Unit 4 - The Muscular System PDF

Unit 4 - The Muscular System Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings The Muscular System Part I: Muscle Movements, Types and Names Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings A. Interactions of Skeletal Musc...

Unit 4 - The Muscular System Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings The Muscular System Part I: Muscle Movements, Types and Names Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings A. Interactions of Skeletal 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 by preventing undesirable movements ▪ Fixator—specialized synergist that stabilizes the origin of a prime mover Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings B. Types of Body Movements ▪ Movement is attained due to a muscle moving a bone it’s attached to ▪ Muscles are attached to bone at least two points ▪ Origin - attachment to the non-moving or less movable bone ▪ Insertion - attachment to the moving bone ▪ When a muscle contracts, the insertion moves toward the origin. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings  Table 6.2 Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Movements ▪ i) Flexion ▪ Decreases the angle of the joint ▪ Brings two bones closer together ▪ Typical of hinge joints like knee and elbow ▪ ii) Extension ▪ Opposite of flexion ▪ Increases angle between two bones Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Types of Body Movements continued Figure 6.13a Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Types of Body Movements continued Figure 6.13b Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Types of Body Movements continued ▪ iii) Rotation ▪ Movement of a bone around its longitudinal axis Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Types of Body Movements continued Figure 6.13c Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Types of Body Movements continued ▪ iv) Abduction ▪ Movement of a limb away from the midline ▪ v) Adduction ▪ Opposite of abduction ▪ Movement of a limb toward the midline Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Types of Body Movements continued ▪ vi) Circumduction ▪ Combination of flexion, extension, abduction, and adduction ▪ Common in ball-and-socket joints ▪ EXAMPLES: Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Types of Body Movements continued Figure 6.13d Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings C. Special Movements ▪ Certain movements don’t fit into any of the previous categories and exist only in a few joints ▪ i) Dorsiflexion ▪ Lifting the foot so that the superior surface approaches the shin (think walking on your heels) ▪ ii) Plantar flexion ▪ Depressing the foot (pointing the toes) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Special Movements continued Figure 6.13e Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Special Movements continued ▪ iii) Inversion ▪ Turn sole of foot medially ▪ iv) Eversion ▪ Turn sole of foot laterally Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Special Movements continued ▪ v) Supination ▪ Forearm rotates laterally so palm faces anteriorly ▪ vi) Pronation ▪ Forearm rotates medially so palm faces posteriorly MEMORY TRICK** - If you lift a cup of soup up to your mouth on your palm, you are supinating (“soup”-inating) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Special Movements continued Figure 6.13g Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Special Movements continued ▪ vii) Opposition ▪ Move the thumb to touch the tips of the other fingers on the same hand Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Special Movements continued Figure 6.13h Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings D. Naming Skeletal Muscles i. By direction of muscle fibers ▪ Usually with reference to the midline ▪ Example : Rectus (straight) Oblique (diagonal) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Naming Skeletal Muscles Continued ii. By relative size of the muscle ▪ Example : Maximus (largest) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Naming Skeletal Muscles Continued iii. By the bone over which the muscle is located ▪ Example : Temporalis (temporal bone) Frontalis (frontal bone) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Naming Skeletal Muscles Continued iv. By number of origins ▪ Example : Triceps (three heads) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Naming Skeletal Muscles Continued v. By location of the muscle’s origin and insertion ▪ Example : Sternocleidomastoid muscle Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Naming Skeletal Muscles Continued vi. By shape of the muscle ▪ Example : Deltoid (triangular) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Naming Skeletal Muscles continued vii. By action of the muscle ▪ Example : Flexor and extensor (flexes or extends a bone) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings E. Skeletal Muscles of the Body A. Head & Neck Muscles Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Head and Neck Muscles continued ▪ Head muscles are divided into facial muscles and chewing muscles. