Muscular System PDF

THE MUSCULAR SYSTEM PREPARED BY ALARZAR OBJECTIVES FUNCTIONS OF THE MUSCULAR SYSTEM 1. Movement of the body. Skeletal muscles are responsible for body movement including walking, running, chewing 2. Maintenance of posture. Skeletal muscles maintain tone keeping up maintain position 3. Respirat...

THE MUSCULAR SYSTEM PREPARED BY ALARZAR OBJECTIVES FUNCTIONS OF THE MUSCULAR SYSTEM 1. Movement of the body. Skeletal muscles are responsible for body movement including walking, running, chewing 2. Maintenance of posture. Skeletal muscles maintain tone keeping up maintain position 3. Respiration. Skeletal muscles of the thorax and diaphragm help us breathe 4. Production of body heat. Skeletal muscles contract to product heat to maintain body temperature 5. Communication. Involved in speaking, writing, typing and smiling 6. Constriction of organs and vessels. Smooth muscles causes structures to constrict that help propel food in the GIT, remove materials from organs and regulate blood flow 7. Contraction of the heart. Cardiac muscle causes the heart to beat, propelling blood to other parts of the body FUNCTIONS OF THE MUSCULAR SYSTEM GENERAL PROPERTIES OF MUSCLES 1. Contractility: the ability to shorten forcibly 2. Excitability: the ability to receive and respond to stimuli 3. Extensibility: the ability to be stretched or extended 4. Elasticity: the ability to recoil and resume the original resting length CONNECTIVE TISSUE COVERING ¡ Fascia is a general term for connective tissue sheets; between adjacent muscles and between muscles and skin ¡ The three muscular fascia, which separate and compartmentalize individual muscles or groups of muscles are: ¡ Epimysium: an overcoat of dense collagenous connective tissue that surrounds the entire muscle ¡ Perimysium: fibrous connective tissue that surrounds groups of muscle fibers called fascicles (bundles) ¡ Endomysium: fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber NERVES AND BLOOD VESSELS ¡ The connective tissue serves as passageway for both nerves and blood vessels ¡ Motor Neurons - specialized nerve cells that stimulates skeletal muscle contractions; originates from the brain and spinal cord ¡ Neuromuscular junctions (synapses) – contact point between axons and muscle fibers ¡ An artery and one or two veins extend with the nerve through the skeletal muscles SKELETAL MUSCLE FIBER ¡ Develop from myoblasts ¡ About 1mm-4cm average in length but some reach 30cm ¡ Number of muscle fibers remain relatively constant after birth, it just enlarges (hypertrophy)  COMPONENTS STRUCTURES OF MUSCLE FIBERS ELECTRICAL COMPONENT MECHANICAL COMPONENT 1. SARCOLEMMA – plasma membrane of the fibers 1. MYOFILAMENTS 2. TRANSVERSE TUBULES (T TUBULES) – tubelike i. ACTIN MYOFILAMENT – thin filament inward folds of the sarcolemma that carry electrical ii. MYOSIN MYOFILAMENT – thick filament impulses into the center of the fiber so every unit 2. MYOFIBRILS – bundles of protein filament that interact contracts in unison to shorten muscle fiber during contraction 3. SARCOPLASMIC RETICULUM - highly specialized smooth ER that stores Ca (upon release causes SARCOMERES – structural and functional unit of skeletal contraction) muscles (organized units of actin and myosin filaments) - Smallest portion of muscle that can contract TERMINAL CISTERNAE – T tubules that lie next to an enlarged reticulum TRIAD – 2 terminal cisternae + T-Tubules SARCOPLASM – cytoplasm of the muscle fibers SARCOMERES 1. Z disks – anchor for actin myofilaments 2. I bands – lighter-staining regions that contain only actin myofilaments 3. A band – central; darker-staining region; containing both myofilaments except the center 4. H zone – center of A band that only contains myosin myofilaments 5. M zone – middle of the H zone that holds the myofilaments in place 6. Titin – a protein aside from actin and myosin that gives the muscle ability to stretch and recoil; largest protein in humans SARCOMERES MYOFILAMENT STRUCTURES ACTIN MYOFILAMENT MYOSIN MYOFILAMENT Proteins: Each myofilament consist of molecules and each 1. Globular Actin (G Actin) – forms into strains to molecule has: become Fibrous Actin (F Actin); receptor sites 1. Head for myosin microfilament 2. Hinge 2. Tropomyosin – cover the active sites on the G 3. Rod actin subunits Myosin heads 3. Troponin 1. Bind to active sites on actin molecules to