muscle
(mŭs'ĕl 
)
[L. musculus, diminutive of mus, mouse]
A type of tissue composed of contractile cells. Each muscle cell is filled with parallel actin and myosin filaments. When activated by an internal release of calcium, the filaments use the energy in adenosine triphosphate to crawl along each other in opposite directions. This movement shortens the length of the cell, which then contracts.
The three classes of myocytes (muscle cells) are skeletal (striated), cardiac (striated), and smooth; most human muscle is skeletal. A typical muscle has a central portion (the belly) and two or more attachment ends with tendons. The more stationary of the attachments is called the origin; the more movable attachment is called the insertion.
SEE: illus. MUSCLE FIBER MORPHOLOGICAL FORMS OF MUSCLE.
abdominal m.A collective term for the external and internal abdominal oblique, cremaster, iliacus, psoas major (and minor if present), pyramidalis, quadratus lumborum, rectus abdominis, and transversus abdominis.
abducens m.Lateral rectus muscle
abductor m.A muscle that draws a part away from the median plane of the body or the axial line of an extremity.
SEE: adductor muscle.
abductor digiti minimi m.An instrinsic muscle of the hand , located in the hypothenar eminence. Proximal attachment: pisiform. Distal attachment: base of proximal phalanx of digit 5. Innervation: ulnar (C8-T1). Action: abducts digit 5.
abductor pollicis brevis m.An intrinsic muscle of the hand , located in the thenar eminence. Proximal attachment: flexor retinaculum, scaphoid and trapezium. Distal attachment: lateral side of base of proximal phalanx of thumb. Innervation: median (C8-T1). Action: abducts thumb, aids in opposition with digit 5.
SEE: arm for illus. (Muscles of the Arm).
adductor m.A muscle that draws toward the midline.
SEE: abductor muscle.
adductor brevis m.A muscle of the medial thigh originating on the ramus of the pubis and inserted in the linea aspera of the femur. Proximal attachment: ramus of the pubis. Distal attachment: linea aspera of the femur. It adducts, flexes, and medially rotates the thigh and is innervated by the obturator nerve.
adductor longus m.A muscle of the medial compartment of the thigh. Proximal attachment: pubis. Distal attachment: linea aspera of femur. Nerve: obturator (L2-L4). Action: adducts, flexes, and rotates thigh medially.
SEE: leg for illus. (Muscles of the Leg).
adductor magnus m.A muscle of the medial and posterior compartments of the thigh. Proximal attachment: inferior ramus of pubis, ramus of ischium, ischial tuberosity. Distal attachment: linea aspera and adductor tubercle of femur. Nerve: obturator and sciatic. Action: adducts, flexes, and rotates thigh medially.
SEE: leg for illus. (Muscles of the leg).
adductor pollicis m.An intrinsic muscle of the hand . Proximal attachment: metacarpals 2-3 and the capitate. Distal attachment: proximal phalanx of digit 1. Nerve: ulnar. Action: adducts thumb. SYN: mesothenar.
agonist m.A muscle whose action is opposed by another muscle (the antagonist muscle). Controlled movements involve two opposing muscles. The agonist muscle produces the main action; the antagonist muscle produces the opposite action to a lesser degree. The balance between agonist and antagonist muscles allows precise control of the final action.
SEE: PNF Stretching Techniques
anconeus m.A short muscle along the back of and outside the elbow. It originates from the lateral epicondyle of the humerus, crosses the back of the elbow joint on the same side, attaches to the lateral surface of the olecranon process and the adjacent surface of the ulna. It extends the forearm and abducts the elbow as the forearm pronates. It is innervated by the radial nerve (C7, C8, T1).
SEE: agonist muscle.
antigravity m.Any of the muscles that pull against gravity to maintain normal upright posture. SYN: postural muscle.
appendicular m.Any of the skeletal muscles of the limbs.
arrector pili m.Arrector pili.
arm m.Any of the muscles of the anterior or posterior compartments of the arm: the biceps brachii, brachialis, coracobrachialis, and triceps.
SEE: arm for illus. (Muscles of the Arm).
articular m.A muscle attached to the capsule of a joint.
arytenoid m.Either of two laryngeal muscles, the oblique and the transverse arytenoid. Origins: arytenoid cartilage. Insertions: contralateral arytenoid cartilage. Nerve: recurrent laryngeal. Action: closes laryngeal inlet by bringing arytenoid cartilages toward each other.
auditory m.The tensor tympani and stapedius muscles.
axial m.A skeletal muscle that moves or stabilizes the head or the trunk.
back m.Any of the muscles on the back. They are divided into layers: Superficial: latissimus dorsi and trapezius. Middle layer: levator scapulae, rhomboid major, and rhomboid minor muscles. Deep layer (the true back muscles): erector spinae and splenius. Deepest layer: interspinalis, intertransverse, multifidus, rotatores, semispinalis, and spinalis capitis.
biceps brachii m.One of the arm muscles. Proximal attachment: supraglenoid tubercle, coracoid process of scapula. Distal attachment: tuberosity of radius, posterior border of ulna (via bicipital aponeurosis). Innervation: musculocutaneous (C5-C6). Action: flexes forearm, supinates hand .
SEE: arm for illus. (Muscles of the Arm).
biceps femoris m.One of the muscles of the thigh. Proximal attachment: ischial tuberosity, linea aspera, and second supracondylar ridge of femur. Distal attachment: lateral condyle of tibia, head of fibula. Innervation: sciatic (L5-S2). Action: flexes and laterally rotates leg, extends thigh.
SEE: leg for illus. (Muscles of the Leg).
bipennate m.A muscle in which the fibers converge from both sides to a central tendon.
