A&P lab muscles - head/neck and trunk/shoulder

Head muscles

Facial expression

• Epicranus

• Buccinator

• Platysma

Muscles of mastication

• Masseter

• Temporalis

• Buccinator

• Medial pterygoid

• Lateral ptergoid

Epicranius - frontal and occipital bellies

Comments - bipartite muscle consisting of frontal and occipital bellies, which covers dome of skull

Origin - frontal belly - epicranial aponeurosis; occipital belly - occipital and temperal bones

Insertion - frontal belly - skin of eyebrows and root of nose; occipital belly - epicranial aponeurosis

Action - frontal belly raises eyebrows; occipital belly fixes aponeurosis and pulls scalp posteriorly

Buccinator

Comments - principle muscle of cheek; runs horizontally, deep to the masseter

Origin - molar region of maxilla and mandible

Insertion - obicularis oris

Action - compresses cheek

Platysma

Comments - unpaired, thin, sheetlike superficial neck muscle, plays role in facial expression

Origin - fascia of chest (over pectoral muscles and deltoid)

Insertion - lower margin of mandible, skin, and muscle at corner of mouth

Action - tenses skin of neck

Masseter

Comments - covers lateral aspect of mandibular ramus; can be palpated on forcible closure of jaws

Origin - zygomatic arch and zygomatic bone

Insertion - angle and ramus of mandible

Action - prime mover of jaw closure

Temporalis

Comments - fan-shaped muscle lying over parts of frontal, parietal, and temporal bones

Origin - temporal fossa

Insertion - coronoid process of mandible

Action - closes jaw

Medial pterygoid

Comments - runs along internal (medial) surface of mandible (thus largely concealed by that bone)

Origin - sphenoid, palatine, and maxillary bones

Insertion - medial surface of mandible, near its angle

Action - in conjunction with lateral pterygoid, aids in grinding movements of teeth

Lateral pterygoid

Comments - superior to medial pterygoid

Origin - greater wing of sphenoid bone

Insertion - condylar process of mandible

Action - aids in grinding movements of teeth

Neck muscles - anterolateral

Suprahyoid muscles

• Digastric

• Stylohyoid

• Mylohoid

Infrahyoid muscles

• Sternohyoid

• Sternothyroid

• Omohhyoid

• Thyrohoid

• Sternocleidomastoid

• Scalenes

Digastric

Comments - consists of two bellies united by an intermediate tendon, forming a V shape under the chin

Origin - lower margin of mandible (anterior belly) and mastoid process of temporal bone (posterior belly)

Insertion - by a connective tissue loop to hyoid bone

Action - open mouth and depress mandible

Nerve supply - mandibular branch of trigeminal nerve (cranial V) for anterior belly; facial nerve (cranial VII) for posterior belly

Stylohyoid

Comments - slender muscle below angle of jaw; parallels posteroid belly of digastric muscle

Origin - styloid process of temporal bone

Insertion - hyoid bone

Action - elevates and retracts hyoid

Nerve supply - facial nerve

Mylohoid

Comments - flat, triangular muscle just deep to digastric muscle; this muscle pair makes a sling that forms the floor of the anterior mouth

Origin - medial surface of mandible

Insertion - hyoid bone and median raphe

Action - elevates hyoid bone and floor of mouth

Nerve supply - mandibular branch of trigeminal nerve

Sternohyoid

Comments - most medial muscle of the neck: thin, superficial except inferiorly, where covered by sternocleidomastoid

Origin - manubrium and medial end of clavicle

Insertion - lower margin of hyoid bone

Action - depresses larynx and hyoid bone if mandible is fixed

Nerve supply - cervical spine nerves 1-3 through ansa cervicalis (slender nerve root in cervical plexus)

Sternothyroid

Comments - lateral and deep to sternohyoid

Origin - posterior surface of manubrium of sternum

Insertion - thyroid cartilage

Action - Depresses larynx and hyoid bone

Nerve supply - “as for sternohyoid” - cervical spine nerves 1-3 through ansa cervicalis (slender nerve root in cervical plexus)

Omohyoid

Comments - straplike muscle with two bellies united by an intermediate tendon; lateral to sternohyoid

Origin - superior surface of scapula

Insertion - hyoid bone, lower border

Action - depresses and retracts hyoid bone

Nerve supply - “as for sternohyoid” - cervical spine nerves 1-3 through ansa cervicalis (slender nerve root in cervical plexus)

