1. Muscular System

2. Characteristics of Muscle Tissue
Irritability
Ability to respond to a stimulus (either external or internal)
Stimulation produces a muscle contraction
Contractibility
Ability to shorten or contract
Extensibility
Ability to stretch or extend
Elasticity
Ability of muscle to return to its original shape after contraction or extension

3. Types of Muscles Skeletal – striated and voluntary
Smooth – involuntary
Cardiac – heart

5. Skeletal Muscle Characteristics
Most attach to bones by tendon
Cells are multinucleate
Striated—have visible binding
Voluntary
Cells surrounded & bundled by connective tissue

6. Smooth Muscle Characteristics
Has no striations
Spindle-shaped cells
Single Nucleus
Involuntary—no conscious control
Found mainly in the walls of hollow organs

7. Characteristics of Cardiac Muscle
Has striations
Usually has a single nucleus
Joined to another cardiac muscle cell
Involuntary
Found only in the heart
Made to work continuously

8. Muscles and Muscle Fibers
Each muscle is an organ comprised of skeletal muscle tissue, connective tissues, nervous tissue, and blood
Muscles are composed of many fibers that are arranged into bundles called fascicles
Muscle fiber = muscle cell

9. Connective Tissue Coverings
Fascia – strong, dense connective tissue that surround and separates each muscle
Tendon – connective tissue that goes beyond the muscle to join with the periosteum of the bone
Aponeuroses – broad sheets of connective tissue

10. Connective Tissue Coverings
Epimysium – layer of connective tissue around each whole muscle
Perimysium – layer of connective tissue around each bundle of muscle fibers
Endomysium – layer of connective tissue around each muscle cell

12. Muscle Fibers
Each muscle fiber membrane is the sarcolemma; muscle cytoplasm is called sarcoplasm
Within the sarcoplasm are many fibers called myofibrils; myofibrils are individual muscle fibers made up of myofilaments
These filaments are found in two types: myosin (thick) and actin (thin). The organization of these filaments produces striations found in skeletal muscle

13. Muscle Fibers
A bands (dark bands) are made up of overlapping thick and thin filaments. In the center of A bands is an H zone, consisting of myosin filaments only.
I bands (light bands) are made up of actin filaments anchored to Z lines
Sacromere – extends from Z line to Z line
Z lines – lines across the muscle fiber

15. Transverse tubules – passageways for the nerve impulse to travel into the muscle fiber
Sacroplasmic reticulum – passageway that stores and releases Ca+
Calcium ions – Ca+ binds with troponin and tropomyosin which allows the actin and myosin to bind together

17. It is important to remember the heirarchy
myosin
myofibrils
fasicles
myofilaments
actin

18. It is important to remember the heirarchy
fasicles
myofibrils
myofilaments
actin
myosin

19. muscle fiber
myofilament
myofibrils
epimysium
muscle
sarcomere

20. myofilament
muscle
sarcomere
epimysium
myofibrils
muscle fiber

21. Neuromuscular Junction
The site where the motor neuron and muscle fiber meet
Activates the muscle
Also called the motor unit

22. 1.  Neuron         2.  Sarcolemma   (or motor end plate)       
3.  Vesicle      4.  Synapse        5.  Mitochondria
Motor Unit or Neuromuscular Junction

23. Neurotransmitters
Acetylcholine – this neurotransmitter released from the end of the neuron which relays impulses to the muscle cell
Acetylcholinesterase – enzyme that quickly breaks down and removes acetylcholine

25. Sliding Filament Theory
The theory of how muscle contracts
The contraction of a muscle occurs as the thin filament slides past the thick filaments
Involves five different molecules plus calcium ions
Myosin
Actin
Tropomyosin
Troponin
ATP

28. Video of sliding filament theory

29. Other Terms
Threshold stimulus – minimal strength required to cause a contraction
All-or-None response – fibers do not contract partially, either they do or they don’t
Motor unit – the muscle fiber + the motor neuron
Recruitment – more and more fibers contract as the intensity of the stimulus increases
Muscle tone – sustained contraction of individual fibers, even when muscle is at rest
Hypertrophy – muscles enlarge
Atrophy – muscles become small and weak due to disuse
Muscle fatigue – muscle loses ability to contract after prolonged exercise or strain
Muscle cramp – a sustained involuntary contraction