Chapter 11: The Muscular System

Transcription

1 Chapter 11: The Muscular System I. Muscle Organization and Function, p. 327 Objectives 1. Describe the arrangement of fascicles in the various types of muscles and explain the resulting functional differences. 2. Describe the classes of levers and how they make muscles more efficient. Muscle organization affects the power, range and speed of muscle movement. Muscle cells or fibers are organized in bundles called fascicles. Skeletal muscles are classified according to the way fascicles are organized, and their relationships to tendons. Organization of Skeletal Muscle Fibers, p. 327 The 4 patterns of fascicle organization are: 1. parallel 2. convergent 3. pennate 4. circular Figure 11-1a Most skeletal muscles are parallel muscles. Their fibers parallel the long axis of the muscle. (e.g. biceps brachii) When a parallel muscle contracts, the center or body of the muscle thickens. Parallel muscles contract about 30% in length. Tension in parallel muscle depends on the total number of myofibrils. Therefore, the cross section of the muscle is directly related to tension. One square inch (6.45 sq. cm) of cross section develops about 50 pounds (23 kg) of tension. Figure 11-1b Convergent muscles have a broad area that converges on an attachment site such as a tendon, aponeurosis or raphe (a thin band of collagen fibers). Convergent muscle fibers pull in several different directions, depending on which portion of the muscle is stimulated. (e.g. pectoralis muscles) Figure 11-1c,d,e Pennate muscles form an angle with the tendon, so they do not move as far as parallel muscles. But, pennate muscles contain more myofibrils than parallel muscles, and develop more tension.

2 Pennate muscles can be subdivided into: 1. unipennate: all muscle fibers on 1 side of the tendon (e.g. extensor digitorum) 2. bipennate: muscle fibers on both sides of the tendon (e.g. rectus femoris) 3. multipennate: tendon branches within the muscle (e.g. deltoid) Figure 11-1f Circular muscles or sphincters open and close to guard entrances of the body (e.g. obicularis oris) Levers, p. 328 To produce motion, skeletal muscles are attached to the skeleton. Like muscle organization, the type of muscle attachment affects the power, range and speed of muscle movement. Mechanically, each bone is a lever (a rigid, moving structure) and each joint is a fulcrum (a fixed point). The muscles provide the applied force (AF) required to overcome resistance (R). The function of a lever is to change: 1. the direction of an applied force 2. the distance and speed of movement produced by an applied force 3. the effective strength of an applied force There are 3 classes of levers, depending on the relationship between the applied force, the fulcrum, and the resistance: Figure 11-2a first-class lever: - e.g. seesaw - the fulcrum is in the center, between the applied force and the resistance - force and resistance are balanced Figure 11-2b second-class lever: - e.g. wheelbarrow - the resistance is in the center, between the applied force and the fulcrum - a small force can move a large weight Figure 11-2c third-class lever: - the most common levers in the body - the applied force is in the center, between the resistance and the fulcrum - requires a greater force to move a smaller resistance, but maximizes speed and distance traveled

3 Key Most skeletal muscles can shorten to roughly 70% of their ideal resting length. The versatility in terms of power, speed and range of body movements results from differences in the positions of muscle attachments relative to the joints involved. II. Muscle Terminology, p. 330 Objectives 1. Predict the actions of a muscle on the basis of the relative positions of its origin and insertion. 2. Explain how muscles interact to produce or oppose movements. 3. Explain how the name of a muscle can help identify its location, appearance or function. Origins and Insertions, p. 330 Most muscles have one end that is fixed and another end that moves toward the fixed end during a contraction. The point of attachment at the fixed end is called the origin. The point of attachment to the structure that moves is the insertion. The origin is usually proximal to the insertion. The movement a muscle contraction produces is called its action. Actions are body movements such as flexion, extension, adduction, etc. (review Figures 9-2 to 9-5). Actions, p. 330 Most muscles either originate or insert on the skeleton. Actions are described in terms of the bone, joint or region affected. Muscles usually work in groups to maximize efficiency. The smaller muscles reach maximum tension first, followed by the larger, primary muscles. Muscles are described based on their functions: 1. An agonist (prime mover) is a muscle that produces a particular movement. 2. An antagonist opposes the movement of a particular agonist. - agonists and antagonists work in pairs (flexors-extensors, abductors-adductors, etc.) When one contracts, the other stretches. 3. A synergist is a smaller muscle that assists a larger agonist. They may help start a motion or stabilize the origin of the agonist (fixators). Names of Skeletal Muscles, p. 331