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Head and Neck Muscles continued i. Facial muscles ▪ Frontalis—superficial to the frontal bone, raises eyebrows Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Head and Neck Muscles continued ▪ Orbicularis oculi—superior and inferior to each eye; closes eyes, squints, blinks, winks Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Head and Neck Muscles continued ▪ Orbicularis oris—around the mouth; closes mouth and protrudes the lips ▪ “kissing muscle” Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Head and Neck Muscles continued ▪ Buccinator – posterior to o.o.;controls the cheek, raises it (whistling) and compresses it to hold food between the teeth during chewing Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Head and Neck Muscles continued ▪ Zygomaticus—extends from the zygomatic bone to the o.o.; raises corners of the mouth ▪ “the smiling muscle” Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Head and Neck Muscles continued ii. Chewing muscles ▪ Buccinator is both a facial and chewing muscle ▪ Masseter—along the corner of the jaw line; closes the jaw and elevates mandible Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Head and Neck Muscles continued ▪ Temporalis—superficial to the temporal bone; synergist of the masseter, closes jaw Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Head and Neck Muscles continued iii. Neck muscles ▪ Platysma—anterolateral neck; pulls the corners of the mouth inferiorly (frowning) ▪ Sternocleidomastoid—paired, one on each side of the neck; rises from the sternum and clavicle and inserts into the temporal bone; flexes the neck, rotates the head, “prayer muscle” Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Head and Neck Muscles continued Figure 6.15 Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings B. Muscles of Trunk, Shoulder, Arm i. Anterior muscles ▪ Pectoralis major—upper part of the chest; adducts and flexes the humerus (upper arm) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued ▪ Intercostal muscles ▪ Found between each rib; raise and depress rib cage during breathing Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued Figure 6.16a Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued ▪ Muscles of the abdominal girdle Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued ▪ Rectus abdominis—most superficial muscles of the abdomen; flexes vertebral column and compresses abdominal contents (defecation, childbirth, forced breathing) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued ▪ External and internal obliques—lateral walls of the abdomen; flex vertebral column; rotate trunk and bend it laterally ▪ Transversus abdominis—deepest muscles of the abdomen; compresses abdominal contents Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued ii. Posterior muscles ▪ Trapezius—posterior neck and upper trunk; extends the head; stabilize the scapula; “shrugging shoulders” Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued ▪ Posterior muscles continued ▪ Latissimus dorsi—lower back; extends and adducts the humerus ▪ “Swimming or striking a blow” Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued ▪ Posterior muscles continued ▪ Deltoid—form the round shape of shoulders; arm abduction ▪ Favored site for intramuscular injections below 5 mL Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued Figure 6.17a Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued ▪ Biceps brachii—anterior upper arm; supinates forearm, flexes elbow ▪ Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued ▪ Brachialis—deep to the Biceps; elbow flexion, lifts ulna Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued ▪ Triceps brachii—posterior upper arm; elbow extension (antagonist to biceps brachii and brachialis) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of Trunk, Shoulder, and Arms Continued Figure 6.17a Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings C. Muscles of the Lower Limb ▪ HIP AND THIGH MOVEMENT ▪ Gluteus maximus—forms most flesh of buttocks ▪ Hip extensor ▪ Not important for walking ▪ Climbing stairs, jumping Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of the Lower Limb continued ▪ Gluteus medius—deep to the maximus; hip abduction, steadies pelvis when walking ▪ Imp’t for injections above 5 mL Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of the Lower Limb continued ▪ Iliopsoas—run from the lower vertebrae over the pelvis and attach to the femur; hip flexion, keeps the upper body from falling backward when standing erect ▪ Important for standing, walking, and running Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of the Lower Limb continued ▪ Adductor muscles—medial side of each thigh; adduct the thighs (press thighs together) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of the Lower Limb continued Figure 6.19a Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of the Lower Limb continued ▪ MUSCLES CAUSING MOVEMENT AT THE KNEE ▪ Hamstring group—hip extension and knee flexion Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of the Lower Limb continued ▪ Muscles causing movement at the knee joint cont’d ▪ Sartorius—flexes the thigh ▪ Quadriceps group—extends the knee ▪ Rectus femoris ▪ Vastus muscles (three) ▪ Injection site in infants Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of the Lower Limb continued Figure 6.19c Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of the Lower Limb continued ▪ MUSCLES CAUSING MOVEMENT AT THE ANKLE AND FOOT ▪ Gastrocnemius – “upper calf” ▪ Inserts into the heel via the Achilles’ tendon ▪ Plantar flexion ▪ Soleus—plantar flexion Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of the Lower Limb continued