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The trunk of the body, or torso, is the central, main part to which the head and limbs are attached. The trunk houses all the vital organs of the human body, including the heart, lungs, stomach, liver, small intestines, large intestines, pancreas, gall bladder, and oesophagus. The trunk muscles are all of the muscles of the axial skeleton and are responsible for making and keeping the body erect, sitting, standing, and maintaining posture. These muscles also assist essential body activities such as breathing, movement, defecation, and micturition.
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What You'll Learn
The trunk houses all vital organs except the brain
The trunk, or torso, is the central part of the human body, not counting the head and limbs. It houses all vital organs except the brain. These vital organs include the heart, lungs, liver, kidneys, and pancreas. The heart and lungs are protected by the rib cage in the upper chest, while the abdomen contains most of the organs responsible for digestion, including the stomach, liver, gallbladder, large and small intestines, and pancreas. The pelvic region houses the male and female reproductive organs.
The trunk also contains several muscle groups, including the pectoral, abdominal, lateral, and epaxial muscles. The diaphragm, a large, dome-shaped muscle, separates the thoracic and abdominal cavities and facilitates breathing. The abdominal wall consists of four muscle pairs and their fascia. The anterior trunk muscles include the thoracic cage muscles (such as the pectoralis major and minor, serratus anterior, and intercostal muscles) and the abdominal wall muscles (such as the rectus abdominis, external and internal abdominal obliques, and transversus abdominis). These muscles contribute to essential body activities such as breathing, movement, defecation, and micturition.
The trunk muscles can be divided into two large groups based on their location: those that attach to the skeletal core of the trunk and those that form the thoracic and abdominal walls. The erector spinae muscles, for example, are a large muscle mass on each side of the vertebral column that helps maintain erect posture. The intercostal muscles between the ribs assist with breathing by contracting during forced expiration and inspiration.
The trunk houses all these vital organs and muscles, which work together to ensure the body's survival and perform essential functions. The brain, being the control center of the body, is notably located outside the trunk in the head, where it governs nerve impulses, thoughts, emotions, and physical sensations.
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Axial muscles help move the body as a whole
The axial muscles are those that originate on the axial skeleton, which includes the bones in the head, neck, and core of the body. These muscles are involved in moving the joints of the axial skeleton and are grouped based on location, function, or both.
The axial 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 erector spinae group of muscles, for example, is a large muscle mass that extends from the sacrum to the skull and is responsible for extending the vertebral column to maintain an erect posture. The intercostal muscles, located in the spaces between the ribs, are involved in breathing and contract during forced expiration.
The abdominal wall is composed of four muscle pairs and their fascia. These muscles include the rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique, and transversus abdominis. They are involved in movements of the trunk, such as flexion and rotation, and also contribute to changing intra-abdominal pressure, which is essential for basic bodily functions.
The diaphragm is another important muscle within the trunk. It is a large, dome-shaped muscle that separates the thoracic and abdominal cavities. The diaphragm is the primary muscle responsible for breathing and facilitates inspiration by depressing the costal cartilages.
In summary, the axial muscles of the trunk play a crucial role in moving the body as a whole. They enable essential functions such as breathing, facilitate basic bodily activities, and provide stability and support to the axial skeleton.
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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 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, the muscles that form the thoracic and abdominal walls, and those that cover the pelvic outlet.
The diaphragm is a dome-shaped muscle located within the trunk. It separates the thoracic and abdominal cavities and facilitates the passage of anatomical structures via openings called hiatuses. The diaphragm is made up of three parts: the sternal, costal, and lumbar parts. The sternal part originates from the posterior aspect of the xiphoid process. 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 (medial and lateral). All fibres converge on a central tendon in the middle of the trunk, which has no bony insertions.
The diaphragm is the main muscle responsible for breathing, or inspiration. When the diaphragm contracts, the muscle is flattened, increasing the volume of the thoracic cavity, which decreases intrapulmonary pressure, allowing air to enter the lungs. When the diaphragm relaxes, the volume of the thoracic cavity decreases, intrapulmonary pressure increases, and air flows out of the lungs.
