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KINE4505 > Topic 9- Basal Ganglia > Flashcards

Topic 9- Basal Ganglia Flashcards

1
Q

What are the four main parts of the basal ganglia?

A

The four main parts are the Striatum (caudate and putamen), Globus Pallidus (external and internal segments), Substantia nigra (pars compacta and pars reticulata), and Subthalamic nucleus.

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2
Q

What is the role of the basal ganglia in movement?

A

The basal ganglia influence movement by modulating activity in upper motor neurons.

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3
Q

Does the basal ganglia have direct connections to cortical spinal tracts?

A

No, the basal ganglia does not have direct connections to cortical spinal tracts.

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4
Q

How does the basal ganglia contribute to motor control and coordination?

A

The basal ganglia plays a supervisory and indirect role in motor control and coordination.

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5
Q

What are the main input areas to the basal ganglia?

A

The main input areas to the basal ganglia are the striatum, specifically the caudate and putamen, receiving inputs from most of the cerebral cortex and other regions.

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6
Q

What type of neurons receive cortical signals in the basal ganglia?

A

“Medium spiny neurons” in the basal ganglia receive cortical signals.

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7
Q

Where do cortical signals to the caudate come from?

A

The caudate receives cortical signals from association cortical areas and eye movement areas.

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8
Q

Where do cortical signals to the putamen come from? (7)

A

1) primary sensory cortex (SI)
2) secondary sensory cortex (S2), 3) primary motor cortex (M1), 5)premotor cortex, 6) secondary audio cortex, and 7) secondary visual cortex.

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9
Q

What is the name of the pathway through which cortical signals reach the basal ganglia?

A

The pathway is called the “corticostriatal pathway.”

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10
Q

Where does the output from the basal ganglia go in terms of motor areas?

A

The output from the basal ganglia goes to motor areas via the thalamus.

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11
Q

What are the two main output structures from the basal ganglia?

A

The main output structures are the Globus Pallidus (internal segment) and the substantia nigra (pars reticulata).

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12
Q

What is the main output structure for eye movement control?

A

The substantia nigra (pars reticulata) serves as the main output structure for eye movement control.

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13
Q

What is the main output from the basal ganglia that goes to the thalamus?

A

The main output that goes to the thalamus is the Globus Pallidus (internal segment).

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14
Q

Where does the output from the substantia nigra (pars reticulata) go for eye movements?

A

The output from substantia nigra (pars reticulata) goes to brainstem structures like the superior colliculus instead of the thalamus for controlling eye movements.

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15
Q

What happens when the basal ganglia isn’t functioning properly?

A

When the basal ganglia isn’t working correctly, it can lead to either making movements when you aren’t supposed to or not making movements when you are supposed to.

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16
Q

Two main outputs from basal ganglia

A

1) To motor areas via the thalamus from from Globus Pallidus (int.)
2) To eye mvt areas of brainstem​ from substantia nigra (pars reticulata) ​

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17
Q

Four circuits of the basal ganglia

A

Motor - controlling voluntary movements ​

  1. Limbic - associated with regulating “emotional behaviour”​
  2. Executive - regulating cognitive processes “cognitive processes”
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18
Q

What is the role of the basal ganglia during rest?

A

During rest, the basal ganglia continuously inhibit motor areas in a tonic (continuous) manner, acting like a “brake pedal” for motor activity.

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19
Q

What is the pattern of activity in the Globus Pallidus internal segment (GPi) and substantia nigra during rest?

A

The GPi and substantia nigra often exhibit low levels of spontaneous activity during rest.

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20
Q

What type of cells are the efferent cells in the basal ganglia?

A

The efferent cells in the basal ganglia are GABAergic, meaning they release the neurotransmitter GABA, which has an inhibitory effect on target neurons (making them less likely to generate an action potential or transmit signals)

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21
Q

What kind of projections do the output nuclei of the basal ganglia send?

A

The output nuclei of the basal ganglia send GABAergic projections either to the thalamus or the superior colliculus.

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22
Q

What is the nature of the tonic activity received by the output nuclei from the basal ganglia?

A

The output nuclei of the basal ganglia receive tonic GABAergic activity continuously from the basal ganglia, maintaining a state of inhibition during rest.

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23
Q

Why is the tonic inhibition from the basal ganglia significant for movement initiation?

A

The tonic inhibition from the basal ganglia must be removed before movements can be initiated.

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24
Q

What are the two main groups of projection neurons in the striatum?

A

The two main groups of projection neurons in the striatum are those that project to the GP(int) and SN pars reticulata (forming the direct pathway) and those that project to GP(ext) (forming the indirect pathway).

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25
Q

What is the primary function of the direct pathway in the basal ganglia?

A

The direct pathway decreases tonic inhibitory output from the basal ganglia.

