Bones & Muscles of Trunk and Pelvic Floor

Cervical vertebrae

7 vertebrae located in the neck region.

Thoracic vertebrae

12 vertebrae located in the thorax; articulate with the ribs.

Lumbar vertebrae

5 vertebrae located in the small of the back.

Sacrum

5 fused vertebrae that articulate with the hip bones.

Coccyx

Usually 4 fused coccygeal vertebrae; commonly called the tailbone.

Vertebral column regions

Cervical → thoracic → lumbar → sacrum → coccyx.

Ribs

12 pairs of bones that articulate with the thoracic vertebrae and sternum.

Sternum

Bone of the anterior thorax consisting of the manubrium, body, and xiphoid process.

Manubrium

Superior portion of the sternum.

Body of sternum

Large middle portion of the sternum.

Xiphoid process

Inferior portion of the sternum.

Three regions of the sternum

Manubrium, body, and xiphoid process.

Hip bones

Part of the appendicular skeleton; important attachment sites for muscles.

Three regions of the hip bone

Ilium, ischium, and pubis.

Ilium

Superior region of the hip bone.

Iliac crest

Superior border of the ilium.

Ischium

Posteroinferior portion of the hip bone.

Ischial tuberosity

Part of the ischium commonly called the 'sits bone.'

Pubis

Anterior portion of the hip bone.

Superficial back muscles

Back muscles primarily involved in moving the upper limbs.

Deep back muscles

Back muscles that move and stabilize the vertebral column.

Quadratus lumborum

Deep back muscle that extends and laterally flexes the lumbar vertebral column.

Bilateral action of quadratus lumborum

Both quadratus lumborum muscles together extend the lumbar vertebral column.

Unilateral action of quadratus lumborum

One quadratus lumborum laterally flexes the vertebral column.

Quadratus lumborum location

Extends from the iliac crest of the hip bone toward the lumbar region/rib.

Erector spinae

Group of deep back muscles that extend the vertebral column and help maintain erect posture.

Function of erector spinae

Extends the vertebral column and maintains erect posture.

Three muscles of erector spinae

Iliocostalis, longissimus, and spinalis.

Iliocostalis

Lateral muscle of the erector spinae group.

Longissimus

Intermediate muscle of the erector spinae group.

Spinalis

Medial muscle of the erector spinae group.

Erector spinae arrangement

Lateral to medial: iliocostalis → longissimus → spinalis.

Superficial thorax muscles

Primarily move the upper limbs and are not primarily involved in respiration.

Deep thorax muscles

Include the diaphragm and intercostal muscles involved in respiration.

Diaphragm

Dome-shaped muscle whose contraction pulls its central portion downward, increasing the vertical dimension of the thorax.

Diaphragm attachments

Attaches to the ribs, sternum, and vertebrae.

Diaphragm during inhalation

Contracts and flattens, increasing the vertical dimension of the thoracic cavity.

Diaphragm during exhalation

Relaxes and returns to its dome shape.

External intercostals

Muscles located between adjacent ribs that elevate the ribs during inhalation.

External intercostal fiber direction

Fibers run inferomedially.

Internal intercostals

Muscles between the ribs that depress the ribs during forced exhalation.

Internal intercostal fiber direction

Fibers run inferolaterally.

Main muscle actions during inhalation

Diaphragm contracts and external intercostals elevate the ribs, increasing the dimensions of the thoracic cavity.

Abdominal muscles

Muscles that bilaterally flex the vertebral column and compress the abdominal wall.

Bilateral action of abdominal muscles

Flex the vertebral column and compress the abdominal wall.

Unilateral action of abdominal obliques

External and internal abdominal obliques laterally flex the vertebral column when acting unilaterally.

External abdominal oblique

Abdominal muscle whose fibers run inferomedially; acts in flexion, compression, and lateral flexion of the vertebral column.

External abdominal oblique fiber direction

Fibers run inferomedially, similar to the external intercostals.

Internal abdominal oblique

Abdominal muscle whose fibers run inferolaterally; acts in flexion, compression, and lateral flexion of the vertebral column.

Internal abdominal oblique fiber direction

Fibers run inferolaterally, similar to the internal intercostals.

Transversus abdominis

Abdominal muscle whose fibers run horizontally or straight across the abdomen.

Transversus abdominis fiber direction

Fibers run straight across the abdomen.

Rectus abdominis

Abdominal muscle with fibers running vertically up and down; contributes to flexion of the vertebral column.

Rectus abdominis fiber direction

Fibers run vertically up and down.

"Wash-board abs"

Rectus abdominis.

Muscles that flex the vertebral column

Rectus abdominis and other abdominal muscles; the notes also identify sternocleidomastoid as flexing the head/neck.

Muscles that laterally flex the vertebral column

External abdominal oblique, internal abdominal oblique, and quadratus lumborum.

Pelvis

Bony ring formed by the left and right hip bones and the sacrum.

Pelvic floor muscles

Muscles that attach to the bones of the pelvis and help form the floor of the pelvic cavity.

Pelvic diaphragm

Part of the pelvic floor; formed from 3 separate muscles and described as funnel-shaped.

Shape of pelvic diaphragm

Funnel-shaped.

Functions of the pelvic floor

Closes the inferior opening of the pelvis, supports pelvic organs, and assists with defecation, voluntary urination, and childbirth.

Pelvic floor and pelvic organs

Pelvic floor muscles support the organs located within the pelvis.

Pelvic floor and urination

Pelvic floor muscles assist with the voluntary part of urination.

Pelvic floor and defecation

Pelvic floor muscles assist with defecation.

Pelvic floor and childbirth

Pelvic floor muscles assist with childbirth.

Perineum

Diamond-shaped region between the thighs, commonly described as the crotch.

Two regions of the perineum

Urogenital triangle and anal triangle.

Urogenital triangle

Region of the perineum containing the external genitalia and urethra.

Anal triangle

Region of the perineum containing the anus.

Pelvic organ prolapse

Occurs when damage to the pelvic floor causes pelvic organs to herniate or 'fall.'

Cause of pelvic organ prolapse

Damage or weakening of the pelvic floor.

Possible causes of pelvic floor weakening

Pregnancy, childbirth, older age, obesity, and heavy lifting.

Pelvic organ prolapse treatments

Exercises to strengthen the muscles, devices that help hold the organs in place, or surgery.

Name most superior part of sternum

Manubrium

Name of middle part of sternum

Body

Name of most inferior part of sternum

Xiphoid process

Name yellow part

Ilium

Name green part

Pubis

Name purple part

Ischium

Name this muscle and bone

Quadratus Lumborum (Deep back muscle) and Iliac crest of hip bone

Name blue muscle

Iliocostalis (part of erector spinae)

Name green muscle

Longissimus (part of erector spinae)

Name purple muscle

Spinalis (part of erector spinae)

Name lateral muscle on ribs

External Intercostals

Name medial muscle on ribs

Internal Intercostals

Name muscle

External Abdominal Obliques

Name muscle

Internal Abdominal Obliques

Name muscle that gives six pack abs

Rectus Abdominis

Name muscle

Transversus abdominis

Name muscle in green

Urogenital triangle

Name muscle in purple

Anal triangle