Dissection on a giraffe investigating the recurrent laryngeal nerve httpwwwyoutubecomwatchvcO1a1Ek HD0 Electrochemical Impulses Electrochemical Impulses Nerve impulses are electrochemical messages created by the movement of ions through the neuron cell membrane ID: 577892
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Slide1
One really, really long nerve!
Dissection on a giraffe: investigating the recurrent laryngeal nerve
http://www.youtube.com/watch?v=cO1a1Ek-
HD0Slide2
Electrochemical ImpulsesSlide3
Electrochemical Impulses
Nerve impulses are electrochemical messages created by the movement of ions through the neuron cell membrane
Negative and positive ions are both found in large numbers inside & outside neurons. Slide4
Negative ions
are large & tend to stay inside the cell.
Movement of positive ions involves diffusion, active transport and a Na
+
/
K
+
pump.Slide5
K
+
found inside neurons tends to diffuse out of the cell.
Na
+
found outside the cell tends to diffuse in. Slide6
Electrochemical Gradient
Since the cell membrane is
more permeable to K
+
than Na
+
, K
+ moves out of the cell faster than Na+ moves in.
This results in an electrochemical gradient across the cell membrane, and an
overall external positive charge
which is referred to as
resting potential. Slide7
The Electrochemical Gradient that is created is referred to as the neuron’s
resting potential Slide8
Action Potential
When a message is received by the dendrites of a neuron, the following changes, referred to as an
action potential
occur:
The neuron cell membrane becomes more permeable to Na
+
than to K
+
(Na
+
gates open)
Na
+
rushes into the neuron by diffusion.Slide9
Action Potential
A reversal of charge occurs, called
depolarization
(this is the ‘firing’ of the neuron)
Once the inside of the neuron becomes positive, the Na
+
gates close.
A Na
+
- K
+
pump in the cell membrane moves sodium out and potassium in, restoring the resting potential (called re-polarization)Slide10Slide11
Movement of the Action Potential
D
epolarization occurs as a wave
along the membrane
of the axon
T
he wave of depolarization is followed by a wave of re-polarization
The action potential moves along the axon by jumping from one
node of
Ranvier
to anotherSlide12Slide13
Some Important Terminology
Refractory period
: time it takes for the nerve cell membrane to re-polarize and be able to conduct another action potential
Threshold level
: minimum level of stimulus required for a neuron to respond (varies between neurons)Slide14Slide15
Some Important Terminology
All-or-none response
: neurons fire maximally or not at all (means that increasing the stimulus above threshold level does not increase the response; see
p
. 422)
Speed of transmission
: determined by intensity of the stimulus, amount of myelin and diameter of the axonSlide16