What is the sensory supply of the larynx in an older adult with a history of stroke or neurodegenerative disease presenting with dysphagia?

Sensory Supply of the Larynx

Anatomical Distribution

The internal branch of the superior laryngeal nerve (internal SLN) provides the primary sensory innervation to the larynx, dividing into three distinct divisions that supply different regions critical for protective reflexes. 1

Three-Division Pattern

• Superior division: Supplies the mucosa of the laryngeal surface of the epiglottis 1
• Middle division: Innervates the mucosa of the true and false vocal folds, plus the aryepiglottic fold 1
• Inferior division: Provides sensation to the arytenoid region mucosa, subglottis, anterior hypopharyngeal wall, and upper esophageal sphincter 1

High-Density Sensory Areas

• The laryngeal mucosa contains one of the most dense concentrations of sensory receptors in the human body 1
• Dense sensory plexi that cross the midline are concentrated on the laryngeal surface of the epiglottis and arytenoid region 1
• The areas receiving greatest innervation (epiglottis, false and true vocal folds, arytenoid region) correspond to the most sensate regions demonstrated by physiological experiments 1

Clinical Relevance in Dysphagia

Receptor Mechanisms

• TRPV1 receptors (transient receptor potential cation channel subfamily V member 1) are expressed at free nerve endings of the superior laryngeal nerve and glossopharyngeal nerve 2
• These receptors can be stimulated by capsaicinoids and piperine to enhance swallow reflex latency and improve laryngeal vestibule closure time 2

Impaired Sensation in Neurological Disease

• Reduction in laryngeal sensation occurs in elderly patients, stroke patients, heart-lung transplant recipients, and those with laryngopharyngeal reflux 2
• Loss of dopaminergic neurons in stroke or neurodegenerative diseases contributes to decreased swallow reflex, which is directly associated with impaired sensory function 2
• Even momentary loss of laryngeal sensory function is followed rapidly by life-threatening pneumonia due to failed protective reflexes 1

Silent Aspiration

• Impaired laryngeal sensation leads to silent aspiration, where patients do not cough or clear their throat in response to airway invasion 2
• 55% of patients with aspiration present with silent aspiration without protective cough reflex 3, 4
• Older adults have higher rates of silent aspiration than younger patients, reducing reliability of bedside clinical evaluations alone 4

Protective Reflex Pathways

• The dense sensory innervation enables laryngeal protective reflexes during swallowing that prevent aspiration 1
• Substance P is released from sensory nerve terminals in the nasopharynx and enhances the swallow reflex; decreased sputum levels are associated with aspiration pneumonia 2
• The cough reflex sensitivity to tussigenic challenges (citric acid, capsaicin) is mediated through these sensory pathways and is impaired in patients with advanced Parkinson disease compared to controls 2

Motor Component (Notable Exception)

• The internal SLN appears to supply motor innervation to the interarytenoid muscle, contrary to traditional concepts of it being purely sensory 1
• This finding is relevant for understanding complete laryngeal function during swallowing 1