Variant: brachial muscle
SEE: brachialis; arm for illus. (Muscles of the Arm).
brachioradialis m.A muscle lying on the lateral side of the arm and forearm. It flexes the forearm. Innervation is by the radial nerve. Proximal attachment is the lateral supracondylar ridge of the humerus, distal attachment is the styloid process of the radius.
SEE: arm for illus. (Muscles of the Arm).
buccinator m.A muscle of facial expression. Proximal attachment: pterygomand ibular raphe and alveolar processes of jaws. Distal attachment: orbicularis oris at angle of mouth. Nerve: facial (CN VII). Action: compresses cheek against teeth, retracts angle of mouth.
Variant: bulbocavernous muscle
SEE: bulbocavernosus.
bulbospongiosus m.Bulbocavernosus.
cardiac m.The muscle tissue of the heart. This muscle is packed with mitochondria and contains actin and myosin filaments arranged in myofibrils (cylindrical bundles). In each cell, all the myofibrils are aligned in the same direction and are parceled into longitudinal blocks of similar length (sarcomeres). Microscopically, the ends of the blocks appear as lines, which make the cardiac muscle cells appear to have regular striations. In the muscle tissue, the cardiac muscle cells are connected in branching networks.
Cardiac muscle is innervated by sympathetic and parasympathetic fibers. Cardiac muscle is stimulated by bloodborne molecules, can conduct electrical impulses from cell to cell via intercalated disks, and can independently generate rhythmical contractions.
SEE: table - Comparison of Properties of Three Types of Muscle.
chest wall m.Pectoralis major, pectoralis minor, serratus anterior, subclavius, subscapularis, or teres major muscle.
ciliary m.An internal muscle of the eye. Origin: edges of sclera. Insertion: ciliary process of lens. Nerve: oculomotor (CN III). Action: allows lens to become more curved to focus on near objects.
constrictor m. of pharynx A muscle that constricts the pharynx. It is important for swallowing.
core m.Any of the major muscles that stabilize and control the pressure inside the trunk. These are the pelvic floor, abdominal wall, back, and diaphragm muscles. SYN: core.
corrugator m.One of the facial muscles. Proximal attachment: medial part of supraorbital margin. Distal attachment: skin above middle of eyebrow. Nerve: facial (CN VII). Action: pulls eyebrows toward midline and downward. SYN: Corrugator supercilii.
cremaster m.Spermatic cord muscle. Proximal attachment: inguinal ligament and pubic tubercle. Distal attachment: cremasteric fascia covering spermatic cord. Nerve: genitofemoral (L1-L2). Action: elevates testis in males.
SEE: penis for illus.
cricoarytenoid m.Either of two laryngeal muscles, the lateral or the posterior laryngeal. Proximal attachment: cricoid cartilage. Distal attachment: muscular process of arytenoid cartilage. Nerve: recurrent laryngeal of the vagus (CN X). Action: rotates arytenoid cartilages for vocalizations.
cricothyroid m.One of the laryngeal muscles. Proximal attachment: cricoid cartilage. Distal attachment: lower border of thyroid cartilage. Nerve: superior laryngeal of the vagus (CN X). Action: tenses (stretches) vocal cords.
SEE: thyroid for illus.
deep neck m.Any of the various neck muscles that surround the vertebral column and base of the skull and which are contained in the prevertebral cylinder of deep cervical fascia. All these muscles are innervated by cervical spinal nerves, and most of these muscles act primarily to move and stabilize the head.
deltoid m.One of the muscles of the shoulder. Proximal attachment: lateral third of the clavicle over the acromial process and along the spine of the scapula. Distal attachment: deltoid tuberosity of the humerus. Nerve: axillary (C5-C6). Action: abducts arm.
SEE: arm for illus. (Muscles of the Arm).
detrusor m.The three-layered muscular wall of the urinary bladder. Nerve: primarily parasympathetic (S2-S4), secondarily sympathetic (T11-L2). Action: empties bladder. SYN: detrusor urinae.
diaphragm m.Proximal attachment: internal surfaces of lower six ribs, xiphoid process, vertebral bodies L1-L3. Distal attachment: central tendon (of diaphragm). Nerve: phrenic, lower six intercostals. Action: inflates lungs. SYN: thoracic diaphragm muscle.
digastric m.A neck muscle with two bellies. Proximal attachment: anterior belly attaches to the digastric fossa in mand ible at base of anterior midline; posterior belly attaches to mastoid process. Distal attachment: tendon connecting both bellies in a loop of fascia that is attached to the hyoid. Nerve: anterior belly, trigeminal (CN V; posterior belly, facial (CN VII). Action: depresses mand ible and elevates hyoid.
SEE: neck for illus.
erector spinae m.'sAny of three adjacent vertical band s of deep back muscles, the iliocostalis, longissimus, and spinalis. Origins: a wide tendon running along the iliac crest to the sacrum, the lower lumbar and sacral spinous processes. Insertions: along the back in the angles of the lower ribs, transverse processes of the thoracic and cervical vertebrae. Nerves: dorsal rami of the spinal nerves. Actions: extends (bends backward) the vertebral column and neck, twists the back. SYN: sacrospinalis.
extensor carpi ulnaris m.One of the muscles of the forearm. Proximal attachment: lateral epicondyle of humerus, proximal edge of ulna. Distal attachment: proximal end of fifth metacarpal. Nerve: radial (C7-C8). Action: adducts hand , extends wrist.