Figure 6.20b Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscles of the Lower Leg Figure 6.20b Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings The Muscular System Part II: Anatomy of the Muscle Tissue Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings I. Overview of Muscle Tissues Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings A. Muscle Types Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings i. skeletal muscle ▪ Cells are multinucleate ▪ Striated—have visible banding ▪ Voluntary—subject to conscious control ▪ Location – attached to bones throughout the body ▪ Function – movement, maintain posture, stabilize joints, generate heat Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings skeletal muscle cont ▪ Cells are surrounded and bundled by connective tissue ▪ muscle cells - elongated and forming fibers ▪ fascicle - bundle of muscle fibers Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings ii. smooth muscle ▪ Cells have a single nucleus ▪ No striations ▪ Involuntary ▪ Location – the walls of hollow organs like the stomach, bladder, and blood vessels ▪ Function – propel substances along a definite tract, or pathway, within the body Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings iii. cardiac ▪ Cells have a single nucleus ▪ Striated ▪ Involuntary ▪ Each cell meets at a junction called an intercalated disk ▪ Location – heart ▪ Function – pump blood throughout the body Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings B. Skeletal Muscle Functions ▪ 1) Locomotion and facial expressions Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings ▪ 2) Maintaining Posture Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings ▪ 3) Stabilizing joints Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings ▪ 4) Generating heat Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings II. Microscopic Anatomy of a Skeletal Muscle ▪ Within a single muscle cell (fiber), there are many thread-like organelles called myofibrils. ▪ Each myofibril has alternating light (I) bands and dark (A) bands that give skeletal muscle its striated appearance Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings ▪ If we look closer at myofibrils, we find that they are actually chains of tiny contractile units called sarcomeres, aligned end-to-end. ▪ Sarcomeres are made up of two types of myofilaments: thin (actin) filaments and thick (myosin) filaments Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings  Figure 6.3c Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings ▪ Notice that the ends of the thick filaments are studded with small projections, or myosin heads. ▪ Myosin heads connect to thin filaments during muscle contraction, forming cross bridges. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Build a Muscle Activity Muscle Bone Fascicles Tendon Muscle fibers (cells) Fascia (covering muscle) Myofibrils Epimysium Perimysium Thick and thin filaments Endomysium Fascicle Nerve Blood vessel Nucleus Myofibril Filaments Muscle fiber 87 Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings The Muscular System Part III: Skeletal Muscle Physiology Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings A. Unique Properties of Muscle Cells ▪ Muscle cells have 4 unique properties: ▪ 1. Excitability (also called responsiveness or irritability)—ability to receive and respond to a stimulus ▪ 2. Contractility—ability to shorten when an adequate stimulus is received ▪ 3. Extensibility—ability of muscle cells to be stretched ▪ 4. Elasticity—ability to recoil and resume resting length after stretching Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings B. The Nerve Stimulus and Action Potential i. Neuromuscular junction ▪ To contract, skeletal muscle cells must be stimulated by nerve cells (neurons). ▪ A neuron and all the muscle cells it stimulates are called a motor unit. Can include a few muscle cells or hundreds. ▪ Axon terminal – end of a neuron ▪ An axon terminal meets an individual muscle cell at a junction called the neuromuscular junction. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Neuromuscular Junction continued Figure 6.4a Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Neuromuscular Junction continued Figure 6.4b Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Neuromuscular Junction continued Figure 6.5a Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Neuromuscular Junction continued ▪ The nerve and muscle cell do not make contact; there is a space between them called the synaptic cleft. ▪ This space is filled with fluid. The question is, how does an nerve signal get across this space? Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Transmission continued ii. Transmission of a Nerve Impulse to the Muscle ▪ How does a nerve signal get across the synaptic cleft? ▪ It does so using a neurotransmitter, a chemical released by the nerve’s axon upon arrival of nerve impulse. ▪ There are over 100 different n.t., all with specific target cells. ▪ The neurotransmitter for skeletal muscle is acetylcholine (ACh). Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Transmission continued ▪ ACh diffuses across the cleft and attaches to receptors on the sarcolemma (plasma membrane) of the muscle fiber. ▪ If enough ACh is present, the sarcolemma becomes TEMPORARILY permeable to sodium (Na+), which goes in, and potassium (K+), which goes out. