The Muscular System PDF

The Muscular System The Musculoskeletal System Function of the Muscular System ▪ There are more than 600 muscles in the human body, all with special functions. ▪ The muscular system is supported by other sys...

The Muscular System The Musculoskeletal System Function of the Muscular System ▪ There are more than 600 muscles in the human body, all with special functions. ▪ The muscular system is supported by other systems in the body; – the nervous system controls the action of the muscles – the circulatory system supplies the muscles with a rich blood supply, which provides fuel for the muscles. Function of the Muscular System ▪ The muscular system works with other systems to enable them to function. The muscular system helps: the skeletal system to generate body movement develop strength, endurance and speed the heart muscle to pump blood through the body chest muscles to move – to assist in breathing digestive organs move food through the food tract  Types of Muscle Muscle makes up 30-35% (in women) and 42-47% (in men) of body mass. There are three types of muscle tissue in the body: 1. Cardiac Muscles 2. Smooth Muscles 3. Skeletal Muscles  A. Cardiac Muscles ▪ Has characteristics of both skeletal and smooth muscle ▪ Functions to provide the contractile activity of the heart – Responsible for creating the action that pumps blood from the heart to the rest of the body. ▪ Is very fatigue resistant ▪ Activation of cardiac muscle is involuntary (like smooth muscle). They are not controlled consciously, and are instead directed to act by the autonomic nervous system. ▪ Is striated (striped) B. Smooth Muscle ▪ Surrounding the body’s internal organs including: 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 ▪ Their spindle – shaped fibres are usually arranged in dense sheets.  C. Skeletal (Striated) Muscle ▪ Connects the various parts of the skeleton through one or more connective tissue tendons (tendons and ligaments) ▪ During muscle contraction, skeletal muscle shortens and moves various parts of the skeleton ▪ Activated through signals carried to the muscles via nerves (voluntary control) ▪ Repeated activation of a skeletal muscle can lead to fatigue ▪ Also referred to as striated, or striped, because of appearance under a Types of Skeletal Muscle Long Biceps Flat Short Muscle Muscle Muscle Muscle How Muscles Attach to Bone ▪ Muscle attaches to bone either directly or indirectly. Indirect Attachment: When attached indirectly, the epimysium that surrounds the exterior of the muscle fibre extends past the muscle as a tendon and then attached to the periosteum (outer membrane of the bone). Direct Attachment: When attached directly, the epimysium fuses with the periosteum.  Connective Tissues Tendons and ligaments are connective tissue that help to improve the stability of the In orderjoint. for muscles to contract, they must be attached to the bones to create movement A tendon is a connective tissue that attaches the muscle to the bone. Connective Tissues Ligaments are tough connecting tissue that run from bone to bone limiting the movement of Tendons and the joint and helps to ligaments are not very maintain the stability of elastic and lose their ability to perform the joint. correctly when stretched. If repeatedly stretched or torn, surgery may be necessary to repair the damage.  The Structure of a Muscle ▪ Skeletal muscles are made up of cylinder shaped cells called fibres. ▪ Each fibre is made up of long slender cells (myofibrils) ranging from 1mm to 50 mm in length. ▪ Myofibrils are made up of filaments ▪ In each muscle, fibres are grouped together in bundles. The arrangement of the bundle determines the shape and size of each muscle. The Structure of a Muscle ▪ Muscle length has little to do ▪ When many fibres are with strength. Usually, it is stimulated together, the number of fibres that they produce a determine its strength. shortening of the whole muscle between the two ▪ Generally: ends. – short, dense fibres provide ▪ Muscles needed to perform power; precise movements – long dense fibres provide a generally consist of a large number of motor units and greater range of few muscle fibres. movement; ▪ Less precise movements are – the longest muscles have many fibres packed carried out by muscles together to give them a bulkier shape. The Neuromuscular System ▪ The neuromuscular