2. Muscles of the Spine

Suboccipital Nerve **

Is the dorsal primary ramus of the first cervical nerve (C1). It exits the spinal cord between the skull and the first cervical vertebra, the atlas. It lies within the suboccipital triangle along with the vertebral artery, where the artery enters the foramen magnum. Supplies the 4 muscles of the suboccipital triangle.

Trapezius **

Layer 1 Origin: Occipital bone, ligmamentum nuchae, spinous processes of C7 - T12 Insertion: Spine of the scapula, acromion process of the scapula, lateral ⅓ of the clavicle Innervation: Accessory Nerve Function: The upper fibres of the trapezius elevates the scapula and rotates it during abduction of the arm. The middle fibres retract the scapula and the lower fibres pull the scapula inferiorly.

Latissimus Dorsi **

Layer 1 Origin: Vertebral part: spinous processes of 7th-12th thoracic vertebrae Iliacal part: iliac crest Costal part: 9th-12th ribs Scapular part: inferior angle of the scapula Insertion: Intertubercular groove of the humerus Innervation: Thoracodorsal nerve Function: Extends, adducts and medially rotates the arm.

Rhomboids Minor **

Layer 2 Origin: Nuchal ligament and spinous processes of C7 and T1 vertebrae Insertion: Smooth triangular area at the medial end of the spine of the scapula Innervation: dorsal scapular nerve Function: It retracts and rotates the scapula.

Rhomboids Major **

Layer 2 Origin: Spinous processes of T2-T5 Insertion: Medial border (closest to the spine) of the scapula, from the spine of the scapula to the inferior angle Innervation: dorsal scapular nerve Function: retracts and rotates the scapula.

Levator Scapula **

Layer 2 Origin: Transverse process of the atlas and axis, posterior tubercles C3 and C4 Insertion: Superior angle and medial border of the scapula Innervation: dorsal scapular nerve Function: elevates the scapula.

Intermediate group of back muscles

Layer 3 Serratus posterior superior and serratus posterior inferior muscles. These two muscles elevate and depress the ribs. Also called accessory muscles of respiration.

Deep group of back muscles

Layer 4-6 the extensors and rotators of the head and neck: the splenius capitis and cervicis the extensors and rotators of the vertebral column: the erector spinae and transversospinales the short segmental muscles-the interspinales and intertransversarii

Spinalis **

Layer 5 Arises from the common tendinous origin, and attaches to the spinous processes of C2, T1-T8 and the occipital bone of the skull. Straightens the back.

rectus capitis posterior major **

Origin: Spinious Process of Axis Insertion: Lateral portion of occipital bone Innervation: sub-occipital nerve Function: extension of head, rotation of face to same side as muscle

rectus capitis posterior minor **

Origin: posterior tubercle of atlas Insertion: medial portion of occipital bone Innervation: sub-occipital nerve Function: extension of head

obliquus capitis superior **

Origin: spinous process of axis Insertion: occipital bone between superior and inferior nuchal line Innervation: sub-occipital nerve Function: rotation of face to same side

obliquus capitis inferior **

Origin: transverse process of atlas Insertion: transverse process of atlas Innervation: sub-occipital nerve Function: extension of head and bends it to same side

Greater occipital nerve

The nerve arises from between the first and second cervical vertebrae, along with the lesser occipital nerve. Causes headaches from tension.

Suboccipital Triangle

The suboccipital muscles form the boundaries of the suboccipital triangle: • The rectus capitis posterior major muscle forms the medial border of the triangle. • The obliquus capitis superior muscle forms the lateral border. • The obliquus capitis inferior muscle forms the inferior border. Contents: Sub-occipital Nerve (from C1 - motor) and vertebral artery.

Superficial group of back muscle

trapezius, latissimus dorsi, rhomboid major, rhomboid minor, and levator scapulae.

Suboccipital muscles

• rectus capitis posterior major • rectus capitis posterior minor • obliquus capitis inferior • obliquus capitis superior Contraction of the suboccipital muscles extends the head at the atlanto-axial joint. The suboccipital muscles are innervated by the sub-occipital nerve.

Serratus Posterior Superior **

Layer 3 Origin: Lower part of the nuchal ligament and the spinous processes of the vertebrae C7 through T3 and their corresponding supraspinous ligaments Insertion: Superior borders and external surfaces of the second to fifth ribs, lateral to their angles Innervation: Ventral rami of T2, T3, T4, T5 Function: elevates the ribs (and help us breath in).

Serratus Posterior Inferior **

Layer 3 Origin: The spinous processes of the T11 to L2/L3 and their corresponding supraspinous ligaments, blending with the lumbar part of the thoracolumbar fascia Insertion: Inferior borders and outer surfaces of the lower four ribs (9th -12th), lateral to their angles Innervation: intercostal and subcostal nerves Function: depresses the ribs. Doesn't work during rest.

Splenius Capitis **

Layer 4 Origin: Inferior half of ligamentum nuchae (C3-C6) and spinous processes of C7-T3 (possibly down to T6) Insertion: Superior nuchal line of occipital bone and mastoid process of temporal bone Innervation: Dorsal primary rami of spinal nerves C2-C6. Function: Rotates head to the same side.

Splenius Cervicis

Layer 4 Origin: Spinous processes and supraspinous ligaments of T3-6 Insertion: Posterior tubercles of transverse processes of C1-3 Innervation: Posterior primary rami of C5, 6 Function: Rotates head to the same side.

Erector spinae muscles **

Layer 5 Iliocostalis, Longissimus and Spinalis. Allow us to stand on two. The muscles in the erector spinae group are the primary extensors of the vertebral column and head. Acting bilaterally, they straighten the back, returning it to the upright position from a flexed position. The originate from the musculotendinous mass (L3-L5).

Ilicostalis **

Layer 5 Origin: Iliac crest, sacrum, lumbar vertebrae Insertion: Ribs, cervical transverse processes Innervation: Posterior primary rami Function: Straightens the back.

Longissimus **

Layer 5 The largest of the erector spinae. Arises from the musculotendinous mass, and attaches to the lower ribs, the transverse processes of C2 - T12, and the mastoid process of the skull. Straightens the back.

Multifidus **

Layer 6 Deep to the semispinalis. The multifidus muscles are present throughout the length of the vertebral column but are best developed in the lumbar region. Extends and contralaterally rotates the head and vertebral column. If this muscle isn't used it atrophies.

Semispinalis Capitis **

Layer 6 Origin: The muscle originates on the articular processes of the C5 -8 as well as the transverse processes of T 1-6. Insertion: The semispinalis capitis attaches onto the occiput inbetween the superior and inferior nuchal line. Innervation: Greater occipital nerve Function: Extends and contralaterally rotates the head and vertebral column

Transversospinalis muscles

Layer 6 Run obliquely upward and medially from transverse processes to spinous processes, filling the groove between these two vertebral projections. They are deep to the erector spinae and consist of three major subgroups-the semispinalis, multifidus, and rotatores muscles. When muscles in the transversospinales group contract bilaterally, they extend the vertebral column, an action similar to that of the erector spinae group. However, their major function is to cause the trunk to turn or rotate.

Rotators

Layer 6 The deepest of the transversospinales group. They are present throughout the length of the vertebral column but are best developed in the thoracic region. Their fibers pass upward and medially from transverse processes to spinous processes crossing two vertebrae (long rotators) or attaching to an adjacent vertebra (short rotators). Extends and contralaterally rotates the head and vertebral column