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Nervous System Part 1

Nervous System Part 1. Organization Resting Membrane Potential Signaling Graded Potentials Action Potentials. Organization. Control System that receives info about internal and external environment, integrates , and directs activities to respond. Divided into the CNS and the PNS.

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Nervous System Part 1

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  1. Nervous System Part 1 Organization Resting Membrane Potential Signaling Graded Potentials Action Potentials

  2. Organization • Control System that receivesinfo about internal and external environment, integrates, and directs activities to respond. • Divided into the CNS and the PNS.

  3. Organization • Consists of 2 classes of cells: • Neurons (20%) – communication • Neuroglia (80%) – many fnctns: structurally supporting, nurturing, insulating, & protecting neutons • Nerves – Bundles of neurons in the PNS

  4. Organization • 3 types on neurons: • Afferent (sensory) neurons • Interneurons • Efferent (motor) neurons

  5. Organization • Main parts of a neuron:

  6. Resting Membrane Potential • A charge difference across the membrane of -70mV at rest. • Has the potential to do work. • K+ and Na + leak channels in the cell membranes establish electrochemical gradients.

  7. Resting Membrane Potential

  8. Resting Membrane Potential • If the cell only had K + channels the equilibrium potential of the cell would be –90mV.

  9. Resting Membrane Potential • If the cell only had Na+ channels the equilibrium potential of the cell would be 60mV.

  10. Resting Membrane Potential • There are more K+ leak channels so Vm is closer to EK than ENa.

  11. Resting Membrane Potential • Active transport Na+/K+ pumps maintain the ion concentrations as seen in table 6-2.

  12. Signaling • Changes in a cell’s membrane potential produce electrical signals. • Graded potentials – signaling over short distances. • Action potentials – signaling over long distances • Terms for the direction of changes relative to resting potential are seen to the right.

  13. Graded Potentials • Changes in membrane potential confined to a small region of a neuron. • They are graded, meaning they can vary in magnitude.

  14. Action Potentials • If the minimum threshold voltage is reached, a graded potential becomes an action potential.

  15. Action Potentials • Voltage-gated sodium and potassium channels are responsible for the depolarization and repolarization of the membrane.

  16. Action Potentials

  17. Action Potentials • Always an all-or-nothing event. • Propagates away from a neuron’s trigger zone.

  18. Nervous System Part 1 (cont.) Action Potentials Review Synapse

  19. Action Potentials Review • ‘http://outreach.mcb.harvard.edu/animations/actionpotential.swf

  20. Action Potentials Review • A typical neuron would have a resting membrane potential of about (A) +70 mV (B) +70 V (C) -70 mV (D) -70 V (E) All of the above are observed at rest.

  21. Action Potentials Review • At the peak of the action potential, the membrane potential is: (A) exactly at the Na+ equilibrium potential (B) close to but more positive than the Na+ equilibrium potential (C) close to but less positive than the Na+ equilibrium potential (D) exactly at 0 mV (E) the same as the resting membrane potential

  22. Action Potentials Review • True or False: Threshold voltage for opening is approximately the same for voltage-gated Na+ and K+ channels. • Voltage-gated Na+ and K+ channels open at the approximately the same threshold voltage… K+ channels are just much more slower at opening wide and closing completely than Na+ channels.

  23. Action Potentials Review • Schwann cells are glia cells that that for the myelin sheath. • They insulate the axons of neurons and increase the rate of action potential propagation.

  24. Synapse • Synapse: the narrow gap b/w 1 neuron & the next. • Neurotransmitter: the chemicals that cross the synapse

  25. Synapse

  26. Synapse • Response by postsynaptic cell depends on: • Type of neurotransmitter • Conc. of neurotransmitter • Type of receptor • Number of receptors • Responsiveness of the receptors

  27. Synapse • Many axon terminals synapse onto one neuron. • Excitatory and inhibitory signals are integrated • All synaptic potentials are graded potentials

  28. Synapse • EPSP: excitatory post-synaptic potentials; depolarization • IPSP: inhibitory post-synaptic potentials; hyperpolarizing • When threshold is reached an action potential is fired down the post-synaptic neuron.

  29. Synapse • Neurotransmitters need to be removed ASAP after signal is complete. • Many helpers: • Diffusion • Enzymes • Protein pumps

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