Muscular System Anatomy and Physiology

pter 7 Cha MUSCULAR SYSTEM SEELEY'S ESSENTIALS OF ANATOMY AND PHYSIOLOGY, 9TH EDITION. Created by: Johmel De Ocampo  Created by: Johmel De Ocampo MUSCULAR SYSTEM The muscular system is responsible...

pter 7 Cha MUSCULAR SYSTEM SEELEY'S ESSENTIALS OF ANATOMY AND PHYSIOLOGY, 9TH EDITION. Created by: Johmel De Ocampo  Created by: Johmel De Ocampo MUSCULAR SYSTEM The muscular system is responsible for the movement of the human body. FUNCTIONS OF MUSCULAR SYSTEM 1. Movement of the body. Contraction of skeletal muscles is responsible for the overall movements of the body, such as walking, running, and manipulating OVERVIEW OF objects with the hands. MUSCULAR SYSTEM 2. Maintenance of posture. Skeletal muscles constantly maintain tone, which keeps us sitting or standing erect. 3. Respiration. Muscles of the thorax carry out the movements necessary for respiration. 4. Production of body heat. When skeletal muscles contract, heat is given off as a by-product. This released heat is critical to the maintenance of body temperature. 5. Communication. Skeletal muscles are involved in all aspects of communication, including speaking, writing, typing, gesturing, and facial expressions. 6. Constriction of organs and vessels. The contraction of smooth muscle within the walls of internal organs and vessels causes those structures to constrict. This constriction can help propel and mix food and water in the digestive tract, propel secretions from organs, and regulate blood flow through vessels. 7. Contraction of the heart. The contraction of cardiac muscle causes the heart to beat, propelling blood to all parts of the body  Created by: Johmel De Ocampo MUSCULAR SYSTEM STRUCTURE OF A MUSCLE (a) Part of a muscle attached by a tendon to a bone. A muscle is composed of muscle fasciculi, each surrounded by perimysium. The fasciculi are composed of bundles of individual muscle fibers (muscle cells), each surrounded by endomysium. The entire muscle is surrounded by a connective tissue sheath called epimysium, or muscular fascia. (b) Enlargement of one muscle fiber containing several myofibrils. (c) A myofibril extended out the end of the muscle fiber, showing the banding patterns of the sarcomeres. (d) A single sarcomere of a myofibril is composed mainly of actin myofilaments and myosin myofilaments. The Z disks anchor the actin myofilaments, and the myosin myofilaments are held in place by the M line. (e) Part of an actin myofilament is enlarged. (f) Part of a myosin myofilament is enlarged.  Created by: Johmel De Ocampo MUSCULAR SYSTEM CHARACTERISTICS OF SKELETAL MUSCLE SKELETAL MUSCLE Skeletal muscle, with its associated connective tissue, constitutes approximately 40% of body weight. Skeletal muscle is so named because most of the muscles are attached to the skeletal system. It is also called striated muscle because transverse bands, or striations, can be seen in the muscle under the microscope. FOUR MAJOR FUNCTIONAL CHARACTERISTICS CONTRACTILITY is the ability of skeletal muscle to shorten with force. When skeletal muscles contract, they cause the structures to which they are attached to move. Skeletal muscles shorten forcefully during contraction, but they lengthen passively. Either gravity or the contraction of an opposing muscle produces a force that pulls on the shortened muscle, causing it to lengthen. EXCITABILITY is the capacity of skeletal muscle to respond to a stimulus. Normally, the stimulus is from nerves that we consciously control. EXTENSIBILITY means that skeletal muscles stretch. After a contraction, skeletal muscles can be stretched to their normal resting length and beyond to a limited degree ELASTICITY is the ability of skeletal muscles to recoil to their original resting length after they have been stretched.  Created by: Johmel De Ocampo MUSCULAR SYSTEM STRUCTURE OF SKELETAL MUSCLE THE SARCOMERE The striated appearance of skeletal muscle fibers is due to the arrangement of the myofilaments of actin and myosin in sequential order from one end of the muscle fiber to the other. Each packet of these microfilaments and their regulatory proteins, troponin and tropomyosin (a) Organization of skeletal muscle (along with other proteins) is called a sarcomere. components. (b) Electron micrograph of skeletal muscle, showing several sarcomeres in a muscle fiber. (c) Diagram of two adjacent sarcomeres, depicting the structures responsible for the banding pattern.  