Muscles and Nerves

Extrinsic Laryngeal Muscles

• Infrahyoid muscles depress the hyoid bone.
• The sternohyoid depresses the hyoid bone from an elevated position
• The omohyoid depresses and retracts the hyoid and larynx, also tenses the carotid sheath
• The sternothyroid depresses the larynx
• The thyrohyoid depresses the hyoid bone and elevates the larynx

Suprahyoid Muscles

• The stylohyoid elevates and draws the hyoid bone posteriorly.
• The digastric depresses the mandible and elevates the hyoid bone during chewing and swallowing.
• The mylohyoid forms the floor of the oral cavity, elevates the hyoid bone and floor of the mouth, and depresses the mandible
• The geniohyoid elevates and draws the hyoid bone anteriorly, shortens the mouth floor, and widens the pharynx.

Intrinsic Laryngeal Muscles

• These muscles are important for voice production.
• The lateral cricoarytenoid adducts and shortens the vocal folds.
• The transverse arytenoid adducts the arytenoid cartilages and acts as a sphincter on the laryngeal inlet.
• The posterior cricoarytenoid abducts and lengthens the vocal folds and opens the glottis.
• The oblique arytenoid acts as a sphincter for the laryngeal inlet, preventing food or liquid from entering the lower respiratory tract.
• The aryepiglottic acts as a sphincter for the laryngeal inlet, preventing food or liquid from entering the lower respiratory tract.
• The cricothyroid draws the thyroid cartilage anteroinferiorly, lengthening and tensing the vocal ligament to produce high-pitched sounds.
• The thyroarytenoid draws the arytenoid cartilages anteriorly and relaxes the vocal ligament for low-pitch sounds.
• The vocalis tenses the anterior part and relaxes the posterior part of the vocal ligament.
• To improve vocal fold closure, intrinsic laryngeal muscles like the thyroarytenoid, lateral cricoarytenoid, and interarytenoid should be targeted during voice therapy.
• The cricothyroid muscle and the internal branch of the superior laryngeal nerve are responsible for adjusting pitch.
• Extrinsic muscles including the digastric, mylohyoid, and stylohyoid, are often involved in this issue in the setting of a singer with difficulty reaching notes

Muscles of the Tongue

• These muscles are important for articulation and swallowing.
• Genioglossus is a triangular muscle, protrudes, and depresses tongue.
• Hyoglossus is a thin muscle that depresses the tongue.
• Styloglossus draws the tongue up and back and divides it into two parts.
• Palatoglossus elevates the root of the tongue and closes off the oropharynx
• The muscle antagonistic to the genioglossus is the styloglossus.

Intrinsic Tongue Muscles

• The superior longitudinal muscle makes the tongue concave and shortens it, while the inferior longitudinal muscle makes the tongue convex.
• The vertical muscle flattens and widens the tongue
• The transverse muscle narrows and elongates the tongue

Muscles of Resonace

• The levator veli palatini elevates the soft palate and closes off the nasopharynx during swallowing and speech.
• The tensor veli palatini tenses the soft palate and opens the Eustachian tube during swallowing and yawning.
• The muscular uvulae shortens and elevates the uvula, aiding in velopharyngeal closure.
• The palatoglossus elevates the back of the tongue to the palate, narrowing the oropharyngeal opening.
• The palatopharyngeus narrows the pharyngeal cavity, lowers the soft palate, and helps close the nasopharynx.
• The superior pharyngeal constrictor constricts pharyngeal diameter for swallowing and phonation.
• The middle pharyngeal constrictor further constricts the pharynx during swallowing.
• The inferior pharyngeal constrictor constricts the lower pharynx during swallowing, contributing to esophageal closure.
• The levator veli palatini or tensor veli palatini may be implicated by an abnormal sensation in the ear related to soft palate issues

