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Honors Anatomy & Physiology

Muscle System. Honors Anatomy & Physiology. I. Introduction A. Properties 1. Excitability – Ability to receive & respond to a stimulus 2. Contractility – Ability to shorten forcibly (with power) 3. Extensibility – Ability to be stretched

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Honors Anatomy & Physiology

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  1. Muscle System Honors Anatomy & Physiology

  2. I. Introduction A. Properties 1. Excitability – Ability to receive & respond to a stimulus 2. Contractility – Ability to shorten forcibly (with power) 3. Extensibility – Ability to be stretched 4. Elasticity – Ability to resume resting length after being stretched 5. Automaticity – Ability of muscle to contract without a direct nerve supply; cardiac & smooth muscle

  3. B. Types of Muscles 1. Cardiac a) Walls of heart b) Striated c) Involuntary contractions d) Automaticity e) Branched cells i. Intercalated discs where branches fuse →allows coordinated communication

  4. 2. Smooth/visceral a) Walls of internal organs, blood vessels, respiratory tract, digestive tract b) No striations – smooth cytoplasm c) Involuntary contractions d) Automaticity

  5. 3. Skeletal – 40 – 50% of adult body weight a) Attach to and cover bones b) Striated; multinucleated c) Voluntary contractions d) Contract rapidly to generate heat

  6. C. Function of Skeletal Muscle 1. Movement – locomotion/manipulation 2. Posture maintenance 3. Stabilization of joints 4. Heat generation 5. Protection of some internal organs

  7. II. Macroscopic Muscle Structure A. Single muscle cell = Muscle fiber 1. Membrane a) Endomysium b) Loose areolar connective tissue B. Bundle of muscle fibers = Fascicle 1. Membrane a) Perimysium b) Dense, fibrous connective tissue, Irregular

  8. C. Bundle of fascicles = Muscle 1. Membrane a) Epimysium (“overcoat”) b) Dense, fibrous connective tissue, Regular

  9. III. Rules that Skeletal Muscles “Live By!” A. Rule #1 1. Part 1: Muscles must have at least two attachments 2. Part 2: Muscles must cross at least one joint B. Rule #2 1. To produce movement, muscles always pull and get shorter

  10. C. Applying Rules 1 & 2 1. Distal moves toward the proximal 2. Attachment that remains in original position – ORIGIN 3. Attachment that is pulling or moving – INSERTION

  11. D. Rule #3 1. Muscle fibers always point to their attachments and show direction of pull

  12. IV. Identification of Muscle Movement and Location A. Ventral vs. Dorsal and Flexors vs. Extensors 1. Ventral to ventral – Flexor 2. Dorsal to dorsal – Extensor 3. Exceptions to the Rule a) Hip flexion – dorsal → ventral b) Hip extension – ventral → dorsal c) Dorsiflexion – dorsal → dorsal d) Plantar Flexion – ventral → ventral

  13. B. Muscles Work in Opposing Pairs 1. Primary Movers vs. Antagonist a) Muscle that pulls = Primary mover → Flexion b) Opposing muscle = Antagonist - must relax when primary mover contracts 2. Striation Patterns and Strength a) Fan-shaped Muscles provide more strength & power

  14. 3. Bone Markings and Muscle Attachments a) Tendinous attachments – long attachment - look like tree roots (1) Bumps or bars of bone (2) Grow into bone with Sharpey’s fibers   (3) Can be enhanced by stress placed on bone by weight or muscle pull. - Osteoblasts stimulated to deposit more bone around attachment. - Bump grows.

  15. b) Fan-shaped muscles (1) Lay over a flat surface → fossa (2) Attach by growing shorter Sharpey’s fibers into the bone - covers large surface area (3) Fleshy Attachment (4) Three F’s for fan-shaped muscles (a) Fan-shaped muscles attach to (b) Flat parts of bone (fossa) and have (c) Fleshy attachments

  16. Microscopic Structure of Muscle

  17. V. Microscopic Structure of Skeletal Muscle A. Muscle fiber = muscle cell 1. Sarcolemma – Plasma membrane 2. Sarcoplasm - cytoplasm 3. Multinucleated – represents mitosis without cytokinesis 4. Mitochondria – Lots of them - Furnish 95% of energy needed for contraction

  18. 5. Sarcoplasmic reticulum – membranous sac similar to endoplasmic reticulum. 6. Myofibrils a) Cylindrical cord of protein   b) Runs the length of the fiber forming patterns → striations c) Myofilaments (1) Myosin – Thick filament - Bundled together (2) Actin – Thin filament - Thin protein strand plus globular proteins

