1. Chapter 8
Muscular System

2. Objectives 8.1.1 List various outcomes of muscular actions
8.2.2 Describe how connective tissue is part of a skeletal muscle
8.2.3 Name the major parts of a skeletal muscle fiber and describe the function of each
8.2.4 Discuss nervous stimulation of a skeletal muscle

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Introduction:
A. All movements require muscle which are organs using chemical energy to contract.
B. The three types of muscle in the body are skeletal, smooth, and cardiac muscle.

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Skeletal – aides in movement, voluntary, dense connective packaging, striated appearance
Smooth – involuntary, circularly arranged layers, found in digestive tract
Cardiac muscle- heart muscle, involuntary, banded or striated appearance, figure 8 packaging

5. Structure of a Skeletal Muscle
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Structure of a Skeletal Muscle
Each muscle is an organ, comprised of skeletal muscle tissue, connective tissues, nervous tissue, and blood.
Connective Tissue Coverings
1. fascia surround and separate each muscle.
- extends beyond the ends of the muscle and gives rise to tendons

6. epimysium - layer of connective tissue around each whole muscle
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epimysium - layer of connective tissue around each whole muscle
perimysium - surrounds individual bundles (fascicles) within each muscle
endomysium – covers each muscle cell (fiber)

8. Skeletal Muscle Fibers - single, long, cylindrical muscle cell.
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Skeletal Muscle Fibers
- single, long, cylindrical muscle cell.
- sarcolemma (cell membrane)
- sarcoplasm (cytoplasm)
~ contains myofibrils (made of the protein myosin and actin)
* produce striations
- Sarcomeres- units of repeating patterns of striations – functional units of muscle contration

10. Neuromuscular Junction (Synapse)
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Neuromuscular Junction (Synapse)
The site where the motor neuron and muscle fiber meet
- motor end plate – specialized muscle fiber where nuclei and mitochondria are abundant.
- The cytoplasm of the motor neuron contains numerous mitochondria and synaptic vesicles storing neurotransmitters.
~ chemicals used for communication
ex. acetylcholine

11. A motor neuron and the muscle fibers it controls
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Motor Units -
A motor neuron and the muscle fibers it controls
- when stimulated by a nerve impulse, the muscle fibers of the motor unit contract (depolarize) all at once.
Motor neurons have branched ends called axonal terminals. Only a synaptic cleft separates the terminal and motor plate.

13. Objectives 8.1.1 List various outcomes of muscular actions
8.2.2 Describe how connective tissue is part of a skeletal muscle
8.2.3 Name the major parts of a skeletal muscle fiber and describe the function of each
8.2.4 Discuss nervous stimulation of a skeletal muscle

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Study Analogy
Pretend you are going to play a joke on someone and give them 100 pencils. The pencils will represent muscle fibers. First you wrap each individual pencil in tissue paper (dense tissue paper of course!). This would be endomysium. Then you take about 10 pencils in a bundle (a fascicle) and wrap them in paper (perimysium). After that you take all the bundles and wrap them in gift wrap (epimysium). But you are going to mail this joke, so you also have to wrap it in brown paper representing the fascia.

15. Objectives
8.3.5 Identify the major events of skeletal muscle fiber contraction
8.3.6 Describe the energy source for muscle fiber contration
8.3.7 Describe how oxygen debt develops and how a muscle my become fatigued.

16.  Skeletal Muscle Contraction
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 Skeletal Muscle Contraction
Muscle contraction involves several components that result in the shortening of sarcomeres, and the pulling of the muscle against its attachments.

17. Role of Myosin and Actin
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Role of Myosin and Actin
Myosin consists of two twisted strands with globular cross-bridges projected outward along the strands.
Actin is a globular protein with myosin binding sites; tropomysosin and troponin are two proteins associated with the surface of the actin filaments.

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According to the sliding filament theory of muscle contraction, the myosin crossbridge attaches to the binding site on the actin filament and bends, pulling on the actin filament; it then releases and attaches to the next binding site on the actin, pulling again.
Energy from the conversion of ATP to ADP is provided to the cross- bridges from the enzyme ATPase, causing them to be in a “cocked” position.
This allows for future binding.