4 The correct names of all muscles (except the platysma and the diaphragm) include the word muscle. We may use the descriptive term alone, but the word muscle is always implied. Table 11-1 The names of skeletal muscles include descriptive information about: 1. Location in the body: - identified by body regions - e.g. temporalis muscle 2. Origin and insertion - the first part of the name indicates the origin - the second part of the name indicates the insertion - e.g. genioglossus muscle 3. Fascicle organization - describes the fascicle orientation within the muscle - i.e. rectus (straight), transversus, and oblique 4. Relative position - externus (superficialis) are visible at the body surface - internus (profundus) are deep muscles - extrinsic muscles are outside an organ - intrinsic muscles are inside an organ 5. structural characteristics - such as number of tendons (bi = 2, tri = 3) - shape (trapezius, deltoid or rhomboid) - or size longus (long) longissimus (longest) teres (long and round) brevis (short) magnus (large) major (larger) maximus (largest) minor (small) minimus (smallest) 6. Action - muscles may be named after movements (flexor, extensor, retractor, etc.) - or common occupations and habits (e.g. risor = laughter) Figure 11-3 Axial and Appendicular Muscles, p. 333 The muscle system can be divided into axial muscles (60% of the body s skeletal muscles) and appendicular muscles (40%). 1. Axial muscles position the head and spinal column, and move the rib cage. 2. Appendicular muscles support the pectoral and pelvic girdles, and the limbs.

5 III. The Axial Muscles, p. 336 Objective 1. Identify the principle axial muscles of the body and indicate their origins, insertions, actions and innervation. Axial muscles can be divided into 4 groups based on location and function: 1. muscles of the head and neck 2. muscles of the vertebral column 3. oblique and rectus muscles 4. muscles of the pelvic floor Muscles of the Head and Neck, p. 336 Muscles of the head and neck are subdivided into 6 groups: 1. muscles of facial expression 2. extrinsic eye muscles 3. muscles of mastication 4. muscles of the tongue 5. muscles of the pharynx 6. anterior muscles of the neck Figure 11-4 Muscles of facial expression originate on the skull: orbicularis oris constricts the mouth opening buccinator moves food around the cheeks Muscles of the epicranium (scalp) include: temporoparietalis occipitofrontalis the platysma covers the anterior surface of the neck frontal and occipital bellies are separated by the epicranial aponeurosis) Table 11-2: Note the origins, insertions, actions and innervation (nerve supply) of the muscles of facial expression. Figure 11-5 The six extra-ocular or extrinsic eye muscles originate on the surface of the orbit and control the position of the eye: inferior rectus medial rectus superior rectus lateral rectus inferior oblique

6 superior oblique Table 11-3: Note the origins, insertions, actions and innervation of extrinsic eye muscles. Figure 11-6 The muscles of mastication move the mandible. masseter, the strongest jaw muscle temporalis helps lift the mandible pterygoid muscles position the mandible for chewing Table 11-4: Note the origins, insertions, actions and innervation of the muscles of mastication. Figure 11-7 Names of the muscles of the tongue end in glossus. palatoglossus originates at the palate styloglossus originates at the styloid process genioglossus originates at the chin hypoglossus originates at the hyoid bone Table 11-5: Note the origins, insertions, actions and innervation of the muscles of the tongue. Figure 11-8 The muscles of the pharynx begin the swallowing process. pharyngeal constrictor muscles move food into the esophagus laryngeal elevator muscles elevate the larynx palatal muscles lift the soft palate Table 11-6: Note the origins, insertions, actions and innervation of the muscles of the pharynx. Figure 11-9 Anterior muscles of the neck control the position of the larynx, depress the mandible, and support the tongue and pharynx. digastric, from chin to hyoid, and hyoid to mastoid mylohyoid, floor of the mouth geniohyoid, between hyoid and chin stylohyoid, between hyloid and styloid sternocleidomastoid, from the clavicle and sternum to the mastoid omohyoid, attaches scapula, clavicle, 1st rib and hyoid Table 11-7: Note the origins, insertions, actions and innervation of the anterior muscles of the neck.

7 Muscles of the Vertebral Column, p. 344 Figure The muscles of the vertebral column are divided into spinal extensors (superficial and deep) and spinal flexors. The spinal extensors or erector spinae muscles are subdivided into superficial and deep spinal extensors: - the superficial muscles include the: a. spinalis group b. longissimus group c. iliocostalis group - the smaller, deep muscles (transversospinalis) include the: a. semispinalis group b. multifidus muscle c. interspinalis muscles d. intertransversarii muscles e. rotatores muscles The vertebral column has few spinal flexors. In the neck, the longus capitis and longus colli rotate and flex the neck. The lumbar quadratus lumborum muscles flex the spine and depress the ribs. Table 11-8: Note the origins, insertions, actions and innervation of the muscles of the vertebral column. Oblique and Rectus Muscles, p. 346 Figure The oblique and rectus muscles lie within the body wall. - oblique muscles compress underlying structures or rotate the vertebral column - rectus muscles flex the vertebral column, opposing the erector spinae. The oblique muscle group, divided by region, includes: Cervical region: - scalene muscles, flex the neck Thoracic region: - intercostal muscles (external and internal intercostals), respiratory movements of the ribs - transversus thoracis, cross the inner surface of the ribs Abdominopelvic region (the same pattern as the thoracic region): - external and internal oblique muscles - transversus abdominis The rectus group includes the rectus abdominis, the six-pack between the

