These sensations are carried by CN IX, which acts as the afferent limb of the reflex to the ipsilateral nucleus solitarius (also referred to as the gustatory nucleus) after synapsing at the superior ganglion located in the jugular foramen. The stimulus is provided by sensation to the posterior pharyngeal wall, the tonsillar pillars, or the base of the tongue. The nerve roots of cranial nerves IX and X exit the medulla through the jugular foramen and descend on either side of the pharynx to innervate the posterior pharynx, posterior one-third of the tongue, soft palate, and the stylopharyngeus muscle. The gag reflex is controlled by both the glossopharyngeal (CN IX) and vagus (CN X) nerves, which serve as the afferent (sensory) and the efferent (motor) limbs for the reflex arc, respectively. In cases of psychogenic gag reflexes, even the thought of touching a sensitive trigger area, such as occurs when going to the dentist, can induce gagging. A psychogenic gag reflex presents following a mental trigger, typically without direct physical contact. A somatogenic gag reflex follows direct physical contact with a trigger area, which may include the base of the tongue, posterior pharyngeal wall, or tonsillar area. Accessed: April 18, 2017.The gag reflex can be classified as either somatogenic or psychogenic. Amyotrophic Lateral Sclerosis (ALS) and Other Motor Neuron Diseases (MNDs).Diagnosis and management of motor neurone disease. Incidence and lifetime risk of motor neuron disease in the United Kingdom: a population-based study. Alonso A, Logroscino G, Jick SS, Hernán MA.Enterostomy feeding for patients with stroke and bulbar palsy. Khan H, Khan I, Gupta A, Nageshwaran S, Hussain N.The Neurological Exam: Cranial Nerves: V3 Trigeminal Nerve, Motor.Pseudobulbar affect: prevalence and management. The jaw jerk: an instance of misattribution. Erman AB, Kejner AE, Hogikyan ND, Feldman EL.Acute bulbar palsy as a variant of Guillain-Barré syndrome. Emotional incontinence ( pseudobulbar affect).Difficulty in tongue protrusion due to spasticity.Dysphagia, drooling, and nasal regurgitation.Speech: spastic dysarthria (husky, nasal voice).Facial expressions: absent (expressionless face).Dysphagia, drooling, nasal regurgitation.Upper motor neuron palsy of the respective muscles.Bilateral damage or injury of corticobulbar tracts to nerve nuclei of cranial nerves V, VII, IX, X, XI, and XII.Lower motor neuron palsy of the respective muscles.Bilateral damage or injury of the nerve nuclei of cranial nerves IX, X, XI, and XII.Injury or malignancy of the high brainstem.Neurodegenerative disease: amyotrophic lateral sclerosis, progressive supranuclear palsy, multiple sclerosis.Infectious neuropathies: poliomyelitis, diphtheria, neurosyphilis.Autoimmune neuropathies: Guillain-Barré syndrome, myasthenia gravis.Neurodegenerative diseases: amyotrophic lateral sclerosi s, s yringobulbia.CSF analysis and MRI of the brain help identify the etiology. Lower motor neuron signs ( atrophy and fasciculations of the tongue, absent gag reflex) differentiate bulbar palsy from pseudobulbar palsy, which presents with upper motor neuron signs ( spastic tongue, exaggerated gag, and jaw jerk reflexes). In addition, patients with pseudobulbar palsy present with a lack of facial expression, difficulty chewing, and emotional lability. Both bulbar and pseudobulbar palsy are seen mainly in men over 75 years old and present with dysarthria and dysphagia. Any condition which disrupts or damages the cranial nerve nuclei or corticobulbar tracts can cause bulbar or pseudobulbar palsy (e.g., stroke, multiple sclerosis, infections, brain stem tumors). Pseudobulbar palsy is an upper motor neuron palsy that affects the corticobulbar tracts of the V th, VII th, IX th, X th, XI th, and XII th cranial nerves. Bulbar palsy is a lower motor neuron palsy that affects the nuclei of the IX th, X th, XI th, and XII th cranial nerves.
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