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M01.02.019 Facial Expression
The muscles of facial expression are essential for nonverbal communication and contribute to vital functions like eye protection, speech, and eating. These muscles, located in the subcutaneous tissue of the face, originate from bone or fascia and are inserted into the skin. They are unique in their ability to pull on the skin to exert their effects.
Key Characteristics
- Embryological Origin: All facial muscles develop from the second pharyngeal arch and retain their innervation from the facial nerve (cranial nerve VII).
- Categories: These muscles are classified into three groups:
- Orbital Group
- Nasal Group
- Oral Group
Orbital Group
The orbital muscles control eyelid movements, protecting the cornea. Both are innervated by branches of the facial nerve.
1. Orbicularis Oculi
| Feature | Description |
|---|---|
| Attachments | Origin: Medial orbital margin, medial palpebral ligament, lacrimal bone; Insertion: Skin around the orbit and tarsal plates. |
| Actions | Palpebral: Gently closes eyelids; Lacrimal: Drains tears; Orbital: Tightly closes eyelids. |
| Innervation | Temporal and zygomatic branches of the facial nerve. |
2. Corrugator Supercilii
| Feature | Description |
|---|---|
| Attachments | Origin: Medial superciliary arch; Insertion: Skin of the eyebrow. |
| Actions | Draws eyebrows together, creating vertical wrinkles (frowning). |
| Innervation | Temporal branches of the facial nerve. |
Clinical Relevance: Paralysis of Orbital Muscles
- Symptoms:
- Inability to close the eyelids, causing exposure keratitis.
- Drooping of the lower eyelid (ectropion), leading to pooling of tears and corneal ulceration.
- Test: Assess facial nerve palsy by asking the patient to raise eyebrows and close eyelids.
Nasal Group
The nasal muscles regulate nasal openings and movements of the surrounding skin.
1. Nasalis
| Feature | Description |
|---|---|
| Attachments | Transverse: Maxilla (lateral to nose); Alar: Maxilla (over lateral incisor). |
| Actions | Transverse: Compresses nasal opening; Alar: Widens nasal opening. |
| Innervation | Buccal branches of the facial nerve. |
2. Procerus
| Feature | Description |
|---|---|
| Attachments | Origin: Nasal bone; Insertion: Skin of lower medial forehead. |
| Actions | Pulls eyebrows downward, creating transverse wrinkles over the nose. |
| Innervation | Buccal branches of the facial nerve. |
3. Depressor Septi Nasi
| Feature | Description |
|---|---|
| Attachments | Origin: Maxilla (above medial incisor); Insertion: Nasal septum. |
| Actions | Pulls the nasal septum inferiorly, widening the nasal opening. |
| Innervation | Buccal branches of the facial nerve. |
Oral Group
Oral muscles enable movements of the mouth and lips, essential for speech, eating, and facial expressions.
1. Orbicularis Oris
| Feature | Description |
|---|---|
| Attachments | Origin: Maxilla and cheek muscles; Insertion: Skin and mucosa of lips. |
| Actions | Closes lips and narrows the oral opening. |
| Innervation | Buccal branches of the facial nerve. |
2. Buccinator
| Feature | Description |
|---|---|
| Attachments | Origin: Maxilla and mandible; Insertion: Orbicularis oris and skin of lips. |
| Actions | Pulls cheeks inward, preventing food accumulation. |
| Innervation | Buccal branches of the facial nerve. |
3. Minor Oral Muscles
| Group | Muscles |
|---|---|
| Upper Group | Risorius, Zygomaticus (major/minor), Levator labii superioris, Levator labii superioris alaeque nasi, Levator anguli oris. |
| Lower Group | Depressor anguli oris, Depressor labii inferioris, Mentalis. |
Clinical Relevance: Paralysis of Oral Muscles
- Symptoms:
- Difficulty eating, with food collecting in cheeks.
- Sagging of mouth and cheeks, with asymmetry during smiling.
Points to Remember
- All facial expression muscles are innervated by cranial nerve VII (facial nerve).
- Damage to the facial nerve leads to functional impairments, including:
- Difficulty closing eyelids or controlling the mouth.
- Visible asymmetry in expressions like smiling or frowning.
- Understanding anatomy is critical for diagnosing conditions like Bell’s Palsy.
References
- TeachMeSeries Ltd. “Muscles of Facial Expression Anatomy (2024).”
- Gray’s Anatomy for Students.
- Netter’s Clinical Anatomy, 4th Edition.