1. Exercise 14 Microscopic Anatomy, Organization, and
Classification of Skeletal Muscle

2. SKELETAL MUSCLE Voluntary or involuntary? Striated or not?
Multinucleate or uninucleate?

3. Terminology
“Myo-” or “-Mys-” = muscle
“Sarco-” = flesh

4. Microscopic Anatomy
Muscle Fiber = long, slender, cylindrical, MULTInucleate cell
Nuclei located just under sarcolemma (cell membrane)
Fig. 10-2

5. Muscle Fiber Anatomy Sarcolemma Sarcoplasm
Plasma membrane of muscle fiber
Trans-membrane potential: charge differences on either side
Sarcoplasm
Cytoplasm of muscle fiber
Stored glycogen, mitochondria, myoglobin, actin, myosin

6. Fig. 10-3

7. Transverse tubules Myofibrils T tubules
Narrow tubes, continuous with sarcolemma
Extend into sarcoplasm, fluid-filled
Myofibrils
Parallel, extend length of muscle fiber
Each muscle fiber contains 100s-1000s
Composed of myofilaments
Actin (thin filaments) & myosin (thick filaments)

8. Fig. 10-3

9. Sarcoplasmic Reticulum (SR)
Smooth ER
Tubular network around each myofibril
Terminal cisternae: enlarged portion of SR on either side of T tubule
Storage/release of Ca
Triad = T tubule + 2 terminal cisternae
Fig. 10-3

10. Muscle contraction begins when Calcium ions are released
from the terminal cisternae
Into the sarcoplasm
ADAM cd-rom

11. Sarcomeres Organized group of myofilaments
Contractile units, smallest functional unit of muscle fiber
Z-line to Z-line
Fig. 10-4

12. Sarcomeres A band: DARK I band: LIGHT Thick and thin filaments
M line is in the middle of the sarcomere/A band
I band: LIGHT
midline is Z line/disc
Thin filaments only
Fig. 10-4

13. Myofilaments Thick filaments: myosin
Rod-like tail bound to other myosin
Head projects outward
has binding sites for actin (thin filaments), ATP
“cross-bridges”
Contraction: The myosin head changes shape & will grab onto the actin…and pull it toward the M-line
Fig. 10-7

14. Myofilaments Thin filaments: 3 types of protein molecules actin
Double helix (2 strands) coil around each other
has binding sites for myosin
Site is blocked by troponin-tropomyosin complex when muscle’s NOT contracting
Tropomyosin
Rod-like, coils around actin to stiffen it
Covers binding sites
Troponin
3 protein-complex
One of each binds to: actin, tropomyosin, calcium ions (this one’s empty in a resting cell…see ADAM cd)

15. Fig. 10-7

16. Connective Tissue Wrappings: 3 Layers
Epimysium = outer
Perimysium = central
Endomysium = inner

17. Connective Tissue Wrappings
Epimysium
Epi = on (outside layer)
Surrounds entire muscle
Dense layer of collagen fibers, connected to deep fascia
Separates muscle from other tissues/organs
Fig. 10-1

18. Connective Tissue Wrappings
Perimysium
Peri = around (central layer)
Divides muscle into compartments:
Fascicle = bundle of muscle fibers (cells)
Collagen, elastic fibers
Blood vessels, nerves to each fascicle
Connective Tissue Wrappings
Fig. 10-1

19. Connective Tissue Wrappings
Endomysium
Endo = inside (inner layer)
Surrounds individual skeletal muscle cells (fibers)
Interconnects adjacent muscle fibers
Capillary networks to supply blood to cells, nerve fibers to control muscle
Fig. 10-1

20. Connective Tissues, cont.
Layers are continuous & interwoven – blend into one another
Muscle’s ends: layers unite to form
Bundle: TENDON
Attach skeletal muscles to bones
Contraction pulls the bone(s)
Broad sheet: APONEUROSIS
Attach skeletal muscles to bones or other muscles

21. Muscle—covered by epimysium Fascicles—covered by perimysium
Connective tissue layers!
Muscle—covered by epimysium
Fascicles—covered by perimysium
Fiber (cell)—covered by endomysium
Myofibril—covered by sarcoplasmic reticulum
Sarcomere—contains thick and thin filaments

22. Fig. 10-6

23. Blood & Nerve Supply Muscles need lots of energy, lots of oxygen
Blood vessels supply these
Each fiber (cell) has capillary blood supply
Contraction stimulated by nerve impulses
Axons (nerve fibers) penetrate connective tissue layers, & innervate individual muscle fibers (cells)

24. How Muscles Contract: ADAM cd-rom

25. Neuromuscular Junction
Junction of motor neuron & a muscle fiber
Motor neuron sends a signal to cause a movement of a skeletal muscle
Neuron—elongated portion = axon
Ends in expanded branches (synaptic terminals)
synaptic cleft: space between synaptic terminal & muscle fiber’s sarcolemma

26. Neuromuscular Junction
Synaptic terminals
Contain synaptic vesicles
Filled with acetylcholine (ACh)
Neurotransmitter: chemical released by neuron
Release of ACh triggers muscle contraction
Sarcolemma of motor end plate has receptors to bind ACh

27. Neuromuscular Junction
“Motor end plate”
Sarcolemma highly folded
Increases surface area
Sites of ACh binding
“Action Potential”
Fig

28. Neuromuscular Junction
Motor unit = A single motor neuron & ALL the muscle fibers it controls
Fig

29. Fig

30. Fig