w-4 synaptic signaling and structure

Question 1

Overview of electrical synapses:

Answer 1

• Connexons on each pre- andpost-synaptic membrane precisely align to form pore (gap junctions)
• Direct, passive flow of electrical current
• 6 connexins form the connexon hemi-channel
• Each connexin has 4 transmembrane domains
• Connexon pore is >1nm
• Larger than voltage-gated ion channels
• Variety of ions and molecules (>100kDa) can diffuse

Question 2

Electrical synapses allow fast transmission of signal:

Answer 2

• Signal can be bi-directional, which enables synchronization
• Useful in development – patterning of the nervous system
• Enables the release/transfer of hormones between neurons

Question 3

Classes of neurotransmitters:

Answer 3

• small molecule neurotransmitters
• neuropeptides

Question 4

small molecule neurotransmitters:

Answer 4

• Typically mediate rapid action potentials
• Usually synthesized in the presynaptic terminal
• Most are packaged into small clear-core vesicles

Question 5

Neuropeptides:

Answer 5

• Typically modulate slower and ongoing neuronal functions
• Synthesized in the soma and transported in vesicles via axonal transport
• Large dense-core vesicles

Question 6

Synaptic transmission at the neuromuscular junction:

Answer 6

• Stimulating the presynaptic axon results in release of acetylcholine at the NMJ endplate, resulting in an end plate potential (EPP)
• Synaptic delay is observed, which is typical for a chemical synapse
• Spontaneous (no stimulation) mini endplat potentials (MEPP) observed
• Lowering extracellular Calcium results in subthreshold EPPs that fluctuate