Nerve Impulses ppt
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Transcript Nerve Impulses ppt
HOW MESSAGES ARE SENT
A message travelling down a neuron
It comes from:
Another neuron
A sensory receptor
Also called an ACTION POTENTIAL
Sodium (Na+)
Potassium (K+)
Since both are positive…. Its all relative
Positive = more positive ions
Negative = fewer positive ions
Not sending an impulse
Neuron impermeable to Na+
Na+ collects outside
Potassium moves freely (permeable)
Outside is positive
All Na+ and some K+
Inside is negative
Some K+
Polarized
Na+ channels (gates) open
Neurons now permeable to Na+
Na+ diffuse into cell
Polarity reversed
Inside positive
Outside negative
Depolarized
K+ moving out of the cell (closes Na+ gates)
Depolarization occurs in a small area
Affects adjacent gates
▪ Creates “wave” of electricity
▪ Travels length of axon
Na+ gates are only open for a fraction of a
second
Na+ gets trapped inside the cell
Recovery period
Few thousandths of a second
Neuron cannot be stimulated again
Neuron must ne returned to “resting
potential”
Sodium potassium pumps returns membrane
to rest
Na+ moves out
K+ moves in
Repolarized
Outside now +
Inside now -
Myelinated neuron
Faster transmission (100 m/s)
2m/s (unmyelinated)
Jumps from one node of Ranvier to next
Uses less energy
Minimum strength stimulus required for
action potential to occur
Different for each neuron
Impulses are all alike once threshold reached
Strength only changes with number sent