Muscles of the Neck, Back, Thorax, Abdomen, and Pelvic Floor

Comprehensive vocabulary flashcards covering the anatomical structure, origin, insertion, innervation, and actions of muscles of the neck, vertebral column, thoracic cage, abdominal wall, and pelvic floor.

Ligamentum nuchae

A strong, elastic ligament extending from the occipital bone of the skull along the tips of the spinous processes of the cervical vertebrae; it binds cervical vertebrae together and inhibits excessive head and neck flexion to prevent spinal cord damage.

Splenius capitis

A broad, superficial "bandage muscle" originating from the ligamentum nuchae and spinous processes of vertebrae $C_7\text{--}T_6$ and inserting onto the mastoid process of the temporal bone and occipital bone; acts to extend or hyperextend the head, and laterally flexes and rotates the head to the same side.

Splenius cervicis

The inferior portion of the splenius muscle group extending from upper thoracic spinous processes to insert into the transverse processes of vertebrae $C_2\text{--}C_4$; acts to extend the cervical spine and rotate/bend the neck laterally toward the same side.

Erector spinae group

The largest deep back muscle group and prime mover of back extension, consisting of three overlapping columns (iliocostalis, longissimus, spinalis) that provide resistance during forward bending and extend the vertebral column to promote return to an erect position.

Iliocostalis

The most lateral column of the erector spinae group (divided into lumborum, thoracis, and cervicis); extends from the iliac crest and ribs to superior ribs and transverse processes of cervical vertebrae $C_4\text{--}C_6$ to extend and laterally flex the vertebral column.

Longissimus

The intermediate column of the erector spinae group (thoracis, cervicis, capitis); runs mainly between transverse processes from the lumbar region to the mastoid process of the temporal bone; extends and laterally flexes the spine and rotates the head.

Spinalis

The most medial column of the erector spinae group (thoracis and cervicis); extends between spinous processes of the upper lumbar/lower thoracic vertebrae and the spinous processes of upper thoracic/cervical vertebrae to extend the vertebral column.

Semispinalis

A composite intrinsic back muscle (thoracis, cervicis, and capitis) positioned profound to the longissimus, running from transverse processes of $C_7\text{--}T_{12}$ to spinous processes of $T_1\text{--}T_4$, cervical vertebrae, and the occipital bone; extends the column and rotates it toward the opposite (contralateral) side.

Quadratus lumborum

A fleshy muscle forming part of the posterior abdominal wall originating from the iliac crest and lumbar fascia and inserting into transverse processes of $L_1\text{--}L_4$ and the lower margin of the 12th rib; laterally flexes the vertebral column individually and extends the lumbar spine when acting jointly.

Contralateral vs. Ipsilateral

"Contralateral" refers to an action or structure located on the opposite side relative to the muscle, whereas "ipsilateral" refers to an action or structure on the same side as the muscle.

Pectoralis minor

A flat, thin anterior thoracic muscle directly beneath and obscured by the pectoralis major; originates from anterior surfaces of ribs 3–5 (or 2–4) and inserts into the coracoid process of the scapula to pull the scapula forward and downward.

Serratus anterior

A fan-shaped muscle known as the "boxer's muscle" arising by fleshy slips from ribs 1–8 (or 9) and inserting onto the anterior medial border of the scapula; prime mover to protract and hold the scapula against the thoracic wall; injury causes "winging" of the scapula.

Subclavius

A small cylindrical muscle of the anterior thorax extending from the costal cartilage of rib 1 to the inferior groove of the clavicle; functions to stabilize and depress the pectoral girdle.

Trapezius

The most superficial, triangular muscle of the posterior thorax originating from the occipital bone, ligamentum nuchae, and spinous processes of $C_7$ through all thoracic vertebrae, inserting along the acromion, scapular spine, and lateral third of the clavicle; stabilizes, elevates, retracts, and rotates the scapula.

Levator scapulae

A thick, straplike muscle at the back and side of the neck deep to the trapezius, originating from transverse processes of $C_1\text{--}C_4$ and inserting onto the medial border of the scapula superior to the spine; elevates and adducts the scapula.

