Muscles of the Trunk

Diaphragm

ventilation

Action: lowers the floor of the thoracic cavity during inspiration

Origin: sternum, lower ribs, and lumbar vertebrae

Insertion: central tendon of diaphragm

Dome-shaped muscle that separates the thoracic and abdominopelvic body cavities

contracts and flattens and pulls the thoracic cavity and lungs with it, increasing the size and volume of the lungs causing Inspiration

when diaphragm relaxes, the volume of the thoracic cavity decreases, causing Passive Expiration

External & internal intercostals

ventilation

External intercostals raise and spread the ribs to assist with inspiration

Internal intercostals depress the rib cage, causing forced expiration

Sternocleidomastoid & scalenes

ventilation

Assist with forced inspiration by elevating the rib cage

Rectus abdominis

Action: flexes the trunk and compresses the abdomen

Origin: superior part of pubic bones

Insertion: costal cartilage of ribs 5–7

Superficial muscle of the anterior abdomen

powerful flexor of the trunk

enclosed by the Rectus Sheath, formed by fibers from other abdominal muscles with a central tendon along the midline called the Linea Alba

muscle is divided into sections by bands of dense regular collagenous connective tissue that create “six-pack abs” look

Transversus abdominis

Action: compresses the abdominal cavity

Origin: lower six costal cartilages

Insertion: pubic bone

Compresses the abdominal cavity, which raises intra-abdominal pressure

Internal oblique

Action: flexes and rotates the vertebral column and compresses the abdomen

Origin: iliac crest

Insertion: lower four ribs

rotate the trunk and flex it laterally

External oblique

Action: flexes and rotates the vertebral column and compresses the abdomen

Origin: lower eight ribs

Insertion: pubic and iliac crests

rotate the trunk and flex it laterally

Trapezius

Action: extends the head and elevates the scapula

Origin: occipital bone and cervical vertebrae

Insertion: clavicle

Rhomboid major & minor

Action: retract the scapula

Origin: spinous processes of C7–T1 and T1–T5

Insertion: scapula

Teres major

Action: adducts, extends, and rotates the arm laterally

Origin: posterior and inferior part of scapula

Insertion: medial sulcus of humerus

Erector spinae muscle group

Nine muscles arranged in three columns along each side of the vertebral column

important postural muscles and powerful extensors of the vertebral column

What are the 3 columns of the erector spinae?

Iliocostalis = lateral column

Longissimus = middle column

Spinalis = medial column

Iliocostalis muscles

lateral column

Iliocostalis lumborum( in the lower back), iliocostalis thoracis (in the mid back), iliocostalis cervicis (in the neck)

Longissimus muscles

middle column

Longissimus thoracis (in the lower back) , longissimus cervicis (in the neck), and longissimus capitis (inserts into the mastoid process in the head)

Spinalis muscles

medial column

Spinalis thoracis, spinalis cervicis, and spinalis capitis

Transversospinal group

Semispinalis, multifidus, and rotatores

actions are similar to the those of the erector spinae muscle group

generally extend the head, neck, and vertebral column

Quadratus lumborum

Helps extend and laterally flex the vertebral column

Pelvic floor / pelvic diaphragm

Broad, flat sheet of muscle that supports the organs within the pelvis

formed by the levator ani muscle group

Levator ani muscle group

Includes the anterior pubococcygeus, middle iliococcygeus, and posterior ischiococcygeus muscles

supports the pelvic floor, anal canal, and genitourinary organs

Pubococcygeus, iliococcygeus & ischiococcygeus

Three muscles of the levator ani group

They help support the pelvic floor

the anococcygeal ligament extends from the rectum to the coccyxserves as an insertion site for these muscles

Perineum

Diamond-shaped region inferior to the pelvic diaphragm, between the proximal thighs

contains the external genitalia and opening of the anus

Urogenital diaphragm

Contains the external urethral sphincter and deep transverse perineal muscle

The urethra passes through it in males

the urethra and vagina pass through it in females

External urethral sphincter

Surrounds the urethra and provides voluntary control of urination

Circular muscle that surrounds the vagina in the female

Deep transverse perineal muscle

Supports the genitourinary/pelvic organs and helps fix the perineal body (central tendon)

External anal sphincter

Surrounds the anus and provides voluntary control of defecation

attaches to the perineal body/central perineal tendon

Superficial transverse perineal muscles

Help stabilize the perineal body

Bulbospongiosus & ischiocavernosus

Aid erection of the external genitalia during sexual excitement

The bulbospongiosus also helps expel semen and urine from the urethra in males

constricts the vaginal opening in females

the ischiocavernosus helps maintain erection

Kegel exercises

Pelvic floor exercises involving repeated contraction and relaxation of the levator ani muscle

used to strengthen the pelvic floor and help treat urinary incontinence