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Potentials and Synapses

Potentials and Synapses. Ch. 12-4. Graded Potentials. When a stimulus causes a channel to open or close in an excitable cell Causes more polarization (more - inside) Causes less polarization (less – inside) Hyperpolarized (much more – inside) Depolarized (much less – inside)

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Potentials and Synapses

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  1. Potentials and Synapses Ch. 12-4

  2. Graded Potentials • When a stimulus causes a channel to open or close in an excitable cell • Causes more polarization (more - inside) • Causes less polarization (less – inside) • Hyperpolarized (much more – inside) • Depolarized (much less – inside) • Graded signals – vary in size • Spread out along plasma membrane and die out • Only used for short distance communication

  3. Generation of Action Potentials • Action potential (AP) or impulse – sequence of rapidly occurring events that take place in two phases • Depolarizing phase – negative membrane potential becomes • Less negative • Reaches 0 • positive • Repolarizing phase – membrane potential is • Restored to the resting state of -70 mV

  4. Action Potential

  5. Depol. vs. Repol. • Na+ channels open • Na+ rushes into cell • All or none principle • when depolarization reaches the threshold, the AP occurs • AP is always the same size • Like dominos – no matter how hard you push the first domino they will all fall or they won’t – same goes for the AP K+ channels open K+ flows out of cell

  6. Depolarizing Phase Na+ channels open rapidly – Na+ rushes into the cell Potential goes from -55 to +30 (inside is 30 more positive than the outside) The more Na+ there is, the more channels open – this is a ____________-feedback mechanism

  7. Repolarizing Phase K+ channels open as the Na+ channels are closing Na+ inflow slows, K+ outflow increases Potential goes from +30 to -70

  8. Depol. and Repol.

  9. Painkillers Local anesthetics – block pain and other body sensations Novacaine or Lidocaine Block the opening of Na+ channels The nerve impulse can’t go past the blocked region – CNS never gets the message that there is pain

  10. Synaptic vocabulary • Presynaptic neuron – the one sending the signal • Postsynaptic neuron – the one receiving the signal • 3 types • Axodendritic – axon to dendrite • Axosomatic – axon to body cell • Axoaxonic – axon to axon

  11. Electrical Synapse • Action potentials conduct between cells through gap junctions • Tunnels connect the two cells together and the electrical impulse can pass • places: • Smooth muscle, cardiac muscle, developing embryo • advantages: • Faster – don’t have to “jump the gap” • Synchronization – allows groups of cell’s to work together – heart beating

  12. Electrical Synapse

  13. Chemical Synapse • Pre- and post-synapses do not touch – separated by synaptic cleft • Transfer of signal must occur • Pre-synaptic neuron turns electrical signal into chemical signal (neurotransmitter) • Post-synaptic neuron turns chemical signal into electrical signal • this transfer takes more time than electrical signals

  14. Chemical Synapse Nerve impulse arrives Depolarizing phase opens Ca++ channels, Ca++ flows in Ca++ causes release of NT from vesicles NT binds to receptors on postsynaptic neuron Action potential continues (Na+, K+, Cl-)

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