1. Biol 2401
Biol 2401 Fundamentals of Anatomy and Physiology Mrs. Willie Grant (210)

2. 10
Muscle Tissue

3. 10-1 An Introduction to Muscle Tissue
Learning Outcomes
10-1 Specify the functions of skeletal muscle tissue.
10-2 Describe the organization of muscle at the tissue level.
10-3 Explain the characteristics of skeletal muscle fibers, and identify the structural components of a sarcomere.
10-4 Identify the components of the neuromuscular junction, and summarize the events involved in the neural control of skeletal muscle contraction and relaxation.
10-5 Describe the mechanism responsible for tension production in a muscle fiber, and compare the different types of muscle contraction.
10-6 Describe the mechanisms by which muscle fibers obtain the energy to power contractions.
10-7 Relate the types of muscle fibers to muscle performance, and distinguish between aerobic and anaerobic endurance.
10-8 Identify the structural and functional differences between skeletal muscle fibers and cardiac muscle cells.
10-9 Identify the structural and functional differences between skeletal muscle fibers and smooth muscle cells, and discuss the roles of smooth muscle tissue in systems throughout the body.

4. An Introduction to Muscle Tissue
A primary tissue type, divided into:
Skeletal muscle tissue
Cardiac muscle tissue
Smooth muscle tissue
Skeletal Muscles
Are attached to the skeletal system
Allow us to move

5. 10-1 Functions of Skeletal Muscle Tissue
Six Functions of Skeletal Muscle Tissue
Produce skeletal movement
Maintain posture and body position
Support soft tissues
Guard entrances and exits
Maintain body temperature
Store nutrient reserves
Skeletal Muscle Organization
Muscle tissue (muscle cells or fibers)
Connective tissues
Nerves
Blood vessels

6. 10-2 Organization of Muscle
Organization of Connective Tissues
Muscles have three layers of connective tissues
Epimysium
Exterior collagen layer
Connected to deep fascia
Separates muscle from surrounding tiss
Perimysium
Separates muscle from surrounding tissue
Endomysium
Surrounds individual muscle cells (muscle fibers)
Contains capillaries and nerve fibers contacting muscle cells
Contains myosatellite cells (stem cells) that repair damage

8. 10-2 Organization of Muscle
Organization of Connective Tissues
Muscle Attachments
Endomysium, perimysium, and epimysium come together:
At ends of muscles
To form connective tissue attachment to bone matrix
tendon (bundle) or aponeurosis (sheet)
Blood Vessels and Nerves
Muscles have extensive vascular systems that:
Supply large amounts of oxygen
Supply nutrients
Carry away wastes
Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord)

9. Figure 10-2 The Formation of a Multinucleate Skeletal Muscle Fiber
Muscle fibers develop through the fusion of mesodermal cells called myoblasts.
Cells are long
Cells develop from myoblasts
Cells become very large
Cells contain hundreds of nuclei
Myoblasts
A muscle fiber forms by the fusion of myoblasts.
Muscle fiber
LM  612
Nuclei
Sarcolemma
Myofibrils
Myosatellite cell
Nuclei
Mitochondria
Immature muscle fiber
1 Which structure shown releases calcium ions to trigger muscle contraction?
A diagrammatic view and a micrograph of one muscle fiber.
Myosatellite cell
Up to 30 cm in length
Mature muscle fiber 9

10. 10-3 Characteristics of Skeletal Muscle Fibers
The Sarcolemma and Transverse Tubules
The sarcolemma—cell membrane of a muscle fiber
Surrounds the sarcoplasm (cytoplasm of muscle fiber)
A change in transmembrane potential begins contractions
Transverse tubules (T tubules)
Transmit action potential through cell
Allow entire muscle fiber to contract simultaneously
Have same properties as sarcolemma

11. 10-3 Characteristics of Skeletal Muscle Fibers
Myofibrils
Lengthwise subdivisions within muscle fiber
Made up of bundles of protein filaments (myofilaments)
Myofilaments are responsible for muscle contraction
Types of myofilaments:
Thin filaments
Made of the protein actin
Thick filaments
Made of the protein myosin

12. 10-3 Characteristics of Skeletal Muscle Fibers
The Sarcoplasmic Reticulum (SR)
A membranous structure surrounding each myofibril
Helps transmit action potential to myofibril
Similar in structure to smooth endoplasmic reticulum
Forms chambers (terminal cisternae) attached to T tubules
Triad
Is formed by one T tubule and two terminal cisternae
Cisternae
Concentrate Ca2+ (via ion pumps)
Release Ca2+ into sarcomeres to begin muscle contraction

13. Figure 10-3 The Structure of a Skeletal Muscle Fiber
Myofibril
Sarcolemma
Nuclei
Sarcoplasm
MUSCLE FIBER
Mitochondria
Terminal cisterna
Sarcolemma
Sarcolemma
Sarcoplasm
Myofibril
Myofibrils
Thin filament
Thick filament
Triad
Sarcoplasmic reticulum
T tubules 13

14. 10-3 Structural Components of a Sarcomere
Sarcomeres
The contractile units of muscle
Structural units of myofibrils
Form visible patterns within myofibrils
A striped or striated pattern within myofibrils
Alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

15. 10-3 Structural Components of a Sarcomere
Sarcomeres
The A Band
M line
The center of the A band
At midline of sarcomere
The H Band
The area around the M line
Has thick filaments but no thin filaments
Zone of overlap
The densest, darkest area on a light micrograph
Where thick and thin filaments overlap
The I Band
Z lines
The centers of the I bands
At two ends of sarcomere
Titin
Are strands of protein
Reach from tips of thick filaments to the Z line
Stabilize the filaments
3 Which proteins are present in the A band? In the I band?

