Synapses & Neurotransmitter Release (Theme B)

Question 1

Dendritic spines are the site of most of which type of synapse?

Answer 1

Site of most excitatory synapses

Question 2

What is the relationship between size of the dendritic spine & strength of synaptic transmission?

Answer 2

The larger the dendritic spine, the stronger the synaptic transmission (more post-synaptic receptors)

Question 3

What are the structures present within the presynaptic axon terminal?

Answer 3

Mitochondria
Vesicles
SNARE proteins - vesicular v-SNARES, target t-SNARES, chaperones
V-gated Ca2+ channels

Question 4

What are the structures present within the post-synaptic dendritic spine (of central excitatory synapse)?

Answer 4

Post-synaptic density
Ionotropic receptors (ligand-gated ion channels)
Metabotropic receptors
Smooth ER
Microfilaments
Spine apparatus
Coated vesicle

Question 5

What are the ionotropic receptors in a central excitatory synapse?

Answer 5

AMPA & Kainate receptors - glutamate
NMDA receptors - glutamate, aspartame (+glycine)

Question 6

What is the metabotropic receptor in a central excitatory synapse?

Answer 6

mGluRs (1-8)

Question 7

Na+ influx into the post-synaptic element generates…

Answer 7

EPSC - Excitatory post-synaptic current (line goes down)

Which generates…
EPSP - Excitatory post-synaptic potential (line goes up)

Question 8

What is the reversal potential (Nernst) equation for a monovalent cation at body temp?

Answer 8

Ek = 61.5 x log10 x ([X]o/[X]i)

Question 9

What is the reversal potential (Nernst) equation for a monovalent anion at body temp?

Answer 9

Ek = 61.5 x log10 x ([X]i/[X]o)

Question 10

What is an inward current?

Answer 10

Inward flow of +ve ions, or outward flow of -ve ions
Generates EPSCs - resulting in EPSPs
Represented by a DOWNWARDS curve
Cause depolarisation (represented by an upwards curve)

Question 11

What is an outward current?

Answer 11

Inward flow of -ve ions, or outward flow of +veions
Generates IPSC - resulting in IPSPs
Represented by a UPWARDS curve
Cause hyperpolarisation (represented by an downwards curve)

Question 12

The slope of a current-voltage curve is determined by what?

Answer 12

Channel conductance

Question 13

What determines the membrane resistance?

Answer 13

The number of open channels
(Mostly K+ channels at RMP)

Question 14

Current flow is defined by what?

Answer 14

The flow of +ve ions

Question 15

What does Gs do?

Answer 15

Stimulates adenylyl cyclase

Which produces cAMP
Increased [cAMP] in the cell activates cAMP-dependent protein kinase A (PKA) which causes phosphorylation of other proteins (i.e., ion channels)

Question 16

What does Gq do?

Answer 16

• Activates phospholipase C which breaks down cell phospholipid PIP2 —> DAG (diacyglycerol) and inositol ((1,4,5)-triphosphate - InsP3 / IP3)
• InsP3 releases Ca2+ from intracellular stores which activates other processes

Question 17

What does Gi/o do?

Answer 17

Can inhibit adenylyl cyclase and interact with a variety of targets (inc. ion channels)

Question 18

What does the beta-adrenergic GPCR do?

Answer 18

• Stimulates adenylyl cyclase (inc [cAMP])
• Activates PKA (protein kinase A)
  
  • this has additional impacts (e.g. activating Ca2+ channels)

Question 19

What is the process of GPCR coupling?

Answer 19

1. With no agonist bound to the receptor, both the receptor & G-protein are inactive
2. Agonist binding to receptor causing it to undergo a conformational change
3. This causes a conformational change in the G-protein so that the alpha subunit releases the bound GDP molecule
4. GDP molecule replaced by GTP
5. GTP binding causes alpha subunit to dissociate from the beta & gamma subunits and bind to the effector - bringing about a physiological change by either activating / inhibiting the effector
6. Cycle ends when the alpha subunit breaks down GTP —> GDP + Pi
7. Alpha subunit leaves the effector and rejoin the beta & gamma subunits