SEE: arm for illus. (Muscles of the Arm).
extensor digitorum m.One of the muscles of the forearm. Proximal attachment: lateral epicondyle of humerus. Distal attachment: common extensor tendon of fingers. Nerve: radial (C7-C8). Action: extends fingers and wrist.
SEE: arm for illus. (Muscles of the Arm).
extensor digitorum brevis m.One of the muscles of the foot. Proximal attachment: dorsolateral surface of calcaneus. Distal attachment: extensor tendons of toes. Nerve: deep fibular (S1-S2). Action: extends toes.
SEE: leg for illus. (Muscles of the Leg).
extensor digitorum longus m.One of the muscles of the foot. Proximal attachment: lateral condyle of tibia, upper three-fourths of fibula. Distal attachment: extensor tendons of toes 2-5. Nerve: deep fibular (L5-S1). Action: extends toes, dorsiflexes foot
SEE: leg for illus. (Muscles of the Leg).
extensor hallucis longus m.A muscle of the foot. Proximal attachment: middle of fibula. Distal attachment: base of proximal phalanx of big toe. Nerve: deep fibular (S1-S2). Action: dorsiflexes big toe.
SEE: leg for illus. (Muscles of the Leg).
external intercostal m.Any of the outer layer of muscles between the ribs, originating on the lower margin of each rib and inserted on the upper margin of the next rib. During inspiration, they draw adjacent ribs together, pulling them upward and outward, and increasing the volume of the chest cavity. They are innervated segmentally by the intercostal nerves.
external oblique m.A muscle of the abdominal wall. Proximal attachment: inferior costal margin. Distal attachment: anterior half of iliac crest, rectus sheath, inguinal ligament. Nerve: segmental innervation by intercostals 8-12, iliohypogastric, ilioinguinal (L1). Action: tenses and compresses abdomen, flexes and laterally rotates spine, lowers rib cage.
external pterygoid m.Lateral pterygoid muscle.
ABBR: EOM
Any of six muscles that attach outside the eyeball and move the eye in its socket. The EOM are the inferior and superior oblique muscles, and the lateral, medial, inferior, and superior rectus muscles.SEE: extraocular for illus.
ABBR: EM
Any of the muscles outside an organ that control its position, of the eye or tongue.m. of facial expression Any of the thin muscles that insert into the skin of the face and are innervated by the facial nerve (CN VII). Scalp: frontalis and occipitalis muscles. Ear: anterior, posterior, and superior auricular muscles. Eye: orbicularis oculi. Nose: depressor septi, nasalis, and procerus muscles. Mouth: buccinator, depressor anguli oris, depressor labii inferioris, levator anguli oris, levator labii superioris, mentalis, orbicularis oris, risorius, and zygomaticus muscle. Neck: platysma. SYN: mimetic muscle.
fibularis brevis m.Peroneus brevis muscle.
fibularis longus m.Peroneus longus muscle.
fibularis tertius m.Peroneus tertius muscle.
fixation m.A muscle that steadies a part so that more precise movements in a related structure may be accomplished.
flexor carpi radialis m.One of the muscles of the forearm. Proximal attachment: medial epicondyle of humerus. Distal attachment: bases of second and third metacarpals. Nerve: median (C6-C7). Action: abducts hand , flexes wrist.
SEE: arm for illus.
flexor carpi ulnaris m.One of the muscles of the forearm. Proximal attachment: medial epicondyle of humerus, medial side of olecranon, proximal posterior edge of ulna. Distal attachment: pisiform, hamate, and base of fifth metacarpal. Nerve: ulnar (C7-C8). Action: adducts hand , flexes wrist.
flexor digitorum longus m.One of the muscles of the foot. Proximal attachment: posterior surface of middle tibia. Distal attachment: distal phalanges of toes 2-5. Nerve: tibial (S2-S3). Action: flexes toes 2-5, plantarflexes foot.
SEE: leg for illus. (Muscles of the Leg).
flexor digitorum profundus m.One of the muscles of the forearm. Proximal attachment: proximal three fourths of ulna. Distal attachment: distal phalanges of fingers (digits 2-5). Nerve: ulnar, median (C8-T1). Action: flexes distal finger joints, aids in wrist flexion.
flexor digitorum superficialis m.One of the muscles of the forearm. Proximal attachment: medial epicondyle of humerus, coronoid process of ulna. Distal attachment: middle phalanges of fingers (digits 2-5). Nerve: median (C7-T1). Action: flexes fingers and wrist.
SEE: arm for illus. (Muscles of the Arm).
flexor hallucis longus m.One of the muscles of the foot. Proximal attachment: distal two thirds of posterior tibia. Distal attachment: plantar side of distal phalanx of big toe. Nerve: tibial (S2-S3). Action: flexes big toe, plantarflexes foot.
flexor pollicis brevis m.A muscle of the hand with attachment on the flexor retinaculum and trapezium, trapezoid, and capitate and attached distally on the lateral side of the base of the first phalanx of the thumb. It flexes the thumb at both the carpometacarpal joint and the metacarpophalangeal joint and is controlled by the median and the ulnar nerves.
flexor pollicis longus m.One of the muscles of the forearm. Proximal attachment: coronoid process of ulna, anterior surface of radius. Distal attachment: distal phalanx of thumb. Nerve: median (C8-T1). Action: flexes thumb.
SEE: arm for illus. (Muscles of the Arm).
foot m.Dorsal: dorsal interosseous, extensor digitorum brevis, extensor digitorum longus, extensor hallucis longus, and tibialis anterior muscles. Plantar: abductor digiti minimi, abductor hallucis, adductor hallucis, flexor digitorum brevis, flexor digiti minimi brevis, flexor hallucis brevis, lumbrical, plantar interosseous, and quadratus plantae muscles.
