Muscles of the Neck & Vertebral Column

• Head movments - Head Flexors


  muscles originatig from the axial skeleton move the head

  major head flexors r the sternocleidomastoid muscles w help form the suprahyoid + infrahyoid msucles

  
• Head Movement - Lateral 


  rotating/tilting of the head result when the muscles on only side of the neck contract

  these actions r produced by the sternocleidomastoids + a no of deeper neck muscles
• Head Movement - Extension


  head extension = aided by the trapezius muscles of the back, but the main extensors of the head r the splenius muscles deep to the trapezius
• Trunk Extension


  trunk extension is brought about by the deep/intrinsic back muscles associated w the vertebral column

  these muscles also maintain the normal curvatures of the spine, acting as postural muscles

  the superficial back muscles that cover them r concerned primarily w moving the shoulder girdle + upper limbs
• Deep Muscles of the Back


  the deep muscles of the back form a broad, thick column extending from the sacrum to the skull

  many muscles of varying length contribute to this mass
• Deep Muscles of the Back - Erector Spinae Group


  the largest deep back muscle group = erector spinae group

  because the origins + insertions of the diff muscle groups overlap extensively + many of these muscles r long, large regions of the vertebral column can be moved simultaneously + smoothly

  acting together, the deeep back muscles extend the spine
• Lateral Flexion of the Spine


  muscle contraction on only side of cause the spine to bend laterally

  lateral flexion is automatically accompanied by some degree of rotation of the vertebral column

  during vertebral movements, the articular facets of the vertebrae glide on each other
• Small Muscles of the Back

  in addition to the ong back muscles, there a no of short muscles that extend from 1 vertebra to the next

  these small muscles act primarily as synergists in extending + rotating the spine + as spine stabilisers
• Sternocleidomastoid - Origin & Insertion

  two-headed muscle located on anterolateral surface of neck

  origin - manubrium of sternum + medial portion of clavicle

  insertion - mastoid process of temporal bone + occipital bone

  
• Sternocleidomastoid - Action

  flexes + laterally rotates the head

  simultaneous contraction of both muscles flexes neck, as when raising head when lying on back

  acting alone, each uscle rotate heads toward shoulder on opposite side + laterally flexes head to its own side
• Deep Back Muscles


  stabilises the spine

  
• Scalenes

  located more laterally than anteriorly on neck

  deep to sternocleidomastoid

  origin - trnasvere process of cervical vertebrae

  insertion - anterolaterally on first 2 ribs

  
• Scalenes - Action

  elevate first 2 ribs - aid in inspiration

  flex + rotate neck
• Erector Spinae Muscle Group - Components

  prime mover of back extension

  each side consists of 3 columns - iliocostalis, longissimus + spinalis muscles

  = forms the intermediate layer of instrinsic back muscles

  
• Erector Spinae Muscle Group - Action

  provide resistance that helps control action of bending forward at the waist + act as powerful extensors to promote return to erect position
• Erector Spinae Muscles - Iliocostalis

  iliocostalis - most lateral muscle group of erector spinae muscles

  extend from pelvis to neck

  
• Erector Spinae Muscles - Iliocostalis (Action)

  acting together, extend the vertebral column (maintain erect posture)

  acting on one side, laterally flex the vertebral column toward same side
• Erector Spinae Muscles - Longissimus

  longissimus = longest, thickest + most central erector spinae muscle

  divided into 3 parts - capitis, cervicis + thoracis

  = based on their superior attachments + location

  
• Erector Spinae Muscles - Spinalis

  the most medial of the 3 muscles

  also have the the 3 parts - capitis, cervicis + thoracis

  extends vertebral column

  
• Deep Back Muscles - Semispinalis


  semispinalis = composite muscle forming part of deep layer of intrinsic back muscles

  extends from thoracic region to head

  
• Semispinalis - Action


  extends vertebral column + head + rotates them to opposite side

  acts synergistically w sternocleidomastoid muscle of opposite side
• Quadratus Lumborum


  fleshy muscles forming part of posterior abdominal wall

  laterally flexes vertebral column when acting separately

  when paired, aids in forced inspiration + maintains upright posture