Synapse I Flashcards
A synapse is a specialized ______ between neurons at the end of an _____
junction; axon
Synapses are considered _____ (presynaptic/postsynaptic)
directional
Synapses convert action potentials into a ____ signal, also known as a ______
chemical; neurotransmitter
Synaptic _____ contain neurotransmitters and the action potential causes them to fuse with the ___-synaptic membrane
vesicles; pre
Neurotransmitters are released into the _________ which is the space between the neurons via action potenital
synaptic cleft
The transmitter binds to _____ (proteins) in which membrane?
receptors; postsynaptic
Binding of transmitters to receptors first opens the ____, then activates the _____ and lastly causes a response in the ___-synaptic neuron.
ion channel; enzyme; post
Each neuron typically receives 1k-10k synapses, although most are located on the ____
dendrites
An action potential opens ____ gated ____ channels in the axon terminal.
voltage; calcium
Calcium influx causes what structure to fuse with the presynaptic membrane, causing neurotransmitter release into the synaptic cleft?
synaptic vesicles
Neurotransmitters bind to which receptor?
postsynaptic
If the receptor is an ion channel, the channel ____, ions flow ___ the postsynaptic neuron, and causes postsynaptic _____.
opens; into; potential
Vesicles are recycled, meaning that new vesicles bud off from which membrane? What is this process called?
presynaptic; endocytosis
Neurotransmitters are synthesize locally where?
in the axon terminal
Neurotransmitters are loaded into vesicles by _____ proteins and into the ___ membrane.
transport; vesicular
What is the difference between ionotropic and metabotropic?
ionotropic = opens ion channel
metabotropic = g-protein coupled, causes production of 2nd messenger, activates kinase –> modifies proteins
Which type of synapse opens ion channels?
ionotropic
Which type of synapse use signal transduction mechanisms such as g-proteins?
metabotropic
Protein kinases modify the function of many different proteins that change what about the neurons?
their electrical excitability
What are the 2 main types of postsynaptic potentials?
EPSP: excitatory
IPSP: inhibitory
What does a EPSP do?
depolarize the neuron (more likely to fire an action potential)
What does an IPSP do?
hyperpolarize the neuron (less likely to fire an action potential)
Which type of postsynaptic potential will be more likely to fire an action potential?
EPSP
A neuromuscular junction is a synapse from a ____ neuron onto a ___ fiber
motor; muscle
What is the neurotransmitter released at the neuromuscular junction?
ACh (Acetylcholine)
ACh is synthesized by which neurotransmitter in the axon terminal?
ChAT (choline acetyltransferase)
Acetylcholinesterase (AChE) in the synaptic cleft degrades ACh into ____ and ____
acetate; choline
What is pumped into the presynaptic terminal?
Choline
What is pumped into the vesicle by the vesicular transporter (VAChT)?
ACh
What type of synapse is the NMJ?
ionotropic
What is the name of the nonselective cation permeable channel?
Nicotinic cholinergic ACh receptors
Binding of what opens the channels at the NMJ?
2 ACh molecules
Influx of _____ dominates the efflux of ____ which causes the membrane potential to be more negative at rest.
Na+; K+
Excitatory action ____ the muscle cell
depolarizes
Myasthenia Gravis (MG) is an autoimmune disorder in which antibodies attack what important receptors at the NMJ?
Nicotinic ACh
What are the common signs and symptoms of Myasthenia Gravis?
- Muscle Weakness
- Cranial Nerves
- Ptosis (eyelids)
- Extra-occular Eye Muscles (eye movements)
What serious problem can Myasthenia Gravis lead to?
Respiratory Failure
How does the Tensilon (the drug edrophonium) Test aid in diagnosing Myasthenia Gravis?
Tensilon prevents the breakdown of the chemical acetylcholine, a neurotransmitter that nerve cells release to stimulate your muscles.
People with the chronic disease myasthenia gravis don’t have normal reactions to acetylcholine. Antibodies attack their acetylcholine receptors. This prevents muscles from being stimulated and makes muscles easy to tire.
A person tests positive for myasthenia gravis if their muscles get stronger after being injected with Tensilon.
What is Lambert-Eaton Syndrome (LEMS)?
An autoimmune disorder in which antibodies attack voltage-gates calcium channels at the NMJ.
The lowered amount of ACh causes muscle weakness due to the inability to contract the muscles as forcefully. Mainly affects the upper hip/legs especially when rising from a chair, and in the morning.
Related to small-cell lung cancer
MG antibodies attack ___-synaptic ____ receptors, whereas LEMS antibodies attack ___-synaptic ___ channels.
post; ACh
pre; calcium
MG is associated with _____ while LEMS is associated with _____
thymoma; small-cell lung cancer
In MG, muscles are ____ with repetition, whereas in LEMS, muscles are ____ with repetition.
weaker; stronger
MG affects the body more towards the ____ whereas LEMS affects the body especially in the _____
end of the day; morning
Respiratory and ocular muscle involvement is not as severe in ____ as it is in ____
LEMS; MG
NMJ drugs are used to ___ and/or ___ the NMJ
block; enhance
Blocking the NMJ may be used in instances such as surgery and intubation because it causes temporary what?
paralysis
Enhancing the NMJ may be used in instances such as treatment of MG because it helps with what?
normal NMJ function
NMJ blocking drugs include 2 types of agents, which are what?
- Depolarizing Agent
2. Non-depolarizing Agent
A common depolarizing agent (NMJ Blocker) is Succinylcholine, which helps to block the NMJ by binding aggressively to and activating what?
Nicotinic ACh receptors
If the nicotinic ACh receptors are activated via Succinylocholine, the muscle cells _____, voltage-gated __ channels open and then stay inactivated, causing it to be ____ resistant
depolarize; Na+; AChE
Common non-depolarizing agents (NMJ blockers) are Mivacurium and Pancuronium. They are competitive _____ and displace ____ at the nicotinic ACh receptors in the NMJ but do NOT do what?
antagonists; ACh; do NOT open channels
Common NMJ enhancing drugs include Cholinesterase (AChE) Inhibitors, such as edrophonium and physotigmine. These drugs work to enhance the NMJ by blocking ____ and increasing ____ at the cholinergic synapses
AChE; ACh
