Cardiac muscle Smooth muscle Skeletal muscle Endomysium Perimysium fascicle Epimysium tendons aponeuroses Fascia Sarcolemma Sarcoplasmic reticulum

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1 THE MUSCUALR SYSTEM I. Overview of muscle tissue A. Muscle Functions 1. Produce movement all muscle types 2. Maintain posture only skeletal 3. Stabilizing joints only skeletal 4. Generate heat only skeletal B. Muscle types (study Table 6.1) 1. Cardiac muscle cardiac, striated, uninucleated, involuntary, only found in the heart a. Cardiac muscle fibers are cushioned by small amounts of connective tissue and arranged in spiral or figure 8 bundles, fibers are joined at intercalated discs b. Cardiac muscle contracts at a fairly steady rate (rhythmic contractions) set by the pacemaker 2. Smooth muscle visceral, nonstriated, spindle-shaped, uninucleated, and involuntary a. Found in walls of hollow visceral organs such as stomach, urinary bladder, and respiratory passages b. Contractions are slow and sustained as compared to skeletal muscle 3. Skeletal muscle skeletal, striated, multinucleated, long, cylindrical, voluntary, most attached to bones by tendons, some facial muscles attached to skin a. Skeletal muscle fibers are soft and fragile but can exert tremendous force, they do not rip because they are bundled together by connective tissue b. Endomysium delicate connective tissue sheath that encloses each muscle fiber c. Perimysium coarser fibrous membrane that wraps around several sheathed muscle fibers and forms the fascicle (perimysium wraps the fascicle) d. Epimysium tough overcoat that covers all of the fascicles and therefore the entire muscle, it blends into the tendons (cordlike) or into aponeuroses (sheet like) that attach the muscles to bone e. Fascia on the outside of epimysium, covers the entire muscle and separates it from adjacent muscles (Study figure 6.1 on pg. 185) II. Microscopic anatomy of skeletal muscle (study pg. 183) A. Sarcolemma plasma membrane in skeletal muscle cells B. Sarcoplasmic reticulum specialized endoplasmic reticulum (ER), stores calcium C. Myofibrils long ribbon like organelles that nearly fill the cytoplasm and push nuclei aside 1. Alternating light (I) and dark (A) bands along the length of the perfectly aligned myofibrils give the muscle cell as a whole its striped appearance (due to arrangement of the myofilaments) 2. Thin filaments are made up of actin, anchored to Z-disc 3. Thick filaments are made up of myosin, have ATPase enzymes, have heads (extensions, or cross bridges) D. Sarcomere contractile unit of a muscle fiber between 2 Z-discs III. Skeletal muscle activity A. Stimulation and contraction of single skeletal muscle cells 1. Irritability (also called excitability or responsiveness) the ability to receive and respond to stimulus 2. Contractility the ability to shorten (forcibly) when an adequate stimulus is received 3. Extensibility the ability of muscle cells to be stretched 4. Elasticity the ability of muscle cells to recoil and resume their resting length after being stretched 5. Motor unit one neuron and all the skeletal muscle cells it stimulates 6. Neuromuscular junction association site between nerve and muscle 7. Synaptic cleft gap between nerve and muscle, filled with interstitial fluid 8. Acetylcholine the specific neurotransmitter (chemical released by nerve at the axon terminal upon arrival of a nerve impulse) that stimulates skeletal muscle cells 1

2 III. Skeletal muscle activity (cont.) B. Transmission of nerve impulse to muscle (pg. 191) 1. Nerve impulse reaches the axon terminals and a neurotransmitter (acetylcholine) is released 2. Neurotransmitter diffuses across the synaptic cleft and attaches to receptors on the sarcolemma 3. Sarcolemma becomes permeable to sodium (Na+) ions which rush into the cell, and to potassium (K+) ions which diffuse out of the cell 4. Sodium rushing into the cell generates an action potential (cell is more positive on the inside) 5. Once started, muscle contraction cannot be stopped 6. After the contraction the cell has to be returned to the resting state by diffusion of potassium ions out of the cell and operation of the sodium-potassium pump to put ions back to original positions C. Sliding filament theory of muscle contraction 1. Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament 2. Myosin heads then bind to the next site of the thin filament (actin) and this requires Ca+ 3. This continued action causes a sliding of the myosin along the actin (thin filaments past thick ones) 4. The result is that the muscle is shortened (contracted) D. Contraction of a skeletal muscle as a whole 1. Muscle fiber contraction is all or none per muscle cell (not the entire muscle) 2. Within a skeletal muscle, not all fibers may be stimulated during the same interval 3. Different combinations of muscle fiber contractions may give differing responses 4. Graded responses how skeletal muscles react to stimuli with different degrees of shortening a. Can be produced by changing the frequency of muscle stimulation b. Can be produced by changing the number of muscle cells being stimulated c. Types of graded responses i. Twitch single, brief, jerky contraction, not a normal muscle function ii. Tetanus (summing of contractions) one contraction is immediately followed by another, muscle does not return to resting stage, affects are added * Unfused (incomplete) tetanus some relaxation occurs between contractions, results summed * Fused (complete) tetanus no relaxation before the following contractions, results in sustained muscle contraction d. Muscle force depends upon the number of fibers stimulated e. More fibers contracting results in greater muscle tension f. Muscle can continue to contract unless they run out of energy E. Providing energy for muscle contraction initially muscles use stored ATP (4-6 sec.) 1. Direct phosphorylation of ADP by creatine phosphate making more ATP 2. Aerobic respiration in mitochondria, produce 36 ATP for every one glucose, require oxygen continuously, break down glucose and release water and carbon dioxide 3. Anaerobic glycolysis and lactic acid fermentation used after your muscles run out of oxygen, only produces 2 ATP s but does it fast, you get lactic acid build up and therefore the sore feeling the next day F. Muscle fatigue occurs if we exercise our muscles strenuously for a long time, the muscle becomes unable to contract even though it is still being stimulated, results from oxygen deficit (ATP deficit) G. Types of muscle contractions 1. isotonic contractions muscle shortens and movement occurs (bending arm, smiling) 2. isometric contractions muscles do NOT shorten, but the tension increases (pushing against a brick wall) H. Muscle tone state of continuous partial contractions stimulated by the nervous system that helps the muscle remain firm, healthy, and constantly ready for action 2

