HOW MESSAGES ARE SENT. It is a message travelling down a neuron The message comes from: Another...
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Transcript of HOW MESSAGES ARE SENT. It is a message travelling down a neuron The message comes from: Another...
Nerve Impluses
HOW MESSAGES ARE SENT
What is a nerve impluse?
It is a message travelling down a neuron
The message comes from: Another neuron or A sensory receptor
A nerve impulse is also called an ACTION POTENTIAL.
Interesting Ions
Neurons have a rich supply of positive and negative ions both inside and outside the cell.
Sodium (Na+) ions and Potassium (K+) ions play a key role the creation of a nerve impulse.
Sodium (Na+) and Potassium (K+)
Since both are positive…. It’s all relative.▪ Positive = more positive ions▪ Negative = fewer positive ions
Sodium (Na+) and Potassium (K+)
The highly concentrated potassium ions inside the nerve cells have a tendency to diffuse outside the nerve cells.
Similarly, the highly concentrated sodium ions outside the nerve cell have a tendency to diffuse into the nerve cell.
Steps of a Nerve Impulse
Step 1: A Neuron at Rest
Not sending an impulse
The neuron is impermeable to Na+ meaning Na+ remains outside
Potassium (K+) moves freely (permeable) in and out of cell.
Step 1: A Neuron at Rest
Outside is positive All Na+ and some
K+
Inside is negative Some K+
Polarized more positive
outside cell then inside
Step 2:Action Potential
Only when polarization can occur will Na+ be able to enter. Na+ channels (gates) open, allowed Na+
to diffuse into cell… for a fraction of a second!
Charges begin to switch sides… This happens very quickly
Step 2: Action Potential
Polarity reverses: Inside positive Outside negative
“Depolarized”
Step 2: Action PotentialK+ moving out of the cell (closes
Na+ gates), trapping Na+ inside cell. Depolarization (reversal of charges)
occurs in a small area▪ Triggers a “wave” of electricity▪ Travels length of axon
Step 3: Refractory Period
Recovery period Few thousandths of a second Neuron cannot be stimulated again
Neuron must be returned to “resting potential”
Step3: Refractory Period
Sodium potassium pumps returns membrane to rest Na+ moves out K+ moves in
Repolarized Outside now + Inside now -
Saltatory Conduction
Myelinated neuronFaster transmission (100 m/s)
2m/s (unmyelinated) Jumps from one node of Ranvier to
nextUses less energy
Threshold
Minimum strength stimulus required for action potential to occur Different for each neuron
All-or-none Response
Impulses are all alike once threshold reached Strength only changes with number sent
Graph of Action Potential
WOW Website!!!
Great animation of the creation of a nerve impulse: Action Potential Demo (Harvard
University)