Abdominal Wall and Thorax

Anatomy and Physiology 1 Laboratory Muscles of the Abdominal Wall & Thorax Objectives 1. Locate the muscles of the abdominal wall and thorax on laboratory charts and models. 2. Recognize on the models the origin, insertion, and action of the muscles of the abdominal wall and thorax. 3. Describe and demonstrate the action of the muscles of the abdominal wall and thorax. a. The muscles of the abdominal wall and thorax are crucial for various functions, including respiration, trunk stability, and movement. Let's break down their actions and demonstrations: b. Muscles of the Abdominal Wall: i. Rectus abdominis: Located in the anterior abdomen, this muscle helps flex the trunk and compress the abdominal contents. To demonstrate its action, you can lie on your back and perform a sit-up motion, where the trunk flexes, and the chest moves towards the knees. ii. External oblique: These muscles are on the sides of the abdomen. Their action includes trunk flexion, rotation, and lateral flexion. To demonstrate, stand upright and bend sideways, bringing one shoulder towards the hip on the same side. iii. Internal oblique: Situated beneath the external oblique, these muscles aid in trunk rotation and lateral flexion. To demonstrate, stand upright and rotate your torso to one side, feeling the muscles engage in the movement. iv. Transversus abdominis: This deep muscle layer contributes to abdominal compression and trunk stability. To demonstrate its action, imagine pulling your belly button in towards your spine, engaging the deep core muscles. c. Muscles of the Thorax: i. Diaphragm: This primary muscle of respiration contracts and flattens during inhalation, expanding the thoracic cavity and aiding in inspiration. To demonstrate, take a deep breath in, expanding the chest as the diaphragm contracts. ii. Intercostal muscles: These muscles are located between the ribs and assist in breathing by expanding and contracting the rib cage during inhalation and exhalation. To demonstrate, place your hands on your sides and breathe deeply, feeling the expansion and contraction of the rib cage with each breath. Anatomy & Physiology, Edited and Revised by Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick, Jon Runyeon Art edited and created by Leeah Whittier, Open Oregon State, Oregon State University, Contributing Author: An adapted version of the OpenStax Anatomy & Physiology with revised content and artwork, 2019 This work is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported <https://creativecommons.org/licenses/by- sa/3.0/deed.en> United States License.

d. These muscles work in coordination to support movements of the trunk, facilitate breathing, and maintain stability during various activities, from simple daily tasks to more complex physical activities. It is a complex job to balance the body on two feet and walk upright. The muscles of the vertebral column, thorax, and abdominal wall extend, flex, and stabilize different parts of the body’s trunk. The deep muscles of the body’s core help maintain posture as well as provide stability for movement of the limbs. Muscles of the Abdomen There are four pairs of abdominal muscles that make up the abdominal wall: the rectus abdominis , the external abdominal obliques , the internal abdominal obliques and the transverse abdominis There are three flat skeletal muscles in the antero-lateral wall of the abdomen. The external oblique , closest to the surface, extend inferiorly and medially, in the direction of sliding one’s four fingers into pants pockets. Perpendicular to it is the intermediate internal oblique , extending superiorly and medially, the direction the thumbs usually go when the other fingers are in the pants pocket. The deep muscle, the transverse abdominis , is arranged transversely around the abdomen, similar to a belt. This arrangement of three bands of muscles in different orientations allows various movements and rotations of the trunk. The three layers of muscle also help to protect the internal abdominal organs in an area where there is no bone. The linea alba is a white, fibrous band that is made of the bilateral rectus sheaths that join at the anterior midline of the body. These enclose the rectus abdominis muscles that originate at the pubic crest and symphysis, and extend the length of the body’s trunk. Each muscle is segmented by three transverse bands of collagen fibers called the tendinous intersections resulting in the look of “six-pack abs”. The posterior abdominal wall is formed by the lumbar vertebrae, parts of the ilia of the hip bones, psoas major and iliacus muscles , and quadratus lumborum muscle . This part of the core plays a key role in stabilizing the rest of the body and maintaining posture. Anatomy & Physiology, Edited and Revised by Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick, Jon Runyeon Art edited and created by Leeah Whittier, Open Oregon State, Oregon State University, Contributing Author: An adapted version of the OpenStax Anatomy & Physiology with revised content and artwork, 2019 This work is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported <https://creativecommons.org/licenses/by- sa/3.0/deed.en> United States License.