Muscles of Jaw Movement

• Jaw depressors include the digastric (anterior belly), which opens the mandible during chewing.
• The mylohyoid raises the floor of the mouth and aids in pulling the hyoid forward.
• The geniohyoid is a weak depressor of the mandible.
• The external (lateral) pterygoid assists in grinding motion.
• Jaw elevators include the temporalis, running from the styloid process to the dorsolateral and lateral side of the tongue innervated by the mandibular nerve branch of trigeminal CNV.
• The masseter runs from the zygomatic arch to the mandible, innervated by the mandibular nerve CNV and is the main chewing muscle.
• The internal (medial) pterygoid has fibers that run from the sphenoid, palatine, and maxillary bones to the mandible, innervated by the mandibular nerve CNV.
• The external (lateral) pterygoid's fibers run from the sphenoid bone to the condyle of the mandible and temporomandibular joint, innervated by the mandibular nerve CNV, and helps with grinding food.

Muscles of the Face and Bolus Manipulation

• The orbicularis oris prevents bolus from leaking out of the mouth during the oral phase and keeps lips sealed.
• The buccinator is the main muscle of chewing, maintaining cheek tightness by compressing it inwards and holding the cheek close to the teeth, which helps prevent inner cheek injury. Contraction thickens cheeks pushing bolus to the oral cavity's middle.
• When jaw muscles like the masseter and temporalis are underperforming the trigeminal nerve CN V, is most likely implicated

Muscles of VP Closure/ Soft Palate

• Levator veli palatini: pulls soft palate up and backwards towards the posterior pharyngeal wall
• Tensor veli palatini pulls the palate taught and horizontal creating a platform from which other palatini muscles can change position
• Palatoglossus elevates the floor of the tongue and approximates the palatoglossal arch.
• Palatopharyngeus assists in pharyngeal sways.

Muscles of the Pharynx

• Purpose assists in pushing bolus down by squeezing its walls together in a ripple-like effect and by shortening the length
• Includes:Constrictors: band shaped muscles that overlap one another
  • Superior
  • Middle
  • Inferior stylopharyngeus
• Salpingopharyngeus helps to elevate and open the pharynx during swallowing
• Palatopharyngeus also helps to elevate and open the pharynx during swallowing
• The pharyngeal constrictor muscles are defined as: Salpingopharyngeus elevates the lateral pharyngeal wall and moves it medially; Stylopharyngeus elevates and opens the pharynx; Superior pharyngeal constrictor constricts pharyngeal diameter, and pulls the pharyngeal wall forward; Middle pharyngeal constrictor narrows the diameter of the pharynx

Cranial Nerves

• The CN V Trigeminal is responsible for sensory information from the face to mouth and motor functions muscles of mastication (chewing). Damage to the lower motor neuron (LMN) results in weakness, jaw deviation to lesion side, and atrophy. Damage to the upper motor neuron (UMN) results in mild, transitory weakness.
• The VII Facial serves the facial expression muscles, lacrimal glands, and salivary glands. LMN damage involves the entire side of the face, weakness, and limited range of motion and UMN damage involves the lips and neck muscles less than the eye area muscles, with little forehead difficulty, weakness, and limited ROM of affected muscles.
• The IX Glossopharyngeal serves the pharynx (throat) for swallowing and is associated with dysphagia symptoms.
• The X Vagus provides sensation from visceral organs and parasympathetic motor regulation of visceral organs. LMN damage can cause an absence of gag reflex, poor volitional movement of the palate, absent or delayed swallow reflex, aspiration, and a breathy, hoarse voice. Dysfunction in the UMN results in poor palatal movement, harshness, strained-strangled voice quality, and a delayed or absent swallow reflex, as well as aspiration.
• The XI Accessory serves muscles that move the head, neck and shoulder
• The XII Hypoglossal serves the muscles of the tongue. LMN damage leads to atrophy, fasciculation, weakness, reduced range of motion, deviation of the tongue to the side of the lesion, decreased tone, and consonant imprecision and UMN damage, results in weakness, reduced range of motion, deviation of the tongue to the contralateral side, increased tone, and consonant imprecision. When asked to stick out the tongue, deviation to the right indicates a lesion the nerve fibers on the right CN XII.
• CN V - Trigeminal Nerve innervates the muscles of mastication and the mandible
• CN VII - Facial nerve provides sensation to the face, ose, and mouth as well as taste sensation to the anterior ⅔ of the tongue
• CN IX - Glossopharyngeal Nerve provides sensation to the posterior ⅓ of the tongue; motor supply to the stylopharyngeus (elevates pharynx during swallowing)
• CN X - Vagus nerve mediates cough response and sensation in the pharynx
• Cn XII - Hypoglossal Nerve responsible for tongue function; only cranial nerve that provides motor function
• The sternocleidomastoid muscle is innervated by the accessory nerve (CN XI)

