Lecture Notes: Muscles of Facial Expression

Introduction

• Facial expressions are crucial for communication.
• Expressions convey emotions (happiness, curiosity, etc.).

The Scalp

• Definition: Skin and subcutaneous tissue covering the cranium.
• Boundaries:
  • Extends from the supraorbital margins (frontal bone) to the superior nuchal line (occipital bone).
  • Laterally covers the temporal fascia, extending to the zygomatic arches.
• Layers: (Mnemonic: SCALP)
  • S: Skin
  • C: Connective tissue
  • A: Aponeurosis (Epicranial)
  • L: Loose connective tissue
  • P: Pericranium (periosteum of the cranium)
• The first three layers form the 'scalp proper'.

Facial Muscles

• Found in the skin of the scalp, face, and neck.
• Attach to bones/fascia on one end and skin on the other.
• Origin: Mesoderm of the second pharyngeal arch, along with the facial nerve (Cranial nerve VII).
• Innervation: Branches of the facial nerve: Posterior auricular, temporal, zygomatic, buccal, marginal mandibular, and cervical nerves.

Muscles and Their Functions

Occipitofrontalis Muscle

• Structure: Two bellies (frontal and occipital) connected by the epicranial aponeurosis.
• Function:
  • Frontal belly: Protracts the scalp.
  • Occipital belly: Retracts the scalp.
  • Together: Elevate eyebrows, wrinkle forehead (surprised expression).
• Innervation:
  • Frontal belly: Temporal nerve.
  • Occipital belly: Posterior auricular nerve.

Orbicularis Oculi Muscle

• Parts: Palpebral and orbital.
• Function:
  • Palpebral: Closes eyelids gently (blinking, sleep).
  • Orbital: Closes eyelids tightly (winking, squeezing shut).
• Innervation:
  • Superior part: Temporal nerve.
  • Inferior part: Zygomatic nerve.

Corrugator Supercilii Muscle

• Location: Deep to the eyebrows.
• Function: Pulls eyebrows medially and inferiorly (frowning).
• Innervation: Temporal nerve.

Nasal Muscles

• Procerus: Depresses medial ends of the eyebrows, creates transverse wrinkles on the nose.
• Nasalis:
  • Transverse part narrows nostrils.
  • Alar part flares nostrils.
• Levator Labii Superioris Alaeque Nasi: Flares nostrils and raises upper lip.
• Innervation: Zygomatic nerve.

Oral Region Muscles

• Orbicularis Oris: Encircles the mouth, closes lips, and protrudes lips (kissing, whistling).
• Innervation: Buccal nerve.

Upper Lip Muscles

• Risorius: Retracts the corner of the mouth.
• Levator Anguli Oris: Raises the corner of the mouth (grinning).
• Zygomaticus Major and Minor: Elevates the corner of the mouth (smiling), pulls upper lip upward.
• Levator Labii Superioris: Pulls upper lip upward.
• Innervation: Zygomatic and buccal nerves.

Lower Lip Muscles

• Depressor Anguli Oris: Pulls corner of mouth downward (sadness).
• Depressor Labii Inferioris: Lowers lower lip (pouting).
• Innervation: Marginal mandibular nerve.

Chin Muscle

• Mentalis: Elevates and protrudes the lower lip (pouting).
• Innervation: Marginal mandibular nerve.

Neck Muscle

• Platysma: Depresses mandible, draws corners of the mouth down, tenses neck skin.
• Origin: Supraclavicular and infraclavicular regions, inserts on mandible.

Buccinator Muscle

• Location: Deep in cheeks.
• Function: Presses cheeks against teeth (drinking from a straw).
• Innervation: Buccal nerve.

Summary

• Scalp: 5 layers protecting the cranium.
• Facial Muscles: Originate from the second pharyngeal arch and innervated by the facial nerve.
• Facial Expressions: Muscles enable a wide range of expressions essential for communication.