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THE MUSCULAR SYSTEM. INTERACTIONS OF SKELETAL MUSCLES IN THE BODY Muscles only pull; they are not capable of pushing –Generally as a muscle shortens,

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Presentation on theme: "THE MUSCULAR SYSTEM. INTERACTIONS OF SKELETAL MUSCLES IN THE BODY Muscles only pull; they are not capable of pushing –Generally as a muscle shortens,"— Presentation transcript:


2 INTERACTIONS OF SKELETAL MUSCLES IN THE BODY Muscles only pull; they are not capable of pushing –Generally as a muscle shortens, its insertion (attachment on the movable bone) moves toward its origin (its fixed or immovable point of attachment) Muscles can be classified into four functional groups: –1.Prime Movers: The muscle that provides the major force for the specific movement is called the prime mover or the agonist, of that movement –The biceps brachii muscle, which fleshes out the anterior arm (and inserts on the radius), is a prime mover of elbow flexion –2.Antagonists: Muscles that oppose or reverse a particular movement When a prime mover is active, the antagonist muscles are often stretched and may be relaxed Can also help to regulate the action of a prime mover by contracting to provide some resistance, thus helping to prevent overshoot or to slow or stop the movement Prime mover and its antagonist are located on opposite sides of the joint across which they act Antagonists can also be prime movers in their own right –Example: flexion of the forearm by the biceps brachii muscle of the arm is antagonized by the triceps brachii, the prime mover for extending the forearm

3 INTERACTIONS OF SKELETAL MUSCLES IN THE BODY 3.Synergists: –Help the prime movers by: Adding a little extra force to the same movement Or reducing undesirable or unnecessary movements that might occur as the prime mover contracts –When a muscle crosses two or more joints, its contraction causes movement at all of the spanned joints unless other muscles act as joint stabilizers »Example: the finger flexor muscles cross both the wrist and the phalangeal joints, but you can make a fist without bending your wrist because synergistic muscles stabilize the wrist –As some flexors act, undesirable rotation movements occur »Synergists can prevent this, allowing all of the prime mover’s force to be exerted in the desired direction

4 INTERACTIONS OF SKELETAL MUSCLES IN THE BODY 4.Fixators: when synergists immobilize a bone, or a muscle’s origin, they are more specifically called fixators –Examples: Scapula is held to the axial skeleton only by muscles and is quite freely movable –The fixator muscles that run from the axial skeleton to the scapula can immobilize the scapula so that only the desired movements occur at the mobile shoulder joint Muscles that help to maintain upright posture

5 INTERACTIONS OF SKELETAL MUSCLES IN THE BODY Although prime movers seem to get all the credit for causing certain movements, antagonistic and synergistic muscles are also important in producing smooth, coordinated, and precise movements A muscle may act as a prime mover in one movement, an antagonist for another movement, a synergist for a third movement, and so on

6 NAMING SKELETAL MUSCLES 1. Location of the muscle: Some muscle names indicate the bone or body region with which the muscle is associated –Example: Temporalis muscle overlies the temporal bone Intercostal muscles run between the ribs 2. Shape of the muscle: Some muscles are named for their shape –Example: Deltoid muscle is roughly triangular Together the right and left trapezius muscles form a trapezoid 3. Relative size of the muscle: Terms such as maximus (largest), minimus (smallest), longus (long), and brevis (short) are often used in muscle names to indicate relative size of the muscle –Example: Gluteus maximus Gluteus minimus

7 NAMING SKELETAL MUSCLES 4. Direction of muscle fibers: The names of some muscles indicate the direction in which their fibers (and fascicles) run in reference to some imaginary line, usually the midline of the body or the longitudinal axis of a limb bone –Examples: Rectus (straight): fibers run parallel to that imaginary line (axis) –Rectus femoris: straight muscle of the thigh, or femur) Transversus (right angle): muscle fibers run at right angles –Transversus abdominis: transverse muscle of the abdomen Oblique (oblique angle): muscle fibers run at oblique angles –External oblique: oblique muscle of the abdomen

8 NAMING SKELETAL MUSCLES 5. Number of origins: The number of origins a muscle has may be indicated by the word biceps, triceps, or quadriceps –Example: Biceps brachii: muscle of the arm has two origins (heads)

9 NAMING SKELETAL MUSCLES 6. Location of the attachments: Some muscles are named according to the location of their origin and insertion –Origin is always named first Example: –Sternocleidomastoid: muscle of the neck »Has a dual origin on the sternum (sterno) and clavicle (cleido), and it inserts on the mastoid process of the temporal bone

