USMLE Step 1 Review 25 21 Basal Ganglia Disorders

USMLE Step 1 Review 25 21 Basal Ganglia Disorders

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Play USMLE Audio MP3 25 21 Basal Ganglia Disorders Below

Begin 25 21 Basal Ganglia Disorders Transcription

Now let’s take a look at the disorders of the basal ganglia.

What is the pathological process involved in the substantia nigra that can give rise to certain neurological disorders?

  • The destruction of the dopaminergic neurons.

And what are the two neurological disorders that are caused by the destruction of the dopaminergic neurons in the substantia nigra?

  • Parkinson’s Disease and MPTP induced Parkinsonism.

And what is MPTP?

  • This is N-methyl-4-phenyl-1,2,3,6 tetrahydropyridine.

And what type of chemical derivative is MPTP or N-methyl-4-phenyl-1,2,3,6 tetrahydropyridine?

  • It is a pib-pyridine derivative.

Historically, why do we care what MPTP is?

  • Because it is a byproduct of illegally manufactured mepyridine.

What is the trade name of mepyridine?

  • Demerol.

What class of drug is mepyridine, Demerol?

  • It is a narcotic agonist, a synthetic opioid.

What disorder is associated with the damage to subthalamic nucleus?

  • This is hemiballismus.

What is the definition of hemiballismus?

  • This is a unilateral chorea, that is particularly violent because the proximal muscles of the limb are involved.

Is the hemiballismus on the same or opposite side from the damage to the subthalamic nucleus?

  • The hemiballismus that result from the damage to the subthalamic nucleus is on the opposite side. It is a contralateral hemiballismus.

What is a simple definition of chorea?

  • Chorea consists simply of irregular muscle jerks. Involuntary, unpredictable in different parts of the body.

And what again is the compound for the MPTP induced parkinsonism that we talked about?

  • N-methyl-4-phenyl-1,2,3,6 tetrahydropyridine.

And what is the street story behind this?

  • MPTP is a toxic byproduct of the synthesis of street mepyridine Demerol, a narcotic agonist and a synthetic opioid.

What set of neurons are specifically destroyed by the toxic MPTP?

  • Dopaminergic neurons in the substantia nigra.

It also destroys another set of neurons in another location. What is this type of neuron and where is it?

  • Adrenergic neurons in the locus coeruleus.

Now the dopaminergic neurons in the substantia nigra exert what sort of net effect on the caudate nucleus and the putamen?

  • The dopaminergic neurons exert a net inhibitory effect.

And what neurons in the striatum exert a net excitatory effect on the GABAergic output from the caudate nucleus and the putamen?

  • These are the acetylcholine neurons.

So in Parkinson’s Disease the theory simply, is that the inhibitory balance is loss, resulting in four classical symptoms. What are the four classical symptoms of Parkinson’s Disease?

  • Tremor, rigidity, hypokinesia, and abnormal gait and posture.

What is the abnormal posture seen in Parkinson’s disease?

  • A flexed posture.

And what is hypokinesia?

  • Very slow voluntary motion.

Sometimes the rigidity in Parkinson’s Disease is referred to by what term?

  • Cogwheel rigidity.

And what is often distinctive about a patient’s face in Parkinson’s?

  • A masklike faces.

What is the nature of the voice of a patient with Parkinson’s Disease?

  • Very quiet. The term often used for this is hypophonia.

And what about the eyelids in a patient with Parkinsons?

  • They exhibit blepharoclonus.

And what is blepharoclonus?

  • Fluttering of the closed eyelids.

What would be the name given to a more severe form of blepharoclonus?

  • Blepharospasm.

And what is blepharospasm?

  • Blepharospasm is an involuntary tight closure of the eyelids.

What happens if the examiner does repetitive tapping about twice per second on the bridge of a nose of a Parkinson’s patient?

  • There would be sustained blink response.

And what is the name of this sign, the sustained blink response in response to repetitive tapping about twice per second on the bridge of a nose of a Parkinson’s patient?

  • This is called Myerson’s sign.


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