1. The Muscular System There are ~650 muscles in the human body.

2. Terminology Myology: scientific study of muscles Myology: scientific study of muscles Striated: striped Striated: striped Muscle tone: firmness of a muscle that results from motor units being activated Muscle tone: firmness of a muscle that results from motor units being activated Atrophy: deterioration of muscle fibers Atrophy: deterioration of muscle fibers Hypertrophy: bulking up of muscle fibers Hypertrophy: bulking up of muscle fibers Oxygen debt: the amount of oxygen you owe your body after exercise Oxygen debt: the amount of oxygen you owe your body after exercise

3. 3 types of muscle Smooth Smooth Skeletal Skeletal Cardiac Cardiac

4. Muscle Classification Striated vs. Nonstriated Striated vs. Nonstriated Voluntary vs. Involuntary Voluntary vs. Involuntary Remember this??

5. 5 Muscle Functions Produce body movement Produce body movement Stabilize body positions Stabilize body positions Regulate organ volume Regulate organ volume Movement of substances within body Movement of substances within body Producing heat Producing heat –Ever gone to bed hot at night and woke up cold?

6. Muscle Characteristics Excitability: responsiveness to nerve impulses Excitability: responsiveness to nerve impulses Contractility: ability to contract Contractility: ability to contract Contractility Extensibility: ability to stretch and not tear Extensibility: ability to stretch and not tear Elasticity: ability to return to original shape after contraction Elasticity: ability to return to original shape after contraction

7. Smooth Muscle Nonstriated Nonstriated Involuntary Involuntary Found in internal organs and blood vessels Found in internal organs and blood vessels Spindle-shaped cells with one nucleus Spindle-shaped cells with one nucleus

8. Cardiac Muscle Striated with intercalated discs Striated with intercalated discs Involuntary Involuntary Found in heart only Found in heart only Branched cells with one nucleus Branched cells with one nucleus The average heart beats about 75 times per minute. There are LOTS of mitochondria in cardiac muscle.

9. Skeletal Muscle Striated Striated Voluntary Voluntary Cylindrical cells with many nuclei per cell Cylindrical cells with many nuclei per cell Attached to bones by tendons Attached to bones by tendons –Largest = Achilles tendon in heel At least 2 attachment sites of each muscle At least 2 attachment sites of each muscle –Origin: stationary site of attachment –Insertion: movable site of attachment

10. Histology of muscle tissue Muscle cells = muscle fibers Muscle cells = muscle fibers Fibers are held together by fascia Fibers are held together by fascia –Superficial fascia: under skin/on top of muscle –Deep fascia: holds individual fibers together Think about eating roast beef. Think about cleaning a chicken breast. Bundles of fibers are called fascicles Bundles of fibers are called fascicles

11. More histology… Actin (thin protein) + Myosin (thick protein)  filaments*  myofibril  muscle fiber  fascicle Actin (thin protein) + Myosin (thick protein)  filaments*  myofibril  muscle fiber  fascicle * Where filaments overlap is called the sarcomere: the basic functioning unit of muscle Think of a large rope that can be unraveled. Sliding Filament Theory/Mechanism is the description of how muscles move when actin and myosin move over and past one another at the sarcomere, thus allowing the filaments to shorten causing contraction Sliding Filament Theory/Mechanism is the description of how muscles move when actin and myosin move over and past one another at the sarcomere, thus allowing the filaments to shorten causing contraction

12. A look at muscle histology A look at muscle histology

13. Another look…

14. Muscle contraction Occurs after a motor neuron stimulates it Occurs after a motor neuron stimulates it One motor neuron plus all the muscle fibers it stimulates = 1 motor unit One motor neuron plus all the muscle fibers it stimulates = 1 motor unit Remember the pathway from chapter 1?? Control Center ReceptorEffector Sensory neuron Motor neuron

15. Movement types Small precise movements ie. writing, coloring (fine motor skills) use many motor units with few numbers of muscle fibers Small precise movements ie. writing, coloring (fine motor skills) use many motor units with few numbers of muscle fibers Large, powerful movements ie. Jumping, lifting use few motor units with large numbers of muscle fibers. Large, powerful movements ie. Jumping, lifting use few motor units with large numbers of muscle fibers.

16. Muscles and the Nervous System Neuromuscular Junction (NMJ): point where a motor neuron excites a muscle fiber Neuromuscular Junction (NMJ): point where a motor neuron excites a muscle fiber Neuromuscular Junction (NMJ Neuromuscular Junction (NMJ Neurotransmitters: chemicals found within the NMJ that trigger contraction Neurotransmitters: chemicals found within the NMJ that trigger contraction –Acetylcholine is one of the most important –Certain toxins and drugs can affect NMJ events

17. Muscle Contraction Requires Requires –High Calcium –High ATP  Aerobic cellular respiration  Glycolysis  Creatine phosphate within muscles –Acetylcholine Muscle relaxation requires the opposite. Muscles may become fatigued if the above mentioned substances are not maintained at proper levels.

18. Muscle movements Nerve impulses must reach a threshold in order for there to be a response (movement). Nerve impulses must reach a threshold in order for there to be a response (movement). Twitch: brief contraction in response to 1 action potential = nerve impulse Twitch: brief contraction in response to 1 action potential = nerve impulse Tetanus: sustained contraction in response to several action potentials Tetanus: sustained contraction in response to several action potentials Can be read with a myogram: graphical reading of muscle contractions Can be read with a myogram: graphical reading of muscle contractions

19. Myogram

20. Tetanus

21. Motor unit recruitment Allows for smooth rather than jerky movement. Allows for smooth rather than jerky movement. Allows for some units to be contracting while others are relaxing Allows for some units to be contracting while others are relaxing Prevents muscle fatigue Prevents muscle fatigue

22. Types of contractions/exercises Isotonic Isotonic –Causes movement due to muscle shortening  Walking, swimming, biking, running isometric isometric –Causes no movement due to muscle shortening  Wall sits, bar hangs

23. Muscle duties Movement occurs when several muscles act together Movement occurs when several muscles act together Most muscles are arranged in opposing pairs Most muscles are arranged in opposing pairs –Ex: flexor – extensor; abductor – adductor Prime mover: muscle causing main movement Prime mover: muscle causing main movement Synergist: complements prime mover Synergist: complements prime mover Antagonist: opposes prime mover Antagonist: opposes prime mover

24. Example of muscle duties To flex the forearm To flex the forearm –Prime mover: biceps brachii –Synergist: brachialis & brachioradialis –Antagonist: triceps brachii

25. Other helpful hints… Muscles are named based on Muscles are named based on –Origin & insertion points  Ex: sternocleidomastoid –Shape  Ex: trapezius, deltoid –Number of origins  Ex: bicep, tricep, quadricep –Size & length  Ex: longus, brevis, maximus, minimus –Direction of fibers  Ex: rectus, oblique, transverse