Facial nerve examination (Cranial nerve 7)

Examining Cranial Nerve VII (Facial Nerve)

Examining cranial nerve VII, also known as the facial nerve, is a crucial skill for healthcare professionals, particularly in neurology and general medicine. This article will guide you through the examination process, underlying anatomy and physiology, and provide self-assessment questions to enhance your understanding.

Understanding the Facial Nerve

The facial nerve is primarily responsible for motor control of the muscles of facial expression. It also carries sensory information related to taste from the anterior two-thirds of the tongue and provides parasympathetic innervation to glands, including the salivary and lacrimal glands.

The nerve emerges from the brainstem and travels through the internal acoustic meatus, branching into several important components.

Examination of the Facial Nerve

A systematic approach is essential for an accurate assessment.

Step-by-step guide:

1. Patient Interaction
   • Introduce yourself and obtain consent.
   • Example: "I need to examine the nerve supply to your face today. Is that okay with you?"
2. Initial Questions
   • Ask about changes in taste or hearing, as the chorda tympani branch is responsible for taste sensation, and another branch innervates the stapedius muscle in the ear.
3. Motor Function Tests
   • Raise Eyebrows – Tests the temporal branch.
   • Close Eyes Tightly – Assess the zygomatic branch by trying to open them.
   • Puff Cheeks – Evaluate the buccal branch by applying gentle pressure.
   • Smile and Show Teeth – Tests the mandibular branch.
   • Purse Lips – Assesses the cervical branch.
4. Comfort Check
   • Keep the patient informed and comfortable throughout the exam.

Anatomy of the Facial Nerve

The facial nerve has intracranial and extracranial branches.

Intracranial branches:

• Chorda Tympani – Taste sensation from the anterior two-thirds of the tongue.
• Stapedius Branch – Controls the stapedius muscle for sound modulation.

Extracranial branches can be remembered using the mnemonic "To Zanzibar By Motor Car":

• Temporal
• Zygomatic
• Buccal
• Mandibular
• Cervical

Clinical Relevance

Recognizing facial nerve dysfunction is essential.

• Upper motor neuron lesions (e.g., stroke)
  • Only affects the lower half of the contralateral face.
  • Forehead sparing due to bilateral innervation of upper facial muscles.
• Lower motor neuron lesions (e.g., Bell’s palsy)
  • Weakness of the entire ipsilateral face.
  • No forehead sparing.

Self-Assessment Questions

1. What are the primary functions of the facial nerve?
2. What is the role of the chorda tympani in taste sensation?
3. How can you differentiate between upper and lower motor neuron lesions?
4. Can you list the five branches of the facial nerve and their functions?

Conclusion

Mastering the examination of cranial nerve VII is essential for healthcare professionals. Understanding its anatomy, function, and clinical relevance will improve diagnostic skills and patient care.

Practice these techniques and reflect on the self-assessment questions to reinforce your knowledge.

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