form Anchors the troponin to actin cross bridges Prevents tropomyosin from uncovering the 2. Attached to the rod portion that bends and G actin sites in a relaxed muscle straightens during contraction Bind with Ca 3. Composed of ATPase enzymes that breakdown ATP to release energy ACTIN AND MYOSIN FILAMENTS A CROSS-BRIDGE IS FORMED WHEN A MYOSIN HEAD BINDS TO THE ACTIVE SITE ON G ACTIN NEUROMUSCULAR JUNCTION STRUCTURE ¡ Neuromuscular junction – enlarged axon terminals that rests in the sarcolemma and composed of: 1. Axon terminals 2. Area of sarcolemma they innervate Presynaptic terminal > synaptic cleft > Postsynaptic membrane Acetylcholine –(Ach) neurotransmitter, a type of ligand  ¡ When the motor neurons stimulate muscle fibers, the myosin heads latch onto actin and the sliding begins SLIDING FILAMENT ¡ The cross bridges form and break several times during a contraction to generate THEORY tension and propel the thin filaments toward the center of the sarcomere ¡ The muscle cell shortens, however the myofilaments remain the same length SLIDING FILAMENT MODEL ¡ Actin and myosin myofilaments in a relaxed muscle (below) and a contracted muscle are the same length. Myofilaments do not change length during muscle contraction Fig. 8.4  SLIDING FILAMENT MODEL ¡ During contraction, actin myofilaments at each end of the sarcomere slide past the myosin myofilaments toward each other. As a result, the Z disks are brought closer together, and the sarcomere shortens Fig. 8.4 SLIDING FILAMENT MODEL ¡ As the actin myofilaments slide over the myosin myofilaments, the H zones (yellow) and the I bands (blue) narrow. The A bands, which are equal to the length of the myosin myofilaments, do not narrow because the length of the myosin myofilaments does not change Fig. 8.4 SLIDING FILAMENT MODEL ¡ In a fully contracted muscle, the ends of the actin myofilaments overlap at the center of the sarcomere and the H zone disappears Fig. 8.4  PHYSIOLOGY: SKELETAL MUSCLE FIBER EXCITABILITY ¡ Cells have an electrical charge difference across the cell membrane Ion called the resting membrane potential channels 1. K+ > Na+ inside the membrane 2. At rest, only leak channels are opened. There are more K+ leak Nongated Gated channels than Na+ leak channels. (Leak) 3. By virtue of diffusion, K+ will diffuse out and Na+ will diffuse in the membrane. ligand- 4. K+ diffusion is opposed by negatively charged proteins gated 5. Na-K pump maintain the differential levels by pumping out Na out of the cell in exchange for 2 K into the cell (via ATP voltage- hydrolysis) gated 6. Resting Membrane Potential is established when K+ out of the cell is equal to K+ into the cell  ACTING POTENTIAL: ¡ Reversal of the resting membrane potential ¡ 2 Phases: ¡ Depolarization ¡ Repolarization ¡ All or one principle – ¡ A stimulus below threshold produces no action potential ¡ A stimulus at threshold or stronger will produce an action potential PROPAGATION NEUROMUSCULAR JUNCTION EXCITATION-CONTRACTION COUPLING: Occurs at the triad Link between an action potential and the sarcomere shortening When voltage- Troponin causes Starts at the NMJ Action potential is gated Ca+ channels Myosin heads bind tropomyosin to Muscle contracts with the propagated into open, Ca+ diffuses to the exposed move and expose when cross-bridges production of an the muscle fiber into the active sites to form active sites on the move action potential and T tubules sarcoplasm and cross bridges binds to troponin actin myofilaments CROSS-BRIDGE CYCLING  MUSCLE RELAXATION ¡ Occurs when ACh is no longer released at the NMJ ¡ 3 major ATP-dependent events are required for muscle to relax: 1. After an action potential occurred in the muscle fiber, the Na- K pump must actively transport Na out of the muscle fiber and K into the muscle fiber to re-establish RMP 2. ATP is required to detach the myosin heads from the active sites for the recovery stroke 3. ATP is needed for the active transport of Ca into the sarcoplasmic reticulum from the sarcoplasm ¡ It takes twice as long to relax as it does to contract THE MUSCLE TWITCH ¡ Response of a muscle fiber to a single action potential along its motor neuron ¡ 3 Phase include: 1. Lag (latent) Phase – gap between the time of stimulus application to the motor neuron and the beginning contraction 2. Contraction Phase – commences once Ca is released from the SR and