Basal Ganglia and Movement

Cerebral Cortex

• basal ganglia deals with challenging motor functions

• basal ganglia has no direct output to LMNs

Basal Ganglia: main function

motor output circuit regulation

• compares proprioceptive information & movement commands

• regulates muscle force, muscle contraction & tone, and multi-joints movements

• regulates sequencing of movements

• semi-automatic & synergistic movements:

  • locomotion, postural adjustment, ar swing during walking

Basal ganglia circuitry loops associated with the control of other systems:

• goal-directed behavior circuit:

  • decision making, planning, and choosing actions

• social behavior circuit

  • recognizing social cues, regulating self-control

• emotion (limbic)/motivation circuit

  • regulating emotional expressions, motivation, and addiction

• oculomotor circuit

  • decision making about spatial attention and eye movements

Basal Ganglia includes:

• striatum: caudate & putamen

• globus pallidus externus (GPe)

• globus pallidus internus (GPi)

• substantia nigra compacta (SNc)

• substantia nigra reticularis (SNr)

• subthalamic nucleus (STN)

Basal Ganglia Brain photo

Coronal cut

Basal Ganglia Motor Circuit — Overview

• has NO DIRECT output to LMNs

• SNr and GPi = output nuclei of the basal ganglia

• from output nuclei of BG, motor control on LMN is done via 3 routes:

  • via motor thalamus (then to UMN to CTX)

    • controls voluntary muscle activity

  • via the pedunculopontine nucleus (PPN)

    • regulates contraction activity of postural and girdle muscls (via reticulospinal tracts)

  • via midbrain locomotor area

    • regulates rhythmic lower limb movements: walking, running (via stimulation of reticulospinal tracts)

Internal Basal Ganglia Motor circuits (pathways)

• has two main internal feedback loops that work in parallel with the cerebral cortex

  • direct pathway

  • indirect pathway

Internal Feedback loop of BG — Direct & Indirect pathways

BG output nuclei affect VL, PPN, and Midbrain

Basal Ganglia Pathways

• has two main feedback loops

  • direct pathway

  • indirect pathway

• stimulation of:

  • the direct pathway increases the excitatory effect on the cortex, through the thalamus, and therefore facilitates movement

  • the indirect pathway decreases the excitatory effect on the cortex, through the thalamus, and therefore suppresses movement

Simplified Overview

• the direct (GO) pathway facilitates specific movements while at the same time:

• the indirect (STOP) pathway suppresses unwanted (competing) movements

Full direct pathway

Direct Pathway starting with SNc

In the direct pathway:

• SNc releases Dopamine to stimulate the D1 receptors in the striatum (Putamen & Caudate)

• D1 receptors stimulate the striatum to release GABA onto its target: GPi/SNr.

• This will cause a decrease in activation (stimulation) of the GPi/SNr

• GPi/SNr also uses GABA as its neurotransmitter

• Therefore GPi/SNr will release less GABA resulting in:

  • decreased inhibition from GPi/SNr to VL of thalamus

  • that results in VL of thalamus to release more of its Neurotransmitter: Glutamate

  • that causes the VL of thalamus to increase its activation on the cerebral cortex.

• This will trigger an increase in stimulation output from the cerebral cortex to the spinal cord LMNs

Indirect pathway

Indirect pathway starting with SNc

In the indirect pathway

• SNc releases Dopamine to inhibit the D2 receptors in the striatum (Putamen & Caudate)

• D2 receptors stimulate the striatum to release GABA onto its target: GPe

• This will cause a decrease in activation (stimulation) of the GPe

• GPe also uses GABA as its neurotransmitter

• Therefore, GPe will release less GABA.

  • less GABA from GPe to Subthalamic nucleus (STN):

    • causes STN to release more of its neurotransmitter: glutamate onto its target: GPi/SNr

      • This results in stimulation of GPi/SNr to release more GABA

  • less GABA from GPe to GPi/SNr

    • causes GPi/SNr to release more GABA

• Therefore both #1 and #2 (from previous slide) will cause GPi/SNr to release more GABA.

  • This will increase its inhibition onto the VL of the thalamus

  • The VL will release less Glutamate and therefore it will decrease its activation on the cerebral cortex.

• This will result in a decrease in stimulation output from the cerebral cortex to spinal cord LMNs.

Normal BG — Showing BOTH Direct & Indirect Pathways