Notes on Facial Expressions and Related Muscles

Importance of Facial Expressions

• Essential for communication.
• Indicate emotions (e.g., happiness, curiosity).

Introduction to the Scalp

• Definition: Layer of skin and subcutaneous tissue covering the cranium.
• Extends from:
  • Supraorbital margins on frontal bone to superior nuchal line on occipital bone.
  • Covers temporal fascia and extends to zygomatic arches.
• Five Layers of the Scalp (Mnemonic: SCALP):
  • Skin
  • Connective tissue
  • Aerosis (epicranial aerosis)
  • Loose connective tissue
  • Paracranium (periosteum on external surface of the cranium)
• First three layers form a single unit called the scalp proper.

Muscles of Facial Expression

• Found deep in the skin of the scalp, face, and neck.
• Most attach to bones or fascia on one end and skin on the other.
• Originate from the mesoderm of the second pharyngeal arch along with the facial nerve (Cranial Nerve VII).
• Innervated by branches of the facial nerve:
  • Posterior auricular
  • Temporal
  • Zygomatic
  • Buccal
  • Marginal mandibular
  • Cervical
• Mnemonic for remembering branches: To Zanzibar by Motorcar.

Occipital Frontalis Muscle

• Two bellies (frontal and occipital) connected by epicranial aerosis.
• Frontal Belly:
  • Origin: Epicranial aerosis
  • Insertion: Skin superior to eyes and nose
  • Innervation: Temporal nerve
• Occipital Belly:
  • Origin: Superior nuchal line of occipital bone
  • Insertion: Epicranial aerosis
  • Innervation: Posterior auricular nerve
• Function: Elevates eyebrows and wrinkles forehead (surprise).

Orbicularis Oculi Muscle

• Parts: Palpebral (eyelid) and orbital (surrounding orbit).
• Palpebral Part:
  • Origin: Medial palpebral ligament
  • Insertion: Lateral palpebral ligament
• Orbital Part:
  • Origin: Medial orbital margin
  • Insertion: Skin around orbit
• Innervation: Superior part - Temporal nerve; Inferior part - Zygomatic nerve.
• Function: Closes eyelids (gently or tightly).

Muscles of the Eyebrows

• Corrugator Supercilii:
  • Origin: Medial part of the superciliary arch
  • Insertion: Skin of medial half of eyebrow
  • Innervation: Temporal nerve
  • Function: Pulls eyebrows medially and inferiorly (frowning).

Muscles of the Nose

• Muscles: Procerus, Nasalis, Levator labii superioris alaeque nasi.
• Procerus:
  • Origin: Nasal bone, lateral nasal cartilage
  • Function: Depresses medial ends of eyebrows (transverse wrinkles).
• Nasalis:
  • Two parts: Transverse (narrows nostrils) and Alar (flairs nostrils).
  • Origin: Maxilla on either side of the nose.
• Levator Labii Superioris Alaeque Nasi:
  • Origin: Frontal process of maxilla
  • Insertion: Upper lip, AER cartilage
  • Function: Flares nostrils, raises upper lip.

Muscles of the Oral Region

• Orbicularis Oris Muscle:
  • Encircles mouth, originates on maxilla and mandible.
  • Innervated by Buccal nerve.
  • Function: Closes mouth, protrudes lips.

Muscles of the Upper Lip

• Muscles Include:
  • Risorius
  • Levator anguli oris
  • Zygomaticus major
  • Zygomaticus minor
  • Levator labii superioris
• Functions: Raise corners of mouth, smile, and pull upper lip upward.

Muscles of the Lower Lip

• Muscles Include:
  • Depressor anguli oris (pulls mouth down - sadness)
  • Depressor labii inferioris (pulls lower lip down)
• Innervated by Marginal mandibular nerve.

Mentalis Muscle

• Origin: Body of the mandible
• Insertion: Skin of the chin
• Function: Elevates and protrudes lower lip.
• Innervated by Marginal mandibular nerve.

Platysma Muscle

• Broad muscle of the neck.
• Origin: Suprascapular and infraclavicular subcutaneous tissue.
• Insertion: Base of the mandible.
• Function: Depresses mandible, draws corners of mouth down, tenses skin of lower face and neck.

Buccinator Muscle

• Rectangular muscle found deep in the cheek.
• Origin: Alveolar processes of maxilla and mandible.
• Function: Presses cheek against teeth (e.g., drinking from a straw).

Recap

• Scalp is a skin layer covering the cranium with five layers.
• Facial muscles originate from the second pharyngeal arch.
• Key facial muscles discussed include occipital frontalis, orbicularis oculi, corrugator supercilii, procerus, nasalis, orbicularis oris, and buccinator among others.
• Each muscle has specific functions related to facial expressions.