MCB 407

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MCB 407
September 11, 2007 Neural Connections Electrical
Synapses Chemical Synapses
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Monosynaptic reflex
recall the two synapses we encountered in the
monosynaptic spinal reflex
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ELECTROTONIC POTENTIALS passive local graded A
CTION POTENTIAL actively propagated all-or-none
(non-decrementing)
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Types of junctions between nerve cells
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re Rm / p(rad)2 where Rmmembranes specific
resistance (rad)radius of cell process
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rc 2re 2Rm / p(rad)2
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Fig 10-1
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Fig 10-2
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Nicholls 9.2 B,C
Electrical synaptic transmission at crayfish
giant synapse
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Passive Properties Important Here VIR!
Fig 10-3
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Fig 10-4
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Kandel 11-5
Channels in gap-junction membrane (negative- stai
ning TEM)
Kandel 11-5
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Fig 10-4
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Gap-junction channels
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Fig 10-5
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Fig 10-5
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Monosynaptic reflex
recall the two synapses we encountered in the
monosynaptic spinal reflex
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Chemical synapses -- transmission is mediated by
secreted neurotransmitter
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Fig 10-6
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Chemical synapse on a postsynaptic spine
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Fig 10-7
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Ionotropic Receptors Metabotropic Receptors
Fig 10-8
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In-Class Exercise
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At a chemical synapse neurotransmitter acts on
postsynaptic membrane at specific
receptors, changing gion(s) (usually but not
always increasing gion(s))
Because Iion gion (Vm Eion), if the
transmitter changes gion for an ion under a net
driving force ..
Iion will change!
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Which ions are involved determines the effect of
the synaptic event.

• If the transmitter-sensitive g increases net flux
  of charge into
• the postsynaptic cell, then the result is
  ..

depolarization (excitation)
2) If the transmitter-sensitive g increases net
flux of charge out of the postsynaptic
cell, then the result is ..
hyperpolarization (inhibition)
but beware . inhibitory synaptic activity need
not result in hyperpolarization!
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frog neuromuscular junction (nmj)