Neurology RHS 344 Lecture 9 PDF

Neurology RHS 344 Lecture 9 The Neurology of Swallowing Lecture outline The Normal Swallowing The central swallowing system Neurological swallowing disorder  Summary of Normal Swallowing (1 of 2) © Alila Sao Mai/Shutterstock Summary of Normal Swallowing...

Neurology RHS 344 Lecture 9 The Neurology of Swallowing Lecture outline The Normal Swallowing The central swallowing system Neurological swallowing disorder  Summary of Normal Swallowing (1 of 2) © Alila Sao Mai/Shutterstock Summary of Normal Swallowing (2 of 2)  The Oral Preparatory Stage: Overview Voluntary stage of the swallow Length depends on substance eaten Food is placed in the mouth and prepared for swallowing Labial seal established Oral breathing stops and nasal breathing takes its place  Mastication Trigeminal nerve (CN V) innervates the muscles for mastication (i.e., chewing) Mandibular elevators: masseter, temporalis, and pterygoid Mandibular depressors: mylohyoid and anterior belly of digastric muscle  Gland Secretion Saliva works along side mastication to break down food Consists of water and enzymes Three major salivary glands (see next slide): Parotid gland: stimulated by CN IX Submandibular glands: stimulated by CN VII Sublingual glands: stimulated by CN VII Salivary Glands  The Oral Stage: Overview Voluntary stage of the swallow Lasts approximately 1 second Begins once mastication ends Tongue forms ramp and moves bolus from the oral cavity to the pharyngeal cavity Labial seal and nasal breathing maintained  Labial Seal Facial muscles, including lip muscles, controlled by cranial nerve VII, the facial nerve Labial seal important for keeping bolus in the oral cavity  Tongue Retraction Trigeminal nerve helps retract the tongue Controls the following tongue muscles: Digastric muscle Mylohyoid muscle Helps tongue form into a ramp to move the bolus posteriorly  Anterior-Posterior Bolus Movement Hypoglossal nerve (CN XII) controls most of the intrinsic and extrinsic tongue muscles Also helps form tongue ramp Innervates tongue to squeeze bolus from the anterior part of the mouth to the posterior part of the mouth The Oral Stage  The Pharyngeal Stage: Overview Essentially involuntary stage (though you can exercise voluntary control if desired) Lasts approximately 1 second As bolus contacts faucial arches Soft palate elevates Vocal cords adduct Respiration pauses Larynx elevates Cricopharyngeus relaxes  Soft Palate Closure Crucial in keeping food/liquid out of nasal cavity Five muscles are involved in soft palate movement Levator veli palatini (CN X, XI): raises soft palate Palatoglossal (CN X, XI): raises soft palate Tensor veli palatini (CN V): tenses soft palate Musculus uvulae (CN X, XI): closes off soft palate Palatopharyngeus (CN X, XI): pulls up and constricts pharynx  Laryngeal Closure Three valves close to protect the airway from the bolus entering it: Valve #1: Epiglottis Valve #2: False vocal cords Valve #3: True vocal cords (CN X)  Laryngeal Elevation Various suprahyoid muscles contract during the pharyngeal stage These raise the larynx under the closing epiglottis and further seal off the airway, protecting it from the bolus  Pharyngeal Constriction CN X and XI control the following pharyngeal muscles: Superior pharyngeal constrictor Middle pharyngeal constrictor Inferior pharyngeal constrictor This constricting movement accounts for the squeezing sensation we feel in the throat during the pharyngeal swallow The bolus is squeezed through the pharynx  The Esophageal Stage: Overview Involuntary swallowing stage It is variable in length (8–20 seconds) depending on the consistency of the bolus Peristaltic waves move bolus through the esophagus Moves the bolus to the stomach in conjunction with gravity  Esophageal Opening Upper esophageal sphincter controlled by the cricopharyngeus muscle This muscle is innervated by the vagus nerve Normally contracted muscle, but relaxes and opens when bolus moves through the pharynx  Esophageal Constriction Esophagus is 18–25 cm tube that is collapsed when a bolus is not present Contains three segments: Cervical region: made up of striated muscle Thoracic region: made up of mix of striated and smooth muscle Abdominal region: made up of smooth muscle Peristaltic waves move bolus through esophagus to the stomach The Esophageal Stage Summary  The Central swallowing system Brainstem Involvement (1 of 2) Two important brainstem nuclei Nucleus tractus solitarius (NTS) Located in the medulla Acts as a swallowing sensory center Receives afferent information from CN V, VII, IX, and X