Chapter 7 - The Muscular System PDF

Chapter 7 The Muscular System System Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  M...

Chapter 7 The Muscular System System Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Muscle Tissue One of the four primary tissue types Consists of elongated muscle cells specialized for contraction Three types of muscle tissue  Skeletal Muscles Composed of skeletal muscle tissue Also contain connective tissues, nerves, and blood vessels Directly or indirectly attached to bones Muscular system includes about 700 skeletal muscles  Five Skeletal Muscle Functions 1. Move the skeleton Pull on tendons that then move bones 2. Maintain posture and body position 3. Support soft tissues Abdominal wall and pelvic cavity floor composed of skeletal muscles 4. Guard entrances and exits Encircle openings of digestive and urinary tracts 5. Maintain body temperature Muscle contractions generate heat  Organization of Skeletal Muscle Tissue Skeletal muscles contain: Skeletal muscle tissue Connective tissues Blood vessels Nerves Each skeletal muscle cell called a muscle fiber Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Connective Tissue Organization 1. Epimysium Covers the entire muscle 2. Perimysium Divides the muscle into fascicles or bundles of muscle fibers Contains blood vessels and nerves supplying fascicles 3. Endomysium Covers each muscle fiber and ties fibers together Contains capillaries and nerve fibers  Connective Tissue Attachments Collagen fibers from all three layers of connective tissue come together at the end of the muscle to form: Tendon Bundle of fibers Attaches muscle to bone Aponeurosis Broad sheet of fibers Connects muscles to each other  Blood Vessels and Nerves Extensive network of blood vessels in skeletal muscle necessary to supply high energy use Skeletal muscles under voluntary control Require stimulation by central nervous system Axons (nerve fibers) run through connective tissue layers to innervate individual muscle fibers  Features of Skeletal Muscle Fibers Can be very long (up to 60 cm) Each fiber is multinucleate (contains hundreds of nuclei) Have a repeating pattern that gives them a striped or striated appearance  The Sarcolemma and Transverse Tubule Sarcolemma is a muscle cell’s plasma membrane Surrounds the sarcoplasm or cytoplasm Contains openings that lead into network of tubules called transverse tubules, or T tubules T tubules allow electrical impulses from sarcoplasm to reach cell’s interior Allows unified contraction of entire fiber  Myofibrils Cylinder-shaped structures running the length of a muscle fiber Hundreds to thousands in each fiber Encircled by T tubules Bundles of thick and thin myofilaments Their sliding causes muscle fiber contraction  The Sarcoplasmic Reticulum (SR) Specialized smooth endoplasmic reticulum Forms network around each myofibril Expanded portion on either side of T tubules is the terminal cisterna Contains high concentrations of calcium ions Triad Combination of two terminal cisternae and one T tubule  Sarcomeres Repeating functional units of myofilaments Smallest functional units of skeletal muscle fiber Each myofibril has about 10,000 sarcomeres end to end Arrangement of thick and thin filaments produces the banded or striated appearance of the fiber Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Sarcomere Lines Z lines Mark the boundaries of each sarcomere Strands of a protein (titin) connect the Z lines to the thick filaments to maintain alignment M line Located in the center of each sarcomere Made of proteins that connect central portions of the thick filaments Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Sarcomere Bands A band Darker region containing the thick filaments Includes zone of overlap containing both thick and thin filaments I band Lighter region containing the thin filaments Includes the Z line H band When fiber is relaxed, contains only thick filaments Includes the M line and light regions on either side Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Thin Filaments Thin twisted strands of actin molecules Specific active sites on actin interact with myosin At rest, active sites covered by strands of tropomyosin Tropomyosin strands held in position by troponin Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Thick Filaments Composed of myosin molecules Each myosin molecule has tail and globular head Tails point inward; heads project outward Heads interact with active sites on actin during contraction Requires movement of troponin and tropomyosin to uncover active sites  Sliding Filament Theory Explanation for sarcomere contraction Based on observed changes in sarcomere Thin filaments are sliding toward the center of the sarcomere and thick filaments are not