Chapter 10: The Muscular System

Chapter 10: The Muscular System Objectives: 1. Describe the function of prime movers, antagonists, synergists, and fixators. 2. List the criteria used in naming muscles. Provide an example to illustrate the use of each criterion. 3. Name the common patterns of muscle fascicle arrangement and relate these to power generation. 4. Define lever, and explain how a lever operating at a mechanical advantage differs from one operating at a mechanical disadvantage. 5. Name the three types of lever systems and indicate the arrangement of effort, fulcrum, and load in each. Also note the advantages of each type of lever system. 6. Name and identify the muscles described in Tables 10.1 to 10.17. State the origin, insertion and action of each. I. Interactions of Skeletal Muscles in the Body A. Skeletal muscles work together or in opposition B. Muscles only pull (never push) C. As muscles shorten, the insertion generally moves toward the origin D. Whatever a muscle (or group of muscles) does, another muscle (or group) undoes E. Muscle Classification: Functional Groups 1. Prime movers a. provide the major force for producing a specific movement 2. Antagonists a. oppose or reverse a particular movement 3. Synergists a. Add force to a movement b. Reduce undesirable or unnecessary movement 4. Fixators a. synergists that immobilize a bone or muscle s origin II. Naming Skeletal Muscles A. Location of muscle 1. bone or body region associated with the muscle B. Shape of muscle 1. deltoid muscle (deltoid = triangle) C. Relative size 1

1. maximus (largest) 2. minimus (smallest) 3. longus (long) D. Direction of fibers 1. rectus (fibers run straight) 2. transversus, and oblique (fibers run at angles to an imaginary defined axis) E. Number of origins 1. biceps (two origins) 2. triceps (three origins) F. Location of attachments 1. named according to point of origin or insertion E. Action 1. flexor or extensor, as in the names of muscles that flex or extend, respectively III. Muscle Mechanics: Importance of Fascicle Arrangement and Leverage A. Arrangement of Fascicles 1. Parallel a. fascicles run parallel to the long axis of the muscle b. sartorius 2. Fusiform a. spindle-shaped muscles b. biceps brachii 3. Pennate a. short fascicles that attach obliquely to a central tendon running the length of the muscle b. rectus femoris 4. Convergent a. fascicles converge from a broad origin to a single tendon insertion b. pectoralis major 5. Circular a. fascicles are arranged in concentric rings b. orbicularis oris B. Lever Systems: Bone-Muscle Relationship 1. Lever a. rigid bar that moves on a fulcrum, or fixed point 2. Effort a. force applied to a lever 2

3. Load a. resistance moved by the effort C. Lever Systems: Classes 1. First class a. fulcrum is between the load and the effort 2. Second class a. load is between the fulcrum and the effort 3. Third class a. effort is applied between the fulcrum and the load IV. Major Skeletal Muscles of the Body A. Muscles: Name, Action and Innervation 1. Name and description of the muscle a. be alert to information given in the name 2. Origin and insertion a. Origin attachment to the immovable bone b. Insertion attachment to the movable bone c. There is always a joint between the origin and insertion 3. Action a. best learned by acting out a muscle s movement on one s own body 4. Nerve supply a. name of major nerve that innervates the muscle V. Muscles of the Head & Neck A. Muscles of the Scalp 1. Epicranius (occipitofrontalis) a. bipartite muscle consisting of the: 1) Frontalis 2) Occipitalis 2. Galea aponeurotica a. cranial aponeurosis connecting above muscles 3. These two muscles have alternate actions of pulling the scalp forward and backward B. Muscles of the Face 1. 11 muscles are involved in lifting the eyebrows, flaring the nostrils, opening and closing the eyes and mouth, and smiling 2. All are innervated by cranial nerve VII (facial nerve) 3. Usually insert in skin (rather than bone), and adjacent muscles often fuse 3

