Skeletal Muscle Structure PDF

Skeletal muscle structure Three types of muscular tissue Skeletal muscle tissue Mostly attached to bones. it is striated and voluntary. Cardiac muscle tissue Forms most of the wall of the heart. it is striated and involuntary. Smooth muscle tissue Located in the viscera/hollow organs. Ex. Stomach, i...

Skeletal muscle structure Three types of muscular tissue Skeletal muscle tissue Mostly attached to bones. it is striated and voluntary. Cardiac muscle tissue Forms most of the wall of the heart. it is striated and involuntary. Smooth muscle tissue Located in the viscera/hollow organs. Ex. Stomach, intestine and blood vessels. It is nonstriated and involuntary Functions of muscles Movement of the body Positional stabilization Managing the volume of organs Heat production Skeletal muscle Attached to bones as a cord or a sheet. Tendons - strong, cord-like structures composed of cleans dense fibrous connective tissue. Aponeurosis - A flatten, sheet-like tendon. Tendon sheaths: enclose certain muscles in the wrist and ankle Insertion: the site where bone and muscle are attached and move during contraction. Usually the distal point of attachment and the origin is the proximal attachment point  Skeletal muscle structure Connective tissue coverings Endomysium- surrounds individual muscle fibers (cells), binds fibers together, and supports capillaries and nerve endings in the muscle Perimysium- binds muscle fibers together into bundles Cullen fascicles and supports the blood vessels and nerve fibers serving then. Epimysium- covers the entire muscle and holds it all together. Naming of skeletal muscles Named for their location (area of the body) Intercostals (between the ribs) Brachial (on the arm) Femoral ( on the femur) Shape: The deltoid is shaped like the Greek letter delta. Trapezius is shaped like a trapezoid (similar to a kite ) Rhomboid looks like a rhombus Number of heads of origin Biceps (2 heads) Triceps (3 heads) Quadriceps (4 heads) Size: Maximus is large Minimus is small Longus is long Brevis is short. Direction their muscle fibers run Rectus has muscle fibers parallel to a midline ( Rectus abdominis) Transverse muscle fibers run perpendicular to the midline (transverse plane) Oblique muscle fibers run diagonally to the  Skeletal muscle structure Location of attachment Sternocleidomastoid muscle is on the sternum and clavicle and inserts into the mastoid process of the temporal bone Actions Adductor. Abductor Flexor Extensor Pronator Supinator Levator (lifter) Depressor Skeletal muscle cell Each muscle cell is multinucleated with peripheral nuclei. Plasma membrane of muscle fiber is sarcolemma. Myoglobin binds and stores oxygen. Sarcolemma dips down into the muscle cell in regions called the T (transverse) tubules Sarcoplasmic reticulum (sr) surrounds myofibrils within the muscle cell. It works in a storage area for calcium ions needed for muscle contraction. Terminal cisternae- expanded portions of the sr that lie on both sides of the t-tubules Skeletal muscle fiber is composed of smaller fibers called myofibrils. Myofibrils are composed of long myofilaments of actin, myosin and other proteins. They are organized in sarcomeres.  Skeletal muscle structure Sarcomere Basic contractile unit of a skeletal muscle. Myosin: thick filaments Actin: thin filaments Troponin and tropomyosin: regulatory proteins  Contraction of a skeletal muscle Myosin: each molecule is made up of two heads and a tail The head has two binding sites One site is for attachment to actin while the other site binds to an ATP molecule. Actin filament-bears sites for attaching myosin heads. Troponin-binds to calcium which is released during contraction. Tropomyosin- keeps the actin-binding sites covered during the relaxed state of skeletal muscle. Motor unit -A single motor neuron along with muscle fibers. Skeletal muscle contraction process Neuromuscular junction (N M J) is the synapse between a motor neuron and a skeletal muscle fiber. The (N M J) includes axon terminals and synaptic end bulbs of a motor neuron plus the motor end plate of the sarcolemma. Muscle twitch- A muscle contraction