26
Q

What is the primary function of the direct pathway in the basal ganglia?

A

The direct pathway decreases tonic inhibitory output from the basal ganglia (means BG is less actively inhibiting certain brain regions, allowing those regions to become more active and promote movement or action)

27
Q

What is the primary function of the indirect pathway in the basal ganglia?

A

The indirect pathway increases tonic inhibitory output from the basal ganglia (means the BG is more actively inhibiting certain brain regions, reducing their activity and potentially suppressing movement or action)

28
Q

Steps of Direct Pathway

A

1) )nput Source: Cortex sends excitatory (glutamatergic) inputs to the striatum, caudate/putamin which activated medium spiny neurons
2) Both glutamatergic inputs from the cortex and dopaminergic inputs converge on the medium spiny neurons in the striatum.​
3) Threshold Activation: If the combined input is enough to reach the threshold, medium spiny neurons fire off.​
4) Output to Globus Pallidus Internal Segment (GPi): Firing medium spiny neurons send inhibitory signals to the GPi,
5) Release of Brake: Inhibiting the GPi removes the tonic inhibitory activity, acting like lifting a brake pedal.​
6) GPi neurons project to the VA/VL complex of the thalamus, which is involved in relaying information to the cortex, facilitates the initiation of action by allowing the thalamus to function without continuous inhibition from the GPi.

29
Q

What is the primary function of the disinhibitory circuit in the direct pathway of the basal ganglia?

A

The primary function of this circuit is to act as a gate, allowing signals to activate upper motor neurons for muscle activation and facilitate movement.

30
Q

What is the primary function of the indirect pathway in the basal ganglia?

A

To further inhibit the thalamus, which in turn inhibits movement, acting as a brake pedal for the motor system.

31
Q

How does the function of the indirect pathway compare to that of the direct pathway?

A

While the direct pathway encourages action, the indirect pathway advises against certain actions and inhibits movement.

32
Q

What are the key components of the circuit in the indirect pathway?

A

The key components include striatal neurons, both segments of the globus pallidus (internal and external), the subthalamic nucleus, and the thalamus.

33
Q

Indirect Pathway Steps

A

Stridal Neurons: These neurons send signals to both segments of the Globus Pallidus (internal and external).

GPE Inhibition: The external segment of the Globus Pallidus (GPE) inhibits the subthalamic nucleus.

Subthalamic Nucleus Activation: When the subthalamic nucleus is activated, it inhibits the GPE and increases its own inhibitory signals.

Increased Inhibition to GPI: This leads to increased inhibition from the subthalamic nucleus to the Globus Pallidus Internal (GPI).

Disinhibition of GPE: This action prevents the excitation of the thalamus.

Subthalamic Nucleus Activation: It further increases the inhibition of GPI, effectively acting as a brake pedal to inhibit movement.

34
Q

What is the primary function of the hyperdirect pathway in the basal ganglia?

A

The hyperdirect pathway acts like an alarm bell, instantly stopping ongoing actions and initiating a global inhibition of all activities, followed shortly by action.

35
Q

What are the key components of the hyperdirect pathway?

A

The hyperdirect pathway consists of a direct connection between the cortex and the subthalamic nucleus (STN).

36
Q

How does the hyperdirect pathway differ from the indirect pathway in terms of its function?

A

The hyperdirect pathway provides a rapid and strong braking mechanism, instantly stopping ongoing actions, while the indirect pathway advises against certain actions but doesn’t stop them abruptly.

37
Q

What is the process of the hyperdirect pathway?

A

bypasses the striatum and the globus pallidus, with the cortex signaling directly to the STN, resulting in an immediate halt of all activities.

38
Q

What is the purpose of the hyperdirect pathway in the basal ganglia?

A

Allows for a quick pause and assessment before initiating subsequent actions, providing an essential mechanism for rapid decision-making and motor control.

39
Q

What causes the differential effects of dopamine in the basal ganglia?

A

The differential effects of dopamine are due to the presence of different dopamine receptor subtypes.

40
Q

How does dopamine affect medium spiny neurons in the striatum?

A

Medium spiny neurons in the striatum receive dopamine projections from the substantia nigra pars compacta (SN(pc)), and the dopamine excites spiny cells through D1 receptors.

41
Q

How does dopamine affect the direct and indirect pathways through D1 and D2 receptors?

A

1) D1 receptors, excited by dopamine, enhance the direct pathway, promoting the initiation of voluntary movements.
D2 receptors, inhibited by dopamine, reduce the inhibitory influence of the indirect pathway, allowing for smoother execution of motor commands.Both dopamine receptors decrease inhibitory output from the basal ganglia in a healthy state.

42
Q

What is hypokinesia, and what does it involve?

A

Hypokinesia is characterized by a decrease in both the amount and speed of movements, resulting in reduced or slowed motor activity.

