The Nervous System2


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The Nervous System2

  1. 2. <ul><li>Overlapping functions: </li></ul><ul><ul><li>Sensory input </li></ul></ul><ul><ul><li>Integration </li></ul></ul><ul><ul><li>Motor output </li></ul></ul>
  2. 3. <ul><li>Collect information from the environment </li></ul><ul><ul><li>Internal and external </li></ul></ul><ul><ul><li>Also called the sensory input </li></ul></ul><ul><ul><ul><li>Give the specific type of nerves found in the five basic senses </li></ul></ul></ul>
  3. 4. <ul><li>Processing of input to be interpreted and associated with the correct response </li></ul><ul><li>Processed in the CNS </li></ul><ul><ul><li>Give an example of a correct response from a stimulus </li></ul></ul>
  4. 5. <ul><li>Conduction of signals from integration to effector cells </li></ul><ul><li>Signals are conducted by nerves </li></ul><ul><ul><li>Nerve= tissue (composed of nerve cells) </li></ul></ul><ul><ul><li>Neuron= nerve cells </li></ul></ul>
  5. 6. <ul><li>Through a combination of chemical and electrical signals </li></ul>
  6. 7. <ul><li>Structural and functional unit of the nervous system </li></ul><ul><li>Axon hillock </li></ul>
  7. 8. <ul><li>Dendrites </li></ul><ul><li>Axons </li></ul><ul><li>Axon hillock </li></ul><ul><li>Myelin sheath </li></ul><ul><li>Synaptic terminals </li></ul><ul><li>Synapse </li></ul><ul><li>Presynaptic cell </li></ul><ul><li>Postsynaptic cell </li></ul><ul><li>Neurotransmitter </li></ul>
  8. 9. <ul><li>Simplest- reflex arc </li></ul><ul><ul><li>Reflex – an automatic response </li></ul></ul><ul><ul><li>Simplest reflex arc= two kinds of nerve cells </li></ul></ul><ul><ul><ul><li>Motor and sensory </li></ul></ul></ul><ul><ul><ul><li>Effector cells – muscle or gland </li></ul></ul></ul><ul><ul><ul><li>Knee-jerk= more complex </li></ul></ul></ul><ul><ul><ul><ul><li>Front thigh contracts/inhibition of back thigh </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Involves second circuit (three parts) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Sensory neurons from quadriceps= synapse with interneuron and motor neuron </li></ul></ul></ul></ul>
  9. 11. <ul><li>Always in the CNS </li></ul><ul><li>Also called association neuron, local circuit neuron </li></ul><ul><li>Multi-branched </li></ul><ul><li>Always communicate with each other </li></ul><ul><li>“ memory” </li></ul>
  10. 12. <ul><li>Both are clusters of cell bodies </li></ul><ul><li>Nuclei- found inside the CNS </li></ul><ul><li>Ganglion- found outside CNS </li></ul><ul><ul><ul><li>Take note the difference in structures of sensory neuron, motor neuron and interneuron </li></ul></ul></ul><ul><ul><ul><li>Relate it to their function </li></ul></ul></ul>
  11. 13. <ul><li>Single presynaptic neuron to several postsynaptic neurons </li></ul><ul><li>Convergent of several presynaptic neuron to a single postsynaptic neuron </li></ul><ul><li>Circular path (memory) </li></ul>
  12. 14. <ul><li>Outnumber neurons 10:1 </li></ul><ul><ul><li>Then: glial cells do not participate in nerve signalling </li></ul></ul><ul><ul><li>Now: presence of some synaptic interactions </li></ul></ul><ul><li>Important in structural integrity of the Nervous system </li></ul><ul><li>Normal functioning of neurons </li></ul>
  13. 15. <ul><li>Embryo: radial glia- form tracks where neurons migrate </li></ul><ul><li>Mature CNS: astrocytes – structural and metabolic support; stimulate formation of tight junctions between cells lining the capillaries of the brain (blood-brain barrier </li></ul>
  14. 16. <ul><li>Glia that form myelin sheath around axons of neurons </li></ul><ul><li>Oligodendrocytes – CNS </li></ul><ul><li>Schwann cells- PNS </li></ul><ul><li>Myelin sheath- provides electrical insulation </li></ul>
  15. 21. <ul><li>Change in the voltage across the plasma membrane of neurons </li></ul><ul><li>Caused by movement ions across the plasma membrane </li></ul><ul><ul><li>Ion channels </li></ul></ul>
  16. 22. <ul><li>All cells have voltage across theri plasma membrane </li></ul><ul><li>This membrane potential exists because of difference in ion concentration </li></ul><ul><li>Electrically polarized </li></ul><ul><ul><li>Anion- inside </li></ul></ul><ul><ul><li>Cation-outside </li></ul></ul>
