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Understanding Facial Expressions and Muscles

Apr 1, 2025

Lecture Notes: Facial Expressions and Muscles

Introduction

  • Importance of facial expressions in communication
    • Indicate emotions such as happiness, curiosity, etc.

Scalp Anatomy

  • Definition: Layer of skin and subcutaneous tissue covering the cranium
  • Extends from: Supraorbital margins (frontal bone) to superior nuchal line (occipital bone)
  • Lateral Coverage: Temporal fascia to zygomatic arches
  • Five Layers of the Scalp (acronym: SCALP)
    1. Skin
    2. Connective tissue
    3. Aerosis (epicranial aerosis)
    4. Loose connective tissue
    5. Pericranium (periosteum of the cranium)
  • First three layers form a single unit called the scalp proper

Muscles of Facial Expression

  • Location: Deep in the skin of the scalp, face, and neck
  • Attachment: One end to bones/fascia and the other to skin
  • Origin: Mesoderm of the second pharyngeal arch
  • Innervation: By branches of the facial nerve (Cranial Nerve VII)
    • Branches: Posterior auricular, temporal, zygomatic, buccal, marginal mandibular, cervical
    • Mnemonic: "To Zanzibar by Motor Car"

Key Facial Muscles

  1. Occipital Frontalis Muscle

    • Bellies: Frontal (anterior) and Occipital (posterior)
    • Frontal Belly:
      • Origin: Epicranial aerosis
      • Insertion: Skin above eyes/nose
      • Innervation: Temporal nerve
      • Function: Protracts scalp, elevates eyebrows
    • Occipital Belly:
      • Origin: Superior nuchal line of occipital bone
      • Insertion: Epicranial aerosis
      • Innervation: Posterior auricular nerve
      • Function: Draws scalp back
  2. Orbicularis Oculi Muscle

    • Parts: Palpebral and Orbital
    • Palpebral Part:
      • Origin: Medial palpebral ligament
      • Insertion: Lateral palpebral ligament
      • Function: Closes eyelids gently (blinking/sleeping)
    • Orbital Part:
      • Origin: Medial orbital margin
      • Insertion: Skin around orbit
      • Function: Closes eyelids tightly (winking)
  3. Corrugator Supercilii (Eyebrow muscle)

    • Origin: Medial superciliary arch
    • Insertion: Skin of medial eyebrow
    • Innervation: Temporal nerve
    • Function: Pulls eyebrows medially/inferiorly (frowning)
  4. Muscles of the Nose

    • Procerus:
      • Origin: Nasal bone
      • Insertion: Skin between eyebrows
      • Function: Depresses medial ends of eyebrows
    • Nasalis (Two parts):
      • Transverse Part: Narrows nostrils
      • Alar Part: Expands/flairs nostrils
    • Levator Labii Superioris Alaeque Nasi:
      • Origin: Frontal process of maxilla
      • Insertion: Upper lip/nasal cartilage
      • Function: Flares nostrils, raises upper lip
  5. Orbicularis Oris Muscle

    • Origin: Maxilla, mandible, angle of mouth
    • Insertion: Mucus membrane of lips
    • Innervation: Buccal nerve
    • Function: Closes mouth, protrudes lips

Upper Lip Muscles

  • Muscles: Risorius, Levator Anguli Oris, Zygomaticus Major, Zygomaticus Minor, Levator Labii Superioris
  • Functions: Elevate and retract corners of the mouth for smiling/grinning

Lower Lip Muscles

  • Muscles: Depressor Anguli Oris, Depressor Labii Inferioris
  • Functions: Pull corners downwards for sadness/pouting
  • Innervation: Marginal mandibular nerve

Muscle of the Chin: Mentalis

  • Origin: Body of mandible
  • Insertion: Skin of chin
  • Function: Elevates and protrudes lower lip (pouting)

Platysma (Neck Muscle)

  • Origin: Supraclavicular and infraclavicular tissue
  • Insertion: Base of mandible
  • Function: Draws mouth downwards

Buccinator Muscle

  • Origin: Alveolar processes of maxilla/mandible, pterygomandibular raphe
  • Insertion: Merges with orbicularis oris
  • Innervation: Buccal nerve
  • Function: Presses cheek against teeth (drinking)

Recap of Key Points

  • Scalp Structure: Five layers define it
  • Facial Muscles Origin: Mesoderm of second pharyngeal arch
  • Muscle Functions: Various facial expressions involve specific muscles
  • Innervation: Mostly by facial nerve branches

Conclusion

  • Understanding facial muscles is crucial for communication and expression