Muscular System Functions: •Movement •Posture •Stabilize Joints •Generate Heat Types: • Skeletal- voluntary, striated, movement • Cardiac- involuntary, striated, heart • Smooth- involuntary, not striated, visceral Anatomy of Skeletal Muscle • Muscle fiber (cell) is wrapped by endomysium • Several wrapped fibers are bundled and wrapped by perimysium • Each bundle is called a fascicle • Many fascicles are wrapped by tough epimysium • Epimysium ends in a cord like tendon or a sheet like aponeuroses Muscle Fiber (Cell) • Made of many myofibrils covered by a plasma membrane called the sarcolema • Each myofibril has contractile units called a sarcomere mm Sarcomere • Alternating dark (A) bands and light (I) bands • Z disc- midway in (I) band • H zone midway in (A) band • M line- center of H zone Sarcomere • 2 types of protein filaments: –Thick filaments= myosin –Thin filaments= actin • Cross bridges on myosin filaments connect the two Sliding Filaments • Thin fibers are pulled to center of the sarcomere by myosin head cross bridge • Triggered by rise in Ca ++ which attaches to myosin head to pull it back • ATP releases the head and it springs forward and pushes the thin filaments over the thick filaments = Muscle Shortens Skeletal muscle must be stimulated by a nerve • Motor Unit = one neuron and all the muscle cells it stimulates • More fibers stimulated by one neuron, the greater the force • Less fibers stimulated by one neuron than the finer the movement Glucose is necessary to provide ATP • Muscle can store glucose as glycogen • Muscle contains myoglobin which will bind oxygen 3 pathways to ATP production • 1. Creatine phosphate (CP) good for minutes • 2. Aerobic respiration= C6H12O6 + O2 CO2 + H2O + ATP 95% of all ATP produced (38 ATP / glucose) • 3. Anaerobic glycolysis= without oxygen, glucose is broken into 2 pyruvate acid, releases 2 ATP and a by product lactic acid, causes muscle soreness Types of muscle contraction • Isotonic – contraction occurs and results in movement • Isometric- the myosin filaments try to contract but the muscle is against something immovable • Muscle tone- even when the muscle is relaxed, few of the muscle fibers continue to contract and make the muscle firm Exercise effect • Aerobic- endurance – does NOT increase size – DOES resist fatigue – more blood hemoglobin, more mitochondria, more glycogen • more myoglobin- holds oxygen Exercise effect continued • Isometric- resistance – Does increase size and strength – more myofilaments – more connective tissue • larger cells 5 Golden Rules • 1. muscles cross at least one joint • 2. the bulk of the muscle lies proximal to the joint • 3. all muscles have at least two attachments: --origin and insertion • 4. muscles can only pull; never push • 5. during contraction, the insertion moves towards the origin Naming Muscles • 1. Directions of fibers: Rectus, Oblique • 2. Relative size: Maximus, Minimus • 3. Location over bone: Frontalis, Temporalis • 4. Number of origins: Biceps, Triceps • 5. Location of origin and insertion: sternocleidomastoid • 6. Shape: Deltoid • 7. Action: adductor, flexor • Prime Mover- major responsibility for move • Antagonist- when prime mover is contracted, it is relaxed • Synergist- helper to prime mover • Fixator- special synergists that hold a muscle stable Shapes of Muscles • • • • Circular- sphincters Convergent- fan shaped Parallel- strap like Fusiform- special parallel with big body • Pennate- feather like Muscles of the Head • • • • Frontalis- raises eyebrows Orbicularis oculi- blinking, squinting Zygomaticus- smile Depressor anguli oris- frown, (antagonists= smile / frown) • Lavator labii superioris- disgust • Depressor labii- pout Chewing (Mastication) • Masseter- prime mover (from zygomatic to ramus of mandible) • Temporalis- synergist • Buccinator- holds food between teeth/ sucking • Platysma- tenses skin of neck during shaving Swallowing • Digastric- open mouth- depress mandible • Mylohyoid- forces bolus into pharynx • Pharyngeal constrictors- propels bolus to esophagus Neck • Sternocleidomastoid- head flexion, neck flex, rotate head towards opposite shoulder • Scalenes- flex and rotate neck Shoulder Joint • Trapezius- depress shoulder/ adducts scapula • Pectoralis major- prime mover of arm flexion, adducts arm, rotates medial Shoulder continued • Latissimus dorsi- prime mover of arm extension, arm adductor brings arm down in hammering, swimming, rowing • Deltoid- antagonist of pectoralis major, and latissimus dorsi, prime mover of arm abduction, swinging arm movement while walking Shoulder (rotator cuff) • Supraspinatus- prevents downward dislocation, assists in abduction • Infraspinatus- rotates humerus laterally • Teres major- medial rotation of humerus, extends • Also: Coracobrachialis• coracoid – humerus, flexion and adduction of humerus Elbow Joint • Triceps brachii- antagonist to forearm flexors, strong forearm extensor, stabilizes shoulder • Biceps brachii- flexes elbow, supinates forearm, lifts radius • Brachialis- forearm flexor, lifts ulna • Brachioradialis- synergist to forearm flexion Back Trunk • Erector Spinae- prime mover of back extension- made of 3 muscles: Iliocostalis, Longissimus, and Spinalis • Bending forward at the waist touching fingers to the floor they are relaxed ( held together by ligaments!) that is why lifting can be problem Thorax (breathing) • External intercostals- synergist to diaphragm in inspiration, elevates rib cage • Diaphragm- prime mover of inspiration • Internal intercostals- aid in expiration, depress the rib cage Thorax continued • Serratus anterior- “boxer’s muscle” raises the point of the shoulder, abduction and raising the arm, pushing, punching Abdominal Girdle • Rectus Abdominus- pubic crest to xiphoid process, flex and rotate lumbar vertebrae • External oblique- diagonal fibers, “sit-up” flex abdomen • Internal oblique- under external oblique • Transverse abdominus- runs across under obliques Hip and Knee • Iliopsoas- prime mover of hip flexion • Sartorius- strap like, superficial, flexes and laterally rotates thigh, flexes knee, “cross leg position” • Adductor magnus: • Adductor longus: adducts thigh • Adductor brevis: • Gracilis- adducts thigh, medial rotation when walking Quadriceps group (ant. Thigh) • All extend knee: • Rectus Femoris: also flexes hip on thigh • Vastus lateralis • Vastus intermedius • Vastus medialis Hip and Thigh posterior • Gluteus Maximus- major, powerful, extensor of the thigh, (rising from chair, stairs, running) • Gluteus medius- injection site • Gluteus minimus- adducts thigh Hamstring group • Posterior thigh, sciatic nerve runs through, powerful knee flexors, extends thigh: • Biceps Femoris- extends thigh, flexes knee, lateral rotation of leg when knee is flexed • Semitendinosus • Semimembranosus Lower Leg • Gastrocnemius- prominent belly forms proximal curve of the calf, plantar flexion, large Achilles Tendon (Calcaneal) • Soleus- lies under gastrocnemius, also plantar flexor