43
Q

Define hyperkinesia and explain what it represents.

A

refers to the presence of unwanted or excessive movements, which can be involuntary or uncontrollable.

44
Q

What is the difference between a positive sign and a negative sign in the context of movement disorders?

A

A positive sign, such as hyperkinesia, refers to something happening that’s not supposed to happen (unwanted movements). A negative sign, like hypokinesia, refers to something not happening that is supposed to happen (a decrease in normal voluntary movements).

45
Q

What is one of the primary characteristics of Parkinson’s Disease in terms of cellular changes?

A

Characterized by Loss of dopamine-producing cells in SNc ​

46
Q

In Parkinson’s Disease, which pathway experiences overactivity, and what is its effect on the basal ganglia?

A

In Parkinson’s Disease, there is overactivity in the indirect pathway, which passes through the subthalamic nucleus and leads to increased firing of the Globus Pallidus Internal (Gpi).

47
Q

What roles do D1 and D2 receptors play in the basal ganglia circuitry under normal conditions?

A

D1 receptors are inhibitory and contribute to the direct pathway, while D2 receptors are excitatory and contribute to the indirect pathway.

48
Q

How does the lack of D1 receptor activation in Parkinson’s Disease impact the basal ganglia pathways?

A

In Parkinson’s Disease, the absence of D1 receptor activation leads to overactivity in the indirect pathway and reduced activity in the direct pathway.

49
Q

What compensatory mechanism occurs in response to the loss of dopamine in Parkinson’s Disease?

A

To compensate for the loss of dopamine, more excitatory activity is required from the cortex onto the striatum.

50
Q

What is the overall consequence of the changes in basal ganglia circuitry in Parkinson’s Disease?

A

The net result is increased tonic inhibitory output from the basal ganglia, which makes it more challenging to perform basic movements.

51
Q

What is akinesia, and what does it involve?

A

Refers to difficulty initiating voluntary movements.

52
Q

What is bradykinesia, and how is it characterized?

A

Bradykinesia is characterized by very slow movements once they are initiated.

53
Q

What happens when there is a loss of acetylcholine-producing cells in the pedunculopontine nucleus?

A

The loss of acetylcholine-producing cells in the pedunculopontine nucleus leads to rigidity, which involves an inability to inhibit reticulospinal and vestibulospinal tracts, resulting in muscle stiffness.

54
Q

What is the purpose of pallidotomy in Parkinson’s Disease treatment, and how does it achieve this?

A

Pallidotomy involves lesioning Globus pallidus cells to reduce tonic inhibition, facilitating easier threshold activation for movement.

55
Q

How does thalamotomy contribute to the treatment of Parkinson’s Disease, and what is its mechanism?

A

Thalamotomy is a targeted lesioning procedure in the thalamus that achieves a similar reduction in inhibition, aiding in Parkinson’s Disease treatment.

56
Q

What is the role of lesioning the subthalamic nucleus in Parkinson’s Disease treatment, and how does it impact the circuitry?

A

Lesioning the subthalamic nucleus decreases the impact of the indirect pathway in the treatment of Parkinson’s Disease.

57
Q

Why is L-DOPA used as a treatment for Parkinson’s Disease (PD)?

A

L-DOPA is used to replace missing dopamine in PD because dopamine itself cannot cross the blood-brain barrier.

58
Q

What is Deep Brain Stimulation (DBS), and how is it used to treat PD?

A

DBS is a surgical procedure used to treat PD by implanting electrodes in specific brain areas, such as the subthalamic nucleus (STN) or globus pallidus interna (GPi), which are involved in motor control.

59
Q

What is a characteristic feature of Huntington’s Disease in terms of neuronal loss?

A

Huntington’s Disease involves the preferential loss of striatal neurons in the caudate nucleus that make up the indirect pathway.

60
Q

What is the primary concept associated with the Direct Pathway in Basal Ganglia Circuitry?

A

In the Direct Pathway, transiently inhibitory projections from the caudate and putamen target tonically active inhibitory neurons in the internal segment of the globus pallidus. (ignals briefly put the brakes on active inhibitory neurons in the globus pallidus.)

61
Q

What are the main characteristics of Hemiballismus (Hemiballism)?

A

Characterized by uncontrolled and involuntary flinging movements of the limbs on the side opposite to the brain lesion, often resulting from a reduction in the output of the Globus Pallidus Internal (Gpi).

62
Q

What can lead to Hemiballismus, and how does it relate to the basal ganglia circuitry?

A

Hemiballismus can occur due to a reduction in Gpi output, often caused by a lesion in the subthalamic nucleus (STN), typically resulting from a stroke. This reduction in output impairs the indirect pathway’s ability to inhibit inappropriate movements.

KINE4505 (16 decks)

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