Biology - 47
Skeletal Muscle Histology:
Myofiber Structure: Specialized Nomenclature
Root words: Sarkos = “flesh” & Myo = “muscle”
1. Sarcolemma : Lemma = Sheath”
Highly Specialized :
a. Neuromuscular Junction:
Region of :
Specialized folded region of membrane
Motor end plate contains a high density of:
b. Sarcolemma: Conducts:
1. High density of :
2. Invaginations of sarcolemma:
Carry electrical signals to :
Stimulates contraction of :
2. Sarcoplasm: Muscle Cytoplasm
• Contents :
a. Myofibrils : Groups of :
1° Component of :
b. Organelles :
1. Mitochondria :
3. Endoplasmic Reticulum: Modified to store & release:
Terminal Cisternae: Enlarged region of :
Store and releases the majority of:
“Triad” : Arrangement of terminal cisternae “sandwiched” around:
Connects the electrical signal to the :
3. Myofibril Structure:
• Bundle of :
3 strands of overlapping protein
• 3 Types of Myofilaments :
1. Thick Filament :
2. Thin Filament :
3. Titin Protein : “Spring like”
Involved in :
• Myofilament Organization :
Sarcomere: Repeating :
“Functional Contractile Unit”
Sarcomere Structure : Review
1. A-BAND : “Anisotropic”
An = not ; Iso = same ; Tropic = turning
Changes in :
Thick, dark central band
2. I-BAND : “Isotropic”
Iso = same ; Tropic = turning
No changes in :
Thick, light, outer band
3. Z-DISC : “Zwischenscheibe”
Zwischen = between ; Scheibe = disc
Thin, dark, outer boundary of :
4. H-BAND :
Thin, light, middle band (Center of sarcomere)
5. M-LINE :
Thin, dark, middle line
Theory Of Muscle Contraction : “Sliding Filament Theory”
Contractions result from cumulative shortening of :
Thin filaments :
Slide over :
Produce muscle :
• Ability to regain original tension & length following :
• Titin Protein : Responsible for :
(Science Oct. 1995)
Mechanism : “spring-like” :
Returns sarcomere to :
Study Questions :
1. What is the difference between the muscle and muscle fiber (myofiber)?
2. What is a neuromuscular junction? What is the motor end plate? How is it specialized in the muscle to respond
to nerve cells (neurons)?
3. Describe the difference between myofibers & myofibrils, and myofilaments (Thick and thin).
4. Define sarcoplasm, sarcolemma, and sarcoplasmic reticulum.
5. What specializations are in the sarcolemma that allow it to carry electrical signals (action potentials) to the
interior of the muscle cells
6. What are the calcium storing structures called? What is the unique close relationship between the calcium storing
structures and the electrical signal carrying structures called?
7. What are the three myofilaments contained within the myofiber? How does the arrangement of myofilaments
produce the characteristic striations of skeletal muscle?
8. What is the sarcomere? Draw the overlapping pattern of myofilaments in 2 sarcomeres. Label the characteristic
sarcomere bands (A, I, H Bands, & Z-lines and M-lines).
9. What happens to the myofilaments during contraction? What is the sliding filament theory?
10. Why does it make sense to say muscle contraction results from protein filaments sliding rather than compressing
(use evidence provided by the light microscope).
11. What allows a muscle to have recoil and the ability to regain its original shape following a contraction?