Extrapyramidal Physiology - Motor Cortex & Basal Ganglia

What is the difference between the direct and indirect pathway for the motor systems?

Direct: axons project via pyramidal tracts & directly synapse onto LMN

Indirect: axons do NOT make direct connections with LMNs

* both originate from UMNs

UMN output is modulated by inputs from? (2)

Basal ganglia & cerebrocerebellum (via thalamus)

Function of primary somatosensory cortex?

Relays information to?

Touch & proprioception

Primary motor cortex

Function of primary motor cortex?

Receives input from?

Movement execution

Primary somatosensory cortex

What is the function of the posterior parietal cortex?

Visual, auditory, and other sensory input to guide movement

What is the function of the medial premotor cortex?

What an example of this & how does this relate to the primary motor cortex?

Thought-guided movement planning

Active during a complex movement (tapping fingers in a precise order)

When doing the movement, primary motor cortex becomes active

What is the function of the lateral premotor cortex?

Visual & auditory guided movement planning

Lesions of primary motor cortex or the pyramidal tracts lead to deficits of?

Fine motor control of upper limbs, hands, and fingers

What structures make up the basal ganglia?

Caudate nucleus, putamen, globus pallidus internal (GPi) & external (GPe), subthalamic nucleus (STN), substantia nigra pars reticulata (SNr) and pars compacts (SNc)

Cortical inputs to the basal ganglia are received in the?

Striatum

What where does output from basal ganglia come from? (2)

GPi & SNr

Is output from basal ganglia excitatory or inhibitory?

Inhibitory (GABA)

- largely targeted to thalamus

What is the motor control areas once basal ganglia project to the ventral lateral nuclei of the thalamus?

Excitatory (glutamate)

Describe the direct pathway in terms of the basal ganglia?

Lower GPi (inhibitory) activity

More activity of thalamic neurons -> increased movement

Associated with D1 = increased excitation of medium spiny neurons

Describe the indirect pathway in terms of the basal ganglia?

Higher GPi (inhibitory) activity

Less activity of thalamic neurons -> decreased movement

Associated with D2 = decreased excitation of medium spiny neurons

Motor areas of basal ganglia receive dopamine projections from?

Dopamine connections target what structure in the putamen?

SNc

Medium spiny neurons

Dopamine enhances movement by activation of the ____ pathway & inhibition of the _____ pathway

Direct

Indirect

What neurotransmitter modulates direct & indirect pathways by binding to muscarinic receptors & excites medium spiny striatal neurons (both direct & indirect)?

Acetylcholine (ACh)

What are the most common diseases that impact basal ganglia and therefore movement? (3)

Parkinson's disease

Chorea

Hemiballism

What is the basal ganglia's role in movement? (3)

Action selection

- gating of initiation of movement

- suppresses inappropriate movements that would interfere with selected task

Facilitate motor learning

- procedural memory

Motivating movement

- reinforcement motor learning

- avoiding movement with adverse outcome

How are the direct/indirect pathways affected with Parkinson's disease?

Reduced dopamine = decrease activity within direct pathway

Increased activity in indirect pathway (less inhibition)

What is the clinical presentation of Parkinson's disease?

Bradykinesia & dyskinesia

Bursting activity of GPi neurons -> tremors

Pallidotomy (destroys GPi) is a surgical treatment for?

Parkinson's disease

* also can treat with dopamine agonist or deep brain stimulation

How are the direct/indirect pathways affected in Huntington's Chorea?

Preferential loss of medium spiny neurons from indirect pathway

Loss of inhibition from GPi -> increased activity of thalamic neurons

What is the clinical presentation of Huntington's Chorea?

Inappropriate involuntary movement

Reduction in GPi activity -> hyperkinesia

What is an effective treatment for Huntington's Chorea?

Deep brain stimulation

What causes hemiballism & what is the clinical presentation?

Loss of STN neurons due to highly localized stroke

Removal of primary excitatory signal to GPi

Uncontrolled ballistic movements

Drug-induced dyskinesia is seen in? (2)

What is the clinical presentation?

PD patients & patients taking anti-psychotic drugs that block dopamine D2 receptors (expressed by indirect pathway)

Chorea like movements (inappropriate involuntary movements)

What is the effect of taking L-Dopa or a dopamine agonist?

Higher receptor levels produce an exaggerated response -> motor problems