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Sensory and motor neurons
Central nervous system made up
of brain and spinal cord
Peripheral nervous system
consists of all the other parts of the
nervous system: the nerves and the
receptors
Stimuli changes in the environment,
either inside or outside the body. The
stimuli are detected by receptors…read more

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Neurons
Carry nerve impulses
Have a cell body containing nucleus, and
organelles e.g. mitochondria, ribosome and
endoplasmic reticulum
Dendrites are extensions of the cell body.
They have a large surface area to reduce nerve
impulses
Axon carries nerve impulses away from the
cell body
Schwann cells surround the axon. The
cytoplasm of the Schwann cell is squeezed…read more

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Neurons at rest
Very negatively charged inside the cell
(polarised)
Difference between the inside and
outside the neurone called resting
potential.
-70mV
Achieved by distribution of ions…read more

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Sodium-potassium pump (active-
transport)
Sodium higher conc. outside cell lower
inside cell the pump moves sodium out
of the cell
Potassium lower conc. Inside cell higher
outside cell so the pump moves
potassium into the cell
Potassium : Sodium 2:3
More sodium gets moved out the cell than
potassium into the cell so the difference
gets bigger…read more

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Action potential
Resting state -70mV
Sodium channels closed
Some potassium channels open
Depolarisation
Stimulus causes Na+ to open. K+ channels closed
Sodium ions are positively charged the potential difference
reverses when they enter the cell
Threshold potential is the membrane potential required to
generate an action potential (nerve impulse) ~50mv
Depolarisation cont.
Once Na + enters the cell more channels open further
changing the potential
Has to be over -50mV to create an action potential
Peaks around +40mV
All or nothing response (has to get to -50mV)…read more

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