moving Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Mechanism for Sliding Filaments Myosin heads of thick filaments bind to active sites on thin filaments Binding produces cross-bridges Heads then pivot toward center of sarcomere, pulling thin filament in that direction Cross-bridges detach and return to original position Process repeats Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved The Neuromuscular Junction Specialized intercellular connection between a motor neuron and a skeletal muscle fiber Consists of an axon terminal and a motor end plate Axon terminal of the neuron Expanded end that contains vesicles filled with acetylcholine (ACh), a neurotransmitter Motor end plate is portion of muscle sarcolemma Separated from the axon terminal by the synaptic cleft The Neuromuscular Junction cont. The Contraction Cycle  Skeletal Muscle Contraction Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Skeletal Muscle Relaxation Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Sarcomere Shortening Produces Tension Sarcomere shortening causes entire muscle fiber to contract Muscle fiber contraction pulls on the collagen fibers of tendons, creating tension Tension tends to pull object towards source of tension Movement will occur only if the tension is greater than the object’s resistance Compression is a push applied to an object Muscle cells can only contract and produce tension They cannot generate compression  Amount of Tension Produced Depends on number of cross-bridges in muscle fiber All sarcomeres in the fiber are involved in contraction Individual muscle fibers are either fully contracted (“on”) or relaxed (“off”) Cannot vary tension by changing number of contracting sarcomeres  Factors Affecting Amount of Tension In an individual muscle fiber Resting length of muscle fiber Determines degree of overlap Frequency of stimulation Affects concentrations of calcium ions In a whole skeletal muscle Frequency of muscle fiber stimulation Number of fibers activated  Muscle Twitch A single stimulus-contraction-relaxation cycle in a muscle fiber 7.5 msec as in eye muscle fiber Up to 100 msec in fibers of the soleus (small calf muscle) Myogram Graph of tension development in a muscle fiber during a twitch  Three Phases of a Muscle Twitch 1. Latent period Begins at stimulation Lasts about 2 msec Includes the action potential and release of Ca2+ No tension produced 2. Contraction phase Period of cross-bridge interaction Maximum tension reached within about 15 msec  Three Phases of a Muscle Twitch Cont. 3. Relaxation phase Tension falls to resting levels Calcium levels drop Active sites are covered Number of cross- bridges declines Lasts about 25 msec  Summation Addition of one muscle twitch to another Causes a more powerful contraction Result of a second stimulus arriving before the relaxation phase has ended  Incomplete Tetanus vs. Complete Tetanus Incomplete tetanus Producing almost peak tension during rapid cycles of contraction and relaxation Complete tetanus Occurs when rate of stimulation increased until relaxation phase is eliminated Produces maximum tension Result of high calcium ion concentration in the cytosol Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Number of Muscle Fibers Activated Smooth contraction accomplished by controlling number of muscle fibers stimulated within a skeletal muscle Most motor neurons control hundreds or thousands of fibers through multiple axon terminals  Motor Unit Single motor neuron and all the muscle fibers it controls Muscle fibers of each motor unit intermingle with fibers from other motor units  Motor Unit Cont. Size of motor unit indicates degree of control Precise movements such as muscles of the eye Motor units contain very few fibers per neuron Gross movements such as muscles in the leg Motor units contain up to 2000 muscle fibers per neuron Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Recruitment Activation of more and more motor units Mechanism for increasing tension to create more movement Smallest motor units recruited first Gradually more motor units added Result is smooth, steady increase in muscle tension Peak tension produced when all motor units are recruited and contracting in complete tetanus  Muscle Tone vs. Atrophy Muscle tone Resting tension in skeletal muscle Stabilizes positions of bones and joints Maintains posture and body position Atrophy Occurs in a muscle that is not regularly stimulated by a motor neuron Muscle fibers become smaller and weaker Can be observed after a cast comes off a fracture Reversible if caused by temporary reduction in use Dying muscle fibers are not replaced Isotonic Contraction vs. Isometric Contraction Isotonic contraction Length of the muscle changes Tension remains constant until relaxation Examples: lifting