Rhomboids (major and minor)

Two diamond-shaped muscles deep to the trapezius originating from the spinous processes of $C_7\text{--}T_1$ (minor) and $T_2\text{--}T_5$ (major), inserting into the medial border of the scapula; they retract (adduct) and stabilize the scapulae ("squaring shoulders") and rotate the glenoid cavity downward.

External intercostals

Eleven pairs of superficial thoracic muscles whose fibers run obliquely downward and forward from the rib above to the rib below; pull the ribs toward each other to elevate the rib cage and expand thoracic dimensions during inspiration.

Internal intercostals

Eleven pairs of intermediate thoracic muscles located deep to and oriented at right angles to the external intercostals (running downward and posteriorly); they pull the ribs together and depress the rib cage to aid forced expiration.

Diaphragm

A broad, dome-shaped internal muscle pierced by the aorta, inferior vena cava, and esophagus that forms the floor of the thoracic cavity; prime mover of inspiration that flattens upon contraction, expanding vertical thoracic volume; innervated by the phrenic nerves.

Rectus abdominis

A medial, superficial abdominal muscle pair extending from the pubic crest and symphysis to the xiphoid process and costal cartilages of ribs 5–7, segmented by three tendinous intersections; flexes and rotates the lumbar spine and stabilizes the pelvis.

Linea alba

A tendinous median seam ("white line") running from the sternum to the pubic symphysis formed by the fused aponeuroses of the lateral abdominal wall muscles.

Rectus sheath

A snug, fibrous envelope formed by the aponeuroses of the external oblique, internal oblique, and transversus abdominis that encloses the rectus abdominis muscles, preventing them from bowing outward during contraction.

External oblique

The largest and most superficial lateral abdominal muscle whose fibers run downward and medially (inferomedially); its aponeurosis inserts into the linea alba and turns under inferiorly to form the inguinal ligament.

Internal oblique

The intermediate lateral abdominal muscle lying beneath the external oblique, with fibers running primarily upward and medially (superomedially); acts in trunk rotation, lateral flexion, and compressing abdominal viscera.

Transversus abdominis

The deepest muscle of the lateral abdominal wall whose fibers run horizontally across the abdomen; compresses the abdominal contents to support viscera and increase intra-abdominal pressure.

Valsalva maneuver

A maneuver in which the abdominal wall muscles contract forcefully while the airway is closed, elevating intra-abdominal pressure to assist in defecation, urination, childbirth, vomiting, coughing, and heavy lifting.

Direct inguinal hernia

An abdominal protrusion that exits from the abdominal cavity directly forward through the superficial (medial) inguinal ring rather than passing through the entire inguinal canal.

Indirect (oblique) inguinal hernia

A hernia where abdominal contents enter through the deep (lateral) inguinal ring and traverse the length of the inguinal canal, which can extend into the scrotum.

Pelvic diaphragm

The deep, funnel-shaped muscular floor of the pelvis composed of the levator ani and coccygeus muscles; supports the pelvic organs, seals the inferior pelvic outlet, and resists elevated intra-abdominal pressure.

Levator ani

A broad, thin, three-part muscle of the pelvic diaphragm (pubococcygeus, puborectalis, and iliococcygeus) originating from the pubis to the ischial spine and inserting on the coccyx, forming a muscular sling around the urethra, vagina, and anorectal junction.

Coccygeus (Ischiococcygeus)

A small triangular muscle located posterior to the levator ani that originates from the spine of the ischium and inserts on the sacrum and coccyx; supports pelvic viscera and pulls the coccyx forward following defecation and childbirth.

Perineal membrane

A triangular fibrous sheet in the anterior pelvic outlet (historically termed the urogenital diaphragm) situated inferior to the pelvic diaphragm that anchors the external genitalia and fuses anteriorly with the arcuate ligament of the pubis.

Perineal body

A strong central fibromuscular tendon in the median plane of the perineum between the urogenital triangle and the anal triangle where multiple perineal muscles insert.