Synapse Transmissin

Question 1

What are the properties of electrical synapses?

Answer 1

Synchronize electrical activity among cells
Properties:
• Mediated by gap
junctions
• Voltage-sensitive • Pass ions directly
between cells • Intercellular
communication rapi

Question 2

What are chemical synapses?

Answer 2

Most common synaptic contact among mammalian neurons
• Presynaptic cells release chemicals that bind to receptors
• Post-synaptic receptors mediate altered postsynaptic neuronal function
• Presynaptic receptors regulate exocytosis
• Synapses can persistently
change in function to
mediate learning

Question 3

What are the types of chemical synapses?

Answer 3

1. Axosomatic Synapse: Often reduce probability of AP at target cell
2. Axo-dendritic synapse
   Influence likelihood of AP at target cell
3. Axoaxonic Synapse: Diminish magnitudes of AP’s and thus reduce transmitter release

Question 4

What are tripartite synaapses?

Answer 4

Astrocytes take up glutamate released by neurons

• Glutamate metabolized to glutamine
• Glutamine returned to neurons for conversion back to glutamate

Question 5

Describe Ionotropic ACh receptors

Answer 5

Ionotropic: Nicotinic Change in ion flux (Na+, K+) Rapid Effects (milliseconds)

Question 6

Describe metabotropic ACh receptors

Answer 6

Muscarinic Metabolic changes (e.g., phosphorylation)
Slower effects (seconds to minutes)

Question 7

Explain the functioning of metabotropic receptors

Answer 7

• Receptor coupled to G-proteins
• Ligand binding dissociatesa subunit from B-y complex
• a subunit can be stimulatory or inhibitory
  
  • Effects on ion channels, metabolism and gene expression

Question 8

Explain the functioning of metabotropic receptors

Answer 8

• Receptor coupled to G-proteins
• Ligand binding dissociatesa subunit from B-y complex
• a subunit can be stimulatory or inhibitory
  
  • Effects on ion channels, metabolism and gene expression

Question 9

Describe the synaptic delay

Answer 9

0.5-100 MS

Arrival of AP

1. Activation of voltage gated Ca2+ channel
2. Fusion of vesicle and release of transmitter into cleft
3. Diffusion of transmitter across cleft to postsynaptic neuron 4. Transmitter-receptor binding
4. Ionic flux or induction of enzyme activity

Postsynaptic Response

Question 10

What is Quantal size?

Answer 10

Smallest post-synaptic response (relates to transmitter released from a single vesicle)

Question 11

What is quantal content?

Answer 11

number of quanta/impulse

Question 12

What is mean quantal content?

Answer 12

Mean Size of EPP/Mean size of Mini EPP

Question 13

What is the NMJ quantal content? What are the quantal contents of other synapses?

Answer 13

NMJ Quantal content (QC) = 200 (vesicles exocytosed per impulse)

In other synapses QC = 1, 1 impulse = one vesicle released

In some cases QC = O = failed release

Question 14

What is the effect of magnesium blocking?

Answer 14

Magnesium Blocking: Replace Ca2+ with Mg2+ (Blocks voltage gated Ca2+
channels)

Overall reduced Ca2+ in response to stimulus and reduced EPPs

Question 15

Describe the quantal release of neurotransmitters

Answer 15

• 4000-10,000 ACh molecules per vesicle

• total NT release = p*n
• p = probability of release
• n = number of vesicles
• p increases with increased intracellular calcium
• p is greater than zero in absence of stimulation, i.e. some spontaneous vesicle release at NMJ