a book, walking Isometric contraction Muscle length stays the same Tension produced does not exceed the load Example: pushing against a wall Muscle Elongation Following Contraction No active mechanism exists for returning a muscle to a pre-contracted, elongated state Passive processes are a combination of: Elastic forces Movements of opposing muscles Gravity  Energy Storage as Creatine Phosphate Muscle contraction requires large amounts of energy in the form of ATP Resting muscle fiber generates more ATP than needed while at rest Excess ATP transfers energy to creatine forming creatine phosphate (CP)  Using Creatine Phosphate Reserves During contraction, each cross-bridge breaks down ATP into ADP and a phosphate group Energy stored in CP used to recharge ADP back to ATP Reaction regulated by enzyme, creatine phosphokinase (CPK or CK) Energy reserves exhausted in about 15 seconds ATP must then be generated by different means Examples: aerobic metabolism and anaerobic glycolysis  Aerobic Metabolism Requires oxygen Normally provides 95% of resting muscle cell’s ATP needs Occurs in the mitochondria Involves breaking down of carbohydrates, lipids, and proteins into the smaller components End products are ATP, water, and carbon dioxide About 15 ATP produced per pyruvate entering the citric acid cycle Aerobic Metabolism Aerobic Metabolism Cont.  Glycolysis Breaks glucose down to pyruvate Occurs in the cytoplasm of the cell Anaerobic process Can continue to provide ATP when mitochondria are limited by low oxygen levels Only yields 2 ATP per glucose Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Muscle Fatigue Muscle will no longer perform at required level, even if stimulated Caused by depletion of energy reserves or a decline in pH due to buildup of H+ ions Affects muscles of endurance athletes after using stores of glycogen and lipids Affects sprinters more quickly as they rapidly build up lactic acid  The Recovery Period Time of returning muscle to normal pre-exertion conditions by: Restoring oxygen levels Removing lactic acid Replacing intracellular energy reserves Losing heat produced during contraction  Changes during the Recovery Period Breathing rate and depth remain increased to repay oxygen debt, or additional oxygen required to restore resting conditions Lactate is converted back to glucose Rate of heat loss increases Sweat gland secretions increase Blood flow to skin increases  Muscle Performance Measured in force Maximum amount of tension produced by a muscle or muscle group Measured in endurance Amount of time a particular activity can be performed Two factors determine performance 1. Types of fibers in muscle (fast-twitch and slow-twitch) 2. Physical conditioning or training  Fast (Fast-twitch) Fibers Reach peak tension very quickly in 0.01 sec or less Majority of muscle fibers in the body Large in diameter Large glycogen reserves Relatively few mitochondria, so rely on glycolysis As a result, fatigue rapidly Densely packed myofibrils So produce very powerful contractions  Slow (Slow-twitch) Fibers About half the diameter of fast fibers Three times slower than fast fibers (i.e., they take three times as long to reach peak tension) Specialized to contract for extended periods Fatigue resistant because of three factors: 1. Oxygen supply is greater due to extensive capillary network 2. High levels of oxygen storage by myoglobin 3. Oxygen use is efficient due to large numbers of mitochondria  Percentages of Muscle Fiber Types Vary Percentage of fast and slow fibers varies among skeletal muscles White muscles Dominated by fast fibers and appear pale Red muscles Dominated by slow fibers and appear reddish due to extensive blood vessels and myoglobin Human muscle is a mixture of fiber types and appears pink  Muscle Conditioning and Performance Physical conditioning and training can increase power and endurance Anaerobic endurance Length of time muscle contractions can be supported by glycolysis and existing ATP reserves Increased by brief, intense workouts Hypertrophy of muscles results Aerobic endurance Length of time muscle contractions are supported by mitochondrial activity Increased by sustained, low levels of activity  Cardiac Muscle Tissue Found only in heart Cardiac muscle cells Relatively small with usually only one central nucleus Striated and branched Intercalated discs connect cells to other cells Contain gap junctions that allow rapid communication between all cells, resulting in simultaneous contraction  Cardiac and Skeletal Muscle Differences Automaticity Cardiac muscle tissue contracts without neural stimulation Pacemaker cells, specialized cardiac muscle cells, determine timing of contraction Cardiac muscle cells have longer contractions (about 10 times longer) than skeletal muscle