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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}} {{Alison}}
|QuestionAuthor= {{YD}} (Reviewed by  {{YD}} and  {{AJL}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Pathology
|MainCategory=Pathology
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|MainCategory=Pathology
|MainCategory=Pathology
|SubCategory=Neurology
|SubCategory=Neurology
|MainCategory=Pathology
|MainCategory=Pathology
|MainCategory=Pathology
|MainCategory=Pathology
|MainCategory=Pathology
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|MainCategory=Pathology
|MainCategory=Pathology
|SubCategory=Neurology
|SubCategory=Neurology
|Prompt=A 43-year-old male presents to the physician’s office with complaints of an inability to differentiate between sweet and sour tastes at the tip of his tongue. Upon further questioning, the patient denies inability to swallow and reports normal sensation of food in his tongue.  The physician suspects an injury of a specific cranial nerve (CN) might be causing the patient’s symptoms.  Which of the following additional findings will further confirm the physician’s diagnosis?
|Prompt=A 43-year-old man presents to the physician’s office complaining that he is unable to differentiate between sweet and sour tastes at the tip of his tongue. Upon further questioning, the patient denies dysphagia, and reports he has normal somatosensation of his tongue.  The physician suspects the patient's symptoms are caused by an injury to a specific cranial nerve.  Which of the following additional findings will further confirm the physician’s diagnosis?
|Explanation=The [[tongue]] is a complex structure that receives neural innervations from several [[cranial nerves]] (CN). The [[facial nerve]] ([[CN VII]]) is responsible for taste at the anterior 2/3 of the tongue, while sensation in the anterior 2/3 of the tongue is controlled by the [[mandibular branch]] of the [[trigeminal nerve]] ([[CN V3]]). The taste and sensation of the posterior 2/3 of the tongue is dependent on the [[glossopharyngeal nerve]] (CN IX). Motor innervation of the tongue is provided by the [[hypoglossal nerve]] ([[CN XII]]).
|Explanation=The [[tongue]] is a complex structure that receives neural innervations from more than one [[cranial nerve]] (CN). The chorda tympani, which joins CN VII (facial nerve) as the latter exits the stylomastoid foramen, is responsible for the taste sensation in the anterior 2/3 of the tongue. On the other hand, somatosensation in the anterior 2/3 of the tongue is provided by the [[mandibular or 3rd branch]] of CN V (trigeminal nerve). The taste sensation and somatosensation of the posterior 2/3 of the tongue are both provided by CNIX (glossopharyngeal nerve). Motor innervation of the tongue is provided by CN XII (hypoglossal nerve). This patient presents with symptoms of a [[CN VII]] injury.  [[CN VII]] innervates the [[stapedius muscle]], which is responsible for dampening vibrations and preventing excessive oscillations of the [[stapes]] bone.  [[Hyperacusis]], the perception of normal sounds as abnormally loud, results from the paralysis of the [[stapedius]] muscle, which is often due to a [[CN VII]] injury. This injury causes a very wide oscillation of the [[stapes]] and an abnormally large reaction of the [[ossicles]] in response to normal sounds.
The patient in this scenario presents with symptoms of an [[CN VII]] defect.  [[CN VII]] innervates the [[stapedius muscle]], the smallest skeletal muscle in the human body, which is responsible for [[dampening vibrations]] and preventing excessive movement of the [[stapes]].  [[Hyperacusis]], the perception of normal sounds as abnormally loud, is caused by paralysis of the [[stapedius]] muscle due to an [[CN VII]] injury. This injury often causes a very wide oscillation of the [[stapes]] and an abnormally large reaction of the [[ossicles]] in response to normal sounds.  
 
|EducationalObjectives= [[CN VII]], the facial nerve, innervates the anterior 2/3 of the tongue, providing tongue sensation in that region.  It also innervates the [[stapedius muscle]] in the ear, which is responsible for dampening the vibration of the [[stapes]].  Injury of [[CN VII]] frequently will cause an inability to taste from the anterior 2/3 of the tongue and [[hyperacusis]].
|References= First Aid 2014 page 446 
 
