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HUMAN ANATOMY LECTURE NINE MUSCLES MUSCLE FUNCTIONS • • • • • Body movement Posture Respiration and heart beat Production of body heat - maintains body temperature Communication - speaking, writing, gesturing, facial and body language • Constriction of organs and vessels - helps food move through digestive tract and blood flow • Protects and supports soft tissues • Storage of nutrients PROPERTIES OF MUSCLE • Contractility - ability of a muscle to shorten with force • Excitability - capacity of muscle to respond to a stimulus • Extensibility - muscle can be stretched beyond its normal resting length • Elasticity - ability of muscle to recoil to original resting length after being stretched TYPES OF MUSCLE • Skeletal Muscle - voluntary muscle - responsible for movement, respiration, posture, facial expressions • Smooth Muscle - involuntary - around organs, blood vessels, glands, skin - controlled by endocrine and autonomic nervous system • Cardiac Muscle - autorhythmic - only found in heart - controlled by endocrine and autonomic nervous system SKELETAL MUSCLE • Composed of muscle cells (fibres), connective tissue, blood vessels, nerves • Fibres are long, cylindrical, multinucleated • Smaller in diameter in small muscles and larger in larger muscles • Striated appearance due to light and dark banding SKELETAL MUSCLE STRUCTURE • Epimysium (fascia) - sheath surrounding entire muscle - holds muscle together and separates them into groups - allows freedom of movement - carries nerves, blood vessels, lymphatic vessels - continuous with connective tissue of tendons and periosteum • Muscle Fasciculi - muscle bundles - composed of several muscle fibres - surrounded by connective tissue layer called perimysium • Endomysium - connective tissue surrounding individual muscle fibres NERVE AND BLOOD SUPPLY • Muscle cells are stimulated to contract by motor neuron axons at a neuromuscular junction (synapse) • Axons are branched so that every muscle fibre is innervated • Blood vessels and nerves enter the muscle together and follow the same branching pathway through the perimysium • Within the endomysium arterioles branch into capillary beds surrounding each muscle fibre SKELETAL MUSCLE CELLS (FIBRES) • Sarcoplasm - cytoplasm containing numerous myofibrils • Myofibril - thread-like structure extending length of muscle fibre - made up of proteins (actin and myosin myofilaments) • Sarcomeres - repeating arrangment of actin and myosin - smallest section of muscle capable of contracting • Sarcolemma - cell membrane surrounding a muscle fibre (cell) • Sarcoplasmic reticulum - similar to smooth ER - forms tubular network around each myofibril TRANSVERSE TUBULES • Transverse tubules - narrow tubes continuous with sarcolemma extending into sarcoplasm at right angles to muscle fibre - distributes signal (action potential) to contract through to interior of cell ensuring all cells contract simultaneously • Terminal cisternae - thickening on either side of t-tubule • Triad - terminal cisternae + t-tubule ACTIN (THIN) FILAMENTS • Two strands (F-actin) of pearl-like proteins (G-actin) form a double helix extending the length of the muscle fibre • Thin strand of nebulin holds the Factin together • G-actin contains the active site that binds the myosin during muscle contraction • Tropomyosin winds through the Factin and covers the active sites • Troponin protein found at the ends of the tropomyosin forming the tropomyosin/troponin complex binds Ca+2 and changes position during muscle contraction MYOSIN (THICK) FILAMENTS • Each ‘club’ consists of two heavy myosin molecules wound together to form a rod portion lying parallel with heads that extend laterally • Myosin ‘heads’ - bind to active sites on the active sites on the actin molecules to form crossbridges - attach to the ‘rod’ portion by a hinge that bends and straightens during contraction SARCOMERES Repeating units of actin and myosin along the myofibril - smallest portion of muscle capable of contracting • Z Line - network of protein fibres serving as attachment for actin • I Band - actin filaments only (thin/light) • A Band - length of myosin (thick/dark) • H Zone - myosin only (lighter) • M Line - myosin filaments are attached in center of H Zone Alternating A and I