SEE: leg for illus. (Muscles of the Leg).
frontalis m.One of the facial muscles. Proximal attachment: epicranial (scalp) aponeurosis. Distal attachment: skin of eyebrows, root of nose. Nerve: facial (CN VII). Action: elevates eyebrows, wrinkles forehead
fusiform m.A muscle resembling a spindle.
SEE: bipennate muscle for illus.
gastrocnemius m.One of the leg muscles. Origin: medial condyle of femur, lateral condyle of femur. Insertion: calcaneus (via the Achilles tendon). Nerve: tibial (S1-S2). Action: plantarflexes foot, flexes knee.
SEE: leg for illus. (Muscles of the Leg).
gemellus m.Either of two muscles (superior, inferior) that attach to the medial surface of the greater trochanter of the femur (the trochanteric fossa) where they mesh with the tendon of the obturator internus. The superior gemellus arises from the ischial spine and is innervated by the nerve to the obturator internus. The inferior arises from the ischial tuberosity and is innervated by the femoral nerve. Both muscles hold the head of the femur in the acetabulum, rotate (laterally) the thigh in extension, and abduct the thigh when it is flexed.
genioglossus m.A muscle of the tongue. Proximal attachment: genial tubercle on inside of mand ibular symphysis. Distal attachment: ventral tongue, hyoid. Nerve: hypoglossal (CN XII). Action: protrudes and depresses tongue.
gluteus maximus m.One of the thigh muscles. Origin: upper outer edge of ilium and sacrum. Insertion: iliotibial tract of fascia lata, gluteal tuberosity of femur. Nerve: inferior gluteal (L5-S2). Action: extends, abducts, and laterally rotates thigh.
gluteus medius m.One of the thigh muscles. Proximal attachment: upper outer edge of ilium and sacrum. Distal attachment: iliotibial tract of fascia lata, gluteal tuberosity of femur. Nerve: inferior gluteal (L5-S2). Action: extends, abducts, and laterally rotates thigh.
gracilis m.One of the thigh muscles. Proximal attachment: lower half of pubis. Distal attachment: proximal medial tibia. Nerve: obturator (L2-L3). Action: adducts, flexes, and medially rotates thigh.
SEE: leg for illus. (Muscles of the Leg).
hamstring m.Any of the posterior muscles of the thigh that originate on the ischial tuberosity and act across both the hip and knee joints. They are the biceps femoris, gracilis, sartorius, semitendinosus, and semimembranosus muscles.
hand m.Abductor digiti minimi, abductor pollicis brevis, adductor pollicis, dorsal interossei, flexor digiti minimi, flexor pollicis brevis, lumbrical, opponens digiti minimi, opponens pollicis, palmaris brevis, and palmar interossei.
SEE: under Hilton, John.
hyoglossus m.A sheet of muscle extending up from the hyoid bone to the ipsilateral base and sides of the tongue. It depresses the sides of the tongue and is innervated by cranial nerve XII (hypoglossal nerve).
iliacus m.One of the thigh muscles. Proximal attachment: iliac fossa. Distal attachment: lesser trochanter of femur, psoas major tendon. Nerve: femoral (L2-L3). Action: flexes thigh.
iliopsoas m.The iliacus and psoas major muscles considered together.
SEE: leg for illus. (Muscles of the Leg).
inferior oblique m.An extraocular muscle. Proximal attachment: inside front lower margin of the maxillary part of orbit. Distal attachment: lateral surface of eye posterior to its equator. Nerve: oculomotor (CN III). Action: turns eye up and outward with lateral rotation.
SEE: extraocular for illus.
inferior rectus m.An extraocular muscle. Proximal attachment: tendinous ring around optic nerve at rear of orbit. Distal attachment: lower edge of eyeball in front of its equator. Nerve: oculomotor (CN III). Action: turns eye down and medially.
SEE: extraocular for illus.
infraspinatus m.One of the muscles of the shoulder. Proximal attachment: medial two thirds of infraspinatus fossa of scapula. Distal attachment: posterior side of greater tubercle of humerus. Nerve: suprascapular (C4-C6). Action: rotates arm laterally.
internal intercostal m.Any of the muscles between the ribs, lying beneath the external intercostals. During expiration, they pull the ribs downward and inward, decreasing the volume of the chest cavity and contributing to a forced exhalation.
internal pterygoid m.Medial pterygoid muscle.
intrinsic m.A muscle that has both its proximal and distal attachments within a structure, as of the tongue, eye, hand , or foot.
involuntary m.A muscle not under conscious control: smooth, cardiac, and some skeletal muscles.
ischiocavernosus m.A muscle investing the crura of the corpora cavernosa of the penis or clitoris and assisting in their erection.
SEE: Langer muscle.
laryngeal m.Any of six short muscles inside the larynx that move the vocal apparatus and (except for the cricothyroid muscle) are innervated by the recurrent laryngeal branch of the vagus nerve (CN X).
lateral pterygoid m.One of the muscles for chewing. Proximal attachment: greater wing of sphenoid bone, lateral pterygoid plate. Distal attachment: pterygoid fovea of condyle of mand ible. Nerve: trigeminal (CN V). Action: opens mouth, protrudes mand ible. SYN: external pterygoid muscle.
SEE: arm for illus.
lateral rectus m.An extraocular muscle. Proximal attachment: tendinous ring around optic nerve at rear of orbit. Distal attachment: temporal edge of eyeball in front of its equator. Nerve: abducens (CN VI). Action: turns eye laterally. SYN: abducens muscle; abducens oculi.
