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Human Physiology

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The Nervous System, Membrane Potential ... The Nervous System, The Action Potential. Factors that influence the speed of an AP: ... The Nervous System ... – PowerPoint PPT presentation

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Title: Human Physiology


1
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

2
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 cells Vm
  • Where P is the relative permeability of the
    membrane to the ion
  • See Table 8-2

3
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

4
Human Physiology
The Nervous System, Membrane Potential
  • Passive and active forces that establish and
    maintain the resting membrane potential

5
Human Physiology
The Nervous System, Membrane Potential
  • Graded Potentials

6
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)

7
Human Physiology
The Nervous System, Membrane Potential
8
Human Physiology
The Nervous System, Membrane Potential
  • Graded potentials decreases in strength as they
    spread out from the point of origin

9
Human Physiology
The Nervous System, Membrane Potential
  • Relationship between stimulus strength, local
    potential production, and action potential

10
Human Physiology
The Nervous System, Membrane Potential
  • Neural Integration

11
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

12
Human Physiology
The Nervous System, The Action Potential
  • Changes in membrane permeability during an Action
    Potential

13
Human Physiology
The Nervous System
  • Na channels have two gates

14
Human Physiology
The Nervous System
  • Electrotonic conduction

15
Human Physiology
The Nervous System
  • Saltatory conduction

16
Human Physiology
The Nervous System, The Action Potential
  • Factors that influence the speed of an AP
  • Diameter
  • Resistance to current

17
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

18
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

19
Human Physiology
The Nervous System, The Synapse
20
Human Physiology
The Nervous System, The Synapse
  • The Electrical Synapse

21
Human Physiology
The Nervous System, The Synapse
  • The Chemical Syapse

22
Human Physiology
The Nervous System, The Synapse
  • Types of Chemical Synapses

23
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

24
Human Physiology
The Nervous System, The Synapse
  • Factors Influencing Transmitter Release
  • Amplitude of arriving Action Potential
  • Nerve terminals ability to synthetize, package,
    store, mobilize, and release neurotransmitter
  • Prior activity of presynaptic ending
  • Concentration of Ca in ECF

25
Human Physiology
The Nervous System
  • Types of Synapses

26
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

27
Human Physiology
The Nervous System, Neurotransmitters
  • 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
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