Dominic Stone
The muscles of the trunk assist with essential body activities such as breathing, movement, defecation, and urination. The erector spinae muscles, which extend from the sacrum to the skull, are responsible for extending the spine and returning the body to an upright position. The quadratus lumborum, originating from the iliac crest and iliolumbar ligament, is also involved in extending the trunk. These muscles work together to maintain posture and stability, making them crucial for our daily lives.
| Characteristics | Values |
|---|---|
| Muscles that extend the trunk | Erector spinae, semispinalis, deep posterior spinal muscles, quadratus lumborum |
| Location of Erector Spinae | Vertebral column, from the sacrum to the skull |
| Function of Erector Spinae | Extend the vertebral column to maintain erect posture |
| Other Superficial Muscles of the Back | Trapezius, latissimus dorsi, rhomboid major and minor, levator scapulae |
| Function of Trapezius | Supports and draws the scapula superiomedially, extends, rotates and laterally flexes |
| Function of Rectus Abdominis | Flexes the trunk forward, acts as an accessory muscle of expiration |
Explore related products
What You'll Learn
Erector spinae muscles
The erector spinae muscles are a group of muscles that lie on either side of the vertebral column, extending from the pelvis to the base of the cranium. They are one of the core and paraspinal muscles, and they play a crucial role in spinal stability. These muscles are responsible for extending the vertebral column and maintaining an erect posture. The erector spinae muscles are divided into three sections: the iliocostalis, the longissimus, and the spinalis.
The iliocostalis is the most lateral part of the erector spinae muscles. It originates from the sacrum, erector spinae aponeurosis, and iliac crest. The iliocostalis has three insertions: the iliocostalis lumborum, which inserts into the 12th to 7th ribs; the iliocostalis thoracis, which inserts into the last 6 ribs to the first 6 ribs; and the iliocostalis cervicis, which inserts into the first 6 ribs to the transverse process of C6-C4. The tightness in the iliocostalis muscles can affect the position of the rib cage and hips.
The longissimus muscles are the central and thickest erector spinae muscles. They are divided into three parts: the longissimus capitis, which originates from the transverse processes of vertebrae C4-T5 and inserts into the mastoid process of the temporal bone; the longissimus colli, which extends between the transverse processes of vertebrae T1-T5 and C2-C6; and the longissimus thoracis, which consists of thoracic and lumbar parts. The longissimus thoracis originates from the sacrum, lumbar vertebrae, and thoracic vertebrae, inserting into the ribs and costal processes of the thoracic vertebrae.
The spinalis muscles are the most medial erector spinae muscles and are also divided into three groups: spinalis capitis, spinalis colli, and spinalis thoracis. The spinalis capitis originates from the cervical and upper thoracic vertebrae and inserts into the external occipital protuberance. The spinalis colli originates from the same points as the spinalis capitis, as well as the nuchal ligament, and inserts into the spinous processes of C2-C4 vertebrae. The spinalis thoracis extends from the spinous process of T11-L2 vertebrae to the spinous process of T2-T8 vertebrae. The spinalis muscles receive their blood supply from various arteries, including the vertebral, deep cervical, occipital, intercostal, and lumbar arteries.
The erector spinae muscles are essential for spinal stability and posture control. In healthy individuals without low back pain, these muscles relax in a range from an upright position to full lumbar flexion. However, in individuals with low back pain, the erector spinae muscles may exhibit increased activity to stabilize the lumbar spine, which can lead to a higher risk of injury. Lumbar stabilization exercises can help restore the function and flexibility of the erector spinae muscles, reducing low back pain.
Sternocleidomastoid Muscle: Convergence and Its Implications
You may want to see also
Explore related products
Semispinalis muscles
The semispinalis muscles are long, flat skeletal muscles that are found along the upper back and posterior neck regions. They are the most superficial of the transversospinal muscles. The semispinalis muscles are divided into three parts: the semispinalis capitis, semispinalis cervicis, and semispinalis thoracis.
The semispinalis capitis is the superior portion of the semispinalis muscle and is the largest muscle in the posterior neck. It lies deep to the upper trapezius. It receives its innervation through the greater occipital nerve and spinal nerve C3. Its muscle tendons arise from the articular processes of vertebrae C4-C7 and transverse processes of vertebrae T1-T6. From these attaching tendons, the muscle fibres of the semispinalis capitis converge into a single muscle belly that runs superiorly across the lateral side of the vertebral column.
The semispinalis cervicis is the middle portion of the semispinalis muscle. It covers the cervical and thoracic multifidus muscles.
The semispinalis thoracis (or semispinalis dorsi) is the inferior portion of the semispinalis muscle. It consists of thin, narrow, fleshy fasciculi, interposed between tendons of considerable length. It arises by a series of small tendons from the transverse processes of the sixth to the tenth thoracic vertebrae and is inserted, by tendons, into the spinous processes of the upper four thoracic and lower two cervical vertebrae.
Together, the semispinalis, multifidus, and rotatores muscles comprise the deep (transversospinal) layer of the back muscles. These muscles participate in the extension, lateral flexion, and rotation of the head, cervical, and thoracic spine.
