11.4 Axial Muscles of the Abdominal Wall, and Thorax
3 min read•june 18, 2024
The , thoracic, and muscles form a dynamic system crucial for . These muscle groups work together to protect organs, support posture, and enable movement in daily activities and exercise.
Understanding how these muscles function is key to grasping their roles in breathing, organ support, and body mechanics. Their coordinated actions impact everything from maintaining continence to powering athletic performance and preventing injuries.
Abdominal Wall Muscles
Structure of abdominal muscles
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- Outermost layer of abdominal muscles runs inferiorly and medially from lower ribs to and (midline raphe)
- Compresses and supports abdominal viscera (organs), flexes and rotates trunk (sit-ups, twisting motions)
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- Middle layer of abdominal muscles runs perpendicular to external obliques, superiorly and medially from to lower ribs and
- Compresses and supports abdominal viscera, flexes and rotates trunk in opposite direction of external obliques (stabilizes spine during rotational movements)
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- Innermost layer of abdominal muscles runs horizontally around the abdomen, attaching to lower ribs, iliac crest, and pubic bone
- Compresses and supports abdominal viscera, stabilizes the spine and pelvis (acts like a corset)
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- Paired, vertical muscles on the anterior abdominal wall separated by the linea alba, attaches to and
- Flexes the trunk (crunches), compresses abdominal viscera (increases intra-abdominal pressure)
- These muscles collectively form the abdominal wall, which provides protection and support for internal organs
Thoracic Muscles and Breathing
Breathing mechanics of thoracic muscles
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- Dome-shaped muscle separating thoracic and abdominal cavities, attaches to lower ribs, sternum, and lumbar vertebrae
- Contraction flattens the , increasing vertical dimension of ()
- Relaxation allows the diaphragm to rise, decreasing vertical dimension of ()
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- Fibers run inferiorly and anteriorly from rib to rib
- Contraction elevates the ribs, increasing anteroposterior and transverse dimensions of thoracic cavity (inhalation)
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- Fibers run inferiorly and posteriorly from rib to rib
- Contraction depresses the ribs, decreasing anteroposterior and transverse dimensions of thoracic cavity (exhalation)
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- Breathing mechanism
- Inhalation: Diaphragm contracts and flattens, external intercostals contract and elevate ribs, increasing thoracic cavity size and decreasing pressure, causing air to flow into lungs
- Exhalation: Diaphragm relaxes and rises, internal intercostals contract and depress ribs, decreasing thoracic cavity size and increasing pressure, causing air to flow out of lungs
- These muscles are collectively known as and play a crucial role in the mechanics of breathing within the
Pelvic Floor and Perineal Muscles
Pelvic vs perineal muscle functions
- Pelvic floor muscles
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- Broad, thin muscle forming the floor of the pelvic cavity, attaches to pubic bone, ischial spine, and coccyx
- Supports pelvic organs (bladder, uterus, rectum), resists intra-abdominal pressure (prevents )
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- Triangular muscle extending from ischial spine to coccyx
- Supports the posterior pelvic floor, assists in stabilizing the sacrum and coccyx
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- Superficial perineal muscles
- , , and
- Support and control external genitalia (erection, ejaculation) and urethral sphincter (urinary continence)
- Deep perineal muscles
- and
- Control opening and closing of anus (fecal continence) and urethra (urinary continence)
- Superficial perineal muscles
- Roles in excretory and reproductive functions
- Pelvic floor muscles
- Maintain continence by supporting bladder and rectum, prevent prolapse
- Aid in childbirth by relaxing and stretching during delivery, support uterus during pregnancy
- Perineal muscles
- Control voluntary urination and defecation by regulating external urethral and anal sphincters
- Support and control external genitalia during sexual function (erection, ejaculation, orgasm)
- Pelvic floor muscles
- The , formed by these muscles, plays a crucial role in maintaining pelvic organ position and function
Core Stability and Functional Integration
- Abdominal wall muscles, thoracic muscles, and pelvic floor muscles work together to provide core stability
- This integrated system helps maintain posture, support the spine, and facilitate efficient movement
- Core stability is essential for everyday activities, athletic performance, and injury prevention
Key Terms to Review (58)
Abdominal Wall: The abdominal wall is the layered structure that forms the anterior and lateral walls of the abdomen. It is responsible for protecting the internal organs, facilitating movement, and supporting the body's core.
