Revision notes on neurones and the adaptations of neurones. A level biology OCR A revision notes. Notes on module 5: Communication, homeostasis and energy. Summary/ information you need to memorize for a level biology OCR A exams.
Neurones are specialised cells that transmit an action potential
from one part of the body to another.
Dendrites are the small extensions of the cell body that create a
large surface area, carrying impulses towards the cell body.
Axons are the single long fibre that carries electrical impulses
away from the cell body.
Adaptations of neurones:
o Long – transmit action potentials over a long distance.
o Sodium-potassium pumps – actively transport sodium out
of the cell and potassium into the cell (uses ATP).
o Gated ion channels – control entry/exit of sodium/
potassium/ calcium ions.
o Organelles in cell body – mitochondria, nucleus,
ribosomes, ER for production of neurotransmitters.
o Myelin sheath – fatty sheath insulates neurone from
other electrical activity (20-30 layers of Schwann cell
membrane).
Myelinated neurones:
o Have Schwann cells wrapped around the axon many
times.
o There are gaps between Schwann cells called nodes of
Ranvier (these occur every 1-3mm in humans).
o Myelination speeds up conduction 100 times by allowing
for long local currents (saltatory conduction) along the
neurone.
o This is where depolarisation only occurs at the, nodes &
so the action potential appears to “jump” from node to
node.
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