7 The Muscular System Overview of Muscular System Types of Muscle Tissue • Under voluntary control • Skeletal muscles • The muscular system • Under involuntary control • Cardiac muscle • Heart wall • Smooth muscle • Visceral organs Overview of Muscular System • Skeletal muscles attach to bones directly or indirectly • Perform five functions • Produce movement of skeleton • Maintain posture and body position • Support soft tissues • Guard entrances and exits • Maintain body temperature Anatomy of Skeletal Muscles Gross Anatomy • Connective tissue organization • Epimysium • Fibrous covering of whole muscle • Perimysium • Fibrous covering of fascicle • Endomysium • Fibrous covering of a single cell (a muscle fiber) • Tendons (or aponeurosis) Anatomy of Skeletal Muscles The Organization of a Skeletal Muscle Anatomy of Skeletal Muscles Microanatomy of a Muscle Fiber • Sarcolemma

• Muscle cell membrane • Sarcoplasm • Muscle cell cytoplasm • Sarcoplasmic reticulum (SR) • Like smooth ER • Transverse tubules (T tubules) • Myofibrils (contraction organelle) • Sarcomeres Anatomy of Skeletal Muscles Sarcomere—Repeating structural unit of the myofibril • Components of a sarcomere • Myofilaments • Thin filaments (mostly actin) • Thick filaments (mostly myosin) • Z lines at each end • Anchor for thin filaments Anatomy of Skeletal Muscles The Organization of a Single Muscle Fiber Anatomy of Skeletal Muscles The Organization of a Single Muscle Fiber Anatomy of Skeletal Muscles The Organization of a Single Muscle Fiber Anatomy of Skeletal Muscles Changes in the Appearance of a Sarcomere During Contraction of a Skeletal Muscle Fiber Anatomy of Skeletal Muscles Changes in the Appearance of a Sarcomere During Contraction of a Skeletal Muscle Fiber Control of Muscle Contraction Steps in Neuromuscular Transmission • Motor neuron action potential • Acetylcholine release and binding • Action potential in sarcolemma • T tubule action potential • Calcium release from SR Control of Muscle Contraction The Neuromuscular Junction • Synaptic terminal • Acetylcholine release • Synaptic cleft

• Motor end plate • Acetylcholine receptors • Acetylcholine binding • Acetylcholinesterase • Acetylcholine removal Control of Muscle Contraction The Structure and Function of the Neuromuscular Junction Anatomy of Skeletal Muscles The Contraction Process • Actin active sites and myosin cross-bridges interact • Thin filaments slide past thick filaments • Cross-bridges undergo a cycle of movement • Attach, pivot, detach, return • Troponin-tropomyosin control interaction • Prevent interaction at rest Control of Muscle Contraction Summary of Contraction Process Control of Muscle Contraction Key Note Skeletal muscle fibers shorten as thin filaments interact with thick filaments and sliding occurs. The trigger for contraction is the calcium ions released by the SR when the muscle fiber is stimulated by its motor neuron. Contraction is an active process; relaxation and the return to resting length is entirely passive. Muscle Mechanics Some Basic Muscle Definitions • Muscle tension—The pulling force on the tendons that muscle cells generate when contracting • Muscle twitch—A brief contraction-relaxation response to a single action potential Muscle Mechanics The Twitch and Development of Tension Muscle Mechanics The Frequency of Muscle Fiber Stimulation • Summation—Addition of twitch tension when a stimulus is applied before tension has completely relaxed • Incomplete tetanus—Tension peaks and falls repeatedly and builds up beyond twitch tension • Complete tetanus—Tension is steady (no relaxation phase) and largest if stimuli arrive at very high rates

Muscle Mechanics The Effects of Repeated Stimulations Muscle Mechanics Motor Units • Motor Unit —A motor neuron and all the muscle cells it controls • Recruitment—To increase muscle tension by activating more motor units • Small motor units provide finer control • Motor units are intermixed in the muscle to pull evenly on the tendon Muscle Mechanics Motor Units Muscle Mechanics Key Note All voluntary (intentional) movements involve the sustained, subtetanic contractions of skeletal muscle fibers organized into distinct motor units. The force generated can be increased by increasing the frequency of action potentials or by recruiting additional motor units. Muscle Mechanics • Muscle tone—Tension in a “resting” muscle produced by a low level of spontaneous motor neuron activity. Distinct from resting tension produced by passive stretching. • Function of muscle tone • Stabilizes bones, joints • Prevents atrophy (muscle wasting ) Muscle Mechanics Types of Contractions • Isotonic contraction The tension (load) on a muscle stays constant (iso = same, tonic = tension) during a movement. (Example: lifting a baby) • Isometric contraction The length of a muscle stays constant (iso = same, metric = length) during a “contraction” (Example: holding a baby at arms length) Muscle Mechanics Muscle Elongation • Muscle contracts actively • Muscles can only pull • Muscles never push