Created by: Johmel De Ocampo MUSCULAR SYSTEM EXCITABILITY OF MUSCLE FIBERS ION CHANNELS AND THE ACTION POTENTIAL Step 1 illustrates the status of Na+ and K+ channels in a resting cell. Steps 2 and 3 show how the channels open and close to produce an action potential. Next to each step, the charge difference across the plasma membrane is illustrated.  Created by: Johmel De Ocampo MUSCULAR SYSTEM NERVE SUPPLY & MUSCLE FIBER STIMULATION NEUROMUSCULAR JUNCTION Another specialization of the skeletal muscle is the site where a motor neuron’s terminal meets the muscle fiber—called the neuromuscular junction (NMJ). This is where the muscle fiber first responds to signaling by the motor neuron. Every skeletal muscle fiber in every skeletal muscle is innervated by a motor neuron at the NMJ. Excitation signals from the neuron are the only way to functionally activate the fiber to contract. (a) In a neuromuscular junction, several branches of an axon junction with a single muscle fiber. (b) Photomicrograph of neuromuscular junctions.  Created by: Johmel De Ocampo MUSCULAR SYSTEM FUNCTION OF NEUROMUSCULAR JUNCTION  Created by: Johmel De Ocampo MUSCULAR SYSTEM SKELETAL MUSCLE CONTRACTION (a) The active site on actin is exposed as calcium binds to troponin. (b) The myosin head is attracted to actin, and myosin binds actin at its actin-binding site, forming the cross-bridge. (c) During the power stroke, the phosphate generated in the previous contraction cycle is released. This results in the myosin head pivoting toward the center of the sarcomere, after which the attached ADP and phosphate group are released. (d) A new molecule of ATP attaches to the myosin head, causing the cross-bridge to detach. (e) The myosin head hydrolyzes ATP to ADP and phosphate, which returns the myosin to the cocked position.  Created by: Johmel De Ocampo MUSCULAR SYSTEM SUMMARY OF SKELETAL MUSCLE CONTRACTION MUSCLE METABOLISM Some ATP is stored in a resting muscle. As contraction starts, it is used up in seconds. More ATP is generated from creatine phosphate for about 15 seconds. Each glucose molecule produces two ATP and two molecules of pyruvic acid, which can be used in aerobic respiration or converted to lactic acid. If oxygen is not available, pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue. This occurs during strenuous exercise when high amounts of energy are needed but oxygen cannot be sufficiently delivered to muscle.  Created by: Johmel De Ocampo MUSCULAR SYSTEM Aerobic respiration is the breakdown of glucose in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Approximately 95 percent of the ATP required for resting or moderately active muscles is provided by aerobic respiration, which takes place in mitochondria. BREAKDOWN OF ATP AND CROSS-BRIDGE MOVEMENT DURING MUSCLE CONTRACTION  Created by: Johmel De Ocampo MUSCULAR SYSTEM PHASE OF A MUSCLE MULTIPLE WAVE TWITCH SUMMATION ENERGY REQUIREMENT FOR MUSCLE CONTRACTION Muscle fibers are very energy-demanding cells whether at rest or during any form of exercise. This energy comes from either aerobic (with O2) or anaerobic (without O2) ATP production Generally, ATP is derived from four processes in skeletal muscle: 1. Aerobic production of ATP during most exercise and normal conditions 2. Anaerobic production of ATP during intensive short-term work 3. Conversion of a molecule called creatine (kr̄ ′ a-t̄n) phosphate to ATP 4. Conversion of two ADP to one ATP and one AMP (adenosine monophosphate) during heavy exercise  Created by: Johmel De Ocampo MUSCULAR SYSTEM FATE OF ATP IN RESTING AND EXCERCISING MUSCLE Glycolysis is an anaerobic (non-oxygen-dependent) process that breaks down glucose (sugar) to produce ATP. Aerobic respiration is the breakdown of glucose or other nutrients in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP. Muscle tension, force generated by the contraction of the muscle (or shortening of the sarcomeres) Isotonic contractions, where the tension in the muscle stays constant, a load is moved as the length of the muscle changes (shortens). A concentric contraction involves the muscle shortening to move a load. An eccentric contraction occurs as the muscle tension diminishes and the muscle lengthens. Isometric contractions involve sarcomere shortening and increasing