Basal ganglia [0]

Question 1

In cerebellar disorders, there are no sensory deficits or loss loss in muscular strength. What about in basal ganglia disorders?

Answer 1

Ditto

Question 2

Basal ganglia

Answer 2

• Masses of cells (gray matter) at base of cerebrum
• Next to, but do not include thalamus
• No direct connection with sensory systems or spinal motor apparatus
  
  • exert effect by motor cortex
• Major feedback loop to motor and association cortex
• MOTOR PROGRAM SELECTION

Question 3

Basal ganglia on one side interacts with cortex on ____ side. Unilateral defects in basal ganglia are seen as ____ deficits in fxn.

Answer 3

Ipsilateral
contralateral

(ie: left basal ganglia control movements on right side of body - opp of cerebellum)

Question 4

Major direct pathway of basal ganglia feedback loop on cortical fxn

Answer 4

Cortex →
Caudate + putamen (striatum) →
Globus pallidus interna →
VA/VL thalamus→
Cortex

Basal ganglia circuit : pallidal neurons fire spontaneously

Question 5

In internal feedback loops with basal ganglia, the substantia nigra (pars compacta) and the substantia nigra (pars reticulata) play which roles?

Answer 5

substantia nigra (pars compacta)

• receives from striatum
• projects back to striatum (and releases DA)

the substantia nigra (pars reticulata)
- projects to thalamus
(additional output pathway for basal ganglia)

Question 6

Striatal neurons that express:
D1 dopamine receptors project to _____

D2 dopamine receptors project to _____

Answer 6

D1 → GPinternus (main output structure of globus palidus)
- excitatory G prot
(- Excited by DA (released by SNc))

D2 → GPe → Subthalamic nucleus (STN) → GPi
- indirect pathway through basal ganglia
- inhibitory G prot
(- Inhibited by DA)
(extra synapse in GPe which creates sign inversion + neg feedback)

Question 7

Thalamic neurons either receives EPSP from _____ or IPSP from ______, but never both

Answer 7

dentate nucleus

Globus pallidus

Question 8

List whether excite or inhibit cells

Cortex →
Caudate + putamen (striatum) →
Globus pallidus interna →
VA/VL thalamus→
Cortex

*overall output of basal ganglia (globus pallidus) is excitatory or inhibitory?

Answer 8

Cortex — excite (GLu) →
Caudate + putamen (striatum) —-Inhibit (GABA) →
Globus pallidus interna —inhibit (GABA)→
VA/VL thalamus— excite→
Cortex

*overall output of basal ganglia (globus pallidus) is inhibitory without cortical input

Question 9

Hemi-ballismus

Answer 9

loss of excitation to inhibitory neurons of Globus pallidus (lose inhib)

• (decreased subthalamic excitation in GP –> less inhib of thalamus –> inappropriate movement on one side

Question 10

Why is DA loss so significant in PD?

Answer 10

DA is excitatory to some striatal neurons, so loss of DA reduces the effective “disinhibition” that striatum would normally produce in thalamus by way of globus pallidus

• motor acts become harder to get started

Question 11

Deep brain stimulation

Answer 11

stimulation of subthalmic nucleus (STN) or globus pallidus internal (GPi) provides a state like well medicate state

• ideal candidate: idiopathic PD, with substantial improvement with meds, but freq on/off fluctuations, severe off periods, or medication induced dyskinesias

Question 12

When activity in the direct pathway is reduced relative to the indirect pathway, the result is a ______ of movement

Answer 12

paucity

hypokinetic disorder

Question 13

When activity in the indirect pathway is reduced relative to the direct pathway, the result is a ______ of movement

Answer 13

hyperkinetic disorder (like HD)

• results when stroke from small ganglionic br. of the posterior cerebral artery –> damg of subthalamic nucleus on 1 side