Anal triangle: The anal triangle is a region of the human body located in the perineum that encompasses the anus and its surrounding structures. It's distinguished from the urogenital triangle in anatomy, focusing on supporting and controlling the excretory functions.
Bulbospongiosus: The bulbospongiosus is a muscle located in the perineum, the region between the genitals and the anus. It is part of the superficial perineal muscles and plays a role in the functioning of the urinary and reproductive systems.
Caval opening: The caval opening is an aperture in the diaphragm that allows the passage of the inferior vena cava, transmitting deoxygenated blood from the lower body to the heart. It is located at the level of the eighth thoracic vertebra.
Coccygeus: The coccygeus is a small muscle located in the pelvic floor that attaches the coccyx (tailbone) to the pelvic bone. It plays a role in supporting the pelvic organs and stabilizing the coccyx during movement.
Compressor urethrae: The compressor urethrae is a muscle that assists in the voluntary control of urination by compressing the urethra, aiding in the stoppage of urine flow. It is part of the pelvic floor muscles and plays a critical role in the mechanism of continence.
Core Stability: Core stability refers to the ability of the muscles in the abdominal wall and thorax to maintain proper alignment and support the spine during movement and physical activities. It is a crucial component of overall physical function and performance.
Deep transverse perineal: The deep transverse perineal muscle is a muscle of the perineum that supports the pelvic floor and helps stabilize the central tendon of the perineum. It plays a crucial role in maintaining continence as part of the pelvic diaphragm.
Diaphragm: The diaphragm is a dome-shaped sheet of muscle and tendon that serves as the primary muscle for respiration, separating the thoracic (chest) cavity from the abdominal cavity. It contracts and flattens when you inhale, allowing the lungs to expand and fill with air, and relaxes and domes upwards during exhalation, pushing air out of the lungs.
Diaphragm: The diaphragm is a dome-shaped muscle that separates the thoracic and abdominal cavities. It is the primary muscle of respiration, playing a crucial role in the process of breathing and gas exchange within the body.
Exhalation: Exhalation is the process of expelling air from the lungs, which occurs as part of the respiratory cycle. It involves the contraction of the abdominal muscles and the relaxation of the diaphragm, leading to the expulsion of air from the body.
External Anal Sphincter: The external anal sphincter is a ring-shaped muscle that surrounds the anal canal and plays a crucial role in maintaining continence by controlling the opening and closing of the anus. It is an important component of the pelvic floor and is closely associated with the axial muscles of the abdominal wall and thorax.
External intercostal: External intercostal muscles are a group of skeletal muscles located between the ribs that expand the chest cavity to facilitate inhalation. They contract during breathing in, elevating the ribs and increasing the space in the thoracic cavity.
External Intercostals: The external intercostals are a group of skeletal muscles located between the ribs that play a crucial role in the process of breathing, gas exchange, and the movement of the abdominal wall.
External oblique: The external oblique is a large, thin layer of muscle located on the lateral and anterior parts of the abdomen. Its primary function includes assisting in the rotation and lateral flexion of the trunk, as well as helping to compress the abdominal cavity.
External Obliques: The external oblique muscles are a pair of broad, flat muscles located on the lateral aspects of the abdominal wall. They play a crucial role in the axial musculature of the abdomen and thorax, contributing to core stability, trunk rotation, and various other functions.
External Urethral Sphincter: The external urethral sphincter is a circular muscle that surrounds the urethra and helps control the release of urine from the bladder. It is an important component of the urinary system and plays a crucial role in maintaining continence.
Iliac crest: The iliac crest is the upper, curved edge of the ilium, which is one of three bones that make up the hip bone. It serves as an attachment point for several muscles and ligaments in the lower body.
Iliac Crest: The iliac crest is the curved upper border of the ilium, the largest part of the hip bone. It serves as an important anatomical landmark and attachment site for various muscles and ligaments in the body.
Iliococcygeus: The iliococcygeus is a muscle that forms part of the pelvic floor, specifically within the levator ani muscle group. It extends from the ilium's spine to the coccyx (tailbone), acting to support pelvic organs and maintain continence.
Inhalation: Inhalation is the process of drawing air into the lungs during breathing. It is the first phase of the respiratory cycle, where air is taken in through the nose or mouth and travels down the respiratory tract to the alveoli in the lungs, allowing for the exchange of oxygen and carbon dioxide.
Innermost intercostal: The innermost intercostals are muscles located deep within the ribcage, specifically between the ribs, and play a crucial role in facilitating breathing by aiding in the contraction and expansion of the chest. They are part of a group of three intercostal muscle layers that contribute to the mechanical aspect of breathing.
