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: Skeletal muscle Smooth muscle Cardiac muscle

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)

Muscle Properties Irritability - A muscle irritability refers to the ability of the muscle to respond to a stimulus. Contractility - A muscle contractility refers to the muscle’s ability to shorten in length. Elasticity - This refers to the muscles ability to stretch and return to normal length. Extensibility - This refers to the muscle’s ability to extend in length. Conductivity - This refers to a muscle’s ability to transmit nerve impulses.

Motor unit

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

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

Muscle Anatomy Muscles are made of many cells called muscled fibres. Each fibre is contained within the endomysium. Muscle fibres are gathered together and contained within the perimysium. Groups of these bundles are contained within the epimysium. Like all cells muscle cells have a membrane and cytoplasm called the sarcolemma and sarcoplasm respectively. Myofibrils run along the length of the membrane in bands (giving muscles their striated appearance) and are comprised of myosin (thick filaments) and actin (thin filaments) which work together to contract the muscle fibre by sliding over each other and overlapping

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

Sarcomeres separated by narrow zones of dense material called Z lines within a sarcomere is a dark area called the A band (thick filaments; myosin) ends of the A band are darker because of overlapping thick and thin filaments the light coloured area is called the I band (thin filaments; actin) the combination of alternating dark A bands and light I bands gives the muscle fibre its striated appearance

High microscope magnification of a single sarcomere within a single myofibril

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 Eg. Elbow flexion: agonist is biceps brachii. Antagonist is triceps brachii

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 Contraction during exercise

Types of Muscle Contraction