Basal Ganglia

Question 1

What are the three major input nuclei of the basal ganglia?

Answer 1

Striatum.
Subthalamic nucleus.
Substantia nigra pars compacta.

Question 2

The striatum is a collective term for what?

Answer 2

Caudate nucleus and putamen.

Question 3

What is the largest nucleus of the basal ganglia?

Answer 3

Striatum.

Question 4

Which five areas does the striatum receive direct input from?

Answer 4

Cerebral cortex.
Brainstem.
Substantia nigra pars compacta.
Midbrain raphe.
Pedunculopontine nucleus.

Question 5

The basal ganglia receives input about which four classes of processes?

Answer 5

Motivational.
Emotional.
Cognitive.
Sensorimotor.

Question 6

Which three areas does the subthalamic nucleus receive input from?

Answer 6

Frontal cortex.
Thalamus.
Brainstem.

Question 7

What is unique about the subthalamic nucleus?

Answer 7

It is the only component of the basal ganglia that has excitatory (glutamatergic) output connections.

Question 8

Where does the subthalamic nucleus project to?

Answer 8

Output nuclei and intrinsic external globus pallidus.

Question 9

The substantia nigra pars compacta contains what population of neurons?

Answer 9

An important population of dopaminergic neurons.

Question 10

What do the dopaminergic neurons in the substantia nigra pars compacta give rise to?

Answer 10

Nigrostriatal dopamine projections.

Question 11

Where does the substantia nigra pars compacta receive input from?

Answer 11

Other basal ganglia nuclei.
Brainstem structures.
Frontal cortex.
Amygdala.

Question 12

What does the pattern of connectivity in the substantia nigra pars compacta suggest?

Answer 12

That the most important direct influence over the dopaminergic neurons arises from evolutionary ancient parts of the brain.

Question 13

What is the role of the internal globus pallidus?

Answer 13

It is one of the two principal output nuclei.

Question 14

Where does the internal globus pallidus receive input from?

Answer 14

Other basal ganglia nuclei.

Question 15

Where does the internal globus pallidus project to?

Answer 15

External targets in the thalamus and brainstem.

Question 16

Describe the neurons of the internal globus pallidus.

Answer 16

GABAergic with high levels of tonic activity.

Question 17

What is the role of the substantia nigra pars reticulata?

Answer 17

It is the second principal output nucleus.

Question 18

Where does the substantia nigra pars reticulata receive inhibitory (GABAergic) inputs from?

Answer 18

Striatum.
Globus pallidus.

Question 19

Where does the substantia nigra pars reticulata receive excitatory input from?

Answer 19

Subthalamus.

Question 20

What type of neurons are in the substantia nigra pars reticulata?

Answer 20

GABAergic.

Question 21

Where do the substantia nigra pars reticulata neurons provide output to?

Answer 21

Thalamus.
Brainstem.
Midbrain.
Medullary reticular formation.

Question 22

In the traditional model of the basal ganglia, where are signals originating in the cerebral cortex distributed to?

Answer 22

Two populations of medium spiny output neurons in the striatum.

Question 23

In the traditional model of the basal ganglia, what is the proposed direct pathway?

Answer 23

Neurons containing a preponderance of D1 dopamine receptors make direct inhibitory contact with the basal ganglia output nuclei.

Question 23

In the traditional model of the basal ganglia, what is the proposed indirect pathway?

Answer 23

Striatal neurons containing mainly D2 dopamine receptors make excitatory contact with the output nuclei via relays in the globus pallidus and subthalamus.

Question 24

Summarise the traditional model of the basal ganglia.

Answer 24

Basal ganglia output was thought to reflect a cortically determined balance between inhibitory and excitatory projections terminating on the two output structures (internal globus pallidus and substantia nigra pars reticulata).

Question 25

List three recent findings that have shown that the internal circuitry of the basal ganglia is more complex that the traditional model implies.

Answer 25

Medium spiny neurons of the direct pathway also provide collateral input to the globus pallidus. Globus pallidus neurons also make direct contact with the output nuclei in addition to the traditional indirect connections to the subthalamus. The globus pallidus also projects back to the striatum and to the structures outside the basal ganglia.

Question 26

The connections between the cerebral cortex and basal ganglia can be viewed as a series of what?

Answer 26

Re-entrant parallel projecting, partly segregated, cortico-striato-nigro-thalamo-cortical loops or channels.