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Transmission continued Figure 6.5c Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Transmission continued ▪ More Na+ rushes into the cell than K+ rushes out. ▪ This upsets the electrical conditions in the cell, which starts the contraction. ▪ Once started, the contraction will travel the entire length of the muscle fiber. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Transmission continued Figure 6.6 Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings 3. The Sliding Filament Theory of Muscle Contraction ▪ After receiving an impulse, how do muscles shorten, or contract? Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings ▪ Remember, thick filaments have myosin heads. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings The Sliding Filament Theory of Muscle Contraction ▪ When an action potential hits a muscle cell, it causes the cell to release stored calcium. ▪ Calcium allows myosin heads to attach to the actin - forming cross bridges Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings The Sliding Filament Theory of Muscle Contraction ▪ The free myosin heads are “cocked”, and the attachment of these to actin “springs the trap”, causing the myosin heads to snap toward the center. ▪ Because actin and myosin are still attached when this happens, the thin filaments slid toward the center of the sarcomere. ▪ ATP provides the energy needed to release and recock each myosin head so that it’s ready to attach to a binding site farther along the thin filament. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings The Sliding Filament Theory of Muscle Contraction ▪ This continued action causes a sliding of the actin along the myosin ▪ The result is that the muscle is shortened (contracted) Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Animations https://www.youtube.com/watch?v=GneonFlcZG8 https://www.youtube.com/watch?v=BVcgO4p88AA Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings D. Energy for Muscle Contraction ▪ Initially, muscles use stored ATP for energy ▪ ATP bonds are broken to release energy to make ADP ▪ Only 4–6 seconds worth of ATP is stored by muscles ▪ After this initial time, other pathways must be utilized to produce ATP Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Energy for Muscle Contraction ▪ Muscles contain another chemical: creatine phosphate (CP) ▪ Muscle cells store a high-energy molecule called CP ▪ After ATP is depleted, ADP is left ▪ In this reaction, CP gives a phosphate group to ADP to regenerate ATP. ▪ Pros – muscles store 5x as much CP as ATP so this process works quickly. ▪ Cons - CP supplies are exhausted in less than 15 seconds. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Energy for Muscle Contraction Figure 6.10a Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Energy for Muscle Contraction ▪ Aerobic respiration ▪ Glucose is broken down into carbon dioxide and water, releasing energy (ATP) ▪ Pros – this reaction creates a large supply of ATP (about 32 ATP per 1 glucose molecule) ▪ Cons - This is a slower reaction that requires continuous oxygen Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Energy for Muscle Contraction Figure 6.10b Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Energy for Muscle Contraction ▪ Anaerobic glycolysis and lactic acid formation ▪ Reaction that breaks down glucose without oxygen ▪ Glucose is broken down to produce some ATP and some lactic acid ▪ Pros – This reaction is very fast and doesn’t require oxygen. Works for 30-60 sec of strenuous activity. ▪ Cons – Not as efficient as aerobic respiration (makes about 5% the amount of ATP); requires huge amounts of glucose; lactic acid causes muscle fatigue Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Energy for Muscle Contraction Figure 6.10c Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Muscle Fatigue and Oxygen Deficit ▪ When a muscle is fatigued, it is unable to contract even with stimulation. ▪ Common cause for muscle fatigue is oxygen debt ▪ Oxygen must be “repaid” to tissues to remove oxygen deficit ▪ Oxygen is required to get rid of accumulated lactic acid ▪ Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less ▪ True muscle fatigue, in which the muscle quits entirely, rarely occurs in most of us. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings The Muscular System Part IV: Disorders of the Muscular System ▪ Muscle strain – tearing of muscle fibers and/or the connective tissues surrounding muscles ▪ Dystonia – movement disorder where the muscles contract uncontrollably ▪ Tetanus – bacterial infection that blocks nerve signals from nerves to muscles, leading to severe muscle spasms. ▪ Muscular Dystrophy – genetic diseases that causes an abnormal weakening of muscle fibers ▪ Dermatomyositis - group of diseases causing chronic inflammation of the muscles and muscle weakness - usually accompanied by a skin rash Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Disorders of the Muscular System ▪ Amyotrophic lateral sclerosis (ALS) – the deterioration of motor neurons leads to muscle atrophy - AKA Lou Gehrig’s disease ▪ Myasthenia gravis - autoimmune disorder in which antibodies destroy communication between nerves and muscles ▪ Rhabdomyolysis - occurs when damaged muscle tissue releases proteins and electrolytes into the blood which can damage the heart and kidneys; can be fatal Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings