11.2 Muscles and Movement

Learning Objectives To describe the components of the skeletal system To be familiar with one joint and its structure – the elbow To compare the functioning of different sorts of joint To describe the macro and micro structures of skeletal muscle To explain the sliding-filament action of muscular contraction

The Skeletal System The skeletal system consists of: BONES LIGAMENTS MUSCLES TENDONS NERVES The interaction between these structures enables human movement

The Elbow

The structures of the Elbow BONES: Humerus Radius & Ulna MUSCLES (Antagonistic pair) Biceps Triceps CARTILAGE JOINT CAPSULE & SYNOVIAL FLUID

The Knee and Hip joints The knee is a HINGE joint and allows movement in one plane only The hip is a ball and socket joint and allows movement in three planes

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

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 d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly

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 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 which bend a joint - FLEXORS Antagonist: - the muscle or group of muscles which straighten a joint – EXTENSORS When one group of muscles is contracting and doing work, the other group is relaxing. This teamwork allows fine control of joint movement.

Bending or straightening of elbow requires the coordinated interplay of the biceps (flexor) and triceps (extensor) muscles

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

High microscope magnification of sarcomeres within a myofibril

Contractile Machinery: Crossbridge formation and movement Cross bridge formation: - a signal comes from the motor nerve activating the fibre by causing the release of calcium ions from the sarcoplasmic reticulum - the heads of the myosin filaments temporarily attach themselves to the actin filaments 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 Longitudinal section of myofibril