Intercostal muscles: Intercostal muscles are groups of muscles found between the ribs that help form and move the chest wall. They are primarily involved in the mechanical aspect of breathing, assisting with the expansion and contraction of the thoracic cavity to facilitate respiration.
Intercostal Muscles: The intercostal muscles are a group of skeletal muscles located between the ribs that play a crucial role in the mechanics of breathing and the structural integrity of the thoracic cavity. These muscles are closely associated with the respiratory system, the thoracic cage, and the abdominal wall.
Internal intercostal: The internal intercostal muscles are a group of skeletal muscles located between the ribs that assist with the process of breathing by helping to lower the rib cage and decrease the volume of the thoracic cavity during exhalation. They are found deep to the external intercostal muscles and run in a direction opposite to them.
Internal Intercostals: The internal intercostals are a set of muscles located between the ribs that play a crucial role in the process of breathing and the movement of the abdominal wall. These muscles are part of the axial musculature and contribute to the overall function of the thoracic and abdominal regions.
Internal oblique: The internal oblique is a muscle of the abdominal wall that lies beneath the external oblique and above the transverse abdominis. It helps in rotating and side-bending the trunk, as well as providing support for abdominal contents.
Internal Obliques: The internal oblique muscles are a pair of flat, broad muscles that make up part of the lateral abdominal wall. They are responsible for various functions related to the abdominal wall and thorax, including trunk rotation, flexion, and stabilization.
Ischiocavernosus: The ischiocavernosus is a muscle located in the perineum that plays a role in sexual function. It is one of the muscles that forms the floor of the pelvis and is involved in the erection and ejaculation processes.
Ischiococcygeus: The ischiococcygeus muscle, part of the pelvic floor muscles, extends from the ischium's spine to the coccyx, aiding in supporting the pelvic organs. It acts alongside other pelvic muscles to maintain pelvic floor integrity and assist in minor movements of the coccyx.
Levator ani: The levator ani is a broad, thin muscle group situated on either side of the pelvis, functioning primarily to support the pelvic viscera (organs) and maintain continence as part of the pelvic floor. It consists of three muscles: the pubococcygeus, iliococcygeus, and puborectalis.
Levator Ani: The levator ani is a group of muscles that form the floor of the pelvic cavity and play a crucial role in supporting the pelvic organs, maintaining continence, and assisting in defecation and childbirth. This muscle group is an important component of the axial musculature of the abdominal wall and thorax.
Linea alba: The linea alba is a fibrous structure that runs vertically down the middle of the abdomen, connecting the left and right abdominal muscles. It is made up of collagen fibers and serves as an attachment point for these muscles.
Linea Alba: The linea alba is a tendinous intersection or band of connective tissue that runs vertically along the midline of the abdominal wall, from the xiphoid process of the sternum to the pubic symphysis. It serves as an important landmark and attachment point for various abdominal muscles.
Pelvic diaphragm: The pelvic diaphragm is a structure formed by the levator ani and coccygeus muscles, stretching across the pelvic cavity to support the organs within it. It plays a crucial role in maintaining continence and supporting the rectum, bladder, and, in females, the uterus.
Pelvic Diaphragm: The pelvic diaphragm is a muscular structure that forms the floor of the pelvic cavity and supports the pelvic organs. It is an important component of the axial musculature and plays a crucial role in maintaining the integrity of the thoracic and abdominal cavities.
Pelvic Floor: The pelvic floor is a group of muscles and connective tissues that form a hammock-like structure at the base of the pelvis. It plays a crucial role in supporting the pelvic organs, maintaining continence, and facilitating functions such as urination, defecation, and sexual activity.
Perineal Muscles: The perineal muscles are a group of muscles located in the pelvic floor region, responsible for supporting the pelvic organs and maintaining continence. These muscles are an important component of the axial musculature, specifically in the context of the abdominal wall and thorax.
Perineum: The perineum is the anatomical region in humans located between the pubic symphysis and the coccyx, encompassing the pelvic floor and the structures it contains in both males and females. This area supports the structures of the urogenital triangle anteriorly and the anal triangle posteriorly, playing a critical role in bodily functions such as urination and defecation.
Prolapse: Prolapse refers to the abnormal descent or protrusion of an organ or structure from its normal position within the body. This term is particularly relevant in the context of the axial muscles of the abdominal wall and thorax, where prolapse can occur due to weakened or damaged supporting structures.