3 III. Skeletal muscle activity (cont.) I. Effect of exercise on muscle 1. Aerobic (endurance) exercise results in stronger, more flexible muscles with greater resistance to fatigue (running, biking, aerobics class) 2. Resistance (isometric) exercise increases muscle size and strength due to the enlargement of individual muscle cells (weight lifting) IV. Muscle movements, types, & names A. The five golden rules of skeletal muscle activity 1. With a few exceptions, all muscles cross at least one joint 2. Typically, the bulk of the muscle lies proximal to the joint crossed 3. All muscles have at least 2 attachments: the origin (attachment to immovable bone) and the insertion (attached to the movable bone) 4. Muscles can only pull; they never push 5. During contraction, the muscle insertion (attached to the movable bone) moves toward the origin (attached to the immovable bone) B. Types of body movements 1. Flexion decreases the angle of a joint and brings 2 bones closer together (bending) 2. Extension increases the angle or distance between 2 bones (straightening) 3. Rotation movement of a bone around its longitudinal axis (shaking head no ) 4. Abduction moving a limb away from the midline of the body 5. Adduction moving a limb toward the midline of the body 6. Circumduction combination of flexion, extension, abduction, and adduction, seen in ball and socket joints, the limb outlines a cone 7. Dorsiflexion bringing foot up 8. Plantarflexion bringing foot down 9. Inversion turning the sole of the foot medially 10. Eversion turning the sole of the foot outward or laterally 11. Supination - palms up (like holding a cup of soup) 12. Pronation palms down 13. Opposition touching your thumb to the tips of the other fingers C. Interactions of skeletal muscles 1. Prime mover the muscle that has the major responsibility for causing a particular movement (bicep is prime mover of elbow flexion) 2. Antagonist muscles that oppose or reverse a movement (tricep is antagonist of bicep) 3. Synergists help prime movers by producing the same movement or by reducing undesirable movements (make a fist without bending wrist) 4. Fixators specialized synergists that hold a bone still or stabilize the origin of a prime mover so all the tension can be used to move the insertion bone (postural muscles of vertebral column) V. Naming muscles A. Direction of muscle fibers rectus, oblique, transverse B. Relative size of muscle maximus, major, minimus, minor C. Location of the muscle bone names D. Number of origins triceps E. Location of the origin or insertion sterno sternum F. Shape of the muscle deltoid, trapezius G. Action of the muscle flexor, extensor For Muscle Origin/Insertion/Movement look at tables 6.3 and 6.4 on pages 217 and 219 in text book. 3