• Muscle elongates passively • Elastic forces • Contraction of opposing muscles • Effects of gravity Energetics of Muscle Contraction ATP and Creatine Phosphate Reserves • Muscle contraction consumes much ATP • ATP transfers energy directly to cycling cross-bridges and calcium pumping • CP stores energy and regenerates ATP • CP transfers its energy to ADP • Creatine phosphokinase (CPK) catalyzes • ADP (2 “P”s) becomes ATP(3 “P”s) • CP levels greatly exceed ATP levels Energetics of Muscle Contraction ATP Generation • Light activity • Aerobic metabolism of fatty acids • Storage of glucose as glycogen • Moderate activity • Breakdown of glycogen to glucose • Glycolysis of glucose • Peak activity • Anerobic breakdown of glucose • Production of lactic acid Energetics of Muscle Contraction Muscle Metabolism Energetics of Muscle Contraction Muscle Metabolism Energetics of Muscle Contraction Muscle Metabolism Energetics of Muscle Contraction Muscle Fatigue—When a muscle loses ability to contract due to a low pH (lactic acid buildup), low ATP levels, or other problems Recovery Period—Time after muscle activity that it takes to restore pre-exertion conditions Oxygen Debt—Amount of excess oxygen used during the recovery period Energetics of Muscle Contraction Key Note

Skeletal muscles at rest metabolize fatty acids and store glycogen. During light activity, muscles can generate ATP through the aerobic breakdown of carbohydrates, lipids, or amino acids. At peak levels of activity, most of the energy is provided by anaerobic reactions that generate lactic acid. Muscle Performance Two Types of Skeletal Muscle Fibers • Fast fibers Large diameter, abundant myofibrils, ample glycogen, scant mitochondria. Produce powerful, brief contractions • Slow fibers Smaller diameter, rich capillary supply, many mitochondria, much myoglobin. Produce slow, steady contractions Muscle Performance Physical Conditioning • Anaerobic endurance Time over which a muscle can contract effectively under anerobic conditions. • Hypertrophy Increase in muscle bulk. Can result from anerobic training. • Aerobic endurance Time over which a muscle can contract supported by mitochondria. Muscle Performance Key Note What you don’t use, you lose. When motor units are inactive for days or weeks, muscle fibers break down their contractile proteins and grow smaller and weaker. If inactive for long periods, muscle fibers may be replaced by fibrous tissue. Cardiac and Smooth Muscle Cardiac Muscle Tissue • Small cells • Single nucleus/cell • Aerobic metabolism • Intercalated discs • Long contraction time • Self-exciting (automaticity) • No tetanic contraction Cardiac and Smooth Muscle Smooth Muscle Tissue

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Nonstriated cells (no sarcomeres) Calcium control of contraction different from striated muscle Wide range of operating lengths Involuntary muscle • Under hormonal or local control • Pacesetter cells • Motor neurons often unneeded Cardiac and Smooth Muscle Cardiac Muscle Tissue Cardiac and Smooth Muscle Smooth Muscle Tissue Cardiac and Smooth Muscle Anatomy of the Muscular System An Overview of the Major Skeletal Muscles Anatomy of the Muscular System An Overview of the Major Skeletal Muscles Anatomy of the Muscular System Origins, Insertions, and Actions • Origin Muscle attachment that remains fixed • Insertion Muscle attachment that moves • Action What joint movement a muscle produces Anatomy of the Muscular System Primary Action Categories • Prime mover (agonist) • Main muscle in an action • Synergist • Helper muscle in an action • Antagonist • Opposed muscle to an action Anatomy of the Muscular System Muscle Terminology • Names of muscles provide clues to location, orientation, or action • Axial musculature—Muscles with origins on the axial skeleton that position and move head, spine, rib cage • Appendicular musculature—Muscles that stabilize or move appendicular components

Anatomy of the Muscular System The Axial Muscles • Four groups of axial muscles • Head and neck • Spine • Trunk • Pelvic floor Anatomy of the Muscular System Selected Muscles of the Head • Frontalis • Orbicularis oris • Buccinator • Masseter • Temporalis • Pterygoids Anatomy of the Muscular System Selected Muscles of the Neck • Platysma • Digastric • Mylohyoid • Stylohyoid • Sternocleidmastoid Anatomy of the Muscular System Muscles of the Head and Neck Anatomy of the Muscular System Muscles of the Head and Neck Anatomy of the Muscular System Muscles of the Head and Neck Anatomy of the Muscular System Muscles of the Anterior Neck Anatomy of the Muscular System Selected Muscles of the Spine • Splenius capitis • Semispinalis capitis • Erector spinae groups • Spinalis • Longissimus • Iliocostalis Anatomy of the Muscular System Muscles of the Spine