muscle tension, but do not move a load, as the force produced cannot overcome the resistance provided by the load. You have 640 skeletal muscles in your body Sartorius – the longest muscles, located in your upper thigh Stapedius – the tinniest muscle, located in the middle ear Muscles Are Actually PULLING Their Insertions toward their origins  Created by: Johmel De Ocampo MUSCULAR SYSTEM SKELETAL MUSCLE PRIME MOVERS Muscles that are primary concern with the movement (Agonist Muscles) ANTAGONISTS working in reverse of that particular movement, preventing the prime mover to over extend SYNERGISTS Helps the prime movers lending a little extra oomph stabilizing joints against dislocation FIXATORS if a synergist immobilize the muscles’ origin bone so that the prime mover can be more effective. MOTOR UNITS a group of muscle fibers that all get their Signals from the same, single motor neuron LARGE MOTOR UNIT motor neurons may synapse with and innervate a thousand muscle fibers SMALL MOTOR UNIT A hand full of motor neuron connect to a single fine neuron that produce a specialized movement/ function TYPES OF MUSCLE FIBERS SLOW OXIDATIVE Slow oxidative (SO) fibers contract relatively slowly and use aerobic respiration (oxygen and glucose) to produce ATP. FAST OXIDATIVE Fast oxidative (FO) fibers have fast contractions and primarily use aerobic respiration, but because they may switch to anaerobic respiration (glycolysis),can fatigue more quickly than SO fibers. FAST GLYCOLYTIC Fast glycolytic (FG) fibers have fast contractions and primarily use anaerobic glycolysis. The FG fibers fatigue more quickly than the others.  Created by: Johmel De Ocampo MUSCULAR SYSTEM FATIGUE Fatigue is a temporary state of reduced work capacity. Without fatigue, muscle fibers would be worked to the point of structural damage to them and their supportive tissues. Historically it was thought that buildup of lactic acid and the corresponding drop in pH (acidosis) was the major cause of fatigue. However, it is now established that there are multiple mechanisms underlying muscular fatigue. These mechanisms include: Acidosis and ATP depletion due to either an increased ATP consumption or a decreased ATP production Oxidative stress, which is characterized by the buildup of excess reactive oxygen species (ROS; free radicals) 3. Local inflammatory reactions TYPES OF MUSCLE CONTRACTIONS ISOMETRIC isometric (equal distance) contractions, the length of the muscle does not change, but the amount of tension increases during the contraction process. Isometric contractions are responsible for the constant length of the body’s postural muscles, such as the muscles of the back. ISOTONIC isotonic (equal tension) contractions, the amount of tension produced by the muscle is constant during contraction, but the length of the muscle decreases. CONCENTRIC CONTRACTION Concentric (kon-sen′ trik) contractions are isotonic contractions in which muscle tension increases as the muscle shortens. Many common movements are produced by concentric muscle contractions. ECCENTRIC CONTRACTION Eccentric (ek-sen′ trik) contractions are isotonic contractions in which tension is maintained in a muscle, but the opposing resistance causes the muscle to lengthen. Eccentric contractions are used when a person slowly lowers a heavy weight. MUSCLE TONE Muscle tone is the constant tension produced by body muscles over long periods of time. Muscle tone is responsible for keeping the back and legs straight, the head in an upright position, and the abdomen from bulging. Muscle tone depends on a small percentage of all the motor units in a muscle being stimulated at any point in time, causing their muscle fibers to contract tetanically and out of phase with one another.  Created by: Johmel De Ocampo MUSCULAR SYSTEM SMOOTH MUSCLE Smooth muscle fibers are spindle-shaped (wide in the middle and tapered at both ends, somewhat like a football) and have a single nucleus; Although they do not have striations and sarcomeres, smooth muscle fibers do have actin and myosin contractile proteins, and thick and thin filaments. These thin filaments are anchored by dense bodies. A dense body is analogous to the Z-discs of skeletal and cardiac muscle fibers and is fastened to the sarcolemma. Calcium ions are supplied by the SR in the fibers and by sequestration from the extracellular fluid through membrane indentations called calveoli.  