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. Muscle Tissue Skeletal muscle Cardiac muscle Smooth muscle
Voluntary striated muscle
controlled by nerves of the central nervous system
Multinucleated and tubular
Attacked to skeleton
Cardiac muscle
Involuntary striated muscle
Uninucleated, tubular, and branched
Intercalated disks contain gap junctions
spread contractions quickly throughout the heart wall
Cardiac fibers relax completely between contraction
Prevent fatigue
Smooth muscle
Involuntary nonstriated muscle
Uninucleated
Cells arranged in parallel lines, forming sheets
Located in the walls of hollow internal organs
Slower to contract, sustain prolonged contractions
does not fatigue easily

4. Review: 3 types of muscle tissue
12.1 Overview of the muscular system
Review: 3 types of muscle tissue

5. 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
- Contraction causes ATP to break down, releasing heat
Assist in movement in the cardiovascular and lymphatic vessels via muscular contractions
Protect internal organs and stabilize joints
Muscles pad bones
Tendons hold bones together at joints

6. 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
Muscles covered with fascis that extends beyond the muscle and becomes the tendon
Origin – attachment of a muscle on a stationary bone
Insertion – attachment of a muscle on a bone that moves
Muscle contraction pulls on the tendon at its insertion causing the bone to move
Action:
Nervous system does not stimulate a single muscle, it stimulates an appropriate group of muscles
1. Prime mover – muscle that does most of the work
2. Antagonistic – muscles that work in opposite pairs
- biceps brachii and triceps brachii are antagonist
3. Synergistic – muscles working in groups for a common action
- assist the prime mover, enhances action

7. An example of muscle arrangement

8. How to Name Skeletal Muscles
Size
Maximus: largerst; Minimus: smallest
Vastus: huge; Longus: long; Brevis: short
Shape
Deltoid: triangular (Greek letter delta is Δ)
Trapezius: trapezoid; Latissimus: wide; Terres: round
Location
Frontalis overlies the frontal bone
External and internal obliques; pectoralis; gluteus; brachii

9. How to Name Skeletal Muscles
Direction of muscle fiber
Rectus abdominus (rectus means straight)
Transverse: across; oblique: diagonal
Attachment
Brachioradialis: attached to the brachium and radium
Sternocleidomastoid: attached to sternum, clavicle, and mastoid
Number of attachments
the biceps brachii has two attachments
Action
extensor digitorum extends the digits
adductor (to midline), flexor (flexes), levator (lift)

11. Muscle fibers/cells Terminology for cell structure
The plasma membrane is called the sarcolemma
Transverse tubules penetrate cell to contact with sarcoplasmic reticulum
The cytoplasm is called the sarcoplasm
Contains glycogen (store energy) and myoglobin (binds oxygen) needed for muscle contraction
The SER of a muscle cell is called the sarcoplasmic reticulum and stores calcium

12. Skeletal Muscle Fibers
Sarcoplasm contains networks of SER called sarcoplasmic reticulum (SR)
Sarcoplasmic Reticulum:
Function:
store calcium and help transmit action potential to myofibril
SR forms chambers attached to T-tubules
Concentrate Ca2+ (via ion pumps)
Release Ca2+ into sarcomeres to begin muscle contraction
All calcium is actively pumped from sarcoplasm to SR (SR has 1000X more Ca2+ than sarcoplasm)

13. Skeletal Muscle Fibers
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

14. 12.2 Skeletal muscle fiber contraction

15. 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
Globular head allows for cross-bridges
Actin: are the thin filaments
Two other proteins are present
Tropomyosin and troponin
These filaments slide over one another during muscle contraction

17. Actin
Myosin

18. Regions of the Sarcomere
A-band:
- whole width of thick filaments, looks dark
microscopically
M line: at midline of sarcomere
- Center of each thick filament, middle of A-band
- Attaches neighboring thick filaments
H-zone:
- Light region on either side of the M line
- Contains thick filaments only
Zone of overlap:
- ends of A-bands
- place where thin filaments intercalate between thick
filaments (triads encircle zones of overlap)

19. Regions of the Sarcomere
I-band:
- Contains thin filaments outside zone of overlap
- Not whole width of thin filaments
Z lines/disc:
- the centers of the I bands

