1. Muscular System Chapter 9

2. Types of Muscles Muscle tissue makes up 40-50% of our body. There are 3 types of muscles: 1. Skeletal muscle a. Generally attached to bone (skeletal system) b. Classified as voluntary (contracts when “told” to contract) c. Appears striped (striated) d. Functions i. Movement of the skeleton ii. Maintain posture iii. Stabilize joints iv. Produce heat (contributes to body temperature) If damaged, limited capacity for regeneration.

3. Types of Muscles 2. Smooth muscle a. Found in the walls of viscera (organs) and tubes (such as breathing passages) b. Also called visceral smooth muscle i. Bronchiolar smooth muscle ii. Vascular smooth muscle iii. Gastrointestinal smooth muscle c. Classified as involuntary (contracts without the person “telling” it to contract) d. Does not appear striped (nonstriated) e. Function: enables the organ to perform its function (smooth muscle of the urinary bladder contracts and expels urine) 2 important functions- Maintain smooth muscle tone Ex: capillaries and BP.

4. Types of Muscles 3. Cardiac muscle- If damaged it will not regenerate!!! a. Found in the heart (myocardium) b. Classified as involuntary (you don’t have to “tell” your heart to contract) c. Appears striped (striated) d. Contains intercalated discs (increases speed of heart’s electrical signal)

6. Structures of the Whole Muscle 1. Whole muscle a. Composed of thousands of muscle cells b. Belly: large fleshy part of a muscle located between the points of attachment 2. Layers of connective tissue (Figure 9-2) a. Epimysium i. Layer of fascia that surrounds the whole muscle ii. Tapers at the ends of the muscle to form a tendon (usually attaches to bone) b. Perimysium: connective tissue that surrounds bundles of muscle fibers (fascicles) within the whole muscle c. Endomysium: connective tissue that surrounds each muscle fiber (muscle cell) Clinical CorrelatesCompartment syndrome 3. Muscle attachments- Muscles attach to structures 3 different ways! a. Tendons: attach muscle to bone b. Muscles attach directly to bone or soft tissue (without tendons) c. Aponeurosis (flat, sheetlike fascia) attaches muscle to muscle or muscle to bone

7. Structure and Function of a single Muscle Fiber 1. Muscle fiber (same as muscle cell) (Figure 9-2, B) a. Sarcolemma: cell membrane that surrounds the muscle fiber b. Transverse tubules (T tubules): sites where the sarcolemma penetrates to the interior of the muscle fiber c. Sarcoplasmic reticulum: endoplasmic reticulum that stores calcium d. Each muscle fiber is composed of myofibrils arranged in elongated cylinders. e. Each myofibril is composed of sarcomeres arranged in series (end on end) 2. Sarcomere (Figure 9-2, C) a. The sarcomere is the contractile unit of the muscle b. Structure i. Actin ( thin) filaments extend inward from the Z lines ii. Myosin (thick) filaments lie between the actin; there are myosin heads that make contact with the actin during muscle contraction c. Striated (striped) appearance is due to the orderly arrangement of the sarcomere components

9. How Muscles contract 1. Changes in sarcomere length a. Muscles contract when the sarcomeres shorten b. Sarcomeres shorten because the actin and myosin filaments SLIDE past each other (thus the name sliding filament theory) c. Sliding (and shortening) is possible because the myosin heads briefly bind to the actin (forming crossbridges) and swivel d. The sliding resembles the sliding of the trombone e. Note that the contracted sarcomere is shorter than the relaxed sarcomere 2. The role of ATP in the sliding filament hypothesis a. ATP is found within the sarcomere b. ATP is necessary for both the formation and release of the crossbridges 3. The role of calcium in the sliding filament theory a. Calcium is necessary for the binding of the myosin heads to the actin (formation of crossbridges) b. Calcium is stored within the SR c. When the muscle membrane is stimulated the SR releases its Ca 2+ into the sarcomere, causing crossbridge formation (contraction) d. Muscle relaxation occurs when the Ca 2+ is pumped away from the actin and myosin back into the SR Clinical CorrelatesRigor mortis (see DYK p. 141)

10. Skeletal Muscles & Nerves 1. Somatic motor neuron- nerve that supplies the skeletal muscle. a. Skeletal muscle must be stimulated by a motor nerve b. Motor nerve activity originates in the motor cortex of the brain (frontal lobe of the cerebrum) and descends down the spinal cord c. The area where the motor nerve meets the muscle is called the neuromuscular junction (NMJ); also called the myoneural junction.

