Chapter 8 The Muscular System

Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc
Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Chapter 8 The Muscular System
Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Objectives List, locate in the body, and compare the structure and function of the three major types of muscle tissue. Discuss the microscopic structure of a skeletal muscle sarcomere and motor unit. Discuss how a muscle is stimulated and compare the major types of skeletal muscle contractions. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Objectives (Cont’d.) Name, identify on a model or diagram, and give the function of the major muscles of the body discussed in this chapter. List and explain the most common types of movement produced by skeletal muscles. Name and describe the major disorders of skeletal muscles. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Introduction Muscular tissue enables the body and its parts to move
Movement caused by ability of muscle cells (called fibers) to shorten or contract Muscle cells shorten by converting chemical energy (obtained from food) into mechanical energy, which causes movement Three types of muscle tissue exist in body What causes movement of the body? (Skeletal muscle contraction) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscle Tissue Types of muscle tissue
Skeletal muscle—also called striated or voluntary muscle Is 40% to 50% of body weight (“red meat” attached to bones) Microscope reveals crosswise stripes or striations Contractions can be voluntarily controlled What are the three types of muscle tissue? (Skeletal, cardiac, and smooth) If someone weighs 120 pounds, about 50 pounds of the body weight comes from the skeletal muscles. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Cardiac muscle—composes bulk of heart Cardiac muscle cells branch frequently Characterized by unique dark bands called intercalated disks Interconnected nature of cardiac muscle cells allows heart to contract efficiently as a unit What is the value of the interconnected nature of the cardiac muscle? (It increases the efficiency of the heart muscle in pumping blood.) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Nonstriated muscle or involuntary muscle—also called smooth or visceral muscle Lacks cross stripes or striations when seen under a microscope; appears smooth Found in walls of hollow visceral structures such as digestive tract, blood vessels, and ureters Contractions not under voluntary control; movement caused by contraction is involuntary Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Structure of Skeletal Muscle
Each skeletal muscle is an organ composed mainly of skeletal muscle cells and connective tissue Most skeletal muscles extend from one bone across a joint to another bone What are the origin and the insertion point, and what are their roles in movement of the body? Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Parts of a skeletal muscle Origin—attachment to the bone that remains relatively stationary or fixed when movement at the joint occurs Insertion—point of attachment to the bone that moves when a muscle contracts Body—main part of the muscle Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscles attach to bone by tendons—strong cords of fibrous connective tissue; some tendons enclosed in synovial-lined tubes and are lubricated by synovial fluid; tubes called tendon sheaths Bursae—small synovial-lined sacs containing a small amount of synovial fluid; located between some tendons and underlying bones Tendons do not tear or pull away from bone easily, yet emergency department physicians and nurses frequently see torn or severed tendon injuries. Small, fluid-filled sacs called bursae lie between some tendons and the bones beneath them. What is the role of bursae? (Bursae make it easier for a tendon to slide over a bone when the muscle shortens.) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Microscopic structure Contractile cells called fibers—grouped into bundles Fibers contain thick myofilaments (containing the protein myosin) and thin myofilaments (composed of actin) What are thick and thin myofilaments composed of? (Thick myofilaments formed from protein myosin; thin myofilaments composed of actin) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Microscopic structure Basic functional (contractile) unit called sarcomere; sarcomeres separated from each other by dark bands called Z lines Sliding filament model explains mechanism of contraction Thick and thin myofilaments slide past each other as a muscle contracts Contraction requires calcium and energy-rich ATP molecules As the osteon (Haversian system) serves as basic building block in compact bone, sarcomere serves that function in muscle. What is required for contraction? (Calcium and energy-rich ATP molecules) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Functions of Skeletal Muscle
Movement Muscles produce movement; as a muscle contracts, it pulls the insertion bone closer to the origin bone; movement occurs at the joint between the origin and the insertion Describe how muscles produce movement. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Movement Groups of muscles usually contract to produce a single movement Prime mover—muscle whose contraction is mainly responsible for producing a given movement Synergist—muscle whose contractions help the prime mover produce a given movement Antagonist—muscle whose actions oppose the action of a prime mover in any given movement When a muscle group produces movement, what are the components of the group called? (Prime mover, synergist, antagonist) When antagonist muscles contract, roles are reversed and they produce opposite movement. Voluntary movement is normally smooth and free of jerks because skeletal muscles work in coordinated teams, not separately. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Posture A specialized type of muscle contraction, called tonic contraction, enables us to maintain body position In tonic contraction, only a few of a muscle’s fibers shorten at one time Tonic contractions produce no movement of body parts Good posture means that body parts are held in positions that favor best function. Bad posture causes fatigue and may lead to deformity. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Posture Tonic contractions maintain muscle tone called posture Good posture reduces strain on muscles, tendons, ligaments, and bones Poor posture causes fatigue and may lead to deformity Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Heat production Survival depends on the body’s ability to maintain a constant body temperature Fever—an elevated body temperature—often a sign of illness Hypothermia—a reduced body temperature Contraction of muscle fibers produces most of the heat required to maintain normal body temperature Heat is produced by the breakdown of adenosine triphosphate (ATP) during contractions. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Fatigue Reduced strength of muscle contraction
