Structural Components of Skeletal Muscle

Structural components of skeletal muscle ● ● ● ● Individual muscle fibre → fascicle (bundle of individual fibres) → skeletal muscle (bundle of fascicles) Muscle cells span the whole length of the muscle (this is why its called a fibre) Direction and length of fibres tells us the strength and ROM of the muscle ○ Wider = more fascicles = stronger ○ Longer = greater ROM Each fibre is wrapped in connective tissue (for ease of movement, prevent sticking together) ○ Individual muscle fibre is wrapped in endomysium ○ Fascicle is wrapped in perimysium ○ Skeletal muscle is wrapped in epimysium (connects bone to muscle, compartmentalise the muscles that they can maximise movement and prevent over contraction - control the movement) Functions of skeletal muscle ● Movement (acts on the synovial joints) ● Maintain posture (minor muscles act to maintain upright position) ● Heat (Increasing muscle activity = more chemical reactions with heat released as a byproduct, skeletal muscle generates 85% of body heat) ● Protection and support for internal organs (compartmentalise, maintain position) and body openings (eyelids, mouth) Muscle classification according to shape ● Shape is based on fascicle arrangement, during contraction the muscles shorten along the line of the fascicle (no haphazard arrangement) Parallel muscles ● Fascicles are in parallel ● Parallel (strap) → ROM (longer than they are wide), high endurance - it can continue to pull on a joint for long periods of time ● Fusiform (cylindrical) → strong, short movements, tire faster because they're using more power (greater force of contraction), POWER AND ENDURANCE (long and packed with muscle fibres in the width) ● Fusiform increase in width at the central part (have more fascicles) Convergent ● Triangular ● Common site of attachment for the widespread fibres ● Centre fibres are parallel and the other side is diagonal ● Can pull on a joint in more than one plane ● Versatile in movement and direction of action on the joint, can allow more than one action in an action pair (can be in a biaxial or multiaxial joint) ● Can isolate a movement in the fibres (isolate a fascicle) = weaker ● Full strength of the muscle = engage all of the fibres together ● Spiral is a type of convergent muscle that twists as it gets to the insertion point on the bone across the joint Pennate muscles ● Fibres run at an oblique angle to the tendon (diagonal) ● Strength and high power ● Contraction is stronger than parallel muscles because there is a greater number of muscle fibres and there's multiple short fascicles Circular muscles ● Fibres are arranged around a circular opening ● Muscle contractions decrease the diameter of the hole ● Found in the rectum, urethra, around the digestive system (sphincter muscles where you can close the opening to prevent things from going into that passage) Muscle movement rules 1. All muscles cross at least one joint 2. Muscle belly (bulk) is on top of the joint that it acts on (proximal to the joint which is crossed) → there’s more power if you pull on a joint from above 3. All muscles have at least two attachment points - Origin and insertion 4. Muscles can only pull → shorten the muscles during contraction 5. During contraction, the muscle insertion moves towards the origin (the muscle grabs on the bone and pull it back towards the origin) Muscle action pairs ● Muscles DO NOT act alone (Need an opposing action to go out and back to anatomical position) ● Agonist → brings about the movement, provides most of the force ● Synergist → smaller muscles that assist the agonist (reduce undesirable movements) ● Antagonist → opposes the actions of the agonist (typically on the opposite side) Name of the muscle - action, appearance, location ● Location ● Direction of the muscle fibres e.g. oblique ● Number of origins e.g. biceps brachii have two origin sites in the arm region ● Size e.g. maximus, medius, minimus ● Action e.g. flexor, extensor (can help determine which is the agonist/antagonist) ● Shape e.g. deltoid = triangle ● Origin-insertion Clues for identifying: ● Compartment that it is in (anterior, posterior, medial, lateral) ● The joint that it crosses (muscle should be proximal to the joint) ● Region of the body ○ Axial normally works on the vertebral column Appendicular normally works on the limbs