Motor Systems II and Basal Ganglia

hierarchy of the motor system

• cortex > brainstem > spinal cord

• basal ganglia and cerebellum run in parallel

what are the 3 main functions of the basal ganglia?

motor loop, cognitive loop, emotional loop

within the motor loop of the basal ganglia, what are the 4 major functions?

voluntary movement regulation, action selection, procedural learning, regulation of movement vigor

what is procedural learning?

a category of long term memory that involves implicit memory and can only be demonstrated indirectly through some type of motor action

what is disinhibition

an inhibitory neuron inhibits another inhibitory neuron

basal ganglia inputs and outputs

1. multiple cortical regions dump excitatory glutamate onto striatum

2. GPi projects GABA neuron to VA/VL thalamus and fires tonically

3. thalamus has reciprocal projections with the motor cortex (both excitatory)

the Direct Pathway of the Basal Ganglia: neurons? peptides? where does it project?

• subgroup of striatal GABA neurons

• GABA, substance P, and dynorphin

• project to the GPi

what is the main result of the direct pathway of the basal ganglia?

disinhibition of thalamocortical drive —> greater excitatory input of thalamus to prefrontal/premotor cortex

• increased motor output

the Indirect Pathway of the Basal Ganglia: neurons? peptides? where does it project?

• striatal GABA/enkephalin neurons project to the GPe

• from GPe, tonic projections to the STN and GPi

• from STN, excitatory projection to GPi GABA neuron —> inhibition of the thalamus

what is the main result of the indirect pathway of the basal ganglia?

inhibition of thalamocortical drive —> decreased excitatory input of thalamus to prefrontal/premotor cortex

• suppresses unwanted movement

what aspects of behavior does dopamine affect?

voluntary movement, reward, motivation, formation of habits

where are cell bodies of dopaminergic neurons found?

Ventral tegmental area (VTA) and Substantia nigra compacta (SNc)

what are the major types of dopamine receptors? what are their functions?

D1-like: stimulate adenylate cyclase

D2-like: inhibit adenylate cyclase

what type of dopamine receptors are associated with the direct and indirect pathways of the basal ganglia?

direct: D1 located of striatal GABA SP/dynorphin cells (stimulates these cells)

indirect: D2 located on striatal GABA enkephalin cells (inhibits these cells)

origin and function of the corticospinal tract

primary motor cortex, voluntary movement

origin and function of the rubrospinal tract

red nucleus, supplemental to corticospinal tract

origin and function of the tectospinal tract

superior colliculus, head orienting reflexes or

origin and function of the vestibulospinal tract

vestibular nuclei, coordinates head/neck movement

origin and function of the pontine and medullary reticulospinal tract

reticular formation, adjustment of spinal reflexes