10 NAMING SKELETAL MUSCLES 7. Action: A muscle may be named for its action by using such words as flexor (flex), extensor (extend), adductor (brought toward), or supinate (bend backward) in its name –Example: Adductor longus: located in the medial thigh –Brings about thigh adduction (toward the main axis of the body or a limb) Supinator muscle: –Supinates the forearm: »Turn the forearm or hand so that the palm faces upward –Supinates the leg and foot: »To rotate the foot and leg outward

11 NAMING SKELETAL MUSCLES Several criteria are combined in the naming of some muscles –Example: extensor carpi radialis longus –Action of the muscle: the muscles action (extensor) –Location of attachment: joint it acts on (carpi = wrist) –Location of muscle: lies close to the radius of the forearm (radialis) –Relative size of muscle: relative to other wrist extensor muscles (longus) Unfortunately, not all muscle names are this descriptive

12 MUSCLE MECHANICS: IMPORTANCE OF FASCICLE ARRANGEMENT AND LEVERAGE In skeletal muscles the common arrangement of the fascicles varies, resulting in muscles with different shapes and functional capabilities

13 Arrangement of Fascicles Fascicle: bundle of nerve or muscle fibers (cells) bound together by connective tissue All skeletal muscles consist of fascicles, but fascicle arrangement vary, resulting in muscles with different shapes and functional capabilities


15 Arrangement of Fascicles (a): Circular pattern: –Fascicles arranged in concentric rings –Muscles with this arrangement surround external openings, which they close by contracting –General term for these muscles is sphincters (squeezers) –Examples: Orbicularis muscles surrounding the eyes (Orbicularis oculi) and the mouth (Orbicularis oris)

16 Arrangement of Fascicles (b): Convergent pattern: –Muscle has a broad origin, and its fascicles converge toward a single tendon of insertion –Such a muscle is triangular or fan shaped like the pectoralis major muscle of the anterior thorax

17 Arrangement of Fascicles (c)(f): Parallel pattern: –The long axes of the fascicles run parallel to the long axis of the muscle –Such muscles are either: straplike (c: parallel) spindle (f: fusiform) –shaped with an expanded belly (midsection) –Examples: Sartorius of thigh (c) Biceps brachii muscle of the arm (f)

18 Arrangement of Fascicles (d)(e)(g): Pennate pattern: –In a pennate (feather) pattern of arrangement the fascicles are short and attach obliquely to a central tendon that runs the length of the muscle –Types: Unipennate: d –Fascicles insert into only one side of the tendon –Example: extensor digitorum muscle of the leg Bipennate: g –Fascicles insert into the tendon from opposite sides (muscle grains resemble a feather) –Example: rectus femoris muscle of the thigh Multipennate: e –Arrangement looks like many feathers situated side by side, with all their quills inserted into one large tendon –Example: deltoid muscle, which forms the roundness of the shoulder


20 MUSCLE MECHANICS: IMPORTANCE OF FASCICLE ARRANGEMENT AND LEVERAGE The operation of most skeletal muscles involves the use of leverage and lever systems, partnerships between the muscular and skeletal systems –A lever is a rigid bar that moves on a fixed point, or a fulcrum, when a force is applied to it –The applied force, or effort is used to move a resistance or load –In your body, your joints act as the fulcrums, the bones as the levers, and the muscle contraction as the effort (force) Load (resistance) is the bone itself, along with overlying tissues and anything else you are trying to move with that lever

21 Lever Systems A lever allows a given effort (force) to lift a heavier load (resistance), or to move a load (resistance) farther or faster, than it otherwise could –(a):First-Class: the load is close to the fulcrum and the effort is applied far from the fulcrum A small effort exerted over a relatively large distance can be used to move a large load over a small distance Such a lever is said to operate at a mechanical advantage and is commonly called a power lever

22 Lever Systems (b): Third-Class: –Load is far from the fulcrum and the effort is applied near the fulcrum, the force exerted by the muscle must be greater than the load moved or supported –This lever system operates at a mechanical disadvantage and is a speed lever –These levers are useful because they provide rapid contractions with a wide range of motion


24 Lever Systems All levers follow the same basic principle: –Effort farther than load from fulcrum = mechanical advantage –Effort nearer than load to fulcrum = mechanical disadvantage Lever systems that operate at a mechanical disadvantage (speed levers), force is lost but speed and range of movement are gained, and this can be a distinct benefit Lever systems that operate at a mechanical advantage (power levers) are slower, more stable, and used where strength is a priority

