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 11.1 below).
Review Table 11.1 Structure of a skeletal muscle.
Organizational level
Description
(Gross to microscopic)
A. Skeletal muscle (an
--Consists of many muscle cells, plus connective
organ)
tissue wrappings, blood vessels, and nerve fibers
B. Fascicle (a portion of --Discrete bundle of muscle cells, segregated from
the muscle)
the rest of the muscle by a connective tissue sheath
C. Muscle fiber (cell)
D. Myofibril (organelle
composed of bundles
of myofilaments)
E. Sarcomere (a portion
of a myofibril)
F. Myofilament
(extended
macromolecular
structure)
--Elongated multinucleate cell; has a banded
(striated) appearance
Connective tissue
wrappings
Covered externally by
the epimysium
Surrounded by a
perimysium
Covered by the
endomysium (right
outside sarcolemma)
--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
--The contractile and functional unit (physically between neighboring
Z disc) composed of myofilaments made up of contractile proteins
--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
2. (7 points) Label endomysium, perimysium, epimysium, fascicle, muscle cell, myofibril, and
myofilaments.
Review Figure 11.1—Connective tissues of a skeletal
muscle.
None
Chap. 11 (muscular tissue) homework (Questions 2, 3, 4, 6 only) with review questions;
page 2 of 4
3. (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) __________________.
Review Figure 11.2—Muscle striations and sarcomeres
4. (7 points) Label thick filaments, thin filaments, head of myosin, myosin molecule, globular actin,
troponin, and tropomyosin.
Review Figure 11.3—Molecular structure of myofilaments
Chap. 11 (muscular tissue) homework (Questions 2, 3, 4, 6 only) with review questions;
page 3 of 4
5. (SELF-STUDY QUESTIONS; RELATED TO SECTION 11.2 IN THE TEXTBOOK )
A. What is the function of sarcoplasmic reticulum, T (Transverse) tubules, and myofilaments?
B. What is a sarcomere? Describe the arrangement of proteins in a sarcomere. How does a sarcomere
function during muscle contraction?
C. Why do we see striations in muscle tissue when viewed with a light microscope?
6. (5 points) Label junctional folds, motor end plate, synaptic cleft, synaptic knob, and synaptic vesicles.
Review Figure 11.4—The neuromuscular junction
7. (SELF-STUDY QUESTIONS ) Read the textbook (section 11.3) to understand the physiology of the neuromuscular
junction.
A. What makes up a motor unit?
B. Are motor units all the same size?
C. Do motor units all fire at the same time within a given muscle?
D. Describe the events that occur at the neuromuscular junction.
Chap. 11 (muscular tissue) homework (Questions 2, 3, 4, 6 only) with review questions;
page 4 of 4
8. (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 calcium play in
muscle contraction? How is ATP involved in muscle contraction?
A. Excitation of a muscle fiber— a nerve signal leads to electrical excitation in a muscle fiber:
STEP 1.
STEP 2.
STEP 3.
STEP 4.
STEP 5.
Arrival of a nerve signal results in calcium channels open and calcium enters the neuron
Acetylcholine (Ach) release into the synaptic cleft
Ach binds to its receptors on the sarcolemma
Creation of end plate potential (EPP)
Creation of muscle action potential
B. Excitation-contraction coupling—electrical excitation of a muscle fiber leads to exposure of the
active sites on the actin molecules:
STEP 6.
STEP 7.
STEP 8.
STEP 9.
Action potentials spread down T tubules
Calcium released from calcium channels in the terminal cisternae of the sarcoplasmic reticulum into
the cytosol
Calcium binds to troponin of the thin filaments
Exposure of active sites on actin
C. 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-bridge resulting from binding of new ATP to myosin head
D. 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.)
Fig. 11.5— Sliding mechanism of contraction