CRL Quiz 3 Muscles 1


In skeletal muscle, the Ca2+ for contraction comes from


  extracellular fluid

  sarcoplasmic reticulum

  B and C

  A, B, and C


Muscle contraction starts when the muscle fiber depolarizes due to the release of calcium into the cytoplasm.




Put these events in the correct chronological sequence:

1 end plate potentials trigger action potentials
2 transverse tubules convey potentials into the interior of the cell
3 acetylcholine binds to receptors on the motor end plate
4 binding sites on actin are uncovered, allowing myosin to bind and carry out power strokes
5 Ca2+ is released from the sarcoplasmic reticulum
6 chemically regulated ion channels open, causing depolarization
7 Ca2+ ions bind to troponin-C, pulling on tropomyosin

  5, 3, 2, 1, 4, 7, 6

  3, 6, 1, 2, 5, 7, 4

  4, 1, 3, 7, 2, 6, 5

  2, 4, 7, 6, 3, 1, 5

  3, 6, 1, 5, 7, 2, 4


As ATP binds to the myosin head at the beginning of a muscle contraction cycle...

  the myosin head detaches from actin

  the myosin head initiates binding with actin.

  the myosin head tightens its bond to actin.

  ATP does not bind to the myosin head.

  None of these complete the statement correctly.


Regulation of cross-bridge formation is accomplished by



  calcium ions

  A and B

  A, B, and C


A contraction that generates force and moves a load is known as __________, whereas one that generates force without movement is known as __________.

  isometric, eccentric

  isotropic, isometric

  isometric, isotonic

  isotonic, eccentric

  isotonic, isometric


The components of muscle that allow force generation without a change in length are the

  series collagenous components.

  parallel collagenous components.

  series elastic components.

  overlapping actin filaments with myosin crossbridges.

  none of the above


This question shows a diagram in which a weight hung from a simulation "muscle fiber". Initially the weight is supported below and no movement occurs. The support is then removed. What happens next?

  Weight is lifted

  Weight is dropped

  Weight is lowered

  Weight is maintained stationary

  Can't tell what will happen


This question shows two simulated muscles, A and B. that form an "opposing group". Muscle B is thicker. When they are both activated...

  A will always shorten as it is stronger

  B will always shorten as it is stronger

  Can't tell what will happen

Can't tell because we don't know the level of activation - i.e. how many motor units are recruited at that time by each muscle


Why do lengthening (eccentric, pliometric) contractions more frequently cause injury to skeletal muscle fibres?

  greater forces developed during stretch (force is up to two-fold greater)

  greater velocities developed during stretch (velocity is up to two-fold greater)