Bands give muscle striated appearance SMOOTH & CARDIAC MUSCLE Smooth Muscle • Not striated, made up of separate distinct cells with an obvious nucleus – less actin and myosin • Contract more slowly with no oxygen dept • Two types: (i) Multinuceate - cells operate independently (ie: iris of eye, blood vessels, erectile muscles of hair (ii) Visceral - cells operate together (ie: surrounding digestive tract, reproductive and excretory organs) Cardiac Muscle • Long, branching cells • Cells are striated but less organized than skeletal muscle • All cells work together as a single unit - autorhythmic contraction • Cells do not develop oxygen dept or fatigue • Connected by intercalated discs GROSS MUSCLE ANATOMY Most muscles extend from bone to bone and cross at least one joint • Tendons - attach muscle to bone • Aponeuroses - broad, sheetlike tendon Muscle terminology: • • • • Origin/head - end of muscle attached to most stationary bone Insertion - end of muscle attached to bone with most movement Belly - largest area between origin and insertion Synergists - muscles that work together to cause a movement - prime mover - plays major role in movement - fixator - hold one bone in place while other bone is moved • Agonist - muscle that causes an action when it contracts • Antagonist - muscle working in opposition to agonist MUSCLE ATTACHMENT MUSCLE TYPES MUSCLE SHAPES MUSCLE NOMENCLATURE Muscles are named according to: • Location - pectoralis, gluteus, brachial • Size - maximus, minimus, longus, brevis • Shape - deltoid, quadratus, teres • Orientation - rectus • Origin and Insertion - sternocleidomastoid, brachioradialis • Number of Heads - biceps, triceps • Function - adductor, masseter MUSCLE MOVEMENT • Muscles, their tendons and bones act together as lever systems to move parts of the body • Muscle contractions are a pull or force by relative positions of the: lever - bone fulcrum - joint weight or resistance - force of gravity due to weight of body parts or weight of object being moved CLASSES OF LEVERS Class I • Fulcrum between force and weight • See saw • Head movement at the atlantooccipital joint Class II • Weight is between fulcrum and pull • Wheelbarrow • Standing on toes, metatarsophalangeal joint Class III • Pull located between fulcrum and weight • Using a shovel • Biceps brachii with elbow as fulcrum BODY MOVEMENTS Flexion vs Extension Flexion - moves body part in anterior or ventral direction Extension - moves body part in posterior or dorsal direction Plantar Flexion vs Dorsiflexion Plantar Flexion - movement of foot toward plantar surface ie: standing on toes Dorsiflexion - movement of foot toward shin ie: walking on heel Abduction vs Adduction Abduction - movement away from midline Adduction - movement toward midline Medial vs Lateral Rotation Medial Rotation - anterior surface of limb rotates toward body Lateral Rotation - anterior surface of limb rotates away from body Pronation vs Supination Pronation - rotation of forearm so palm is down Supination - rotation of forearm so palm is up Elevation vs Depression Elevation - movement in superior direction Depression - movement in inferior direction Protraction vs Retraction Protraction - gliding part horizontally forward Retraction - gliding part horizontally backward Circumduction Movement in a cone/circular shape Inversion vs Eversion Inversion - turning foot so plantar surface faces medially Eversion - turning foot so plantar surface faces laterally MUSCLE ANATOMY ANTERIOR VIEW MUSCLE ANATOMY POSTERIOR VIEW HEAD MUSCLES Divided into groups by function: Facial Expression Origin and insertion in the superficial fascia When muscles contract the skin moves • Orbicularis oris - around mouth • Obicularis oculi - opens and closes eyelids Mastication (chewing) Involves elevation/depression of mandible and excursion to grind the teeth together Act with muscles of hyoid in movement of mandible Muscles of cheek and tongue aid mastication by pushing food under the teeth • Temporalis - lifts mandible • Masseseter - largest jaw muscle Muscles of the Hyoid Tongue Movements Important in speech - changes shape Swallowing - moves food around in mouth - holds food in place during grinding - pushes food up to palate and back toward pharynx Intrinsic - entirely within the tongue, allow tongue to change