Caused by repeated muscle stimulation without adequate periods of rest Repeated muscular contraction depletes cellular ATP stores and outstrips the ability of the blood supply to replenish oxygen and nutrients What can cause a decrease in the strength of muscle contraction? (Muscle cells being repeatedly stimulated without adequate rest) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Fatigue Contraction in the absence of adequate oxygen produces lactic acid, which contributes to muscle soreness Oxygen debt—term used to describe the metabolic effort required to burn excess lactic acid that may accumulate during prolonged periods of exercise; the body is attempting to return the cells’ energy and oxygen reserves to pre-exercise levels Labored breathing is required to help the body pay the oxygen debt—an example of homeostasis at work. What is the body attempting to do on the cellular level during labored breathing after exercise? (To return the cells’ energy and oxygen reserves to pre-exercise levels) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Role of Other Body Systems in Movement
Muscle functioning depends on the functioning of many other parts of the body Most muscles cause movements by pulling on bones across movable joints Respiratory, circulatory, nervous, muscular, and skeletal systems play essential roles in producing normal movements Normal function of one body part depends on the normal function of all other parts. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Role of Other Body Systems in Movement
Muscle functioning depends on the functioning of many other parts of the body Multiple sclerosis, brain hemorrhage, and spinal cord injury are examples of how pathological conditions in other body organ systems can dramatically affect movement What are some examples of pathological conditions that might affect movement of the body? (Skeletal system disorders, multiple sclerosis, brain hemorrhage, and spinal cord injury) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Motor Unit Stimulation of a muscle by a nerve impulse is required before a muscle can shorten and produce movement A motor neuron is the specialized nerve that transmits an impulse to a muscle, causing contraction Specialized chemicals are released by the motor neuron in response to a nerve impulse. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Motor Unit A neuromuscular junction is the specialized point of contact between a nerve ending and the muscle fiber it innervates A motor unit is the combination of a motor neuron with the muscle cell or cells it innervates Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscle Stimulus A muscle will contract only if an applied stimulus reaches a certain level of intensity A threshold stimulus is the minimal level of stimulation required to cause a muscle fiber to contract Once stimulated by a threshold stimulus, a muscle fiber will contract completely, a response called all or none What is a threshold stimulus? Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscle Stimulus Different muscle fibers in a muscle are controlled by different motor units having different threshold–stimulus levels Although individual muscle fibers always respond all or none to a threshold stimulus, the muscle as a whole does not Different motor units responding to different threshold stimuli permit a muscle as a whole to execute contractions of graded force How is a graded response of a muscle accomplished? (Different motor units responding to different threshold stimuli permit a muscle as a whole to execute contractions of graded force.) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Types of Skeletal Muscle Contraction
Twitch and tetanic contractions Twitch contractions are laboratory phenomena and do not play a significant role in normal muscular activity; they are a single contraction of muscle fibers caused by a single threshold stimulus Tetanic contractions are sustained and steady muscular contractions caused by a series of stimuli bombarding a muscle in rapid succession About 30 stimuli per second evoke tetanic contractions in certain types of skeletal muscles. Are twitch contractions significant for normal activity? (No) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Isotonic contractions Contraction of a muscle that produces movement at a joint During isotonic contractions, the muscle changes length, causing the insertion end of the muscle to move relative to the point of origin Most types of body movements such as walking and running are caused by isotonic contractions What is an isotonic contraction? Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Isometric contractions Isometric contractions are muscle contractions that do not produce movement; the muscle as a whole does not shorten Although no movement occurs during isometric contractions, tension within the muscle increases What is an isometric contraction? What are the differences between isotonic and isometric contractions? Pushing against a wall is an example of an isometric contraction. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Effects of Exercise on Skeletal Muscles
