Voluntary Motion: Basal Ganglia and the Big Picture

Question 1

What is role of the Basal Ganglia?

Answer 1

1. Involved in planning and programming of movement
2. Input is particularly important in the INITIATION of movement

*** Work by inhibition and withdrawal of the inhibition

Question 2

List the various Basal Ganglia.

Answer 2

1. Subthalamic Nucleus
2. Substantia Nigra
   - Pars Compact
   - Pars Reticulata
3. Putamen Nucleus
4. Caudate Nucleus
5. Globus Pallidus
   - Internal Segment
   - External Segment

Striatum = Putamen + Caudate Nucleus
*** (Recieves INPUTS to the basal ganglia)

Question 3

Describe the Nigrostriatal Dopaminergic System.

Answer 3

From: Substantia Nigra (Pars Compacta)

To: Nuclei of Striatum

Neurotransmitter: DOPAMINE

Receptors: D1 receptors (+); D2 receptors (-)

Question 4

Describe the Intrastriatal Cholinergic System.

Answer 4

Between the NUCLEI in the striatum

Effects –> Excitatory

Neurotransmitter: Acetylcholine

Question 5

Describe the Striatonigral Gaba-ergic Pathway.

Answer 5

From: Striatum

To: Substantia Nigra (Pars Reticulata) and (Globus Palludis - Internal Segment)

Neurotransmitter: GABA

“DIRECT Pathway”

Function: Leads to INITIATION of movement

Question 6

Through which structures is information going to leave the basal ganglia?

Where do axons of these structures leave and go to?

Which neurotransmitter is used in the Thalamus

Answer 6

1. Substantia Nigra (Pars Reticulata)
2. Internal Segment of Globus Pallidus

*** Axons from these structures will go to the THALAMUS

*** Release GABA within the Thalamus to INHIBIT (allows motion to occur)

Question 7

List the major inputs to the basal Ganglia.

Answer 7

1. Substantia Nigra (Pars Compacta) receives inputs and relats them to the Striatum
2. Cortex via the Corticostriate Track (Releases EAAs)

Question 8

Differentiate between the Direct and Indirect Pathways in terms of which receptors are used.

Answer 8

Direct –> D1 Receptors (Excited by Dopamine and ALLOWS Motion)

Indirect – D2 Receptors (Inhibited by Dopamine, Excited by EAA/Ach, INHIBITS Motion)

Question 9

Describe the components of the Direct Pathway.

Answer 9

From: Striatum

To: Substantia Nigra (Pars reticulata) and Internal Segment of the Globus Pallidus

1. Substantia Nigra Pars Compacta (input) is going to release Dompamine to excite striatal cells
2. Striatal cells release GABA in the SNPR and GPi
3. Inhibition in the Thalamus
4. SNPR and GPi cannot release EAAs and Ach to excite the Thalamus so there will be LESS GABA released from the Thalamus which is going to allow the Cortex to INITIATE MOVEMENT!

Question 10

Describe the components of the Indirect Pathway.

Answer 10

1. Cortical Areas will release EAA and Intrastriatal Cholinergic Pathway will release Acetylcholine to Excite the STRIATUM
2. Neurons from Striatum sends axons (release GABA) to the External Segment of the Globus Pallidus
3. External Segment of the Globus Pallidus is going to be inhibited by the striatum which means it will NOT release as much GABA onto the Subthalamic Nucleus
4. Subthalamic Nucleus is going to release EAA to the thalamus which is going to Excite the thalamus
5. When the Thalamus is EXCITED, it is going to release a lot of GABA which will inhibit the CORTEX and NO MOVEMENT will occur

Question 11

Describe how we allow motion to occur (putting the Direct and Indirect Pathways together).

Answer 11

Patients with damage to the SNPC means that you cannot activate the Direct Pathway!!!!

AND the Indirect Pathway is OVER-ACTIVE!!!

You do not have the dopamine release and will present with Parkinson’s Disease

Question 12

Describe the main role of the Association Cortex.

Answer 12

1. Planning of complex motor actions
2. Carrying out of “thought” processes

Question 13

Describe the function of the Prefrontal Cortex.

Answer 13

1. Interacts with parieto-temporal-occipital (PTO) association area (sensory input for relationship to other things) and all levels of motor cortex
2. Planning of complex motor actions (i.e. is it appropriate to move right now?

Question 14

Interactions between which structures will determine IF the motion will occur?

Answer 14

1. Frontal
2. Premotor
3. Supplementary Motor Cortex
4. and the Basal Ganglia (Dopamine)

Question 15

Describe the concept of “alpha-gamma coactivation”.

Answer 15

To make motion occur, if the brain ACTIVATES the alpha-motor neuron, it also ACTIVATES the gamma-motor neuron for spindles in the contracting (agonist) muscle.

*** Allows the muscle spindle to change at the same rate as the Alpha Motor Neuron Contraction (keeps muscle spindle @ the right length during muscle contraction)

In the ANTAGONIST muscle, the Alpha motor nueron is inhibited along with the Gamma motor neuron (decrease the sensitivity of the gamma motor neuron and you will NOT get an opposing stretch reflex)