Afferent information includes taste and touch as well as respiratory and cardiovascular input Sends information to second nucleus  Brainstem Involvement (2 of 2) Nucleus ambiguous (NA) Located in the medulla Motor swallowing center Innervates the swallowing muscles via CN IX, X, and XII NTS and NA are often discussed as a functional unit and called the swallowing center of the medulla Brainstem Swallowing Nuclei Cranial Nerve Involvement in Swallowing  Subcortical and Cortical Controls Primary motor cortex (BA 4) activates voluntary muscles of swallowing. Primary sensory cortex (BA 1-3) processes sensation of eating. Insula may mediate motor and sensory information involved in swallowing as well as provide some level of swallow control. Anterior cingulate cortex may provide the attention needed in swallowing. Premotor cortex (BA 6) may play role in the motor planning of swallowing. Thalamus and basal ganglia may incorporate sensory information from food and liquid into swallowing as food and liquid pass through the swallowing structures.  Neurology of the Cough Response Coughing is an important defensive act that keeps food out of airway Three main components: Afferent vagus fibers convey sensory information from cough receptors in swallowing tract This information goes to a cough center in brainstem Efferent signals are sent from cough center to respiratory muscles and larynx to generate cough  Neurology of Silent Aspiration Aspiration occurs when the bolus penetrates the airway below the level of the vocal cords. About one-third of dysphasic patients aspirate without any signs (i.e., no cough). Neurological damage can suppress the cough response system discussed in previous slide. Clinical Indicators of Aspiration  Neurological swallowing disorder Causes of Dysphagia Neurological Causes Mechanical Causes Stroke Acute inflammations TBI Cancer Spinal cord injury Cervical spinal Degenerative diseases disease Brain tumors NG tubes Artificial airways  Dysphagia Can Cause Aspiration Pneumonia Malnutrition Dehydration  Swallowing Problems Associated with Neurological Damage (1 of 2) Oral preparatory stage Difficulty chewing Food falling out of mouth (poor lip seal) Oral stage Food remaining in mouth (pocketing) Difficulty forming bolus Difficulty moving bolus backwards in mouth (anterior to posterior movement)  Swallowing Problems Associated with Neurological Damage (2 of 2) Pharyngeal stage Swallow delay Swallow absence Pooling of bolus Esophageal stage Bolus staying in esophagus (dysmotility due to lack of peristaltic waves)  Stroke (1 of 4) In the cortex, these patients will most likely show: Weakness or paralysis and loss of sensory information of the oral structures resulting in: Poor oral prep stage Residue due to sensory deficits Slow oral transit Delayed swallow initiation Weak pharyngeal phase Weakness/paralysis of vocal cord Apraxia: an impairment in the motor planning for swallowing Will be unable to complete a dry swallow on evaluation but often do better with trials  Stroke (2 of 4) In the subcortex: Impaired motor control of oral structures may result in: Slow oral phase Slow oral transit Delayed pharyngeal phase  Stroke (3 of 4) In the brainstem: Impaired center for automatic swallow response may result in: Impaired oral prep stage Complete loss of or delayed swallow response  Stroke (4 of 4) In the cerebellum: Loss of coordination may result in: Poor oral phase due to difficulty coordinating formation of bolus Discoordination of swallow response in pharyngeal phase  TBI Trauma to the head Often diffuse so dysphagia may or may not be involved, depends on location of injury Cranial nerves may be injured from trauma Injury to mouth or jaw will impact oral and oral prep stages May have delayed or poorly coordinated pharyngeal phase or absent swallow response Often will have feeding tubes and/or trachs after initial injury  Parkinson Disease Uncoordinated movement affects the oral phase of swallowing Premature spillage occurs in pharyngeal phase Delayed swallow initiation Weak pharyngeal constriction causes excessive residue in pharyngeal phase and incomplete airway closure Esophageal abnormalities are common  ALS Early in the disease, patients will exhibit weight loss and mild difficulty due to weakness of the oral and pharyngeal structures Initially will need texture modifications and increased time to eat due to transport issues As the disease progresses, weakness becomes so severe that patients will need a feeding tube Eventually patients become unable to handle their own secretions and have to be suctioned