1. Chapter 12
Muscular System

2. Points to Ponder What are the three types of muscle tissue?
What are the functions of the muscular system?
How are muscles named and what are the muscles of the human body?
How are skeletal muscles and muscle fibers structured?
How do skeletal muscles contract?
How do skeletal muscle cells acquire ATP for contraction?
What is rigor mortis?
What are some common muscular disorders?
What are some serious muscle diseases?
How do the skeletal and muscular system help maintain homeostasis?
How are these 2 systems related to other systems in maintaining homeostasis?

3. Review: 3 types of muscle tissue
12.1 Overview of the muscular system
Review: 3 types of muscle tissue
Smooth – involuntary muscle found in hollow organs and vessels
Cardiac – involuntary muscle found in the heart
Skeletal – voluntary muscle that is attached to the skeleton

4. What are the functions of skeletal muscles?
12.1 Overview of the muscular system
What are the functions of skeletal muscles?
Support the body by allowing us to stay upright
Allow for movement by attaching to the skeleton
Help maintain a constant body temperature
Assist in movement in the cardiovascular and lymphatic vessels
Protect internal organs and stabilize joints

5. How are skeletal muscles arranged?
12.1 Overview of the muscular system
How are skeletal muscles arranged?
Attachments:
Tendon – connective tissue that connects muscle to bone
Origin – attachment of a muscle on a stationary bone
Insertion – attachment of a muscle on a bone that moves
Action:
Antagonistic – muscles that work in opposite pairs
Synergistic – muscles working in groups for a common action

6. An example of muscle arrangement
12.1 Overview of the muscular system
An example of muscle arrangement

7. Examples of how skeletal muscles are named
12.1 Overview of the muscular system
Examples of how skeletal muscles are named
Size – the gluteus maximus is the largest buttock muscle
Shape – the deltoid is triangular (Greek letter delta is Δ)
Location – the frontalis overlies the frontal bone
Direction of muscle fiber – the rectus abdominus (rectus means straight)
Attachment – the brachioradialis is attached to the brachium and radium
Number of attachments – the biceps brachii has two attachments
Action – the extensor digitorum extends the digits

8. Muscles of the human body
12.1 Overview of the muscular system
Muscles of the human body

9. Muscle fibers/cells Terminology for cell structure
12.2 Skeletal muscle fiber contraction
Muscle fibers/cells
Terminology for cell structure
The plasma membrane is called the sarcolemma
The cytoplasm is called the sarcoplasm
The SER of a muscle cell is called the sarcoplasmic reticulum and stores calcium
Terminology for structure within a whole muscle
Muscle fibers are arranged in bundles called fascicles
Myofibrils are a bundle of myofilaments that run the length of a fiber
Myofilaments are proteins (actin and myosin) that are arranged in repeating units
Sarcomeres are the repeating units of actin and myosin found along a myofibril

10. Visualizing muscle structure
12.2 Skeletal muscle fiber contraction
Visualizing muscle structure

11. The sarcomere Made of two protein myofilaments
12.2 Skeletal muscle fiber contraction
The sarcomere
Made of two protein myofilaments
Myosin: are the thick filaments shaped like a golf club
Actin: are the thin filaments
These filaments slide over one another during muscle contraction

12. The beginning of muscle contraction: The sliding filament model
12.2 Skeletal muscle fiber contraction
The beginning of muscle contraction: The sliding filament model
Nerve impulses travel down motor neurons to a neuromuscular junction
Acetylcholine (ACh) is released from the neurons and bind to the muscle fibers
This binding stimulates fibers causing calcium to be released from the sarcoplasmic reticula

13. The beginning of muscle contraction
12.2 Skeletal muscle fiber contraction
The beginning of muscle contraction

14. Muscle contraction continued…
12.2 Skeletal muscle fiber contraction
Muscle contraction continued…
Released calcium combines with troponin, a molecule associated with actin
This causes the tropomyosin threads around actin to shift and expose myosin binding sites
Myosin heads bind to these sites forming cross-bridges
ATP bind to the myosin heads and is used as energy to pull the actin filaments towards the center of the sarcomere = contraction now occurs

15. Visualizing the role of calcium and myosin in muscle contraction
12.2 Skeletal muscle fiber contraction
Visualizing the role of calcium and myosin in muscle contraction

