Complete revision notes for Topic 14 of the CIE IGCSE Biology course: Coordination and response. Explanations with diagrams for every specification point. These notes are written for candidates taking the Extended paper.
Describe a nerve impulse as an electrical signal that passes along nerve cells called neurones
Information is sent through the nervous system as nerve impulses – electrical signals that
pass along nerve cells known as neurones.
A bundle of neurones is called a nerve.
Describe the human nervous system in terms of:
The central nervous system consisting of brain and spinal cord
The peripheral nervous system
Coordination and regulation of body functions
The human nervous system consists of two parts:
1) Central nervous system (CNS)
a. Brain and spinal cord
2) Peripheral nervous system (PNS)
a. All the nerves in the body
,Why do we need a nervous system?
Make sense of our surroundings
Respond to our surroundings
Coordinate and regulate body functions
Distinguish between voluntary and involuntary actions
A voluntary response is one where you make a conscious decision to carry out a particular
action therefore it starts with your brain.
An involuntary (or reflex) response does not involve the brain as the coordinator of the
reaction, and you are not aware you have completed it until after you have carried it out.
Involuntary actions are usually ones which are essential to basic survival and are rapid,
whereas voluntary responses often take longer as we consider what the response might be
before doing it.
Identify motor (effector), relay (connector) and sensory neurones from diagrams
There are three main types of neurone: sensory, relay and motor
1) Sensory neurones carry impulses from sense organs to the CNS (brain or spinal cord)
2) Relay neurones are found inside the CNS and connect sensory and motor neurones
3) Motor neurones carry impulses from the CNS to effectors (muscles or glands)
Neurone structure
Neurones have a long fibre (axon): this means that less time is wasted transferring the
impulse from one cell to another.
The axon is insulated by a fatty sheath with small uninsulated sections along it (called
nodes): this means that the electrical impulse does not travel down the whole axon,
but jumps from one node to the next.
Their cell body contains many extensions called dendrites: this means they can connect to
many other neurones and receive impulses from them, forming a network for easy
communication.
, Each category of neurone has a distinct structure:
Describing the difference:
Sensory neurones are long and have a cell body branching off the middle of the axon
Relay neurones are short and have a small cell body at one end with many dendrites
branching off it
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