C. Muscles of Mastication 1. There are four pairs of muscles involved in mastication a. Prime movers 1. temporalis 2. masseter b. Grinding movements 1. pterygoids 2. buccinators 2. All are innervated by cranial nerve V (trigeminal nerve) D. Extrinsic Tongue Muscles 1. Three major muscles that anchor and move the tongue 2. All are innervated by cranial nerve XII (hypoglossal nerve) E. Muscles of the Anterior Neck and Throat: Suprahyoid 1. Four deep throat muscles 2. Form the floor of the oral cavity 3. Anchor the tongue 4. Elevate the hyoid 5. Move the larynx superiorly during swallowing F. Muscles of the Anterior Neck and Throat: Infrahyoid 1. Straplike muscles that depress the hyoid and larynx during swallowing and speaking G. Muscles of the Neck: Head Movements 1. Major head flexor is the sternocleidomastoid 2. Synergists to head flexion are the suprahyoid and infrahyoid 3. Lateral head movements are accomplished by the sternocleidomastoid and scalene muscles 4. Head extension is accomplished by the deep splenius muscles and aided by the superficial trapezius VI. Muscles of the Trunk A. Deep Back Muscles 1. The prime mover of back extension is the erector spinae a. Erector spinae, or sacrospinalis, muscles consist of three columns on each side of the vertebrae 1) iliocostalis 2) longissimus 3) spinalis 2. Lateral bending of the back is accomplished by unilateral contraction of these muscles 4

3. Other deep back extensors include the semispinalis muscles and the quadratus lumborum B. Short Muscles 1. Four short muscles extend from one vertebra to another 2. These muscles are synergists in extension and rotation of the spine C. Muscles of Respiration: External Intercostals 1. The primary function of deep thoracic muscles is to promote movement for breathing 2. External intercostals a. more superficial layer that lifts the rib cage and increases thoracic volume to allow inspiration D. Internal Intercostals 1. Internal intercostals a. deeper layer that aids in forced expiration 2. Diaphragm a. most important muscle in inspiration E. Muscles of the Abdominal Wall 1. The abdominal wall is composed of four paired muscles a. internal and external obliques b. transversus abdominis c. rectus abdominis 2. Fascicles of these muscles run at right and oblique angles to one another, giving the abdominal wall added strength 3. In addition to forming the abdominal wall, these muscles: a. Are involved with lateral flexion and rotation of the trunk b. Help promote 1) urination 2) defecation 3) childbirth 4) vomiting 5) coughing 6) screaming F. Muscles of the Pelvic Floor (Pelvic Diaphragm) 1. The pelvic diaphragm is composed of two paired muscles a. levator ani b. coccygeus 2. These muscles: a. Close the inferior outlet of the pelvis b. Support the pelvic floor 5

c. Elevate the pelvic floor to help release feces d. Resist increased intra-abdominal pressure G. Muscles Inferior to the Pelvic Floor 1. Two sphincter muscles allow a. voluntary control of urination (sphincter urethrae) b. defecation (external anal sphincter) H. Extrinsic Shoulder Muscles 1. Muscles of the thorax 2. Anterior a. pectoralis major b. pectoralis minor c. serratus anterior d. subclavius 3. Posterior a. latissimus dorsi b. trapezius muscles c. levator scapulae d. rhomboids 4. These muscles are involved with the movements of the scapula including a. elevation b. depression c. rotation d. lateral and medial movements 5. Prime movers of shoulder elevation are a. trapezius b. levator scapulae I. Muscles Crossing the Shoulder 1. Nine muscles cross the shoulder joint and insert into the humerus 2. Prime movers include: a. Pectoralis major 1) arm flexion b. Latissimus dorsi and posterior fibers of the deltoid 1) arm extension c. Middle fibers of the deltoid 1) arm abduction 3. Rotator cuff muscles a. supraspinatus b. infraspinatus 6

c. teres minor d. subscapularis 4. Function mainly to reinforce the capsule of the shoulder 5. Secondarily act as synergists and fixators 6. The coracobrachialis and teres major: a. Act as synergists b. Do not contribute to reinforcement of the shoulder joint VII. Muscles of the Upper Limb A. Muscles Crossing the Elbow 1. Forearm extension a. The triceps brachii is the prime mover of forearm extension b. The anconeus is a weak synergist 2. Forearm flexion a. Brachialis and biceps brachii are the chief forearm flexors b. Brachioradialis acts as a synergist and helps stabilize the elbow B. Muscles of the Forearm 1. Forearm muscle groups: a. cause wrist movement b. those that move the digits 2. Anterior muscles are flexors 3. Posterior muscles are extensors 4. The pronator teres and pronator quadratus are not flexors, but pronate the forearm 5. The supinator muscle is a synergist with the biceps brachii in supinating the forearm C. Muscles of the Forearm: Anterior Compartment 1. These muscles are primarily flexors of the wrist and fingers D. Muscles of the Forearm: Posterior Compartment 1. These muscles are primarily extensors of the wrist and fingers E. Intrinsic Muscles of the Hand 1. These small muscles: a. Lie in the palm of the hand (none on the dorsal side) b. Move the metacarpals and fingers c. Control precise movements (e.g., threading a needle) d. Are the main abductors and adductors of the fingers e. Produce opposition move the thumb toward the little finger F. Finger and Thumb Movements 1. Flexion 7

