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Part Fundamentals of Physiology Part II Food, Energy, and Temperature Part III Integrating systems Part IV Movement and

Part Fundamentals of Physiology Part II Food, Energy, and Temperature Part III Integrating systems Part IV Movement and Muscle Part V Oxygen, Carbon dioxide, and Internal Transport Part VI Water, Salts and Excretion. Part III Integrating System. Chp 11 Neurons Chp 12 Synapses

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Part Fundamentals of Physiology Part II Food, Energy, and Temperature Part III Integrating systems Part IV Movement and

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  1. Part Fundamentals of Physiology • Part II Food, Energy, and Temperature • Part III Integrating systems • Part IV Movement and Muscle • Part V Oxygen, Carbon dioxide, and Internal Transport • Part VI Water, Salts and Excretion

  2. Part III Integrating System • Chp 11 Neurons • Chp 12 Synapses • Chp 13 Sensory processes • Chp 14 Nervous system organization and biological clocks • Chp 15 Endocrine and Neuroendocrine Physiology • Chp 16 Reproduction • Chp 17 Integrating Systems at Work: Animal Navigation

  3. Chp 11Neurons Integrating System

  4. Integration: process of summing and coordinating responses for harmonious function Whole animal integration involves many system, especially CNS and endocrine systems Nervous control tends to control fast process Endocrine system controls body functions which take a long time to develop The physiology of control:Neurons and endocrine cells

  5. Tissue organization • Neurons • Glial cells (support cells) • Astrocytes • Microglia • Ependymal cells • Oligodendrocytes • Schwann cells • http://fig.cox.miami.edu/~cmallery/150/neuro/neurophysiology.htm

  6. Basis for Membrane Potentials • The cell membrane is selectively permeable and does not allow free crossing of the following ions: • Na+ ions are more abundant in the IF • K+ ions are more abundant in the ICF • Proteins, mostly negatively charged are abundant in the ICF (and plasma) but not in the IF • The imbalance in ions creates a difference in potential  -70 mV (more – ions inside)

  7. Membrane potential

  8. Resting membrane potential • At rest, the ions are at electrochemical equilibrium (-65-70 mV) • The equilibrium can be calculated using Nernst equation • E = RT/zF ln(Cout/Cin) • For mammals, at 37oC: E(mV) = 61 log10(Cout/Cin) • Ions are slowly leaking out through leak channels • Ions are shipped back by the Na+K+ATPase pump.

  9. The Action Potential • Not all neurons are able to generate an action potential • Action potentials are voltage-dependent, all-or-none electric signals • They are triggered when the membrane potential reaches the threshold • Once initiated, they travel along the axon, unchanged, at constant speed

  10. Phases of the Action Potential • The rising phase: Na+ channels (activation gate) open  Na+ rushes into the cell  the membrane potential becomes positive • The increase in membrane potential to +40mV triggers the closure of the Na+ channel (inactivation gate) and the opening of the K+channels • The membrane potential turns more negative until overshoot -90 mV • The Na+ channel activation gate closes while the inactivation gate opens • Na+K+ATPase pump re-establish normal state

  11. Ion movements during an AP do not significantly changes bulk ion concentrations There are variations in the mechanisms of cell excitation However, the AP described is found in vertebrate, invertebrate myelinated and unmyelinated neurons Two variations in this model: Graded potentials in non-spiking neurons Pacemaker potentials of spontaneously active cells

  12. Pacemaker cells • Rapid entry of Na+ through channels  rapid rise in voltage • Opening of K+ channels  beginning of repolarisation • Also, opening of calcium ion channels  opposes K+ effect  plateau around 0 mV • Closure of Ca++ channels after 20 ms  long plateau phase • Repolarisation proceeds • This enables the cardiac muscle to pump blood

  13. Propagation of action potential • The change in voltage from an AP affects the neighboring Na+ channels  they open  new AP • Previous channels are still recovering from the passing AP they cannot re depolarize  refractory period • The speed of an AP is a function of the myelination state of the axon and its diameter

  14. Propagation of action potential

  15. Types of conduction: • Continuous • Saltatory

  16. Nerve fibers are organized in circuits which enable a reaction to stimulation

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