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 cell’s 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 terminal’s 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. 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