Exercise, if regular and properly practiced, improves muscle tone and posture, results in more efficient heart and lung functioning, and reduces fatigue Effects of exercise on skeletal muscles Muscles undergo changes related to the amount of work they normally do Prolonged inactivity causes disuse atrophy Regular exercise increases muscle size, called hypertrophy What are some of the health benefits of regular exercise? What type of changes do muscles undergo relative to the amount of work they normally do? (Disuse atrophy, hypertrophy) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Strength training is exercise involving contraction of muscles against heavy resistance Strength training increases the numbers of myofilaments in each muscle fiber, and as a result, the total mass of the muscle increases Strength training does not increase the number of muscle fibers What are examples of strength training? (Isometric exercises and weight lifting) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Endurance training is exercise that increases a muscle’s ability to sustain moderate exercise over a long period; it is sometimes called aerobic training Endurance training allows more efficient delivery of oxygen and nutrients to a muscle via increased blood flow Endurance training does not usually result in muscle hypertrophy What are the differences between strength training and endurance training? Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Skeletal Muscle Groups
Muscles of the head and neck Facial muscles Orbicularis oculi Orbicularis oris Zygomaticus What are the names of the “kissing muscle” and the “smiling muscle”? (Orbicularis oculi is the kissing muscle, and zygomaticus is the smiling muscle.) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscles of the head and neck Muscles of mastication Masseter Temporal Sternocleidomastoid—flexes head Trapezius—elevates shoulders and extends head Mastication muscles are among the strongest muscles in the body. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscles that move the upper extremities Pectoralis major—flexes upper arm Latissimus dorsi—extends upper arm Deltoid—abducts upper arm Biceps brachii—flexes forearm Triceps brachii—extends forearm The upper extremity is attached to the thorax by the pectoralis major. What is the name of the “boxer’s muscle”? (Triceps brachii) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscles of the trunk Abdominal muscles Rectus abdominis External oblique Internal oblique Transversus abdominis Respiratory muscles Intercostal muscles Diaphragm Rectus abdominis flexes the spinal column. Which muscles change the size of the chest during respiration? (Respiratory muscles) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscles that move the lower extremities Iliopsoas—flexes thigh Gluteus maximus—extends thigh Adductor muscles—adduct thighs Hamstring muscles—flex lower leg Semimembranosus Semitendinosus Biceps femoris Iliopsoas normally flexes the thigh, but it can flex the trunk if the thigh is fixed/immovable, as in sit-ups. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscles that move the lower extremities Quadriceps femoris group—extend lower leg Rectus femoris Vastus muscles Tibialis anterior—dorsiflex foot Gastrocnemius—plantar flex foot Peroneus group—flex foot Gastrocnemius is sometimes called the toe dancer’s muscle. Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Types of Movements Produced by Skeletal Muscle Contractions
Flexion—movement that decreases the angle between two bones at their joint: bending Extension—movement that increases the angle between two bones at their joint: straightening Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Abduction—movement of a part away from the midline of the body Adduction—movement of a part toward the midline of the body Rotation—movement around a longitudinal axis What are examples of the types of movements listed here? (Flexion: bending elbow or knee; extension: straightening elbow or knee; abduction: lowering arm; rotation: shaking head “no”) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Supination and pronation—hand positions that result from rotation of the forearm; supination results in a hand position with the palm turned to the anterior position; pronation occurs when the palm faces posteriorly What are the origins of the words “supination” and “pronation”? (Supine and prone) Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Dorsiflexion and plantar flexion—foot movements; dorsiflexion results in elevation of the dorsum or top of the foot; during plantar flexion, the bottom of the foot is directed downward Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Major Muscular Disorders
Myopathies—muscle disorders; can range from mild to life threatening Muscle injury Strain—injury from overexertion or trauma; involves stretching or tearing of muscle fibers Often accompanied by myalgia (muscle pain) May result in inflammation of muscle (myositis) or of muscle and tendon (fibromyositis) If injury is near a joint and involves ligament damage, it may be called a sprain Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscle injury Cramps are painful muscle spasms (involuntary twitches) Crush injuries result from severe muscle trauma and may release cell contents that ultimately cause kidney failure Stress-induced muscle tension can cause headaches and back pain Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Infections Several bacteria, viruses, and parasites can infect muscles Poliomyelitis is a viral infection of motor nerves that ranges from mild to life threatening Why is polio no longer a threat to the U.S. population? (Vaccination) Is polio a threat anywhere in the world? (It is still contracted in third world regions where the population has not been vaccinated, but it is becoming less and less of a threat.) What are the effects of polio on the body? Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Muscular dystrophy A group of genetic disorders characterized by muscle atrophy Duchenne (pseudohypertrophic) muscular dystrophy is the most common type Characterized by rapid progression of weakness and atrophy, resulting in death by age 21 X-linked inherited disease, affecting mostly boys Copyright © 2007, 2005, 2002, 1997, 1992 by Mosby, Inc., an affiliate of Elsevier Inc. All rights reserved.

Chapter 8 The Muscular System

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