  19. 8. Sarcomere = Smallest contractile unit of muscle a) A Band – Dark area made up of myosin + actin b) H Band – seen in middle of A band → only myosin (sarcomere at rest) c) I Band – Light band → only actin d) Z Line – In middle of I band e) Sarcomere found between two Z lines

  20. Sarcomere

  21. B. Nerve Supply 1. Motor Neuron a) Origin – spinal cord or brain b) Synaptic knob (Synaptic bulb) (1) Terminal end of motor neuron is flattened into disc containing vesicles with neurotransmitter (acetylcholine)

  22. 2. Neuromuscular junction a) Site where motor neuron meets muscle fiber b) Synaptic cleft (synaptic gap) – space between synaptic knob & motor end plate c) Motor end plate – depression on sarcolemma→ highly folded

  23. Neuromuscular junction

  24. VI. Energy for Contraction A. If energy demand is low – use stored ATP 1. Cellular Respiration a) ATP – produced by mitochondria & stored in the cell b) Glucose metabolized C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP

  25. B. If demand is strenuous 1. Creatine Phosphate – high energy molecule – stored in muscle for long period of time 2. Six times more abundant than ATP in muscle 3. Releases phosphate group provides energy to re-synthesize ATP from ADP

  26. C. If demand is prolonged 1. Glycogen – complex carbohydrate → Storage form of glucose 2. Glycogen breakdown → releases glucose → aerobic respiration → ATP D. After glycogen is used up, body goes to fat stores

  27. VII.Oxygen Debt A. Aerobic respiration 1. Requires oxygen 2. At rest, adequate oxygen provided by respiratory & circulatory systems B. Anaerobic fermentation – when oxygen is not present in adequate amounts, pyruvic acid (glycolysis end product) is converted to lactic acid + 2 ATP C. Oxygen debt – amount of O2 required to allow liver to convert lactic acid back into glucose

  28. D. Oxygen debt repaid through rapid, deep breathing - may take several hours to repay E. Muscle fatigue 1. Muscle loses ability to contract 2. Most likely due to accumulation of lactic acid F. Cramp – occurs when muscle contracts spasmodically without relaxing between contractions

  29. VIII. Physiology of Muscle contraction A. Sliding Filament Theory 1. Sliding action – sarcomere shortens because crossbridges pull on thin filaments 2. Z lines move closer together B. Role of Stimulus 1. Electrical stimulus moves down motor neuron and reaches synaptic knob causing release of acetylcholine into synaptic gap 2. Acetylcholine contacts motor end plate; signal travels along sarcolemma, down T- tubules to sarcoplasmic reticulum 3. Threshhold level reached → Calcium ions released

  30. C. Muscle Contraction 1. In presence of high calcium concentration, myosin breaks ATP into ADP→sliding activity occurs →sarcomere shortens 2. Duration of contraction →depends on duration of stimulus 3. Acetylcholinesterase released by sarcolemma →breaks down acetylcholine →stops stimulus 4. Calcium taken back up by sarcoplasmic reticulum 5. End of contraction – sarcomere does not automatically return to original length →external forces must stretch sarcomere to original length

  31. IX. Muscular Responses A. "All or None" Principle 1. Muscle FIBER at rest when stimulated to contract, will always produce the same amount of tension 2. "On” or “Off" →no mechanism to regulate the amount of tension 3. Amount of tension in a muscle BUNDLE determined by a) Frequency of stimulation b) Number of muscle fibers stimulated

  32. Motor Unit

  33. B. Types of Muscle Contractions 1. Twitch Contraction – lab phenomenon - Response of a motor unit to a single action potential a) Range – 7.5 → 100 msec b) Phases (1) Latent period- begins at stimulation - ~2msec. Long - Calcium being released by sarcoplasmic reticulum (2) Contraction period – crossbridges become active and tension rises to peak (3) Relaxation period- Continues for another 25 msec. while calcium is taken back up by sarcoplasmic reticulum - Muscle tension falls to resting levels

  34. Twitch contraction

  35. 2. Wave Summation a) If a second stimulus arrives before the relaxation phase has ended, a second, more powerful contraction occurs. b) Addition of one wave to another constitutes the summation of twitches

  36. 3. Incomplete Tetanus a) If you continue to stimulate the muscle, never allowing it to relax completely, tension will rise to a peak. b) A muscle producing peak tension during rapid cycles of contraction and relaxation is said to be in “incomplete tetanus”

  37. 4. Complete Tetanus a) Obtained by increasing the rate of stimulation until the relaxation phase is completely eliminated.

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