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The torso, or trunk, is the central part of the body, housing all of the body's organs except the brain. The torso contains over 30 pairs of skeletal muscles, which are responsible for enabling movement of the lumbar and thoracic spine, ribs and limbs, as well as facilitating breathing and protecting vital organs. The torso can be divided into the upper torso (thorax), the mid-section (abdominal segment), and the lower torso (pelvic and perineal segments). The muscles of the torso can be grouped by location or function, with major muscle groups including the abdominal muscles, pectorals, erector spinae, serratus anterior and posterior, intercostals, latissimus dorsi, and rhomboids.
| Characteristics | Values |
|---|---|
| Definition | The torso, or trunk, is the central part, or core, of the body. |
| Number of Bones | Over 40 |
| Number of Skeletal Muscles | 30 pairs |
| Function | Enable movement of the lumbar and thoracic spine, ribs and proximal limbs, to facilitate breathing, and protect vital organs. |
| Muscle Groups | Abdominal, pectorals, erector spinae, serratus anterior and posterior, intercostals, latissimus dorsi, and rhomboids. |
| Subregions | Upper torso (thorax), lower torso (abdomen, pelvic and perineal segments), anterior and posterior torso. |
| Muscle Cells | Formed by the fusion and elongation of precursor cells called myoblasts. |
| Nerve Supply | Nerves originate from the thoracic and lumbar parts of the spinal cord. |
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What You'll Learn
- Torso muscle groups: abdominal, pectorals, erector spinae, serratus anterior, intercostals, latissimus dorsi, and rhomboids
- Intercostal muscles: external, internal, and innermost intercostals
- Abdominal muscles: pyramidalis, rectus abdominis, external obliques, internal obliques, and transversus abdominis
- Upper torso: thorax, where the forelimbs extend
- Lower torso: pelvic and perineal segments, where the hindlimbs extend
Torso muscle groups: abdominal, pectorals, erector spinae, serratus anterior, intercostals, latissimus dorsi, and rhomboids
The torso, or trunk, contains over 30 pairs of skeletal muscles. These muscles are responsible for enabling movement of the lumbar and thoracic spine, ribs, and proximal limbs, facilitating breathing, and protecting the vital organs.
Abdominal Muscle Group
The abdominal muscles are located between the ribcage and the pelvis on the front of the body. There are five main abdominal muscles: pyramidalis, rectus abdominis, external obliques, internal obliques, and transversus abdominis. These muscles help hold organs in place, support the body during movement, and stabilise the trunk.
Pectoral Muscle Group
The pectoral muscles are a group of skeletal muscles that connect the upper extremities to the anterior and lateral thoracic walls. They facilitate a wide range of movements, including flexion, adduction, and internal rotation of the humerus, as well as stabilisation of the scapula. The pectoralis major and pectoralis minor are the primary muscles involved in these actions.
Erector Spinae Muscle Group
The erector spinae are the most superficial muscles of the posterior trunk, ascending on either side of the vertebral column. They provide vertical stability to the spine and help maintain upright posture. The erector spinae can be divided into three groups: iliocostalis, longissimus, and spinalis.
Serratus Anterior Muscle
The serratus anterior is a fan-shaped muscle that originates on the superolateral surfaces of the first to eighth or ninth ribs. It acts on the scapula and is responsible for scapular protraction and upward rotation. It is also a key stabiliser, keeping the shoulder blades against the rib cage.
Intercostal Muscle Group
The intercostal muscles are intrinsic rib cage muscles occupying the 11 intercostal spaces. They are divided into three groups: external, internal, and innermost intercostals. All three groups support the rib cage and are accessory respiratory muscles. The external intercostals facilitate forced inspiration, while the internal and innermost intercostals aid forced expiration.
Latissimus Dorsi Muscle
The latissimus dorsi is a large, flat muscle on the back that stretches to the sides, behind the arm. It is responsible for extension, adduction, transverse extension, flexion, and internal rotation of the shoulder joint. It also plays a role in the extension and lateral flexion of the lumbar spine.
Rhomboid Muscle Group
The rhomboids are a group of muscles formed by the rhomboid major and minor. They are important for upper limb movement and stability of the shoulder girdle and scapula. They work with other muscles to retract, elevate, and rotate the scapula.
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Intercostal muscles: external, internal, and innermost intercostals
The torso, or trunk, is the central part of the body, containing over 30 pairs of skeletal muscles. The muscles of the torso are responsible for enabling the movement of the lumbar and thoracic spine, ribs, and proximal limbs, facilitating breathing, and protecting the vital organs. The intercostal muscles are a group of muscles that support the rib cage and participate in the process of breathing. There are three groups of intercostal muscles: external, internal, and innermost intercostals.
The external intercostals are the most superficial intercostal muscles. They originate from the inferior border of one rib and insert into the superior border of the rib below. The function of the external intercostal muscles is to elevate the ribs during forced inspiration. They are innervated by the anterior rami of spinal nerves T1-T11, also known as the intercostal nerves of the corresponding intercostal space. The blood supply to the external intercostals comes from the anterior and posterior intercostal arteries.
The internal intercostals lie deep to the external intercostals and extend from the rib above to the one below, but in the opposite direction (inferoposteriorly). They are continuous with the internal oblique muscle of the abdominal wall. The internal intercostals stabilise the position of the ribs during normal respiration and depress the ribs during forced expiration. They are innervated by the intercostal nerves T1-T11 and receive their blood supply from the anterior and posterior intercostal arteries, as well as from the costocervical trunk, internal thoracic, and musculophrenic arteries.
