S10 EPHE141 S24 Axial muscle

EPHE141 – Muscles of the Axial Skeleton

  • Relevant sections of Chapters 9 & 10 will be studied.

  • All course content is exclusive for registered students and is copyrighted.

  • Content will not be included in the midterm but will be assessed in the final exam.

Learning Outcomes for Axial Musculature

  • Identify body regions and muscle actions:

    • Anterior neck

    • Posterior neck and back

    • Muscles of respiration

    • Anterior abdominal wall

    • Posterior abdominal wall

  • Distinguish between primary vs accessory muscles of breathing.

  • Understand special structures of abdominal muscles.

    • For splenius, erector spinae, and transversospinalis muscles, only group names are required, not individual muscles.

Axial Muscle Categories

  • Categories of axial muscles include:

    • Head and neck

    • Vertebral column

    • Respiration

    • Abdominal wall

    • Pelvis and perineum

  • Many axial muscles are paired:

    • Bilateral actions: Contract together

    • Unilateral actions: Only one side contracts

Muscles of the Anterior Neck

  • Sternocleidomastoid Muscle:

    • Bilateral Action: Flexion of head at neck.

    • Unilateral Actions:

      • Lateral flexion (side-bending)

      • Contralateral rotation (head turns to opposite side of muscle contracting).

Muscles of the Posterior Neck and Back

  • Erector Spinae Muscles:

    • Important for posture, extending from sacrum to skull.

    • active all the time (just a bit of tension to keep you upright) 

    • Bilateral Action:

      • Extends neck and vertebral column.

      • Maintains upright posture.

    • Unilateral Action:

      • Lateral flexion.

Muscles of Respiration

  • Diaphragm Muscle:

    • Muscle contraction during inspiration causes it to flatten (active process)

      Active process = requires energy

      Central tendon pulls down to cause diaphragm to flatten

      This increases the size of the thoracic cavity and draws breath in , allowing for greater lung expansion and improved oxygen intake.

  • Other Muscle Groups Involved in Respiration:

    • Muscles that Elevate Ribs:

      • External intercostal muscles

      • Scalene muscle group

    • Muscles that Depress Ribs:

      • Internal intercostal muscles

      • Transversus thoracis muscles

      • Abdominal muscles (also involved).

Muscles of the Anterior Abdominal Wall

  • Key Muscles Include:

    • Rectus abdominis

    • External oblique

    • Internal oblique

    • Transversus abdominis

  • Functions:

    • Compresses the abdomen during forced expiration.

    • Contralateral rotation: turns to opposite side.

    • Ipsilateral rotation: turns to same side.

Special Structures in the Abdominal Region

  • Aponeurosis: Dense regular connective tissue formed by abdominal muscles.

  • Rectus Sheath: Encloses the rectus abdominis muscle, formed by aponeuroses.

  • Linea Alba: Vertical landmark where aponeuroses meet.

  • Tendinous Inscriptions: Fibrous horizontal lines of connective tissue. Dense CT with a lot of collagen. Biomechanically, stop the rectus abdominis from bulging out during flexion and prevents fluid build-up 

Rectus Abdominis Muscle

  • Bilaterally:

    • Assists in flexion of the vertebral column.

    • Compresses the abdominal wall.

External Abdominal Oblique Muscle

  • Bilaterally:

    • Assists in flexion of the vertebral column.

    • Compresses abdominal wall.

    • Depresses ribs.

  • Unilaterally:

    • Lateral flexion of the vertebral column.

    • Contralateral rotation of the vertebral column.

Internal Abdominal Oblique Muscle

  • Bilaterally:

    • Assists in flexion of the vertebral column.

    • Compresses abdominal wall.

    • Depresses ribs.

  • Unilaterally:

    • Lateral flexion and ipsilateral rotation of the vertebral column.

Transversus Abdominis Muscle

  • Deepest of the anterior abdominal muscles with horizontal fibres.

  • Function:

    • Bilaterally compresses the abdominal wall and supports abdominal organs.

Muscles of the Posterior Abdominal Wall

  • Primary Muscles:

    • Psoas major and iliacus muscles:

      • Primary Movement: Hip flexion.

      • When femurs are fixed, they contribute to flexion of the vertebral column.

    • Quadratus Lumborum:

      • Function: Lateral flexion of the vertebral column (weak action).