Musculature of the Human Body

Section B: Extrinsic Muscles of the Vertebral Column

Overview

• Also known as hypaxial muscles (below the axis of the vertebral column).
• Act on the thoracic cage (as thoracic wall) or on the superior limb.
• Two main categories:
  • Respiratory muscles: Act on the thoracic cage.
  • Axio-appendicular muscles: Deep posterior and superficial posterior subsets.

Respiratory Muscles

• Originate: Spinous processes.
• Insert: Angles of ribs.
• Function: Help in respiration, mainly forceful inhalation.
• Innervation: Anterior rami of spinal nerves.
• Types:
  1. Serratus Posterior Superior: Elevates ribs 2-5.
  2. Serratus Posterior Inferior: Depresses ribs 9-12.
• Combined Effect: Increase in the superior-inferior diameter of the thorax.

Deep Posterior Axio-Appendicular Muscles

• Originate: Vertebral processes (both transverse and spinous).
• Insert: Scapula.
• Function: Act on the scapulothoracic joint.
• Innervation: Anterior rami of spinal nerves.
• Types:
  1. Levator Scapulae: Elevates and rotates scapula inferiorly.
  2. Rhomboid Minor: Elevates and retracts the scapula.
  3. Rhomboid Major: Elevates and retracts the scapula.
  • All innervated by the dorsal scapular nerve.

Superficial Posterior Axio-Appendicular Muscles

• Originate: Spinous processes.
• Insert: Superior limb.
• Function: Act on the scapulothoracic joint.
• Innervation: Anterior rami of spinal nerves.
• Types:
  1. Latissimus Dorsi: Produces extension, medial rotation, and adduction of the arm at the glenohumeral joint.
  2. Trapezius: Divided into three parts:
     • Superior (Descending) Part: Elevates the shoulder.
     • Middle (Transverse) Part: Retracts the shoulder.
     • Inferior (Ascending) Part: Depresses the scapula.

Lumbar Triangle

• Borders:
  • Superior Lateral: Medial margin of external abdominal oblique.
  • Superior Medial: Lateral margin of latissimus dorsi.
  • Inferior: Superior margin of iliac crest.
• Clinical Significance: Area prone to herniation.

Section A: Intrinsic Muscles of the Vertebral Column

Overview

• Also known as epaxial muscles (above the axis of the body).
• Act on the vertebral column itself, not the superior limbs.
• Surrounded by thoracolumbar fascia (anterior, middle, and posterior laminae).

Types of Intrinsic Muscles

1. Suboccipital Muscles: Form the suboccipital triangle and assist in head extension and rotation.
   • Includes: Rectus Capitis Posterior Major, Rectus Capitis Posterior Minor, Obliquus Capitis Superior, Obliquus Capitis Inferior.
2. Segmental Muscles: Develop segmentally between vertebrae, mainly act in proprioception and posture.
   • Includes: Interspinales, Intertransversarii, Levator Costarum.
3. Transversospinalis Muscles: Connect transverse processes to spinous processes, aiding in back extension and contralateral rotation.
   • Includes: Rotatores, Multifidus, Semispinalis.
4. Erector Spinae Muscles: Major back extensors and lateral flexors.
   • Subdivided into Iliocostalis, Longissimus, Spinalis.
5. Spinotransversalis Muscles: Extend and rotate the head and neck.
   • Includes: Splenius Capitis, Splenius Cervicis.

Section C: Anterior Lateral Abdominal Wall Musculature

Overview

• Consists of four main muscles from internal to external:
  • Transversus Abdominis
  • Internal Abdominal Oblique
  • Rectus Abdominis
  • External Abdominal Oblique
• Function: Compresses the abdominopelvic cavity, aids in expiration.

Details

1. Transversus Abdominis
   • Origin: Costal margin, thoracolumbar fascia, iliac crest.
   • Insertion: Linea alba, pubic crest.
   • Action: Compresses the abdominopelvic cavity.
2. Internal Abdominal Oblique
   • Origin: Thoracolumbar fascia, iliac crest, inguinal ligament.
   • Insertion: Linea alba.
   • Action: Flexes the trunk anteriorly (bilateral), ipsilateral trunk rotation (unilateral).
3. Rectus Abdominis
   • Origin: Pubic crest, pubic symphysis.
   • Insertion: Costal cartilages of ribs 5-7, xiphoid process.
   • Action: Compresses abdominopelvic cavity, flexes the trunk.
4. External Abdominal Oblique
   • Origin: Inferior ribs (mainly 5-12).
   • Insertion: Linea alba, iliac crest.
   • Action: Flexes and rotates the trunk (contralaterally).

Other Features

• Linea Alba: Vertical line of fibrous tissue extending from the xiphoid process to the pubic symphysis.
• Rectus Sheath: Formed by the aponeuroses of the abdominal muscles, enclosing the rectus abdominis.
• Arcuate Line: Horizontal line marking the lower limit of the posterior layer of the rectus sheath.

Posterior Abdominal Wall Musculature

Overview

• Consists of: Psoas Major, Psoas Minor, Iliacus, Quadratus Lumborum.
• Function: Flexion and stabilization of the spine, aid in hip flexion.

Other Key Musculatures

Facial Muscles

• Responsible for facial expressions and innervated by the facial nerve.
• Includes muscles like Frontalis, Orbicularis Oculi, Corrugator Supercilii, Nasalis.

Masticatory Muscles

• Originate from cranial bones and insert into the mandible.
• Function in chewing.
• Includes: Masseter, Temporalis, Lateral Pterygoid, Medial Pterygoid.

Extrinsic Eye Muscles

• Originate from the common annular tendon.
• Function: Move the eye in various directions.
• Includes: Superior Rectus, Medial Rectus, Inferior Rectus, Lateral Rectus, Superior Oblique, Inferior Oblique.

Palatine Muscles

• Important for soft palate movement and functions.
• Includes: Tensor Veli Palatini, Levator Veli Palatini, Musculus Uvulae, Palatoglossus, Palatopharyngeus.

Pharyngeal Muscles

• Constriction and elevation of the pharynx.
• Constrictor muscles include: Superior Pharyngeal Constrictor, Middle Pharyngeal Constrictor, Inferior Pharyngeal Constrictor.
• Longitudinal muscles: Palatopharyngeus, Salpingopharyngeus, Stylopharyngeus.

Prevertebral Muscles

• Located in the neck, aiding in head flexion and stabilization.
• Includes muscles like Longus Capitis, Longus Colli, Scalenes (anterior, middle, posterior).

Suprahyoid and Infrahyoid Muscles

• Suprahyoid: Elevate the hyoid bone; include Digastric, Stylohyoid, Mylohyoid, Geniohyoid.
• Infrahyoid: Depress the hyoid bone; include Omohyoid, Sternohyoid, Sternothyroid, Thyrohyoid.