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Nervous system (Reflex Arc (Stimulus (Receptor (Sensory neurones (Relay…
Nervous system
Reflex Arc
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E.G. the withdrawal reflex, when you immediately withdraw your hand if, for example you touch something hot.
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Nerve nets
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Sensory cells
Detect stimuli e.g. light, sound, touch or temperature
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Synapses
Electrical synapse
3nm across, small enough that an electrical impulse is transmitted directly from one neurone to the next.
Chemical synapse
20nm across. Impulse id transmitted by a neurotransmitter, a chemical that diffuses across the synaptic cleft, form the pre-synaptic membrane of one neurone to the post-synaptic membrane of an adjacent neurone, where a new impulse is initiated.
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Nervous impulse
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Action potential
The rapid rise and fall of the electrical potential across a nerve cell membrane as a nervous impulse passes
Depolarisation
A temporary reversal of potential across the membrane of a neurone such that the inside becomes less negative than the outside as an action potential is transmitted.
Repolarisation
Potassium channels open and k+ ions diffuse out. the cell becomes less positive inside as more diffuse out and the membrane is repolarised.
Hyperpolarised
More K+ diffuse out than Na+ ions in, so the potential difference across the membrane becomes even more negative than the resting potential.