  17. 23. <ul><li>Animal cell: normally -50V to -100V </li></ul><ul><li>Resting state of neuron: -70V </li></ul><ul><li>Resting potential- membrane potential of an unstimulated neuron </li></ul>
  18. 24. <ul><li>Presence of special ion channels </li></ul><ul><li>Selective permeability of the membrane </li></ul><ul><li>Anions do not diffuse readily outside the membrane </li></ul>
  19. 25. <ul><li>Plasma membrane- lipid bilayer </li></ul><ul><li>Lipid- not electrically charged </li></ul><ul><li>Ions cannot dissolved readily (do not diffuse easily) </li></ul><ul><li>Presence of pumps or channels </li></ul>
  20. 26. <ul><li>Presence of more K + channels than Na + channels due to high permeability to K + </li></ul>
  21. 27. <ul><li>Ion channels do not determine the rate and direction of ion movement </li></ul><ul><li>Electrochemical concentration is responsible </li></ul>
  22. 29. <ul><li>-85mV- amount that can counterbalance concentration gradient of K </li></ul><ul><ul><li>Called the equilibrium potential of potassium </li></ul></ul>
  23. 30. <ul><li> </li></ul>
  24. 31. <ul><li>All cells have membrane potential but only neurons and muscle cells can generate large amount of membrane potential </li></ul><ul><ul><li>Excitable cells </li></ul></ul><ul><ul><li>Resting potential- membrane potential of resting cell </li></ul></ul>
  25. 32. <ul><li>Nerve impulses are the action potential generated in a cell that travel through pulse-like wave of voltage though membranes </li></ul><ul><li>Due to stimulus </li></ul>
  26. 33. <ul><li>Ungated ion channels- open all the time </li></ul><ul><li>Gated ion channels </li></ul><ul><ul><li>Chemically-gated ion channel- stimulus: chemical (e.g. Neurotransmitter) </li></ul></ul><ul><ul><li>Voltage-gated ion channel- stimulus: change in membrane potential </li></ul></ul>
  27. 34. <ul><li>Graded potential: change in membrane potential due to strength of stimulus </li></ul><ul><ul><li>Hyperpolarization- membrane potential is more negative </li></ul></ul><ul><ul><li>Depolarization- membrane potential is more positive </li></ul></ul>
  28. 35. <ul><li>Recall: muscle contraction at the cellular level </li></ul><ul><li>Threshold potential </li></ul><ul><ul><li>Action potential- response when threshold potential is met (generated only in axons) </li></ul></ul><ul><ul><li>Threshold potential usually -50mV to -55 mV </li></ul></ul><ul><ul><li>Hyperpolarization do not produce action potentials </li></ul></ul>
  29. 36. <ul><li>Voltage-gated ion channels are stimulated </li></ul><ul><ul><li>Potassium- single voltage-sensitive gate </li></ul></ul><ul><ul><ul><li>Closed- resting state </li></ul></ul></ul><ul><ul><ul><li>Opens slowly in response depolarization </li></ul></ul></ul><ul><ul><li>Sodium- two voltage sensitive gates </li></ul></ul><ul><ul><ul><li>Activation- closed (resting state); opens rapidly during depolarization </li></ul></ul></ul><ul><ul><ul><li>Inactivation- open (resting state); closes slowly in response to depolarization </li></ul></ul></ul>
  30. 37. <ul><li>Responsible in the restoration of the internal membrane potential </li></ul><ul><ul><li>Due to low permeability to sodium </li></ul></ul><ul><ul><li>Inc permeability to potassium </li></ul></ul><ul><ul><li>Hyperpolarization- responsible for refractory period </li></ul></ul>
  31. 39. <ul><li>A domino effect </li></ul><ul><ul><li>always in a forward direction due to refractory period </li></ul></ul>
  32. 40. <ul><li>Diameter of axon- faster if higher diameter </li></ul><ul><ul><li>Current is inversely proportional to the cross section of a wire </li></ul></ul><ul><li>Presence of Schwann cells </li></ul><ul><ul><li>Node of Ranvier- gaps between Schwann cells </li></ul></ul><ul><ul><ul><li>Ion channels are concentrated, extracellular fluid is in contact with the axon membrane at the node </li></ul></ul></ul><ul><ul><ul><li>Saltatory conduction </li></ul></ul></ul>
  33. 41. <ul><li>Unique cell junction that control communication </li></ul><ul><ul><li>Between: 2 neurons, sensory receptors and sensory neurons, motor neurons and muscle cell, neurons and gland cell </li></ul></ul><ul><li>Two types </li></ul><ul><ul><li>Electrical synapse </li></ul></ul><ul><ul><li>Chemical synapse </li></ul></ul>