SEE: extraocular for illus.
latissimus dorsi m.A muscle of the back. Distal attachment: bicipital groove of humerus. Nerve: thoracodorsal (C6-C8). Action: adducts, extends, and medially rotates arm.
leg m.Anterior and lateral: extensor digitorum longus, extensor hallucis longus, peroneus, peroneus longus, peroneus tertius, and tibialis anterior muscles. Posterior: flexor digitorum longus, flexor hallucis longus, gastrocnemius, plantaris, popliteus, soleus, and tibialis posterior muscles.
SEE: leg for illus. (Muscles of the Leg).
levator ani m.The set of pelvic floor muscles, which include the iliococcygeus, levator prostatae or vaginal sphincter, pubococcygeus, and puborectalis muscles. Proximal attachments: insides of pelvic bones (pubis, tendinous arch, ischial spine, and sacrospinous ligament). Distal attachments: perineal body, coccyx, anococcygeal ligament, sacrum. Nerve: pudendal and its branches. Action: supports pelvic viscera, contributes to urethral, vaginal, and anal sphincters.
levator palpebrae m.Eyelid muscle. Proximal attachment: inner roof of orbit. Distal attachment: skin and tarsal plate of upper eyelid. Nerve: oculomotor (CN III). Action: raises upper eyelid.
SEE: extraocular for illus.
lumbrical m.Any of the muscles of the hand and foot. Proximal attachments: tendons of flexor digitorum profundus or flexor digitorum longus. Distal attachments: extensor tendons of digits 2-5. Nerve, hand : median (C8-T1), ulnar (C8-T1). Nerve, foot: medial plantar (S2-S3), lateral plantar (S2-S3). Action: flex the straightened digits (specifically, flex the metacarpophalangeal or metatarsophalangeal joints while extending the interphalangeal joints).
masseter m.One of the muscles for chewing. Proximal attachment: zygomatic process of maxilla, zygomatic arch. Distal attachment: coronoid process, lower half of ramus, and angle of mand ible. Nerve: trigeminal (CN V). Action: elevates mand ible to close jaw
SEE: head for illus.
mastication m.Any of the muscles for chewing, which are innervated by the mand ibular division of the trigeminal nerve (CN V). These muscles include the masseter, temporalis, and medial and lateral pterygoid muscles.SYN: chewing muscle.
medial pterygoid m.One of the muscles for chewing. Proximal attachment: lateral pterygoid plate. Distal attachment: medial surface of ramus and angle of mand ible. Nerve: trigeminal (CN V). Action: closes mouth, protrudes mouth, moves jaw sideways SYN: internal pterygoid muscle.
medial rectus m.An extraocular muscle. Proximal attachment: tendinous ring around optic nerve at apex of orbit. Distal attachment: medial aspect of eye anterior to its equator. Nerve: oculomotor (CN III). Action: adducts eye.
mentalis m.One of the facial muscles. Proximal attachment: incisive fossa of mand ible. Distal attachment: skin of chin. Nerve: facial (CN VII). Action: raises and protrudes lower lip.
mimetic m.Muscle of facial expression.
multipennate m.A muscle with several tendons of proximal and distal attachment, in which fibers pass obliquely between attachments.
SEE: bipennate muscle for illus.
mylohyoid m.Neck muscle. Proximal attachment: mylohyoid line of mand ible. Distal attachment: hyoid bone, mylohyoid raphe. Nerve: trigeminal (CN V). Action: elevates hyoid and larynx, lowers jaw.
nasalis m.. The major muscle of the nose and a muscle of facial expression.
neck m.Anterior and lateral: digastric, geniohyoid, mylohyoid, omohyoid, platysma, sternocleidomastoid, sternohyoid, sternothyroid, stylohyoid, and thyrohyoid muscles. Posterior: levator scapulae, scalene muscles, and trapezius. Suboccipital: obliquus capitis and rectus capitis muscles.
SEE: head for illus.
obturator m.Either of the two muscles (the obturator internus and obturator externus) on each side of the pelvic region that rotate the thighs outward.
occipitofrontalis m.A two-part muscle of the face and scalp. Nerve: the posterior auricular and temporal branches of the facial nerve (cranial nerve VII). Action: elevate the eyebrows and moves the scalp. SYN: epicranius.
opponens pollicis m.A muscle of the hand . It is attached to the trapezium and flexor retinaculum and distally attached to the first metacarpal. It flexes and adducts the thumb (brings it across the palm) and is innervated by the median nerve.
orbicular m.A muscle encircling an opening.
orbicularis oculi m.A facial muscle. Proximal attachment: completely surrounds eye, attaches to medial palpebral ligament (and adjacent bones) and lacrimal crest (and adjacent bones). Distal attachment: medial palpebral raphe (after encircling orbit), lateral palpebral raphe, tarsi of eyelids. Nerve: facial (CN VII) Action: closes eyelids, lifts cheeks, compresses lacrimal sac.
orbicularis oris m.A facial muscle. Proximal attachment: adjacent facial muscles that surround mouth. Distal attachment: into itself and skin of lips while encircling mouth. Nerve: facial (CN VII). Action: closes and purses lips.
m. of the palate Levator veli palatini, musculus uvulae, palatoglossus, palatopharyngeus, pharyngeal constrictor, salpingopharyngeus, and tensor veli palatine muscles.
palmaris longus m.One of the muscles of the forearm. Proximal attachment: medial epicondyle of humerus. Distal attachment: palmar surface of flexor retinaculum, palmar aponeurosis. Nerve: median (C7-C8). Action: flexes hand .
