Deck 20: Skeletal Muscle Mechanics

Question 1

A m us cle with a ra dius of 3 c m exe rts about 20 N cm -2 of force at zero velocity. Which of the following afterloads wo uld ca us e a n e cc en tric contraction? Use g = 9.81 m s -2. Assume the muscle is a right circular cylinder with a pennation angle of 0o.

A) 60 g
B) 600 g
C) 6kg
D) 60 kg
E) 600 kg

Answer 1

D

Question 2

In an isometric contraction

A) The m uscle lengthens
B) The m uscle shortens
C) Muscle length does not change
D) Maximum force is generated
E) Maximum muscle velocity is recorded

Answer 2

C

Question 3

The m uscle twitch

A) Lasts 5 ms or less in humans
B) Is involuntary
C) Takes less time in slow twitch muscles
D) Is the contraction resulting from a single action potential on eac h o f a se t of m us cle fibers
E) Lasts longer in fast twitch muscles

Answer 3

D

Question 4

Passive force

A) Ha s a b ipha sic re lations hip w ith m usc le leng th, be ing m axim al at res t length
B) Is the force exerted by a muscle without nervous excitation
C) Is inve rse ly related to m usc le veloc ity
D) Is inversely related to the active force
E) Is directly related to the active force

Question 5

Maximum force in muscle is produced

A) At ab out o ne-th ird m axim um length
B) At zero afterload
C) W hen the velocity of contraction is zero
D) During eccentric contractions
E) During concentric contractions

Question 6

The ad va nta ge of m us cle pe nn atio n is tha t it

A) Increases the velocity of muscles
B) Increases the force of muscles, but slows their speed
C) Increases the endurance of muscles
D) Decreases the metabolic cost of muscles
E) Packs m ore muscle into a given volume

Question 7

A muscle twitch in a human returns to baseline 50 ms after the initial stimulus. This muscle is

A) Sm oo th m us cle
B) C ar dia c m us cle
C) Fa st tw itch m us cle
D) Slo w tw itch m us cle
E) Fatigue-resistant

Question 8

Active tension

A) Is th e inc rem en t in fo rce c au sed by e xcita tion of th e m us cle
B) Is directly related to the passive force
C) Varies biph asically with m uscle leng th, being m axima l near the rest leng th
D) Is caused by phosphorylation of myosin light chains
E) Both A and C are correct

Question 9

If a m us cle twitc h is 0.2 s lo ng , it will first be gin to s how sum m ation u pon repe titive stim ulation at a frequency of about

A) 2 Hz
B) 5 Hz
C) 20 Hz
D) 50 Hz
E) 500 Hz

Question 10

Tetanic force is typically about

A) 10% greater than twitch force
B) 50 % greater than twitch force
C) 5 times the twitch force
D) 20 times the twitch force
E) 50 times the twitch force

Question 11

Maximum power in muscle is produced

A) At ab out o ne-th ird m axim um length
B) At about one-third of the maximum isometric force
C) At zero afterload
D) W hen the velocity of contraction is zero
E) At sub-maximal recruitment

Question 12

The contraction that results from a single action potential on each of a set of motor neurons is called

A) Tetany
B) Tetanus
C) A tic
D) A muscle twitch
E) A muscle spasm

Question 13

The m uscles with the greatest endurance are the

A) Fast twitch glycolytic muscles
B) Slow twitch oxidative muscles
C) Fast twitch oxidative muscles
D) Fast twitch intermediate muscles
E) Slow twitch glycolytic muscles

Question 14

Physiological recruitm ent of m uscle fibers

A) Is random
B) Beg ins w ith the sm all moto r units and progres ses to large m otor un its
C) Be gins with larg e m otor u nits an d the n the sm aller m otor u nits
D) Is inve rse ly related to m usc le veloc ity
E) Begins with slow twitch fibers and progress es to fast twitch fibers

Question 15

If a muscle twitch lasts 0.08 s, it first be gins to sh ow s um m ation u pon repe titive stim ulation at a stimulation frequency of

A) 8 Hz
B) 80 Hz
C) 12.5 Hz
D) 125 Hz
E) 1.25 Hz

Question 16

A m oto r un it is

A) A motor neuron and all of the muscle fibers it innervates
B) A single muscle fiber innervated by a single motor neuron
C) All o f th e m us cle fibe rs with in a m us cle fas icle
D) A single muscle fiber innervated by several motor neurons
E) A piston, spark plug, intake valve and ex haust valve

Question 17

"Re cru itm ent" re fers to

A) Increasing muscle force by repetitive stimulation
B) Increasing muscle force by stretching prior to activation
C) Excitation or activation of additional motor units
D) Excitation of additional muscle fibers by a given motor neuron
E) Increasing the for ce of a lre ad y ac tive m us cle

Question 18

Sk ele tal m us cle is described by all of the following EXCEPT

A) It is striated
B) It consists of large multinucleated cells or fibers
C) It is c on tro lled vo lun tar ily
D) It generally connects one bone to another
E) Its contraction is controlled by hormones