Motor loop and associated disorders

Question 1

SNc ( pars compacta) neurons are dopaminergic and produce what? as a byproduct of dopamine metabolism?

Answer 1

Neuromelanin

Question 2

In the striatum you have the dopamine receptors, what do the D1 and D2 receptors cause?

Answer 2

D1 receptor –> excitatory; mediating facilitation of striatum firing rate
D2 receptor —> inhibitory

Question 3

The GPi (globus pallidus- internal segment ) and SNr (substancia nigra pars reticulata) function as a single unit and have what effect on the thalamus?

Answer 3

exert inhibition on the thalamus which will modulate the excitatory signal between the thalamus and the SMA (BA-6)

Question 4

Direct Pathway facilitates what?

Answer 4

movement (intrinsic effect)

Question 5

The direct pathway removes inhibition on the thalamus and excites the cortex to facilitate movement, how is this done?

Answer 5

Cortex excites the inhibitory neuron leaving the striatum and this inhibitory neuron leaving the striatum will then inhibit GPi/SNr (So therefore no inhibition on the thalamus)

Question 6

Dopamine influence from the SNc (substantia Nigra) will do what to the striatum in the direct pathway?

Answer 6

enhance the effect of the pathway

interacting with D1 receptors

Question 7

Indirect pathway does what?

Answer 7

Inhibits movement (in the absence of dopamine)

Question 8

In the indirect pathway the upregulation of the GPi/SNr will stimulate its inhibitory effect on the thalamus and therefore inhibit movement, how??

Answer 8

The striatum downregulates the GPe so therefore because the GPe is downregulated now the STN is not inhibited and this goes and acitvates the GPi/SNr which will therefore inhibit the thalamus

Question 9

In the event of the presence of dopamine, the D2 receptors becomes activated in the striatum what effect does this have on the indirect pathway then???

Answer 9

So D2 is inhibitory therefore these D2 neurons will inhibit the inhibitory signal from the striatum to the GPe.
Now that the GPe is not inhibited anymore, it can place its inhibitory effects on the STN and therefore the STN does not activate the GPi/SNr which will now not inhibit the thalamus anymore.

Question 10

With parkinson disease, what happens to the dopaminergic cells?

Answer 10

Bilateral degeneration of dopaminergic cells in the SNc

Question 11

what therefore happens to the indirect and direct pathways in parkinsons disease if the dopaminergic cells start to degenerate???

Answer 11

Indirect —> overactivation of the inhibitory effect
direct —> underactivation of the excitatory effect
excessive inhibition —> therefore hypokinetic disorder

Question 12

With Huntington’s Chorea, what happens to the strial neurons?

Answer 12

Bilateral Degeneration of the strial neurons

Question 13

In huntingtons disease what happens to the indirect and direct pathways now that there is degeneration of the strial neurons?

Answer 13

Indirect —> loss of inhibition effect from the indirect pathway (GPe now inhibits the STN on its own) and therefore without the STN the GPi/SNr will not be activated to inhibit the thalamus so you have excessive motor activity

Question 14

what are the signs associated with huntingtons chorea?

Answer 14

irregular bilateral movements
dyskinesia (Excessive motor activity )
involuntary movement of the head, arms, and legs
marked change in mental status

Question 15

With Hemiballismus, what happens to the Subthalamic Nucleus (STN)?

Answer 15

Lesion of the STN usually from a stroke

Question 16

In hemiballismus there is a lesion of the STN, what affect is this then going to have on the patient?

Answer 16

causes underactivity of the indirect pathway on one side of the midline
so if the STN is lost then it is unable to excite the GPi/SNr and therefore there is loss of inhibition of movement

Question 17

what symptoms are associated with hemiballismus?

Answer 17

irregular movements of the limbs and trunk on the contralateral side
involuntary flinging of the arms and writhing movements of the leg on ONE SIDE

Question 18

The basal ganglia, in general, does what?

Answer 18

Exchanges information about motor commands with prefrontal, premotor and primary motor cortex

Question 19

Does the basal ganglia have direct synaptic connection with motor neurons?

Answer 19

NOOOO

Question 20

Name the four nuclei of the basal ganglia

Answer 20

a. Striatum: caudate nucleus and putamen
b. Globus Pallidus: external (GPe) and internal (GPi) segments
C. Subthalamic Nucleus (STN)
D. Substantia Nigra: pars reticulata (SNr) and pars compacta (SNc)

Question 21

On a CT or MRI of a brain of a patient with huntingtons disease what do the ventricles show?

Answer 21

Boxcar ventricles

Question 22

what are some drugs for huntingtons, since there is no treatment?

Answer 22

Antidepressants

Antichorea drugs–> Antagonists of D2 receptors and vasicular monoamine transporter (VMAT) inhibitors