Neurotransmission

Question 1

What are the seven events that lead up to neurotransmitter release?

Answer 1

1. Action potential in pre-synaptic neuron
2. Opening of voltage-gated Ca2+ channels
3. Exocytosis of vesicle contents
4. Diffusion of neurotransmitter across synapse
5. Binding of neurotransmitter to receptors on post-synaptic neuron
6. Stimulation of a post-synaptic potential
7. Action potential in post-synaptic cell

Question 2

What happens during an EPSP?

Answer 2

• Ligand gated Na+ channels open
• AP
• Post-synaptic potential more positive (depolarization)
• Output depends on: summation of info and frequency of firing

Question 3

What happens during an IPSP?

Answer 3

• Ligand gated Cl- channels open
• No AP
• Post-synaptic potential more negative (hyperpolarization)

Question 4

What is the graded potential? And what are two things that influence whether an action potential occurs?

Answer 4

• Graded potential: local change in potential at the site of stimulation on the post-synaptic neuron
2 things that influence whether an AP occurs: size of graded potential, direction of membrane potential change

Question 5

What are the two types of summation?

Answer 5

Spatial- when where are enough synapses close together

Temporal- when post-synaptic membrane is depolarized in rapid succession

Question 6

What are the five fates of NTs after release?

Answer 6

• Bind to receptors on post-synaptic cell
• Destroyed by enzymes
• Re-uptake by pre-synaptic terminal (saves energy)
• Diffuse away
• Reuptake by glia (astrocytes)

Question 7

What is a chemical synapse?

Answer 7

neurotransmitters, synaptic delay

Question 8

What is an electrical synapse?

Answer 8

reflexes, gap junctions, efficient, versatile, rare (some parts of brain, eyes, PNS)

Question 9

What are the three points in the definition of a neurotransmitter?

Answer 9

Must be synthesized and stored in the pre-synaptic neuron
Must be released by the pre-synaptic axon terminal upon stimulation
When experimentally applied, must produce a response in the post-synaptic cell that mimics the response produced by the release of neurotransmitter from the pre-synaptic neuron

Question 10

What are the three structural classifications of NTs and what are examples?

Answer 10

• Amino acids (fast, GABA, glutamate)
• Classical/amine (mainly slow, serotonin)
• Neuropeptides (slow, opioids)

Question 11

What is Dale’s principle? Which type of hormone does not follow it?

Answer 11

a single neuron has a single neurotransmitter, PEPTIDE hormones don’t follow (co-transmitters)

Question 12

Peptides: where is the precursor converted? How does it become a NT? Where is it stored?

Answer 12

• Precursor peptide @ RER
• Precursor to Golgi where it becomes a neurotransmitter
• Vesicle away from Golgi
• Secretory granules down axon (anterograde transport) where it is stored at the terminal

Question 13

Amine and amino acids: where is the precursor converted? Where is it stored?

Answer 13

• Enzymes convert precursor molecules to NT in cytosol

- Transported proteins load NT in synaptic vesicles in terminal where they are stored

Question 14

What are the two mechanisms of action and their characteristics?

Answer 14

Ionotropic: faster, directly bonds to ligand-gated channels and opens
Metabotropic: slower, via secondary messengers like G-coupled protein receptors where they activate effector proteins or ion channels or enzymes to intracellular second messengers (such as cAMP or IP3) cascade

Question 15

What does cAMP do?

Answer 15

binding stimulates GPCR, activates adenylate cyclase and converts ATP to cAMP which impacts membrane permeability and protein synthesis

Question 16

What does IP3 do?

Answer 16

stimulates GPCR, activates phospholipase and coverts membrane phospholipids to IP3 which causes the release of calcium with affects metabolism

Question 17

What is an example of a cholinergic neuron? Synthesis requires what enzyme? What is it degraded by?

Answer 17

acetylcholine
ChAT
AChE

Question 18

What are the two receptor sub-types of acetylcholine, where can they be found and what is the mechanism of action?

Answer 18

nicotinic: skeletal, ionotropic
muscarinic: cardiac and glands, metabotropic

Question 19

What is the precursor for all catecholaminergic NTs? What are 4 examples? What enzyme does their synthesis require? How are they degraded?

Answer 19

TYROSINE
dopamine, norepinephrine, epinephrine, serotonin
tyrosine hydroxylase
taken back into pre-synaptic neuron

Question 20

What is the precursor of dopamine? What enzyme is needed for its formation? Where can high levels be found?

Answer 20

L-Dopa
dopamine beta-hydroxylase
basal ganglia

Question 21

Where can epinephrine be found? What does it do and through what?

Answer 21

CNS
EPSP
through G-proteins

Question 22

Where can norepinephrine be found? What does it do?

Answer 22

CNS and PNS

attention, concentration, body temp

Question 23

What is serotonin synthesized from? Where can it be found? What does it do? How does it degrade? What can low levels cause and how is this treated?

Answer 23

tryptophan
intestine and brain
appetite, sleep, mood, decreases pain
pre-synaptic neuron, broken down by MAO
depression (MAO inhibitors or selective serotonin reuptake inhibitors)

Question 24

How are GABA and glutamate broken down?

Answer 24

glia by GABA transaminase

Question 25

What is glutamate synthesized from? What does it do? Works directly or indirectly?

Answer 25

glucose etc.
EPSP
both

Question 26

What is GABA synthesized from? What is its direct and indirect effect?

Answer 26

glutamate

direct: permits passage of Cl- into post-synaptic neuron, IPSP
indirect: open K+ channels for efflux, blocks entry of Ca2+

Question 27

What rule does ATP break? What receptors does it bind to and how is it degraded?

Answer 27

not stored in pre-synaptic neuron
purinergic receptors
enzymes

Question 28

What rule do endocannabinoids break? What do they bind to and do?

Answer 28

not packaged in vesicles
membrane permeable
CB1 receptors (GPCR)
reduces opening of [re-synaptic Ca2+

Question 29

What rule does nitric oxide break? What are they synthesized from? What do they do?

Answer 29

not from pre-synaptic neuron
acid arginine
regulates blood flow through endothelial cells (diffuse freely)