This chapter should help the student to:

• Know the three major muscle tissue types and compare their structure, function, and location.
  
• Know the function(s) of muscle and the measures required to sustain life without it.
  
• Know the relationships among muscle fascicles, muscle fibers, myofibrils, and myofilaments.
  
• Explain the roles of T tubules and the sarcoplasmic reticulum in striated muscle function.
  
• Describe muscle stimulation, contraction, and relaxation at molecular, cellular, and tissue levels.
  
• Recognize the type of muscle tissue present in a micrograph and describe its function(s).

1. Compare skeletal, cardiac, and smooth muscle in terms of:

1. 
   

   Cell size and shape (Table 10–1)

   
   
2. 
   

   Overlap of adjacent cells (IV.C)

   
   
3. 
   

   Presence of striations (I.F; Table 10–1)

   
   
4. 
   

   Ratio and arrangement of thick and thin filaments (II.B.1.c.[1]; IV.B.1.c; Table 10–1)

   
   
5. 
   

   Presence of distinct myofibrils (II.G; III.B.1; IV.B.1.c; Table 10–1)

   
   
6. 
   

   Intracellular membrane systems (e.g., triads, dyads, caveolae) (II.B.2; III.B.1; IV.B.2; Table 10–1)

   
   
7. 
   

   T-tubule placement (II.B.2; III.B.1; Table 10–1)

   
   
8. 
   

   Nuclear number and position (Table 10–1)

   
   
9. 
   

   Motor control (voluntary or involuntary; Table 10–1)

   
   
10. 
    

    Motor end-plates (myoneural junctions; Table 10–1)

    
    
11. 
    

    Intercalated disks (III.B.2; Table 10–1)

    
    
12. 
    

    Capillary abundance (III.C)

2. Compare muscles, fascicles, fibers, and myofibrils of skeletal muscle (II.G; Fig. 10–2) in terms of their structural subunits and the structure that ensheathes each.

3. Sketch a longitudinal section of two resting sarcomeres attached end-to-end and label the thin filaments, thick filaments, A band, I band, Z line, H band, and M line (Fig. 10–2).

4. Which bands or lines in question 3 contain the following?

1. 
   

   Thin filaments only (II.B.1.d)

   
   
2. 
   

   Thick filaments only (II.B.1.d)

   
   
3. 
   

   Both thick and thin filaments (II.B.1.d)

   
   
4. 
   

   α-Actinin (II.B.1.c.[2])

   
   
5. 
   

   No actin (II.B.1.d)

   
   
6. 
   

   No myosin (II.B.1.d)

5. Sketch the arrangement of myofilaments (Fig. 10–2) in a cross-section of a sarcomere cut through (1) the H band lateral to the M line, (2) the A band lateral to the H band, and (3) the I band.

6. Sketch a longitudinal section through two adjacent sarcomeres during contraction (II.D; Fig. 10–2). Which bands or lines shrink (compared with your drawing for question 3)?

7. How are thin filaments attached to the Z lines in skeletal muscle (II.B.1.c.[2]) and to dense bodies in smooth muscle (IV.B.1.a)?

8. Compare thick filaments and thin filaments (II.B.1.a and b) in terms of their proteins and the names and arrangement of their subunits or components.

9. Compare troponin and tropomyosin (II.B.1.a.[2] and [3]) in terms of their structure, association with thin filaments, and function during contraction.

10. Sketch a myoneural junction (motor end-plate) and label the terminal bouton, synaptic (acetylcholine) vesicles, presynaptic membrane, postsynaptic membrane, junctional folds, primary synaptic cleft, secondary synaptic clefts, and the basal lamina (Fig. 10–3).

11. How does the localized membrane depolarization caused by acetylcholine binding to the postsynaptic membrane of the myoneural junction spread throughout the muscle fiber (II.D; Fig. 10–4)?

12. Beginning with an impulse traveling down the axon of a motor neuron, list the events of skeletal muscle fiber stimulation, contraction, and relaxation (II.D and E; Fig. 10–4).

13. Compare red and white skeletal muscle fibers (II.B.3) in terms of:

1. 
   

   Myoglobin content

   
   
2. 
   

   Cytochrome content

   
   
3. 
   

   Contraction rate

   
   
4. 
   

   Main energy source

   
   
5. 
   

   Capacity for sustained activity

   
   
6. 
   

   Location

14. List the intercalated disk’s components. Describe the structure and function of each (III.B.2).

15. Compare atrial and ventricular cardiac muscle cells (III.B.3.a and b) in terms of T-tubule number, cell size, and presence of small cytoplasmic granules.

16. Compare vascular and visceral smooth muscle in terms of the type(s) of intermediate filaments they contain (IV.B.3.a and b).

I. General Features of Muscle Tissue

A. Terminology

Special terms applied to muscle include the prefixes sarco and myo.

B. Specialization for Contraction

Muscle cells are structurally and functionally specialized for contraction, which requires two types of special protein filaments called myofilaments; these include thin filaments containing actin and thick filaments containing myosin.

C. Mesodermal Origin

Nearly all muscle arises from mesoderm. Mesenchymal cells differentiate into muscle cells through a process involving an accumulation of myofilaments in the cytoplasm and the development of special membranous channels and compartments. Exception: Smooth muscles of the iris arise from ectoderm.

D. Cell Shape

The length of muscle cells, which sometimes reaches 4 cm, is greater than their width. Muscle cells are, therefore, often called muscle fibers or myofibers.

E. Organization

Muscle tissues are groups of muscle cells organized by connective tissue. This arrangement allows the groups to act together or separately, generating mechanical forces of varying strength. The muscles of the body (e.g., biceps brachii) are organs made up of highly organized muscle tissue (II.G).

F. Types of Muscle Tissue

The main muscle tissue types are striated muscle, which includes both skeletal and cardiac muscle, and smooth muscle. Smooth muscle (IV) occurs mainly in the walls of hollow organs (e.g., intestines and blood vessels); its contraction is slow (often occurring in waves) and involuntary. In histologic section, it lacks the banding pattern, or striations, seen in the other two types. Skeletal muscle (II) occurs mainly in association with bones, which act as pulleys and levers to multiply the force of its quick, strong, voluntary contractions. Cardiac muscle (III) occurs exclusively in the heart; its contractions are quick, strong, rhythmic, and involuntary. Characteristics of the different muscle types are summarized in Table 10–1.