Chapter 7 The Muscular System

Chapter 7 Lesson 7.1

Introduction Muscular tissue enables the body and its parts to move Movement is 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 the body What causes movement of the body? (skeletal muscle contraction)

Muscle Tissue Types of muscle tissue Skeletal muscle—also called striated or voluntary muscle Is 40% to 50% of body weight; attached to bones Microscope reveals crosswise stripes or striations Contractions can be voluntarily controlled (Cont’d…) 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.

Muscle Tissue Types of muscle tissue (cont’d) 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 (Cont’d…) What is the value of the interconnected nature of the cardiac muscle? (It increases the efficiency of the heart muscle in pumping blood.)

Muscle Tissue Types of muscle tissue (cont’d) Nonstriated muscle or involuntary muscle—also called smooth or visceral muscle Lacks cross stripes or striation 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 contractions is involuntary Function—all muscle cells specialize in contraction (shortening)

Muscle Tissue (…Cont’d) Muscle tissue

Structure of Skeletal Muscle Skeletal muscle: an organ composed mainly of skeletal muscle cells and connective tissue Extend from one bone across a joint to another bone (Cont’d…)

Structure of Skeletal Muscle (…Cont’d) Structure Parts of a skeletal muscle: Origin—attachment to the bone that remains relatively 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 (Cont’d…) What are the origin and the insertion point, and what are their roles in movement of the body?

Structure of Skeletal Muscle (…Cont’d) Muscles attach to the bone by tendons—strong cords of fibrous connective tissue Some tendons: enclosed in synovial-lined tubes and lubricated by synovial fluid Bursae—small synovial-lined sacs containing a small amount of synovial fluid (Cont’d…) Tendons do not tear or pull away from bone easily, yet emergency room 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.)

Structure of Skeletal Muscle (…Cont’d) Attachments of a skeletal muscle

Structure of Skeletal Muscle (…Cont’d) Microscopic structure Muscle tissue consists of specialized contractile cells called fibers Each fiber contains two kinds of very fine, threadlike structures: Thick myofilaments =Myosin Thin myofilaments =Actin (Cont’d…) What are thick and thin myofilaments composed of?thick myofilaments formed from protein myosin; thin myofilaments composed of actin)

Structure of Skeletal Muscle (…Cont’d) Sarcomere: basic functional (contractile) unit 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 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)

Functions of Skeletal Muscle Movement Muscles produce movement As muscle contracts, it pulls the insertion bone closer to the origin bone Movement occurs at the joint between the origin and the insertion (Cont’d…) Describe how muscles produce movement.

Functions of Skeletal Muscle (Cont’d…) Movement Groups of muscles usually contract to produce a single movement Prime mover—contraction is mainly responsible for producing a movement Synergist—contractions help the prime mover produce a movement Antagonist—actions oppose the action of a prime mover in a 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.

Functions of Skeletal Muscle (…Cont’d) Posture Tonic contraction: specialized muscle contraction that enables us to maintain body position Only a few of a muscle’s fibers shorten at one time Tonic contractions produce no movement Tonic contractions maintain muscle tone called posture (Cont’d…) Good posture means that body parts are held in positions that favor best function. Bad posture causes fatigue and may lead to deformity.

Functions of Skeletal Muscle (…Cont’d) Heat production Survival depends on the ability to maintain 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.

Fatigue Reduced strength of muscle contraction Caused by repeated muscle stimulation Repeated muscular contraction depletes cellular ATP store and outstrips the ability of the blood supply to replenish oxygen and nutrients (Cont’d…) What can cause a decrease in the strength of muscle contraction? (muscle cells being repeatedly stimulated without adequate rest)

Fatigue (…Cont’d) Contraction in the absence of adequate oxygen produces lactic acid, which contributes to muscle soreness Oxygen debt—the continued metabolic effort required to burn excess lactic acid that may accumulate during prolonged periods of exercise 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 following exercise? (to return the cells’ energy and oxygen reserves to pre-exercise levels)

Role of Other Body Systems in Movement Muscle functioning depends on the functioning of many other parts of the body 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. What are some examples of pathologic conditions that might affect movement of the body? (skeletal system disorders. multiple sclerosis, brain hemorrhage, and spinal cord injury)

Motor Unit Stimulation of a muscle by a nerve impulse is required to produce movement Motor neuron: specialized nerve that transmits an impulse to a muscle, causing contraction Neuromuscular junction: specialized point of contact between a nerve ending and the muscle fiber it innervates Motor unit: the combination of a motor neuron with the muscle cell(s) it innervates Specialized chemicals are released by the motor neuron in response to a nerve impulse.

Muscle Stimulus A muscle will contract only if an applied stimulus reaches a certain level of intensity Threshold stimulus: 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 (Cont’d…) What is a threshold stimulus?