  34. 42. <ul><li>Less common than chemical synapse </li></ul><ul><li>Cells are connected by gap junctions </li></ul><ul><li>Allows action potential to spread directly from presynaptic terminals to postsynaptic terminals </li></ul><ul><li>No loss of signal strength and delay </li></ul><ul><li>Responsible for rapid movement </li></ul>
  35. 43. <ul><li>Presence of synaptic cleft (gap) </li></ul><ul><li>Electrical signals not directly transmitted </li></ul><ul><li>Signal: electrical-chemical-electrical </li></ul><ul><li>Presence of synaptic vesicles containing neurotransmitter in the presynaptic axon </li></ul><ul><li>Presence of chemical-gated ions </li></ul>
  36. 44. <ul><li>Recall: structure of a neuron </li></ul><ul><li>Presence of inhibitory and excitatory synapses </li></ul>
  37. 45. <ul><li>Depolarization of the plasma membrane </li></ul><ul><li>Results from influx of positive ions (e.g. Na ions) </li></ul><ul><li>Depolarization may lead to an action potential if the threshold potential is met </li></ul><ul><li>This is called EXCITATORY POSTSYNAPTIC POTENTIAL or EPSP </li></ul>
  38. 46. <ul><li>Inc permeability of Cl and K ion channels </li></ul><ul><li>Hyperpolarization </li></ul><ul><li>INHIBITORY POSTSYNAPTIC POTENTIAL or IPSP </li></ul>
  39. 47. <ul><li>Depends on the type of receptor and ion channel at the receiveing end </li></ul>
  40. 48. <ul><li>Region where voltage-gated sodium channels open </li></ul><ul><li>Production of action potential: </li></ul><ul><ul><li>Several synaptic terminals acting simultaneously on one postsynaptic terminal </li></ul></ul><ul><ul><li>Few synaptic terminal discharging neurotransmitter at a greater frequency </li></ul></ul><ul><ul><ul><li>Summation is produced </li></ul></ul></ul>
  41. 49. <ul><li>Temporal: frequency of chemical transmission is great; no time to return to resting potential </li></ul><ul><li>Spatial: presence of many presynaptic neurons stimulating one postsynaptic neuron </li></ul><ul><ul><li>Both are present in IPSP and EPSP </li></ul></ul>
  42. 50. <ul><li>Effects vary </li></ul><ul><ul><li>Can be within a few millisecond </li></ul></ul><ul><ul><li>Can be longer due to signal transduction pathways it enters </li></ul></ul><ul><ul><li>Can remain active over a long period of time </li></ul></ul>
  43. 51. <ul><li>One of the most common among vertebrate and invertebrate </li></ul><ul><li>Can be inhibitory or excitatory depending on the receptor </li></ul><ul><li>Excitatory in muscle cell </li></ul><ul><li>In heart muscle: inhibitory </li></ul><ul><ul><li>Dec ability to create action potential through hyperpolarization </li></ul></ul>
  44. 52. <ul><li>Derived from amino acids </li></ul><ul><li>Function as transmitters in the CNS </li></ul><ul><li>Imbalances result in different disorders </li></ul><ul><ul><li>Parkinson’s disease- low dopamine </li></ul></ul><ul><ul><li>Schizophrenia-high dopamine </li></ul></ul><ul><ul><li>Psychoactive drugs like LSD and mescaline- produce hallucinatory effects by binding to receptors of serotonin and dopamine </li></ul></ul>
  45. 53. <ul><li>Catecholamines- from tyrosine </li></ul><ul><li>Dopamine </li></ul><ul><ul><li>Epinephrine and norepinephrine </li></ul></ul><ul><ul><ul><li>Also functions as hormones </li></ul></ul></ul><ul><li>Serotonin- from tryptophan </li></ul><ul><ul><li>Affects signal transduction pathway </li></ul></ul><ul><ul><li>Affects biochemical processes </li></ul></ul>
  46. 54. <ul><li>GABA- gamma aminobutyric acid </li></ul><ul><ul><li>Transmitter of most inhibitory synapses </li></ul></ul><ul><ul><li>Produces IPSPs by inc Cl permeability </li></ul></ul><ul><ul><li>Present in Valium </li></ul></ul><ul><li>Glycine </li></ul><ul><li>Glutamate </li></ul><ul><li>Aspartate </li></ul>
  47. 55. <ul><li>Short chain amino acids </li></ul><ul><li>Operate via signal transduction pathways </li></ul><ul><li>Substance P- mediates pain </li></ul><ul><li>Endorphins- feel good hormone </li></ul><ul><ul><li>Analgesic; counters pain </li></ul></ul><ul><ul><li>Dec urine output </li></ul></ul><ul><ul><li>Also acts as a hormone </li></ul></ul>
  48. 56. <ul><li>NO and CO as regulators </li></ul><ul><li>Release of NO in penis </li></ul><ul><ul><li>Viagra inhibits enzyme that masks the effect of NO </li></ul></ul><ul><li>Gaseous messengers are not store rather are synthesized </li></ul>