Transcript Chapter 3
Chapter 11 The Muscular System HOW SKELETAL MUSCLES PRODUCE MOVEMENT Principles of Human Anatomy and Physiology, 11e 1 Muscle Attachment Sites: Origin and Insertion • Skeletal muscles shorten & pull on the bones they are attached to • Origin is the bone that does not move when muscle shortens (normally proximal) • Insertion is the movable bone • Fleshy portion of the muscle in between attachment sites = belly Principles of Human Anatomy and Physiology, 11e 2 Lever Systems and Leverage • Muscle acts on rigid rod (bone) that moves around a fixed point called a fulcrum • Resistance is weight of body part & perhaps an object • Effort or load is work done by muscle contraction • Mechanical advantage – the muscle whose attachment is farther from the joint will produce the most force – the muscle attaching closer to the joint has the greater range of motion and the faster the speed it can produce Principles of Human Anatomy and Physiology, 11e 3 First - Class Lever • Can produce mechanical advantage or not depending on location of effort & resistance – if effort is further from fulcrum than resistance, then a strong resistance can be moved • Head resting on vertebral column – weight of face is the resistance – joint between skull & atlas is fulcrum – posterior neck muscles provide effort Principles of Human Anatomy and Physiology, 11e 4 Second - Class Lever • Similar to a wheelbarrow • Always produce mechanical advantage – resistance is always closer to fulcrum than the effort • Sacrifice of speed for force • Raising up on your toes – resistance is body weight – fulcrum is ball of foot – effort is contraction of calf muscles which pull heel up off of floor Principles of Human Anatomy and Physiology, 11e 5 Third - Class Lever • Most common levers in the body • Always produce a mechanical disadvantage – effort is always closer to fulcrum than resistance • Favors speed and range of motion over force • Flexor muscles at the elbow – resistance is weight in hand – fulcrum is elbow joint – effort is contraction of biceps brachii muscle Principles of Human Anatomy and Physiology, 11e 6 Coordination Within Muscle Groups • Most movement is the result of several muscle working at the same time • Most muscles are arranged in opposing pairs at joints – prime mover or agonist contracts to cause the desired action – antagonist stretches and yields to prime mover – synergists contract to stabilize nearby joints – fixators stabilize the origin of the prime mover • scapula held steady so deltoid can raise arm Principles of Human Anatomy and Physiology, 11e 7 HOW SKELETAL MUSCLES ARE NAMED • The most important characteristics include the direction in which the muscle fibers run, the size, shape, action, numbers of origins, and location of the muscle, and the sites of origin and insertion of the muscle • Examples from Table 11.2 – triceps brachii -- 3 sites of origin – quadratus femoris -- square shape – serratus anterior -- saw-toothed edge Principles of Human Anatomy and Physiology, 11e 8 Muscles of Facial Expression • Orbicularis oculi closes the eye • Orbicularis oris puckers the mouth Principles of Human Anatomy and Physiology, 11e 9 Muscles that Move the Mandible • Masseter, temporalis Arise from skull & insert on mandible • Protracts, elevates or retracts mandible – Temporalis & Masseter elevate the mandible (biting) Principles of Human Anatomy and Physiology, 11e 10 Muscles that Move the Head • Sternocleidomastoid muscle – arises from sternum & clavicle & inserts onto mastoid process of skull – contraction of one, laterally flexes the neck and rotates face in opposite direction Principles of Human Anatomy and Physiology, 11e 11 Muscles of Abdominal Wall Principles of Human Anatomy and Physiology, 11e 12 Muscles of Abdominal Wall • sheetlike muscles – rectus abdominis = vertically oriented – external & internal obliques • wrap around body to form anterior body wall Principles of Human Anatomy and Physiology, 11e 13 Muscles Used in Breathing • Breathing requires a change in size of the thorax • During inspiration, thoracic cavity increases in size – external intercostal lift the ribs – diaphragm contracts & dome is flattened • During expiration, thoracic cavity decreases in size – internal intercostal used in forced expiration Principles of Human Anatomy and Physiology, 11e 14 Stabilizing the Pectoral Girdle • Anterior thoracic muscles – Subclavius extends from 1st rib to clavicle – Pectoralis minor extends from ribs to coracoid process – Serratus anterior extends from ribs to inner surface of scapula • Posterior thoracic muscle – Trapezius extends from skull & vertebrae to clavicle & scapula – Rhomboideus extends from thoracic vertebrae to vertebral border of scapula Principles of Human Anatomy and Physiology, 11e 15 Axial Muscles that Move the Arm • Pectoralis major & Latissimus dorsi extend from body wall to humerus. Principles of Human Anatomy and Physiology, 11e 16 Muscles that Move the Arm • Deltoid arises from acromion & spine of scapula & inserts on arm – abducts, flexes & extends arm • Rotator cuff muscles extend from scapula posterior to shoulder joint to attach to the humerus – supraspinatus & infraspinatus: above & below spine of scapula – subscapularis on inner surface of scapula Principles of Human Anatomy and Physiology, 11e 17 Flexors of the Forearm (elbow) • Biceps brachii – scapula to radial tuberosity – flexes shoulder and elbow & supinates hand • Brachialis – humerus to ulna – flexion of elbow Principles of Human Anatomy and Physiology, 11e 18 Extensors of the Forearm (elbow) • Triceps brachii – long head arises scapula – medial & lateral heads from humerus – inserts on ulna – extends elbow & shoulder joints Principles of Human Anatomy and Physiology, 11e 19 Muscle that Pronate & Flex • Flexor carpi muscles – radialis – ulnaris • Flexor digitorum muscles Principles of Human Anatomy and Physiology, 11e 20 Muscles that Supinate & Extend • Extensors of wrist and fingers – extensor carpi – extensor digitorum Principles of Human Anatomy and Physiology, 11e 21 Muscles Crossing the Hip Joint • Quadriceps femoris has 4 heads – Rectus femoris crosses hip – 3 heads arise from femur • Vastus lateralis, intermedius and medialis – all act to extend the knee Principles of Human Anatomy and Physiology, 11e 22 Adductor Muscles of the Thigh • Adductor group of muscle extends from pelvis to linea aspera on posterior surface of femur – adductor longus – gracilis Principles of Human Anatomy and Physiology, 11e 23 Muscles of the Butt & Thigh • Gluteus muscles – maximus, medius & minimus – maximus extends hip – medius & minimus abduct • Hamstring muscles – semimembranosus (medial) – semitendinosus (medial) – biceps femoris (lateral) – extend hip & flex knee Principles of Human Anatomy and Physiology, 11e 24 Muscles of the Calf (posterior leg) • muscles insert onto calcaneus – gastrocnemius arises femur • flexes knee and ankle – soleus arise from leg • flexes ankle Principles of Human Anatomy and Physiology, 11e 25 Muscles of the Leg and Foot • Anterior compartment of leg – extensors of ankle & toes • tibialis anterior • extensor digitorum longus • Shinsplints syndrome – pain or soreness on anterior tibia – running on hard surfaces Principles of Human Anatomy and Physiology, 11e 26