Nerve Tissue Physiology

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Nerve Tissue Physiology
2010-04-01 04:49:06

Notes from Dr. Brames Class
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  1. What makes up the nervous system organization?
    • Central Nervous System (CNS)
    • Peripheral Nervous System (PNS)
  2. What makes up the Central Nervous System?
    The Brain and Spinal Cord
  3. The PNS is divided into what two systems?
    • 1. The Somatic Nervous System (motor neurons)
    • 2. The Autonomic Nervous System (ANS)
  4. What makes up the Peripheral Nervous System?
    All other nerve tissues
  5. The autonomic nervous system has two branches. They are?
    • Sympathetic nervous system
    • Parasympathetic nervous system
  6. Nervous tissue contains what two primary cell types?
    Neuron and Glial Cells
  7. What does a neuron cell do?
    Transmits nerve impulses from one part of the body to another
  8. What do glial cells do?
    They are the support cell for the nervous system. Some glial cells are found in the CNS, others in the PNS.
  9. How many and what are the glial cells in the CNS?
    There are 4 glial cells in the CNS,and they are the Astrocytes, Ependymal cells, Oligodendrocytes, and Microglia.
  10. What are the astrocytes?
    Constitute 90% of CNS tissue in some areas of the brain. Star-like shape. Physically support neurons and form the Blood-Brain-Barrier (BBB)
  11. What are the Ependymal cells?
    Like cubodial epithelium (but no basement membrane). Line the internal cavities of the brain. Create the cerebrospinal fluid by filtering fluid out of the choroid plexus (a tuft of blood vessels next to the brain).
  12. What are the Oligodendrocytes?
    They form the myelin sheath in the CNS by wrapping each arm around a neuron. Look like an octopus, with up to 15 arms (one cell can wrap up to 15 neurons).
  13. What is the microglia?
    It acts as immune cells for nervous tissue. Phagocytize (=eat) dead matter or debris in the CNS, respond to infections
  14. What are the glial cells in the PNS?
    Schwann cells and Satellite cells
  15. What are Schwann Cells?
    Form the myelin sheath in the PNS by wrapping themselves around neurons. Unlike oligodendrocytes, one Schwann cell wraps around one neuron.
  16. What are Satellite cells?
    They surround neuron cell bodies. Function unknown.
  17. What is the nerve structure from outside to inside?
    • Epineurium-surrounds the nerve as a whole
    • Perineurium-surrounds each fascicle (bundle of neurons)
    • Endoneurium-surrounds each neuron on the outside of the myelin sheath
    • Neurons are arrange in connective tissue sheaths similar to muscles. The terms "neuron" and "nerve" are NOT synonymous.
  18. What is the reflex arc made up of?
    • 1. Sensory receptor
    • 2. Sensory (afferent) neuron
    • 3. Interneuron
    • 4. Motor (efferent) neuron
    • 5. Muscle or gland
  19. What does the Sensory Receptor do in the reflex arc?
    Such as a receptor on the skin. Receives input from the environment, such as pain from putting your hand on a hot stove.
  20. What is the Sensory (Afferent) Neuron in the reflex arc?
    It transmits the pain signal from the receptor to the CNS.
  21. What is the Interneuron in the reflex arc?
    Inside the spinal cord. A neuron that connects the sensory neuron with the motor neuron. Makes up 90% of the body's neurons. Process information and make decisions about how to respond to stimuli.
  22. What does the Motor (Efferent) Neuron do in the reflex arc?
    Carries information from the CNS to muscles (skeletal muscles) and glands (smooth muscles).
  23. What does the Muscle or Gland have to do with the reflex arc?
    Contracts in an adaptive response to the original stimulus.
  24. What are the parts of the neuron?
    Cell body (soma), dendrite, axon hillock, axon, synaptic knob, axolemma, neurilemma, myelin sheath, node of ranvier, synaptic gap
  25. What does the Cell Body (Soma) contain?
    It contains the nucleus, endoplasmic reticulum, mitochondria, ribosomes, etc.