Created by: Johmel De Ocampo MUSCULAR SYSTEM CARDIAC MUSCLE Cardiac muscle tissue is only found in the heart. Highly coordinated contractions of cardiac muscle pump blood into the vessels of the circulatory system. Similar to skeletal muscle, cardiac muscle is striated and organized into sarcomeres, possessing the same banding organization as skeletal muscle. Contractions of the heart (heartbeats) are controlled by specialized cardiac muscle cells called pacemaker cells that directly control heart rate. Although cardiac muscle cannot be consciously controlled, the pacemaker cells respond to signals from the autonomic nervous system (ANS) to speed up or slow down the heart rate. The pacemaker cells can also respond to various hormones that modulate heart rate to control blood pressure. This group of cells is self-excitable and able to depolarize to threshold and fire action potentials on their own, a feature called autorhythmicity; they do this at set intervals which determine heart rate. Because they are connected with gap junctions to surrounding muscle fibers and the specialized fibers of the heart’s conduction system, the pacemaker cells are able to transfer the depolarization to the other cardiac muscle fibers in a manner that allows the heart to contract in a coordinated manner.  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLE TYPES Interactions of Skeletal Muscles, Their Fascicle Arrangement, and Their Lever Systems  Created by: Johmel De Ocampo MUSCULAR SYSTEM SUPERFICIAL BODY MUSCULATURE  Created by: Johmel De Ocampo MUSCULAR SYSTEM SUPERFICIAL BODY MUSCULATURE  Created by: Johmel De Ocampo MUSCULAR SYSTEM FASCICLE ARRANGEMENT  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLES OF THE HEAD AND NECK  Created by: Johmel De Ocampo MUSCULAR SYSTEM FACIAL EXPRESSION MASTICATION TONGUE AND SWALLOWING MUSCLE  Created by: Johmel De Ocampo MUSCULAR SYSTEM DEEP NECK AND BACK MUSCLE  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLE OF THE THORAX  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLE OF THE ABDOMINAL WALL  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLE OF THE PELVIC FLOOR AND PERINEUM  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLE OF THE SHOULDER  Created by: Johmel De Ocampo MUSCULAR SYSTEM ARM MUSCLES  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLES OF THE FOREARM  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLES OF THE UPPER LIMB  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLES OF THE HIP AND THIGH  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLES OF THE LOWER LIMB  Created by: Johmel De Ocampo MUSCULAR SYSTEM MUSCLES OF THE LEG  Created by: Johmel De Ocampo MUSCULAR SYSTEM  Created by: Johmel De Ocampo MUSCULAR SYSTEM DISEASES AND DISORDERS  Created by: Johmel De Ocampo SUMMARY FUNCTIONS OF THE MUSCULAR SYSTEM The muscular system produces body movement, maintains posture, causes respiration, produces body heat, performs movements involved in communication, constricts organs and vessels, and pumps blood. CHARACTERISTICS OF SKELETAL MUSCLE Skeletal muscle has contractility, excitability, extensibility, and elasticity. SKELETAL MUSCLE STRUCTURE 1. Muscle fibers are organized into fasciculi, and fasciculi are organized into muscles by associated connective tissue. 2. Each skeletal muscle fiber is a single cell containing numerous myofibrils. 3. Myofibrils are composed of actin and myosin myofilaments. 4. Sarcomeres are joined end-to-end to form myofibrils. EXCITABILITY OF MUSCLE FIBERS 1. Cell membranes have a negative charge on the inside relative to a positive charge outside. This is called the resting membrane potential. 2. Action potentials are a brief reversal of the membrane charge. They are carried rapidly along the cell membrane. 3. Sodium ions (Na+) move into cells during depolarization, and K+ moves out of cells during repolarization. NERVE SUPPLY AND MUSCLE FIBER STIMULATION 1. Motor neurons carry action potentials to skeletal muscles, where the neuron and muscle fibers form neuromuscular junctions. 