|AnswerA=Inability to tolerate normal sounds
|AnswerA=Inability to tolerate normal sounds
|AnswerAExp=the inability to tolerate normal sounds, or hyperacusis, may be caused by an injury to [[CN VII]].
|AnswerAExp=Inability to tolerate normal sounds, or hyperacusis, may result from an injury to [[CN VII]] (facial nerve).
|AnswerB=Absence of salivation from the parotid gland
|AnswerB=Absence of salivation from the parotid gland
|AnswerBExp=Salivation from the parotid gland is dependent on CN IX, while salivation from the submandibular and sublingual glands is provided by CN VII.
|AnswerBExp=Parotid gland is innervated by CN IX (glossopharyngeal nerve), while submandibular and sublingual glands are innervated by CN VII (facial nerve).
|AnswerC=Inappropriate balance
|AnswerC=Inability to move the tongue
|AnswerCExp=Balance is dependent on [[CN VIII]].
|AnswerCExp=Motor innervation to the tongue is provided by CN VII (hypoglossal nerve)
|AnswerD=Absence of pupillary constriction
|AnswerD=Absence of pupillary constriction
|AnswerDExp=Pupillary constriction is provided by [[CN III]].
|AnswerDExp=Pupillary constrictor muscles are innervated by the [[CN III]] (oculomotor nerve).
|AnswerE=Absence of cough reflex
|AnswerE=Absence of cough reflex
|AnswerEExp=Cough reflex is provided by [[CN X]].
|AnswerEExp=Absence of cough reflex may result from an injury to [[CN X]] (vagus nerve).
|EducationalObjectives=[[CN VII]] (facial nerve) innervates the anterior 2/3 of the tongue, which provides the taste sensation in that region. It also innervates the [[stapedius]] muscle in the ear, which is responsible for dampening the vibration of the [[stapes]]. CN VII injury should be suspected when patients present with complains of both inability to taste from the anterior 2/3 of the tongue and [[hyperacusis]].
|References=First Aid 2014 page 446
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=Cranial, nerve, hyperacusis, tongue, taste, nerves, nervous system, muscles
|WBRKeyword=Cranial nerve, Hyperacusis, Tongue, Taste, Nervous system, Facial nerve, CN VII, Somatosensation
|Approved=Yes
|Approved=Yes
}}
}}

Latest revision as of 00:31, 28 October 2020

 
Author [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D. and Alison Leibowitz [1])]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Pathology
Sub Category SubCategory::Neurology
Prompt [[Prompt::A 43-year-old man presents to the physician’s office complaining that he is unable to differentiate between sweet and sour tastes at the tip of his tongue. Upon further questioning, the patient denies dysphagia, and reports he has normal somatosensation of his tongue. The physician suspects the patient's symptoms are caused by an injury to a specific cranial nerve. Which of the following additional findings will further confirm the physician’s diagnosis?]]
Answer A AnswerA::Inability to tolerate normal sounds
Answer A Explanation [[AnswerAExp::Inability to tolerate normal sounds, or hyperacusis, may result from an injury to CN VII (facial nerve).]]
Answer B AnswerB::Absence of salivation from the parotid gland
Answer B Explanation AnswerBExp::Parotid gland is innervated by CN IX (glossopharyngeal nerve), while submandibular and sublingual glands are innervated by CN VII (facial nerve).
Answer C AnswerC::Inability to move the tongue
Answer C Explanation AnswerCExp::Motor innervation to the tongue is provided by CN VII (hypoglossal nerve)
Answer D AnswerD::Absence of pupillary constriction
Answer D Explanation [[AnswerDExp::Pupillary constrictor muscles are innervated by the CN III (oculomotor nerve).]]
Answer E AnswerE::Absence of cough reflex
Answer E Explanation [[AnswerEExp::Absence of cough reflex may result from an injury to CN X (vagus nerve).]]
Right Answer RightAnswer::A
Explanation [[Explanation::The tongue is a complex structure that receives neural innervations from more than one cranial nerve (CN). The chorda tympani, which joins CN VII (facial nerve) as the latter exits the stylomastoid foramen, is responsible for the taste sensation in the anterior 2/3 of the tongue. On the other hand, somatosensation in the anterior 2/3 of the tongue is provided by the mandibular or 3rd branch of CN V (trigeminal nerve). The taste sensation and somatosensation of the posterior 2/3 of the tongue are both provided by CNIX (glossopharyngeal nerve). Motor innervation of the tongue is provided by CN XII (hypoglossal nerve). This patient presents with symptoms of a CN VII injury. CN VII innervates the stapedius muscle, which is responsible for dampening vibrations and preventing excessive oscillations of the stapes bone. Hyperacusis, the perception of normal sounds as abnormally loud, results from the paralysis of the stapedius muscle, which is often due to a CN VII injury. This injury causes a very wide oscillation of the stapes and an abnormally large reaction of the ossicles in response to normal sounds.

Educational Objective: CN VII (facial nerve) innervates the anterior 2/3 of the tongue, which provides the taste sensation in that region. It also innervates the stapedius muscle in the ear, which is responsible for dampening the vibration of the stapes. CN VII injury should be suspected when patients present with complains of both inability to taste from the anterior 2/3 of the tongue and hyperacusis.
References: First Aid 2014 page 446]]

Approved Approved::Yes
Keyword WBRKeyword::Cranial nerve, WBRKeyword::Hyperacusis, WBRKeyword::Tongue, WBRKeyword::Taste, WBRKeyword::Nervous system, WBRKeyword::Facial nerve, WBRKeyword::CN VII, WBRKeyword::Somatosensation
Linked Question Linked::
Order in Linked Questions LinkedOrder::