Impact of Cranial Nerve Damage on Swallow Function
Impact of Cranial Nerve Damage on Swallow Function
Impact of Cranial Nerve Damage on Swallow Function
In chapter 1, the impact of CN damage was briefly addressed and is reviewed here. Injury to the sensory and motor innervation pathways can result in deficits in feeding or swallowing especially when cranial nerves V, VII, IX, X, XI, or XII are involved. Understanding the role of these cranial nerves allows you to anticipate the impact that CN damage will have on swallow function. In a focal injury, swallow function will be altered in a predictable pattern depending on the location and extent of the damage. Box 2.29 through 2.34 schematically indicate risks to swallow physiology in the event of cranial nerve damage.
CN V: Trigeminal Nerve
CN V carries sensory function to the oral cavity and motor function to jaw and floor of mouth muscles. Damage to this nerve may result in reduced awareness of oral bolus, which can lead to poor bolus control, oral residue or/and reduced mastication. It also impacts hyo-laryngeal trajectory thereby altering UES opening (Box 2.29).
Box 2.29: CN V and associated impact on swallow function if damaged
CN VII: Facial Nerve
CN VII carries sensory fibers for taste to the anterior tongue and motor fibers to the lips and cheek region. Damage to this nerve may result in (a) reduced taste perception for foods and liquids in the anterior oral cavity, (b) reduced lip motor function which may impact anterior oral containment, and (c) reduced buccal contraction yielding reduction in oral pressure and bolus control (Box 2.30). The latter may yield leakage into the oral lateral sulci. Damage to CN VII may also impact function of submandibular glands resulting in reduced saliva production, which may lead to difficulty in generating a cohesively formed bolus. Reduced saliva production is also implicated in tooth decay and increased oral bacteria.
Box 2.30: CN VII and associated impact on swallow function if damaged
Clinical Note
Damage to CN VII may result in the following.
- Reduced lip function may impact oral containment as evidenced by anterior spillage or drooling.
- Poor bolus control as evidenced by residue in buccal pockets.
- Reduced taste sensation in anterior tongue.
- Damage to secreto-motor systems may impact function of sublingual and submandibular glands and decreased oral saliva production.
CN IX, X & XI: Glossopharyngeal, Vagus, & Accessory Nerves
Although this text defines activities specific to each cranial nerve, in reality fibers from CNs IX, X, and XI combine at various points in the nerve’s journey. However, for simplicity, the damage profiles are presented per cranial nerve.
CN IX carries sensory, taste and motor fibers important for swallowing (Box 2.31). Taste fibers innervate the posterior tongue and palate. Therefore, damage to this CN may alter taste perception. Damage to this nerve may also result in reduced sensory function in the posterior oral cavity and pharynx, which may impact swallow trigger resp