25 Lever Systems There are three types of levers: –First-class –Second-class –Third-class

26 Lever Systems First-Class Levers (a): Effort is applied at one end of the lever and the load is at the other, with the fulcrum somewhere between Examples: –Seesaws –Scissors –Lift your head off your chest Some operate at a mechanical advantage Others operate at a mechanical disadvantage –Action of the triceps muscle in extending the forearm against resistance (pushing)

27 Lever Systems Second-Class Levers (b): Effort is applied at one end of the lever and the fulcrum is located at the other, with the load between them All second-class levers in the body work at a mechanical advantage because the muscle insertion (effort) is always farther from the fulcrum than is the load to be moved Levers of strength, but speed and range are sacrificed for that strength Examples: –Wheelbarrow –Uncommon in the human body Best example is the act of standing on your toes

28 Lever Systems Third-Class Levers (c): Effort is applied between the load and the fulcrum Operate with great speed and always at a mechanical disadvantage Most skeletal muscles of the body –Tend to be thicker and more powerful –Permits a muscle to be inserted very close to the joint across which movement occurs Allows rapid, extensive movements with relatively little shortening of the muscle Examples: –Tweezers (forceps) –biceps


30 Skeletal Muscles Over 600 –Book only list approximately 125 pairs of them





35 Facial Muscles Muscles of the Head: Facial Expression –Muscles of the scalp include the epicranius consisting of the frontalis and the occipitalis –Muscles of the face include corrugator supercilii, orbicularis oculi, zygomaticus, risorius, levator labii superioris, depressor labii inferioris, depressor anguli oris, orbicularis oris, mentalis, buccinator, and platysma

36 MAJOR SKELETAL MUSCLES OF THE FACE Frontalis:cranial (facial nerve) VII –Raises the eyebrows (as in surprise) –Wrinkles forehead skin horixzontally –Cranial nerve VII Orbicularis oculi:cranial (facial nerve) VII –Protects eyes from intense light and injury –Produces blinking, squinting –Draws the eyebrows inferiorly Orbicularis oris:cranial (facial nerve) VII –Closes lips –Purses (pucker) and protrudes (stick out) lips –Kissing and whistling muscle


38 Muscles of the Head Mastication and Tongue Movement: –Muscles of mastication include the masseter, temporalis, medial pterygoid, lateral pterygoid, and the buccinator –Muscles promoting tongue movement are the genioglossus, hypoglossus, and the styloglossus

39 Mastication Muscles Masseter:Temporalis:cranial (trigeminal) nerve V –Prime mover of jaw closure –Elevates mandible Temporalis:cranial (trigeminal) nerve V –Closes jaw –Elevates and retracts mandible Buccinator:cranial (facial) nerve VII –Trampoline-like action –Keeps food between grinding surfaces of teeth during chewing

40 Mastication Muscles


42 Mastication Muscles

43 Tongue Muscles Genioglossus:cranial (hypoglossal) nerve XII –Primarily protrudes tongue, but in concert with other extrinsic muscles to retract tongue


45 MAJOR SKELETAL MUSCLES OF THE BODY Muscles of the Anterior Neck and Throat: Swallowing –Suprahyoid muscles include digastric, stylohyoid, mylohyoid, and geniohyoid –Infrahyoid muscles include sternohyoid, sternothyroid, omohyoid, thyrohyoid, and the pharyngeal constrictor muscles (superior, middle, and inferior)

46 Neck and Throat Muscles Mylohyoid:cranial (trigeminal) nerve V –Elevates hyoid bone and floor of mouth –Enables the tongue to exert backward and upward pressure that forces food bolus into pharynx

47 Neck and Throat Muscles Pharyngeal constrictor muscles (superior, middle, and inferior):cranial (vagus) nerve X –Working as a group and in sequence, all constrict pharynx during swallowing –Propels food bolus to esophagus peristalsis



50 MAJOR SKELETAL MUSCLES OF THE BODY Muscles of the Neck and Vertebral Column: Head and Trunk Movement –Anterolateral neck muscles include the sternocleidomastoid, and scalenes (anterior, middle, and posterior) –Intrinsic muscles of the back include splenius capitis, erector spinae or sacrospinalis, iliocostals, longissimus, spinalis, semispinalis, and the quadratus lumborum

51 Neck Muscles Sternocleidomastoid: cranial (accessory) nerve XI and branches of cervical nerves 2- 4: –Prime mover of head flexion –Neck flexion –Head movement side-to- side




