Muscle Structure and Function Chapter 3 Sport Books Publisher

Learning Objectives To describe muscle’s macro and micro structures To explain the sliding-filament action of muscular contraction To differentiate among types of muscle fibres To describe group action of muscles Sport Books Publisher

Types of Muscle Skeletal muscle Smooth muscle Cardiac 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: Skeletal muscle Smooth muscle Cardiac muscle Sport Books Publisher

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 Sport Books Publisher

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 Sport Books Publisher

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) Sport Books Publisher

Components of skeletal muscle d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly Sport Books Publisher

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 Sport Books Publisher

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 Sport Books Publisher

Bending or straightening of elbow requires the coordinated interplay of the biceps and triceps muscles Sport Books Publisher

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 Longitudinal section of myofibril (a) At rest Sport Books Publisher

High microscope magnification of sarcomeres within a myofibril Sport Books Publisher

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 Sport Books Publisher

Contractile Machinery: Optimal Crossbridge formation Longitudinal section of myofibril Sarcomeres should be optimal distance apart For muscle contraction: optimal distance is (0.0019-0.0022 mm) At this distance an optimal number of cross bridges is formed If the sarcomeres are stretched farther apart 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 Sport Books Publisher