1. Muscle Tissue and Organization
Muscular System
Muscle Tissue and Organization

2. Muscle Tissue Muscle tissue is one of the 4 primary tissue types
Three types of muscle tissue
Skeletal – moves the body
Cardiac – heart muscle
Smooth – moves fluid and solids through the digestive tract

3. Characteristics of Muscle Types
SKELETAL
Voluntary
Striated
Multinucleate
CARDIAC
Involuntary
Single nuclei
Intercalated discs
SMOOTH
Not striated
Single nucleus

4. Features of Muscle Tissue
Contractility – ability to shorten and pull
Excitability – responds to stimuli
Elasticity – muscle can rebound to its original shape after contraction
Extensibility – ability to contract over a range of resting lengths

5. Functions of Skeletal Muscle
Movement
Posture
Stabilize joints
Support soft tissue
Generation of heat
Regulate entrances and exits (orifices)

6. Muscle Attachment TENDONS attach muscle to bone Dense regular CT
Each muscle has an ORIGIN and INSERTION, and a specific ACTION
The origin remains stationary while the insertion moves

7. Connective Tissue of Muscle
Skeletal muscle has three layers of connective tissue
1. EPIMYSIUM – dense irregular CT that surrounds the entire muscle
2. PERIMYSIUM – divides muscle into compartments or bundles of muscle fibers called FASCICLES
3. ENDOMYSIUM – surrounds each muscle fiber (muscle cell)

10. Muscle Cell Terminology
Muscle cells are very long; muscle fibers
SARCOLEMMA – cell membrane
SARCOPLASM – cytoplasm
Sarcoplasm is filled with thousands of MYOFIBRILS that are responsible for contraction
Myofibrils are composed of MYOFILAMENTS
Myofilaments are composed of the proteins ACTIN and MYOSIN

12. Sarcomere
Organization of thick(myosin) and thin filaments(actin) in the myofibrils
Movements of these filaments causes muscle contraction
Sliding filament theory
1954 Sir Andrew Huxley and Rolf Niedeigerke
Myosin heads bind to the actin and pull or “slide” the actin past the myosin to shorten the sarcomere

13. Sarcomere Z line = end of sarcomere I band = thin (actin) filaments
H zone = thick (myosin) filaments
A band = zone of overlap, thick and thin

14. Thin Filaments Twisted strands of globular G actin molecules
Each molecule of G actin has an active site that can bind to a myosin molecule
Thin filaments also have two other proteins associated it
Tropomyosin – covers active sites on actin
Troponin - holds tropomyosin in place

15. Thick filaments Bundles of myosin molecules
About 500 myosin molecules per bundle
Myosin molecules have heads that can cross bridge to actin active sites
The binding of myosin heads to actin result in muscle contraction

17. Figure 9.4b Sarcomere Structure

18. Muscle contraction-Sliding filament theory
Contraction exerts a pull – tension
Interaction between actin and myosin triggered by calcium ions and presence of ATP
Sliding filament theory:
H band and I band get smaller
Zone of overlap gets larger
Z lines move closer together
Width of A band remains constant

19. Sliding Filament Theory
Myosin heads cross bridge to the actin active sites
Myosin attachment “pulls” the actin toward the center of the sarcomere
Contraction begins with release of Ca2+ from the terminal cisternae of the sarcoplasmic reticulum
The release of ions is the result of electrical stimulation of the muscle fiber

20. Terminal cisternae and T tubules

21. T-tubules
The t-tubules distribute the electrical signal for contraction deep into the muscle fiber
As the signal travels the terminal cisternae release calcium ions
Release of calcium cause the troponin molecule to change shape
Change in troponin causes a change in the position of tropomyosin, myosin can bind to action and contraction occurs!

22. Nervous System Control of Contraction
Skeletal muscle fibers are controlled by a motor neuron
Place where the nerve fiber and muscle meet is called the neuromuscular junction
Synaptic terminal – end of axon
Acetylcholine – neurotransmitter
Motor unit – all the muscle fiber controlled by a single motor neuron

23. Neuromuscular Junction

24. Neuromuscular junction

25. Muscle contraction

26. Muscle relaxation

28. Sarcomere contraction

29. Sliding filaments

30. Sliding filaments
Sarcomere shortens, fiber contracts

31. Other components of the sarcomere
Sarcoplasmic reticulum – stores Ca+² ions for muscle contraction
Transverse tubules – carry impulse to stimulate and coordinate contraction

32. Sarcoplasmic reticulum

33. Types of Skeletal Muscle Fibers
Fast fibers
Short duration, rapid fatigue
Anaerobic metabolism
Few mitochondria
Brief periods of intense exercise
Slow fibers
Longer duration
Aerobic metabolism
Myoglobin present for oxygen binding
Marathon running
Intermediate fibers
Greater resistance to fatigue
Similar to fast fibers but with more mitochondria

35. Organization of Muscle Fibers
Parallel
Convergent
Unipennate
Bipennate
Multipennate
Circular

38. Muscles and Leverage Muscles “work” by leverage, moving at a joint
In the body the bone is the lever, the joint is the fulcrum
Three types of levers in the body
First-class
Second-class
Third-class (most common)

42. Muscle Actions Prime movers Synergist Antagonists
Muscle mainly responsible for producing a certain action
Biceps brachii is prime mover for elbow flexion
Synergist
Assists the prime mover
Antagonists
Action opposite of prime mover
Triceps brachii is antagonist of biceps brachii