Physiology G6001 Nerve and Synapse

Classical elements of synaptic transmission: Neuromuscular junction

Transmitter release

Synaptic currents

Synaptic potentials

Nerve-nerve synapses

Synaptic integration

Summation

Facilitation

Recording from the neuromuscular junction (NMJ).

Spontaneous release of a vesicle of Ach causes a miniature endplate potential or MEPP

Evoked release following stimulation of the motor neuron causes an endplate potential or EPP

Presynaptic calcium channels at the neuromuscular junction (NMJ)

Pre and postsynaptic changes in membrane potential during transmitter release

The quantal nature of transmitter release.

Decrease the amplitude of evoked release by recording in low Ca2+ bath.

NMJ – an inward current drives the change in membrane potential

Slide 16

Reversal potential
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I_EPSP = g_EPSP x (Vm-E_EPSP)

Membrane time constant – a review

Synaptic potential is not actively propagated

ACh binds to the nicotinic ACh receptor, causing it to gate open. The channel is permeable to both Na⁺ and K⁺.

The end-plate potential causes voltage gated Na⁺ channels to open and an action potential to fire.

An EPP in normal muscle is super-threshold for firing action potential

Heuser and Reese – two synapses in the cerebellum

Classes of neurotransmitter receptors

Excitatory synaptic transmission is mediate by glutamate receptors

Current-voltage relationship for synaptic currents mediated by AMPA and NMDA receptors

Inhibitory synaptic transmission is mediated by GABA and glycine receptors

Membrane time constant – a review

What determines the time course of the synaptic potential?

Temporal summation depends on the passive membrane properties of the neuron or muscle

Summation is postsynaptic while facilitation is usually presynaptic

Summation of EPSP and IPSP

The trigger zone

The synaptic potential is not actively propagated. The rate of decay with distance is exponential:
DV(x) = DV₀ e^-x/^land l ~ (r_m/r_a)

Different synaptic configurations including axo-somatic, axodendritic and axo-axonic

Implications of synapse location

Temporal and spatial summation: importance of time constant t and length constant l

Three forms of modulation of synaptic transmission mediated by metabotropic receptors

Berne and Levy – chapter 4

or

Kandel, Schwartz, and Jessell – chapters 11 and 12

or

Kandel, Schwartz, and Jessell – chapters 10-15

The reversal potential is determined by the concentrations of ions flowing through the synaptic channel.


		Classical elements of synaptic transmission: Neuromuscular junction
			Transmitter release
			Synaptic currents
			Synaptic potentials
		Nerve-nerve synapses
		Synaptic integration
			Summation
			Facilitation