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The trunk, or torso, is the central part of the body to which the head and limbs are attached. The trunk houses all the vital organs of the human body, except for the brain. The muscles of the trunk include those that move the vertebral column, form the thoracic and abdominal walls, and cover the pelvic outlet. The trunk muscles are divided into two large groups, depending on their location: the anterior trunk muscles and the muscles of the lumbar spine. The mover actions of a muscle refer to the structural location of a muscle and its function.
| Characteristics | Values |
|---|---|
| Definition | The trunk (torso) is the central part of the body to which the head and the limbs are attached. |
| Components | The trunk includes the muscles that move the vertebral column, the muscles that form the thoracic and abdominal walls, and those that cover the pelvic outlet. |
| Muscle Groups | The trunk muscles are divided into two large groups based on their location: the anterior trunk muscles and the muscles of the thoracic cage. |
| Anterior Trunk Muscles | These muscles cover the anterolateral part of the trunk by attaching to the bony framework of the thoracic cage and pelvis. |
| Muscles of the Thoracic Cage | Pectoralis major, pectoralis minor, serratus anterior, subclavius, intercostal (external, internal, and innermost), subcostal, and transversus thoracis muscles, including the diaphragm. |
| Abdominal Wall Muscles | Rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique, and transversus abdominis. |
| Functions | The trunk muscles have various functions, including protecting the thoracic and abdominopelvic viscera and assisting with essential body activities such as breathing, movement, defecation, and micturition. |
| Structural Groups | The structural location of a muscle largely determines its functional group. |
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What You'll Learn
- The diaphragm is a dome-shaped muscle that separates the thoracic and abdominal cavities
- The erector spinae is a large muscle mass that extends from the sacrum to the skull
- The abdominal wall consists of four muscle pairs and fascia
- The lumbar spine muscles are located in the low back and pelvis region
- The intercostal muscles are located in the spaces between the ribs
The diaphragm is a dome-shaped muscle that separates the thoracic and abdominal cavities
The trunk, or torso, is the central part of the body to which the head and limbs are attached. The trunk muscles are divided into two large groups based on their location. They have several important functions, including protecting the thoracic and abdominopelvic viscera and assisting with essential body activities such as breathing, movement, defecation, and micturition.
The diaphragm is composed of three parts: the sternal, costal, and lumbar. The sternal part originates from the posterior aspect of the xiphoid process, while the costal part originates from the internal surfaces of the lower costal cartilages and ribs 7-12. The lumbar part originates from the bodies of vertebrae L1-L3, intervertebral discs, the anterior longitudinal ligament, and the arcuate ligaments. All three parts converge on a central tendon in the middle of the trunk, with no bony insertions.
The diaphragm is pierced by several structures, including the oesophagus, aorta, and inferior vena cava. It also provides a passageway for certain structures from the thorax to the abdomen. The diaphragm is in direct contact with several organs, such as the heart, lungs, liver, stomach, and spleen.
The diaphragm is a crucial muscle that plays a significant role in breathing and other bodily functions. Its contraction and relaxation facilitate inspiration and expiration, respectively, while also assisting with expulsive actions such as coughing, sneezing, vomiting, and defecation.
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The erector spinae is a large muscle mass that extends from the sacrum to the skull
The erector spinae muscles are divided into three groups, from medial to lateral: the spinalis, longissimus, and iliocostalis. The spinalis muscles are the most medial, or closest to the midline of the body, and are the smallest of the three groups. The longissimus muscles are the central erector spinae muscles and are the thickest and longest. The iliocostalis muscles are the most lateral, or farthest from the midline, and are attached to the ribs.
The function of the erector spinae muscles is to straighten and rotate the back, as well as to extend and laterally flex the spine. They work together with the glutes to maintain stable posture, whether standing or sitting. The erector spinae muscles also help to maintain posture by steadying the spine on the pelvis during walking.
The erector spinae muscles play an important role in spinal stability and can be targeted through exercises to strengthen the lower back. However, it is important to exercise caution to avoid injury to the lower back when targeting these muscles directly.