Trap Muscles: Understanding Their Role and Function
You may want to see also
Explore related products
Quadratus lumborum
The quadratus lumborum (QL) is a muscle in the posterior inferior trunk, located lateral to the spine. It is the deepest abdominal and back muscle, often described as part of the ventral trunk musculature. The muscle is flat and quadrangular in shape, with a complex organisation of fibres. The QL originates from the iliac crest and the iliolumbar ligament and inserts onto the inferior border of the 12th rib and the transverse processes of the lumbar vertebrae L1-L4.
The quadratus lumborum is involved in several functions, including extending the trunk and flexing it laterally to the ipsilateral side. It also acts as an extensor of the lumbar spine, stabiliser of the lumbar area, and accessory muscle for inspiration. During extension, the QL exerts a force of 10 N, which is significantly lower than the forces produced by the erector spinae and multifidus muscles.
The QL is part of the thoracolumbar fascia, a myofascial system covering the posterior area of the human body, including the upper and lower limbs. It works with the multifidus and erector spinae muscles to create an antagonist force to the muscles of the anterolateral abdominal wall. The QL can be a source of back pain when overused or in association with conditions such as scoliosis or weak gluteal muscles.
The complex arrangement of the QL muscle fibres makes it challenging to precisely identify the actions resulting from their contraction. However, its strategic position and fibre arrangement suggest that it may serve as a junction for the forces exerted by neighbouring muscles, influencing the vectors of different tensions. This unique configuration also makes the QL a significant means of access for anaesthesia during surgery in the back, lower limbs, or abdominal region.
Protein Power: Muscle Repair and Growth
You may want to see also
Explore related products
$134.99 $149.99
Trapezius, latissimus dorsi, rhomboid major and minor
The trunk is moved by various muscles, including those that move the vertebral column, form the thoracic and abdominal walls, and cover the pelvic outlet. The muscles that extend the trunk include the erector spinae group, which is a large muscle mass on each side of the vertebral column, extending from the sacrum to the skull.
The trapezius, latissimus dorsi, rhomboid major, and rhomboid minor muscles all play a role in trunk extension, posture, and movement.
Trapezius
The trapezius muscles are two large muscles found on either side of the upper back, starting at the base of the neck and extending across the shoulders to the middle of the back. These muscles help maintain posture and move the head, neck, and upper back. They also assist in twisting the torso, shrugging the shoulders, and moving the shoulder blades during arm movements.
Latissimus Dorsi
The latissimus dorsi is a broad, flat muscle occupying most of the lower posterior thorax. It is considered a respiratory accessory muscle and plays a role in deep inspiration, coughing, and sneezing. This muscle assists in pulling the trunk forward and upward when the upper extremities are fixed overhead, as in climbing or performing a chin-up. It also helps hold the scapula against the thorax during upper limb movements.
Rhomboid Major and Minor
The rhomboid muscles, including the rhomboid major and minor, are located in the upper back and covered by the trapezius muscle. They contribute to upper body posture and shoulder mechanics by fixing and stabilizing the scapula, providing an anchor point for various muscles of the upper limb to act upon. The rhomboid major, in particular, is a broad quadrilateral muscle originating from the thoracic vertebrae.
Muscle Fatigue: Why Do Muscles Get Tired?
You may want to see also
Explore related products
Thoracic and abdominal wall muscles
The trunk muscles assist essential body activities such as breathing, movement, defecation, and urination. 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.
Thoracic Wall Muscles
The thoracic wall is made up of five muscles: the external intercostal muscles, internal intercostal muscles, innermost intercostal muscles, subcostalis, and transversus thoracis. These muscles are primarily responsible for changing the volume of the thoracic cavity during respiration. The intercostal muscles are located in the spaces between the ribs. They contract during forced expiration. External intercostal muscles contract to elevate the ribs during the inspiration phase of breathing. The diaphragm is a dome-shaped muscle that forms a partition between the thorax and the abdomen. It separates the thoracic and abdominal cavities, and is dome-shaped at rest. The superior surface of the diaphragm is convex, creating the elevated floor of the thoracic cavity. The inferior surface is concave, creating the curved roof of the abdominal cavity.
Abdominal Wall Muscles
There are four pairs of abdominal muscles that cover the anterior and lateral abdominal region and meet at the anterior midline. These muscles of the anterolateral abdominal wall can be divided into four groups: the external obliques, the internal obliques, the transversus abdominis, and the rectus abdominis. The rectus abdominis acts as a flexor of the trunk and an accessory muscle of expiration. It also compresses the abdominal contents to protect them. The pyramidalis is a small triangular muscle found in the lower abdomen. It lies anterior to the rectus abdominis muscle.
Crying: A Natural Way to Relax Muscles and Mind
You may want to see also
Frequently asked questions
The erector spinae group of muscles, which extend from the sacrum to the skull, are responsible for extending the vertebral column and maintaining an erect posture.
Yes, the semispinalis muscles also contribute to trunk extension, along with the deep posterior spinal muscles.
The erector spinae muscles help to return the body to an upright position from a forward or backward bend. This is important as many of us spend a lot of time sitting, which can weaken our back muscles.
It is important to distribute the curve throughout the lower back when bending back, rather than pivoting at one point. This helps to strengthen the muscles evenly. Yoga poses like Cobra can also help, but be sure not to use your arms to push yourself into the pose.
The rectus abdominis muscle, also known as the "six-pack," is responsible for flexing the trunk forward. However, repetitive spinal flexion can negatively impact your natural lumbar curve, so it's important to balance this with other exercises.
