Neurotransmission Flashcards
What are the seven events that lead up to neurotransmitter release?
- Action potential in pre-synaptic neuron
- Opening of voltage-gated Ca2+ channels
- Exocytosis of vesicle contents
- Diffusion of neurotransmitter across synapse
- Binding of neurotransmitter to receptors on post-synaptic neuron
- Stimulation of a post-synaptic potential
- Action potential in post-synaptic cell
What happens during an EPSP?
- Ligand gated Na+ channels open
- AP
- Post-synaptic potential more positive (depolarization)
- Output depends on: summation of info and frequency of firing
What happens during an IPSP?
- Ligand gated Cl- channels open
- No AP
- Post-synaptic potential more negative (hyperpolarization)
What is the graded potential? And what are two things that influence whether an action potential occurs?
• 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
What are the two types of summation?
Spatial- when where are enough synapses close together
Temporal- when post-synaptic membrane is depolarized in rapid succession
What are the five fates of NTs after release?
- Bind to receptors on post-synaptic cell
- Destroyed by enzymes
- Re-uptake by pre-synaptic terminal (saves energy)
- Diffuse away
- Reuptake by glia (astrocytes)
What is a chemical synapse?
neurotransmitters, synaptic delay
What is an electrical synapse?
reflexes, gap junctions, efficient, versatile, rare (some parts of brain, eyes, PNS)
What are the three points in the definition of a neurotransmitter?
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
What are the three structural classifications of NTs and what are examples?
- Amino acids (fast, GABA, glutamate)
- Classical/amine (mainly slow, serotonin)
- Neuropeptides (slow, opioids)
What is Dale’s principle? Which type of hormone does not follow it?
a single neuron has a single neurotransmitter, PEPTIDE hormones don’t follow (co-transmitters)
Peptides: where is the precursor converted? How does it become a NT? Where is it stored?
- 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
Amine and amino acids: where is the precursor converted? Where is it stored?
- Enzymes convert precursor molecules to NT in cytosol
- Transported proteins load NT in synaptic vesicles in terminal where they are stored
What are the two mechanisms of action and their characteristics?
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
What does cAMP do?
binding stimulates GPCR, activates adenylate cyclase and converts ATP to cAMP which impacts membrane permeability and protein synthesis
What does IP3 do?
stimulates GPCR, activates phospholipase and coverts membrane phospholipids to IP3 which causes the release of calcium with affects metabolism
What is an example of a cholinergic neuron? Synthesis requires what enzyme? What is it degraded by?
acetylcholine
ChAT
AChE
What are the two receptor sub-types of acetylcholine, where can they be found and what is the mechanism of action?
nicotinic: skeletal, ionotropic
muscarinic: cardiac and glands, metabotropic
What is the precursor for all catecholaminergic NTs? What are 4 examples? What enzyme does their synthesis require? How are they degraded?
TYROSINE
dopamine, norepinephrine, epinephrine, serotonin
tyrosine hydroxylase
taken back into pre-synaptic neuron
What is the precursor of dopamine? What enzyme is needed for its formation? Where can high levels be found?
L-Dopa
dopamine beta-hydroxylase
basal ganglia
Where can epinephrine be found? What does it do and through what?
CNS
EPSP
through G-proteins
Where can norepinephrine be found? What does it do?
CNS and PNS
attention, concentration, body temp
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?
tryptophan intestine and brain appetite, sleep, mood, decreases pain pre-synaptic neuron, broken down by MAO depression (MAO inhibitors or selective serotonin reuptake inhibitors)
How are GABA and glutamate broken down?
glia by GABA transaminase
