Nervous System Revision Sheets

These cover the topic of the nervous system for A2 Biology. Mainly for use with WJEC exam board but can be applicable to other boards.

Covers everything on the nervous system apart from nerve nets, synapses and photoperiodism. 

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The nervous system

The nervous system is divided into two main parts: The central nervous system and the peripheral nervous

The central nervous system (CNS) comprises the brain and spinal chord. Its role is to process the
information from the peripheral nervous system and initiate a response.

The peripheral…

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A cell body containing a nucleus and granular cytoplasm containing many ribosomes. These ribosomes
are grouped together forming Nissl granules which are concerned with the formation of
neurotransmitter substances.

Dendrites ­ many thin extensions which carry impulses towards the cell body. These receive
impulses from other nerve cells. Some neurones…

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Most of the channels that allow the potassium ions to diffuse in are open while most of the sodium
channels are closed

As a result, the axon membrane is more permeable to potassium ions that sodium ions, so these
diffuse out faster than sodium ions diffuse in

The result is…

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The action potential causes a small electric current across the membrane and as a portion of the membrane
is depolarised, depolarisation of the next portion is initiated. There is a series of local currents propagated
along the axon.

The sodium/potassium pump is active all the time and behind the transmission,…


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