Exam 3 Week 12 Basal added pathways

Question 1

Structure very similar function and structure to globus pallidus internus

Answer 1

Substantia Nigra Pars Reticulata

Question 2

Substantia Nigra Pars Reticulata receives input from what structure? Causes inhibition of what structure?

Answer 2

striatum (striatonigral fibers)

inhibits thalamus with GABAnergic inhibitory neurons

Question 3

What neurotransmitter does Substantia Nigra Pars Compacta use in the indirect pathway

Answer 3

dopamine

Question 4

What does Substantia Nigra Pars Compacta inhibit via D2 receptors in the indirect pathway

Answer 4

striatal neurons

Question 5

Where and how does Substantia Nigra Pars Compacta

act on the direct pathway?

Answer 5

Produces excitation via D1 receptors on striatal neuronsof the direct pathway

Question 6

How does Substantia Nigra Pars Compacta promotes thalamic excitation?

Answer 6

by activating the direct pathway and inhibiting the indirect pathway

Substantia Nigra Pars Compacta are Inhibited by striatal GABAnergic input but are Excited by cholinergic input from pedunculo-pontine nucleus (PPN).

Question 7

What 2 ways does pedunculo-pontine nucleus (PPN) contribute to movement?

Answer 7

1. can initiate voluntary movement by facilitating disinhibition of the thalamus and in turn motor cortex.
2. contributes to the pontine reticulospinal tract and can produce descending excitation of spinal LMN (related to posture).

Question 8

Four parallel channels of functions involving the basal nuclei

Answer 8

1. Motor channel (loop)
2. Oculomotor channel (loop)
3. Prefrontal channel (loop)
4. Limbic channel (loop)

Question 9

Function of the Motor Loop

Answer 9

1. Initiated by the intention to act
2. Preparation, organization and execution of action
3. Endogenous generation of responses when environmental stimuli fail to provoke responses

Question 10

Path of the motor loop

Answer 10

1. Arises from Supplementary motor cortex & other cortical areas
2. Regulates VA/VL thalamic and motor cortex excitability via connections through the Putamen & Globus pallidus internus (direct pathway) and globus pallidus externus and subthalamus (indirect pathway).
3. SMA (supplementary motor area) generating the readiness that precedes volitional, self-paced, voluntary movements

Question 11

Path of Oculomotor loop

Answer 11

1. It begins in the SMA (supplementary motor area) & Posterior parietal cortex
2. Projects via caudate nucleus, globus pallidus internus & Substantia nigra pars reticulata to regulate excitability of the VA and MedioDorsal (also called dorsomedial) thalamic nuclei.
3. Thalamic Output is to prefrontal areas in the vicinity of the frontal eye fields.

Question 12

Functions of Oculomotor loop

Answer 12

1. Higher-order control of eye movements
2. Orientation of eyes towards specific objects in the environment
3. Implicated in visual exploration and visual learning

Question 13

Path of Prefrontal loop

Answer 13

1. Dorsolateral pre-frontal cortex input to the head of the caudate
2. The caudate then influences globus pallidus internus & Substantia nigra pars reticulata to regulate excitability of the ventral anterior and mediodorsal (MD) thalamic nuclei.
3. These nuclei in turn project to the prefrontal cortex (PFC)

Question 14

Functions of Prefrontal loop

Answer 14

1. Processing information about fairness of decision-making,
2. Trusting in these “fair” decisions & those who make them
3. ‘Altruistic punishment’ – the desire to punish violations of social norms even when we have not been personally wronged
4. Regulation of ‘worry’

Question 15

Pathway of limbic loop

Answer 15

1. Input from temporal cortex, hippocampus & amygdala into the basal nuclei is via the nucleus accumbens, ventral putamen & caudate.
2. These structures are in turn connected globus palldus internus for output to the mediodorsal thalamic nucleus. 3. The MD projects to the anterior cingulate cortex & orbitofrontal cortex

Question 16

Functions of Limbic Loop

Answer 16

1. Evaluation of personal actions and environmental resources
2. Social, behavioral and affective self-regulation

**This may be the channel implicated in excessive gambling seen in Parkinson’s patients on L-Dopa & dopamine agonists