Anatomy of the Muscular System Axial Muscles of the Trunk • Thoracic region • External intercostals • Internal intercostals • Diaphragm • Abdominal region • Rectus abdominis • External oblique • Internal oblique • Transversus abdominis Anatomy of the Muscular System Oblique and Rectus Muscles and the Diaphragm Anatomy of the Muscular System Oblique and Rectus Muscles and the Diaphragm Anatomy of the Muscular System Oblique and Rectus Muscles and the Diaphragm Anatomy of the Muscular System Muscles of the Pelvic Floor (Perineum) • Sheets of muscle • From sacrum and coccyx • To pubis and ischium • Pelvic organ support • Control of material passing through urethra and anus Anatomy of the Muscular System Muscles of the Perineum—Female Anatomy of the Muscular System Muscles of the Perineum—Male Anatomy of the Muscular System The Appendicular Muscles • Two functionally distinct groups • Muscles of the shoulder and upper limbs • Muscles of the pelvic girdle and lower limbs Anatomy of the Muscular System Selected Shoulder Muscles • Trapezius • Rhomboid • Levator scapulae • Serratus anterior • Pectoralis minor

Anatomy of the Muscular System Muscles of the Shoulder Anatomy of the Muscular System Muscles of the Shoulder Anatomy of the Muscular System Muscles the Move the Arm • Deltoid • Supraspinatus • Subscapularis • Teres major • Infraspinatus • Teres minor • Pectoralis major • Latissiumus dorsi Anatomy of the Muscular System Muscles that Move the Arm Anatomy of the Muscular System Muscles that Move the Arm Anatomy of the Muscular System Muscles That Move the Forearm • Biceps brachii • Triceps brachii • Brachialis • Brachioradialis • Pronators • Supinator Anatomy of the Muscular System Muscles That Move the Wrist • Wrist flexors • Flexor carpi ulnaris • Flexor carpi radialis • Palmaris longus • Wrist extensors • Extensor carpi radialis • Extensor carpi ulnaris Anatomy of the Muscular System Muscles That Move the Forearm and Wrist Anatomy of the Muscular System Muscle of the Pelvis and Lower Limbs • Three functional groups

• Thigh movement • Leg movement • Ankle, foot, and toe movement Anatomy of the Muscular System Muscles That Move the Thigh • Gluteal muscles • Thigh adductors • Adductor magnus • Adductor brevis • Adductor longus • Pectineus • Gracilis • Thigh flexors • Iliopsoas (psoas major + iliacus) Anatomy of the Muscular System Muscles That Move the Thigh Anatomy of the Muscular System Muscles That Move the Thigh Anatomy of the Muscular System Flexors of the Knee • Biceps femoris • Semimembranosus • Semitendinosus • Sartorius • Popliteus • Synergist muscle unlocks knee Anatomy of the Muscular System Extensors of the Knee • Quadriceps femoris group • Rectus femoris • Vastus lateralis • Vastus intermedius • Vastus medialis Anatomy of the Muscular System Muscles That Move the Leg Anatomy of the Muscular System Muscles That Move the Foot • Plantar flexion • Gastrocnemius • Soleus

• Eversion and plantar flexion • Fibularis (peroneus) • Dorsiflexion • Tibialis anterior Anatomy of the Muscular System Muscles That Move the Foot and Toes Anatomy of the Muscular System Muscles That Move the Foot and Toes Anatomy of the Muscular System Muscles That Move the Foot and Toes Anatomy of the Muscular System Muscles That Move the Foot and Toes Aging and the Muscular System Age-Related Reductions • Muscle size • Muscle elasticity • Muscle strength • Exercise tolerance • Injury recovery ability The Integumentary System • Removes excess body heat; synthesizes vitamin D3 for calcium and phosphate absorption; protects underlying muscles • Skeletal muscles pulling on skin of face produce facial expressions The Skeletal System • Maintains normal calcium and phosphate levels in body fluids; supports skeletal muscles; provides sites of attachment • Provides movement and support; stresses exerted by tendons maintain bone mass; stabilizes bones and joints The Nervous System • Controls skeletal muscle contractions; adjusts activities of respiratory and cardiovascular systems during periods of muscular activity • Muscle spindles monitor body position; facial muscles express emotion; muscles of the larynx, tongue, lips and cheeks permit speech The Endocrine System • Hormones adjust muscle metabolism and growth; parathyroid hormone and calcitonin regulate calcium and phosphate ion concentrations • Skeletal muscles provide protection for some endocrine organs

The Cardiovascular System • Delivers oxygen and nutrients; removes carbon dioxide, lactic acid, and heat • Skeletal muscle contractions assist in moving blood through veins; protects deep blood vessels The Lymphatic System • Defends skeletal muscles against infection and assists in tissue repairs after injury • Protects superficial lymph nodes and the lymphatic vessels in the abdominopelvic cavity The Respiratory System • Provides oxygen and eliminates carbon dioxide • Muscles generate carbon dioxide; control entrances to respiratory tract, fill and empty lungs, control airflow through larynx, and produce sounds The Digestive System • Provides nutrients; liver regulates blood glucose and fatty acid levels and removes lactic acid from circulation • Protects and supports soft tissues in abdominal cavity; controls entrances to and exits from digestive tract The Urinary System • Removes waste products of protein metabolism; assists in regulation of calcium and phosphate concentrations • External sphincter controls urination by constricting urethra The Reproductive System • Reproductive hormones accelerate skeletal muscle growth • Contractions of skeletal muscles eject semen from male reproductive tract; muscle contractions during sex act produce • pleasurable sensations