1. Chapter 8
Muscular System

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Recap:
-The three types of muscle in the body are skeletal, smooth, and cardiac muscle.

3. 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
-blood

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Connective Tissue Coverings
Fascia: Layers of dense connective tissue that surround and separate each muscle.
Fascia extends beyond the ends of the muscle and gives rise to
tendons which are fused to bones

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Epimysium: The layer of connective tissue around each whole muscle Perimysium : The layer of connective tissue surrounding individual bundles (fascicles) within each muscle Endomysium: The layer of connective tissue around each muscle cell (fiber)

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Skeletal Muscle Fibers -Each muscle fiber is a single cell with… -Sarcolemma: cell membrane -Sarcoplasm : cytoplasm containing many mitochondria and nuclei -Myofibrils: organelles that are separated into compartments called sarcomeres -Sarcomeres: structures that have thick and thin protein filaments

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The Sarcomere: -Thick filaments of myofibrils are made up of the protein myosin. -Thin filaments of myofibrils are made up of the protein actin. -The organization of these filaments produces striations.

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A sarcomere extends from Z line to Z line. -I bands (light bands) made up of actin filaments are anchored to Z lines. -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.

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

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-Sliding filament theory: the myosin attaches to the binding site on the actin filament, pulls and releases it *After release, it will move on to the next actin binding site

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Stimulus for Contraction 1. The motor neuron releases acetylcholine (signalled from brain) *Signals muscle to contract 2. Calcium is released 3. Myosin is able to bind to actin and the fiber contracts (sarcomeres shorten) How does this stop?

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Energy Sources for Contraction 1. Energy for contraction comes from ATP.

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Muscle Fatigue -Muscle Fatigue: A muscle loses its ability to contract during strenuous exercise -Usually arises from the accumulation of lactic acid (lowered pH) in the muscle. -As a result, no muscle response to stimulation

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Muscle Cramp Muscle cramp: sustained involuntary contraction *Changes in fluid around cell *Uncontrolled stimulation of muscle (dehydration…)

22. Muscular Response THRESHOLD STIMULUS
Muscles will only respond (contract) if the stimulus strength reaches a certain point
Minimum strength required to make a muscle fiber contract is called the

23. Muscular Response ALL – OR – NONE RESPONSE
Muscles can’t “partially” contract
They will either contract
fully or not at all
Increasing the stimulus
intensity does not increase the force of a single muscle’s response

24. Twitches
Twitch: period of contraction and relaxation of a single muscle fiber
Movements result from multiple muscle fibers contracting together
Fast Twitch: weight lifting, sprints,
Slow Twitch: low intensity, long distance run, swimming

25. “Nervous” Twitches involuntarily Can be caused by:
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Skeletal muscle contracts
involuntarily
Can be caused by:
*Muscle fatigue/strain
*Stress/anxiety
*Medication
*Caffeine

26. Sustained Contractions
MUSCLE TONE –Even at “rest” a muscle is contracting
Important in
maintaining posture
When a person collapses,
muscle tone has been lost

27. Types of Contractions
ISOTONIC - Muscle changes length and produces force; causes motion
○ Ex. Lifting weights
ISOMETRIC - Muscle doesn’t move but creates force
Ex. Yoga

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 Smooth Muscles Smooth muscle cells: -elongated with tapered ends -lack striations
tw0 relaxed smooth muscle cells

29. Types of Smooth Muscle Multiunit Visceral Blood vessels
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Multiunit
Visceral
Blood vessels
Iris of the eye
Individual fibers
Walls of hollow organs
Sheets
Self-stimulating and rhythmic
Peristalsis in tubes and hollow organs

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Smooth Muscle Contraction -Slower to contract and relax than skeletal muscle -Can contract longer using the same amount of ATP (sustainable contractions)

31. self-exciting and rhythmic the whole heart contracts as a unit
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 Cardiac Muscle
- has structures that supply extra calcium, and can thus contract for longer periods
intercalated disks: join cells and transmit impulses throughout the heart
self-exciting and rhythmic
the whole heart contracts as a unit