SEE: arm for illus. (Muscles of the Arm).
palpebral m.1The palpebral portion of the orbicularis oculi.
SEE: orbicularis oculi muscle.
2Levator palpebrae superioris.papillary m.Any of the internal conical heart muscles. Proximal attachment: ventricular wall. Distal attachment: tricuspid and biscuspid (mitral) atrioventricular valve leaflets via chordae tendinae. Action: anchor leaflets of valves during heart contractions.
pectinate m.A ridge of myocardium on the inner wall of either atrium of the heart.
pectoralis major m.A muscle of the chest wall. Proximal attachment: medial half of clavicle, sternum, costal cartilages 4-6. Distal attachment: lateral edge of bicipital groove of humerus. Nerve: lateral and medial pectoral (C5-T1). Action: adducts and medially rotates arm.
pectoralis minor m.A muscle of the chest wall. Proximal attachment: anterior medial surface of ribs 3-5. Distal attachment: coracoid process of scapula. Nerve: medial pectoral (C6-C8). Action: pulls shoulder forward and down, elevates rib cage.
peroneus brevis m.The muscle arising from the distal two thirds of the lateral fibula and attaching to the styloid process of the base of the fifth metatarsal. The peroneus brevis assists in plantar flexion of the foot and eversion of the ankle. SYN: fibularis brevis muscle.
peroneus longus m.One of the muscles of the leg. Proximal attachment: lateral two-thirds of fibula. Distal attachment: medial cuneiform bone, base of first metatarsal. Nerve: superficial fibular (peroneal; L5-S1). Action: everts and plantar flexes foot. SYN: fibularis longus muscle.
SEE: leg for illus. (Muscles of the Leg).
peroneus tertius m.The muscle arising from the anterior portion of the distal third of the tibia and the adjacent portion of the interosseous membrane and attaching on the dorsal surface of the fifth metatarsal. It is a secondary contributor to ankle dorsiflexion and eversion. The muscle is absent in a significant proportion of the population. SYN: fibularis tertius muscle.
pharynx and tongue m.Cricothyroid, genioglossus, geniohyoid, hyoglossus, palatoglossus, pharyngeal constrictor, styloglossus, stylopharyngeus, salpingopharyngeus, and thyrohyoid muscles.
piriformis m.One of the thigh muscles. Proximal attachment: anterior surface of sacrum. Distal attachment: upper part of greater trochanter of femur. Nerve: spinal L5-S2. Action: laterally rotates thigh.
platysma m.A muscle of facial expression. Proximal attachment: superficial fascia of anterior aspect of upper thorax. Distal attachment: skin of lower face. Nerve: facial (CN VII). Action: lowers jaw, widens neck
postaxial m.A muscle on the posterior or dorsal aspect of a limb.
postural m.Antigravity muscle.
preaxial m.A muscle on the anterior or ventral aspect of a limb.
procerus m.A muscle of facial expression that links the nose to the forehead. Proximal attachment: the nasal bone. Distal attachments: forehead muscles and skin. Nerves: Buccal branch of cranial nerve VII. Action: It pulls the eyebrows inferiorly.
pronator teres m.An arm muscle. Proximal attachment: medial epicondyle of humerus, coronoid process of ulna. Distal attachment: lateral side of middle of radius. Nerve: median (C6-C7). Action: pronates forearm.
psoas major m.One of the thigh muscles. Proximal attachment: bodies of vertebrae T12-L1. Distal attachment: lesser trochanter of femur. Nerve: lumbar L1-L3. Action: flexes thigh.
pterygoid m.The lateral or the medial pterygoid muscle.
puborectalis m.A pelvic muscle, part of levator ani. Proximal attachment: internal surface of pubis. Distal attachment: joins other levator ani muscles forming part of the bowl-shaped pelvic diaphragm, encircles anal canal, and attaches to sacrum and coccyx. Nerve: inferior rectal and sacral (S4). Action: supports pelvis, tonic contraction pulls anal canal forward to maintain fecal continence. Proximal attachment: internal surface of pubis.
quadriceps m.The rectus femoris, vastus intermedius, vastus lateralis, and vastus medius muscles together.
rectus abdominis m.A muscle of the abdominal wall. Proximal attachment: crest and symphysis of pubis. Distal attachment: xiphoid process, costal cartilages 5-7. Nerve: spinal T7-T12. Action: tenses abdomen, flexes vertebral column.
rectus femoris m.One of the thigh muscles. Proximal attachment: anterior inferior iliac spine, upper edge of acetabulum. Distal attachment: tibial tuberosity. Nerve: femoral (L2-L4). Action: extends leg, flexes thigh.
SEE: leg for illus. (Muscles of the Leg).
red m.Twitch skeletal muscle cells containing myoglobin and many mitochondria. These cells largely generate energy via aerobic oxidation and are suited for maintaining contractions for an extended time.
SEE: white muscle.
m. of respiration Any of the muscles used in breathing, including the diaphragm, the muscles of the rib cage, and the abdominal muscles.
SEE: diaphragm; expiration; inspiration.
rhomboid m.Either of two muscles of the shoulder, the major rhomboid or the minor rhomboid. Proximal attachment: nuchal ligament, spinous processes of vertebrae C7-T5. Distal attachment: vertebral edge of scapula. Nerve: dorsal scapular (C4-C5). Action: pulls scapulae toward each other.
SEE: trunk for illus. (Muscles of the Trunk).
rotator cuff m.Any of the muscles of the shoulder that hold the head of the humerus in the glenoid fossa of the scapula. These muscles are the infraspinatus, subscapularis, supraspinatus, and teres minor.
sartorius m.A long, ribbon-shaped muscle in the leg that flexes, abducts, laterally rotates the thigh, and flexes the lower leg. Proximal attachment: anterior superior iliac spine. Distal attachment: medial side of proximal tibia. Nerve: femoral (L2-L3). Action: flexes thigh and leg, laterally rotates thigh.