4 VI. Head and neck muscles A. Facial muscles 1. Frontalis raises eyebrows 2. Orbicularis oculi closes eyes, squints, blinks, winks 3. Orbicularis oris closes mouth and protrudes the lips, kissing muscle 4. Buccinator sucks in the cheeks (develops in nursing infants), chews, whistling 5. Zygomaticus raises corners of the mouth, smiling B. Chewing muscles 1. Masseter primary jaw closure, and elevates mandible 2. Temporalis synergist of the masseter, closes jaw C. Neck muscles 1. Platysma pulls the corners of the mouth inferiorly (pouty face) 2. Sternocleidomastoid flexes the neck, rotates the head to opposite shoulder VII. Muscles of Trunk, Shoulder, Arm A. Anterior trunk muscles 1. Pectoralis major adducts and flexes the humerus 2. Pectoralis minor pulls scapula forward 3. Diaphragm prime mover of inspiration 4. External intercostals raise rib cage during inhalation 5. Internal intercostals depress the rib cage to move air out of lungs when you exhale forcibly B. Muscles of the abdominal girdle 1. Rectus abdominis flexes vertebral column and compresses abdominal contents (defecation, childbirth, forced breathing) 2. External and internal obliques flex vertebral column & compress abdominal contents; rotate trunk and bend it laterally 3. Transversus abdominis compresses abdominal contents C. Posterior trunk muscles 1. Trapezius elevates, depresses, adducts, and stabilizes the scapula, shrugs shoulders 2. Latissimus dorsi extends and adducts the humerus (arm) 3. Infraspinatus helps to hold head of humerus in glenoid cavity 4. Teres major synergist of latissimus dorsi 5. Erector spinae back extension 6. Quadratus lumborum flexes the spine laterally individually, extend spine together 7. Deltoid arm abduction D. Arm 1. Biceps brachii supinates forearm, flexes elbow, lifts radius 2. Brachialis elbow flexion, lifts ulna 3. Brachioradialis weak muscle, synergist in forearm flexion, stabilizes elbow 4. Triceps brachii elbow extension (antagonist to biceps brachii) 5. Anconeus triceps synergist 6. Flexor carpi ulnaris flex wrist 7. Flexor carpi radialis flex wrist 8. Palmaris longus weak wrist flexor 9. Flexor digitorum superficialis flexes wrist and middle phalanges Flexor digitorum profundus flexes distal interphalangeal joints 11. Extensor carpi radialis longus & brevis extend wrist 12. Extensor carpi ulnaris extend wrist 13. Extensor digitorum prime mover of finger extension 14. Extensor pollicis brevis and longus extend thumb 15. Abductor pollicis longus abducts and extends thumb 4

5 VIII. Muscles of the lower limb A. Butt & thigh muscles 1. Gluteus maximus hip extension 2. Gluteus medius hip abduction, steadies pelvis when walking 3. Gluteus minimus - hip abduction, steadies pelvis when walking 4. Piriformis stabilizes hip joint, assist in thigh abduction 5. Iliopsoas hip flexion, keeps the upper body from falling backward when standing erect 6. Adductor muscles (magnus, longus, brevis) adduct the thighs 7. Gracillis adduct the thighs 8. Hamstring group thigh extension and knee flexion a. Biceps femoris - lateral b. Semimembranosus - medial c. Semitendinosus - medial 9. Sartorius flexes the thigh, longest muscle in the body, tailors muscle 10. Quadriceps group extends the knee a. Rectus femoris helps with hip flexion b. Vastus muscles (three) - vastus medialis, vastus lateralis, vastus intermedius B. Muscles causing movement at ankle and foot 1. Tibialis anterior dorsiflexion and foot inversion 2. Extensor digitorum longus and brevis toe extension and dorsiflexion of the foot 3. Fibularis muscles plantar flexion, everts the foot 4. Gastrocnemius plantar flexion foot, flexes knee 5. Soleus plantar flexion 6. Flexor digitorum longus & brevis flex toes IX. Homeostatic imbalances A. Atrophy muscle wasting due to damage to the nerve supply, muscle becomes paralyzed and turns flaccid (soft and flabby) B. Torticollis injury to the sternocleidomastoid muscle may happen to a baby during a difficult birth ( wryneck ) or to adults who sleep with their neck in an awkward position C. Muscular dystrophy a group of inherited muscle destroying diseases that affect specific muscle groups. The muscles enlarge due to fat and connective tissue deposit, but the muscle fibers degenerate and atrophy * Duchenne s muscular atrophy in males, diagnosed between ages 2-6, children become clumsy and fall frequently as the muscle weaken, in wheel chair by age 12, die by early adulthood, no cure. D. Myasthenia gravis occurs in adulthood, characterized by drooping of the upper eyelids, difficulty in swallowing and talking, and generalized muscle weakness and fatigability. Most likely it is autoimmune, antibodies target receptors for the neurotransmitter acetylcholine. Death results from the inability of the respiratory muscles to function. E. Muscle spasm - a spasm is a sudden involuntary contraction of a muscle, a group of muscles, or a hollow organ such as the heart, commonly, it is a muscle cramp which is accompanied by a sudden burst of pain, usually harmless and ceases after a few minutes, typically caused by ion imbalance or muscle overload. F. Charlie horse - due to long exercise or physical labor, especially in the heat, harmless but can be very painful, awakens a person during the night, usually in the legs, massage can relieve cramping pain, stretches and hydration during exercise prevent a charley horse. G. Shin splints - small tears in the tibialis anterior muscle that s pulled off the bone, an inflammation of the periosteum, an inflammation of the muscle, or some combination of these, treatment includes rest, ice, and pain relievers, no impact exercises, running backwards 5