Axial Muscles

Lecture Presentation by Steven Bassett

The Muscular System: Axial Musculature

Copyright © 2015 Pearson Education, Inc.

Learning Outcomes Overview

  • 10.1: Describe the location and function of the four groups of axial muscles.
  • 10.2: Identify the six subgroups of the muscles of the head and neck and explain how they differ in their origins, insertions, actions, and innervations.
  • 10.3: List the three layers of the muscles of the vertebral column and explain how the muscles differ in their origins, insertions, actions, and innervations.
  • 10.4: Identify the muscles of the oblique and rectus groups and explain how they differ in their origins, insertions, actions, and innervations.
  • 10.5: Name the muscles of the perineum and pelvic diaphragm and explain how they differ in their origins, insertions, actions, and innervations.

Clinical Note: Hernias

  • Description and significance of hernias in relation to the muscular system.

Hot Topics

  • Anatomy of Temporalis Muscle: In-depth discussion on the temporalis muscle, particularly regarding its structure and function. Revised content noted.

Introduction to the Muscular System

  • The skeletal muscle of the body can be subdivided into two major groups:
    • Axial musculature:
    • Muscles that position the head and vertebral column.
    • Muscles that move the rib cage.
    • Appendicular musculature:
    • Muscles that stabilize or move the appendicular skeleton.

Four Groups of Axial Muscles

  • The axial muscles can be categorized into four main groups:
    • Muscles of the Head and Neck
    • Muscles of the Vertebral Column
    • Oblique and Rectus Muscles
    • Muscles of the Pelvic Floor

Muscles of the Head and Neck

  • Muscles can be further divided into the following subgroups:
    • Muscles of Facial Expression
    • Includes: Buccinator, Depressor labii inferioris, Levator labii superioris, Orbicularis oris, Depressor anguli oris, Zygomaticus major and minor, Risorius, Mentalis.
    • Extra-ocular Muscles:
    • Control eye movements: Medial and lateral rectus muscles, Superior and inferior rectus muscles, Superior and inferior oblique muscles.
    • Muscles of Mastication:
    • Masseter, Temporalis, Pterygoids (medial and lateral).
    • Muscles of the Tongue
    • Muscles of the Pharynx
    • Anterior Muscles of the Neck:
    • Includes: Digastric, Mylohyoid, Geniohyoid, Stylohyoid, Omohyoid, Sternohyoid, Sternothyroid, Thyrohyoid.

Muscles of Facial Expression

  • Relating to Facial Expression:
    • Scalp: Occipitofrontalis (frontal and occipital bellies), Temporoparietalis.
    • Eye: Corrugator supercilii, Levator palpebrae superioris (CN III), Orbicularis oculi.
    • Nose: Procerus, Nasalis.
    • Neck: Platysma.

Muscles of Mastication

  • Muscle Details:
    • Masseter:
    • Origin: Aponeurosis and bones of the zygomatic arch
    • Insertion: Lateral surface and angle of mandibular ramus
    • Action: Elevates mandible and closes jaws.
    • Innervation: Trigeminal nerve (NV), mandibular branch.
    • Temporalis:
    • Origin: Along temporal lines of skull
    • Insertion: Coronoid process of mandible.
    • Action: Elevates mandible and assists in moving the mandible from side to side.
    • Innervation: Trigeminal nerve (NV).
    • Pterygoids:
    • Medial Pterygoid:
      • Origin: Medial surface of the lateral pterygoid plate.
      • Action: Elevates the mandible.
    • Lateral Pterygoid:
      • Origin: Lateral surface of the lateral pterygoid plate.
      • Action: Opens the jaw, protrudes mandible, or moves mandible side to side.

Muscles of the Vertebral Column

  • The muscles of the back are organized into three distinct layers:
    • Superficial Layer (Extrinsic Back Muscles)
    • Move the neck (e.g., Trapezius, Latissimus dorsi, Levator scapulae, Rhomboids).
    • Intermediate Layer (Extrinsic Back Muscles)
    • Move the vertebral column (e.g., Serratus posterior: superior and inferior).
    • Deep Layer (Intrinsic Back Muscles)
    • Interconnect the vertebrae and stabilize.
  • Deep Layer Subdivisions:
    • Superficial Intrinsic Muscles (e.g., Splenius).
    • Intermediate Intrinsic Muscles (e.g., Erector spinae: Spinalis thoracis, Longissimus thoracis, Iliocostalis lumborum).
    • Deep Intrinsic Muscles (e.g., Semispinalis, Multifidus, Rotatores).

Oblique and Rectus Muscles

  • These can be grouped into three regions:
    • Cervical Muscles (e.g., Scalene muscles): elevate ribs; flex neck.
    • Thoracic Muscles (e.g., External and Internal intercostals):
    • External Intercostals: Elevate the ribs.
    • Internal Intercostals: Depress the ribs; oppose diaphragm contraction.
    • Serratus Posterior: Superior elevates ribs, inferior depresses.
    • Abdominal Muscles:
    • External Oblique: Flexes and rotates the vertebral column (contralateral).
    • Internal Oblique: Rotates the vertebral column (ipsilateral).
    • Transversus Abdominis: Compresses the abdomen.
    • Rectus Abdominis: Flexes the vertebral column; divided by linea alba.

Muscles of the Perineum and Pelvic Diaphragm

  • Main Functions:
    • Support organs of the pelvic cavity.
    • Flex joints of the sacrum and coccyx.
    • Control movement through urethra and anus.
  • Divisions:
    • Urogenital Triangle and Anal Triangle.
  • Separation: By the superficial transverse perineal muscle.