SEE: leg for illus. (Muscles of the Leg).
scalene m.Any of three muscles of the neck, the anterior, the middle, or the posterior scalene. Proximal attachments: transverse processes of vertebrae C1-C7. Distal attachments: upper surfaces of ribs 1-2. Nerves: cervical spinal C4-C8. Actions: raises ribs 1-2, bends neck ipsilaterally.
semimembranosus m.One of the thigh muscles. Proximal attachment: ischial tuberosity. Distal attachment: medial condyle of tibia. Nerve: sciatic (L5-S2). Action: extends thigh, flexes and medially rotates leg.
SEE: leg for illus. (Muscles of the Leg).
semitendinosus m.One of the thigh muscles. Proximal attachment: ischial tuberosity. Distal attachment: upper medial aspect of the tibia near tuberosity as part of the pes anserinus. Nerve: sciatic (L5-S2). Action: extends thigh, flexes and medially rotates leg.
SEE: leg for illus. (Muscles of the Leg).
serratus m.Any of several muscles arising from the ribs or vertebrae by separate slips.
serratus anterior m.A chest muscle. Proximal attachment: outer surface of ribs 1-8. Distal attachment: anterior side of medial border of scapula. Nerve: long thoracic (C5-C7). Action: pulls scapula anteriorly and laterally (abduction), rotates scapula upward.
shoulder m.Deltoid, infraspinatus, subscapularis, supraspinatus, teres major and teres minor muscles.
skeletal m.A tissue composed of muscle cells (often multinucleated) that contain neatly packed actin and myosin filaments. These filaments are arranged in myofibrils (cylindrical bundles). In each cell, the myofibrils are all aligned in the same direction and are parceled into sarcomeres (longitudinal blocks) of similar lengths. Under the microscope, the ends of the blocks look like lines, making skeletal muscle cells appear to have regularly arranged striations.
Skeletal muscle is innervated by somatic (as opposed to autonomic) motor axons at a synaptic structure (motor endplate) where acetylcholine is the neurotransmitter. Most skeletal muscles can be controlled consciously, and skeletal muscle is sometimes referred to as voluntary muscle. Skeletal muscle cells contract more forcefully than smooth or cardiac muscle cells.
Skeletal muscle is so called because it usually attaches at one end to bone. Skeletal muscle is by far the most common type of muscle in the body. It plays a major role in normal metabolism, e.g., after a meal, excess glucose is removed from the blood stream primarily by skeletal muscle.
smooth m.A tissue composed of muscle cells that contain loosely organized actin and myosin filaments. Smooth muscle cells do not appear striated when examined under a microscope. Smooth muscle tissue tends to occur as sheets and is typically found in the walls of tubes (such as arteries) and sacs (such as the gastrointestinal system).
Smooth muscles are innervated by both sympathetic and parasympathetic autonomic motor axons; they are also stimulated by bloodborne molecules.
Smooth muscles cannot be consciously controlled, i.e., they are involuntary muscles. Smooth muscle cells contract more slowly and maintain contraction longer than skeletal or cardiac muscle.
SYN: nonstriated muscle; unstriated muscle..SEE: table - Comparison of Properties of Three Types of Muscle.
soleus m.One of the muscles of the leg. Proximal attachment: proximal ends of tibia and fibula. Distal attachment: calcaneus via Achilles tendon. Nerve: tibial (S1-S2). Action: plantarflexes foot.
SEE: leg for illus. (Muscles of the Leg).
somatic m.Muscle derived from mesodermal somites, including most skeletal muscle.
sphincter m.A muscle that encircles a duct, tube, or orifice and controls its opening.
sphincter m. of urinary bladder The smooth muscle fibers around the origin of the urethra that forms the sphincter urethrae in the male. Tonic contraction of this muscle prevents urination; relaxation permits it.
stabilizer m.A muscle that supports a body segment so that muscles attached to it can function.
stapedius m.A muscle of the middle ear. Proximal attachment: posterior wall of middle ear. Distal attachment: neck of stapes. Nerve: facial (CN VII). Action: tilts stapes, dampens excessive vibrations.
sternocleidomastoid m.A neck muscle. Proximal attachment: upper edge of manubrium, middle of upper clavicle. Distal attachment: mastoid process. Nerve: accessory (CN XI), spinal C2. Action: contralaterally rotates head.
SEE: table - Comparison of Properties of Three Types of Muscle.
subscapularis m.One of the muscles of the shoulder. Proximal attachment: medial subscapular fossa. Distal attachment: lesser tubercle of humerus. Nerve: upper and lower subscapular (C5-C7). Action: medially rotates arm.
superior oblique m.An extraocular muscle. Proximal attachment: sphenoid bone deep in medial side of orbit. Distal attachment: lateral surface of eye posterior to its equator. Nerve: trochlear (CN IV). Action: turns eye down and outward with medial rotation.
superior rectus m.An extraocular muscle. Proximal attachment: tendinous ring around optic nerve at apex of orbit. Distal attachment: upper edge of eye in anterior to its equator. Nerve: oculomotor (CN III). Action: turns eye up and medially.