  26. What does the Dendrite do?
    It receives the nerve impulse coming from the pre-synaptic neuron, or repsonds to the mechanical, electrical, or thermal (heat/cold) stimulation.
  27. What is the Axon Hillock?
    It the the enlarged portion of the axon, where the cell body connects with the axon.
  28. What does the Axon do?
    It transmits action potential to the synaptic bulb.
  29. What is the Synaptic knob and what does it contain?
    (=synaptic bulb, terminal button) it is a small enlargement at the end of the axon; contains neurotransmitters
  30. What is the Axolemma?
    The cell membrane around the axon.
  31. What is the Neurilemma?
    The outermost layer of the Schwann cell around the neuron.
  32. What is Myelin Sheath?
    Fatty substance surrounding many neurons, speeds up impulse transmission.
  33. What is a Node of Ranvier?
    The small gap between myelin sheaths, about 1mm apart, where the axon is exposed to the extracellular fluid.
  34. What is the Synaptic Gap?
    The tine space between the pre-synaptic neuron and the target tissue (dendrite of post-synaptic neuron, muscle sarcolemma, gland, etc) Not technically part of the neuron.
  35. The cell body contains what? Give another name for it?
    It contains rough endoplasmic reticulum (=ER + attached ribosomes), which is also known as Nissl substance ( or Nissl bodies) in the neuron
  36. Resting Membrane Potential: Outside the axon? Inside the axon?
    • Outside the axon: sodium (+), chloride (-)
    • Inside the axon: proteins (-), potassium (+)
  37. What is the value of the Resting Membrane Potential?
  38. True or False? The inside of the axon must be maintained relatively negative, when compared to the outside.
  39. True or False: The sodium builds up on the outside, creating an overall positive charge on the outside.
  40. What is the Membrane Permeability?
    The membrane is hardly permeable to both Na+ and K+, but is slightly more permeable for K+ than for Na+
  41. What are Potassium Leak Channels and Sodium Leak Channels?
    • Potassium Leak Channels: Allow a small amount of potassium to leak out of the cell
    • Sodium Leak Channels: Allow a very small amount of sodium to leak into the cell
  42. What is the Sodium-Potassium pump?
    Uses active transport to simultaneously pump 3Na+ OUT and 2K+ IN. Consumes 1 ATP for every exchange cycle.
  43. What is Depolarization?
    A change in the membrane potential toward zero
  44. What is Repolarization?
    A change in the membrane potential back toward the negative
  45. What is hyperpolarization?
    A change in the membrane potential beyond the resting potential (below -70mV)
  46. What is Action Potential?
    Involves the movement (=propagation) of the nerve impulse down the axon, by using changes in the membrane potential. An action potential only occurs if the threshold (-55mV) is met.
  47. What are the 7 steps of Action Potential?
    • 1. A neuron at rest maintains a resting potential of -70mV
    • 2. An incoming impulse cause the potential to become slightly depolarized
    • 3. If the threshold is reached, the action potential will occur. If the threshold is NOT reached, the potential will just fall back to the resting potential. This is called the "All-or-None Principle"
    • 4. If the threshold is reached, the sodium voltage-gated channels will open, and sodium will rush INTO the axon. This causes the membrane potential to rise quickly from -55mV up to about +35mV (=depolarization)
    • 5. At this peak, the sodium voltage gated channels will close, and potassium voltage-gated channels will open, allowing potassium to rush OUT of the azon. This causes the membrane potential to drop back down to -70mV and beyond (=repolarization)
    • 6. Because potassium gates stay open longer than sodium gates, the potential typically drops below 70mB, moving down to about -72mV. The name of this phase where the potential goes very low is-hyperpolarization. During hyperpolarization the action potential cannot be re-activated because the starting point would be too low for the initial stimulus to reach the threshold - this is called the refractory period. At the end of this phase, both sodium and potassium voltage-gated channels are closed.
    • 7. The Na+K+ pump now quickly pumps out the sodium back out and the potassium back in, using a 3 Na+/2K+ ratio. This causes the membrane potential to move back up to the resting potential of -70mV. The neuron is now ready to "fire" again.
