Dominic Stone
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 muscles of the trunk are divided into six major functional groups: flexors and extensors in the sagittal plane, right and left lateral flexors in the frontal plane, and right and left rotators in the transverse plane. The direction of a muscle's fibres determines its function, with muscles that perform flexion, extension, right lateral flexion, and/or left lateral flexion having a vertical component to their fibre direction, and muscles that perform rotation having a horizontal component. The rectus abdominis, a long, strap-like, paired muscle that passes vertically over the entire length of the abdomen, acts as a flexor of the trunk. The abdominal oblique muscles, including the external and internal obliques, are also involved in trunk flexion. The erector spinae, composed of iliocostalis, longissimus, and spinalis subgroups, extend, laterally flex, and ipsilaterally rotate the trunk at the spinal joints. The quadratus lumborum, a muscle of the posterior wall, is involved in extending the trunk and flexing it laterally to the ipsilateral side.
| Characteristics | Values |
|---|---|
| Muscles of the trunk | Rectus Abdominis, External Oblique, Internal Oblique, Transversus Abdominis, Erector Spinae, Quadratus Lumborum, Trapezius, Latissimus Dorsi, Rhomboid Major, Rhomboid Minor, Levator Scapulae, Serratus Posterior Superior, Serratus Posterior Inferior |
| Function | Flexion, Extension, Lateral Flexion, Rotation |
| Major Actions | Bilateral activity of Rectus Abdominis, External and Internal Oblique, Psoas Major |
| Innervation | Intercostal, Subcostal, Iliohypogastric, Ilioinguinal |
| Superficial Muscles | Trapezius, Latissimus Dorsi, Rhomboid Major, Rhomboid Minor, Levator Scapulae |
| Intermediate Muscles | Serratus Posterior Superior, Serratus Posterior Inferior |
Explore related products
What You'll Learn
The role of the rectus abdominis
The rectus abdominis is a long, flat, segmented skeletal muscle that extends along the whole length of the front of the abdomen. It is commonly referred to as the ""abs"" or "six-pack". The rectus abdominis acts as a flexor of the trunk and plays a crucial role in maintaining core stability, protecting the lower back from injury, and assisting with breathing and respiration during forceful exhalation.
The rectus abdominis is a paired muscle, with each muscle running vertically on either side of the linea alba, a band of dense connective tissue that separates the two muscles at the midline. The muscle originates from the pubic crest, pubic symphysis, and pubic tubercle inferiorly, and inserts into the xiphoid process of the sternum and the costal cartilages of the 5th to 7th ribs superiorly. In some cases, the muscle's attachment may extend to the 3rd and 4th ribs.
The rectus abdominis is innervated by the thoracoabdominal nerves, which enter the rectus sheath and supply the abdominal wall. The blood supply to the rectus abdominis comes predominantly from the inferior and superior epigastric arteries, although it receives blood from other vessels as well. The muscle is enclosed within the rectus sheath, which is formed by the merging of the aponeurosis of the transversus abdominis and the external and internal oblique abdominal muscles.
The rectus abdominis plays a crucial role in maintaining core stability and protecting the lower back from injury. Along with the transversus abdominis, erector spinae, and oblique muscles, the rectus abdominis acts like a natural weight belt to support the spine and prevent spinal problems. A weak rectus abdominis can predispose individuals to back pain and spinal issues.
The rectus abdominis also assists with breathing and respiration. It aids in forceful exhalation, as seen after exercise or in conditions where exhalation is difficult, such as emphysema. Additionally, the rectus abdominis helps to create intra-abdominal pressure, which is essential for basic bodily functions such as micturition (urination) and defecation.
Intercostal Muscles: Their Function and Anatomy Explained
You may want to see also
Explore related products
External and internal oblique muscles
The trunk is made up of muscles that move the vertebral column, form the thoracic and abdominal walls, and cover the pelvic outlet. The abdominal wall muscles, for example, are made up of four muscle pairs, arranged in layers. The muscles of the thoracic wall are involved in the breathing process.
The internal and external obliques are abdominal muscles. The internal oblique is a muscle of the anterior abdominal wall. It is a broad, sheet-like muscle, located deep to the external oblique. The internal obliques originate on the inguinal ligament, which is a ligament that runs from the anterior iliac spine to the pubic bone. They insert onto the costal cartilages of the lower four ribs and the abdominal aponeurosis, a superficial sheet of connective tissue over the abdomen. The external obliques, on the other hand, originate from the external surfaces of ribs 5-12 and insert onto the abdominal aponeurosis, the linea alba, the iliac crest, and the pubic bone.
The internal obliques can function bilaterally, meaning both sides work together, or unilaterally, meaning one-sided. Bilaterally, they flex the trunk and compress its contents. Unilaterally, they laterally flex the trunk and rotate it to the same side. The external obliques function in a similar way bilaterally, but when working unilaterally, they rotate the trunk to the opposite side.
The internal and external obliques work together as synergists during twisting motions. For example, in the yoga posture marichyasana C, as you twist to the right, the left side of the external oblique contracts with the right side of the internal oblique.
Prevent Muscle Atrophy: Strategies to Maintain Muscle Mass
You may want to see also
Explore related products
Quadratus lumborum
The muscle originates from the iliac crest and iliolumbar ligament. It inserts onto the inferior border of the 12th rib and the transverse processes of the lumbar bodies of L1 to L4. As it ascends, it also attaches to the transverse processes of L1-L4 vertebrae. The muscle is an integral part of the thoracolumbar fascia, a myofascial system that covers the posterior area of the human body, involving part of the lower and upper limbs.
