor neurone do?
Carries impulses from the CNS to an effector.
What does a relay neurone do?
Found inside the CNS, it connects sensory neurones to motor neurones.
Describe the structure of a sensory neurone.
It is long, with its cell body branching off the middle of the axon.
Describe the structure of a motor neurone.
It is long, with a large cell body at one end and long dendrites branching from it.
What is the function of the axon?
It is the long fibre that carries the electrical impulse away from the cell body.
Give the order of the pathway from stimulus to response.
stimulus → receptor → sensory neurone → CNS → motor neurone → effector → response
A bundle of neurones is known as a ＿＿＿＿＿＿＿＿.
A bundle of neurones is known as a nerve.
Information travels along a neurone as an ＿＿＿＿＿＿＿＿ impulse.
Information travels along a neurone as an electrical impulse.
True or False?
Relay neurones are found inside the CNS.
True.
They connect sensory neurones to motor neurones within the brain and spinal cord.
True or False?
An effector detects a stimulus.
False.
A receptor detects the stimulus. An effector carries out the response.
Define synapse.
The gap between two neurones.
How does an impulse cross a synapse?
The impulse triggers the release of neurotransmitters.
These diffuse across the gap and bind to receptor molecules on the next neurone, starting a new impulse.
Why is the signal at a synapse chemical rather than electrical?
An electrical impulse cannot jump the gap, so a chemical neurotransmitter carries the signal across.
How do synapses make sure impulses travel one way only?
Neurotransmitters are released on one side of the gap and their receptors are on the other, so the signal cannot travel backwards.
Why are neurotransmitters broken down after use?
To stop continued stimulation of the next neurone, which would keep sending repeated impulses.
Why does a synapse slow the transmission of an impulse?
Neurotransmitters must diffuse across the gap, which takes longer than an electrical impulse travelling along an axon.
How does the nervous system reach every part of the body?
Neurones extend to all parts of the body, so a stimulus anywhere can be detected and responded to.
Why does having many links between neurones help coordination?
One neurone can connect with many others, so a single stimulus can produce a full, coordinated response.
Why does the body need different types of sensory receptor?
Each type detects a different stimulus — light, sound, touch, temperature or chemicals — so the body can respond to all of them.
What is the function of the myelin sheath?
It insulates the axon and speeds up the transmission of the impulse.
Define voluntary response.
A conscious response to a stimulus, coordinated by the brain.
Why is a voluntary response slower than a reflex?
The brain must consciously decide what to do, which takes extra time.
Give the main difference between a voluntary and a reflex response.
A voluntary response involves a conscious decision by the brain.
A reflex response is automatic and you are only aware of it afterwards.
Chemicals called ＿＿＿＿＿＿＿＿ carry the signal across a synapse.
Chemicals called neurotransmitters carry the signal across a synapse.
Branched endings called ＿＿＿＿＿＿＿＿ create links between neurones.
Branched endings called dendrites create links between neurones.
True or False?
Impulses can travel in either direction across a synapse.
False.
Synapses make sure impulses travel in one direction only.
True or False?
A very long axon speeds up transmission.
True.
A long axon means fewer synapses to cross, and crossing a synapse is the slow step.
Define reflex action.
An automatic, rapid response to a stimulus that does not involve the conscious part of the brain.
Define reflex arc.
The nerve pathway taken by an impulse during a reflex action.
Why are reflex actions important?
They are rapid and automatic, which protects the body from harm.
Why is a reflex faster than a voluntary response?
The impulse does not travel to the conscious brain for a decision — it takes a short route through the spinal cord.
List the stages of a reflex arc in order.
stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response
Which three neurones are involved in a reflex arc?
Sensory, relay and motor neurones.
Which part of the body coordinates a simple reflex?
The spinal cord, which contains the relay neurone.
Describe the reflex arc when a hand touches a sharp pin.
Pain receptors in the skin detect the stimulus and a sensory neurone carries the impulse to the spinal cord.
A relay neurone passes it to a motor neurone, and the muscle contracts to pull the hand away.
When do you become aware that a reflex has happened?
After the response has already been carried out.
Define reaction time.
The time taken to respond to a stimulus — usually less than a second.
How does the ruler drop test measure reaction time?
A ruler is dropped and caught between the fingers.
The further down the ruler it is caught, the slower the reaction time.
Give two control variables for the ruler drop test.
Using the same hand each time.
Dropping the same ruler from the same height each time.
Why should the ruler drop test be repeated several times?
To calculate a mean, which reduces the effect of random error and anomalous results.
Why is a computer test of reaction time more accurate?
It removes human error from the measurement and can record in milliseconds.
In a reflex arc, the ＿＿＿＿＿＿＿＿ neurone connects the sensory neurone to the motor neurone.
In a reflex arc, the relay neurone connects the sensory neurone to the motor neurone.
A reflex response is described as ＿＿＿＿＿＿＿＿ because it happens without conscious thought.
A reflex response is described as involuntary because it happens without conscious thought.
True or False?
A reflex action involves the conscious part of the brain.
False.
It is coordinated by the spinal cord or the unconscious part of the brain, which is why it is so fast.
True or False?
Catching a ruler lower down means a slower reaction time.
True.
The ruler falls further before being caught, so more time has passed.
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