USMLE Step 1 Neuroanatomy Review 27 15 Lesions to the Peripheral Nervous System

USMLE Step 1 Neuroanatomy Review 27 15 Lesions to the Peripheral Nervous System

 

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Play USMLE Audio MP3 27 15 Lesions to the Peripheral Nervous System Below

Begin 27 15 Lesions to the Peripheral Nervous System Transcription

All right, now we’re going to take a look at lesions to the peripheral nervous system.

 

What viral infection of the dorsal root ganglia results in a sharp burning pain in the affected dermatome?

  • This is herpes zoster.

Now, is the affected dermatome always unilateral, bilateral, or either?

  • With herpes zoster the affected dermatome is always unilateral, that is, on one side of the body only.

And again, what structure of the nervous system is affected with herpes zoster?

  • The dorsal root ganglia.

Student doctor, what kind of paralysis occurs with Guillain Barre syndrome?

  • Guillain Barre syndrome is characterized by an ascending paralysis with lower motor neuron syndromes.

Student doctor, what is the syndrome caused by a dorsal column trans-section and characterized by ipsilateral loss of tactile discrimination, position, and vibration sensation, and form perception?

  • This is Brown-Sequard syndrome.

Student doctor, what is the syndrome characterized by contralateral loss of pain and temperature sensation one segment below the lesion?

  • This is a lateral spinothalamic tract trans-section.

Student doctor, what is the syndrome characterized by contralateral loss of crude touch three to four segments below the level of the lesion?

  • This is a ventral spinothalamic tract lesion.

A dorsal spinocerebellar tract trans-section is characterized by ipsilateral leg dystaxia.

Student doctor, would a trans-section in the ventral spinocerebellar tract result in ipsilateral or contralateral leg dystaxia?

  • A ventral spinocerebellar tract transection results in contralateral leg dystaxia.

Student doctor, what would be the result of a trans-section of the lateral corticospinal tract?

  • A transection of the lateral corticospinal tract would result in ipsilateral spastic paresis below the upper motor neuron lesion with Babinski’s sign.

And what would be the result of a trans-section to the ventral corticospinal tract?

  • Contralateral muscle weakness below the lesion.

Student doctor, what would be the result of destruction of the ventral horn?

  • Destruction of the ventral horn would result in ipsilateral flaccid paralysis of the affected somatic muscles.

And what would be the result of destruction to the dorsal horn?

  • Destruction of the dorsal horn would result in ipsilateral anesthesia and arreflexia of the involved dermatome.

Student doctor, please pause and name as many of the seven clinical features as you can of a complete trans-section of the spinal cord.  A complete trans-section of the spinal cord would result in the following characteristics:

One, complete anesthesia below the lesion.

Two, spastic paralysis below the lesion.

Three, incontinence.

Four, anhidrosis and loss of vasomotor tone.

Five, if the trans-section is above C5, paralysis of the voluntary and autonomic respiration.

Six, if the lesion is between C4 and C5, quadriplegia.

Seven, if the lesion is below T1, paraplegia.

 

Let’s turn some of those around.  In a complete trans-section of a spinal cord, where the transection is above C5, what particular characteristics would you look for?

  • Paralysis of the voluntary and autonomic respiration. 

Now if the trans-section is between C4 and C5?

  • Quadriplegia.

And if the trans-section is below T1?

  • Paraplegia.

****END OF TRANSCRIPTION****

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