a. Thumb bends medially along the palm b. Fingers bend anteriorly 2. Extension a. Thumb points laterally b. Fingers move posteriorly G. Intrinsic Muscles of the Hand: Groups 1. There are two groups of intrinsic hand muscles a. Thenar eminence (ball of the thumb) b. Hypothenar eminence (ball of the little finger) c. Each have a flexor, an abductor, and an opponens muscle 2. The midpalm muscles a. the lumbricals b. interossei c. extend the fingers 3. The interossei also abduct and adduct the fingers VIII. Muscles of the Lower Limb A. Muscles Crossing Hip and Knee Joints 1. Most anterior compartment muscles of the hip and thigh flex the femur at the hip and extend the leg at the knee 2. Posterior compartment muscles of the hip and thigh extend the thigh and flex the leg 3. The medial compartment muscles all adduct the thigh 4. These three groups are enclosed by the fascia lata B. Movements of the Thigh at the Hip 1. The ball-and-socket hip joint permits a. flexion b. extension c. abduction d. adduction e. circumduction f. rotation 2. The most important thigh flexors are the a. iliopsoas (prime mover) b. tensor fasciae latae c. rectus femoris 3. The medially located adductor muscles and sartorius assist in thigh flexion 4. Thigh extension is primarily effected by the hamstring muscles a. biceps femoris 8

b. semitendinosus c. semimembranosus 5. Forceful extension is aided by the gluteus maximus 6. Abduction and rotation are effected by a. gluteus medius b. gluteus minimus c. are antagonized by the lateral rotators 7. Thigh adduction is the role of five adductor muscles a. adductor magnus b. adductor longus c. adductor brevis d. pectineus e. gracilis C. Movements of the Knee Joint 1. The sole extensor of the knee is the quadriceps femoris 2. The hamstring muscles flex the knee, and are antagonists to the quadriceps femoris D. Fascia of the Leg 1. A deep fascia of the leg is continuous with the fascia lata 2. This fascia segregates the leg into three compartments a. anterior b. lateral c. posterior 3. Distally, the fascia thickens and forms the flexor, extensor, and fibular retinaculae E. Muscles of the Leg: Movements 1. Various leg muscles produce the following movements at the: a. Ankle dorsiflexion and plantar flexion b. Intertarsal joints inversion and eversion of the foot c. Toes flexion and extension F. Muscles of the Anterior Compartment 1. These muscles are the primary toe extensors and ankle dorsiflexors 2. They include a. tibialis anterior b. extensor digitorum longus c. extensor hallucis longus d. fibularis tertius G. Muscles of the Lateral Compartment 1. These muscles plantar flex and evert the foot 9

2. They include a. fibularis longus b. fibularis brevis H. Muscles of the Posterior Compartment 1. These muscles primarily flex the foot and the toes 2. They include a. gastrocnemius b. soleus c. tibialis posterior d. flexor digitorum longus e. flexor hallucis longus I. Muscle Actions of the Thigh 1. Flex and extend the thigh (posterior compartment) 2. Extend the leg (anterior compartment) 3. Adduct the thigh (medial compartment) J. Muscle Actions of the Leg 1. Plantar flex and evert the foot (lateral compartment) 2. Plantar flex the foot and flex the toes (posterior compartment) 3. Dorsiflex the foot and extend the toes (anterior compartment) K. Intrinsic Muscles of the Foot 1. These muscles help flex, extend, abduct, and adduct the toes 2. In addition, along with some leg tendons, they support the arch of the foot 3. There is a single dorsal foot muscle, the extensor digitorum brevis, which extends the toes 4. The plantar muscles occur in four layers L. Plantar Muscles: First Layer (Superficial) 1. Superficial muscles of the plantar aspect of the foot 2. These muscles are similar to the corresponding muscles of the hand 10