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Neurotransmission of Electrical and Chemical Signals

Neurotransmission of Electrical and Chemical Signals -...

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Neurotransmission of Electrical and Chemical Signals (Chapter 8, pp. 255 - 286) 1. Know the Goldman-Hodgkin-Katz equation and be able to predict the membrane potential of a cell given intracellular and extracellular concentrations of Na + and K + V m = 61 log [K+]out + α[Na+] out [K+]in + α[Na+]in GHK is used to calculate the resting membrane potential that results from  the contribution of all ions that can cross the membrane. For mammalian cells,  we assume that Na + , K + , and Cl -  are the three ions that influence membrane  potential in resting cells.  GHK Eq. Vm  =  Pk   [K + ]out  +  P Na [Na +] out  +  P Cl [Cl - ]in/ P [K + ]in  +  P Na [Na +] in  +  P Cl [Cl - out A change in either K   concentration gradient or ion permeability changes the  membrane potential. Example.  At rest, the cell membrane of a neuron is only slightly permeable  to Na + , however, if the membrane suddenly increases its Na +  permeability, Na enters the cell, moving down its electrochemical gradient. The addition of positive  Na +  to the ICF  DEPOLARIZES  the cell membrane and creates an electrical  signal. If the cell membrane suddenly becomes more permeable to K + , positive  charge is lost from inside the cell and the cell becomes  HYPERPOLARIZED  (more negative). A cell may also  HYPERPOLARIZE  if negatively charged ions,  such as Cl - , enter the cell from the ECF. K +  ECF range (3.5-5 mM) ICF 150 mM E ion  = -90 mV Na +  ECF range (135-145 mM) ICF 15 mM E ion  = +60 mV Cl -  ECF range (100-108 mM) ICF (5-15 mM) E ion  = -63 mV 2. Know the events that occur during chemical communication at the synapse o When depolarization of action potential reaches the axon terminal of the pre-synaptic cell: voltage-gated Ca2+ channels open
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Ca2+ moves into the cell and binds to regulatory proteins and initiates exocytosis. Membrane of vesicles that contain neurotransmitters fuses with neuron’s cell membrane (aided by multiple membrane proteins) and the neurotransmitter is released into the synaptic cleft (area between post and pre synaptic neurons). Neurotransmitter moves across gap to bind with membrane receptors on the post-synaptic cell and initiates a response in the post-synaptic cell. 3. Define graded potential. Identify where and how a graded potential can occur on a neuron. Strength can vary Point of origin- dendrites Determined by size of stimulus Only can send short distances- lose strength for long distance Initiated on cell body of dendrites (chemical/electrical channels) 4. Define threshold and action potential. Identify where and how an action potential can occur on a neuron.
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