55 Neck and Vertebral Column Muscles Longissimus: thoracis, cervicis, and capitis: spinal nerves: –Capitis: extends head and turns face side to side –Thoracis and cervicis: extend vertabral column side to side


57 Thorax and Abdominal Muscles Muscles of the Thorax: Breathing –Muscles of the thorax include the external intercostals, internal intercostals, and the diaphragm Muscles of the Abdominal Wall: Trunk Movement and Compression of Abdominal Viscera –Muscles of the anterolateral abdominal wall include the rectus abdominis, external oblique, and the transversus abdominis

58 Thorax Muscles External intercostals: intercostal nerves: –Elevate rib cage –Aids in inspiration Internal intercostals: intercostal nerves: –Depress rib cage –Aids in expiration Diaphragm:cervical (phrenic) nerve (C 3 -C 5 ) –Breathing



61 Abdominal Muscles Rectus abdominis: Intercostal (thoracic) nerves: –Flex and rotate lumbar region External oblique: Intercostal (thoracic) nerves: –Compression of abdominal wall Transversus abdominis: Intercostal (thoracic) nerves: –Compression of abdominal wall



64 MAJOR SKELETAL MUSCLES OF THE BODY Muscles of the Pelvic Floor and Perineum: Support of Abdominopelvic Organs: –Muscles of the pelvic diaphragm include the levator ani and the coccygeus –Muscles of the urogenital diaphragm include the deep transverse perineus and the sphincter urethrae –Muscles of the superficial space include the ischiocavernosus, bulbospongiosus, and the superficial transverse perineus


66 Pelvic Floor Muscles Ischiocavernosus: pudendal (sacral) nerve: –Retards venous drainage and maintains erection of penis or clitoris Bulbospongiosus: pudendal (sacral) nerve: –Empties male urethra –Assist in erection of penis in males and of clitoris in females


68 MAJOR SKELETAL MUSCLES OF THE BODY Superficial Muscles of the Anterior and Posterior Thorax: Movements of the Scapula –Muscles of the anterior thorax include the pectoralis minor, serratus anterior, and the subclavius –Muscles of the posterior thorax include the trapezius, levator scapulae, and the rhomboids (major and minor)

69 MAJOR SKELETAL MUSCLES OF THE BODY Muscles Crossing the Shoulder Joint: Movement of the Arm –Muscles moving the arm include the pectoralis major, latissimus dorsi, deltoid, subscapularis, supraspinatous, infraspinatous, teres minor, teres major, and the coracobrachialis

70 Thorax Muscles Deltoid: cervical nerves: –Prime mover of arm abduction –Antagonists of pectoralis major and latissimus dorsi Pectoralis major: cervical and thoracic nerves: –Prime mover of arm flexion –Adduction Trapezius: cervical nerves: –Stabilizes, raises, retracts, and rotates scapula Latissimus dorsi: cervical nerves –Prime mover of arm extension –Powerful arm adductor Striking a blow Swimming Rowing



73 MAJOR SKELETAL MUSCLES OF THE BODY Muscles crossing the Elbow Joint: Flexion and Extension of the Forearm –Posterior muscles include the triceps brachii, and the anconeus –Anterior muscles include the biceps brachii, brachialis, and the brachioradialis

74 SHOULDER MUSCLES Triceps brachii: cervical nerves: –Powerful forearm extensor Biceps brachii: cervical nerves: –Flexes elbow joint and supinates forearm Brachialis: musculocutaneous nerve: –Major forearm flexor Lifts ulna as biceps lifts the radius Brachioradialis: radial nerve: –Synergist in forearm flexion



77 Forearm Muscles Flexor carpi radialis: median nerve: –Powerful flexor of wrist –Abducts hand Flexor carpi ulnaris: ulnar nerve: –Powerful flexor of wrist –Adducts hand


79 Forearm Muscles Extensor carpi radialis brevis: radial nerve: –Extends and abducts wrist Extensor digitorum: branch of radial nerve: –Prime mover of finger extension –Extends wrist





84 MAJOR SKELETAL MUSCLES OF THE BODY Muscles of the Forearm: Movements of the Wrist, Hand, and Fingers –Anterior superficial muscles include the pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and the flexor digitorum superficialis –Anterior deep muscles include the flexor pollicis longus, flexor digitorum profundus, and the pronator quadratus –Posterior superficial muscles include the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, and the extensor carpi ulnaris –Posterior deep muscles include the supinator, abductor pollicis longus, extensor pollicis longus, and the extensor pollicis brevis

