USMLE Step 1 Neuroanatomy Review 27 13 Lesions of the Spinal Cord

USMLE Step 1 Neuroanatomy Review 27 13 Lesions of the Spinal Cord

 

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Play USMLE Audio MP3 27 13 Lesions of the Spinal Cord Below

Begin 27 13 Lesions of the Spinal Cord Transcription

Now let’s take a look at lesions of the spinal cord.  Please refer to figure 14.2.

Lower motor neuron lesions are caused by damage to the motor neurons of the ventral horns of the motor neurons of the cranial nerve nuclei.

Student doctor, what are the six characteristics of lower motor neuron lesions?

  • Lower motor neuron lesions are characterized by the following: First, arreflexia.  Two, fasciculations.  Three, flaccid paralysis.  Four, fibrillations.  Five, hypotonia, and six, muscle atrophy. 

What is arreflexia?

  • Arreflexia refers to the loss of muscle stretch reflexes and superficial reflexes.  Upper motor neuron lesions are caused by damage to the cortical neurons that give rise to the corticospinal and corticobulbar tracts. 

Student doctor, what are the characteristics of upper motor neuron lesions?

  • In alphabetical order, upper motor neuron lesions are characterized by the following.  First, Babinski’s sign.  Two, clonus.  Three, muscle weakness.  Four, spastic paralysis, and five, superficial reflex loss. 

Now in terms of characteristics of upper motor neuron lesions vs. lower motor neuron lesions, which contrasting pair of characteristics are you most likely to see on tests?

  • This would be the pair, the contrasting pair, of flaccid paralysis vs. spastic paralysis.

Now, flaccid paralysis is associated with which type of motor neuron lesion?

  • With lower motor neuron lesions. 

What is a memory device for remembering which goes with which?

  • Lower tone, lower motor neuron.  Lower tone, of course, meaning flaccid paralysis.  Upper tone with upper motor neurons, meaning spastic paralysis. 

Student doctor, what type of motor neuron lesion is poliomyelitis and Werdnig-Hoffman disease?

  • Poliomyelitis and Werdnig-Hoffman disease are both disease of the lower motor neurons.

All right, in terms of motor neuron lesions, what is involved in amyotrophic lateral sclerosis (ALS)?

  • ALS, amyotrophic lateral sclerosis is a combined upper and lower motor neuron lesion.

What are the two characteristics most distinctive of ALS, amyotrophic lateral sclerosis?

  • Muscle atrophy and muscle weakness without sensory loss.

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