Lab 10.3: Auditory system and lesions
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- Which cochlear nucleus is involved in sound identification? Which cochlear nucleus is involved in sound localization?
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*dorsal cochlear nucleus does sound identification
*ventral cochlear nucleus does sound localization - Outline the pathway for sound identification.
- Input is received by the cochlea and converted to impulses which are sent to the dorsal cochlear nucleus. Info is then sent bilaterally to both lateral lemniscus nuclei, and from there bilaterally to both inferior colliculi. Next, info travels to the medial geniculate body and finally to the primary auditory cortex in the temporal lobe.
- Outline the pathway for sound localization.
- Input is received by the cochlea and converted to impulses which are transmitted to the ventral cochlear nucleus. From there fibers project bilaterally to both superior olivary nuclear complexes, and then to both nuclei of the lateral lemniscus, and then to both inferior colliculi. Next, fibers project to the ipsilateral medial geniculate body and finally to the primary auditory complex.
- What kind of lesion is likely to cause a unilateral decrease in auditory ability?
- The lesion is at the level of the cochlear nerve or the dorsal or ventral cochlear nucleus, but not more proximal.
- What is the effect of a lesion to the left nucleus of the lateral lemniscus?
- There would be little effect as bilateral innervation at this level would compensate.
- what is the function of the superior olivary nuclear complex? How does the function of the medial portion of this structure differ from that of the lateral portion?
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*integration of sound localization information
*medial portion compares timing of inputs
*lateral portion compares intensity of inputs - What deficits can be expected from damage to the principal sensory nucleus of V as it passes through the lateral pons?
- Loss of fine touch and vibratory sense from the ipsilateral face.
- Damage to which structure in the lateral pons will result in loss of pain and temperature sensation in the ipsilateral face?
- Damage to the spinal nucleus and tract of CN V.
- How might body motor function and sensation be affected with a unilateral lesion to the lateral pons?
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*loss of contralateral pain and temperature sensation due to damage to the spinothalamic tract
*ipsilateral gait ataxia due to damage to the MCP - How might a unilateral lateral pontine lesion be diagnosed by looking at the patient's eyes and eye function?
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*ipsilateral ptosis due to damage to the MFB causing Horner's
*loss of lateral gaze in the ipsilateral eye due to damage to the abducens nucleus
*ipsilateral paralysis of facial muscles due to damage to the facial nucleus
*ipsilateral nystagmus due to damage to the vestibulocochlear nucleus - Why would a lesion in the lateral pons cause loss of fine touch and pain and temperature sensation from the ipsilateral face?
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*loss of fine touch due to damage to principal sensory nucleus of V
*loss of pain and temperature due to damage to the spinal nucleus of V - What sensory deficits would be produced in the body with a lesion of the lateral pons?
- Contralateral loss of pain and temperature due to damage to the spinothalamic tract.
- What kinds of deficits would be seen in the body with a unilateral lesion in the medial pons? What structures are damaged to produce these deficits?
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*contralateral paralysis/weakness due to damage to the pyramid and descending CST
*contralateral loss of fine touch, vibratory sense, and proprioception due to damage to the medial lemniscus - Why would the ipsilateral eye be deviated inward with a unilateral lesion to the medial pons?
- Damage to the abducens nucleus or nerve would leave the medial rectus on the side of the lesion unopposed.
- How would motor function of the face be affected with a unilateral lesion to the medial pons?
- There would be ipsilateral paralysis of the face due to damage in the facial nucleus or nerve.
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In lateral medullary syndrome, give the damaged structure causing each deficit:
1.hoarseness and dysphagia
2.vertigo, nystagmus, nausea
3.ataxia. -
1.Nucleus ambiguus
2.Vestibular nucleus
3.ICP, cerebellum - Why would there be loss of pain and temperature sensation to the ipsilateral face but contralateral body in lateral medullary syndrome?
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*facial deficits due to damage in the spinal nucleus and tract of V
*body deficits due to damage of the spinothalamic tract, which decussates in the spinal cord - What structure, when damaged during lateral medullary syndrome, produces the symptoms of Horner's syndrome? Describe the location of this structure in the medulla.
- The MFB, which runs alongside the spinothalamic tract through the medulla.
- Will an infarct of the anterior spinal artery in the medulla cause unilateral or bilateral deficits?
- Bilateral.
- Why is slurred speech seen in medial medullary syndrome?
- There is damage to the hypoglossal nucleus and nerve.