Cardiac muscle cells cannot undergo tetanus (sustained contraction)  Cardiac and Skeletal Muscle Differences Cont. Extracellular calcium ions Action potential increases permeability of cardiac muscle cell plasma membrane to extracellular calcium Allows entry of additional calcium Cardiac muscle cells rely on aerobic metabolism  Smooth Muscle Tissue Overview Smooth muscle cells Similar in size to cardiac muscle cells Spindle-shaped and have a single nucleus Found in the walls of most organs, in the form of sheets, bundles, or sheaths  Smooth Muscle Tissue Arrangement Smooth muscle lacks myofibrils, sarcomeres, and striations Thick filaments are scattered throughout sarcoplasm Thin filaments are anchored to the sarcolemma Anchoring sites not in a straight line Contraction causes twisting like a corkscrew Adjacent cells bound together Contractile force transmitted throughout tissue  Functional Differences in Smooth Muscle Tissue Contractions triggered differently Most of calcium for trigger enters from extracellular fluid Contract over greater range of lengths Actin and myosin filaments not rigidly organized Automacity or neural or hormonal stimulation Can contract automatically in response to pacesetter cells or in response to hormones Can also respond to motor neurons  Divisions of Skeletal Muscles Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Origin, Insertion, and Action Origin The end of the muscle that stays stationary Insertion The end of the muscle that moves when the muscle contracts Action What happens when the muscle contracts Examples: flexion, extension, adduction, or abduction  Description of Actions Described as relative to the bone that is moved Example, biceps brachii performs “flexion of the forearm” Described as the joint that is involved Example, biceps brachii performs “flexion at the elbow”  Primary Actions of Muscles Prime mover, or agonist The muscle that is chiefly responsible for producing a movement (the biceps brachii is prime mover that flexes elbow) Antagonist Muscle that opposes a movement by another muscle (the triceps brachii is antagonist to the biceps brachii)  Primary Actions of Muscles Synergist Muscle that helps the prime mover work efficiently (the brachialis assists the biceps brachii in flexion of the elbow Fixators are synergists that stabilize the origin of a prime mover by preventing movement at another joint (the rhomboid muscles are fixators during flexion of the elbow in that they stabilize one of the origins of the biceps brachii)  Basis for Names of Skeletal Muscles Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Basis for Names of Skeletal Muscles What does the name flexor carpi radialis longus tell you about this muscle? Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Axial Muscles Muscles of the head and neck Muscles of the spine Muscles of the trunk Muscles of the pelvic floor  Muscles of the Head and Neck Muscles of the face Originate on surface of skull Insert into dermis of the skin Contraction causes movement of the skin Muscles associated with the mouth: Orbicularis oris – constricts the opening of the mouth Buccinator – compresses cheeks when blowing forcefully Temporalis and pterygoid – assist the masseter in chewing  Muscles of the Head and Neck cont. Epicranium, or scalp, contains a two-part muscle, the occipitofrontalis 1. Anterior is the frontalis muscle 2. Posterior is the occipitalis muscle Two are connected by the epicranial aponeurosis Platysma Covers ventral neck Extends from the base of the neck to the mandible  Muscles of the Neck Muscles of the neck Control position of the larynx Depress the mandible Tense the floor of the mouth Provide stable foundation for muscles of the tongue and pharynx  Muscles of the Spine Splenius capitis and semispinalis capitis Work together to either extend the head or tilt the head Erector spinae, or spinal extensors Maintain an erect spinal column and head Quadratus lumborum Flex the spinal column and depress the ribs Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Axial Muscles of the Trunk External and internal intercostals Externals elevate ribs and internals depress ribs External and internal obliques, and the transversus abdominis Compress abdomen, can flex spine Rectus abdominis Depresses ribs, flexes spine  Axial Muscles of the Trunk Diaphragm Separates the thoracic and abdominopelvic cavities  Muscles of the Pelvic Floor Pelvic cavity floor called the perineum Formed by broad sheet of muscles that: Support the organs of the pelvic cavity Flex the coccyx Control movement of material through the anus and urethra  Appendicular Muscles Muscles of the shoulder and upper limbs Muscles that position the pectoral girdle Muscles that move the arm, forearm, and wrist Muscles that move the hand