2: Detailed Notes on Deep Back Muscles and Spinal Cord Anatomy

Deep Back Muscles

  • Segmental Back Muscles: These complete the deep back, including:

    • Levatoris Costarum

    • Interspinalis

    • Intertransversi

Splenius Group

  • Splenius: Underneath the erector spinae.

    • Splenius means "bandage".

  • Muscle Fiber Direction:

    • Fibers travel from spinous process (medial) to transverse process (lateral).

    • Action: Ipsilateral.

  • Rotation:

    • Muscles in this group rotate ipsilaterally or contralaterally depending on the muscle fiber orientation.

    • Muscles with opposite fiber orientation will cause contralateral rotation.

  • Splenius as a Group:

    • Bundled together with other muscles.

    • Can differentiate the cervicis portion by dissecting underneath capitis.

  • Splenius Capitis Lateral Flexion:

    • Can laterally flex the neck if working on one side.

    • If the right side is working/contracting, it can create a bit of lateral flexion.

  • Superficial vs. Deep:

    • One side of the visual presented is superficial, the other is deeper allowing for multiple muscle groups to be seen and discussed.

  • Rhomboids vs. Serratus Posterior Superior:

    • Rhomboid minor and major are visible on the superficial side.

    • Serratus posterior superior is visible on the deeper side.

  • Dorsal Scapular Nerve:

    • Runs parallel to the medial border of the scapula.

    • Pierces the underbelly of the rhomboid minor and major.

  • Splenius Capitis and Cervicis:

    • Superficial side shows splenius capitis.

    • Rhomboids must be reflected to find splenius cervicis.

  • Nerve Identification:

    • Dorsal scapular nerve pathway visible.

    • Greater occipital nerve runs spine to spine and is easier to find.

Erector Spinae Group

  • General Information:

    • Originates down by the lumbar vertebrae.

    • Extends to ribs in the lumbar and thoracic area.

    • Goes up to the mastoid process.

    • Lumborum portion in the lumbar area.

    • Thoracic portion in the thoracic area.

  • Subdivisions:

    • Spinalis

    • Longissimus

    • Iliocostalis

    • Origin and insertion for each subdivision is the bottom-most origin to the top-most insertion.

  • Thoracolumbar Fascia:

    • Thick white fascia.

    • Some of the erector spinae originate from it.

    • Latissimus dorsi also attaches to it.

  • Tendinous Attachments:

    • Striations show tendinous attachments and insertion of muscles.

  • Muscle Identification:

    • Spinalis is visible on one side.

    • Subdivisions are iliopostalis, longissimus, and spinalis.

Multifidus

  • Action:

    • Contraction on both sides causes extension.

    • Contraction on one side pulls spinous process towards transverse process.

  • Location:

    • Found throughout the spine, but largest in the lumbar region.

  • Dissection:

    • Dissect underneath erector spinae to find this deeper group.

Semispinalis

  • Orientation: Runs more vertically.

  • Relationship to Splenius: Underneath the splenius.

  • Semispinalis Capitis: Topmost portion.

  • Greater Occipital Nerve: Typically runs straight through the muscle belly of the semispinalis capitis.

  • Suboccipital Region: Deep to the semispinalis capitis. Trace the greater occipital nerve from its origin coming out of C2.

  • Pathway: Travels right underneath one of the suboccipital muscles before exiting.

Suboccipital Muscles

  • Characteristics:

    • Have their own insertion.

    • Have their own innervation.

    • Have a specific artery.

  • Vertebral Artery: Runs within this region.

  • Clinical Relevance:

    • During cervical spine manipulations, test for vertebral artery functioning and impingement.

    • Impingement can cause patients to pass out.

    • Avoid maneuvers in patients with plaque or arteriosclerosis.

Spinal Nerves

  • C1 and C2 Spinal Nerves:

    • C1 spinal nerve.

    • C2 spinal nerve and down.

    • Branch into dorsal primary rami and ventral primary rami.

  • Dorsal Primary Rami:

    • Tend to innervate the back of the body.

  • Specificity:

    • Longissimus thoracis for the thoracic region.

    • Innervation corresponds to specific spinal nerves.

  • Level Determination:

    • Not required to state the side of the body as a level of specificity.

Suboccipital Triangle

  • Muscles Forming the Triangle:

    • Obliquus capitis inferior

    • Obliquus capitis superior

    • Rectus capitis posterior major

  • C1 Characteristics

    • Posterior tubercle area.

  • Actions in general for this area

    • Extension.

  • Muscles of that area for Function

    • Retractors of C1/C2.

  • Suboccipital Nerve:

    • Motor mostly.

    • Cutaneous part from C1, C2, and C3 nerve roots.

  • Relationship to Greater Occipital Nerve:

    • Suboccipital triangle.
      minor to c1 and major further down

  • Muscles:

    • Obliques

    • Rectus capitis posterior major

Central Nervous System

  • Components: Brain and spinal cord.

Spinal Column

  • Anatomy: Vertebrae, vertebral bodies, spinous processes.

  • Vertebral Canal: Houses the spinal cord.

  • Spinal Nerves: Each level of the spinal cord is associated with a specific numbered spinal nerve.

  • Intervertebral Foramen: Spinal nerves exit through this.

  • Transition Point: Between cervical and thoracic regions, spinal nerves exit above or below the same number vertebrae.

  • Cervical Region: Spinal nerves exit above the same number vertebral level.

  • Thoracic Region: Spinal nerves exit at the same number vertebral level.

  • Number of Vertebrae: 7 cervical, 12 thoracic.

  • Number of Cervical Spinal Nerves: 8.

Spinal Cord

  • White Matter: Periphery, contains myelinated axons, motor and sensory information.

  • Gray Matter: Horns in the middle.

  • Columns:

    • Anterior (Ventral)

    • Posterior (Dorsal)

    • Lateral

  • Horns:

    • Dorsal (Posterior)

    • Ventral (Anterior)

    • Lateral (Thoracic region only)

  • Diagram Example:

    • Spinal nerve exits as T1, T3, etc. through intervertebral foramen.

    • Spinal nerve is motor and sensory wrapped in one.

    • Motor and sensory information divides closer to the spinal cord.

    • Sensory information goes to the back.

    • Motor information goes to the front to skeletal muscles.

  • Dorsal Root Ganglia:

    • Bulbous area on the dorsal root.

Meninges

  • Protective Layers: Surround the spinal cord and brain.

  • Three Layers:

    • Dura mater (outermost, thickest)

    • Arachnoid mater (inner surface, translucent)

    • Pia mater (directly adheres to the spinal cord, cannot be isolated and picked off)

Spinal Cord Anchors

  • Spinal Filum Terminale: Extension of the pia mater down to the sacrum, anchors longitudinally

  • Denticulate Ligaments: Lateral anchors of the spinal cord made of pia mater, anchor from side-to-side.

Dermatomes and Myotomes

  • Definitions:

    • Dermatome: Peripheral cutaneous map for sensory distribution from a single spinal nerve.

    • Myotome: Motor aspect of a single spinal level, the muscles innervated by a specific nerve
      Clinical utility to knowing the differences in both maps