system refers to the complex link between the nervous system and muscular system. ▪ Muscle movement is controlled by the motor nerve. Motor nerves extend from the spinal cord to the muscle fibres. ▪ Impulses are transmitted from the brain, through the central nervous system to the motor unit. The Motor Unit ▪ A motor unit is a group of muscle fibres activated by the same nerve. ▪ Motor units can be categorized into small or large units Small motor units may have only a few muscle fibres that it stimulates. Necessary for fine motor control – eye Larger motor units may stimulate 300-800 muscle fibres to produce gross movement – arms and legs ▪ All muscle fibres of a particular motor unit always of the same fibre type The Motor Unit ▪ Each motor unit has a nerve cell (neuron) is made up of an axon and a dendrite. ▪ The dendrite receives the motor impulse and it passes through the nerve cell to the axon. ▪ At the muscle the fibre splits into numerous branches with each branch ending at the motor end plate. ▪ Each muscle fibre is activated by impulses delivered through its motor end plate. The Motor End Plate ▪ At the motor end plate a chemical reaction takes place at the neuromuscular junction between the nervous system and the muscular system. ▪ If a motor unit is activated it causes the muscle fibres to contract. This contraction is called a muscle twitch. ▪ To ensure smooth movement the nerves send impulses in waves. All – or – None Principle In order for maximum muscle force to be Once enough produced all of the motor units in a muscle or strength is muscle group must be activated. transmitted Every motor unit has a specific threshold that the entire muscle fibre or group of must be reached in order to be activated. fibres will contract Each motor unit must be activated at the same according to the time. all or none As the resistance increases, more motor units principle. must be activated by stronger, more intense impulses. When a motor A weak nerve impulse will activate only unit contracts it those motor units that have a low will contract threshold of activation. completely or not A stronger nerve impulse will activate at all. additional motor units with higher thresholds. Muscle Contractions ▪ Skeletal muscles are arranged in opposing pairs. ▪ Since a muscle cannot expand, another muscle is required to move the bone in the opposite direction and stretch the first muscle. These muscles are antagonist muscles. ▪ The muscle that contracts to initiate movement is called the agonist or prime mover. ▪ When the agonist contracts the antagonist must relax. The antagonist is a muscle that opposes movement. Examples of Opposing Muscles Action Agonist (Prime Antagonist Mover) Elbow Flexion Biceps brachii Triceps brachii Shoulder abduction Deltoid Latissimus dorsi Medial shoulder rotation Pectoralis major Infraspinatus Knee extension Quadriceps Hamstrings Wrist flexion Flexor carpi radialis Extensor carpi radialis Dorsi flexion Tibialis anterior Gastrocnemius Trunk flexion Rectus abdominus Erector spinae group Hip flexion Iliopsoas Gluteus maximus Types of Muscle Contractions ▪ Muscle contraction results in tension developed within the muscle which either overcomes a resistance, equals a resistance or is overcome by resistance. ▪ Concentric Contraction occurs when tension overcomes the resistance. ▪ Concentric (shortening) contraction occurs when ▪ The origin and insertion move muscle fibres shorten – for closer together. example, the biceps shorten when lifting an ▪ e.g.: Biceps contract object. concentrically during flexion of the elbow Types of Muscle Contractions ▪ Eccentric Contraction occurs when the tension is overcome by the resistance. ▪ Eccentric (lengthening) contraction occurs when the muscle fibres lengthen – for example, the biceps lengthens as a weight is placed back on the ground. ▪ Any controlled lowering where gravity would otherwise accelerate the ▪ The origin and the insertion of the movement involves eccentric muscle move apart. contraction. ▪ Biceps contract eccentrically during the controlled lowering of the pail. Types of Muscle Contractions ▪ Isometric Contraction results when tension is developed in the muscle but no movement is produced by the contraction. ▪ Isometric (static) contraction occurs when the fibres do not change length – for example, when you try to lift or move an immovable object.