SEE: extraocular for illus.
supraspinatus m.One of the muscles of the shoulder. Proximal attachment: medial supraspinous fossa of scapula. Distal attachment: greater tubercle of humerus. Nerve: suprascapular (C4-C6). Action: abducts arm.
synergistic m.Any of the muscles that each other in function.
temporalis m.One of the muscles for chewing. Proximal attachment: temporal fossa of skull. Distal attachment: coronoid process of mand ible. Nerve: trigeminal (CN V). Action: closes mouth, clenches teeth, retracts jaw.
SEE: head for illus.
tensor fasciae latae m.One of the thigh muscles. Proximal attachment: iliac crest, anterior superior iliac spine. Distal attachment: iliotibial tract of fascia lata. Nerve: superior gluteal (L4-L5). Action: stabilizes (abducts) thigh, extends and laterally rotates leg.
tensor tympani m.Middle ear muscle. Proximal attachment: wall of auditory tube. Distal attachment: hand le of malleus. Nerve: trigeminal (CN V). Action: tenses tympanic membrane, dampens excessive vibrations.
teres major m.One of the muscles of the shoulder. Proximal attachment: lower lateral edge of scapula. Distal attachment: bicipital groove of humerus. Nerve: lower scapular (C6-C7). Action: adducts and medially rotates arm.
teres minor m.One of the muscles of the shoulder. Proximal attachment: upper lateral edge of scapula. Distal attachment: greater tubercle of humerus. Nerve: axillary (C4-C6). Action: laterally rotates arm.
thenar m.The abductor, opponens, or flexor muscle of the thumb.
thigh m.Anterior: iliopsoas, quadriceps (rectus femoris, vastus intermedius, vastus lateralis, and vastus medius), and sartorius. Medial: adductor brevis, adductor longus, adductor magnus, gracilis, and pectineus. Gluteal region: superior and inferior gemellus, gluteus maximus, gluteus medius, gluteus minimus, obturator externus, obturator, internus, piriformis, quadratus femoris, and tensor fasciae lata. Posterior: biceps femoris, semimembranosus, and semitendinosus.
SEE: leg for illus. (Muscles of the Leg).
thoracic diaphragm m.Diaphragm muscle
thyroepiglottic m.A muscle arising on the inner surface of the thyroid cartilage. It extends upward and backward and is inserted on the epiglottis. It depresses the epiglottis.
SEE: thyroarytenoid.
tibialis anterior m.One of the muscles of the leg. Proximal attachment: lateral side of proximal tibia. Distal attachment: medial side of cuneiform bone, base of metatarsal 1. Nerve: deep fibular (L4-L5). Action: inverts and dorsiflexes foot.
tibialis posterior m.One of the muscles of the leg. Proximal attachment: anterior tibia and fibula. Distal attachment: navicular, cuneiform, and cuboid bones; metatarsals 2-4. Nerve: tibial (L4-L5). Action: inverts and plantarflexes foot.
tonic m.A muscle whose fibers contract slowly and cannot propagate an action potential along their cell membranes. Tonic muscles are uncommon in humans and are found only in the extraocular muscles, stapedius muscle, and intrafusal fibers of the muscle spindles. The remainder of human skeletal muscle contains only twitch fibers.
trapezius m.A muscle of the neck and back. Proximal attachment: occipital bone (superior nuchal line), nuchal ligament, spinous processes of vertebrae C7-T12. Distal attachment: posterior edge of lateral clavicle, acromion, posterior edge of spine of scapula. Nerve: accessory (CN XI), spinal C3-C4. Action: elevates, retracts, and rotates scapula.
triangular m.A flat muscle with a broad origin and narrow insertion.
triceps m.One of the arm muscles. Proximal attachment: infraglenoid tubercle of scapula, posterior of proximal humerus, posterior of distal humerus. Distal attachment: olecranon process. Nerve: radial (C6-C8). Action: extends forearm. SYN: triceps brachii muscle.
SEE: arm for illus. (Muscles of the Arm).
triceps brachii m.Triceps muscle.
tricipital m.A muscle with three tendons of origin and a single common insertion.
twitch m.A muscle whose fibers can conduct axon potentials along their cell membranes. Almost all skeletal muscle in humans is twitch muscle. A very few muscles in humans are tonic muscles. Twitch muscles cells can be categorized into a number of types on the basis of the biochemical cycle that they use to produce their energy: red (oxidative), white (glycolytic), or intermediate (oxidative/glycolytic). Most human muscles are composed of a mix of twitch muscle cell types.
unipennate m.A muscle whose fibers converge on only one side of a tendon.
SEE: bipennate muscle for illus.
SEE: Myometrium.
vastus intermedius m.One of the thigh muscles. Proximal attachment: anterior and lateral sides of proximal femur. Distal attachment: common tendon of quadratus muscles, tibial tuberosity via patellar ligament. Nerve: femoral (L2-L4). Action: extends leg.
vastus lateralis m.One of the thigh muscles. Proximal attachment: lateral side of proximal femur. Distal attachment: common tendon of quadratus muscles, tibial tuberosity via patellar ligament. Nerve: femoral (L2-L4). Action: extends leg.
SEE: leg for illus. (Muscles of the Leg).
vastus medialis m.One of the thigh muscles. Proximal attachment: medial side of femur Distal attachment: common tendon of quadratus muscles, tibial tuberosity via patellar ligament. Nerve: femoral (L2-L4). Action: extends leg.
vocalis m.One of the laryngeal muscles. Proximal attachment: midline of inner surface of thyroid cartilage. Distal attachment: arytenoid cartilage. Nerve: recurrent laryngeal of vagus (CN X). Action: changes tension of vocal cords.
voluntary m.A muscle that can be controlled voluntarily. Most skeletal muscles are voluntary.
white m.A muscle composed primarily of fast-twitch fibers.
SEE: red muscle.