11.1 Basal Ganglia

Question 1

What are the components of the Basal Ganglia

Answer 1

Striatum (caudate and putamen)
Palidum (Globus pallidus inc pars reticulata of the substantia nigra)
Subthalamic nucleus
Substantia nigra (pars compacta)

Question 2

What are the components of the neotriatum and what is their role?

Answer 2

Caudate: connected mainly to the frontal and pre-frontal areas and posteior parietal cortex.
Concerned with reuglation of social/moral behaviours
Active during the acquisition of new motor skills

Putamen: mainly connected to the somatic cortical areas and has a mapped representation of the body

Question 3

Where is the input for the neostriatum?

Answer 3

Cortex and substantia nigra -> compacta
Prefrontal and parietal cx - caudate
SMA, M1 and S1 - putamen

Question 4

Where is the output from the stiratum?

Answer 4

to the globus pallidus (internal for direct and external for indirect)

Question 5

What is the motor loop of the stiratum?

Answer 5

Comes in the putamen to thalamic nuclei and onto the SMA and M1

Question 6

What is the cognitive loop?

Answer 6

Planning ahead for motor actions via the caudate
Caudate is important for the learning of new motor skills
Returns to the prefrontal and premotor cortices via VA of thalamus and when the task is well practised it will become under the control of the motor loop

Question 7

What is the limbic loop?

Answer 7

Loop for reward, motivational behaviour, memory and motor expression relevant to emotions
Comes in the nucleus accumbens and connected to the inferior pre-frontal Cx of the limbic system

Question 8

What is the role of the basal ganglia in the motor pathway?

Answer 8

To instruct the motor areas (pre motor and SMA)

Question 9

What is the role of SMA?

Answer 9

sequence instructions to M1

Question 10

What is the main output of the GPi and GPe?

Answer 10

GPi to the thalamus in the direct pathway to project back to the cortex

GPe to the subthalamic and pedunculo-pontine nuclei in the indirect pathway

Question 11

What is the main input and output to the subthalamic nucleus and what are the cells of the subthalamic nuelcus??

Answer 11

Input: GPe (inhibitory) which regulates excitability

Output: GPi for diffuse general projections

Made up of glutaminergic neurons

Question 12

What is the substantia nigra, what are the two nuclei, what are the cells and what is the input and out put of each of the nuclei?

Answer 12

Pars compacta and pars reticulata

Cells in reticulata: GABAergic and contain a high level of melanin, which are produced as a by product of dopamine synthesis

Cells in compacta: dopaminergic

Input to SNc: cortex, PPt, STN and neostriatum
Output: Neostriatum (+)

Input to SNr: neostriatum
Output: (-) to thalamus, STN and PPt

Question 13

What is the role of the pedunculo-pontine reticular formation?

Answer 13

involved in regulating respiratory, CV and GIT activity and has profound influences on posture and locomotion via reticulospinal tracts that terminate at all levels of the spinal cord

Question 14

What is the major input and output to the pedunculo-pontine reticular formation?

Answer 14

Input: from cortex, SP and SNr
Output: SPINAL CORD

Question 15

How do the GPe and GPi work with the STN to control movement?

Answer 15

The STN is generating an overall level of background activity, internal segment is being kept active and by doing this it is suppressing the thalamus. The indirect pathway can inhibit parts of the STN to take that excitatory input to inhibitory nucleus away to increase the inhibition to circuits of the thalamus

Question 16

What is the role of the pars compacta of the subthalamic nuclei?

Answer 16

Tweaking the direct and indirect pathways to focus attention on a sequence or program of movements that needs to happen

Question 17

What is the general pathway of information through the basal ganglia?

Answer 17

1. Plan of action sent to the basal ganglia from Cx
2. SNc adjusts the balance between direct and indirect pathways of specific motor programs
3. Refined motor programs to SMA - M1 and PPt for execution (thalamus under tonic suppression until instructed otherwise)
4. Spinal cord instructed: fine movement via CCT and posture via RST

Question 18

What is the effect of parkinsons disease?

Answer 18

SNc dopaminergic cells lost which means striatum neurons eventually die. The direct pathway will be disengaged and indirect pathway will prevail by default
There will be increased excitation of and decreased disinhibition of GPi, resulting in enhanced inhibition of the thalamus leading to hypokinesia

Question 19

What happens in huntingtons?

Answer 19

GABAergic cell death in the neostriatum which causes the breaks to be applied harder to teh STN, reduced basal inhibition on thalamus, execution of otherwise suppressed motor behaviours

Will also have retrograde loss of cortical neurons because striatal targets die