The document explains the nervous system's coordination and response mechanisms, focusing on synapses, which facilitate impulse transmission between neurons. It details reflex actions, describing the reflex arc pathway that allows for automatic responses to stimuli, such as touching something hot. Key terms like effector, neurotransmitter, and sensory neuron are defined to enhance understanding of how the nervous system functions.

1. Coordination and Response
The Nervous System

14. Synapse [sin´aps]
the junction between the processes of two
neurons or between a neuron and an
effector organ, where neural impulses are
transmitted by chemical means.
Synapses transmit nerve impulses from
one neurone to another. In doing so, they
act as junctions, allowing:
a single impulse along a neurone to be
transmitted to a number of different
neurones at a synapse.
This allows a single stimulus to create a
number of simultaneous responses.
a number of different impulses combined at
a synapse.
This allows stimuli from different receptors
to interact in order to produce a single
response.

15. Reflex actions
A reflex action is a way for the body to automatically and rapidly respond to a stimulus to
minimise any further damage to the body. It follows this general sequence and does not involve
the brain:
stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector →
response
The nerve pathway followed by a reflex action is called a reflex arc. For example, a simple
reflex arc happens if we accidentally touch something hot.
● Receptor in the skin
detects a stimulus (the
change in temperature)
● Sensory neurone sends
impulses to relay
neurone.
● Motor neurone sends
impulses to effector.
● Effector produces a
response (muscle
contracts to move hand
away).

24. diffuse
When particles spread out from a region of higher concentration to a region of lower concentration.
effector
The organ, tissue or cell that produces a response.
hormone
Chemical messenger produced in glands and carried by the blood to specific organs in the body.
motor neurone
The nerve cell that carries electrical impulses from the CNS to effectors such as muscles or glands.
neuron
Another term for a nerve cell that is specialised to transmit electrical impulses.
neurotransmitter
Chemical involved in passing nerve impulses from one nerve cell to the next across a synapse.
reflex action
Automatic and rapid response to a stimulus.
relay neurone
The nerve cell that transmits electrical impulses from sensory neurones to motor neurones.
sensory neurone
The nerve cell that transmits electrical impulses from receptors in the sense organs to the CNS.
stimulus
Something that sets off a reaction in the nervous system, for example, light, heat, sound, gravity, smell, taste,
or temperature. These changes in the environment are detected by receptors in an organism. The plural is
stimuli.

25. https://www.bbc.com/bitesize/guides/zkdnb9q/revision/5
https://www.bbc.com/bitesize/guides/zprxy4j/test
https://www.bbc.com/bitesize/guides/zprxy4j/revision/1