and fingers Muscles of the pelvic girdle and lower limbs Muscles that move the thigh and leg Muscles that move the foot and toes  Muscles That Position the Pectoral Girdle Trapezius Diamond-shaped muscle, has many actions depending on the region Rhomboid Adducts and rotates scapula laterally Levator scapulae Elevates scapula (as in shrugging your shoulders)  Muscles That Position the Pectoral Girdle Serratus anterior Abducts and rotates scapula Pectoralis minor and subclavius Depress and abduct scapula  Muscles That Move the Arm Deltoid Major abductor of the arm Supraspinatus assists at beginning of movement Pectoralis major Flexes the arm at the shoulder  Muscles That Move the Arm Subscapularis, teres major, infraspinatus, and teres minor Rotate the arm Latissimus dorsi Extends the arm at the shoulder  Rotator Cuff Tendons of four muscles form a supportive capsule around the shoulder joint, called the rotator cuff 1. Supraspinatus 2. Infraspinatus 3. Teres minor 4. Subscapularis Common site of sports injuries such as a muscle strain (tear or break in muscle) Animation: A&P Flix: Rotator cuff muscles: An overview (a) Animation: A&P Flix: Rotator cuff muscles: An overview (b)  Muscles Moving the Forearm and Wrist Biceps brachii Flexes the elbow and supinates forearm Triceps brachii Extends elbow Brachialis and brachioradialis Flex elbow Flexor carpi ulnaris, flexor carpi radialis, and palmaris longus Flex wrist Muscles Moving the Forearm and Wrist Cont. Extensor carpi radialis and extensor carpi ulnaris Extend wrist Pronators and the supinator Rotate radius  Muscles That Move the Hand and Fingers Extensor digitorum and flexor digitorum Extend and flex fingers respectively Abductor pollicis and extensor pollicis Abducts and extends thumb respectively  Muscles That Move the Hand and Fingers Muscles located in the forearm Only tendons cross the wrist Wide bands of connective tissue (retinacula) hold tendons in place Inflammation of this tissue can result in carpal tunnel syndrome  Muscles of the Pelvis and Lower Limbs Divided into three functional groups: 1. Muscles that work across the hip joint to move the thigh 2. Muscles that work across the knee joint to move the leg 3. Muscles that work across various joints of the foot to move the ankles, feet, and toes  Muscles That Move the Thigh Gluteal muscles Cover lateral surfaces of iliac bones Includes the gluteus maximus, the largest and most posterior Produce extension, rotation, and abduction at hip joint  Other Muscles That Move the Thigh Adductors Include the adductor magnus, adductor brevis, adductor longus, the pectineus, and the gracilis Largest hip flexor is the iliopsoas Composed of the psoas major and the iliacus Copyright © 2020, 2017, and 2013 Pearson Education, Inc. All Rights Reserved  Muscles That Move the Leg Flexors are on posterior and medial surfaces Three are collectively known as the hamstrings Biceps femoris, semimembranosus, and semitendinosus Sartorius crosses hip and knee joints and produces lateral rotation at the hip Popliteus unlocks the knee joint  Muscles That Move the Leg Extensors are on anterior and lateral surfaces Collectively known as the quadriceps femoris Include the rectus femoris and the three vastus muscles  Muscles That Move the Foot Gastrocnemius Largest muscle of the calf Assisted by the underlying soleus They share a common calcaneal tendon Both muscles are plantar flexors  Other Muscles That Move the Foot Fibularis, or peroneus muscles Produce eversion and plantar flexion Tibialis muscles Cause inversion of the foot Tibialis anterior is largest and produces dorsiflexion  Muscles That Move the Toes Originate on surface of the tibia, fibula, or both Tendons surrounded by synovial tendon sheaths at ankle joint Sheaths stabilized by retinacula Smaller intrinsic muscles originate on tarsal and metatarsal bones Contractions move the toes Muscles That Move the Foot and Toes  Four Effects of Aging on Skeletal Muscle 1. Skeletal muscle fibers become smaller in diameter 2. Skeletal muscles become less elastic Increasing fibrous tissue (fibrosis) makes muscle less flexible 3. Tolerance for exercise decreases Tendency to tire quickly Decrease in thermoregulation 4. Ability to recover from injury is decreased  Exercise Engages Multiple Systems Muscular system Active muscles consume oxygen and generate CO2 and heat Cardiovascular system Increases heart rate and speeds up delivery of oxygen Respiratory system Increases rate and depth of respiration Integumentary system Dilation of blood vessels and sweating combine to increase cooling Nervous and endocrine systems Control heart rate, respiratory rate, sweat gland activity, and release of stored energy How the Muscular System Integrates with the Skeletal and Integumentary Systems