1.11 - Excitation, Inhibition & Neurmodulation

Question 1

What are the three types of functional groups of synapses?

Answer 1

Excitatory –> directly increases excitability of the postsynaptic membrane
Inhibitory –> directly decreases the excitability of the postsynaptic membrane
Modulatory –> To indirectly change the excitability of the pre- or postsynaptic membrane, but without having any direct effect itself. I.e. It regulates or modifies the effect of other inhibit of excitatory synapses

Question 2

Describe Excitatory synapses

Answer 2

Most are glutaminargic (use glutamate or aspartate)
Result in an EPSP by opening a non-selective Na+/K+ ion channel. EPSPs increase the excitability of the membrane, as they bring Vm closer to the action potential threshold.

Question 3

Describe Inhibitory synapses

Answer 3

Most inhibitory synapses are GABAergic or Glycinergic
Result in an IPSP by opening a selective Cl- channel
IPSPs decrease the excitability of the membrane, as they take Vm further away from the action potential threshold.
They oppose EPSPs

Question 4

Describe modulatory synapses

Answer 4

Generally have no effect on membrane excitability
directly, but will dampen or brighten the response of
other neurotransmitters
They are generally mediated by slower metabotropic
receptors (G-protein coupled receptors) that active a signalling cascade

Question 5

What is an example of a gaseous neurotransmitter

Answer 5

Nitric Oxide (NO)

Question 6

What are some amino acid transmitters

Answer 6

Glutamate, GABA, Glycine, Aspartate

Question 7

What are some monoamine transmitters

Answer 7

Acetylcholine, serotonin, histamine

Question 8

What are some catecholamine transmitters

Answer 8

Dopamine, noradrenaline, adrenaline

Question 9

What are some purine transmitters

Answer 9

Adenosine, ATP

Question 10

What are some lipid metabolite transmitters?

Answer 10

Endocannabinoids, Arachidonic acid

Question 11

What are some peptide transmitters

Answer 11

CCK, SP, NPY, ADH, Oxytocin

Question 12

What are ionotropic receptors and what are some examples of transmitter that act at them?

Answer 12

Ionic channels receptors.
Glutamate (AMPA, NMDA)
GABA (GABAa receptor)
ACh (nAChR)

Question 13

What are metabotropic receptors and what are some examples of transmitter that act at them?

Answer 13

G-protein receptors that then alter ion channel function.
GABA (GABAb receptors
Acetylcholine (M1 to M5 receptors)
Dopamine (D1-D5 receptors)
Noradrenaline (alpha, beta receptors)

Question 14

Describe the synthesis, mechanism of action and degradation of Glutamate

Answer 14

Produced from glutamine by glutaminase
Act at ionotropic glutamate receptors (AMPA, NMDA) to elicit fast excitation (workhorse of CNS excitation).
Removed from the synapse by Excitatory Amino Acid Transporters (EAATs) either into nearby astrocytes or the presynaptic nerve terminal for reuse.

Question 15

Describe the synthesis, mechanism of action and degradation of ACh

Answer 15

Synthesised from Choline and AcetylCoA by choline acetyltransferase.
Work are ionotropic nicotinic receptors (in the NMJ, non-selective Na+/K+ channel) and metabotropic muscarinic receptors (such as in vagal effecerents to the heart
Broken down to choline and acetate by AChE located in the synaptic cleft

Question 16

Describe the synthesis, mechanism of action and degradation of GABA

Answer 16

Produced from Glutamate via GAD (glutamic acid decarboxylase)
Work at ionotropic GABAa receptors (Permeable to Cl- –> fast inhibitory signalling in the CNS) and metabotropic GABAb receptors (slow activation/deactivation, –> inhibition in CNS post- and presynaptically)
Deactivated via diffusion, uptake in to glia and reuptake as glutamine