Thyrohyoid

Comments - appears as a superior continuation of sternothyroid muscle

Origin - thyroid cartilage

Insertion - hyoid bone

Action - depresses hyoid bone or elevates larynx if hyoid is fixed

Nerve supply - first cervical nerve via hypoglossal nerve

Sternocleidomastoid

Comments - two-headed muscle located deep to platysma on anterolateral surface of neck; indicate limits of anterior and posterior triangles of neck

Origin - manubrium of sternum and medial portion of clavicle

Insertion - mastoid process of temporal bone and superior nuchal line of occipital bone

Action - flexion of neck, rotate head toward shoulder on opposite side

Scalenes - anterior, middle, and posterior

Comments - located more on lateral than anterior neck; deep to platysma and sternocleidomastoid

Origin - transverse process of cervical vertebrae

Insertion - anterolaterally on ribs 1-2

Action - elevate ribs (aid in inspiration)

Muscles of the neck and vertebral column: head movements and trunk extension

• Iliocostalis

• Longissimus

• Spinalis

• Semispinalis

• Quadratus lumborum

Splenius

Comments - broad two-part superficial muscle extending from upper thoracic vertebrae to skull; capitis portion known as “bandage muscle” because it covers and holds down deeper neck muscles

Origin - ligamentum nuchae, spinous processes of vertebrae C7-T6

Insertion - mastoid process of temporal bone and occiptial bone (capitis); transverse processes of C2-C4 vertebrae (cervicis)

Action - extend or hyperextend head; prime mover

Errector spinae

Prime mover of back extension/trunk extension

Full length of back

Lifting a load or moving suddenly from a bent over position can injure muscles

Includes iliocostalis, longissimus, and spinalus

Iliocostalis

Comments - most lateral muscle group of erector spinae muscles; extend from pelvis to neck

Origin - iliac crests; inferior 6 ribs (thoracis); ribs 3-6 (cervicis)

Insertion - angles of ribs

rib to rib

Action - extend the vertebral column, laterally flex the vertebral column

Nerve supply - spinal nerves (dorsal rami)

Longissimus

Comments - intermediate 3-part muscle group of erector spinae; extend by many muscle slips from lumbar region to skull; mainly pass between transverse processes of vertebrae

Origin - transverse process

Insertion - transverse process

Action - extend vertebral column; laterally flex the vertebral column; extend and rotate the head

Nerve supply - spinal nerves (dorsal rami)

Spinalis

Comments - most medial muscle column of erector spinae; cervicis usually rudimentary and poorly defined

Origin - spinous process

Insertion - spinous process

Action - extends vertebral column

Nerve supply - spinal nerves (dorsal rami)

Semispinalis

Comments - composite muscle forming part of deep layer of intrinsic back muscles; extends from thoracic region to head

Origin - transverse process

Insertion - spinous process

Action - extends vertebral column and head; synergistically with opposite side

Nerve supply - spinal nerves (dorsal rami)

Quadratus lumborum

Comments - fleshy muscle forming part of posterior adominal wall

Origin - iliac crest and lumbar fascia

Insertion - transverse processes

Action - laterally flexes vertebral column

Nerve supply - T12 and upper lumbar spinal nerves (ventral rami)

Superficial Muscles of the Anterior and Posterior Thorax: Movements of the Scapula and Arm

Extrinsic shoulder muscles

Anterior muscles

• Pectoralis major (arm moving)

• Pectoralis minor (move scapula)

• Seratus anterior (move scapula)

Posterior muscles

• Latissimus dorsi (arm moving)

• Trapezius

• Levator scapulae (move scapula)

• Rhomboids (move scapula)

Pectoralis minor

Comments - flat, thin muscle directly beneath and obscured by pectoralis major

Origin - ribs 3-5 (or 2-4)

Insertion - coracoid process

Action - with ribs fixed, pulls scapula forward and downward

Nerve supply - medial and lateral pectoral nerves

Serratus anterior

Comments - fan shaped muscle; lies deep to scapula, deep and inferior to pectoral muscles on lateral rib cage; forms medial wall of axilla; origins have serrated (sawtooth) appearance; paralysis results in “winging” of vertebral border of scapula away from chest wall, making arm elevation impossible

Origin - ribs

Insertion - medial border of scapula

Action - rotates scapula, prime mover to protract

Nerve supply - long thoracic nerve

Trapezius

Comments - most superficial muscle of posterior thorax; flat and triangular, upper fibers run inferiorly to scapula; middle fibers run horizontally to scapula; lower fibers run superiorly to scapula

Origin - occipital bone, ligamentum nuchae, spinous process, all thoracic vertebrae

