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Nerve Impluses

HOW MESSAGES ARE SENT. Nerve Impluses. 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.

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Nerve Impluses

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  1. HOW MESSAGES ARE SENT Nerve Impluses

  2. 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.

  3. 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.

  4. Sodium (Na+) and Potassium (K+) • Since both are positive…. It’s all relative. • Positive = more positive ions • Negative = fewer positive ions

  5. 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.

  6. Steps of a Nerve Impulse

  7. Step 1: A Neuron at Rest • Not sending an impulse • The neuron isimpermeable to Na+ • meaning Na+ remains outside • Potassium (K+) moves freely (permeable) in and out of cell.

  8. 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

  9. 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

  10. Step 2: Action Potential • Polarity reverses: • Inside positive • Outside negative • “Depolarized”

  11. Step 2: Action Potential • K+ 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

  12. Step 3: Refractory Period • Recovery period • Few thousandths of a second • Neuron cannot be stimulated again • Neuron must be returned to “resting potential”

  13. Step3: Refractory Period • Sodium potassium pumps returns membrane to rest • Na+ moves out • K+ moves in • Repolarized • Outside now + • Inside now -

  14. Saltatory Conduction • Myelinated neuron • Faster transmission (100 m/s) • 2m/s (unmyelinated) • Jumps from one node of Ranvier to next • Uses less energy

  15. Threshold • Minimum strength stimulus required for action potential to occur • Different for each neuron

  16. All-or-none Response • Impulses are all alike once threshold reached • Strength only changes with number sent

  17. Graph of Action Potential

  18. WOW Website!!! • Great animation of the creation of a nerve impulse: • Action Potential Demo (Harvard University)

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