Muscles of Back (Pages 117-129)

Overview of Back Muscles

• Body weight distribution is anterior to the vertebral column, necessitating strong back muscles for support and movement.
• Major muscle groups: extrinsic (superficial and intermediate) and intrinsic (deep) back muscles.

Extrinsic Back Muscles

• Superficial Extrinsic Muscles:

  • Include trapezius, latissimus dorsi, levator scapulae, and rhomboids.
  • Connect axial skeleton to pectoral girdle and humerus, facilitating limb movements.
  • Primarily innervated by anterior rami of cervical nerves; trapezius specifically innervated by spinal accessory nerve (CN XI).

• Intermediate Extrinsic Muscles:

  • Serratus posterior (superior and inferior) act as slender respiratory muscles, likely more proprioceptive in function.
  • Innervated by intercostal nerves; superior part by the first four intercostals, inferior by the last four.

Intrinsic Back Muscles

• Muscles specifically act on the vertebral column, maintaining posture and controlling movements.
• Innervated by posterior rami of spinal nerves.
• Enclosed by deep fascia, attaching medially to nuchal ligament, spinous processes, supraspinous ligament, and sacrum.

Deep Fascia

• Thoracic and lumbar regions have distinct fascial structures:
  • Thoracolumbar fascia serves as a thick covering for lumbar muscles and encases thoracic intrinsic back muscles.

Muscle Layers

• Superficial Layer:

  • Splenius muscles (splenius capitis and splenius cervicis) cover deep neck muscles, resembling a bandage.
  • Arise from midline and extend to cervical vertebrae and cranium.

• Intermediate Layer:

  • Erector spinae muscles lie in a groove alongside the vertebral column, crucial for spinal extension.
  • Divided into three columns:
    • Iliocostalis (lateral column)
    • Longissimus (intermediate column)
    • Spinalis (medial column)