Cranial Nerves Associated with Speech and Swallowing stages

• The CN V Trigeminal impacts Articulation and Resonance during the Oral Prep swallow stage.
• The CN VII Facial impacts Articulation during the Oral Prep and Oral swallow stages.
• The CN IX Glossopharyngeal impacts Articulation, Resonance during the Oral Pharyngeal swallow stage.
• The CN X Vagus impacts Phonation, Resonance during the Pharyngeal, Esophageal swallow stages.
• The CN IX Spinal Accessory impacts Phonation, Resonance during the Pharyngeal swallow stage.
• The CN XII Hypoglossal impacts Articulation during the Oral Prep and Oral swallow stages.

Swallowing Process and Cranial Nerve Involvement

• Mouth opens to allow entry of bolus (CN V)
• Lips seal bolus within oral cavity (CN VII)
• Sensation of bolus within oral cavity (CN V)
• Salivation (CN VII)
• Food collected and moved anteriorly to teeth (CN XII)
• Chewing of bolus/begin propulsion (CN V, XII)
• Sensation of arrival of bolus at palate (CN IX)
• Bolus pushed up and back against soft palate (CN XII)
• Hyoid elevates and moves anteriorly to bring larynx up beneath tongue (CN XII)
• SP elevates to occlude nasopharynx
• Epiglottis flips forward to covered the elevated and titled larynx
• Tongue base “pushes” bolus into pharynx
• Hypopharynx dilates allowing bolus to pass into esophagus
• Pharynx constricts
• UES relaxes
• Esophageal peristalsis begins. Involves CN X although cranial nerves V, IX, XI, and XII are largely involved

Brain Damage and Results

• Damage to the primary motor cortex results in weakness or paralysis of muscle groups on the contralateral side of the body, while damage to the premotor cortex causes disruption of complex volitional movements; the anterior frontal lobe impairments encompass disturbed affect, attentional impairments, and difficulties initiating and maintaining behavior.
• Posterior strip of the cortex results in tactile agnosia or astereognosis & the Association cortex causes disturbed position sense & visuospatial impairments
• Temporal association cortex damage leads to auditory agnosia, while posterior temporal lobe or low parietal lobe damage results in contralateral visual field blindness.
• Visual cortex damage in either hemisphere results in blindness in regions of the contralateral visual fields; association cortex damage adjacent to leads to visual agnosia and distorted visual perceptions.
• Visual association cortex damage in the left hemisphere causes severe reading impairment, and bilateral destruction of visual cortex leads to cortical blindness.
• Extrapyramidal system damage distorts or eliminates volitional movement causing weakness, slowness, and rigidity, while damage to nerve fibers in the corpus callosum produces disconnection syndromes. Degeneration of the BG and damage to the connection between BG and frontal lobe causes Huntington's disease
• Upper and lower motor neuron damage is from ALS occurs
• Anterior cerebral artery damage leads to sensorimotor cortices and Prefrontal cortex (PFC) damage. Symptoms include contralateral sensorimotor and cognition issues
• Middle cerebral artery damage leads to sensorimotor cortices and pre-frontal cortex and temporoparietal, internal capsule damage. Symptoms include vision, aphasia, apraxia, and cognition issues
• Posterior cerebral artery: - Structures affected: -- Calcarine cortex (Primary visual)-- Thalamus-- Upper midbrain-- Hippocampus- Vision, low pain tolerance, coma, movement disorder, memory

Speech Clarity and Muscle Involvement

• Speech issues can stem from the innervation of muscles involved in speech, including cranial nerves X and XI

