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Muscle Tissue & Skeletal Muscle Notes 3 Types of Muscle Tissue • Skeletal muscle- striated and voluntary (it is subject to conscious control) • Smooth muscle- not striated and involuntary (we do not consciously control it) – Lines our digestive system and empties our bladder and bowels • Cardiac muscle- striated and involuntary – Only found in the heart Functions of Skeletal Muscle • • • • • Produce movement Maintain posture Support soft tissue Guard entrances and exits Body temperature THE ANATOMY OF A MUSCLE Anatomy of Skeletal Muscle • Each muscle is composed of bundles of muscle fibers. • Each muscle fiber (cell) has many nuclei and is a cluster of myofibrils • Myofibrils contain two types of protein filaments that are arranged in a regular, over-lapping pattern – Myosin – thicker filament – Actin – thinner filament Sarcomere • The functional unit of contraction in skeletal muscle myofibrils • Located between two Z lines • One end of each actin filament is attached to the Z line • Myosin filaments are located between two actin filaments and overlap them on each end Muscle Tissue Anatomy • Epimysium - outer covering of muscles • Fascicle - a bundle of muscle fibers Muscle Tissue Anatomy • Perimysium - each fascicle is covered by the perimysium • Endomysium - thin covering around each muscle fiber - Both perimysium & endomysium contain blood vessels and nerve endings Muscle Tissue Anatomy • Myofibrils - each muscle fiber (muscle cell) contains bundles of myofibrils • Sarcomere - what gives skeletal muscle its STRIATIONS • A – BAND - area where actin & myosin overlap • I – BAND - area of actin only CW: Color and Label Muscle Contractions Sliding Filament Theory • The myosin filaments pull the actin filaments towards the center of the sarcomere • This shortens the sarcomere which in turn shortens the muscle • Pink is actin • Blue is myosin The myosin pulls the actin toward the center of each sarcomere which in turn shortens or contracts the muscle All-or-None Response • The shortening of the sarcomere occurs along the entire length of the muscle fiber • The strength of a muscle contraction depends on – How often the individual muscle fibers are stimulated to contract – How many muscle fibers contract within a given muscle Skeletal Muscle Contractions • Controlled voluntarily by the nervous system • Motor Unit – a motor neuron (nerve cell) and all of the muscle fibers it controls Steps to Muscle Contraction Neuron action potential arrives at end of motor neuron 2 ACH is released 3 ACh binds to receptors on motor end plate 4 Permeability of sarcolemma changes (Na rushes in)(an action potential is produced) 5 Muscle action potential sweeps into the T tubules triggering 6 release of Ca from the cisternae of the sarcoplasmic reticulum 7 CA binds to troponin 8 Troponin changes shape and shifts tropomyosin to expose binding sites of actin 9 myosin binds to actin (cross bridge is formend)(ADP released from myosin) 10 Myosin head pivots (pulling actin) 11 Myosin releases from actin (cross bridge is broken)(another ATP binds to myosin) 12 Myosin re-extends into "ready" position (ATP->ADP+Pi)(ADP is bound to myosin) Energy for Muscle Contractions • Energy for muscle contractions comes from ATP (adenosine triphosphate) • Glucose is converted into ATP by mitochondria during cellular respiration Two Cellular Respiration Pathways • Aerobic Respiration requires a supply of oxygen in order to take place • Produces the maximum number of ATP molecules (36-38 ATP’s for each glucose molecule converted) • ATP is used in long continuous exercise (distance running) Two Cellular Respiration Pathways • Anaerobic Respiration occurs when available oxygen has been depleted • Produces only 2 ATP’s per glucose molecule • Also produces Lactic Acid – causes muscle soreness & fatigue • Typically occurs during short periods of intense exercise Cellular Respiration Summary (glucose) 2 Lactic acid 36-38 Oxygen Supply • Oxygen is carried to the muscle cells by red blood cells through the circulatory system Fatigue • Decrease in the strength of muscle contractions due to repeated stimulation without periods of rest • If continued, muscle will lose ability to contract • Occurs when ATP supply is depleted and oxygen is not replenished fast enough – lactic acid builds up in the muscle fibers Oxygen Debt & Recovery Period • Oxygen debt – amount of oxygen needed to restore pre-exertion oxygen levels • During recovery (rest) period, oxygen is replenished along and more ATP is produced while lactic acid is broken down Skeletal Muscles • Attached to bones by tendons • Origin – the end of the muscle attached to the bone that remains stationary during a muscle contraction • Insertion – the end of the muscle attached to the bone that moves during a muscle contraction • The insertion always moves toward the origin Skeletal Muscles • Attached to the bones of the appendicular skeleton in opposing pairs (flexors and extensors) • Flexors – cause the limb to bend at the joint • Extensors – cause them to straighten Notes: Naming Muscles Types of Muscles Prime mover – muscle with the major responsibility for a