practice q's - SMS

Question 1

What is the neurotransmitter released at the neuromuscular junction?

Answer 1

acetylcholine

Question 2

What type of receptor does acetylcholine bind to at the motor end plate?

Answer 2

nicotinic receptor

Question 3

What type of receptor does acetylcholine bind to at the motor end plate?

Answer 3

calcium (Ca2+)

Question 4

what is the role of T-tubules?

Answer 4

transmits action potentials deep into the muscle fiber

Question 5

What is the direct function of the dihydropyridine receptor (DHPR)?

Answer 5

voltage sensor to activate RyR

Question 6

what is the primary role of troponin C in muscle contraction?

Answer 6

binds calcium

Question 7

what is the cause of myasthenia gravis?

Answer 7

autoantibodies block nicotinic receptors

Question 8

What ion is responsible for muscle fiber depolarization?

Answer 8

sodium (Na+)

Question 9

what does the tropomyosin protein do?

Answer 9

covers the myosin-binding sites on actin at rest

Question 10

what is the role of SERCA (Ca2+ ATPase)?

Answer 10

reuptakes calcium into the sarcoplasmic reticulum

Question 11

which best describes the cross-bridge cycle?

Answer 11

ATP binds to myosin, allowing detachment

Question 12

what is the role of RyR and what is it activated by?

Answer 12

activated by DHPR to release calcium

Question 13

which drug blocks acetylcholine release at NMJ? which drug causes explosive release of ACh at NMJ?

Answer 13

blocks: botulinum toxin (BOTOX- fights wrinkles)

explosive release: black spider venom (so much contraction that muscle paralyzes)

Question 14

Which of the following best describes malignant hyperthermia?

Answer 14

uncontrolled calcium release from sarcoplasmic reticulum

malignant hyperthermia: rapid rise in body temp & severe muscle contractions

Question 15

A researcher applies a drug to a neuromuscular junction that prevents opening of voltage-gated calcium channels in the presynaptic terminal.

What will be the primary effect on synaptic transmission?

Answer 15

Decreased acetylcholine release

Question 16

skeletal muscle contraction is tightly regulated by what?

Answer 16

conc. of Ca2+ in the sarcoplasm

Question 17

name 2 differences b/w smooth and skeletal muscle contraction

Answer 17

1. Smooth muscle contraction uses less energy and lasts longer compared to skeletal muscle - resistant to fatigue
2. Smooth muscle contraction does not require an action potential

Question 18

smooth muscle maximal force of contraction

Answer 18

higher maximal force of contraction b/c of slower cross-bridge cycle

Question 19

which of the following best describes an attribute of visceral smooth muscle not shared by skeletal muscle?

Answer 19

contracts in response to stretch

Question 20

what does the H zone contain?

Answer 20

myosin but no actin

H zone: region in center of sarcomere composed of light bands on either of and including the M line
- there are no overlapping actin filaments here

Question 21

Resting membrane potential of nerve fiber is near to the equilibrium potential of which of the following ion?

Answer 21

potassium (K+)

Question 22

Resting membrane potential of a typical nerve cell is primarily maintained by

Answer 22

The sodium-potassium pump (Na+/K+ ATPase)

Question 23

Which enzyme is responsible for the dephosphorylation of myosin light chain in smooth muscle relaxation?

Answer 23

Myosin light-chain phosphatase (MLCP)

responsible for smooth muscle relaxation

Question 24

Hydrolysis of ATP by myosin is directly responsible for what?

Answer 24

Generating the power stroke during muscle contraction

Question 25

During a laboratory experiment, a researcher applies a drug that **blocks voltage-gated sodium channels** in a nerve fiber. What will happen to the action potential?

Answer 25

No action potential will be generated *Voltage-gated Na+ channels are essential for the depolarization phase of an action potential*

Question 26

A 60-year-old man with a neuromuscular disorder has impaired calcium release from the sarcoplasmic reticulum. How does this affect the sliding filament model?

Answer 26

Tropomyosin remains covering the myosin-binding sites

Question 27

which structure is mainly responsible for conductivity in cardiac muscle?

Answer 27

gap junctions

Question 28

Cardiac failure patients are prescribed digitalis to increase contractile strength of the heart. It targets the Na+/K+ pump in cardiac myocytes. a. what sort of transport mechanism is this pump? b. explain the working of this pump. c. what is its significance in normal cells? d. how does inhibition of Na+/K+ pump in cardiac myocytes increase force of contraction?

Answer 28

a. **primary active transport** b. 3 Na+ bind inside of cell and are pumped out, 2 K+ bind outside and are pumped into cell - ATP is broken down in the process to phosphorylate the pump and make this happen c. maintains resting membrane potential, regulates cell volume, provides gradient for other transporters d. affects another pump called **Na+/Ca2+ exchanger (1 Ca out for 3 Na in)** = less Ca2+ moved from cell = more Ca2+ is released during contraction = stronger contraction

Question 29

explain how positive feedback mechanism is involved in converting the endplate potential into action potential at the motor end plate.

Answer 29

**end plate potential**: local depolarization of the muscle cell membrane at NMJ when ACh binds to receptors positive feedback helps amplify initial depolarization caused by the end plate potential, quickly converting it into a full action potential

Question 30

during the upstroke of the nerve action potential

Answer 30

there is net inward current and the cell interior becomes less negative *inward current= moving on Na+*

Question 31

Accumulation of which solute in intracellular fluid is responsible for the tetanus?

Answer 31

**Ca2+** - repeated stimulation = Ca2+ is released rom SR more quickly than it can be removed

Question 32

which characteristic/component is shared by skeletal & smooth muscle?

Answer 32

elevation of intracellular Ca2+ for excitation-contraction coupling

Question 33

Which of the following would occur as a result of the inhibition of Na+, K+-ATPase?

Answer 33

Increased intracellular Ca2+ concentration