20. Sliding Filaments
Figure 10–8

21. Sliding Filament Theory
Contraction of skeletal muscle is due to thick filaments and thin
filament sliding past each other
not compression of the filaments
H-zones and I-bands decrease width during contraction
Zones of overlap increase width
Z-lines move closer together
A-band remains constant
Sliding causes shortening of every sarcomere in every myofibril in every fiber
Overall result = shortening of whole skeletal muscle

22. 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 reticulum

23. Skeletal Muscle: Neuromuscular Junction
Figure 10–10a, b (Navigator)

25. 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
ATP is bind to myosin
ATP is split to ADP and 2 Phosphates
ADP and P remain on the myosin heads
- Heads attach to an actin filament forming cross bridges
ADP and P is released, cross-bridges bend sharply
- Power stroke pulls action filament toward the center of the sarcomere
ATP molecule binds again to myosin to break cross bridge

26. 12.2 Skeletal muscle fiber contraction

27. 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

28. Tension Production
For a single muscle fiber contraction is all–or–none:
as a whole, a muscle fiber is either contracted or relaxed

29. Resting Length Greatest tension produced at optimal resting length
Optimal resting length = Optimum overlap
Overlap determines the number of pivoting cross-bridges
Figure 10–14

30. Frequency of Stimulation
Twitch = single contraction due to a single neural stimulation, 3 phases:
Latent period: post stimulation but not tension
Action potential moves across the sarcolemma
Ca2+ is released
Contraction phase: peak tension production
- Ca2+ bind
- Active cross bridge formation
Relaxation phase: decline in tension
Ca2+ is reabsorbed
Cross bridges decline

31. 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

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

33. Total Number of Muscle Fibers Stimulated
Each skeletal muscle has thousands of fibers organized into motor units
Motor units = all fibers controlled by a single motor neuron
Axon branches to contact each fiber
Number of fibers in a motor unit depends on the function
Fine control: 4/unit (e.g. eye muscles)
Gross control: 2000/unit (e.g. leg muscles)
Fibers from different units are intermingled in the muscle so that the activation of one unit will produce equal tension across the whole muscle

34. Motor Units in a Skeletal Muscle
Figure 10–17

35. Recruitment (Multiple Motor Unit Summation)
In a whole muscle or group of muscles, smooth motion and increasing tension is produced by slowly increasing size or number of motor units stimulated
Recruitment = order of activation of a motor unit
Slower weaker units are activated first
Strong units are added to produce steady increases in tension

36. Contraction Skeletal Muscle
During sustained contraction of a muscle
Some units rest while others contract to avoid fatigue
For maximum tension, all units in complete tetanus
Leads to rapid fatigue
Muscle tone = maintaining shape/definition of the muscle
Some units are always contracting
Exercise = Increase # of units contraction 
Increase in metabolic rate 
Increase in speed of recruitment (better tone)

37. 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

38. 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
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
best long term source

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

40. Muscle fibers come in two forms
Fast-twitch fibers:
rely on CP and fermentation (anaerobic)
Lactate buildup is possible which leads to quick fatigue
Designed for strength
Provide explosions of energy, develop max. tension more rapidly (sprinting, weight lifiting)
Light in color
Few mitochondria
Little or no myoglobin
Fewer blood vessels than slow-twitch
Motor units contain many fibers
Slow-twitch fibers:
Rely on aerobic respiration
Tire when fuel supply is gone
Designed for endurance
Long distance running
Biking and swimming
Dark in color
Many mitochondria
Myoglobin
Many blood vessels
Provide oxygen
Low maximum tension but high resistance to fatigue

41. 12.3 Whole muscle contraction
Types of muscle fibers

42. Health focus: Benefits of exercise
12.3 Whole muscle contraction
Health focus: Benefits of exercise
Increases muscle strength, endurance and flexibility
Increases cardiorespiratory endurance
Heart rate and capacity increase
Air passages dilate so that the heart and lungs are able to support prolonged muscular activity
HDL increases thus improving cardiovascular health
Prevents development of plaque
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

43. 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

44. Common muscle disorders
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

45. Muscular diseases Fibromyalgia Muscular dystrophy Myasthenia gravis
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

46. 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

48. 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?