Nerve Impulse Every time you move a muscle & every time you think a thought, your nerve cells are hard at work. They are processing information: receiving.

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Presentation transcript:

Nerve Impulse Every time you move a muscle & every time you think a thought, your nerve cells are hard at work. They are processing information: receiving signals, deciding what to do with them, & dispatching new messages off to their neighbors. Some nerve cells communicate directly with muscle cells, sending them the signal to contract. Other nerve cells are involved solely in the bureaucracy of information, spending their lives communicating only with other nerve cells. But unlike our human bureaucracies, this processing of information must be fast in order to keep up with the ever-changing demands of life.

Main idea:Transmission of a Nerve Impulse Is how the nervous message moves along the length of a neuron

Nerve impulse is… An electrochemical message Created by the movement of IONS across the cell membrane (sodium potassium)

Transmission of a signal – THINKING!!! How is a signal transmitted down/along neuron? “All or None response” Think Dominoes! 2007

Nerve Impulse is…. Tricky!!!!! VOCAB- Resting Potential Action Potential Sodium & Potassium Gates (passive) Sodium &Potassium Pumps (active) Depolarization Repolarization Recovery

Nerve Impulse Order of the Impulse 1- Resting Potential 2-Action Potential 3- Recovery

1- Resting Potential There is a greater concentration of sodium ions outside the neuron & a greater concentration of potassium ions inside the neuron. Inside the neuron has a relatively negative charge. Resting potential is -65 mV Think KIN (potassium in) K+ Na+ K+ Cl- aa- + – K+ 2007

1- Resting Potential Resting potential is maintained by the sodium-potassium pumps. (active transport)

2 – Action potential – + + – + – – + A) Depolarization - a Stimulus causes the Na+ channels to open (change in pH, electric shock, pressure, light) Na+ ions diffuses into cell charges reverse at that point on neuron cell becomes depolarized (+ 40 mV) – + + – Na+ + – – +

How does a nerve impulse travel? Wave: nerve impulse travels down neuron change in charge opens other Na+ gates in next section of cell “voltage-gated” channels Na+ ions continue to move into cell “wave” moves down neuron = action potential – + + – Na+ + – – + wave 

2- Action Potential + – B) Repolarization: K+ channels open up K+ ions diffuse out of cell Restoration of the same potential as resting (- 65 mV) Causes the channels to close behind impulse + – Na+ K+ wave  Opening gates in succession = - same strength - same speed - same duration 2007

3- Recovery + – – + – + + – After firing a neuron has to re-set itself Na+ needs to move back out K+ needs to move back in Sodium Potassium pumps work to re-establish the ion distribution of resting potential Na+ K+ K+ + – – + Na+ K+ Na+ – + + – wave  2007

Neuron is ready to fire again!!! Na+ K+ aa- resting potential (- 65 mV) + – 2007

Action potential - all together! Resting potential Stimulus reaches threshold potential Na+ channels open; K+ channels closed Na+ channels close; K+ channels open Recovery - Na+ / K+ pumps 2007

Myelin sheath Schwann cells insulate neuron (Na+ / K+ cannot enter cell) Na+ / K+ can only enter at the nodes of ranvier Increase speed of impulse signal hops from node to node 150m/sec (330mi/hr) (vs. 5m/sec) signal direction myelin sheath 2007

T cells attack myelin sheath loss of signal Multiple Sclerosis T cells attack myelin sheath loss of signal 2007