Muscles

There are over 660 skeletal muscles in the body. Used to create all voluntary movement. Contract and relax There are three types of muscle tissue: Skeletal Cardiac Smooth

Skeletal Muscles Attached to bones and/or skin Also known as striated muscles Responsible for movement and posture Any other functions?

Anterior and posterior view of superficial muscles

Anterior and posterior view of major muscles of the arms, torso & legs

How muscles “work” A muscle’s origin occurs where it is attached to a stable bone. A muscle’s insertion occurs where it attached to a bone that it pulls on and moves. Muscles work in pairs or groups. The muscle that creates the movement is known as the agonist whilst the opposite muscle is known as the antagonist. Reciprocal inhibition occurs when one muscle contracts and its opposite relaxes to allow movements to occur.

Smooth Muscle Smooth muscle is found in the walls of hollow visceral (internal) organs such as the stomach, bladder and respiratory passages. Smooth muscle acts to propel substances along a pathway. Involuntary

Cardiac Muscle Cardiac muscle is found only in the heart. When these muscles contract the internal chambers of the heart become smaller, forcing blood into the large arteries that leave the heart. Involuntary

Connective Tissue Cartilage: Slightly elastic tissue that is found on the ends of bones in synovial joints, in between vertebrae, joining the ribs to the sternum, in the pubic arch and in the ears and nose. Ligaments Cross over joints, joining bone to bone and providing stability at the joints. Slightly elastic Tendons Attach muscle to bones and allows the muscles to move the bones. Inelastic

Cartilage Hyaline cartilage End of bones (in joints), nose, ribs, trachea, larynx Embryonic skeleton Elastic cartilage Ears Epiglottis Fibrocartilage Intervertebral discs & pubic arch Where tendons and ligaments join to bone

*The next image shows surgery on an Achilles tendon. It contains blood etc.

Nervous control of muscle contractions Nerves deliver messages to the muscles to tell them to contract.

Muscle fibres Fusiform Fibres run in the same direction as the tendon. Low force but large movement. Quick contractions and high power. Long muscle fibres. Penniform Fibres run at angles to the tendon. 75% of all skeletal muscle. Great force/strength but slower contractions than fusiform. Short muscle fibres.

Muscle fibre arrangement

The microscopic structure of muscles p 16 – 18* Each muscle belly consists of thousands of fibres. Each fibre is surrounded by endomysium. Bundles of fibres are called fascicles. Fascicles are surrounded by perimysium. Bundles of fascicles are held together by epimysium (outside of the muscle).

The microscopic structure of muscles Muscle fibres are made up of myofibrils. Myofibrils consist of sarcomeres, which are arranged end to end for the entire length of the fibre, and are separated by dark lines called Z-lines. Myofibrils are further divided into myofilaments. Myofilaments a think filament (myosin) a thin filament (actin)

The microscopic structure of muscles

Nervous control of muscular contractions Motor neurons convey nerve impulses from the brain to muscles A motor neuron and the fibres it controls/stimulates are known as the motor unit Sensory neurons convey nerve impulses from muscles, organs and cells to the brain

The all or nothing principles states: It is not until an electrical threshold is surpassed that all of the fibres linked to a motor unit will fire together and maximally. Gross movements requiring major muscle involvement require more motor units than precise/ fine movements Fibres will be recruited according to the activity demand and this is known as preferential recruitment

How muscles contract (p. 21) Insert 1.23

Types of Contractions There are three types of muscular contraction: Isotonic Isometric Isokinetic

Isotonic These contractions change the length of the muscle while creating the force. There are two types of isotonic contractions: Concentric Shortening the muscle Eccentric Lengthening the muscle

Isometric These contractions create a force, but do not change the length of the muscle. For example: Pushing against an opponent Holding a netball These types of contractions create more force than any other type of contraction, and cause the muscle to tire quickly.

Isokinetic Tension developed is maximal throughout the entire range of motion and is common on hydraulic fitness equipment. The amount of force applied by the machine always equals the amount of force applied by the muscle. This can only be done with isokinetic equipment.

Muscle Fibres Slow twitch Type I fibres Suited to endurance athletes Increased capacity to use oxygen Contract slowly with less force Capacity to contract for long period of time Don’t fatigue easily

Muscle Fibres cont… Fast twitch Type II fibres Type A – partially aerobic Type B – purely aerobic Suited to speed and strength Contract rapidly with greater force Capacity to contract for short periods of time Fatigue easily

% of fast-twitch muscle fibres found in various athletes

Characteristics of muscle fibres Table 1.4, page 25.

Factors affecting muscle strength Fibre arrangement Pennate Vs Fusiform Muscle fibre recruitment More motor units recruited = more strength Muscle fibre type Fast twitch are stronger than slow twitch Speed of contraction As the speed of contraction increases, strength decreases. Gender differences Same cross-sectional area = same strength Age differences Muscles are strongest between

Activity Choose three actions/physical activities: Name the major muscles being used. Name the type of contraction being demonstrated. Name the muscle fibre needed to best perform this action, and explain why.