Muscle Stimulus (…Cont’d) 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 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.)

Types of Skeletal Muscle Contraction Twitch and tetanic contractions Twitch contractions—a quick, jerky response to stimulus Single contraction of muscle fibers caused by a single threshold stimulus Tetanic contractions—sustained, steady muscular contractions Caused by a series of stimuli bombarding a muscle in rapid succession (Cont’d…) About 30 stimuli per second evoke tetanic contractions in certain types of skeletal muscles. Are twitch contractions significant for normal activity? (no)

Types of Skeletal Muscle Contraction (…Cont’d) Isotonic contractions Contraction of a muscle that produces movement at a joint 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 isotonic contractions (Cont’d…) What is an isotonic contraction?

Types of Skeletal Muscle Contraction (…Cont’d) Isometric contractions Muscle contractions that do not produce movement The muscle as a whole does not shorten No movement occurs during isometric contractions, but 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.

Types of Skeletal Muscle Contraction (…Cont’d) Types of Muscle Contraction

Effects of Exercise on Skeletal Muscles Regular, properly practiced exercise improves muscle tone and posture, Results in more efficient heart and lung functioning Reduces fatigue (Cont’d…) What are some of the health benefits of regular exercise?

Effects of Exercise on Skeletal Muscles Prolonged inactivity causes disuse atrophy Regular exercise increases muscle size, called hypertrophy (Cont’d…) What type of changes do muscles undergo relative to the amount of work they normally do? (disuse atrophy, hypertrophy)c

Effects of Exercise on Skeletal Muscles (…Cont’d) Strength training: exercise involving contractions of muscles against heavy resistance Increases number of myofilaments in each muscle fiber Total mass of the muscle increases Does not increase the number of muscle fibers (Cont’d…) What are examples of strength training? (isometric exercises and weight lifting)

Effects of Exercise on Skeletal Muscles (…Cont’d) Endurance training: exercise that increases a muscle’s ability to sustain moderate exercise over long periods Sometimes called aerobic training Allows more efficient delivery of oxygen and nutrients to a muscle via increased blood flow Increases the number of blood vessels in a muscle Does not usually result in muscle hypertrophy What are the differences between strength training and endurance training?

Chapter 7 Lesson 7.2

Skeletal Muscle Groups Muscles of the head and neck Facial muscles Orbicularis oculi, orbicularis oris, zygomaticus Muscles of mastication Masseter, temporal Sternocleidomastoid—flexes head Trapezius—elevates shoulders and extends head (Cont’d…) What are the names of the “kissing muscle” and the “smiling muscle”? (Orbicularis oculi is the kissing muscle, and zygomaticus is the smiling muscle.) Mastication muscles are among the strongest muscles in the body.

Skeletal Muscle Groups (…Cont’d) Muscles of the head and neck (Cont’d…)

Skeletal Muscle Groups (…Cont’d) 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 (Cont’d…) The upper extremity is attached to the thorax by the pectoralis major. What is the name of the “boxer’s muscle”? (triceps brachii)

Skeletal Muscle Groups (…Cont’d) Muscles of the trunk Abdominal muscles Rectus abdominis External oblique Internal oblique Transversus abdominis Respiratory muscles Intercostal muscles Diaphragm (Cont’d…) Rectus abdominis flexes the spinal column. Which muscles change the size of the chest during respiration? (respiratory muscles)

Skeletal Muscle Groups (…Cont’d) Muscles of the trunk (Cont’d…)

Skeletal Muscle Groups (…Cont’d) 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 (Cont’d…) Iliopsoas normally flexes the thigh, but can flex the trunk if the thigh is fixed/immovable as in sit-ups.

Skeletal Muscle Groups (…Cont’d) Muscles that move the lower extremities Quadriceps femoris group—extend lower leg Rectus femoris Vastus muscles Tibialis anterior—dorsiflexes foot Gastrocnemius—plantar flexes foot Peroneus group—flex foot Gastrocnemius is sometimes called the toe dancer’s muscle.

Types of Movements Produced by Skeletal Muscle Contractions Flexion—decreases the angle between two bones at their joint: bending Extension—increases the angle between two bones at their joint: straightening 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 (Cont’d…) 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”)

Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d) Flexion and extension of the elbow (Cont’d…)

Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d) Supination and pronation—hand positions from rotation of the forearm Supination: palm turned to the anterior position Pronation: palm faces posteriorly Dorsiflexion and plantar flexion—foot movements Dorsiflexion: elevation of the dorsum or top of the foot Plantar flexion: bottom of the foot is directed downward (Cont’d…) What are the origins of the words “supination” and “pronation”? (supine and prone)

Types of Movements Produced by Skeletal Muscle Contractions (…Cont’d) Examples of body movements