Cervical Spine Muscles

Sternocleidomastoid Action

Bilateral Contraction:

• forward translation of C-spine (protraction)

• flexion of lower C-spine

Unilateral Contraction:

• contralateral rotation of upper & lower C-spine

• ipsilateral flexion of lower C-spine

• Extension of upper C-spine

What does the SCM resist?

forceful extension & backward movements of C-spine (whiplash)

Is the SCM usually under or over active?

Overactive

Does forward head posture (protraction) which we are usually in

If the SCM is over active, what can also be over active?

Upper Traps and Levator Scapulae

Are overactive to prevent your head from falling forward

Scalenes Action

Bilateral Contraction:

• synergist to C-spine flexion when ribs are fixed

Unilateral Contraction:

• ipsilateral lateral flexion with slight contralateral rotation when ribs are fixed

Accessory muscle of respiration:

• elevate 1st/2nd rib

What do the scalenes resist?

prevent excessive posterior shear forces

Are the scalenes usually under or over active?

Overactive

Phasic muscle

Longus Colli/Capitus Action

• Deep anterior neck flexors

• primary anterior stabilizers of upper and lower c-spine bc they are closest to the vertebrae

• Chin tucks make this more active

How do the longus colli/capitis increase C-spine stability?

provide increase compression force between the vertebrae

Rectus Capitis Anterior/Lateral Action

• Limited to the OA joint and have separate roles

• RCA= flexor of OA joint

• RCL= lateral flexor of OA joint

• large proprioceptive input to position of head & neck

Upper Trapezius Action

Scapula:

• elevation & upward rotation

C-spine: 

• ipsilateral lateral flexion, extension, and contralateral rotation

Dynamic stabilizer of the C-spine & scapula during UE tasks

What is the passive insufficiency position of the upper traps?

Contralateral lateral flexion + ipsilateral rotation + downward rotation of scapula + depress scapula (put hand behind back/under butt)

Levator Scapulae Action

Scapula:

• elevation & downward rotation

C-spine: 

• ipsilateral lateral flexion & slight ipsilateral rotation

• some neck extension

‘bring your nose to your clavicle’

What does the Levator Scapulae resist?

• Resists anterior shear forces due to natural lordosis of C-spine

• Provides a posterior shear force on vertebrae

What is the passive insufficiency position of Levator Scapulae?

Neck flexion + contralateral lateral flexion + contralateral rotation + depression + upward rotation (put hand behind your head)

Splenius Capitis/Cervisis Action

Bilateral contraction:

• extension of the head/neck

Unilateral contraction: 

• ipsilateral lateral flexion and ipsilateral rotation of c-spine

• similar to lev scap

What is the passive insufficiency position of the splenius capitis/cervicis?

neck flexion + contralateral lateral flexion + contralateral rotation

Semispinalis capitis/cervicis Action

• Primary C-spine extensors!! Always active during extension, just might not have the largest MA

• maintains the lordosis of C-spine

• Semispinalis Cervicis= primary stabilizer of upper c-spine so that suboccipital muscles can function at the AA joint (more precise flexion)

What do semispinalis capitis/cervicis resist?

resists excessive anterior shear forces

Longissimus Capitis/Cervicis Action

• stabilization of the head/neck in the frontal plane

• ipsilateral lateral flexors of c-spine

• small MA to produce cervical extension & ipsilateral rotation

Suboccipital Muscles Action

• Movement of the OA & AA joints independent of the C-spine

• Proprioception of head/neck & rate of movement

• sensations needed for balance, equilibrium, and head-eye coordination

What are the big takeaways from this image?

• majority of your suboccipitals are NOT doing rotation EXCEPT for Obliquus Capitis Inferior

• the rest are contributing to upper c-spine extension