cross-bridge cycling occurs 3. Relaxation Phase – concentration of CA in the sarcoplasm decreases slowly into the SR ¡ Muscle contraction is measured as a force = Tension TYPES OF MUSCLE CONTRACTIONS ISOMETRIC ISOTONIC Muscle does not shorten Muscles shorten Increases the tension in the muscle Increased the tension in the muscle and the length decreases e.g. lifting something heavier than your e.g. lifting an object and moving it ability to lift Isometric muscle produces tension as it Muscle Contraction Concentric shortens Isotonic muscle produces tension Eccentric as it resists lengthening MOTOR UNIT CONSIST OF A MOTOR NEURON AND ALL THE MUSCLE FIBER IT INNERVATES FORCE OF CONTRACTION ¡ Muscle Contraction strength depends on: 1. Summation – amount of force in one muscle fiber 2. Recruitment – amount of force in a whole muscle ¡ The amount of force generated depends on the number of cross bridges formed ¡ 3 factors affect the number of cross-bridges formation: 1. Frequency of stimulation 2. Muscle fiber diameter 3. Muscle fiber length at the time of contraction FREQUENCY OF STIMULATION ¡ TREPPE - an increase in the force of contraction during the first few contractions of a rested muscle ¡ The stimulus frequency must allow the muscle fiber to completely relax followed by an immediate stimulation ¡ For athletes, the treppe during warm-up can contribute to improved muscle frequency ¡ When the frequency of stimulation is beyond what caused treppe, the muscle fiber will contract with even greater force until maximum force with no relaxation is achieved. ¡ Multiple motor unit summation - For a whole muscle, stimuli of increasing strength result in graded contractions of increased force as more motor units are recruited ¡ Multiple-wave summation - Stimulus of increasing frequency increase the force of contraction ¡ Incomplete tetanus is partial relaxation between contractions, and complete tetanus is no relaxation between contractions TREPPE WAVE SUMMATION sprinters rapid increase in movement ENERGY SOURCES FOR MUSCLE CONTRACTION ¡ Muscle fibers store enough ATP to contract for about 5-6 seconds ¡ 4 Processes: 1. Conversion of 2 ADP to ATP and adenosine monophosphate (AMP) by adenylate kinase side product lack of oxygen 2. Transfer of phosphate from creatine phosphate by creatine kinase side product 3. Anaerobic production of ATP 4. Aerobic production of ATP increase acidity of blood ENERGY SOURCES FOR MUSCLE CONTRACTION MUSCLE FATIGUE ¡ Refers to a temporary state of INCREASED MUSCULAR FATIGUE reduced work capacity Physiological Contracture – too little ATP to bind ¡ 3 mechanisms underlying muscular myosin, cross-bridges cannot be broken and muscles fatigue: cannot relax 1. Acidosis and ATP depletion (either d/t decreased production or increased Rigor Mortis – rigid muscles after death, no ATP for consumption) release of myosin heads 2. Oxidative stress (buildup of excess Psychological fatigue – involves the CNS rather than the reactive oxygen species (ROS)) muscles due to acetylcholine 3. Local inflammatory reactions  SMOOTH MUSCLE ¡ Actin and myosin filaments are organized as loose bundles instead of as sarcomeres ¡ Has slower contraction speed than skeletal muscles ¡ No troponin bound to action ¡ Ca+ binds to calmodulin that activates myosin kinase ¡ Relaxation results from the activity of myosin phosphatase that releases the cross-bridge TYPES OF SMOOTH MUSCLE VISCERAL MULTIUNIT Occurs in sheets Can be found in sheets, small bundles or as single cells Found in the digestive, Found in the walls of blood vessels, reproductive and urinary tracts arrector pili, iris of the eye, capsules of the spleen Numerous gap junctions Fewer gap junctions Wave of contraction traverses Contracts only when stimulated by the entire smooth muscle sheet nerves or hormones  ligand gated ELECTRICAL PROPERTIES OF SMOOTH MUSCLE FUNCTIONAL PROPERTIES OF SMOOTH MUSCLES ¡ 4 FUNCTIONAL PROPERTIES THAT DIFFERS FROM SKELETAL MUSCLES 1. Has autorhythmic contractions 2. Smooths muscles tend to contract in response to being stretched (slow increase in length produces less response) 3. Exhibits a relatively constant tension (muscle tone) over a long period 4. Amplitude of contractions also remains constant REGULATION OF SMOOTH MUSCLE ¡ Autonomic nervous system > smooth muscles ¡ Somatic motor nervous system > skeletal muscle ¡ Smooth muscles are