Muscle Structure and Function

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 • Through graded activation of the muscles, the speed and smoothness of the movement can be gradated • Activated through signals carried to the muscles via nerves (voluntary control) • Repeated activation of a skeletal muscle can lead to fatigue • Biomechanics: assessment of movement and the sequential pattern of muscle activation that move body segments

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 • Functions to alter the activity of various body parts to meet the needs of the body at that time • Is fatigue resistant • Activation is involuntary

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

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

7. Muscle Fibres • Cylinder-shaped cells that make up skeletal muscle • Each fibre is made up of a number of myofilaments • Diameter of fibre (0.05-0.10 mm) • Length of fibre (appr. 15 cm) • Surrounded by a connective tissue sheath called Sarcolemma • Many fibres are enclosed by connective tissue sheath Perimycium to form bundle of fibres • Each fibre contains contractile machinery and cell organelles • Activated through impulses via motor end plate • 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. 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

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

12. 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

13. 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

14. 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

15. Muscle Biopsy Glycogen fibresLarge diameter Capillary blood vessels Oxidative fibres Small diameter

16. The Histochemistry • The biopsy samples are first sectioned (8-10 μm thickness) • Sections are processed for myosin ATPase: Fast twitch fibres – rich in myosin ATPase (alkaline labile) Slow twitch fibres – low in myosin ATPase (acid labile) • Sections are processed for other metabolic characteristics

17. 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

18. 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

19. 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 • All muscle fibres of one particular motor unit are always of the same fibre type • 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

20. All-or-none Principle • Whether or not a motor unit activates upon the arrival of an impulse depends upon the so called all-or-none principle • An impulse of a certain magnitude (or strength) is required to cause the innervated fibres to contract • Every motor unit has a specific threshold that must be reached for such activation to occur

21. Intra-muscle Coordination • The capacity to apply motor units simultaneously is known as intra-muscle coordination • Many highly trained power athletes, such as weightlifters, wrestlers, and shot putters, are able to activate up to 85% of their available muscle fibres simultaneously (untrained: 60%) • Force deficit: the difference between assisted and voluntarily generated maximal force (trained: 10%, untrained: 20-35%)

22. Intra-muscle Coordination cont. • Trained athletes have not only a larger muscle mass than untrained individuals, but can also exploit a larger number of muscle fibres • Athletes are more restricted in further developing strength by improving intra-muscular coordination • Trained individuals can further increase strength only by increasing muscle diameter

23. Inter-muscle Coordination • The interplay between muscles that generate movement through contraction (agonists) and muscles responsible for opposing movement (antagonists) is called inter-muscle coordination • The greater the participation of muscles and muscle groups, the higher the importance of inter-muscle coordination • To benefit from strength training the individual muscle groups can be trained in relative isolation • Difficulties may occur if the athlete fails to develop all the relevant muscles in a balanced manner

24. Inter-muscle Coordination cont. • High-level inter-muscle coordination greatly improves strength performance and also enhances the flow, rhythm, and precision of movement • Trained athlete is able to translate strength potential to enhance inter-muscle coordination

25. 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

26. Discussion Questions 1) What are the 3 types of muscle found in the human body? 2) Skeletal muscle is made up of bundles of ________, each of which are made up of a number of ________. 3) What are the 3 types of muscle fibres? Give two characteristics of each type of fibre. 4) What are the main types of fibre contraction? Give real life examples of each. 6) Discuss the differences between inter- and intra-muscle coordination

27. Make a Table with muscles from pg. 44-45 in text There will be some information that is not in your text. Do your best for now.

28. Skeletal muscle Smooth muscle Cardiac muscle Biomechanics Muscle fibres Myofilaments Motor unit Sarcomeres Cross bridge formation Slow twitch fibres Fast twitch fibres Muscle biopsy Isometric contraction Isotonic contraction Isokinetic contraction Concentric contraction Eccentric contraction Plyocentric contraction Key Terms