Pubic Crest: The pubic crest is a prominent ridge of bone located at the superior aspect of the pubic symphysis, forming the inferior boundary of the anterior abdominal wall. It serves as an important anatomical landmark and attachment site for various muscles and ligaments.
Pubococcygeus: The pubococcygeus is a muscle that stretches from the pubic bone to the coccyx, forming part of the pelvic floor and supporting the pelvic organs. It plays a crucial role in urinary continence and sexual function.
Quadratus lumborum: The quadratus lumborum is a deep muscle in the lower back, situated on either side of the lumbar spine, connecting the iliac crest to the lower ribs and vertebral column. It aids in stabilizing the pelvis and spine, especially during movement or lifting.
Rectus abdominis: The rectus abdominis is a long, flat muscle that extends along the front of the abdomen. It is crucial for maintaining posture and facilitating movements such as bending forward at the waist.
Rectus Abdominis: The rectus abdominis is a paired muscle that runs vertically along the front of the abdomen. It is a key muscle involved in core stability, posture, and various movements of the trunk and spine.
Rectus sheaths: Rectus sheaths are fibrous sleeves that enclose the rectus abdominis muscles, providing structural support and protection. They are formed by the aponeuroses of the three flat abdominal muscles (external oblique, internal oblique, and transversus abdominis) wrapping around these vertically oriented muscles.
Respiratory Muscles: Respiratory muscles are the skeletal muscles responsible for the mechanical process of breathing, allowing for the inhalation and exhalation of air. These muscles play a crucial role in the respiratory system by facilitating the expansion and contraction of the thoracic cavity, enabling the lungs to draw in and expel air.
Sphincter urethrovaginalis: The sphincter urethrovaginalis is a muscle in women that surrounds the urethra and the vagina, aiding in the control of urination. It functions to constrict these passages, playing a crucial role in urinary continence.
Superficial Transverse Perineal Muscles: The superficial transverse perineal muscles are a pair of small, flat muscles located in the perineal region. They are part of the axial musculature and play a role in supporting the pelvic floor and maintaining the integrity of the perineal body.
Tendinous intersections: Tendinous intersections are bands of connective tissue that transect the muscle fibers of certain muscles, notably the rectus abdominis in the abdominal wall. These intersections segment the muscle into multiple parts, giving it a segmented appearance.
Thoracic cavity: The thoracic cavity is the area of the body located between the neck and the abdomen, enclosed by the rib cage, and containing organs such as the heart and lungs. It plays a vital role in the respiratory and circulatory systems.
Thoracic Cavity: The thoracic cavity is the central compartment of the body, located between the diaphragm and the neck, that houses the heart, lungs, and other vital organs. It is an essential component of the body's respiratory and cardiovascular systems, playing a crucial role in various physiological processes.
Thorax: The thorax is the part of the body located between the neck and the abdomen, commonly referred to as the chest area. It houses essential organs such as the heart and lungs and is enclosed by the rib cage, which provides structural support and protection. The thorax plays a crucial role in respiration and is integral to the muscular system, particularly concerning movement and stability in both the axial muscles of the abdominal wall and associated structures.
Transversus abdominis: The transversus abdominis is a muscle located on the lateral sides of the abdominal wall, beneath the internal oblique muscle. It acts to compress the abdominal contents, playing a crucial role in maintaining abdominal pressure and stabilizing the spine.
Transversus Abdominis: The transversus abdominis is a flat, sheet-like muscle that forms the innermost layer of the abdominal wall. It plays a crucial role in stabilizing the trunk and assisting in various abdominal functions.
Urogenital triangle: The urogenital triangle is the anterior half of the perineum that includes the external genitalia and urethra in both sexes, playing a key role in urinary excretion and reproductive functions. It is bounded by the pubic symphysis anteriorly, and laterally by the ischiopubic rami, forming an important part of the pelvic floor muscles.
Xiphoid process: The xiphoid process is a small, cartilaginous projection at the lower end of the sternum, which becomes ossified (turned into bone) in adults. It serves as an attachment point for various muscles and ligaments involved in the functioning of the diaphragm, abdominal wall, and thoracic cage.
Xiphoid Process: The xiphoid process is a small, pointed projection of bone at the lower end of the sternum, the central bone of the chest wall. It serves as an attachment point for several muscles and ligaments, and its position and shape can vary among individuals.