Insertion - acromion, spine of scapula, lateral third of clavicle

Action - stabilizes, elevates, retracts, and rotates scapula

Nerve supply - acccessory nerve (cranial XI); C3 and C4

Levator scapulae

Comments - located at back and side of neck, deep to trapezius; thick straplike muscle

Origin - transverse processes

Insertion - medial border scapula

Action - stabilizes, elevates, retracts, and rotates scapula

Nerve supply - cervical spinal nerves and dorsal scapular nerve (C3-C8)

Rhomboids

Comments - two roughly diamond-shaped muscles lying deep to trapezius and inferior to levator scapulae; rhomboid minor is the more superior muscle

Origin - spinous process

Insertion - medial border of scapula

Action - retract (adduct); rotate downward

Nerve supply - dorsal and scapular nerve (C4 and C5)

Deep muscles of the thorax: breathing

• External intercostals

• Internal intercostals

• Diaphragm

External intercostals

Comments - 11 pairs lie between ribs; fibers run obliquely (down and forward) from each rib to rib below; in lower intercostal spaces, fibers are continuous with external oblique muscle, forming part of abdominal wall

Origin - inferior border of rib above

Insertion - superior border of rib below

Action - pull ribs toward one another to elevate rib cage

Nerve supply - intercostal nerves

Internal intercostals

Comments - 11 pairs lie between ribs; fibers run deep to and at right angles to those of external intercostals (ie run downward and posteriorly); lower internal intercostal muscles are continuous with fibers of internal oblique muscle of abdominal wall

Origin - superior border of rib below

Insertion - inferior border of rib above

Action - pull ribs together and depress rib care

Nerve supply - intercostal nerves

Diaphragm

Comments - broad muscle pierced by the aorta, inferior vena cava, and esophagus; forms floor of thoracic cavity; dome shaped in relaxed state; fibers converge from margins of thoracic cage toward a boomerang-shaped central tendon

Origin - surface of rib cage and sternum

Insertion - lumbar vertebrae, central tendon

Action - prime mover of inspiration; flattens on contraction

Muscles of the Abdominal Wall: Trunk Movements and Compression of Abdominal Viscera

• Rectus abdominis

• External obliques

• Internal obliques

• Transversus abdominis

Rectus abdominis

Comments - medial superficial muscle pair; extend from pubis to rib cage; ensheathed by aponeurases of lateral muscles; segmented by three tendinous intersections

Origin - pubic crest and symphysis (not underlined)

Insertion - xiphoid process and costal cartilages of ribs

Action - flex lumbar region of vertebral column

External oblique

Comments - largest and most superficial of the three lateral muscles; fibers run downward and medially

Origin - lower eight ribs

Insertion - linea alba, pubic crest

Action - flex vertebral column and compress abdominal wall; trunk rotation and lateral flexion

Internal oblique

Comments - most fibers run upward and medially; however, the muscle fans so it is inferior fibers run downward and medially

Origin - lumbar fascia, iliac crest, and inguinal ligament

Insertion - linea alba, pubic crest

Action - “as for external oblique” - flex vertebral column and compress abdominal wall; trunk rotation and lateral flexion

Transverse abdominis

Comments - deepest (innermost) muscle of abdominal wall; fibers run horizontally

Origin - inguinal ligament, lumbar fascia, cartilages

Insertion - linea alba, pubic crest

Action - compresses abdominal contents

Muscles of the Pelvic Floor and Perineum: Support of Abdominopelvic Organs

Pelvic floor and perineum: three muscle layers that support the abdominopelvic organs (from inside out, superior to inferior):

1. Pelvic diaphragm (deep) - levator ani, coccygeus

2. urogenital diaphragm (NOW: PERINEAL MEMBRANE)- deep transverse perineal muscle 

3. superficial perineal space (covered by skin) - ischiocavernosus, bulbospongiosus (SAME as bulbocavernosus!), superficial transverse perineal

Levitator ani

Comments - Broad, thin, three-part muscle (pubococcygeus, puborectalis, and iliococcygeus); its fibers extend inferomedially, forming a muscular “sling” around prostate (male) or vagina (female), urethra, and anorectal junction before meeting in the median plane

Origin - extensive linear origin inside pelvis from pubis to ischial spine

Insertion - inner surface of coccyx, levator ani of opposite side, and (in part) into the structures that penetrate it

Action - supports and maintains position of pelvic organs

Coccygeus, now ischiococcygeuus

Comments - Small triangular muscle lying posterior to levator ani; forms posterior part of pelvic diaphragm

Origin - spine of ischium

Insertion - sacrum and coccyx

Action - supports pelvic organs