shape Extrinsic - insert in tongue, allow shape change and movement • Glossals – tongue muscles (genioglossus, hyoglossus, palatoglossus, styloglossus) Eye Muscles 6 eye muscles originate on surface of the orbit and control movement of eyeball • Extra-ocular eye muscles NECK MUSCLES Flexion - muscles deep within neck anterior margins of vertebral bodies Extension - posterior neck muscles attached to occipital bone Rotation and abduction - lateral and posterior muscle groups • Sternocleidomastoid - from sternum to mastoid of skull, on either side of neck • Trapezius - back of skull and upper vertebrae across to scapular spine Posterior Deep Neck Muscles Muscles of the Vertebral Column Muscles that extend, laterally flex, and rotate the vertebral column - used to produce erect posture Divided into deep and superficial groups Deep - vertebrae to vertebrae Superficial - vertebrae to ribs THORACIC MUSCLES Involved in breathing • External Intercostals - elevate ribs during inspiration • Internal Intercostals - contract and depress ribs during exhalation • Diaphragm - flattens during contraction - separates thoracic and abdominal cavities ABDOMINAL MUSCLES Flex and rotate vertebral column, decrease volume of abdominal and thoracic cavities Aid in forced expiration, vomiting, defecation, urination, childbirth Crossing pattern of muscles adds strength to abdominal wall to support organs • Rectus abdominus - inserts at xiphoid process down to pubic symphysis • Internal and external abdominal obliques – flex and rotate abdomen PERINEAL MUSCLES Pelvic Diaphragm - funnel shaped, supports the pelvic viscera - pierced by anal canal, urethra, vagina Perineum - diamond shaped area inferior to pelvic diaphragm - divided into urogenital triangle and anal triangle regions • Bulbospongiosus - base of penis or sides of vagina • Levator ani - tenses pelvic floor, elevates and retracts anus • Sphincter ani externus - around anus • Sphincter urethrae - around urethral opening ARM MUSCLES Scapular Movements Muscles that attach the upper limb to the body and move or stabilize the scapula and clavicle Originate on axial skeleton • Trapezius - covers back, portion of neck and base of skull • Rhomboid - attached to thoracic vertebrae and scapula posterior • Levator scapulae - attached to cervial vertebrae and scapula • Supraspinatus - scapula to humerus • Pectoralis minor - scapula to thoracic ribs Arm Movements Muscles attach to arm and thorax • Pectoralis major - humerus to superior thoracic vertebrae • Latismus dorsi - humerus to lower thoracic vertebrae Flexion and extension of shoulder • Deltoid - across front of shoulder - works with pectoralis - abducts medially and rotates laterally Rotator Cuff Primary muscles holding humerus in glenoid cavity Form cuff over proximal humerus Involved in movement of the shoulder • Supraspinatus - across scapula Forearm Movement Movement at elbow: Extension • Triceps brachii - scapula to forearm Flexion • Biceps brachii - scapula to forearm Wrist, Hand and Finger Movements Muscles on anterior surface of forearm - flexion, abduction, adduction of the wrist Muscles on posterior surface of forearm - extension and abduction Flexors and Extensors of the Hand LEG MUSCLES Thigh Movement • Gluteus maximus - attached to ilium, sacrum, coccyx • Gluteus medius - iliac crest to greater trochanter of femur • Adductor group - attach ischium to femur • Tensor fasciae latae - iliac crest to tibia - thick band of connective tissue - rotates hip and supports knee Leg Movement • Quadriceps femoris - anterior surface of thigh - extension at knee - inserted by patellar tendon • Sartorius - originates on edge of pelvis, crosses medially to insert on tibia and fibula - flexes knee and hip, rotates thigh • Hamstrings - posterior thigh muscle Muscles that move leg Lower Leg Movement Divided into 3 sections: anterior, posterior, lateral Anterior - extensors of foot and toes • Tibialis anterior - front of shin Posterior - flexors of foot • Gastrocnemius - condyles of femur to calcaneal(Achilles) tendon to calcaneus, superficial position • Soleus – fibula and tibia through calcaneal tendon to calcaneus, deep position Movement of the Foot Analogous to muscles of hand but also serve in support and locomotion 20 foot muscles flex, extend, abduct and adduct toes