11. Neuromuscular Junction a. What happens: the signal is chemically transmitted from the nerve to the muscle b. Steps in the transmission of the signal across the NMJ (Figure 9-3, B) i. Stimulation of the nerve causes the electrical signal to move along the nerve toward the nerve ending. ii. The electrical signal causes the vesicles to fuse with the membrane and release neurotransmitter, acetylcholine (ACh). iii. ACh diffuses from the nerve to the muscle membrane where it binds to receptors. iv. The ACh activates the receptors on the muscle membrane causing an electrical signal on the muscle membrane. v. ACh activity is terminated by an enzyme located near the muscle membrane. The enzyme is called acetylcholinesterase.

12. Responses of a whole Muscle 1. Partial versus all-or-none response a. A single muscle fiber contracts all-or-nothing b. A whole muscle (thousands of muscle fibers) can adjust its contractile force i. The muscle contracts weakly to lift a light load and more forcefully to lift a heavier load ii. The ability to lift a heavier load is accomplished by recruitment of additional fibers.

13. Responses of whole Muscles 2. Twitch and tetanus a. Twitch: the response of a muscle to a single electrical stimulus; the muscle contracts and completely relaxes (not useful physiologically) b. Tetanus: sustained muscle contraction i. Important for the maintenance of posture (standing for a period of time) ii. Do not confuse with the disease tetanus.

14. Responses of whole Muscles Cont’d 3. Muscle tone a. Continuous state of partial muscle contraction b. Loss of tone can prove fatal (loss of vascular smooth muscle tone lowers blood pressure to dangerous levels). 4. Energy sources for muscle contraction a. Aerobic metabolism: glucose  CO 2 + H 2 O + energy (ATP) b. Anaerobic metabolism: glucose  energy (ATP) + lactic acid c. Metabolism of creatine phosphate: replenishes ATP

15. Muscle Terms G. Muscle Terms 1. Origin and insertion (Figure 9-6) a. Origin: site of attachment on the more stationary bone b. Insertion: site of attachment on the more movable bone 2. Prime mover, synergist, and antagonists a. Prime mover: the muscle that is primarily responsible for a movement b. Synergists: helper muscles (work with the prime mover muscle) c. Antagonists: muscles that oppose the action of another muscle Clinical CorrelatesHypertrophy Atrophy Contracture

16. How Muscles are Named H. How Skeletal Muscles Are Named 1. Size: vastus (huge), maximus( LG), minimus(small), longus(long), brevis (short). 2. Shape: deltoid, latissimus, trapezius, rhomboideus, teres 3. Direction of fibers: rectus, oblique, transverse, circularis 4. Location: pectoralis, gluteus, brachii, supra, infra, sub, lateralis 5. Number of origin: the number of sites to which it is anchored (biceps, triceps, quadriceps) 6. Origin and insertion: sites of attachment; sternocleidomastoid (sternum, clavicle, mastoid process of the temporal bone) 7.Muscle action: adductor muscle, abductor muscle, flexor, extensor, levator

17. Muscles from Head to Toe 1. Muscles of the head (Figure 9-8) a. Facial muscles i. Frontalis: raises eyebrows (“surprised”); wrinkles forehead ii. Orbicularis oculi: closes the eye (winking, blinking, and squinting) iii. Orbicularis oris: closing mouth, forming words, pursing lips (“kissing” muscle) iv. Buccinator: flattens cheek (trumpeter’s muscle) helps position food between the teeth v. Zygomaticus: smiling muscle b. Chewing muscles i. Masseter: closes jaw ii. Temporalis: closes jaw

18. Muscles of the Neck 2. Muscles of the neck a. Sternocleidomastoid i. Flexes the head on the chest ii. Contraction of one muscle causes the head to rotate to the opposite side. b. Trapezius i. Contraction tilts head back as in looking at the sky. ii. Also moves the shoulder.