The QL muscle is innervated by the subcostal nerve and the anterior rami of the L1-L4 spinal nerves. It receives blood supply from the branches of lumbar, subcostal, median sacral, and iliolumbar arteries. The muscle is involved in extending the trunk and flexing it laterally to the ipsilateral side. It also fixes the 12th rib during movements of the thoracic cage and this way supports expiration (accessory muscle of expiration).
Overuse and strain of the quadratus lumborum are one of the major causes of chronic pain in the lower back. One typical cause is the habit of sitting at a desk using a reclined seat, which releases the intrinsic back muscles and weakens them in the long term.
Intercostals: Accessory Muscles or Not?
You may want to see also
Explore related products
Erector spinae
The erector spinae is a large superficial muscle that lies just deep to the thoracolumbar fascia. It is one of the core and paraspinal muscles, with its fibres running vertically throughout the lumbar, thoracic, and cervical regions. The erector spinae is composed of three subgroups: iliocostalis, longissimus, and spinalis.
The iliocostalis is the most lateral part of the erector spinae muscles and attaches to the ribs. It originates from the sacrum, erector spinae aponeurosis, and iliac crest. The longissimus forms the middle part of the erector spinae muscles and is the thickest and longest. It attaches along the transverse process of the vertebrae. The spinalis is the smallest and most medial column. It connects the spinous process of the adjacent vertebrae.
The erector spinae muscles play an important role in spinal stability and low back pain. They help to move the vertebral column, extend the spine, and maintain posture by steadying the spine on the pelvis during walking. Bilateral contraction of the erector spinae muscles causes back and head extension. They also control the forward flexion of the thorax.
The erector spinae muscles can be strengthened through various exercises, including lumbar stabilization exercises, which can help restore the erector spinae flexion-relaxation phenomenon and decrease low back pain.
The Power of a Smile: Which Muscle Makes It Happen?
You may want to see also
Explore related products
Superficial and deep muscles
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 muscles of the back are divided into two groups: superficial (extrinsic) muscles, which move the upper limb, and deep (intrinsic) muscles, which act on the trunk.
Superficial Muscles
The superficial muscles of the back are arranged into two layers. The superficial layer contains the trapezius, latissimus dorsi, rhomboid major and minor, and levator scapulae muscles. The trapezius is the most superficial muscle of the back and forms a broad, flat triangle. It originates from the skull and spine of the upper back and neck and attaches to the clavicle and scapula. The superior region of the trapezius supports the arm and elevates and rotates the scapula, the intermediate region retracts the scapula, and the inferior region rotates and depresses the scapula. The levator scapulae is located deep to the trapezius and superior to the rhomboid minor muscle. It originates from the transverse processes of the C1-C4 vertebrae and attaches to the medial border of the scapula. The levator scapulae elevates the scapula superomedially, rotates the glenoid cavity inferiorly, and laterally flexes the neck. The latissimus dorsi originates from the lower spine, ribs, and upper pelvis and fascia of the deep trunk muscles. It converges into a tendon that attaches to the humerus. The latissimus dorsi extends, adducts, and medially rotates the upper arm.
The intermediate layer possesses the serratus posterior superior and inferior muscles. The serratus posterior superior originates from the nuchal ligament and spinous processes of vertebrae C7-T3 and inserts on the superior borders of ribs 2-5, elevating them.
Deep Muscles
The deep back muscles occupy the space between the spinous and transverse processes of adjacent vertebrae. The intercostal muscles are located in the spaces between the ribs and play a key role in respiration. They contract during forced expiration, elevating the ribs during the inspiration phase of breathing. The external intercostal muscles are the most superficial of the intercostal muscles, while the internal intercostal muscles lie below the external intercostals. The internal intercostals elevate or depress the ribs. The innermost intercostals are the deepest lying of the intercostals and are similar in structure to the internal intercostals. The abdominal oblique muscles are another group of deep muscles that include the external and internal oblique muscles. These muscles are involved in trunk flexion, ipsilateral rotation, and compression of abdominal viscera. The final muscle in the abdominal area of the anterior trunk is the transversus abdominis muscle, which consists of transversely running fibres.
The erector spinae group of muscles is also considered a deep muscle group. This group includes the iliocostalis, longissimus, and spinalis muscles and is responsible for extending, laterally flexing, and ipsilaterally rotating the trunk at the spinal joints. The quadratus lumborum is another deep muscle that is involved in extending and flexing the trunk laterally.
Replenishing Muscle Glycogen: Strategies for Optimal Recovery
You may want to see also
Frequently asked questions
Muscles that flex the trunk include the rectus abdominis, external and internal oblique, and psoas major. The rectus abdominis is a long, strap-like muscle that passes vertically over the entire length of the abdomen. The external and internal oblique muscles involve trunk flexion and ipsilateral rotation.
The erector spinae group of muscles on each side of the vertebral column is a large muscle mass that extends the vertebral column. The erector spinae group is composed of three subgroups: iliocostalis, longissimus, and spinalis. The quadratus lumborum is also involved in extending the trunk.
The muscles that flex the trunk are involved in movements of the trunk, mainly flexion and rotation. They also contribute to changing the intra-abdominal pressure, which is essential for basic bodily functions such as micturition and defecation.
The six major functional groups of muscles of the trunk are flexors and extensors in the sagittal plane, right and left lateral flexors in the frontal plane, and right and left rotators in the transverse plane.