innervated by ACh (Acetylcholine) and Norepinephrine (NE) ¡ Hormones (Epinephrine and Oxytocin) and some chemical substances (histamine, prostaglandin) affect smooth muscle function CARDIAC MUSCLE ¡ Striated but with only one nucleus ¡ Adjacent cells join to form branching muscle fibers by specialized cell-to-cell attachments called Intercalated disks ¡ Muscles are autorhythmic and normally act as pacemakers conduct their own ekectricty ¡ Contraction by Ca2+ is similar to skeletal muscle MUSCULAR SYSTEM GENERAL PRINCIPLES OF SKELETAL MUSCLE ANATOMY ¡ 2 POINTS OF ATTACHMENT ¡ Origin – fixed end, proximal end of the muscle ¡ Insertion – mobile end, distal end of the muscle ¡ Belly – part of the muscle between the origin and the insertion ¡ Tendons – connect muscle to bone connective tissue ¡ Aponeuroses – broad, sheet-like tendons GENERAL PRINCIPLES OF SKELETAL MUSCLE ANATOMY ¡ Muscle actions can either be ¡ Agonists – action of a single muscle/ group of muscle ¡ Antagonists – opposed action of the agonists ¡ E.g. Elbow flexion: biceps brachii (agonist) and the triceps brachii (antagonist) ¡ Synergists – muscles that tend to function in groups to accomplish specific movements ¡ Prime mover – muscles that contribute the most to the movement in a group of synergists ¡ Fixators – muscles that use to stabilize the prime mover FASCICLE ARRANGEMENT FASCICLE ARRANGEMENT MUSCLE NAMES 1. Location (e.g. pectoralis (chest), gluteus (buttocks) and brachial (arm) 2. Size (e.g. gluteus maximus (large), gluteus minimus (small), longus (long) and brevis (short) 3. Shape (e.g. deltoid (triangular), quadratus (quadrate) and teres (round) 4. Orientation of the fascicles (e.g. rectus (straight), oblique (lie at an angle) 5. Origin and insertion (e.g. sternocleidomastoid) 6. Number of heads (biceps (2 origins) and triceps (3 origins) 7. Function (e.g. abductors and adductors) MUSCLE MOVEMENT ¡ TERMS ¡ LEVERS – consisting of a rigid pole or beam that can move at a stationary hinge ¡ FULCRUM – hinge ¡ WEIGHT – application of force ¡ PULL – force of muscle contraction ¡ Bones are levers, joints are fulcrums and muscles provide the pull MUSCLE MOVEMENT SUPERFICIAL BODY MUSCULATURE (OVERVIEW) SUPERFICIAL BODY MUSCULATURE (OVERVIEW) HEAD AND NECK MUSCLES Involved in Facial expression Mastication (chewing) Movement of the tongue Movement of the head and neck MUSCLES OF THE FACIAL EXPRESSION MUSCLES OF MASTICATION chewing Mainly deal with the movement of the mandible Temporalis and masseter muscles elevate the mandible Gravity opens the jaw Digastric muscle depresses the mandible Pterygoid muscles move the mandible from side to side TONGUE MOVEMENT Important in mastication and speech Two types of muscles Intrinsic muscles Change the shape of the tongue Found entirely within the tongue Extrinsic muscles Move the tongue Found outside of the tongue but are attached to it palette tongue HEAD AND NECK MOVEMENT Neck muscles cause flexion, extension, rotation, and lateral flexion of the head and neck Head extension is accomplished by the splenius capitis and trapezius muscles Major head flexor is the sternocleidomastoid Lateral head movements are accomplished by the sternocleidomastoid and scalene muscles THORACIC MUSCLES Mainly involved in the process of breathing Diaphragm: most important muscle in respiration External intercostals: more superficial layer that lifts the rib cage and increases thoracic volume to allow inspiration breathing in Internal intercostals: deeper layer that aids in forced expiration internal intercostal deeper breathing out MUSCLES OF THE THORAX MUSCLES OF THE BACK These muscles extend, laterally flex, and rotate the vertebral column. They also hold the vertebral column erect A superficial group of muscles, the Erector spinae, runs from the pelvis to the skull, extending from the vertebrae to the ribs Consist of three subgroups on each side of the vertebrae: Iliocostalis, Longissimus, and Spinalis Lateral bending of the back is accomplished by unilateral contraction of these muscles SCAPULAR MUSCLES AND MOVEMENTS The scapula is attached to the rest of the skeleton only by the clavicle Six muscles attach the scapula to the trunk and enable the scapula to function as an anchor point for the muscles and bones of the arm Trapezius Levator scapulae Rhomboideus (major and minor) Serratus anterior Pectoralis minor Prime movers