SynapsesA. Neuromuscular Junction (typical ACh synapse)

1. arrival of action potential at terminal bulb triggers opening of voltage-gated Ca++ channels

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Synapses2. Ca++ influx phosphorylation

a. vesicle liberated from presynaptic actin networkb. vesicle binds to presynaptic membrane

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Synapsesexamples of phosphorylated proteins: N-ethylmaleimide-sensitive fusion protein (NSF)

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Synapsessoluble NSF attachment proteins (SNAPs)

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SNAP receptors (SNAREs)

Synapsesvesicle recycled via endocytosis

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Synapsessome neurotransmitter leaks out of cleft

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some inactivated (acetylcholinesterase)

Neuromuscular Junctionremainder binds to postsynaptic receptor on motor end plate

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each vesicle contains enough ACh to trigger miniature end-plate potential (mepp)

Neuromuscular Junctionmepps can sum to generate end-plate potential (epp)

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epps can sum to threshold to generate action potential adjacent to the motor end plate

Neuromuscular Junction DisordersCurare

binds to AChRparalysis

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Neuromuscular Junction DisordersBotulinum toxin

prevents release of AChparalysiscleaves SNARE proteins

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Neuromuscular Junction DisordersMyasthenia gravis

antibody generated against AChRweakness worsens progressively

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Neuromuscular Junction DisordersNeuromyotonia

antibody generated against presynaptic K+ channelsaxon terminal constantly depolarized (cramping)

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Potential TransmissionA. Electrotonic

1. graded2. receptor (generator) potentials

Potential Transmissiona. stimulus, then ∆ Vm

b. electrical signal spreads from source of stimulusc. problem: no voltage-gated channels hered. signal decay“passive electrotonic transmission”

Potential TransmissionA. Electrotonic

3. good for only short distances4. might reach axon hillock

- that’s where voltage-gated channels are- where action potentials may be triggered

Potential TransmissionB. Action potential

1. propagation without decrement2. to axon terminal

Synaptic TransmissionC. Alternation of graded and action potentials

Intraneuron TransmissionA. All neurons have electrotonic conduction (passive)B. Cable properties

1. determine conduction down the axon process2. some cytoplasmic resistance to longitudinal flow3. high resistance of membrane to current

“but membrane is leaky”

Intraneuron TransmissionC. Propagation of action potentials

1. ∆ Vm much larger than threshold- safety factor

Intraneuron TransmissionC. Propagation of action potentials

2. spreads to nearby areas- depends on cable properties- inactive membrane depolarized by electrotonically conducted current

Intraneuron TransmissionC. Propagation of action potentials

- K+ efflux behind region of Na+ influx

Intraneuron TransmissionC. Propagation of action potentials

3. unidirectionala. refractory periodb. K+ channels still open

Intraneuron TransmissionC. Propagation of action potentials

4. speeda. relates to axon diameter and presence of myelinb. axon diameter, speed of conduction

Intraneuron TransmissionD. Saltatory conduction

1. myelinationa. Rm , Cm

b. the more layering, the greater the resistance between ICF and ECF

Intraneuron TransmissionD. Saltatory conduction

c. charge flows more easily down the axon than across the membrane

Intraneuron TransmissionD. Saltatory conduction

2. nodes of Ranviera. internodes (between Schwann cells or oligodendrocytes)b. only exit for currentc. only location along axon where APs are generated

Neuronal Integration

A. Motor neurons as example1. thousands of excitatory and inhibitory terminals on dendrites and soma

- density often highest around hillock- proximity often confers preference

Neuronal Integration

A. Motor neurons as example2. control frequency of firing of motor neuron

- only excitatory stimuli can cause behavior change

Neuronal Integration

A. Motor neurons as example3. these terminals are weak

- multiple stimuli needed to trigger AP- prevents spontaneous activation of motor neurons

Neuronal Integration

B. Spatial summation1. inputs from several synapses summed to simultaneously change Vm

2. often a battle between EPSPs and IPSPs

Neuronal Integration

C. Temporal summation1. second potential follows close after first2. “piggybacks”3. amplifies potential4. spatial and temporal often together