  48. Depolarization is an example of what? Why?
    Is an example of a positive feedback system (where the "outcome accelerates the process") because depolarization of one area of the axon triggers depolarization of the next area.
  49. What is Propagation?
    The action potential causes full depolarization of area #1. That area becomes overall positive, which attracts the negative proteins from area #2. As area #2 now becomes slightly more positive (=less negative), it reaches threshold, causing the opening of sodium voltage-gated channels, and sodium rushes into the axon. As the inside of the axon in area #2 becomes fully positive, that attracts proteins from area #3. And so on. This movement of the action potential is called propagation or conduction.
  50. What is Continuous Conduction?
    The movement of an action potential down an umyeylinated axon using the mechanism described above in propagation. Relatively slow, around 2m/sec
  51. What is Saltatory Conduction?
    The movement of an action potential down a myelinated axon. The neural impulse "jumps" from one node of Ranvier to the next (they are spaced about 1mm apart), and gets recharged at the Node of Ranvier. Much faster: up to 120m/sec
  52. What is a Synapse?
    The area where one neuron's synaptic bulb meets up with the target tissue (muscle cell, second neuron, etc.)
  53. What is the Synaptic Gap?
    The microscopic gap between the pre-synaptic neuron and the target tissue (if neuron, called post-synaptic neuron).
  54. True or False: As the action potential travels down the axon, it eventually reaches the synaptic bulb. There, the changes in voltage trigger the release of calcium into the axon.
  55. True of False: The calcium facilitates the release (exocytosis) of neurotransmitter vesicles into the synaptic gap. These vehicles had been stored at the synaptic bulb. The vesicles then fuse with the synaptic bulb membrane, causing the release of their contents (neurotransmitters), which then float across the synaptic gap.
  56. T or F: The neurotransmitters then bind with the membrane on the target tissue (the sarcolemma of a skeletal muscle cell, or the dendrite of a post-synaptic neuron)
  57. What are two possible effects of synaptic transmission?
    The target tissue is excited (=stimulated) or the target tissue is inhibited
  58. What are the Neurotransmitters?
    Acetylcholine, Norepinephrine, Dopamine, Serotonin, Glycine, GABA, and Glutamate.
  59. What is Acetylcholine?
    Used for activating skeletal muscle cells, and used for activating neurons in the autonomic nervous system. For skeletal muscle cells, the acetylcholine is released from the pre-synaptic neuron. Acetylcholine binds to receptors on the sarcolemma at the neuromuscular junction. This triggers activation of an action potential that spreads across the sarcolemma, dives down the T-tubule, triggers release of calcium from the SR, etc. End result: MUSCLE CONTRACTION
  60. What is Norepinephrine?
    Has a primary role in the sympathetic division of the autonomic nervous system. Also has a role in dreaming, waking, and elevating mood.
  61. What is dopamine?
    Found in the "pleasure center" of the brain. Involved in elevation of mood and control of skeletal muscles.
  62. What is Serotonin?
    Has a role in relaxing the body during sleep, and elevating mood
  63. What is Glycine?
    Inhibitory neurotransmitter, and also an amino acid
  64. What is GABA?
    An inhibitory neurotransmitter, and also an amino acid
  65. What is Glutamate?
    Excitatory neurotransmitter, and also an amino acid. Involved in learning and memory. MSG (monosodium glutamate, a food additive) causes overstimulation of these receptors.
  66. T or F: Neurons form pathways of circuits, which helps the nervous system stay organized and "plastic"
  67. What are the type of Neural circuits?
    • Diverging Circuit
    • Converging Circuit
    • Reverberating Circuit
  68. What is the Diverging Circuit?
    One nerve fiber synapses with several postsynaptic cells. Allows one motor neuron to ultimately stimulate thousands of muscle fibers
  69. What is a Converging Circuit?
    several nerve fibers converge into one neuron. Allows multiple neurons to be channeled to a particular area of the brain
  70. What is a Reverberating Circuit?
    Neurons stimulate each other in a linear sequence, but some neurons send an axon collateral back to the first neuron. Allows repetitious signals to be sent to your diaphragm, to make you inhale.