of shoulder elevation are the trapezius and levator scapulae ABDOMINAL WALL MUSCLES PELVIC FLOOR AND PERINEUM The pelvic diaphragm is composed of two paired muscles: Levator ani and Coccygeus These muscles: Close the inferior outlet of the pelvis Support the pelvic floor Elevate the pelvic floor to help release feces Resist increased intra-abdominal pressure Two sphincter muscles allow voluntary control of urination (External urethral sphincter) and defecation (External anal sphincter) The Ischiocavernosus and Bulbospongiosus assist in erection of the penis and clitoris UPPER LIMB MUSCLES Nine muscles attach the humerus to the scapula. Two additional muscles attach the humerus to the trunk Trunk muscles moving the arm: Pectoralis major: flexes the extended shoulder and extends the flexed shoulder Latissimus dorsi: adducts and medially rotates arm; shoulder extension Muscles located in the shoulder moving the arm: Posterior fibers of the deltoid: shoulder extension Anterior fibers of the deltoid: shoulder flexion Lateral fibers of the deltoid: arm abduction and rotation Teres major: shoulder extension ANTERIOR MUSCLES UPPER LIMB MUSCLES AND ARM MOVEMENTS Muscles located in the shoulder that move the arm (cont): Rotator cuff muscles: Supraspinatus, Infraspinatus, Teres minor, and Subscapularis (mnemonic SITS) Function mainly to reinforce the capsule of the shoulder by holding the head of the humerus in the glenoid cavity Secondarily act as synergists and fixators Muscles located in the arm that move the arm Coracobrachialis Biceps brachii Triceps brachii Actions of the trunk, shoulder, and arm muscles on the shoulder and arm are summarized in Table 9.12 FOREARM MOVEMENT Flexion and extension of the elbow are accomplished by three muscles located in the arm and two in the forearm Most anterior muscles are flexors, and posterior muscles are extensors Forearm flexion Brachialis and Biceps brachii are the chief forearm flexors The Brachioradialis acts as a synergist and helps stabilize the elbow Forearm extension The Triceps brachii is the prime mover of forearm extension The Anconeus is a weak synergist Supination and pronation are accomplished primarily by forearm muscles The Supinator muscle is a synergist with the Biceps brachii in supinating the forearm The Pronator teres and Pronator quadratus pronate the forearm FOREARM MUSCLES, WRIST, HAND AND FINGER MOVEMENTS Most anterior muscles are flexors, and posterior muscles are extensors Forearm muscles Muscles that originate on the medial epicondyle are responsible for flexion of the wrist and fingers Muscles extending the wrist and fingers originate on the lateral epicondyle Forearm muscles moving the wrist, hand and fingers are summarized in Table 9.14 Extrinsic hand muscles are in the forearm Retinaculum: covers the flexor and extensor tendons and holds them in place around the wrist Intrinsic hand muscles are in the hand Thenar muscles, hypothenar muscles, midpalmar muscles HIP AND LOWER LIMB MUSCLES Most anterior compartment muscles of the hip and thigh flex the femur at the hip and extend the leg at the knee Posterior compartment muscles of the hip and thigh extend the thigh and flex the leg The medial compartment muscles all adduct the thigh These three groups are enclosed by the fascia lata HIP MUSCLES AND THIGH MOVEMENTS Gluteus maximus extends the hip Gluteus medius and minimus help hold the hip level while walking or running Deep hip muscles laterally rotate the thigh Anterior hip muscles flex the hip The thigh can be divided into three compartments Anterior muscles flex the hip Posterior muscles extend the hip Medial muscles adduct the thigh THIGH MUSCLES AND LEG MOVEMENTS Anterior thigh muscles Quadriceps femoris: extends the knee Sartorius: flexes the knee Tensor fasciae latae: stabilizes the knee Posterior thigh muscles flex the knee One medial thigh muscle flexes the knee: Gracilis Summarized in Table 9.16 LOWER LIMB MUSCLES AND ANKLE, FOOT AND TOE MOVEMENT The leg is divided into three compartments Muscles in the anterior compartment cause dorsiflexion, inversion, or eversion of the foot and extension of the toes Muscles of the lateral compartment plantar flex and evert the foot Muscles of the posterior compartment flex the leg, plantar flex and invert the foot, and flex the toes Intrinsic foot muscles flex or extend and abduct or adduct the toes