spinal muscles

Muscles of the Craniocervical & Cervicothoracic Region

• Craniocervical muscles position the head upright against gravity.
• Craniocervical muscles position the head to optimize sensory organ function, including vestibular and vision.
• Cervicothoracic muscles position the head and neck in space.
• Cervicothoracic muscles stabilize the head and neck against the pull of muscles that produce or control scapula and upper extremity motion.
• The line of gravity (LOG) falls anterior to the axis of rotation in the cervical region in an upright position.
• The LOG produces a flexion moment in the cervical region
• Posterior cervical muscles oppose the flexion moment.

Upper Trapezius

• Shoulder complex stabilized, bilateral action extends the head and neck
• Acting unilaterally causes ipsilateral lateral flexion and contralateral rotation of the head and neck when the shoulder complex is stabilized.

Levator Scapula

• With a stabilized neck, the levator scapula elevates the scapula
• The levator scapula serves as a downward rotator of the scapula when the neck is stabilized
• With a stabilized scapula, the levator scapula creates ipsilateral lateral flexion and ipsilateral rotation of the cervical spine.
• The levator scapula helps resist anterior shearing forces created by gravity and the lordosis of the c-spine
• Excessive forward head posture increases anterior shearing on cervical vertebrae, causing overactivity of levator scapulae.

Splenius Capitis & Cervicis

• The splenius capitis & cervicis are prime movers of head and neck due to large CSA & large MAs
• Bilateral action extends the head and neck.
• Unilateral action rotates head and neck to the ipsilateral side.
• There is little activity in normal quiet standing.

Semispinalis Capitis & Cervicis

• An optimal line of pull and large MA leads to extension and increased cervical lordosis
• The greater occipital nerve runs through the semispinalis capitis
• Nerve entrapment can happen if that muscle is overactive or shortened
• Prolonged forward head posture may occur
• This may be the source of occipital headaches.

Longissimus Capitis & Cervicis

• A deep position places them close to the axis of rotation for flexion and extension, creating a smaller MA
• It is less effective as extensors because of the deep position
• It produces compression of cervical segments
• Acting bilaterally they are frontal plane stabilizers of the c-spine
• Unilateral action produces ipsilateral lateral flexion.

Suboccipital Muscles

• The rectus capitis posterior major and minor are suboccipital muscles.
• The obliquus capitis superior and inferior are suboccipital muscles.
• They allow independent movement of craniovertebral region on the lower c-spine
• They produce capital (cranial) extension as a group
• Acting unilaterally causes ipsilateral rotation and lateral flexion of occiput or atlas.
• They serve a proprioceptive role to fine-tune a craniocervical position, especially somatosensory
• They are involved with integrated functions of oculomotor and vestibular systems.

Scalenes

• As a group, scalenes function as frontal plane stabilizers, especially in conjunction with longissimus muscles
• Scalenes work synergistically with levator scapulae
• The anterior scalene has bilateral and unilateral actions
• Acting bilaterally flexes the c-spine and produces anterior shear.
• Acting unilaterally produces ipsilateral side bending (SB) and contralateral rotation of the c-spine.
• The middle scalene is a frontal plane stabilizer
• The posterior scalene is predominantly a side bending (SB) neck muscle

Scalenes & Levator Scapula

• Anterior scalene muscles work in synergy with levator scapulae to stabilize c-spine.

Interscalene Triangle

• Anterior & middle scalenes form the interscalene triangle.
• The brachial plexus and subclavian artery pass through the interscalene triangle
• This triangle can become a site for compression of the neurovascular structures (thoracic outlet syndrome).

Sternocleidomastoid

• The sternocleidomastoid muscle lies anterior to the axis of rotation in the lower c-spine but posterior to the atlantooccipital axis
• Bilateral action allows for cervical flexion and capital extension
• Unilateral action causes ipsilateral lateral flexion of head & neck and contralateral rotation of head & neck.

Longus Capitis & Colli

• They function as cervical flexors
• They lie relatively close to the axis of rotation
• This allows for contribution to cervical compression, stabilizing the spine
• They work synergistically with the trapezius
• They stabilize the head and neck so the trapezius can effectively work on the scapula
• Without co-contraction of the longus colli and capitis, the head would extend when the scapula elevates or upwardly rotates.

Rectus Capitis Anterior & Lateralis

• They are capital flexors
• small CSA and MAs mean they are not major prime movers
• They serve a greater proprioceptive function.

Thoracolumbar Fascia (TLF)

• Blends with the latissimus dorsi
• Blends with the gluteus maximus
• Blends with the internal/external abdominal obliques
• Blends with the transverse abdominis
• The thoracolumbar fascia surrounds the erector spinae & lumbar multifidi
• Tensile forces are exerted on the TLF through active/passive tension in muscles
• Tension in the TLF leads to compressive force to abdominal contents.

