Synaptic Transmission

Question 1

What special function do presynaptic terminals serve?

Answer 1

They are able to convert electrical signals propagated down the axon into chemical signals.

Question 2

How do post synaptic potentials differ from action potentials?

Answer 2

They are small graded changes

Question 3

What mediates anterograde transport in axons? What is the cargo?

Answer 3

Kinesin (ATP driven) mediates transport of mitochondria and vesicles from soma to terminals.

Question 4

What mediates retrograde transport in axons? What is the cargo?

Answer 4

Dynein transports degraded vesicular membranes and absorbed toxins/ viruses/ growth factors from terminal to soma

Question 5

What are gap junctions more commonly used for?

Answer 5

They are common and critical for synchronous electrical coupling in visceral smooth muscle and cardiac muscle.

Question 6

What do electical synapses allow?

Answer 6

Speed and synchrony. They are fast and often bi directional.

Question 7

What do chemical synapses allow?

Answer 7

They provide directionality, amplification, potential for both excitation and inhibition, plasticity, and integration in space and time.

Question 8

What is a Postsynaptic density (PSD)? What are they useful for?

Answer 8

PSDs contain an electron dense area with many receptors. They are near active zones of the presynaptic axon. PSDs increase with plasticity and memory.

Question 9

How is exocytosis controlled at the presynaptic terminal?

Answer 9

By voltage gated calcium channels that open when depolarized. There a V-SNAREs and Ca++ receptors that when activated trigger fusion and release.

Question 10

The vesicle membrane has which proteins and what are they used for?

Answer 10

Synaptobrevin the V-SNARE. Synaptotagmin the Ca receptor.

Question 11

What proteins are on the presynaptic target membrane?

Answer 11

T-SNAREs including SNAP-25 and syntaxin

Question 12

How does Botulinum toxin (and tetanus toxin) work?

Answer 12

They cause muscle weakenss by cleaving the SNAP-25 or synaptobrevin proteins in the presynaptic terminal. This happens in alpha motor neurons.

Question 13

Give an example of a fast, moderate, and slow acting receptor.

Answer 13

Fast - Ligand-gated ion channels (nicotinic cholinergic receptor) Moderate - metabotropic glutamate and muscarinic cholinergic. Slow- peptides and protein receptors

Question 14

What is an ionotropic receptor?

Answer 14

They contain an ion channel as part of their structure and transmitter bidning triggers a rapid response

Question 15

What is a metabotropic receptor?

Answer 15

They are commonly linked to G-proteins (heterotrimeric) that transduce a slower biochemical signal

Question 16

What is an EPSP? What effect does it have? What causes it?

Answer 16

An excitatory postsynaptic potential. It increases the probability that an action potential will be triggered. Sodium influx

Question 17

What is an IPSP? What effect does it have? What causes it?

Answer 17

An inhibitory postysynaptic potential. It decreases the probability of an action potential being triggered. CL ion influx or K+ efflux or both.

Question 18

What is the major excitatory neurotransmitter (in the brain)? What does it bind to?

Answer 18

Glutamate. Binds ionotropic and metabotropic receptors

Question 19

What is the major inhibitory transmitter (in the brain)?

Answer 19

GABA. It binds to ionotropic and metabotropic receptors

Question 20

What is decremental conduction? What does it cause?

Answer 20

It is the loss of the potential by leakage through the membrane. It is the reason for summation being needed.

Question 21

Describe the process of temporal stimulation.

Answer 21

It is the productiong of EPSPs produced at on synapse by two sequential action potentials.

Question 22

Descrie the process of spatial summation.

Answer 22

Action potentials in two neruons produce EPSPs at their synapses which propagate by passive conduction to the soma and axon hillocks.

Question 23

In temporal summation what happens in a cell with a shorter time constant?

Answer 23

The first EPSP terminates before the second is produced. A longer time constant allows for the two depolarization events to summate.

Question 24

In spatial summation what happens when the space constant in the dedrite is shorter?

Answer 24

The EPSP from synapse 1 decays back to rest before the synapse at 2 occurs. A longer space constant allows the synapse to be able to propagate further along the membrane and summation can result.