19. Stimulus for Contraction
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Stimulus for Contraction
Nerve impulse travels down motor neuron axon
Motor neuron terminal releases neurotransmitter, acetylcholine (ACh)
ACh binds to ACh receptors, increasing permeability to Na+ ions
Sarcolemma is stimulated by increased Na+ and creates muscle impulse
Impulse reaches sarcoplasmic reticulum and Ca+ channels open.

20. Stimulus for Contraction
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Stimulus for Contraction
Nerve impulse travels down motor neuron axon
Motor neuron terminal releases neurotransmitter, acetylcholine (ACh)
ACh binds to ACh receptors
Sarcolemma is stimulated and impulse travels deep into muscle fiber
Impulse reaches sarcoplasmic reticulum and Ca+ channels open.
Ca+ ions diffuse into sarcoplasm and bind to troponin (exposes sites on actin)
Tropomyosin move to expose sites on actin
Actin and myosin link
Actin filaments are pulled toward center of sarcomere by myosin
Muscle fiber shortens as a contraction occurs.

22. Muscle Fiber Relaxation
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Muscle Fiber Relaxation
Acetylcholinesterase (enzyme) decomposes ACh and muscle fiber is no longer stimulated
Ca+ ions return to sarcoplasmic reticulum
ATP breaks linkages b/t actin and myosin filaments
Breakdown of ATP “cocks” the cross-bridges
Troponin and tropomyosin inhibit the interaction b/t myosin and actin
Muscle fiber remains relaxed, but ready

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D. Energy Sources for Contraction Energy for contraction comes from molecules of ATP. This chemical is in limited supply and so must often be regenerated
2. Creatine phosphate, which stores excess energy released by the mitochondria, regenerates ATP from ADP and phosphate.

26. E. Oxygen Supply and Cellular Respiration
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E. Oxygen Supply and Cellular Respiration
1. muscle has a high requirement for oxygen, which enables the complete breakdown of glucose in the mitochondria.
2. Hemoglobin in red blood cells carries oxygen to muscle.
3. The pigment myoglobin stores oxygen in muscle tissue.

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F. Oxygen Debt
1. During rest or moderate activity, there is enough oxygen to support aerobic respiration.
2. Oxygen deficiency may develop during strenuous exercise, and lactic acid accumulates and is sent to the liver

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3. Oxygen debt refers to the amount of oxygen that liver cells require to convert the accumulated lactic acid into glucose, plus the amount that muscle cells need to resynthesize ATP and creatine phosphate to their original concentrations.
4. Repaying an oxygen debt may take several hours.

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G. Muscle Fatigue
1. When a muscle loses its ability to contract during strenuous exercise, it is referred to as fatigue.
2. Muscle fatigue usually arises from the accumulation of lactic acid in the muscle.
a. lowered pH
3. A muscle cramp occurs due to a lack of ATP required to return Ca+ ions back to the sarcoplasmic reticulum so muscle fibers can relax.

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H. Heat Production
1. Contraction of skeletal muscle represents an important source of heat for the body.
2. Much of the energy produced through the reactions of cellular respiration is lost as heat (another source of heat for the body).

31. Objectives
8.3.5 Identify the major events of skeletal muscle fiber contraction
8.3.6 Describe the energy source for muscle fiber contration
8.3.7 Describe how oxygen debt develops and how a muscle my become fatigued.

32. Start Third Day Material
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Start Third Day Material

33. Objectives
Explain how the attachments, locations, and interactions of skeletal muscles make possible certain movements.
Describe the locations and actions of the major skeletal muscles of each body region.

34.  Skeletal Muscle Actions
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 Skeletal Muscle Actions
A. Origin and Insertion
1. The immovable end of a muscle is the origin, while the movable end is the insertion; contraction pulls the insertion toward the origin.
2. Some muscles have more than one insertion or origin.

36. B. Interaction of Skeletal Muscles
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B. Interaction of Skeletal Muscles
1. Of a group of muscles, the one doing the majority of the work is the prime mover.
2. Helper muscles are called synergists; opposing muscles are called antagonists.

37.  Major Skeletal Muscles
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 Major Skeletal Muscles
A. Muscles are named according to any of the following criteria: size, shape, location, action, number of attachments, or direction of its fibers.