Myoelastic Aerodynamic Theory and Vocal Fold Closure

• To improve vocal fold closure and reduce breathy voice after vocal fold surgery, strategies should focus on strengthening the abdominal muscles to increase subglottal pressure

Congenital Palatopharyngeal Incompetence (CPI) during Endoscopy

• Enlarged adenoids obstructing the nasal passage
• Excessive scarring of the soft palate tissues
• Presence of large oropharyngeal tumor
• Incorrect insertion of the levator veli palatini muscles

Vertical Thorax Dimension and Breathing

• The sternocleidomastoid primarily aids in increasing the vertical dimension of the thorax, which supports deep inhalation necessary for loud or prolonged speaking

Tongue Muscles and Related Innervation/Functions

• Hypoglossal nerve innervates the genioglossus muscle
• Hypoglossal nerve innervates the vertical muscles of the tongue
• The primary function of the transverse muscle of the tongue is to narrow and elongate the tongue
• The hyoglossus muscle lowers the tongue
• The genioglossus muscle protrudes the tongue
• The vagus nerve innervates the palatoglossus muscle
• The transverse muscles of the tongue are innervated by the hypoglossal nerve
• The superior longitudinal muscle is innervated by the hypoglossal nerve, curling the tongue tip upwards
• The hyoglossus muscle is innervated by the hypoglossal nerve
• The hypoglossal nerve innervates the styloglossus muscle
• The hypoglossal nerve innervates the inferior longitudinal muscle
• Palatoglossus muscle elevates the back of the tongue
• The vertical muscle of the tongue widens and flattens the tongue
• The styloglossus muscle elevates and retracts the tongue
• All of the above muscles (thyrohyoid, mylohyoid, and geniohyoid) contribute to laryngeal elevation
• A triangular muscle, which protrudes and depresses the tongue, is the genioglossus

Hyoid Bone Muscles

• The geniohyoid muscle pulls the hyoid forward and up, shortening the floor of the mouth during swallowing.
• The mylohyoid muscle elevates the hyoid bone and the floor of the mouth during swallowing and speaking.
• The sternohyoid muscle depresses the hyoid bone after swallowing.
• The digastric muscle is involved in opening the jaw and elevating the hyoid bone.
• The omohyoid muscle lowers the larynx.
• The thyrohyoid muscle elevates the larynx.
• The sternohyoid muscle lowers the hyoid bone after it has been elevated during swallowing
• The digastric muscle opens the jaw and elevates the hyoid bone
• The omohyoid muscle depresses and lowers the larynx
• The thyrohyoid muscle shortens the distance between the thyroid cartilage and hyoid bone, elevating the larynx

Laryngeal and Pharyngeal Muscles

• The sternohyoid depressses the hyoid bone after it has been elevated during swallowing
• The omohyoid depresses the hyoid bone and lowers the larynx
• The sternothyroid depresses the thyroid cartilage, and helps lower the larynx
• The thyrohyoid shortens the distance between the thyroid cartilage and hyoid bone, elevating the larynx
• The thyroarytenoid is an intrinsic laryngeal muscle that is targeted during voice therapy in the setting of of reduced vocal fold closure and breathiness due to adductor weakness
• The function of the posterior cricoarytenoid muscle is to abduct and lengthen the vocal folds, opening the glottis.
• The palatoglossus has the Opposing Action to those that produce velopharyngeal closure.
• The Cricothyroid Muscle is closely related to the fundamental frequency of the laryngeal tone.
• The Posterior Cricoarytenoid Muscle is primarily responsible for Vocal Fold Abduction.

Swallowing Complications and Muscles Involved

• In cases where food or liquid enters the nasal cavity, the palatopharyngeus muscle is most likely underperforming.
• When a patient has difficulty elevating the pharynx resulting in residual food during swallowing, the salpingopharyngeus muscle is most likely impaired.
• Superior, Middle and Inferior constrictor muscles are most responsible for initiating the swallow (weakened contraction of the pharyngeal walls, leading to poor propulsion of the bolus into the esophagus)