The diaphragm also assists in increasing intra-abdominal pressure, which is necessary for actions such as expelling vomit, defecation, micturition (urination), and parturition (childbirth). The diaphragm also provides a passageway for certain structures from the thorax to the abdomen, including the inferior vena cava, esophagus, and aorta.
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The abdominal wall consists of four muscle pairs
Trunk muscles are those that are attached to the skeletal core of the trunk, which 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 abdominal wall, which is part of the trunk, consists of four muscle pairs arranged in layers, with the fascia enveloping them. These muscles are the external oblique, internal oblique, transversus abdominis, and rectus abdominis. The external oblique muscle has two sets of fibres that cover the left and right abdomen and are connected by a wide aponeurosis sheet in the centre of the abdomen. The internal oblique muscles are a pair of muscles that lie on top of the external oblique muscles, just inside the hip bones. They are much thinner and smaller than the external oblique muscles and run from the sides of the trunk towards the middle. The transversus abdominis is the deepest of the flat muscles, layered on top of the internal oblique muscles. The rectus abdominis is a long, paired muscle that runs down either side of the middle of the abdomen from the ribs to the front of the pelvis. These four muscle groups make up the "core" muscles, along with the back muscles, and help protect the spine and keep the body stable and balanced.
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The erector spinae group of muscles helps maintain erect posture
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 erector spinae is a large superficial muscle that lies just deep to the thoracolumbar fascia and arises from the erector spinae aponeurosis (ESA). It is one of the core and paraspinal muscles, and it is formed of three muscles with fibres running vertically through the lumbar, thoracic, and cervical regions. The erector spinae is attached to the medial crest of the sacrum, the spinous processes of the lumbar vertebrae, and the eleventh and twelfth thoracic vertebrae. The erector spinae muscle mass extends from the sacrum to the skull, and it is primarily responsible for extending the vertebral column to maintain an erect posture.
The erector spinae is divided into three sections in the upper lumbar region: the iliocostalis (lateral), longissimus (intermediate), and spinalis (medial). The iliocostalis is the most lateral part of the erector spinae muscles and attaches to the ribs. The longissimus forms the middle part of the erector spinae muscles and is the thickest and longest. The spinalis is the smallest and most medial column, and it connects the spinous processes of adjacent vertebrae.
The erector spinae muscles play an important role in spinal stability and low back pain (LBP). In healthy individuals without low back pain, the erector spinae muscles relax in a range from an upright position to full lumbar flexion, due to the deep back muscles (multifidus) stabilising the lumbar spine. However, in individuals with low back pain, the erector spinae flexion-relaxation phenomenon is absent, and there is decreased activity and atrophy of the multifidus muscle, compromising spinal stability.
The erector spinae muscles help to maintain erect posture by extending the vertebral column and steadying the spine on the pelvis during walking. Bilateral contraction of these muscles causes back and head extension, while unilateral contraction causes lateral flexion and rotation of the vertebral column and head.
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Frequently asked questions
Trunk muscles are the muscles that make up the torso or trunk of the body, including the abdomen, chest, pelvis, and back. They are responsible for maintaining posture and moving the body, including the head and torso.
Anterior trunk muscles are those on the front of the body, including the chest, abdomen, and pelvis. They include the intercostal muscles, which are involved in respiration, and the abdominal muscles, which are involved in torso movement and maintaining balance and posture.
Examples of anterior trunk muscles include the pectoralis major and minor, serratus anterior, subclavius, intercostal (external, internal, and innermost), subcostal, and transversus thoracis muscles, including the diaphragm.
The diaphragm is a large, dome-shaped muscle located within the trunk, separating the thoracic and abdominal cavities. It is the main muscle responsible for breathing and facilitates the movement of anatomical structures via openings called hiatuses.
