Problem 17 - Anatomy and Physiology of Animals

Question

Which of the following abdominal muscles is not a part of the anterior abdominal wall? a. quadratus lumborum b. rectus abdominis c. interior oblique d. exterior oblique

Step-by-Step Solution

Answer

Quadratus lumborum is not part of the anterior abdominal wall.

Step 1: Understanding the Anterior Abdominal Wall

The anterior abdominal wall is formed primarily by a set of muscles that support and protect the abdominal contents. These muscles include the rectus abdominis, internal oblique, external oblique, and the transverse abdominal muscles.

Step 2: Identifying the Options

Examine each muscle given: rectus abdominis, interior oblique (likely meant as internal oblique), external oblique, and quadratus lumborum. Determine their typical locations in the body.

Step 3: Locating the Quadratus Lumborum

The quadratus lumborum is located in the posterior abdomen, adjacent to the lumbar spine, and plays a role in stabilizing the pelvis and lower back during movement, not part of the anterior abdominal wall.

Step 4: Comparing Options to Anterior Wall Muscles

Rectus abdominis, internal oblique, and external oblique are located on the anterior aspect of the abdominal wall, contributing to movement and posture. Quadratus lumborum does not share this anatomical location.

Step 5: Selecting the Correct Answer

Based on the above observations, quadratus lumborum is the muscle that is not located in the anterior abdominal wall.

Key Concepts

rectus abdominis

The rectus abdominis, commonly referred to as the "abs," is a long, flat muscle that extends down the front of the abdomen. This muscle originates from the pubic symphysis and pubic crest at the base and stretches up to the xiphoid process of the sternum and the costal cartilages of the ribs. Its primary function is to flex the lumbar spine, bringing the ribcage closer to the pelvis.

The rectus abdominis is easily identifiable as it forms the classic "six-pack" appearance in individuals with a low percentage of body fat. Not just for aesthetics, this muscle plays a crucial role in maintaining posture and assisting in movements like crunches. Moreover, it helps stabilize the core during physical activities and protects the internal organs in the abdominal cavity.

internal oblique

The internal oblique muscles are an essential part of the anterior abdominal wall. They are situated on each side of the body, just beneath the external oblique muscles. These muscles originate from the inguinal ligament, iliac crest, and the thoracolumbar fascia, and they insert into the lower ribs and the linea alba.

The internal obliques have several functions:

• They assist in rotating and flexing the trunk. This is useful in movements like twisting the torso.
• Work in conjunction with the external obliques to provide lateral flexion of the spine, bending the body sideways.
• Help in exhalation by pressing the rib cage downward and compressing the abdomen.

These movements are critical for many daily activities, helping maintain posture and balance, as well as protecting the internal organs.

external oblique

The external oblique muscles form the outermost layer of the lateral abdominal muscles. These muscles cover the sides and front of the abdomen and are easily palpable. They originate from the outer surfaces of the lower ribs and insert into the linea alba, pubic crest, and iliac crest, making them quite expansive.

What makes external obliques important?

• They aid in rotating the trunk, especially if contraction occurs on one side.
• They help bend the trunk laterally, as when performing side bends.
• These muscles also help compress the abdominal cavity, assisting in lifting actions for the ribcage during breathing.

Without strong external obliques, activities like throwing or running would be less efficient.

quadratus lumborum

The quadratus lumborum is an integral muscle located in the posterior abdomen. Unlike the muscles discussed above, it is not part of the anterior abdominal wall. This muscle resides deep in the back, attaching from the iliac crest to the 12th rib and the transverse processes of the upper lumbar vertebrae.

The quadratus lumborum has several key roles:

• Stabilizing the pelvis and assisting with the side bending of the lumbar spine.
• Playing a significant role in maintaining posture by supporting the lumbar region during standing or walking.
• Facilitating the elevation of the hip, known as "hip-hiking," useful in activities like walking or hiking uneven terrain.

Despite not being part of the anterior abdominal wall, it works in tandem with other abdominal muscles to ensure core stability and balance.