MSK - Physiology - Neuromuscular Junction; Skeletal Muscle; Smooth Muscle Flashcards
What’s the difference between an electrical synapse and a chemical synapse?
Electrical - gap junction flow
Chemical - neurotransmitter diffusion
How does calcium get into nerve terminals to trigger neurotransmitter release?
How does it get back out?
An action potential comes down the axon and triggers voltage-gated calcium channels;
sodium-calcium exchangers, ATPase pumps
What are some methods by which neurotransmitter is removed from the synaptic cleft?
Reuptake;
catabolism;
diffusion;
glial cell uptake
What is unique about the structure of the axon in the neuromuscular junction?
What unique effect does this provide?
It ends in many synaptic boutons (all on one single myocyte per axon);
more neurotransmitter is released (and faster) in these synapses than any other
Different neurotransmitters can have different effects depending on the tissue receptor on which they are acting.
For example acetylcholine is stimulatory to ___________ and inhibitory to ___________ receptors.
Nicotinic;
muscarinic
What drug blocks muscarinic receptors?
What drug blocks nicotinic receptors?
Atropine;
curare
One axon can synapse on how many myocytes?
Only one
Why is so much neurotransmitter needed at the neuromuscular junction?
To go way, way above the myocyte threshold and ALWAYS produce the desired response
(you don’t want your muscles to only sometimes fire when you ask)
In which direction do EPSPs drive the membrane potential?
Towards (or past) threshold
In which direction do IPSPs drive the membrane potential?
Away from threshold (usually hyperpolarizing)
An excitatory post-synaptic potential (EPSP) usually has a membrane potential of about what?
An inhibitory post-synaptic potential (IPSP) usually has a membrane potential of about what?
Well above threshold (typically - 5 to - 10 mV);
below threshold (often similar to EK)
(it can even be above the resting membrane potential and depolarize the cell a bit; however, if it’s potential is below threshold, it’s inhibitory)
Where is the highest concentration of voltage-gated sodium channels in the neuron?
The axon hillock
True/False.
EPSPs and IPSPs sum in a quasi-algebraic manner.
True.
The amount of neurotransmitter released from the axon terminal is directly proportional to:
The amount of calcium entering the axon terminal
Do the antibodies in myasthenia gravis destroy, downregulate, or just inactivate acetylcholine-gated sodium channels?
Likely all three
(inactivation and destruction and downregulation)
What is the penumbra of a stroke?
What change in membrane potential (Em) do cells in the infarcted area undergo?
What change in membrane potential (Em) do the penumbra cells undergo?
Affected tissues that are not as ischemic as the core area of the stroke;
membrane potentials dissipate (to 0 mV);
there is no large change in membrane potentials in the penumbra
What leads to the ‘latched state’ in smooth muscle?
Dephosphorylation of myosin light-chain
Via what intracellular effect does beta-adrenergic stimulation cause smooth muscle relaxation in the bronchi?
Increased cAMP
Growth hormone acts especially on which layer of cartilage in endochondral ossification?
The reserve cartilage
How does colchicine stabilize microtubules and inhibit synthesis?
By binding/sequestering tubulin dimers
What drug inhibits interactions between leukocyte integrins and endothelial cells?
This stops T cell extravasation and may be beneficial in what disease?
Natalizumab;
multiple sclerosis
Which of the following may be beneficial in treating lysosomal storage disorders:
Macromolecule dietary restrictions
Bone marrow transplant
Substrate inhibition therapy
Enzyme replacement therapy
Bone marrow transplant
Substrate inhibition therapy
Enzyme replacement therapy
(NOT macromolecule dietary restrictions)
What can be given to athletes in long-term events (e.g. marathons) to slow down glycogenolysis in the liver?
Oral glucose
How does repetitive nerve activity lead to short-term enhancement of neurotransmitter release?
Ca2+ accumulates in the nerve terminal
