Neurology
Cortical & Subcortical Regions involved in the Swallowing Process
NEURAL CONTROL OF SWALLOWING
Swallowing is a centrally mediated phenomenon that can be divided into supratentorial and infratentorial regions of control. The supratentorial area of control is located in the frontal cortex anterior to the sensorimotor cortex (55). The infratentorial or brainstem areas involved in control of swallowing are located in the dorsal region within and subajacent to the nucleus of the tractus solitarius as well as in the ventral region around the nucleus ambiguus (56). In both brainstem sites the neurons surrounding the adjacent medullary reticular formation are also involved (57).
The cortical and subcortical regions of the brain are important pathways in the voluntary initiation of swallowing (58, 59). Studies using transcranial magneto-electric stimulation to identify corticofugal projections to the muscles of swallowing have demonstrated that oral muscles, such as the mylohyoid, are represented symmetrically between the two cortical hemispheres, while laryngopharyngeal and esophageal muscles are represented asymmetrically, with most people having a dominant swallowing hemisphere (60). The clinical implication of these findings is that one could expect oropharyngeal dysphagia to result from a unilateral cortical stroke (61), which is most often the case.
The dorsal and ventral medullary regions controlling swallowing are represented on both sides of the brainstem and are interconnected. Either side can coordinate the pharyngeal and esophageal stages of deglutition, however because they are interconnected, normal motor and sensory functioning on each side of the laryngopharynx depends on intactness on both sides of the medulla (62, 63). The clinical implication is that a unilateral medullary lesion can result in bilateral pharyngeal motor and sensory dysfunction (64, 65).
Left Hempisphere
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Right Hemisphere
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Subcortex
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Cerebellum
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Brainstem
Pons
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Medulla
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Cranial Nerves
and
Swallowing
Clinical Implications
Cranial Nerves
• I Olfactory
• II Optic
• III Oculomotor
• IV Trochlear
• V Trigeminal
• VI Abducens
• VII Facial
• VIII Vestibulocochlear
• IX Glossopharyngeal
• X Vagus
• XI Spinal accessory
• XII Hypoglossal
Cranial Nerves and Involvement in Swallowing
Trigeminal - V
- Sensory: -Pain, temperature, and tactile to: Face and forehead, Mucous membranes of the nose and mouth, Teeth, Portions of the cranial dura -Deep pressure and kinesthetic info to: Teeth, Gums, Hard palate, TMJ,
- Motor: -Muscles of mastication -Mandibular elevators Masseter, temporalis, and medial pterygoid -Mandibular depressors Digastricus and mylohyoid -Muscles of the ear -Tensor tympani Involved in stapedial reflex -Tensor veli palatini Opens Eustachian tube -Extrinsic (suprahyoid) laryngeal muscles -Digastricus and mylohyoid Elevate the larynx
Facial - VII
- Sensory: -Innervation to submandibular, sublingual, and lacrimal glands -Taste on anterior 2/3s of tongue and nasopharynx
- Motor: -Muscles of facial expression -Muscle of the ear -Stapedial muscle -Involved in the stapedial reflex -Extrinsic (suprahyoid) laryngeal muscles -Digastricus (2nd belly) and stylohyoid -Elevate the larynx
Glossopharyngeal - IX
- Sensory: -Pharynx -Part of velum -Faucial pillars -Posterior 1/3 of tongue -Eustachian tube -Parotid gland -Gag reflex
- Motor: -Stylopharyngeus -Laryngeal elevation -Superior pharyngeal constrictors -Aids in velopharyngeal closure
Vagus - X
- Sensory: -Soft palate -Tongue base -Pharynx -Larynx -External auditory meatus -Subglottal
- Motor: -Pharyngeal branch -Innvervation of all muscles of the soft palate and pharynx (except stylopharyngeus, superior pharyngeal constrictor, and tensor veli palatini) -Palatoglossus muscle of the tongue -Primarily responsible for pharyngeal constriction and elevation of the soft palate during velopharyngeal closure during speech and swallowing -Superior laryngeal branch -Inferior pharyngeal constrictor – important for swallowing -Cricothyroid muscle – important for pitch changes -Recurrent laryngeal branch -Abduction and adduction of vocal folds
Accessory - XI
- Motor: -Cranial portion aids vagus in innervation of the levator veli palatini and intrinsic laryngeal muscles -Also, the spinal portion contribute to head rotation and shoulder shrugging
Hypoglossal - XII
- Motor: -Innervates all intrinsic and all but one (palatoglossus innervated by vagus) extrinsic muscles of the tongue
Spinal Nerves
- For speech, spinal nerves are most important for respiratory purposes
-C3, C4, and C5 (called the phrenic nerve)
-Innervate the diaphragm
-Most important muscle of respiration
-Thoracic spinal nerves
-Innervate the intercostal muscles
-Innervate the abdominal muscles
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CRANIAL NERVE
CN V
CN VII
CN X
CN XII
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Disordered Physiology
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Swallowing Symptoms
N?A
Aspiration before & during swallow
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