Basal Ganglia

What is the basal ganglia’s main role in terms of movement?

The basal ganglia is a movement regulatory component. It does not initiate or execute movement.

What is the basal ganglia’s two “core missions?”

The two core missions include operational learning (constantly learning about muscle function) and action selection (selecting one muscle action only).

What is grouping?

Grouping is the way around doing one thing at a time. For example, opening a door includes twisting the knob and pushing the door. The basal ganglia learns this as one motion.

List the sequence of the skeletal motor loop.

Cortex information is sent to the basal ganglia. The basal ganglia outputs this information and action selection to the ventral lateral thalamus. This then gets inputted back to the cortex.

List the parts of the basal ganglia.

Striatum (Caudate and Putamen)

Globus Pallidus (Externus and Internus)

Subthalamic Nucleus

Substantia Nigra

Ventral Lateral Nucleus of Thalamus

Describe aspects of medium spiny neurons. Include where they are found, their threshold, and amount of dendrites.

They are located in the striatum. Their resting potential is far from their threshold. Their high threshold means that a lot of input is required for them to fire and action potential. They have a lot of dendrites (dendritic trees) allowing for a lot of input sites.

Where do the medium spiny neurons project to from the caudate? What about the putamen?

Medium spiny neurons from the caudate project to the globus pallidus internus and the substantia nigra pars reticulata. Medium spiny neurons from the putamen project to the globus pallidus internus and externus.

What inputs do the medium spiny neurons receive? Which is high quantity, which is high efficiency?

The medium spiny neurons receive input from cortical pyramidal neurons, local circuit neurons, and substantia nigra pars compacta. Pyramidal neurons are high quantity. Local circuit neurons are high quality.

How do the inputs to the caudate differ from the inputs to the putamen?

Caudate’s input are usually for eye movement whereas putamen inputs are for skeletal muscles.

Describe the circuitry of the direct pathway. Describe the relation between each step (excitatory / inhibitory). Describe the end goal and how the pathway achieves this.

Cerebral cortex sends massive input to putamen (excitatory). Putamen medium spiny neurons fire and synapse on the globus pallidus internus (inhibitory). The globus pallidus internus synapses on the thalamus (inhibitory). The thalamus synapses on the cortex (excitatory).

The end goal is excitatory. The cortex excites the putamen. The putamen inhibits the GPi. Now, the GPi can no longer inhibit the thalamus which allows the thalamus to excite the cortex.

Describe the circuitry of the indirect pathway. Describe the relation between each step (excitatory / inhibitory). Describe the end goal and how the pathway achieves this.

Cerebral cortex sends massive input to putamen (excitatory). Putamen medium spiny neurons fire and synapse on the globus pallidus externus (inhibitory). The globus pallidus externus synapses on the globus pallidus internus (inhibitory). The globus pallidus internus synapses on the thalamus (inhibitory). The thalamus synapses on the cortex (excitatory).

The end goal is inhibitory. The cortex excites the putamen. The putamen inhibits the GPe. Now, the GPe can no longer inhibit the GPi which allows the GPi to inhibit the thalamus. Now the thalamus can not fire to the cortex.

Describe the circuitry of the hyper direct pathway. Describe the relation between each step (excitatory / inhibitory). Describe the end goal and how the pathway achieves this.

The cortex fires on the subthalamic nucleus (excitatory). The subthalamic nucleus then fires on the GPi (excitatory). The GPi fires on the thalamus (inhibitory).

The end goal is inhibitory. The cortex fires on the STN which then excites the GPi. This allows the GPi to inhibit the thalamus.

GABA, Glutamate, and Dopamine are neurotransmitters. What does each do?

GABA is inhibitory, Glutamate is excitatory, and Dopamine is modulatory.

What is the role of the substantia nigra involving the putamen?

Medium spiny neurons either have D1 or D2 receptors. The substantia nigra releases dopamine.

Direct pathway medium spiny neurons have D1 receptors. Dopamine acts as an excitatory NT and increases the direct pathway. This leads to more movement.

Indirect pathway medium spiny neurons have D2 receptors. Dopamine act as an inhibitory NT and decreases the indirect pathway. This leads to more movement.