Chap. 11(muscular tissue)homework(Questions 2, 3, 4, 6 only) with review questions; page 1 of 4

Name: ______; Score: ______out of 30

  1. (Self-study questions) Study the levels of skeletal muscle organization (in Review Table 11.1below).

Review Table 11.1 Structure of a skeletal muscle.

Organizational level (Gross to microscopic) / Description / Connective tissue wrappings
  1. Skeletal muscle (an organ)
/ --Consists of many muscle cells, plus connective tissue wrappings, blood vessels, and nerve fibers / Covered externally by the epimysium
  1. Fascicle (a portion of the muscle)
/ --Discrete bundle of muscle cells, segregated from the rest of the muscle by a connective tissue sheath / Surrounded by a perimysium
  1. Muscle fiber (cell)
/ --Elongated multinucleate cell; has a banded (striated) appearance / Covered by the endomysium (right outside sarcolemma)
  1. Myofibril (organelle composed of bundles of myofilaments)
/ --Myofibrils occupy most of the muscle cell volume; composed of sarcomeres arranged end to end; appear banded, and bands of adjacent myofibrils are aligned / None
  1. Sarcomere (a portion of a myofibril)
/ --The contractile and functional unit (physically between neighboring Z disc) composed of myofilaments made up of contractile proteins / None
  1. Myofilament (extended macromolecular structure)
/ --There are three kinds of myofilaments: thick, thin, and elastic.
First, the thick filaments contain bundled myosin molecules.
Second, the thin filaments contain actin molecules (and troponin and tropomyosin). The sliding of the thin filaments past the thick filaments produces muscle shortening.
Third, the elastic filaments (titin molecules) center the thick filament between the thin filaments and prevent overstretching. / None
  1. (7 points) Label endomysium, perimysium, epimysium, fascicle, muscle cell, myofibril, and myofilaments.

  1. (11 points) Label thick filament, thin filament, elastic filament,sarcomere, A band, I band, H zone, and Z disc. What three structures above are shortened during muscle contraction? (i)______, (ii) ______, and (iii) ______.

  1. (7 points) Label thick filaments, thin filaments,head of myosin, myosin molecule, globular actin, troponin, andtropomyosin.

  1. (Self-study questions;related to section 11.2 in the textbook)
  2. What is the function of sarcoplasmic reticulum, T (Transverse) tubules, and myofilaments?
  1. What is a sarcomere? Describe the arrangement of proteins in a sarcomere. How does a sarcomere function during muscle contraction?
  1. Why do we see striations in muscle tissue when viewed with a light microscope?
  1. (5 points) Labeljunctional folds, motor end plate, synaptic cleft, synaptic knob, and synaptic vesicles.

  1. (Self-study questions) Read the textbook (section 11.3) to understand the physiology of the neuromuscular junction.
  1. What makes up a motor unit?
  1. Are motor units all the same size?
  1. Do motor units all fire at the same time within a given muscle?
  1. Describe the events that occur at the neuromuscular junction.
  1. (Self-study questions; related to section 11.4 in the textbook) Describe what happens during muscle contraction beginning with a nerve impulse (phases A-D below). What role does calciumplay in muscle contraction? How is ATP involved in muscle contraction?
  1. Excitation of a muscle fiber— a nerve signal leads to electrical excitation in a muscle fiber:

STEP 1.Arrival of a nerve signal results in calcium channels open and calcium enters the neuron

STEP 2.Acetylcholine (Ach) release into the synaptic cleft

STEP 3.Ach binds to its receptors on the sarcolemma

STEP 4.Creation of end plate potential (EPP)

STEP 5.Creation of muscle action potential

  1. Excitation-contraction coupling—electrical excitation of a muscle fiber leads to exposure of the active sites on the actin molecules:

STEP 6.Action potentials spread down T tubules

STEP 7.Calciumreleased from calcium channels in the terminal cisternae of the sarcoplasmic reticulum into the cytosol

STEP 8.Calciumbinds to troponin of the thin filaments

STEP 9.Exposure of active sites on actin

  1. The sliding filament mechanism of contraction—exposure of the active sites on the actin molecules leads to repetitive binding of myosin to actin and sliding of the thin filaments over the thick filaments: (Steps 10-13: “CAPA”)

STEP 10.Cocking (extended position) of myosin head (energy is from hydrolysis of ATP and into ADP and phosphate

STEP 11.Attach of myosin head to actin and formation of cross-bridge

STEP 12.Pull (or power stroke) (myosin head becomes bending position): sliding the thin filament over thick filament resulting in myosin head releases ADP and phosphate

STEP 13.Apart of cross-bridgeresulting from binding of new ATP to myosin head

  1. Muscle relaxation—the cessation of the nerve signal leads to blockage of the active sites on the actin molecules so myosin can no longer bind to them

STEP 14.Stop of nervous stimulation and Ach release (reverse of step 1.)

STEP 15.Ach breakdown by Acetylcholinesterase (AchE) (reverse of step 2.)

STEP 16.Reabsorption of calcium (from the cytosol) into the cisternae and binds to calsequestrin (a protein) (reverse of step 7.)

STEP 17.Loss of calcium from troponin (reverse of step 8.)

STEP 18.Return of tropomyosin to position blocking active sites of actin (reverse of step 9.)