Question 27

What implies that the re-entrant loop architecture through the basal ganglia must have predated the evolutionary expansion of the cerebral cortex?

Answer 27

The concept of parallel projecting re-entrant loops through the basal ganglia has been extended to their connections with sensorimotor and motivational structures in the brainstem.

Question 28

Name some sensorimotor and motivational structures in the brainstem.

Answer 28

Superior colliculus. Periaqueductal grey. Pedunculopontine nucleus. Parabrachial nucleus.

Question 29

For the cortical loops, where is the thalamic relay located?

Answer 29

On the output side of the loop.

Question 30

For the subcortical loops, where is the thalamic relay located?

Answer 30

On the input side of the loop.

Question 31

What is the fundamental selection problem?

Answer 31

Determining which functional system should be allowed to direct behavioural output at any point in time, e.g. choosing between talking and drinking because it is impossible to do both at the same time.

Question 32

What is the purpose of selective attention?

Answer 32

The sensory systems are continually faced with multiple external stimuli, one of which may drive a movement incompatible with one specified by others. It is important to select a stimulus that will become the focus of attention and direct movement.

Question 33

Describe the input filter of the basal ganglia.

Answer 33

Cortical and some thalamic inputs make comparatively few contacts with individual striatal neurons, so a large population of sufficiently synchronised excitatory inputs is required to depolarise the membrane of a medium spiny neuron enough to fire an action potential.

Question 34

How does the input filter of the basal ganglia promote selection?

Answer 34

It excludes weak or less biologically significant competitors.

Question 35

What causes highly activated striatal elements to suppress activity in adjacent more weakly activated channels?

Answer 35

Local GABAergic inhibitory collaterals between striatal spiny neurons and longer-range inhibitory effects of interneurons.

Question 36

What is the effect of the combination of focused inhibition from the striatum with the more diffuse excitation from the subthalamus?

Answer 36

Decrease activity in selected channels and increase activity in non-selected channels in basal ganglia output nuclei.

Question 37

What is the effect of local inhibitory collaterals between output nuclei neurons?

Answer 37

Further sharpen the difference between inhibited and non-inhibited channels.

Question 38

What is considered the principal function of the basal ganglia?

Answer 38

To select between competing and incompatible behavioural options.

Question 39

What is considered the basic substrate for selection?

Answer 39

The parallel loops originating from and returning to diverse cortical and subcortical functional systems.

Question 40

Explain the concept of normal selection within the basal ganglia.

Answer 40

A reduction in inhibition of selected channels below a proposed selection threshold (central channel) while maintaining or increasing inhibition of non-selected channels (left and right channels).

Question 41

What might account for akinesia in Parkinson's disease?

Answer 41

Insufficient reduction in tonic inhibition of all channels, meaning no target structure would be sufficiently disinhibited.

Question 42

What might account for the distractibility and disordered train of thought in schizophrenic and ADHD patients?

Answer 42

A failure to adequately disinhibit the selected channel or suppress disinhibitory activity in competing channels would cause current selections to be vulnerable to interruption.

Question 43

What might account for the hard selections seen in OCD and addictive behaviours?

Answer 43

One channel may become pathologically dominant either through abnormal disinhibition of the selected channel or excessive tonic inhibition of competing channels. This would make the relevant option easy to select and highly resistant to interruption.

Question 44

What are the three main symptoms of Parkinson's disease?

Answer 44

Akinesia. Bradykinesia. Rigidity.

Question 45

Define akinesia.

Answer 45

Difficulties in initiating movement.

Question 46

Define bradykinesia.

Answer 46

Initiated movements are slow.

Question 47

Define rigidity.

Answer 47

Stiffness and resistance to passive movement.

Question 48

What is thought to be the principal neurological deficit responsible for the motor symptoms of Parkinson's disease?

Answer 48

Progressive degeneration of dopaminergic neurotransmission in the basal ganglia.

Question 49

Describe how Parkinson's disease impairs the normal selective function of the basal ganglia.

Answer 49

Since the output of the basal ganglia is GABAergic, in Parkinson's disease, targeted structures receive high and uneven levels of inhibitory input.

Question 50

In the early stages of Huntington's disease, where is neuronal degeneration most evident?

Answer 50

In the striatal medium spiny neurons.

Question 51

In Huntington's disease, what is chorea?