85 MAJOR SKELETAL MUSCLES OF THE BODY Intrinsic muscles of the Hand: Fine Movements of the Fingers –Thenar muscles in ball of thumb include the abductor pollicis brevis, flexor pollicis brevis, opponnens pollicis, and the adductor pollicis –Hypothenar muscles in ball of little finger include the abductor digiti minimi, flexor digiti minimi brevis, and the opponens digiti minimi –Midpalmar muscles include the lumbricals, palmar interossei, and the dorsal interossei

86 Hand Muscles Abductor pollicis brevis: median nerve (cervical.thoracic) –Abducts thumb Flexor digiti minimi brevis: ulnar nerve: –Flexes little finger



89 MAJOR SKELETAL MUSCLES OF THE BODY Muscles Crossing the Hip and Knee Joints: Movements of the Thigh and Leg –Anteromedial muscles include the iliopsoas, which is composed of the iliacus, the psoas major, and the sartorius –Muscles of the medial compartment of the thigh include the adductor group, which is made up of the adductor magnus, adductor longus and the adductor brevis, the pectineus, and the gracilis –Muscles of the anterior compartment of the thigh include the quadriceps femoris group, which is made up of the rectus femoris, vastus lateralis, vastus medialis and vastus intermedius, and the tensor fasciae latae –Posterior Muscles: gluteal muscles (origin on pelvis) include the gluteus maximus, gluteus medius, and the gluteus minimus –Lateral rotators include the piriformis, obturator externus, obturator internus, gemellus, and the quadratus femoris –Muscles of the posterior compartment of the thigh include the hamstring group, which consist of the biceps femoris, semitendinosus, and the semimembranosus

90 Thigh Muscles Adductor longus: obturator nerve: –Adducts, flexes, and medially rotates thigh Gracilis: obturator nerve: –Adducts thigh, flexes, and medially rotates thigh, especially during walking Quadriceps femoris: –Rectus femoris: femoral nerve: Extends knee and flexes thigh at hip



93 Hip Muscles Gluteus maximus: inferior gluteal nerve: –Major extensor of thigh –Complex, powerful, and most effective when thigh is flexed and force is necessary, as in rising from a forward flexed position and in thrusting the thigh posteriorly in climbing stairs and running –Inactive during standing

94 POSTERIOR THIGH MUSCLES Hamstrings: sciatic nerve Biceps femoris Semitendinosus Semimembranosus –Extends thigh and flexes knee



97 MAJOR SKELETAL MUSCLES OF THE BODY Muscles of the Leg: Movements of the Ankle and Toes –Muscles of the anterior compartment include the tibialis anterior, extensor digitorum longus, fibularis (peroneus) tertius, and the extensor hallucis longus –Muscles of the lateral compartment include the fibularis (peroneus) longus and the fibularis (peroneus) brevis –Superficial muscles of the posterior compartment include the triceps surae, which is composed of the gastrocnemius and the soleus, and the plantaris –Deep muscles of the posterior compartment include the popliteus, flexor digitorum longus, flexor hallucis longus, and the tibialis posterior

98 ANTERIOR LEG MUSCLES Tibialis anterior: fibular nerve (lumbar): –Prime mover of dorsiflexion –Inverts foot –Assists in supporting medial longitudinal arch of foot Fibularis longus: fibular nerve (lumbar): –Plantar flexes and everts foot –May help keep foot flat on ground





103 POSTERIOR LEG MUSCLES Gastrocnemius: tibial nerve (sacral): –Plantar flexes foot when knee is extended –Since it also crosses knee joint, it can flex knee when foot is dorsiflexed Soleus: tibial nerve (sacral): –Plantar flexes foot –Important locomotor and postural muscle during walking, running, and dancing







110 MAJOR SKELETAL MUSCLES OF THE BODY Intrinsic Muscles of the Foot: Toe Movement and Arch Support –The muscle found on the dorsum of the foot is the extensor digitorum brevis –Muscles on the sole of the foot found in the first layer are the flexor digitorum brevis, abductor hallucis, and the abductor digiti minimi –Muscles on the sole of the foot found in the second layer are the flexor accessorius (quadratus plantae) and the lumbricals –Muscles of the sole of the foot found in the third layer include the flexor hallicis brevis, adductor hallucis, and the flexor digiti minimi brevis –Muscles of the sole of the foot found in the fourth layer include the plantar and the dorsal interossei

111 Foot Muscles Dorsum Extensor digitorum brevis: fibular nerve (sacral): –Helps extend toes

112 Foot Muscles Sole Flexor digitorum brevis: medial plantar nerve (sacral): –Helps flex toes




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