8 xiphoid process and the pubic symphysis. The rectus abdominis is divided longitudinally by the linea alba, and transversely by the tendinous inscriptions. The diaphragmatic muscle or diaphragm divides the thoracic and abdominal cavities, and performs respiration. Table 11-9: Note the origins, insertions, actions and innervation of the oblique and rectus muscles. Muscles of the Pelvic Floor, p. 349 Figure The muscles of the pelvic floor: 1. support the organs of the pelvic cavity 2. flex the sacrum and coccyx 3. control movement of materials through the urethra and anus The perineum (the muscular sheet which forms the pelvic floor) is divided into the anterior urogenital triangle and the posterior anal triangle. External genitalia are supported by the superficial muscles of the urogenital triangle. The deep muscular layer between the public bones that supports the pelvic floor and muscles of the urethra is the urogenital diaphragm. The deep muscular layer extending to the pubis, that supports the anal triangle, is the pelvic diaphragm. Table 11-10: Note the origins, insertions, actions and innervation of the muscles of the pelvic floor. IV. The Appendicular Muscles, p. 351 Objectives 1. Identify the principal appendicular muscles of the body and indicate their origins, insertions, actions and innervations. 2. Compare the major muscle groups of the upper and lower limbs and relate their differences to their functional roles. Figure The appendicular muscles position and stabilize the pectoral and pelvic girdles, and move the upper and lower limbs. The 2 major groups of appendicular muscles are the: 1. Muscles of the shoulders and upper limbs 2. Muscles of the pelvis and lower limbs

9 Muscles of the Shoulders and Upper Limbs, p. 353 Muscles of the shoulders and upper limbs are divided into 4 groups: 1. muscles that position the pectoral girdle 2. muscles that move the arm 3. muscles that move the forearm and hand 4. muscles that move the hand and fingers Figure Muscles that position the pectoral girdle include the: trapezius: - superficial - covers the back and neck up to the base of the skull - inserts on the clavicles and scapular spines rhomboid and levator scapulae: - deep to the trapezius - attach to cervical and thoracic vertebrae - insert on the scapular border serratus anterior: - on the chest - originates along ribs - inserts on anterior scapular margin subclavius: - originates on the ribs - inserts on the clavicle pectoralis minor: - attaches to the scapula Table 11-11: Note the origins, insertions, actions and innervation of the muscles that position the pectoral girdle. Figure Muscles that move the arm include the: deltoid: - the major abductor supraspinatus: - assists the deltoid subscapularis and teres major: - produce medial rotation at the shoulder infraspinatus and teres minor: - produce lateral rotation at the shoulder coracobrachialis: - attaches to the scapula - produces flexion and adduction at the shoulder pectoralis major: - between the anterior chest and the greater tubercle of the humerus

10 - produces flexion at the shoulder joint latissimus dorsi: - between thoracic vertebrae and the humerus - produces extension at the shoulder joint Muscles involved in rotation of the shoulder (supraspinatus, subscapularis, infraspinatus, and teres minor) and their tendons form the rotator cuff. Table 11-12: Note the origins, insertions, actions and innervation of the muscles that move the arm. Figure Most of the muscles that move the forearm and hand originate on the humerus and insert on the forearm, except the major flexor (the biceps brachii) and the major extensor (the triceps brachii). Extensors lie mainly on the posterior and lateral surfaces of the arm, and flexors lie mainly on the anterior and medial surfaces. biceps brachii: - flexes the elbow - stabilizes the shoulder joint - originates on the scapula, inserts on the radial tuberosity triceps brachii: - extends the elbow - originates on the scapula, inserts on the olecranon brachialis and brachioradialis: - flex the elbow anconeus: - opposes the brachialis flexor carpi ulnaris - superficial - flexes the wrist - adducts the wrist flexor carpi radialis, - superficial - flexes the wrist - abducts the wrist palmaris longus: - superficial - flexes the wrist extensor carpi radialis: - superficial - extends the wrist - abducts the wrist extensor carpi ulnaris - superficial - extends the wrist - adducts the wrist

