MSK - Physiology - Neuromuscular Junction; Skeletal Muscle; Smooth Muscle

Question 1

What’s the difference between an electrical synapse and a chemical synapse?

Answer 1

Electrical - gap junction flow

Chemical - neurotransmitter diffusion

Question 2

How does calcium get into nerve terminals to trigger neurotransmitter release?

How does it get back out?

Answer 2

An action potential comes down the axon and triggers voltage-gated calcium channels;

sodium-calcium exchangers, ATPase pumps

Question 3

What are some methods by which neurotransmitter is removed from the synaptic cleft?

Answer 3

Reuptake;

catabolism;

diffusion;

glial cell uptake

Question 4

What is unique about the structure of the axon in the neuromuscular junction?

What unique effect does this provide?

Answer 4

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

Question 5

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.

Answer 5

Nicotinic;

muscarinic

Question 6

What drug blocks muscarinic receptors?

What drug blocks nicotinic receptors?

Answer 6

Atropine;

curare

Question 7

One axon can synapse on how many myocytes?

Answer 7

Only one

Question 8

Why is so much neurotransmitter needed at the neuromuscular junction?

Answer 8

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)

Question 9

In which direction do EPSPs drive the membrane potential?

Answer 9

Towards (or past) threshold

Question 10

In which direction do IPSPs drive the membrane potential?

Answer 10

Away from threshold (usually hyperpolarizing)

Question 11

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?

Answer 11

Well above threshold (typically - 5 to - 10 mV);

below threshold (often similar to E_K)

(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)

Question 12

Where is the highest concentration of voltage-gated sodium channels in the neuron?

Answer 12

The axon hillock

Question 13

True/False.

EPSPs and IPSPs sum in a quasi-algebraic manner.

Answer 13

True.

Question 14

The amount of neurotransmitter released from the axon terminal is directly proportional to:

Answer 14

The amount of calcium entering the axon terminal

Question 15

Do the antibodies in myasthenia gravis destroy, downregulate, or just inactivate acetylcholine-gated sodium channels?

Answer 15

Likely all three

(inactivation and destruction and downregulation)

Question 16

What is the penumbra of a stroke?

What change in membrane potential (E_m) do cells in the infarcted area undergo?

What change in membrane potential (E_m) do the penumbra cells undergo?

Answer 16

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

Question 17

What leads to the ‘latched state’ in smooth muscle?

Answer 17

Dephosphorylation of myosin light-chain

Question 18

Via what intracellular effect does beta-adrenergic stimulation cause smooth muscle relaxation in the bronchi?

Answer 18

Increased cAMP

Question 19

Growth hormone acts especially on which layer of cartilage in endochondral ossification?

Answer 19

The reserve cartilage

Question 20

How does colchicine stabilize microtubules and inhibit synthesis?

Answer 20

By binding/sequestering tubulin dimers

Question 21

What drug inhibits interactions between leukocyte integrins and endothelial cells?

This stops T cell extravasation and may be beneficial in what disease?

Answer 21

Natalizumab;

multiple sclerosis

Question 22

Which of the following may be beneficial in treating lysosomal storage disorders:

Macromolecule dietary restrictions

Bone marrow transplant

Substrate inhibition therapy

Enzyme replacement therapy

Answer 22

Bone marrow transplant

Substrate inhibition therapy

Enzyme replacement therapy

(NOT macromolecule dietary restrictions)

Question 23

What can be given to athletes in long-term events (e.g. marathons) to slow down glycogenolysis in the liver?

Answer 23

Oral glucose

Question 24

How does repetitive nerve activity lead to short-term enhancement of neurotransmitter release?

Answer 24

Ca²⁺ accumulates in the nerve terminal