The Muscle System
Exam 3 Extra
Supplemental Instruction
IowaStateUniversity / Leader: / Cody
Course: / AN S 214
Instructor: / Dr. Selsby
Date:
  1. Fill in the diagram at right and answer the pertaining questions:
  1. What is the name of the neurotransmitter released at the NMJ?

Acetylcholine Ach

  1. What kinds of channels will open on the sarcolemma?

voltage-gated ion channels

  1. What major enzyme is present within the synaptic cleft?What is its function?

Acetylcholinesterase-removes Ach from receptors

  1. What is the significance of the junctional folds?

Increase surface area for Ach to bind to receptors

  1. What kinds of receptors are located in the junctional folds?

Ligand-gated ion channels

  1. What kinds of channels do they open?

Na+ channels and K+ channels

  1. What does this ion exchange initiate?

Action Potential

  1. How do we repolarize the sarcolemma to get back to our original state?

Close Na+ channels, open K+ channels

  1. Fill in the blanks and name structures A-D in the diagram below, illustrating the process of excitation-contraction coupling:
  2. What kinds of channels are located at A? Describe the consequences of their activation.

Ligand-gated ion channels, influx of Na+, outflow of K+

  1. Draw the path of the end plate potential along the sarcolemma. What structure does it enter?

T-Tubule

  1. What is the effect of the spreading potential on the structure labeled C? D? Draw an arrow symbolizing any structural changes.

Voltage-sensitive tubule protein (electron-dense feet) change shaperelease Ca2+

  1. What particles are stored within the structure labeled B? What happens as a result of the conformational change to structure D?

Ca2+, Terminal cisternae release Ca2+

  1. What kinds of channels are located at B? Why do the intra-SR ions flood the cell?

Calcium channels, to bind to troponin for muscle contraction

  1. What is the effect of these ions in the sarcoplasm?

Bind to troponin

  1. What pump, by active transport, will pump calcium back into the SR?

Serca

  1. What is the affect of Parvalbumin?Help bring calcium to serca

Calsequestrin?Helps bind calcium, to pump against gradient

  1. Number the following 1-6 in the order that they occur during a muscle contraction.

5 / ADP and Pi are expelled from the myosin head, allowing it to return to the relaxed 90º state.
1 / The myosin head is in the relaxed state, at 90º. Bound to it is an ATP molecule.
3 / Myosin heads bind to the now exposed binding sites on actin.
4 / The flexion of a relaxing myosin head pulls its attached actin strand in towards the center of the sarcomere.
2 / ATP on the myosin head is cleaved into ADP and Pi, forcing myosin heads into the high energy, 'cocked', position.
6 / The myosin head binds an ATP molecule, allowing it to release actin.
  1. How is acetylcholine moved away from receptors and the neuromuscular junction?

Enzyme acetylcholinesterase

  1. What happens if there is no longer an action potential? What happens to the electron dense feet?

No more calcium, they’ll close

  1. What happens to the release of calcium?

Stops

  1. What happens to troponin and tropomyosin?

Unbinding calcium, troponin releasing tropomyosin, tropomyosin covers back-up the myosin binding sites on the actin

  1. Illustrate the actin-myosin interactions responsible for the observed tension potential in the blank boxes of the diagram to the right:
  1. The amount of force generated by a muscle fiber is dependent on the degree of overlap between the actin and myosin subunits within the sarcomere. When there is ____Excesive_ overlap, the ___actin___ strands become a physical obstruction to each other, and __myosin_____ begins to butt into the Z-disks. When there is _____too little____ overlap, too few myosin heads are able to form __cross bridges______, decreasing the amount of force generated.
  1. What are the 3 phases of a twitch and what event is correlated with each?
  • Latent period; events of E-C coupling
  • Period of contraction; cross bridge formation
  • Period of relaxation; calcium reentry into SR, tension declines to zero
  1. Label the diagram to the right’s axis and identify which line belongs to Type I and Type II fibers:
  1. Which of these phases differ in length for fast and slow twitch muscle?

Period of contraction, period of relaxation

  1. Why is contraction faster in fast twitch than in slow twitch muscle?

Rate at which ATP is hydrolyzed

  1. Why is relaxation faster in fast twitch than in slow twitch muscle?

Calcium is reabsorbed faster

  1. Which type of muscle is primarily used for sustained levels of exercised? Type I

Short bursts of activity? Type II

  1. What type of muscle fiber would you expect to find in a 'natural sprinter'? Type II

A 'natural marathon runner'?Type I

  1. On the blank diagrams below, fill in the changes in tension that occur with multiple stimuli for both unfused and fused tetany. Use arrows to indicate stimuli and a line to track the change in muscle tension:

UNFUSED TETANY FUSED TETANY

  1. How do these two types of tetany differ in frequency of stimulus?

Unfused: lower frequency fused: high frequency

  1. How do these two types of tetany differ in amount of calcium released?
  1. Which type of tetany can/cannot occur under normal physiological conditions?

fused

  1. Define threshold stimulus (illustrated in the figure to the right):

The stimulus at which the first observable contraction occurs

  1. What accounts for the gradual increase in contractile strength?

Strength of stimulus increases

  1. What happens if the stimulus is below threshold?

No contraction

  1. What happens when the stimulus reaches maximal strength?

No further increase in contractile strength

  1. Name and define the two main types of muscle contractions discussed in class.
  • ____isotonic__: muscle length changes and moves the load
  • _____isometric_____: produces force, but muscle neither shortens or lenthens
  1. What are the two sub-types of isotonic contractions? Define each.
  • Eccentric contractions: generate force as it lengthens
  • Concentric contractions: muscle shortens and does work
  1. T/F: Muscles never push, they only pull.