From the Guidelines
A deficit in facial expression is the primary issue associated with a 2nd arch nerve problem affecting pre-trematic (pre-branchial) functions. The facial nerve (cranial nerve VII), which develops from the 2nd pharyngeal arch, controls the muscles of facial expression. When the pre-trematic component of this nerve is affected, patients typically present with facial weakness or paralysis on the affected side, manifesting as an inability to smile symmetrically, close the eye completely, wrinkle the forehead, or raise the eyebrow. This results in a characteristic drooping appearance of the face. The pre-trematic designation refers to the evolutionary origin of this nerve component, which developed anterior to the gill slits (trema) in ancestral vertebrates. The facial nerve's special visceral efferent fibers innervate muscles derived from the 2nd pharyngeal arch mesoderm, explaining why these specific muscles of facial expression are affected when this component is compromised. Other functions of the facial nerve, such as taste sensation and lacrimation, may remain intact depending on which specific branches are involved 1.
Some key points to consider in this context include:
- The facial nerve (CN VII) is one of the most complex cranial nerves and contains branchial motor, visceral motor, general sensory, and special sensory functions 1.
- The intracranial course of the facial nerve includes pontine, cisternal, and intratemporal segments, and it may be affected by various conditions such as infarction, vascular malformations, tumors, and multiple sclerosis 1.
- The extracranial segment of the facial nerve courses through the parotid gland and may be affected by parotid tumors, inflammation, and conditions of the neighboring anatomic spaces and skull base 1.
- Facial nerve palsy can present with facial droop, pain around the jaw or ear, hyperacusis, tinnitus, reduced taste, and decreased lacrimation or salivation 1.
Given the complexity of the facial nerve and its various functions, it is essential to carefully evaluate patients with suspected 2nd arch nerve problems to determine the specific branches involved and the underlying cause of the deficit. This will enable healthcare providers to develop an effective treatment plan and improve patient outcomes 1.
From the Research
2nd Arch Nerve Issue and Associated Deficits
The 2nd arch nerve, also known as the facial nerve, has several functions including controlling the muscles of facial expression, transmitting taste sensations from the anterior two-thirds of the tongue, and providing parasympathetic innervation to the lacrimal gland and salivary glands.
- The facial nerve is responsible for parasympathetic stimulation of the lacrimal gland, which is crucial for tear production 2.
- Damage to the facial nerve can lead to decreased tear secretion and dry eye syndromes 3.
- Facial nerve palsy can result in exposure keratopathy, which can be complicated by loss of corneal sensation, leading to a neurotrophic corneal ulcer 4.
Pre-trameric Functions and Associated Deficits
Pre-trameric functions refer to the functions of the facial nerve that are related to the pre-branchial arches.
- The lacrimal gland is innervated by the facial nerve, and damage to this nerve can result in decreased tear production 2, 3.
- The facial nerve also provides parasympathetic innervation to the submandibular gland, which is involved in saliva production.
- Taste to the tip of the tongue is mediated by the facial nerve, specifically the chorda tympani branch.
Deficit Associated with 2nd Arch Nerve Issue
Based on the information provided, the deficit associated with a 2nd arch nerve issue, specifically affecting 'pre-trameric' functions, is likely related to lacrimal gland function.