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Human Physiology. The Nervous System, Membrane Potential. Measurement of Membrane Potential Nernst equation - the electrical potential for a single ion to prevent it from having any net movement across the cell membrane (equilibrium potential, E ion )

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human physiology
Human Physiology

The Nervous System, Membrane Potential

  • Measurement of Membrane Potential
    • Nernst equation - the electrical potential for a single ion to prevent it from having any net movement across the cell membrane (equilibrium potential, Eion)

Where z is the electrical charge on the ion

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Human Physiology

The Nervous System, Membrane Potential

  • Measurement of Membrane Potential
    • Goldman-Hodgkin-Katz equation - the resting membrane potential results from all the ions that can cross the membrane (membrane potential, Vm)
    • In mammalian cells, Na+, K+ and Cl- account for the major contribution to the cell’s Vm

Where P is the relative permeability of the membrane to the ion

    • See Table 8-2
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Human Physiology

The Nervous System, Membrane Potential

  • Nerve and muscle are excitable tissues - they have the ability to generate and propagate electrical signals
    • Depolarized
    • Hyperpolarized
    • Repolarized
    • Hypopolarized
  • Membrane potential influenced by:
    • Concentration gradients
    • Permeability of the membrane to ions
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Human Physiology

The Nervous System, Membrane Potential

  • Passive and active forces that establish and maintain the resting membrane potential
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Human Physiology

The Nervous System, Membrane Potential

  • Graded Potentials
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Human Physiology

The Nervous System, Membrane Potential

  • Graded potentials (depolarization or hyperpolarizations) - see Table 8-3
    • Amplitude varies with strength of triggering event
    • Begin at point where ions enter ECF (local current flow)
    • Local current - net movement of positive charges
    • Amplitude varies inversely with distance
    • They travel until they reach the trigger zone
    • They can be summed - to reach threshold
    • Excitatory PostSynaptic Potential (EPSP)
    • Inhibitory PostSynaptic Potential (IPSP)
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Human Physiology

The Nervous System, Membrane Potential

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Human Physiology

The Nervous System, Membrane Potential

  • Graded potentials decreases in strength as they spread out from the point of origin
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Human Physiology

The Nervous System, Membrane Potential

  • Relationship between stimulus strength, local potential production, and action potential
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Human Physiology

The Nervous System, Membrane Potential

  • Neural Integration
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Human Physiology

The Nervous System, The Action Potential

  • Components/characteristics
    • RMP
    • Depolarizing stimulus
    • Threshold
    • Rapid Na+ entry (depolarization)
    • Isopotential
    • Overshoot
    • Repolarization (K+ moves out)
    • Undershoot (after-hyperpolarization)
    • Absolute refractory period
    • Relative refractory period
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Human Physiology

The Nervous System, The Action Potential

  • Changes in membrane permeability during an Action Potential
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Human Physiology

The Nervous System

  • Na+ channels have two gates
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Human Physiology

The Nervous System

  • Electrotonic conduction
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Human Physiology

The Nervous System

  • Saltatory conduction
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Human Physiology

The Nervous System, The Action Potential

  • Factors that influence the speed of an AP:
    • Diameter
    • Resistance to current
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Human Physiology

The Nervous System, The Action Potential

  • All-or-none response
  • Factors that limit the maximum response of a receptor cell to strong stimuli
    • A finite number of channels
    • Receptor potential cannot exceed the reversal potential of the receptor current
    • Impulse frequencies are limited by the refractoriness
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Human Physiology

The Nervous System

  • Which of the following best describes the physiological significance of the dendrite?
    • A. - Transmitting portion of the neuron
    • B. - Receiving portion of the neuron
    • C. - Conducting portion of the neuron
    • D. - Terminal portion of the neuron
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Human Physiology

The Nervous System, The Synapse

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Human Physiology

The Nervous System, The Synapse

  • The Electrical Synapse
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Human Physiology

The Nervous System, The Synapse

  • The Chemical Syapse
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Human Physiology

The Nervous System, The Synapse

  • Types of Chemical Synapses
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Human Physiology

The Nervous System, The Synapse

  • Events during Synaptic Transmission (Fig 8- 20)
    • Arrival of nerve Action Potential
    • Depolarization of bouton opens Ca++ voltage-gated channels
    • Calcium entry triggers release of neurotransmitter by exocytosis
    • Diffusion of neurotransmitter across synaptic cleft to post-synaptic membrane
    • Transmitter-receptor complex causes change in conductance in post-synaptic membrane
    • Response terminated by removal of neurotransmitter
    • Ionic current flow and generation of post-synaptic potential
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Human Physiology

The Nervous System, The Synapse

  • Factors Influencing Transmitter Release
    • Amplitude of arriving Action Potential
    • Nerve terminal’s ability to synthetize, package, store, mobilize, and release neurotransmitter
    • Prior activity of presynaptic ending
    • Concentration of Ca++ in ECF
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Human Physiology

The Nervous System

  • Types of Synapses
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Human Physiology

The Nervous System, Neurotransmitters

  • Roughly grouped into five (5) classes:
    • Acetylcholine
      • In a class by itself
    • Amino acids
      • Glycine, Glutamate, Gamma-aminobutyric acid (GABA), Aspartate
    • Amino acid-derived amines
      • Catecholamines (Dopamine, Norepinephrine, Epinephrine), Serotonin (5-HT), Histamine
    • Purines
      • Adenosine, ATP
    • Polypeptides
      • Enkaphalins, Endorphins, Dynorphins, Substance P, Somatostatin, Bradykinin, Neuropeptide Y
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The Nervous System, Neurotransmitters

Human Physiology
  • Some criteria for a substance to be a Transmitter Substance
    • Elicits same physiological response when applied to the post synaptic cell
    • It should be released by presynaptic neuron
    • Its action must be blocked by the same agents that block the natural transmission