The Glutes and Lats

• Coupled action of the contralateral latissimus dorsi and gluteus maximus muscles occur together
• This action produces tensing in the thoracolumbar fascia
• This action compresses and stabilizes the lumbosacral region

Erector Spinae

• The superficial layer is longissimus thoracis and iliocostalis lumborum (thoracic regions)
• Tendons create the erector spinae aponeurosis (ESA)
• The tendons insert into the lower lumbar spinous processes, sacrum, & iliac crest
• It is a primary extensor of the region
• Bilateral action results in extension of the thoracic and lumbar regions
• Unilateral action assists with ipsilateral side bend.

Deep Erector Spinae

• The deep layer of the erector spinae is the longissimus thoracis & iliocostalis lumborum
• Insufficient MA isn't sufficient to act as prime movers for extension
• It contributes to ipsilateral lateral flexion
• An oblique orientation allows muscles to exert both posterior shear and compressive forces on vertebrae
• Provide dynamic resistance to anterior shear forces in the lumbar region

Thoracic Multifidi

• They are laterally oriented with an oblique line of pull
• They are activated with rotation but in a variable manner
• They play a greater role in segmental control and stabilization as opposed to motion production

Lumbar Multifidi

• Superficial fibers of each fascicle cross up to 5 segments
• The line of pull is vertically oriented, distant from flexion/extension axis
• They have effective MA for extension by increasing the lumbar lordosis
• Deep fibers work well for lumbar extension.
• They are ideally positioned to control shearing forces via compression
• Work in synergy with abdominals during trunk rotation to counteract the flexion moment they produce.

Intertransversarii & Rotatores Muscles

• They are often considered to: produce lateral flexion (intertransversarii) & rotation (rotatores)
• Small CSAs and MAs suggest that their main purpose is more proprioceptive than for motion

Quadratus Lumborum

• With unilateral action, it causes ipsilateral lateral flexion of the spine
• If the pelvis is free to move, hip hiking occurs on the ipsilateral side due to muscle contraction
• Bilateral action has to potential to weakly assist with trunk extension
• The quadratus lumborum plays a greater role as a frontal plane stabilizer

Abdominal Muscles

• The abdominal wall includes: external obliques (EO), internal obliques (IO), transverse abdominis (TrA), and rectus abdominis (RA)
• Components of an abdominal hoop can form around the entire abdomen
• TrA is an important stabilizer of lumbosacral and sacroiliac region

Rectus Abdominis (RA)

• The RA acts as the prime flexor of the trunk
• The RA is contained within abdominal fascia, separating it into sections and attaching to abdominal aponeurosis
• Fascial connections transmit forces across midline and around trunk contributing to stability

Psoas Major

• The primary function is hip flexion
• A distal tendon merges with iliacus, forming the iliopsoas
• It provides lumbar stability to prevent excessive shearing of vertebrae
• The psoas contributes to lumbar compression during activation
• It limits extension to proper amounts.

Psoas and Hip Flexion

• During active hip flexion, the iliacus creates an anterior pull on the innominate
• If unopposed, this creates anterior pelvic tilt and increased lordosis
• Psoas major creates pull on lumbar vertebrae that counteracts lumbar extension force

Global Vs. Deep Segmental Muscles

• Global muscles are superficial: they are farther from the axis of motion
• They cross several vertebral segments
• They produce motion and provide a large guy wire function
• Global muscles produce compressive loading with strong contractions
• Deep segmental muscles are closer to the axis of motion
• They attach to each vertebral segment, or cross a few
• Deep segmental muscles control segmental motion
• They have a stabilizing function
• They have a greater percentage of type I muscle fibers for endurance

Global Vs Deep Segmental Muscle Control

• Overall stability of spine requires coordination and strength of global & deep segmental musculature
• Without segmental control, contraction of global spinal muscles can lead to functional instability
• Compressive loading from global muscles can overstress inert segmental tissues if adequate segmental stability is not present
• The rectus abdominis, external and internal obliques, lateral quadratus lumborum, erector spinae, and iliopsoas are global lumbar region muscles.
• The transversus abdominis, Multifidus, deep quadratus lumborum, and deep rotators are examples of deep segmental lumbar muscles.
• Sternocleidomastoid, scalene, levator scapulae, upper trapezius, and erector spinae are examples of global cervical region muscles
• Rectus capitis anterior and lateralis, longus colli, longus capitis, and cervical multifidi are all deep segmental cervical muscles.