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LECTURE 8: SYNAPTIC TRANSMISSION OVERVIEW AND NMJ. REQUIRED READING: Kandel text, Chapters 10,11. In humans, 10 11 neurons, each receiving average of 100-1000 synaptic inputs = 10 14 synapses !!!. Multiple synapses allows a neuron to integrate information from many sources.

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slide1

LECTURE 8: SYNAPTIC TRANSMISSION OVERVIEW AND NMJ

REQUIRED READING: Kandel text, Chapters 10,11

In humans, 1011 neurons, each receiving average of 100-1000 synaptic inputs

= 1014 synapses !!!

Multiple synapses allows a neuron to integrate information from many sources.

Purkinje cells are the output cells of cerebellum, each receiving 105 inputs,

enabling the cerebellum to monitor complex body movement and provide continual

corrective signals (a corrective guidance system)

Synapses undergo short-term and long-term functional adaptation.

Adaptation is synapse-specific, not affecting other synapses on same cell.

Short-term adaptation allows an organism to ignore certain repetitive

or prolonged sensory inputs.

Long-term adaptation is a cellular mechanism of learning and memory.

slide3

NEAR-INSTANTANEOUS TRANSMISSION ACROSS ELECTRICAL SYNAPSES

Synaptic transmission is

graded, occuring even

in the absence of

action potential

Transmission can be

BI-DIRECTIONAL

FIGURE 10-3

slide6

STEPS OF TRANSMISSION AT CHEMICAL SYNAPSES

Chemical synaptic transmission has a 0.3 - 5 msec delay,

depending upon type of post-synaptic receptor

Chemical synaptic transmission can depolarize or inhibit depolarization,

depending upon type of post-synaptic receptor

Sub-threshold presynaptic depolarizations are not transmitted

slide8

DIRECTLY GATED MONOSYNAPTIC TRANSMISSION

AT THE NEUROMUSCULAR JUNCTION

Large size of vertebrate neuromuscular junction has facilitated electrophysiological

and morphological analysis of this synapse

Each muscle fiber receives input from a single motor neuron axon

Synaptic transmission employs a single neurotransmitter, acetylcholine (Ach) and a single species of directly-gated neurotransmitter receptor (nicotinic AChR)

slide9

THE EXCITATORY POST-SYNAPTIC POTENTIAL

When recording Vm near

endplate, stimulation of

motor axon generates complex

depolarization in muscle fiber,

consisting of an excitatory

postsynaptic potential (EPSP)

and a following

action potential (AP).

Partial inhibition of AChRs

With curare reduces EPSP

Below firing threshold

For AP.

slide11

EPSP CURRENT OBEYS OHM’S LAW

IEPSP = gEPSP x (VM - EEPSP)

slide12

SMOOTH EPSP CURRENT IS SUM OF CURRENTS

FROM OPEN ON/OFF CHANNELS

SINGLE-CHANNEL PATCH VOLTAGE CLAMP RECORDING OF ACETYLCHOLINE-INDUCED CURRENT

REVERSAL POTENTIAL OF SINGLE CHANNEL SAME AS FOR OVERALL EPSP

slide16

NEXT LECTURE: Synaptic Integration

READING: KANDEL text, Chapter 12