Biomedical Core

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Author:
faulkner116
ID:
192827
Filename:
Biomedical Core
Updated:
2013-01-14 18:42:44
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Module11
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Description:
Objective 20-25
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  1. A synapse is
    a point of contact between a neuron and another neuron, or an effector cell.
  2. A synapse sends information only in one direction, from the axon terminal of the neuron which releases ____________, to the neuron of another cell which has ___________ ________.
    neurotransmitter; transmitter receptors
  3. The cell sending the information is called the
    Presynaptic cell
  4. The cell, with receptors for the transmitter, that receives the information is called the
    Postsynaptic cell
  5. The area between the two cells is called the
    synaptic cleft
  6. Specializations of the presynaptic cell include synaptic vesicles,
    tiny spheres of membrane that contain packets of neurotransmitter molecules. (These packets, called quanta, consist of an estimated 4000 acetylcholine molecules each at the neuromuscular junction).
  7. The presynaptic cell is thrifty with the energy used to make transmitter, and often has
    reuptake pumps that remove transmitter from the synaptic cleft and re-use it.
  8. Some neurons have inactivating enzymes which
    help to terminate the action of transmitter, so that it does not hang out in the cleft and continually re-bind the receptor.
  9. Chemical Synapse:

    First 3 in order
    1. Action potential arrives at synaptic end bulb

    2. The action potential triggers the opening of voltage-gated calcium channels, found only at synapses. Since Ca++ inside the cell is virtually zero, Ca++ ions rush in

    3. Ca++ interacts with synaptic vesicles, causing them to move to the presynaptic terminal membrane and fuse. (resulting shape is called an omega figure)
  10. Chemical Synapse:

    Last 3 in order
    4. Neurotransmitter diffuses across the synaptic cleft and binds to postsynaptic transmitter receptors

    5. The receptor protein changes its shape, which opens or closes a gate, and ions flow

    6. The resulting ion flow causes the cell to become more negative (IPSP) or more positive (EPSP)
  11. In some cases, receptor binding causes a biochemical rather than an electrical change. This type of receptor is called
    Metabotropic
  12. Inactivation or reuptake of neurotransmitter
    inactivation by enzymes

    reuptake by pumps

    or both
  13. Just like the tertiary and quaternary structure of hemoglobin changes when it binds oxygen, the structure of protein channels in neurons can change under on of two conditions:
    1. When a chemical, such as a neurotransmitter, outside the neuron binds to a special site on the channel (ligand-gated channel)

    2. When the voltage (electrical potential) across the membrane changes, changing the distribution of charges surrounding the channel protein (voltage-gated channels)
  14. When ligand (neurotransmitter) binds to its receptor,
    the receptor changes shape and opens a pore
  15. Ion Channels in Neurons:

    Name them
    • Leakage Channels
    • Ligand-Gated Channels

    Mechanically-Gated Channels

    Voltage-Gated Channels
  16. Leakage Channels
    -Gated channels that randomly open and close

    -Nearly all parts of all nerve cells
  17. Ligand-Gated Channels
    -Gated channels that open in response to mechanical stimulus

    -Dendrites of some sensory neuron, dendrites and cell bodies of interneurons and motor neurons
  18. Mechanically-Gated Channels
    -Gated channels that open in response to mechanical stimulus

    -Dendrites of some sensory neurons such as touch, pressure, or pain receptors
  19. Voltage-Gated Channels
    -Gated channels that open in response to a voltage stimulus (change in membrane potential)

    -Axons of all types of neurons
  20. "Leak" channels open and close randomly, not
    gated
  21. Active channels open in response to a stimulus (they are "gated")
    Ligand-gated (neurotransmitter or drug)

    Mechanically-gated (pressure receptor)

    Voltage-gated (essential for action potentials and synapses)
  22. Ligand-Gated Channels vs Voltage-Gated Channels
    • Ligand-gated
    • -Binding of a chemical outside the neuron opens or closes the gate

    -acetylcholine (ACh) binds the ACh receptor ---> protein changes shape, and channel opens

    • Voltage-gated
    • -voltage changes from resting (-70mV) to more positive ("depolarized")---> protein changes shape, and channel opens.
  23. Inhibition is defined as
    any change in the neuron which makes it more difficult to reach threshold.
  24. An inhibitory postsynaptic potential, then, is a change in the
    post-synaptic cell, triggered by the opening or closing of an ion channel, which moves the membrane potential further away from threshold
  25. Excitation is defined as
    any change in the neuron which makes it easier to reach threshold.
  26. Excitatory postsynaptic potential is a change in
    the post-synaptic cell, triggered by the opening or closing of an ion channel, which moves the membrane potential closer to threshold
  27. Spatial Summation
    If EPSPs arrive near the same location, they are more likely to reach threshold
  28. Temporal Summation
    If EPSPs arrive near the same time, they are more likely to reach threshold
  29. Graded potentials such as EPSPs and IPSPs decrement in
    space and time
  30. Neurons Process Information Through Spatial and Temporal Summation of IPSPs and EPSPs
    * An "average" neuron receives 10,000 synaptic inputs

    *This allows an exquisite level of information processing

    *Temporal and spatial summation of graded potentials ends up causing a change at the trigger zone

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