15.10
Muscles of the Vertebral Column
The back muscles that lie deep into the thoracolumbar fascia are called intrinsic or true back muscles. These muscles are divided into four layers: su…
The back muscles associated with the vertebral column are divided into superficial, intermediate, and deep layers.
The superficial layer contains the splenius muscles closely associated with the cervical vertebra, which support head and neck movements, while the intermediate layer contains erector spinae muscles.
The erector spinae are the largest group of long back muscles on either side of the vertebral column extending from the pelvis to the neck.
This group comprises spinalis, longissimus, and iliocostalis muscle columns, subdivided into different parts based on their axial skeleton attachments.
For example, the iliocostalis muscles have three horizontal divisions: the iliocostalis cervicis, iliocostalis thoracis, and iliocostalis lumborum.
The bilateral contraction of these muscles facilitates the vertebral column extension, while unilateral contraction facilitates lateral flexion on the same side.
In contrast, the deep layer comprises the semispinalis, multifidus, and rotatores muscles. These muscles stabilize individual vertebrae positions during localized movements.
For instance, the semispinalis thoracis, spanning between the sixth cervical and tenth thoracic vertebrae, specifically aids the extension, lateral flexion, and thoracic spine rotation.
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Q1: What are the main layers of back muscles associated with the vertebral column?
Back muscles are organized into four distinct layers: superficial, intermediate, deep, and deepest. The superficial layer contains splenius muscles for head and neck movements. The intermediate layer includes erector spinae muscles that extend from the pelvis to the neck. The deep layer comprises transversospinalis muscles like semispinalis and multifidus for stabilization. The deepest layer contains minor muscles such as interspinales and intertransversarii that span between adjacent vertebrae.
Q2: How do erector spinae muscles function during spinal movements?
The erector spinae comprise three muscle columns—iliocostalis, longissimus, and spinalis—that run nearly the entire spine length. Bilateral contraction of these muscles extends the vertebral column, while unilateral contraction causes lateral flexion toward the same side. The erector spinae maintain posture and provide strength for spinal extension, making them crucial for supporting upright body position and controlled bending movements.
Q3: What is the role of deep back muscles in spinal stability?
Deep back muscles, including semispinalis, multifidus, and rotatores, stabilize individual vertebrae during localized movements. These shorter, deeper muscles aid in extension, rotation, and controlled bending of the vertebral column. For example, semispinalis thoracis spans from the sixth cervical to the tenth thoracic vertebra, specifically supporting thoracic spine extension, lateral flexion, and rotation while maintaining vertebral alignment.
Q4: How are iliocostalis muscles subdivided based on their attachments?
Iliocostalis muscles are divided into three horizontal sections based on their axial skeleton attachments: iliocostalis cervicis, iliocostalis thoracis, and iliocostalis lumborum. Each division attaches to different ribs and vertebrae, allowing coordinated movement across multiple spinal regions. This subdivision enables precise control of extension and lateral flexion at different levels of the vertebral column.
Q5: What movements do splenius muscles control?
Splenius muscles, located in the superficial back layer, include splenius capitis and splenius cervicis. These muscles are responsible for head and cervical spine movements including extension, rotation, and lateral bending. Splenius capitis extends from the upper thoracic and lower cervical vertebrae to the skull, while splenius cervicis stretches between thoracic and cervical vertebrae, enabling coordinated neck and head positioning.
Q6: What do the deepest layer back muscles contribute to spinal function?
The deepest back muscle layer includes interspinales and intertransversarii, which span between adjacent vertebrae and contribute to spine stability and localized movements. Additionally, levatores costarum in this layer assist in elevating the ribs, which is particularly important during deep inhalation. These minor deep muscles work together to fine-tune vertebral positioning and support respiratory mechanics.
Q7: How do unilateral versus bilateral muscle contractions affect spinal movement?
Bilateral contraction of back muscles like erector spinae produces vertebral column extension, creating upright posture and forward bending control. Unilateral contraction causes lateral flexion toward the contracting side, enabling side-to-side bending movements. This dual action mechanism allows the spine to perform both symmetrical movements like extension and asymmetrical movements like rotation and lateral bending through selective muscle activation.