certain movement Antagonist – muscle that opposes or reverses a prime mover Synergist – muscle that aids a prime mover in a movement and helps prevent rotation Fixator – stabilizes the origin of a prime mover Naming of Skeletal Muscles Direction of muscle fibers Example: Relative rectus (straight) size of the muscle Example: maximus (largest) Naming of Skeletal Muscles Location of the muscle Example: many muscles are named for bones (e.g., temporalis) Number of origins Example: triceps (three heads) Naming of Skeletal Muscles Location of the muscle’s origin and insertion Example: Shape of the muscle Example: Action sterno (on the sternum) deltoid (triangular) of the muscle Example: flexor and extensor (flexes or extends a bone) • Types of Movements (terminology) • Origin - where a muscle begins • Insertion - where a muscle ends • Action - motion produced • Flexion - joint angle gets smaller • Extension - joint angle gets larger hyperextension - movement beyond 180o of joint motion • • abduction movement away from midline of body • adduction - movement toward midline of body Identifying Muscles Face Muscles TemporalisCloses jaws (chewing) MasseterCloses side of jaw jaws (chewing) FrontalisRaises temporal Bone frontal bone eyebrows and wrinkles forehead horizontally Face Muscles Orbicularis Closes eye Orbicularis Draws Oculi- encircles eye Oris- encircles mouth lips together Mentalis-chin Raises and protrudes lower lip Neck Muscles Sternocleidomastoid- attaches to sternum, clavicle, and mastoid process Turns the head and bows the head Head and Neck Muscles Anterior Trunk Muscles Pectoralis Pulls Major- upper chest upper arm forward and across the chest Rectus Abdominus-connects pubic bones to ribs and sternum Compresses Flexes contents of abdominal cavity spinal column (sit-ups) Anterior Trunk Muscles External Oblique- slant downward from lower ribs to pelvic girdle Tenses abdominal wall Posterior Trunk Muscles Trapezius- triangular muscle extends from the base of skull, cervical & thoracic vertebrae to the shoulder Rotates the scapula (shoulder blade) Latissimus Dorsi- from lower back, around side, to armpit Adducts arm, pulls arm back in swimming, climbing, and rowing Trunk Muscles Deep Trunk and Arm Muscles Arm Muscles Deltoid- covers shoulder joint, connects clavicle and scapula to the humerus Abducts the upper arm (lifts arm) Biceps brachii- in upper arm, connects scapula to radius Flexes upper arm at the elbow, rotates the hand laterally Arm Muscles Brachialis- beneath the biceps brachii, connects the shaft of humerus to the ulna Strongest flexor of the elbow Brachioradialis- connects the humerus to the radius Aids in flexing the elbow Arm Muscles Triceps brachii- 3 heads, back of upper arm connects humerus and scapula to ulna Extensor of the elbow Arm Muscles Arm Muscles Upper Leg Muscles Gluteus Maximus- muscle of the hip that forms most of the butt Extends jumping leg at hip, for climbing and Gluteus Medius- from hip to femur and is under the gluteus maximus Steadies the pelvis during walking Good site for intramuscular injections (shots) Butt Muscles Gluteus Medius Gluteus Maximus Gluteus Minimu s Upper Leg Muscles Rectus Femoris- one of the quadriceps Extends the knee (like when kicking a ball) and can flex the hip Vastus Lateralis- one of the quadriceps (on the outside of leg) Extends the knee Upper Leg Muscles Vastus Medialis – one of the quadriceps (toward the inside of body) Extends the knee Sartorius- thin and straplike and the most superficial Synergist to help cross legs Upper Leg Muscles Biceps Femoris- part of the hamstring group Prime movers of thigh extension and knee flexion. Muscles of the Pelvis, Hip, and Thigh Lower Leg Muscles Tibialis Anterior- From upper tibia to tarsals Acts to dorsiflex and invert the foot Gastrocnemius- a two bellied muscle that form the curve of the calf Plantar flexion of the foot. Needed to lift the heel during walking. Muscles of the Lower Leg Superficial Muscles: Anterior Superficial Muscles: Posterior Diseases of the Muscular System Muscular Dystrophy Congenital muscle-destroying disease affect specific muscle groups Muscle fibers degenerate & atrophy due to an absence of dystrophin, a protein that helps keep muscle cells intact Most common & serious—Duchenne’s M.D. Mostly in males (diagnosed between2-6 yrs) Survival is rare beyond early 30’s X-linked recessive Myasthenia gravis Rare adult disease caused by antibodies to acetylcholine receptors at the neuromuscular junction which prevents the muscle contraction from occurring Drooping upper eyelids, difficulty swallowing & talking, muscle weakness & fatigue Death occurs when respiratory muscles cease to function Disorder of Muscle Tissue • Cramps & Spasms - an “over contraction” – can be due to electrolyte imbalance, fatigue, overuse Hernia - a tear in wall of muscle – can be congenital, or from severe strain ABDOMINAL HERNIA • Muscle Tear - aka: “pulled” muscle or strained muscle – caused by overstretching of muscle during activity • muscle fibers actually tear apart Torn Pectoralis Major • Hamstring Muscle Tear • Hypertrophy - increase in the size of muscle fibers • Atrophy - decrease in size of muscle fiber
