Lecture 17: Basal Ganglia

Question 1

What makes up the striatum?

Answer 1

Putamen and caudate nucleus

Question 2

What makes up the lentiform nucleus?

Answer 2

Putamen and globus pallidus

Question 3

List the components of the basal ganglia

Answer 3

striatum: caudate nucleus & putamen globus pallidus (internal and external) subthalamic nucleus dopaminergic neurons of substantia nigra pars compacta Peduculopontine firbes in brain stem substantia nigra pars reticulata Amygdala septal nuclei claustrum

Question 4

What is the function of the direct pathways of the basal ganglia

Answer 4

planning movement when decision is made to move?

Question 5

Describe the direct pathway of the basal ganglia

Answer 5

When the decision is made to move:

1. The motor cortex activates the striatum via excitatory glutamate.
2. Striatum inhibits the globus pallidus interna via inhibitory GABA. GPi is usually tonically active producing GABA to inhibit the thalamus.
3. Decreased inhibition via the thalamus (ventroanterior and ventrolateral nuclei results in activation activating the cortex via glutamate

Question 6

Describe the indirect pathway of the basal ganglia

Answer 6

1. The motor cortex activates the striatum via excitatory glutamate.
2. Striatum nhibits the globus pallidus externa (which normally inhibits the subthalamic nucleus .
3. The subthalamic nucleus is activated via a decrease in inhibitory GABA, which then activates the internal globus pallidus.
4. The internal globus pallidus is activated resulting in an increase in GABA inhibiting the thalamus (ventroanterior and ventrolateral nuclei) ultimately decreasing excitatory feedback via glutamate to the cortex.

Question 7

Which part of the substantia nigra influences the indirect and direct pathways? How?

Answer 7

Dopaminergic neurons of the substantia nigra pars compacta act on different receptors in the putamen (striatum) to ultimately facilitate transmission in the direct pathway and inhibit the indirect pathway (ultimately facilitating movement). D1 receptors in the striatum are excitatory facilitate transmission of the direct pathway. D2 receptors in the striatum are inhibitory, inhibiting the indirect pathway.

Question 8

What is the pedunculopontine nucleus?

Answer 8

Recieves inhibitory input from globus pallidus interna and has cholinergic projections to the reticular formation in the brainstem which may control muscle tone

Question 9

What are the probable functions of the basal ganglia

Answer 9

Encode fragments of movements that are “assembled” in supplementary motor area and sent to primary motor area for execution. Help with planning of movement Influence muscle tone Control undesirable activities such as tremor via the thalamus

Question 10

Compare basal ganglia and the cerebellum

Answer 10

Basal Ganglia: receive significant input from prefrontal areas output focused to SMA (supplementary motor area) conscious decision making, planning and initiation of movement mechanism by changing balance between direct and indirect loop? Cerebellum: significant input from association and somatosensory areas output focused on area 4 (Motor I or “Primary Motor Cortex”) automated movement (mainly cerebrocerebellum) comparing intended and actual movement (spinocerebellum) automation (“learning”) of movement by “long term depression” of Purkinje cell (PC)activity by climbing fibres from the inferior olivary complex spatial and temporal sharpening of signal: parallel fibres excite the PC’s in its path, inhibit PC’s in neighbouring rows and cut off its own input via Golgi cells

Question 11

What happens to the basal ganglia during parkinson’s?

Answer 11

Parkinson’s is called by the degeneration of dopaminergic inputs to the striatum from the substantia nigra pars compacta which assist to initiate movement. These inputs normally facilitate the direct pathway, which activates the putamen (via glutamate) providing inhibitory GABAergic input to the globus pallidus interna which ultimately decreases inhibition of the ventroanterior and ventrolateral thalamus.

Question 12

What happens to the basal ganglia during Huntington’s?

Answer 12

Huntington’s is caused by a loss of neurons in the striatum (putamen and caudate nucleus). This results in a loss of inhibitory output to the thalamus via relative inhibition of the subthalamic nucleus, and thus inhibitory output from the internal globus pallidus (to the thalamus)