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The abdominal wall consists of four muscle pairs and fascia
The abdominal wall is a complex structure consisting of numerous layers, from superficial to deep. These layers include skin, superficial fascia, muscles and their respective fasciae, and peritoneum. The abdominal wall encases the abdominal cavity and viscera, and it connects the thorax and pelvis. Unlike the thorax and pelvis, the abdomen has no bony reinforcements or protection. Instead, the abdominal wall consists of four muscle pairs arranged in layers and the fascia that envelops them.
The abdominal wall muscles include the rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique, and transversus abdominis. The first three are classified as vertical muscles and are located near the midline. The remaining two are flat muscles located more laterally. The rectus abdominis is a long, paired muscle found on either side of the midline in the abdominal wall. It is split into two by the linea alba. The lateral borders of the muscles create a surface marking known as the linea semilunaris.
The muscles of the anterolateral abdominal wall can be divided into two main groups: the lateral flat muscle group and the anterior vertical muscles. The lateral flat muscle group is situated on either side of the abdomen and includes three muscles: external oblique, internal oblique, and transversus abdominis. The anterior vertical muscles are situated bilaterally to the median fibrous structure called linea alba and are called rectus abdominis and pyramidalis muscles.
The abdominal wall is formed during embryogenesis when the mesoderm develops into the musculature and fascia of the abdominal wall. The abdominal wall receives blood from branches of the abdominal aorta, including the inferior phrenic arteries and four paired lumbar arteries.
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The lumbar spine muscles are located in the low back and pelvis region
The lumbar spine is a five-vertebral bone section of the spine, commonly referred to as the lower back. The lumbar spine supports the weight of the body, protects the spinal cord, and allows for a wide range of body motions. The lumbar spine muscles are located in the low back and pelvis region. These muscles can be divided into posterior and anterior groups, with the trunk muscles divided into four major structural groups, each in its quadrant.
The muscles that attach to the lumbar spine include the latissimus dorsi, a large, flat, wide, triangular-shaped muscle. It starts at the bottom of the sixth thoracic vertebra and the last three or four ribs, covering the width of the middle and lower back. The latissimus dorsi muscle also has its origin in the lower thoracic and lumbar vertebrae, running up to insert into the upper arm bone (humerus). It helps with breathing by lifting the rib cage and aids in maintaining an erect posture.
The iliopsoas, a three-muscle group, moves the hip joint. There is one on each side of the body, and it flexes and stabilises the hip and lower back during walking, running, and getting up from a seated position.
The paraspinals are a group of three muscles located along the length of the spine. The multifidus is another muscle that is targeted by exercises designed to strengthen the lumbar spine.
The lumbar spine and the muscles and ligaments that attach to it allow for a wide range of movements, including walking, running, sitting, and lifting.
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The intercostal muscles are located in the spaces between the ribs
The diaphragm is a large, unpaired, dome-shaped muscle located within the trunk. It separates the thoracic and abdominal cavities and facilitates the passage of anatomical structures through openings called hiatuses. The diaphragm is the main muscle responsible for breathing and inspiration. It also depresses the costal cartilages and receives innervation from the phrenic nerve (C3-C5).
The abdominal wall, which is part of the anterior trunk, consists of four muscle pairs arranged in layers, and the fascia that envelops them. The abdominal wall muscles include the rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique, and transversus abdominis. These muscles form the anterolateral boundary of the abdominal cavity and are involved in movements of the trunk, such as flexion and rotation.
The muscles of the trunk include those that move the vertebral column, form the thoracic and abdominal walls, and cover the pelvic outlet. The erector spinae group of muscles on each side of the vertebral column is a large muscle mass that extends from the sacrum to the skull. These muscles are primarily responsible for extending the vertebral column to maintain an erect posture.
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Frequently asked questions
The trunk, or torso, is the central part of the body to which the head and limbs are attached.
The muscles of the trunk include those that move the vertebral column, the muscles that form the thoracic and abdominal walls, and those that cover the pelvic outlet.
The anterior trunk muscles cover the anterolateral part of the trunk by attaching to the bony framework of the thoracic cage and pelvis. These include the pectoralis major, pectoralis minor, serratus anterior, subclavius, intercostal, subcostal, and transversus thoracis muscles, including the diaphragm.
The diaphragm is a large, dome-shaped, unpaired muscle located within the trunk. It separates the thoracic and abdominal cavities and is responsible for inspiration during breathing.
The abdominal part of the anterior trunk is formed by five muscles: the rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique, and transversus abdominis.
