Chapter 7: Excitation of Skeletal Muscle: Neuromuscular Transmission and Excitation-Contraction Coupling

Question 1

are innervated by large, myelinated nerve fibers that originate from large motoneurons in the anterior horns of the spinal cord

Answer 1

skeletal muscle fibers

Question 2

each nerve ending makes a junction (with the muscle fiber near its midpoint) called the?

Answer 2

neuromuscular junction

Question 3

it initiated in the muscle fiber by the nerve signal travels in both directions toward the muscle fiber ends.

Answer 3

action potential

Question 4

with the exception of about 2% of the muscle fibers how many junction per muscle fiber are there?

Answer 4

only one such junction

Question 5

the entire structure, where it is covered by one or more schwann cells that insulate it from the surrounding fluids

Answer 5

motor end plate

Question 6

invaginated membrane

Answer 6

synaptic gutter or synaptic trough

Question 7

space between the terminal and the fiber membrane is called?

Answer 7

synaptic space or synaptic cleft

Question 8

at the bottom of the gutter are numerous smaller folds of the muscle membrane called?

Answer 8

sub neural clefts

Question 9

the energy source that is used for synthesis of an excitatory transmitter

Answer 9

acetylcholine

Question 10

Acetylcholine is synthesized in the ___________ of the terminal

Answer 10

cytoplasm

Question 11

in the synaptic space are large quantities of the enzyme _______________, which destroys acetylcholine a few milliseconds after it has been released from the synaptic vesicles

Answer 11

acetylcholinesterase

Question 12

when an action potential spreads over the terminal, these channels open and allow calcium ions to diffuse from the synaptic space to the interior of the nerve terminal

Answer 12

voltage-gated calcium channels

Question 13

a process when the vesicles then fuse with the neural membrane and empty their acetylcholine into the synaptic space

Answer 13

exocytosis

Question 14

they are located almost entirely near the mouths of the sub neural clefts lying immediately below the dense bar areas, where the acetylcholine is emptied into the synaptic space.

Answer 14

acetylcholine-gated ion channels

Question 15

the complex is composed of five subunit proteins, what are these?

Answer 15

two alpha proteins, beta, delta, and gamma proteins

Question 16

__________ has a diameter of about 0.65 nanometer, which is large enough to allow the important positive ions __________, __________, __________ to move easily through the opening

Answer 16

acetylcholine-gated channel

sodium (Na), potassium (K) calcium (Ca)

Question 17

more ________ flow through the acetylcholine-gated channels than any other ions.

Answer 17

sodium ions

Question 18

this creates a local positive potential change inside the muscle fiber membrane called?

Answer 18

end plate potential

Question 19

it initiates an action potential that spreads along the muscle membrane and thus causes muscle contraction

Answer 19

end plate potential

Question 20

creating a local potential

Answer 20

end plate potential

Question 21

stimulation of the nerve fiber at rates greater than 100 times per second for several minutes often diminishes the number of acetylcholine vesicles so much that impulses fail to pass into the muscle fiber

Answer 21

fatigue of the neuromuscular junction

Question 22

compound that has the same effect on the muscle fiber as does acetylcholine

Answer 22

methacholine, carbachol, and nicotine

Question 23

these particularly well-known drugs, inactivate the acetylcholinesterase in the synapses so that it no longer hydrolyzes acetylcholine.

Answer 23

neostigmine, physostigmine, diisopropyl fluorophosphate

Question 24

it causes when even a few nerve impulses reach the muscle

Answer 24

muscle spasm

Question 25

combine with acetylcholinesterase to inactivate the acetylcholinesterase for up to several hours, after which these drugs are displaced from the acetylcholinesterase so that the esterase once becomes active.

Answer 25

neostigmine and physostigmine

Question 26

a group of drugs that can prevent passage of impulses from the nerve ending into the muscle.

Answer 26

curariform drugs

Question 27

blocks the action of acetylcholine on the muscle fiber acetylcholine receptors, thus preventing sufficient increase in permeability of the muscle membrane channels to initiate an action potential

Answer 27

D-tubocurarine

Question 28

causes muscle paralysis because of inability of the neuromuscular junctions to transmit enough signals from the nerve fibers to the muscle fibers

Answer 28

myasthenia gravis

Question 29

Some of quantitative aspects of muscle potentials: (3)

Answer 29

1. resting membrane potential
2. duration of action potential
3. Velocity of conduction

Question 30

about -80 to -90 millivolts in skeletal fibers, the same as in large myelinated nerve fibers

Answer 30

resting membrane potential

Question 31

1 to 5 milliseconds in skeletal muscle about five times as long as in large myelinated nerves

Answer 31

duration of action potential

Question 32

penetrate all the way through the muscle fiber from one side of the fiber to the other.

Answer 32

Transverse tubules (T tubules)

Question 33

T-tubule cause release of calcium ions inside the muscle fiber in the immediate vicinity of the myofibrils and these calcium ions then cause contraction. this overall process called?

Answer 33

Excitation-contraction coupling

Question 34

are small and run transverse to the myofibrils. they begin at the cell membrane and penetrate all the way from one side of the muscle fiber to the opposite side.

Answer 34

transverse tubules

Question 35

sarcoplasmic reticulum composed of two major parts;

Answer 35

1. large chambers called terminal cisternae
2. long longitudinal tubules that surround all surfaces of the actual contracting myofibrils

Question 36

as the action potential reaches the t tubule, the voltage change is sensed by __________ receptors that are linked to calcium release channels also called?

Answer 36

dihydropyridine

ryanodine receptor

Question 37

activation of ____________ triggers the opening of the calcium release channels in the cisternae as well as in their attached longitudinal tubules

Answer 37

dihydropyridine receptors

Question 38

the normal resting state concentration of calcium ions in the cytosol that bathes the myofibrils is too little to elicit contraction

Answer 38

<10-⁷ molar

Question 39

keeps the actin filaments inhibited and maintains a relaxed state of the muscle

Answer 39

troponin-tropomyosin

Question 40

full excitation of the _________ and ___________ causes enough release of calcium ions to increase the concentration in the myofibrillar fluid

Answer 40

T-tubule and sarcoplasmic reticulum system

Question 41

the total duration of the calcium pulse in the skeletal muscle fiber last about?

Answer 41

1/20 of a second

Question 42

in heart muscle, the calcium pulse last about?

Answer 42

1/3 of a second

Question 43

during the calcium pulse, MUSCLE CONTRACTIONS OCCUR.