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Physiology of Nerve Transmission

Physiology of Nerve Transmission. How do neurons do their job?. NERVE IMPULSES. The function of a neuron is to transmit information from one part of the body to another. How does this happen?. NERVE IMPULSES.

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Physiology of Nerve Transmission

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  1. Physiology of Nerve Transmission How do neurons do their job?

  2. NERVE IMPULSES • The function of a neuron is to transmit information from one part of the body to another. How does this happen?

  3. NERVE IMPULSES • A. No mitosis occurs in neurons. However, if the cell body is intact, the axon is in the PNS, AND the neuron has a myelin sheath, there is a chance for some repair.

  4. NERVE IMPULSES • B. Rate of transmission: How fast are nerve impulses? • 1. A fibers • 2. B fibers • 3. C fibers

  5. NERVE IMPULSES • C. Nature of nerve transmission: • Electrochemical - why??

  6. NERVE IMPULSES* • D. Similarities to Muscle Contraction: • Electrochemical All-or-none • Polarization Depolarization • Action potential Repolarization • Threshold stimulus Use ATP • Latent period Summation • Calcium needed Neurotransmitters • Refractory period Excitability • Sodium-Potassium pump * Pick any 4 that will be easy for you to remember.

  7. NERVE IMPULSES • E. Nerve transmission • 1. Resting membrane potential: • -70 mV • membranes are polarized • Na+ outside and K + inside • Outside is positively charged; • Inside is negatively charged

  8. NERVE IMPULSES Role of thesodium-potassium pump - Maintains resting membrane potential (polarization) by pumping 3 sodium out and 2 potassium into the cell. (active transport - ATP needed) This keeps the cell membrane polarized & is necessary for repolarization.

  9. NERVE IMPULSES • 2. Stimulus Depolarization • Resting potential goes from -70mV to 0 mV • Na+ ions rush into cell & K + rush out Chain reaction along axon to create an impulse

  10. NERVE IMPULSES • Action potential = nerve impulse • Travels along surface of axon • Nodes of Ranvier increase rate by saltatory conduction • Impulse jumps across nodes

  11. Saltatory conduction http://staff.washington.edu/cdave/pbio505/Week2Presentation.xml

  12. NERVE IMPULSES • 3. Repolarization • Occurs within 0.001 sec (1 millisecond) • Resting membrane potential (polarization) restored by sodium-potassium pump.

  13. Review Questions • What is meant by “reaching the threshold”? • Why is the sodium-potassium pump necessary? • How many Na+ are pumped out of the cell? How many K+?

  14. Action Potential tutorial • Click on the link below and then use the Action Potential animation before going on. • http://outreach.mcb.harvard.edu/animations.htm

  15. NERVE IMPULSES • Propagation of an action potential: • There are 3 stages. • 1. • 2. • 3.

  16. NERVE IMPULSES • 4. Refractory period: • Occurs during depolarization: 2 types • Absolute - NO new impulse (action potential) can be generated • Relative - after absolute, second A.P. can be generated if stimulus is ABOVE threshold (suprathreshold stimulus)

  17. ACTION POTENTIAL ANIMATION http://www.dnatube.com/video/1105/Understanding-Action-Potential-and-Nerve-Impulses GO THROUGH THIS ANIMATION BEFORE CONTINUING WITH THIS PRESENTATION.

  18. NERVE IMPULSES • F. Summation - group of subthreshold stimuli act together to reach threshold level so the neuron “fires”

  19. Review Questions • What is the refractory period and when does it occur? • Explain the differences between the absolute and relative refractory periods. • Why is summation necessary?

  20. NERVE IMPULSES • How does a nerve impulse get from one neuron to another? • 1. Synapse • 2. Neurotransmitter • 3. Synaptic transmission

  21. Nerve Impulse Transmission G. Synaptic transmission - What happens to the action potential once it reaches the end of the axon? Synapse (synaptic cleft)- gap between axon & dendrite of neurons

  22. Nerve Impulse Transmission G. Synaptic transmission 1. Impulse reaches end of axon. Calcium ions enter axon bulb. Vesicles release neurotransmitters into synaptic cleft. 2. Receptor sites on dendrites absorb neurotransmitters & new A.P. is produced. (depolarization)

  23. http://staff.washington.edu/cdave/pbio505/Week2Presentation.xmlhttp://staff.washington.edu/cdave/pbio505/Week2Presentation.xml

  24. Synaptic transmission • Click on the link below and then use the Synaptic Transmission animation before going on. • http://outreach.mcb.harvard.edu/animations.htm

  25. NERVE IMPULSES • H. Types of synaptic transmission: • 1. Excitatory • Lowers threshold, easier to depolarize membrane, weaker stimulus works • Examples: ACh, adrenalin (epinephrine), serotonin, dopamine, histamine

  26. NERVE IMPULSES • H. Types of synaptic transmission: • 1. Inhibitory • Raises threshold, harder to depolarize membrane, inhibits transmission of impulse • Examples: ACh, GABA,glycine, noradrenalin (norepinephrine), glutamate

  27. NERVE IMPULSES • Neurotransmitters have very short-lived effects because they are in the synaptic cleft for a very short time. Three things can happen: 1. absorbed by receptors on dendrites 2. reabsorbed by axon 3. destroyed before reaching receptors on dendrites

  28. Action Potential Animations GO TO THIS WEBSITE: http://brainu.org/movies

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