The innermost intercostals are the deepest intercostal muscles. They originate from the costal groove of one rib and insert into the superior border of the rib below. They are similar in structure to the internal intercostals but are separated from them by the intercostal neurovascular bundle. The innermost intercostals are found in the most lateral portion of the intercostal spaces. Like the internal intercostals, they aid in forced expiration.
Overall, the intercostal muscles play a crucial role in supporting the rib cage and facilitating breathing. Deficient intercostal muscles can lead to respiratory insufficiency, highlighting the importance of these muscles in maintaining respiratory function.
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Abdominal muscles: pyramidalis, rectus abdominis, external obliques, internal obliques, and transversus abdominis
The torso, or trunk, is the central part of the body that connects the upper and lower extremities. It houses all the vital organs, except the brain, and is made up of over 40 bones and 30 pairs of skeletal muscles. The torso can be divided into the upper torso or thorax, and the lower torso, which includes the abdomen and pelvic areas.
The abdominal muscles are a group of five main muscles that line the abdominal walls and are located towards the front of the body, between the ribs and the pelvis. They have several important functions, including supporting the trunk, aiding movement, and holding the internal organs in place.
The rectus abdominis is a vertical muscle that is slung between the ribs and the pubis at the front of the pelvis. It is responsible for the appearance of a 'six-pack' and helps move the body between the ribcage and the pelvis.
The pyramidalis is a small muscle that sits in the lower abdominal wall within the rectus sheath. It is not present in around 20% of people. When present, it assists with abdominal cavity compression.
The external obliques are a pair of flat muscles, one on each side of the rectus abdominis, and are the largest of the flat muscles. They run from the sides of the body towards the middle and allow the trunk to twist from side to side.
The internal obliques are a pair of thin, small muscles that sit on top of the external obliques, just inside the hip bones. They work together with the external obliques to allow the trunk to twist and turn.
The transversus abdominis is the deepest muscle layer and is responsible for stabilising the trunk and maintaining internal abdominal pressure. It is the deepest of the flat muscles and is layered on top of the internal obliques.
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Upper torso: thorax, where the forelimbs extend
The torso, or trunk, is the central part of the body, from which the head, neck, limbs, tail, and other appendages extend. The tetrapod torso is divided into the thoracic segment (upper torso), the abdominal segment (mid-section), and the pelvic and perineal segments (lower torso).
The upper torso, or thorax, is where the forelimbs extend. It is located between the abdomen and the root of the neck. The thorax is formed by the sternum, the thoracic vertebrae, and the ribs. It does not include the upper limbs. The heart, lungs, and thymus gland are housed within the thoracic cavity, as well as many blood vessels. The inner organs are protected by the rib cage and the sternum.
The thoracic wall is formed by 12 ribs, 12 thoracic vertebrae, cartilage, sternum, and five muscles. The muscles extending superiorly include the scalene, sternocleidomastoid, and subclavius muscles. The thoracic wall functions in movement, respiration, and protection of the thoracic cavity.
The aorta, which arises from the left ventricle of the heart, supplies the head, upper limb, and thoracic wall. The brachiocephalic trunk, left common carotid, and left subclavian arteries are also contained within the thorax.
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Lower torso: pelvic and perineal segments, where the hindlimbs extend
The torso, or trunk, is the central part of the body, from which the head, neck, limbs, and other appendages extend. The human torso is divided into the thoracic segment (upper torso), the abdominal segment (mid-section), and the pelvic and perineal segments (lower torso).
The pelvic and perineal segments, where the hindlimbs extend, are also referred to as the lower torso. These segments contain the pelvic floor muscles, which are a group of muscles that form the base of the core muscles. The core muscles include the pelvic floor muscles, abdominal muscles, back muscles, and the diaphragm.
The pelvic floor muscles are made up of layers of muscles and connective tissues. The two main muscles that intertwine to form the pelvic floor muscles are the levator ani and coccygeus. The levator ani composes the majority of the pelvic floor muscles and consists of three separate muscle components: pubococcygeus, puborectalis, and iliococcygeus. The coccygeus is the smaller muscle component and is located towards the back of the pelvis.
The pelvic floor muscles support the pelvic organs, including the bladder, bowel, and internal reproductive organs. They hold these organs in place while also providing the flexibility required for bodily functions such as urination, defecation, and sexual intercourse. In women, the pelvic floor muscles also provide support for the baby during pregnancy and need to be relaxed during childbirth.
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Frequently asked questions
The torso muscles refer to the skeletal muscles that originate from the mesoderm of the somites. They are responsible for the movement and support of the trunk and are essential for various bodily functions.
The torso muscles enable movement of the lumbar and thoracic spine, ribs and proximal limbs, facilitate breathing, and protect the vital organs.
The torso muscles can be grouped by their location or function. The muscles of the thoracic cage include the pectoralis major, pectoralis minor, serratus anterior, subclavius, intercostal, subcostal, and transversus thoracis muscles, including the diaphragm. The abdominal muscles include the pyramidalis, rectus abdominis, external obliques, internal obliques, and transversus abdominis.
The anterior torso includes the pectoral and deltoid region, breast tissue, xiphoid process of the sternum, lower ribs, umbilicus, and the urinary bladder and pubic regions. The posterior torso includes the lower ribs, kidney area, and the coccyx.
The core of the body refers to the central region of the torso, especially the lower and middle regions. The muscles of the core include the abdominal muscles, the middle and lower sections of the erector spinae group, and minor core muscles such as the trapezius, latissimus dorsi, and gluteus maximus.
