BIOL1410 Lecture #11 Muscle System PDF

Lecture #11 Muscle Textbook Chapter 10  The Muscular System The muscular system is only composed of skeletal muscle Doesn’t include cardiac or smooth muscle Skeletal muscle is: Under voluntary control Striated Attached primarily to bone...

Lecture #11 Muscle Textbook Chapter 10  The Muscular System The muscular system is only composed of skeletal muscle Doesn’t include cardiac or smooth muscle Skeletal muscle is: Under voluntary control Striated Attached primarily to bone Produces bodily movements Releases heat as a byproduct of contraction Skeletal muscle is: Composed of individual muscle cells called fibers Groups of fibers are called fascicles Groups of fascicles are whole muscle  Connective Tissue 1. Fascia: Connective tissue enclosing muscle of a group of muscles Epimysium surrounds the entire muscle Perimysium wraps all of the fascicles Endomysium wraps individual muscle fibers 2. Tendons: This is the connective tissue that attaches muscle to bone Extensions of the epi, peri and endomysium covering the muscle Ex: the achilles tendon 3. Aponeurosis: A sheet like tendon Anchors muscle to connective tissue covering of a bone Ex: galea aponeurotica between the frontal and the occipital bones of the skull  Structure of a Fiber A fiber is the unique term for a muscle cell Skeletal muscles are long, cylindrical and multi-nucleate Each fiber consists of: 1. Sarcolemma Specialized muscle cell plasma membrane 2. T-tubules Also called transverse tubules A continuation of the sarcolemma that extends deep into the muscle fiber 3. Sarcoplasm: cytoplasm of muscle fiber 4. Sarcoplasmic reticulum Smooth endoplasmic reticulum with terminal cisternae Expanded regions near the T tubules Triads are T-tubules associated with two terminal cisternae  Structure of a Fiber Myofibrils: Intracellular structures Organelles that form the muscle fiber Made up of bundles of myofilaments Each myofibril is divided into contractile units called sarcomeres The sarcomeres join end to end to form the myofibril  Structure of a Fiber Myofilaments make up myofibrils and come in two forms: 1. Thin myofilaments: Made of actinà functions in muscle contraction Made of tropomyosinà a regulator that stabilizes the actin and blocks binding sites located on actin until contraction needs to occur Made of troponinà another regulator that binds to calcium during muscle contraction Also binds to actin behaving as an inhibitor 2. Thick myofilaments: Composed of myosin--> a rod like tail and two globular heads Globular heads bind to sites on actin facilitating muscle contraction Globular head is also called a cross-bridge Attached to the Z band of the sarcomere by a protein called titin  Structure of a Sarcomere Sarcomeres are the contractile unit of muscle Myofibrils are divided into sarcomeres Each sarcomere is an organized group of myofilaments The dark and the light bands found within a sarcomere provide skeletal muscle with its striated appearance The sarcomere is darkest where the myofilaments overlap and lightest where there is no overlap The alternation of light and dark is what gives the muscle its striated experience  Structure of a Sarcomere Each sarcomere contains: 1. An A band which spans the length of the thick filament This band is dark and composed of actin and myosin 2. An H zone at the center of the A band This is a light band composed of myosin 3. An I band This band is light and composed of actin, titin and the Z disk 4. Z disks connect the sarcomeres Thick filaments are connected to the Z disk by titin protein 5. M line Where the myosin tails connect to one another at the center of the sarcomere 6. T tubules These encircle the myofibrils at the junction of the A and I bands There are two T tubules per sarcomere  How does Movement Occur? Muscles and bones can produce movement by: 1. Muscles pulling on bone when they contract The origin of the muscle is on the stationary bone The insertion of the muscle is on the moving bone 2. Using group action Agonists are the major muscle producing a movement Antagonists act to oppose the agonist The antagonist is inhibited when the agonist contracts Synergists act to help the agonist by either providing extra force that is needed or by preventing undesirable effects by the agonist Ex: prevent the agonist from causing movements at the incorrect joint 3. Forming lever systems Bone and muscle interact at a joint accomplishing movement The lever is the bone The joint is the fulcrum The effort is the contraction of the agonist The resistance opposes movement of the load  How does Movement Occur? Examples of groups 1 and 2: Agonist: Origin of the biceps brachii muscle is on the scapula Insertion of the biceps brachii muscle is on the radius Antagonist: Origin of the triceps brachii muscle is on the scapula Insertion of the triceps brachii muscle is on the ulna Synergist: Brachialis Brachioradialis Example of group 3: Lever is the radius bone Fulcrum is the elbow joint The effort is the contraction of the biceps The resistance is the weight of the forearm which opposes movement  Naming Skeletal Muscles 1. Location: Tibialis anterior vs tibialis posterior 2. Relative size: Gluteus maximus, gluteus medius, gluteus minimus 3. Direction of muscle fibers: Rectus: straight relative to a reference line Transversus: at a 90o angle relative to a reference line Oblique: not at a 90o angle or straight relative to a reference line 4. Number of origins: Biceps brachii: 2 points on the scapula Triceps brachii: 3 points on the scapula and the humerus Quadriceps femoris: 4 points on the ileum and the femur  Naming Skeletal Muscles 5. Shape of the muscle: Deltoid is triangular shaped Trapezius is trapezoid shapedà no 2 parallel sides 6. The action that they perform: Flexors: decrease the angle between 2 bones Extensors: increase the angle between 2 bones Abductors: move the limb away from the midline Adductors: move the limb toward the midline 7. Origin and insertion: Sternocleidomastoid Origin is the sternum and the clavicleà dual origin Insertion is on the mastoid process of the temporal bone