2. Neurons release acetylcholine, which binds to receptors on muscle cell membranes, stimulates an action potential in the muscle cell, and causes the muscle to contract. MUSCLE CONTRACTION 1. Action potentials are carried along T tubules to the sarcoplasmic reticulum, where they cause the release of calcium ions. 2. Calcium ions, released from the sarcoplasmic reticulum, bind to the actin myofilaments, exposing attachment sites. STRUCTURAL AND FUNCTIONAL ORGANIZATION OF THE HUMAN BODY 1. The human body can be organized into six levels: chemical, cell, tissue, organ, organ system, and organism. 2. The eleven organ systems are the integumentary, skeletal, muscular, lymphatic, respiratory, digestive, nervous, endocrine, cardiovascular, urinary, and reproductive systems. 3. Myosin forms cross-bridges with the exposed actin attachment sites. 4. The myosin molecules bend, causing the actin molecules to slide past; this is the sliding filament model. The H and I bands shorten; the A bands do not.  Created by: Johmel De Ocampo SUMMARY 5. This process requires ATP breakdown. 6. A muscle twitch is the contraction of a muscle fiber in response to a stimulus; it consists of a lag phase, a contraction phase, and a relaxation phase. 7. Tetanus occurs when stimuli occur so rapidly that a muscle does not relax between twitches. ENERGY REQUIREMENT FOR MUSCLE CONTRACTION 1. Small contraction forces are generated when small numbers of motor units are recruited, and greater contraction forces are generated when large numbers of motor units are recruited. 2. Energy is produced by aerobic (with oxygen) and anaerobic (without oxygen) respiration. 3. After intense exercise, the rate of aerobic respiration remains elevated to repay the oxygen deficit. FATIGUE Muscular fatigue occurs as ATP is depleted during muscle contraction. Physiological contracture occurs in extreme fatigue when a muscle can neither contract nor relax EFFECT OF FIBER TYPE ON ACTIVITY LEVEL 1. Muscles contract either isometrically (tension increases, but muscle length stays the same) or isotonically (tension remains the same, but muscle length decreases). 2. Muscle tone consists of a small percentage of muscle fibers contracting tetanically and is responsible for posture. 3. Muscles contain a combination of slow-twitch and fast-twitch fibers. 4. Slow-twitch fibers are better suited for aerobic respiration, and fast-twitch fibers are adapted for anaerobic respiration. 5. Sprinters have more fast-twitch fibers, whereas distance runners have more slow-twitch fibers. SKELETAL MUSCLE ANATOMY GENERAL PRINCIPLE 1. Most muscles have an origin on one bone, have an insertion onto another, and cross at least one joint. 2. A muscle causing a specific movement is an agonist. A muscle causing the opposite movement is an antagonist. 3. Muscles working together are synergists. 4. A prime mover is the muscle of a synergistic group that is primarily responsible for the movement. NOMENCLATURE Muscles are named according to their location, origin and insertion, number of heads, or function.  Created by: Johmel De Ocampo SUMMARY MUSCLES OF THE HEAD AND NECK 1. Muscles of facial expression are associated primarily with the mouth and eyes. 2. Four pairs of muscles are involved in mastication. 3. Tongue movements involve intrinsic and extrinsic muscles. 4. Swallowing involves the suprahyoid and infrahyoid muscles, plus muscles of the soft palate, pharynx, and larynx. 5. Neck muscles move the head. TRUNK MUSCLES 1. The erector spinae muscles hold the body erect. 2. Intercostal muscles and the diaphragm are involved in breathing. 3. Muscles of the abdominal wall flex and rotate the vertebral column, compress the abdominal cavity, and hold in and protect the abdominal organs. 4. Muscles form the floor of the pelvis. UPPER LIMB MUSCLES 1. The upper limb is attached to the body primarily by muscles. 2. Arm movements are accomplished by pectoral, rotator cuff, and deltoid muscles. 3. The elbow is flexed and extended by anterior and posterior arm muscles, respectively. 4. Supination and pronation of the forearm are accomplished by supinators and pronators in the forearm. 5. Movements of the wrist and fingers are accomplished by most of the twenty forearm muscles and nineteen intrinsic muscles in the hand. LOWER LIMB MUSCLES 1.. Hip muscles flex and extend the hip and abduct the thigh. 2. Thigh muscles flex and extend the hip and adduct the thigh. They also flex and extend the knee. 3. Muscles of the leg and foot are similar to those of the forearm and hand. REFERENCE Seeley's Essentials of Anatomy and Physiology, 9th Edition. No Copyright Intended.