T1 L7: Physiology of the synapse

Question 1

What are some properties of ionotropic receptors?

Answer 1

They are ligand gated ion channels responsible for fast transmission. The ligands are neurotransmitters that cause a change in conformation which opens the central pore through which ions can travel.

Question 2

Describe the structure of an ionotropic receptor

Answer 2

Channels made of 4/5 subunits that fold together to form a central pore

Question 3

What is an agonist?

Answer 3

Works very similar to the natural neurotransmitter. It causes a physiological reaction

Question 4

What is an antagonist?

Answer 4

A drug that blocks activity

Question 5

Which ion do Glutamate receptors work with?

Answer 5

Na+

Question 6

Describe how Glutamate ionotropic receptors work

Answer 6

An influx of ions causes an Excitatory Post Synaptic Potential (EPSP) that depolarises the postsynaptic neuron which causes an action potential

Question 7

Describe how GABA ionotropic receptors work

Answer 7

An influx of ions causes an Inhibitory Post Synaptic Potential (IPSP) which hyperpolarises the postsynaptic neurone preventing an action potential

Question 8

Which ion do GABA receptors work with?

Answer 8

Cl-

Question 9

Which are the 3 types of ionotropic receptor that respond to glutamate?

Answer 9

NMDA, AMPA, and Kainate

Question 10

What are the properties of non-NMDA receptors (AMPA and Kainate)?

Answer 10

They are fast opening channels permeable to Na+ and K+ responsible for early phase EPSP (excitation)

Question 11

What are the properties of NMDA receptors?

Answer 11

They are slow acting channels permeable to Ca2+, Na+, and K+. They require extracellular glycine as a cofactor to open the channel. They are gated by Mg2+ which plugs the pore at resting potential. They are responsible for late phase EPSP and can only be activated when Glutamate is present

Question 12

Describe when activity-dependent synaptic modification is used

Answer 12

In NMDA receptors. Mg2+ blocks the pore during resting potential and then is ejected from the channel by electrostatic repulsion allowing conductance of the other ions

Question 13

How is EPSP measured?

Answer 13

From resting potential higher than Mg2+ blockade in presence or absence of AMPA or NMDA

Question 14

What does EPSP stand for?

Answer 14

Excitatory Post Synaptic Potential

Question 15

Describe how neuroplasticity actually occurs

Answer 15

An influx of Ca2+ and Na+ leads to activation of a number of enzymes and other events that cause widespread changes in the postsynaptic cell

Question 16

What is the link between NMDA receptors and Schizophrenia?

Answer 16

NMDA receptors can be inhibited by PCP (Phencyclidine (angel dust)) and MK801 which produces symptoms that resemble the hallucinations associated with Schizophrenia

Question 17

What is Glutamate excitotoxicity?

Answer 17

Excessive Ca2+ influx which activates Ca2+-dependent enzymes that degrade proteins, lipids, and nucleic acids

Question 18

When does Glutamate excitotoxicity occur?

Answer 18

After cardiac arrest, stroke, O2 deficiency, and repeated intense seizures

Question 19

What is Status epilepticus?

Answer 19

A seizure that lasts longer than 5 minutes or having more than 1 seizure within 5 minutes without enough time to recover

Question 20

What type of effect do Glutamate receptors have on tissues?

Answer 20

Excitatory

Question 21

What type of effect do GABA receptors have on tissues?

Answer 21

Inhibitory (brain)

Question 22

What type of effect do Glycine receptors have on tissues?

Answer 22

Inhibitory (spinal cord and brain stem)

Question 23

What type of effect do Nicotine receptors have on tissues?

Answer 23

Excitatory at the neuromuscular junction (NMJ) but excitatory or modulatory in the CNS

Question 24

What type of effect do Serotonin receptors have on tissues?

Answer 24

Excitatory or modulatory

Question 25

What type of effect do ATP receptors have on tissues?

Answer 25

Excitatory

Question 26

How do metabotropic receptors work?

Answer 26

They transduce signals into the cells through activation of G-proteins

Question 27

Describe the mechanism that activates G-proteins

Answer 27

In the resting state, the molecule is bound to GDP but on binding to a ligand, the GDP is switched to GTP causing the molecule to split into a G-alpha and G-beta,gamma

Question 28

How does the intrinsic GTP-GDP system work?

Answer 28

The breakdown from GTP to GDP switches off the molecule

Question 29

Describe the structure of a G-protein

Answer 29

~20 alpha subunits including Gs, Gi, and Gq. There are Beta-gamma complexes (5 beta and 12 gamma

Question 30

What does the beta-gamma complex of a G-protein activate?

Answer 30

K+ channels directly

Question 31

Which 2 G-protein complexes work on adenylyl cyclase?

Answer 31

Gs and Gi which then inhibits or activates cAMP and the subsequent activation of PKA

Question 32

Which G-protein complex works on PLC (Phospholipase C)?

Answer 32

Gq. It activates phospholipase C which converts PIP2 into IP3 and DAG. DAG then activates PKC and IP3 releases Ca2+ from internal stores. These two mechanisms activate a Ca2+ dependent enzyme

Question 33

What does a protein kinase do?

Answer 33

Attaches a phosphate

Question 34

What does a protein phosphatase do?

Answer 34

Removes a phosphate

Question 35

What are autoreceptors?

Answer 35

They regulate release of transmitter by modulating it’s synthesis, storage, release, or reuptake. They allow for a feedback loop

Question 36

What are heteroreceptors?

Answer 36

They regulate synthesis or release of transmitters rather than their own ligands

Question 37

Give some examples of metabotropic receptors

Answer 37

Group 1,2, and 3 Glutamate, GABAb, Muscarinic acetylcholine, Dopamine, Noradrenaline, Adrenergic, Serotonin, neuropeptide

Question 38

Which glutamate receptors come under group I?

Answer 38

1 and 5 (Gq)

Question 39

Which glutamate receptors come under group II?

Answer 39

2 and 3 (Gi)

Question 40

Which glutamate receptors come under group III?

Answer 40

4, 6, 7, and 8 (Gs)