Basal Ganglia A/P

Question 1

What are the 4 components that make up the Basal Ganglia?

Answer 1

External and internal Globus Palladus in telencephalon, substantia nigra in midbrain, striatum which is in the telencephalon and consists of caudate nucleus and the putamen, and subthalamic nuclei in the diencephalon.

Question 2

What is the general function of the basal ganglia?

Answer 2

Modulates the thalamic outflow to the motor cortex by either direct (excitatory) or indirect (inhibitory) pathways in order to plan and execute smooth movements. More specifically, the basal ganglia gets movement STARTED, after which the cerebellum takes over to complete the movement.

Question 3

What is the neurotransmitter used by the basal ganglia for inhibitory pathways?

Answer 3

GABA

Question 4

What is the neurotransmitter used between Striatum and Substantia Nigra? Feedback from Substantia Nigra back to the striatum?

Answer 4

GABA; Dopamine.

Question 5

What is the “Corpus Striatum?”

Answer 5

Globus Pallidus + Putamen + Caudate nucleus = Corpus Striatum.

Question 6

What is the “Lentiform Nucleus?”

Answer 6

Globus Pallidus + putamen.= Lentiform nucleus.

Question 7

What is the “Striatum?” (aka Caudatoputamen and neostriatum)

Answer 7

Caudate nucleus + nucleus accumbens + putamen = Striatum.

Question 8

What happens if you have a lesion of the globus palladus?

Answer 8

Loss of postural support.

Question 9

What happens if we have a lesion of the subthalamic nucleus?

Answer 9

Leads to loss of inhibition resulting in wild, flinging movements (hemiballismus).

Question 10

What happens if there is a lesion in the striatum?

Answer 10

Also loss of inhibition like a lesion in subthalamic nucleus, but results in quick, uncontrollable continuous movements as seen in Huntington’s disease.

Question 11

What parts of the brain are the 4 segments of the basal ganglia found? (3 different parts)

Answer 11

In the telencephalon there is both parts of the globus pallidus, and the striatum (putamen + caudate nucleus). In the midbrain there is the substantia nigra, and in the diencephalon there is the subthalamic nucleus.

Question 12

How are the putamen and caudate nucleus seperated?

Answer 12

By the anterior limb of the internal capsule. But, both structures together make up the striatum.

Question 13

How are the direct and indirect pathways connected?

Answer 13

Cerebral cortex sends input into the basal ganglia, which relays the input to the VL (or VA?) nucleus of thalamus, which shoots the input back to the cerebral cortex.

Question 14

What is the general concept of how both the direct and indirect pathways get activated?

Answer 14

By the process of “disinhibition,” meaning that one set of inhibitory neurons inhibit a second inhibitory neuron, and thus allowing a third neuron to become excited and fire.

Question 15

What is the general function of the direct and indirect pathway?

Answer 15

The direct pathway is thought to initiate a muscle movement, whereas the indirect pathway is thought to inhibit the antagonistic muscles of the initial movement, thereby allowing for actual muscle movement (otherwise both agonist and antagonist muscles would contract and there will be no movement).

Question 16

Trace the direct pathway of basal ganglia.

Answer 16

Cortex fires glutamate which excites the striatum. The striatum reacts by shooting GABA and substance P. These GABA and substance P then goes to the internal capsule of globus palladus. The IC of GP then gets inhibited in turn and thus releases the thalamus from its tonic inhibiton. The thalamus gets one of its motor neurons excited and that excited neuron fires back to the motor cortex.

Question 17

Trace the indirect pathway of basal ganglia.

Answer 17

Motor cortex will fire glutamate into the striatum as in direct pathway, but this time it will excite a different set of GABA (with a co neurotransmitter of enkephalin rather than substance P as in the direct). The striatum will fire these GABA into the EXTERNAL segment of the Globus Pallidus, which will fire GABA into the Subthalamic nucleus (releasing it from tonic inhibition), which will be excited and fire glutamate into the INTERNAL segment of the globus pallidus, which will fire GABA into the thalamus and thus induce tonic inhibition of the thalamus.

Question 18

What kind of neurons controls movement in the cortex?

Answer 18

Upper Motor Neurons, which are controlled by the Basal ganglia and the cerebellum.

Question 19

Outline the 4 functions of the basal ganglia in terms of how humans experience them.

Answer 19

Decision to move, direction of movement, amplitude of movement, and motor expression of emotions.

Question 20

What exactly is the nucleus accumbens?

Answer 20

The anterior and ventral part of the striatum where the head of the caudate nucleus and putamen are continuous with each other, it receives extensive dopamine input and is an integral part of the limbic system and the reward system.

Question 21

What is the basic function of the subthalamic nucleus?

Answer 21

It receives input from other structures of the basal ganglia and the motor cortex, and functions as a “clock” that defines output rhythm.

Question 22

What is the job of the striatum?

Answer 22

It is the “integrator” as it receives input from different cortical and subcortical areas.

Question 23

What does “tonic inhibition” mean? What organ in the brain is under tonic inhibiton?

Answer 23

It means that unless something removes that inhibition, it is not going to fire anything to the cortex. The thalamus is under tonic inhibiton.

Question 24

How is the substantia nigra involved in the direct pathway?

Answer 24

Substantia nigra releases dopamine which binds to D1 receptors and excites the striatum to release inhibitory neurons, enhancing the effect of direct pathway, and also binds to D2 receptors which would inhibit the indirect pathway.

Question 25

What provides tonic inhibiton to the substantia nigra?

Answer 25

The subthalamic nucleus.

Question 26

What is the role of substantia nigra in the indirect pathway?

Answer 26

In the striatum, the dopamine released by SN will bind to D2 receptors, which will inhibit the excitatory cholinergic interneurons of the striatum, so the striatum cannot fire into the GPe. Net effect is that the striatum is no longer active via cortical stimulation.

Question 27

How is the SN and the STN related?

Answer 27

SN inhibits STN, and the STN in turn excites the SN.