19. Muscles of the Trunk 3. Muscles of the trunk a. Muscles involved in breathing (Figure 9-9) i. Diaphragm: chief muscle of inhalation ii. Intercostals: between the ribs b. Muscles that form the abdominal wall… TIRE i. Transversus abdominis ii. Internal oblique iii. Rectus abdominis iv. External oblique c. Muscles that move the vertebral column d. Muscles that form the pelvic floor i. Support pelvic viscera ii. Help expel contents of the urinary bladder and rectum

20. Muscles of the Shoulder and Upper Arm 4. Muscles of the shoulder and upper arm a. Trapezius i. Shrugs the shoulders ii. Tilts the head back (looking at the sky) b. Serratus anterior i. Trapezius and serratus anterior attach the scapula to the axial skeleton ii. Lowers the shoulder and moves arm forward as in pushing a cart c. Pectoralis major i. Large flat muscle that helps form the anterior chest wall ii. Connects the humerus to the clavicle and other structures of the anterior chest iii. Contraction moves the upper arm across the anterior chest as in pointing to an object in front of you

21. Muscles Cont’d d. Latissimus dorsi i. Attaches the humerus to the axial skeleton ii. Lowers the shoulder and brings the arm back as in pointing to an object behind you (swimming, rowing) e. Deltoid i. Shoulder pad ii. Raises (abducts) the arm to the scarecrow position iii. Rotator cuff muscles (4) a. Attach the humerus to the scapula. b. The tendons of these muscles form a cap or cuff over the head to the humerus, thereby stabilizing the shoulder joint.

22. Muscles that move the Lower Arm 5. Muscles that move the lower arm a. Triceps brachii b. Biceps brachii i. Lies along the anterior humerus ii. Works synergistically with the brachialis and brachioradialis to flex the forearm c. Pronators: palm down d. Supinators: palm up (facing the sky) 6. Muscles that move the hand and fingers (> 20 muscles for delicate finger movements) a. Flexors i. The muscles lie along the anterior surface of the forearm ii. Tendons attach to the fingers and thumb b. Extensors i. The muscles lie along the posterior surface of the forearm ii. Tendons attach to the fingers and thumb

23. Muscles that move the Lower Extremities 7. Muscles that move the lower extremity a. Thigh i. The muscles that move the thigh all attach to the pelvic girdle and femur ii. Gluteal muscles: gluteus maximus, medius, minimus a. Largest muscles in the body b. Upon which you sit c. Contraction: extends and abducts the thigh at the hip

24. Lower Extremity Muscles b. Leg i. Muscles that move the leg are located in the thigh ii. Quadriceps femoris a. Most powerful muscle in the body b. Prime mover of knee extension (as in kicking a football). c. Composed of vastus lateralis vastus medialis vastus intermedius rectus femoris

25. Leg Muscles Cont’d iii. Sartorius a. Longest muscle in the body b. Lies obliquely across the anterior femur attaching to the hip bone and anterior tibia (tibial tuberosity) c. Allows you to sit on floor with legs crossed iv. Hamstrings a. Group of muscles on the posterior thigh b. All hamstring muscles attach to the ischium (pelvic bone) and the tibia c. Act antagonistically to the quadriceps, causing flexion of the leg at the knee d. Their strong tendons can be felt behind the knee forming the popliteal fossa e. Names: biceps femoris semimembranosus semitendinosis

26. The Foot Muscles c. Foot i. Muscles that move the foot are located on the leg ii. Tibialis anterior: causes dorsiflexion of the foot iii. Peroneus longus: everts the foot, assists in plantar flexion, and supports the arch of the foot iv. Gastrocnemius and soleus: attach to the calcaneus (heel) by the cancaneal (Achilles) tendon; contraction causes plantar flexion (tiptoe) v. Toes are moved by flexors and extensors