16. What role does ATP play in muscle contraction and rigor mortis?
12.2 Skeletal muscle fiber contraction
What role does ATP play in muscle contraction and rigor mortis?
ATP is needed to attach and detach the myosin heads from actin
After death muscle cells continue to produce ATP through fermentation and muscle cells can continue to contract
When ATP runs out some myosin heads are still attached and cannot unattach = rigor mortis
Body temperature and rigor mortis helps to estimate the time of death

17. Terms in whole muscle contraction
Motor unit – a nerve fiber and all of the muscle fibers it stimulates
Muscle twitch – a single contraction lasting a fraction of a second
Summation – an increase in muscle contraction until the maximal sustained contraction is reached
Tetanus – maximal sustained contraction
Tone – a continuous, partial contraction of alternate muscle fibers causing the muscle to look firm

18. Physiology of skeletal muscle contraction
12.3 Whole muscle contraction
Physiology of skeletal muscle contraction

19. Where are the fuel sources for muscle contraction?
12.3 Whole muscle contraction
Where are the fuel sources for muscle contraction?
Stored in the muscle:
Glycogen
Fat
In the blood:
Glucose
Fatty acids

20. What are the sources of ATP for muscle contraction?
12.3 Whole muscle contraction
What are the sources of ATP for muscle contraction?
Limited amounts of ATP are stored in muscle fibers
Creatine phosphate pathway (CP) – fastest way to acquire ATP but only sustains a cell for seconds; builds up when a muscle is resting
Fermentation – fast-acting but results in lactate build up
Cellular respiration (aerobic) – not an immediate source of ATP but the best long term source

21. Acquiring ATP for muscle contraction
12.3 Whole muscle contraction
Acquiring ATP for muscle contraction

22. Muscle fibers come in two forms
12.3 Whole muscle contraction
Muscle fibers come in two forms
Fast-twitch fibers:
rely on CP and fermentation (anaerobic)
Designed for strength Light in color
Few mitochondria
Little or no myoglobin
Fewer blood vessels than slow-twitch
Slow-twitch fibers:
Rely on aerobic respiration
Designed for endurance
Dark in color
Many mitochondria
Myoglobin
Many blood vessels

23. 12.3 Whole muscle contraction
Types of muscle fibers

24. Health focus: Benefits of exercise
12.3 Whole muscle contraction
Health focus: Benefits of exercise
Increases muscle strength, endurance and flexibility
Increases cardiorespiratory endurance
HDL increases thus improving cardiovascular health
Proportion of protein to fat increases favorably
May prevent certain cancers : colon, breast, cervical, uterine and ovarian
Improve density of bones thus decreasing the likelihood of osteoporosis
Enhances mood and may relieve depression

25. Health focus: Exercise
12.3 Whole muscle contraction
Health focus: Exercise

26. Common muscle disorders
Spasms – sudden, involuntary muscle contractions that are usually painful
Seizure – multiple spasms of skeletal muscles
Cramps – strong, painful spasms often of the leg and foot
Strain – stretching or tearing of a muscle
Sprain – twisting of a joint involving muscles, ligaments, tendons, blood vessels and nerves
Tendonitis – inflammation of a tendon usually due to overuse (i.e. tennis elbow)
Bursitis – inflammation of a bursa usually from repetitive use or frequent pressure

27. 12.4 Muscle disorders
Muscular diseases
Fibromyalgia – chronic achy muscles that is not well understood
Muscular dystrophy – group of genetic disorders in which muscles progressively degenerate and weaken
Myasthenia gravis – autoimmune disorder that attacks ACh receptor and weakens muscles of the face, neck and extremities
Amyotrophic lateral sclerosis (ALS) – commonly known as Lou Gehrig’s disease in which motor neurons degenerate and die leading to loss of voluntary muscle movement

28. Homeostasis: the skeletal and muscular systems
Both systems are involved with movement that allows us to respond to stimuli, digestion of food, return of blood to the heart and moving air in and out of the lungs
Both systems protect body parts
Bones store and release calcium need for muscle contraction and nerve impulse conduction
Blood cells are produced in the bone
Muscles help maintain body temperature

29. How the skeletal and muscular systems interact with other body systems
12.5 Homeostasis
How the skeletal and muscular systems interact with other body systems

30. Bioethical focus: Anabolic steroids?
12.5 Homeostasis
Bioethical focus: Anabolic steroids?
Anabolic steroids are a group of steroids that usually increase protein production
Most common side effects are high blood pressure, jaundice, acne and great increased risk of cancer
Abuse of these drugs may also cause impotence and shrinking of the testicles
May lead to increased aggressiveness and violent mood swings
Are they worth the risk?
Should they be legal to use in athletics?