Muscle Structure and Function

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

Characteristics of a Muscle Irritability Muscles have ability to receive and respond to stimuli (force and electrical) Contractility Muscle has the ability to shorten Extendibility Muscle has the ability to lengthen Elasticity Muscle has the ability to return to normal length

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

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

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)

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

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

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

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

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

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

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

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

Glycogen fibres Large diameter Muscle Biopsy Glycogen fibres Large diameter Capillary blood vessels Oxidative fibres Small diameter