Can someone explain the nervous system and synapses (AQA B1)

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This is the topic in B1 that I'm not confident in, if anyone could explain it to the best of their ability it'd be very appreciated! thanks
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The Nervous System consists of:
Sensory Neurones (the neurone cells that are affects by a stimulus and produce a electrical signal)
Relay Neurones (the neurone cells that RELAY the electrical signal to the central nervous system)
The Central Nervous System or CNS (consists of the brain and spine and manages all the signals created by various stimulus to administer a appropriate response to each)
Motor Neurones (the neurones that will transmit the electrical signals formed by the CNS to a muscle or gland)
Effectors (the gland or muscle will perform a action that is a response to the original symbol that has been made at the CNS)

The Nervous System allows reflex responses to be completed (these are involuntary automatic responses in response a known stimulus, e.g. a muscle contraction if you put your hand near fire).

The Reflex Arc is:

Stimulus - Sensory Neurone - Relay Neurone - CNS - Motor Neurone - Effector - Response


A synapse is small gap in between each neurone as the neurones transmit electrical signals to and from the Central Nervous System.
As electricity cannot fly across air, the electrical signal is converted into a chemical signal and the chemical is diffused across the synapse (gap). This allows electrical signals to quickly transport over gaps and go to and from the CNS without their being one long neurone. The synapse is the only factor that slows a reflex response.


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(Original post by dalalaachoui)
This is the topic in B1 that I'm not confident in, if anyone could explain it to the best of their ability it'd be very appreciated! thanks
RECEPTORS- a group of specialised cells that detect changes in the environment.
Eyes- light receptor
Ears- sound receptor
Skin- Touch, pressure, pain and temperature receptor
Nose- smell receptors(chemicals in the air)
Tongue- taste receptors(chemicals in the food)

-where reflexes and actions are coordinated.
-Neurones transmit the info
- CNS Is made up of the brain and spinal cord

- STIMULUS is detected by RECEPTORS
-impulses are sent along a SENSORY NEURONE to the cns
-impulses reach a synapse(a connection between 2 neurones) between the SENSORY NEURONE and the RELAY NEURONE.
-impulses sent along the RELAY NEURONE until they reach a synapse between the RELAY NEURONE and the MOTOR NEURONE: the same thing happens again.
-impulses travel along the MOTOR NEURONE to the EFFECTOR(any part of the body that produces a response)
-the EFFECTORS then produces a response.

HORMONES- chemical messengers sent in the blood to activate target cells.
-slower action.
-acts for a long time
E.g. The release of adrenaline; causing fight or flight response.

NERVES-a bundle of fibres in the body that transmits impulses of sensation to the brain or spinal cords to cause a response.
-very fast action.
-act for a short amount of time
E.g. Pain signals to tell your brain to react.

Tried my best to explain the basic nervous system. Sorry if there's any mistakes or you don't get it. I'm only a student myself, sitting my GCSEs this year.

Here are a few links which help:

Hope these help and I wish you all the luck!
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Report 4 years ago
(Original post by dalalaachoui)
This is the topic in B1 that I'm not confident in, if anyone could explain it to the best of their ability it'd be very appreciated! thanks
Hello, i also struggled with this topic but now I understand it so hope this helps...

The central nervous system consists pf the spinal cord and the brain.
The nervous system contains nurones which help to create an electrical signal due to a stimulus (a change in the environment which then helps to create a reflex action. For example, if you hold your hand above a hot flame, a reflex action will occur due to the stimulus of the change in heat and your hand will automatically move away from the flame.
These neurones consist of the sensory neurone, the relay neurone and the motor neurone. I am not sure if this will help you because it is quite strange but i remeber the order of these neurones by the following:
The sensory neurone is first because it is first to sense the change in the environment.
The relay neurone is the middle neurone because in a relay race the runners pass the baton between the players so the relay neurone passes the signals between the sensory and motor neurone.
The motor neurone therefore is the last neurone in the sequence.

Between these neurones is a gap called a synapse. Chemicals called nerotransmitters are diffised across the gap which then helps to create an electrical signal which helps to create a reflex action.

The use of stimulants increases this rate of diffusion but depressants decrease this.

Bbc bitesize is very useful to help on this topic (

I hope this helps, good luck!

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