neurones 2 Flashcards
what are the three factors that affect the speed of conduction
myelination, axon diameter, temperature
what happens if some neurones are myelinated
they have a myelin sheath
in the peripheral nervous system what is the myelin sheath made out of
a type of cell called a schwann cell
what is between schwann cells
Between the Schwann cells are tiny
patches of bare membrane called the
nodes of Ranvier. Sodium ion channels
are concentrated at the nodes.
in a myelinated neurone where does depolarisation happen
In a myelinated neurone, depolarisation only
happens at the nodes of Ranvier (where
sodium ions can get through the membrane).
what does the neurones cytoplasm conduct enough of and what does this do
The neurone’s cytoplasm conducts enough
electrical charge to depolarise the next node,
so the impulse ‘jumps’ from node to node. this is salatory conduction
in a non myelinated neurone what does the impulse travel as
In a non-myelinated neurone, the impulse travels as a
wave along the whole length of the axon membrane
(so you get depolarisation along the whole length
of the membrane).
this is slower than saltatory conduction though is quite fast stylll.
how does the axon diameter affect the speed of conduction of action potentials
Action potentials are conducted quicker along axons
with bigger diameters because there’s less resistance
to the flow o f ions than in the cytoplasm of a smaller
axon. With less resistance, depolarisation reaches
other parts of the neurone cell membrane quicker.
how does temperature affect the speed conduction of action neurones
The speed of conduction increases as the
temperature increases too, because ions diffuse
faster. The speed only increases up to around
40 °C though — after that the proteins begin to
denature and the speed decreases.