11 pronator teres and supinator: - originate on the humerus and ulna - rotate the radius pronator quadratus: - originates on the ulna - assists the pronator teres Table 11-13: Note the origins, insertions, actions and innervation of the muscles that move the forearm and hand. Figure The muscles of the forearm that move the hand and fingers lie entirely within the forearm. Only their tendons cross the wrist (in bursae sheaths called synovial tendon sheaths). These are called the extrinsic muscles of the hand. The wide band of connective tissue on the posterior surface of the wrist, which holds the tendons of the extensor muscles in place, is the extensor retinaculum. On the anterior surface, the flexor retinaculum stabilizes the tendons of the flexor muscles. Table 11-14: Note the origins, insertions, actions and innervation of the muscles that move the hand and fingers. Figure The intrinsic muscles of the hand. Table 11-15: Note the origins, insertions, actions and innervation of the intrinsic muscles of the hand. Muscles of the Pelvis and Lower Limbs, p. 363 The pelvic girdle is tightly bound to the axial skeleton, permitting little movement (few muscles). The muscles that position the lower limbs are divided into 3 groups: 1. muscles that move the thigh 2. muscles that move the leg 3. muscles that move the foot and toes Figure The muscles that move the thigh can be subdivided into 4 groups: (1) the gluteal muscles cover the lateral surfaces of the ilia a. gluteus maximus: - the largest, most posterior gluteal muscle - produces extension and lateral rotation at the hip b. tensor fasciae latae:

12 - works with the gluteus maximus - stabilizes the iliotibial tract - (band of collagen fibers that braces the knee) c. gluteus medius and gluteus minimus: - originate anterior to the gluteus maximus - insert on the trochanter (2) the lateral rotators are 6 muscles including: a. piriformis b. obturator (3) the adductors include: a. adductor magnus: - produces adduction, extension and flexion b. adductor brevis: - hip flexion and adduction c. adductor longus - hip flexion and adduction d. pectineus - hip flexion and adduction e. gracilis - hip flexion and adduction (4) the iliopsoas muscle (2 hip flexors that insert on the same tendon) a. psoas major b. iliacus Table 11-16: Note the origins, insertions, actions and innervation of the muscles that move the thigh. Figure Muscles that move the leg are divided into flexors of the knee and extensors of the knees. (1) flexors of the knee a. biceps femoris b. semimembranosus c. semitendinosus d. sartorius: - originates superior to the acetabulum e. popliteus: - rotates the tibia to unlock the knee (2) extensors of the knee insert on the patella a. vastus muscles b. rectus femoris muscle Most flexors originate on the pelvic girdle. Most extensors originate on the femoral surface. The biceps femoris, semimembranosus and semitendinosus muscles make up the

13 hamstrings. The 3 vastus muscles and the rectus femoris make up the quadriceps femoris. Table 11-17: Note the origins, insertions, actions and innervation of the muscles that move the leg. Figure The extrinsic muscles that move the foot and toes include: (1) muscles that produce extension at the ankle: a. gastrocnemius b. soleus c. fibularis d. tibialis posterior (2) muscles that produce flexion at the ankle: a. tibialis anterior: - opposes the gastrocnemius (3) muscles that produce extension at the toes: a. extensor digitorum longum b. extensor hallucis longus (4) muscles that produce flexion at the toes: - opposing the extensors. The gastrocnemius and soleus share the calcaneal tendon (Achilles tendon). The fibrous sheaths that hold the tendons of the toes in place as they cross the ankle are the extensor retinacula. Table 11-18: Note the origins, insertions, actions and innervation of the muscles that move the foot and toes. Figure The intrinsic muscles of the foot. Table 11-19: Note the origins, insertions, actions and innervation of the intrinsic muscles of the foot. V. Aging and the Muscular System, p. 371 The effects of aging on the muscular system include: 1. Skeletal muscle fibers become smaller in diameter. 2. Skeletal muscles become less elastic. 3. skeletal muscles develop increasing amounts of fibrous connective tissue (fibrosis). 4. Tolerance for exercise decreases. 5. The ability to recover from muscular injuries decreases.

14 VI. Integration with Other Systems, p. 372 Figure The muscular system is supported by many other systems: - The cardiovascular system delivers oxygen and fuel, and removes carbon dioxide and wastes. - The respiratory system responds to the muscles need for oxygen. - The integumentary system disperses excess heat built up by muscle activity. - The nervous and endocrine systems direct and coordinate the responses of all the systems. SUMMARY In Chapter 11 we learned: - The effects of muscle structure on function. - The organization of skeletal muscle fibers: - (parallel, convergent, pennate, and circular) - The relationship between levers and force, speed and direction of movements. - The actions of 1st, 2nd and 3rd class levers in the body. - The origins and insertions of skeletal muscles. - The actions of skeletal muscles: - (agonist, antagonist, and synergist) - How skeletal muscles are named. - The structures and functions of the axial muscles: - muscles of head and neck - muscle of vertebral column - oblique and rectus muscles - muscles of the pelvic floor - The structures and functions of the appendicular muscles: - muscles of the shoulders and upper limbs - muscles of the pelvis and lower limbs - The effects of aging on the muscular system.