17. Figure 10-6 Levels of Functional Organization in a Skeletal Muscle
Myofibril
Surrounded by: Epimysium
Surrounded by: Sarcoplasmic reticulum
Epimysium
Contains: Muscle fascicles
Consists of: Sarcomeres (Z line to Z line)
Sarcomere
I band
A band
Muscle Fascicle
Contains: Thick filaments
Surrounded by: Perimysium
Thin filaments
Perimysium
Contains: Muscle fibers
Z line
M line
Titin
Z line
H band
Muscle Fiber
2 Which of the following is the smallest:
muscle fiber, thick filament, myofibril?
Which is the largest?
Surrounded by: Endomysium
Endomysium
Contains: Myofibrils 17

18. 10-3 Structural Components of a Sarcomere
Thin Filaments
F-actin (filamentous actin)
Is two twisted rows of globular G-actin
The active sites on G-actin strands bind to myosin
Nebulin
Holds F-actin strands together
Tropomyosin
Is a double strand
Prevents actin–myosin interaction
Troponin
A globular protein
Binds tropomyosin to G-actin
Controlled by Ca2+

20. 10-3 Structural Components of a Sarcomere
Thick Filaments
Contain about 300 twisted myosin subunits
Contain titin strands that recoil after stretching
The mysosin molecule
Tail
Binds to other myosin molecules
Head
Made of two globular protein subunits
Reaches the nearest thin filament

21. Figure 10-7cd Thick and Thin Filaments
Titin
The structure of thick filaments, showing the orientation of the myosin molecules
M line
Myosin head
Myosin tail
Hinge
The structure of a myosin molecule
Myosin Action
During contraction, myosin heads:
Interact with actin filaments, forming cross-bridges
Pivot, producing motion 21

22. 10-3 Structural Components of a Sarcomere
Sliding Filaments and Muscle Contraction
Sliding Filament Theory
1 Thin filaments of sarcomere slide toward M line, alongside thick filaments
2 The width of A zone stays the same
3 Z lines move closer together

23. 4 What happens to the I band and the H zone as muscles contract
4 What happens to the I band and the H zone as muscles contract? Do the lengths of the thick and thin filaments change?

24. 10-3 Structural Components of a Sarcomere
Skeletal Muscle Contraction
The process of contraction
Neural stimulation of sarcolemma
Causes excitation–contraction coupling
Muscle fiber contraction
Interaction of thick and thin filaments
Tension production (the “pull” when a muscle fiber contracts) production

25. Figure 10-9 An Overview of Skeletal Muscle Contraction
Neural control
Contraction occurs when skeletal muscle
Fibers are activated by neurons.
Excitation–contraction coupling
Calcium ions are released from SR.
Excitation
Calcium release
Calcium ions trigger interaction between
thick/thin filaments.
triggers
ATP
Thick-thin filament interaction
Muscle fiber contraction
Mulscle fiber contracts.
leads to
Tension is produced.
Tension production 25

26. 10-4 Components of the Neuromuscular Junction
The Control of Skeletal Muscle Activity
The neuromuscular junction (NMJ)
Special intercellular connection between the nervous system and skeletal muscle fiber
Controls calcium ion release into the sarcoplasm
A single axon may branch to control more than one skeletal muscle fiber, but each muscle fiber has only one neuromuscular junction (NMJ). At the NMJ, the synaptic terminal of the neuronlies near the motor end plate of the muscle fiber.
5 What part of the sarcolemma contains acetylcholine receptors?

28. 10-4 Components of the Neuromuscular Junction
Excitation–Contraction Coupling (The link between the generation of an action potential in the sarcolemma and the start of a muscle contraction)
(1) Action potential reaches a triad (pair of terminal cisternae and one T tubule)
(2) Releasing Ca2+
(3) Triggering contraction
Requires myosin heads to be in “cocked” position
Loaded by ATP energy

30. 10-4 Skeletal Muscle Contraction
The Contraction Cycle
Contraction Cycle Begins
Active-Site Exposure
Cross-Bridge Formation
Myosin Head Pivoting
Cross-Bridge Detachment
Myosin Reactivation

32. Figure 10-12 The Contraction Cycle
Resting Sarcomere
Zone of overlap (shown in sequence above) 32

33. Figure 10-12 The Contraction Cycle
Contracted Sarcomere 33

34. 10-4 Skeletal Muscle Contraction
Fiber Shortening
As sarcomeres shorten, muscle pulls together, producing tension (the “pull” when a muscle fiber contractts)
Muscle shortening can occur at both ends of the muscle, or at only one end of the muscle
This depends on the way the muscle is attached at the ends

35. Figure 10-13 Shortening during a Contraction
When both ends are free to move, the ends of a contracting muscle fiber move toward the center of the muscle fiber.
When one end of a myofibril is fixed in position, and the other end free to move, the free end is pulled toward the fixed end. 35

36. 10-4 Skeletal Muscle Relaxation
Contraction Duration
Depends on:
Duration of neural stimulus
Number of free calcium ions in sarcoplasm
Availability of ATP
Ca2+ concentrations fall
Ca2+ detaches from troponin
Active sites are re-covered by tropomyosin
Rigor Mortis
A fixed muscular contraction after death
Caused when:
Ion pumps cease to function; ran out of ATP
Calcium builds up in the sarcoplasm

37. 10-4 Skeletal Muscle Contraction and Relaxation
Summary
Skeletal muscle fibers shorten as thin filaments slide between thick filaments
Free Ca2+ in the sarcoplasm triggers contraction
SR releases Ca2+ when a motor neuron stimulates the muscle fiber
Contraction is an active process
Relaxation and return to resting length are passive