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Muscle Structure and Function

Muscle Structure and Function. Skeletal muscle. Cardiac muscle. Smooth muscle. Types of Muscle. The human body is comprised of 324 muscles Muscle makes up 30-35% (in women) and 42-47% (in men) of body mass. Three types of muscle:. A. Skeletal (Striated) Muscle.

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Muscle Structure and Function

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  1. Muscle Structure and Function

  2. Skeletal muscle Cardiac muscle Smooth muscle Types of Muscle • The human body is comprised of 324 muscles • Muscle makes up 30-35% (in women) and 42-47% (in men) of body mass. Three types of muscle:

  3. A. Skeletal (Striated) Muscle • Connects the various parts of the skeleton through one or more connective tissue tendons • During muscle contraction, skeletal muscle shortens and moves various parts of the skeleton • Activated through signals carried to the muscles via nerves (voluntary control) • Repeated activation of a skeletal muscle can lead to fatigue

  4. B. Smooth Muscle • Located in the blood vessels, the respiratory tract, the iris of the eye, the gastro-intestinal tract • The contractions are slow and uniform • Activation is involuntary

  5. C. Cardiac Muscle • Has characteristics of both skeletal and smooth muscle • Functions to provide the contractile activity of the heart • Is very fatigue resistant • Activation of cardiac muscle is involuntary (like smooth muscle)

  6. Components of skeletal muscle d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly

  7. Muscle Fibres • Each fibre is made up of a number of myofilaments • Surrounded by a connective tissue sheath called Sarcolemma • Many fibres are enclosed by connective tissue sheath Perimycium to form bundle of fibres • Group of fibres activated via same nerve: motor unit • Each fibre has capillaries that supply nutrients and eliminate waste

  8. Muscle Teamwork • Agonist (prime mover): - the muscle or group of muscles producing a desired effect • Antagonist: - the muscle or group of muscles opposing the action • Synergist: - the muscles surrounding the joint being moved • Fixators: - the muscle or group of muscles that steady joints closer to the body axis so that the desired action can occur

  9. Bending or straightening of elbow requires the coordinated interplay of the biceps and triceps muscles

  10. Longitudinal section of myofibril a) at rest Contractile Machinery:Sarcomeres • Contractile units • Organized in series ( attached end to end) • Two types of protein myofilaments: - Actin: thin filament - Myosin: thick filament • Each myosin is surrounded by six actin filaments • Projecting from each myosin are tiny contractile myosin bridges

  11. Contractile Machinery:Crossbridge formation and movement • Cross bridge movement: • - similar to the stroking of the oars and movement of rowing shell • - movement of myosin filaments in relation to actin filaments • - shortening of the sarcomere • - shortening of each sarcomere is additive • Cross bridge formation: - a signal comes from the motor nerve activating the fibre - the heads of the myosin filaments temporarily attach themselves to the actin filaments Longitudinal section of myofibril b) contraction

  12. Contractile Machinery:Optimal Crossbridge formation Longitudinal section of myofibril • Sarcomeres should be optimal distance apart • If the sarcomeres are stretched fartherapart than optimal distance: - fewer cross bridges can form  less force produced • If the sarcomeres are too close together: - cross bridges interfere with one another as they form  less force produced c) Powerful stretching d) Powerful contraction

  13. Contractile Machinery:Optimal muscle length and optimal joint angle • The distance between sarcomeres is dependent on the stretch of the muscle and the position of the joint • Maximal muscle force occurs at optimal muscle length (lo) • Maximal muscle force occurs at optimal joint angle • Optimal joint angle occurs at optimal muscle length

  14. Muscle tension during elbow flexion at constant speed

  15. Contractile Machinery:Tendons, origin, insertion • In order for muscles to contract, they must be attached to the bones to create movement • Tendons: strong fibrous tissues at the ends of each muscle that attach muscle to bone • Origin: the end of the muscle attached to the bone that does not move • Insertion: the point of attachment of the muscle on the bone that moves

  16. Fast twitch fibres: Fast Glycolytic (Type IIb) Fast Oxidative Glyc. (Type IIb) Slow twitch fibres: Slow Oxidative (Type I) Muscle Fibre Types

  17. A. Slow Twitch Fibres • Suited for repeated contractions during activities requiring a force output of < 20-25% of max force output • Examples: lower power activities, endurance events

  18. B) Fast Twitch Fibres • Significantly greater force and speed generating capability than slow twitch fibres • Well suited for activities involving high power • Examples: sprinting, jumping, throwing

  19. The Muscle Biopsy • Used to determine muscle fibre type 1. Injection of local anesthetic into the muscle being sampled 2. Incision of approximately 5-7mm is made in the skin and fascia of the muscle 3. The piece of tissue (250-300mg) removed via the biopsy needle is imbedded in OCT compound 4. The sample is frozen in isopentane cooled to –180C

  20. Nerve-Muscle Interaction • Skeletal muscle activation is initiated through neural activation • NS can be divided into central (CNS) and peripheral (PNS) • The NS can be divided in terms of function: motor and sensory activity • Sensory: collects info from the various sensors located throughout the body and transmits the info to the brain • Motor: conducts signals to activate muscle contraction

  21. Activation of motor unit and its innervation systems • Spinal cord 2. Cytosome 3. Spinal nerve • 4. Motor nerve 5. Sensory nerve 6. Muscle with muscle fibres

  22. Motor Unit • Motor nerves extend from the spinal cord to the muscle fibres • Each fibre is activated through impulses delivered via motor end plate • Motor unit: a group of fibres activated via the same nerve • Muscles needed to perform precise movements generally consist of a large number of motor units and few muscle fibres • Less precise movements are carried out by muscles composed of fewer motor units with many fibres per unit

  23. Muscle’s Adaptation to Strength Training • Individual’s performance improvements occur through a process of biological adaptation, which is reflected in the body’s increased strength • Adaptation process proceeds at different time rates for different functional systems and physiological processes • Adaptation depends on intensity levels used in training and on athlete’s unique biological make-up • Enzymes adapt within hours, cardiovascular adaptation within 10 to 14 days

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