Basal Ganglia and Cerebellum

Role of Basal Ganglia

1. Movement ON/OFF

2. Movement specificity

3. Learning

Role of Cerebellum

1. Movement Error Detection

2. Movement Error Correction

3. Learning

Basal Ganglia and Cerebellar circuits are predominantly ______

Inhibitory

Basal Ganlia and Cerebellar circuits must be ________ to promote movement

disinhibits

____________ is required for normal voluntary movement

Basal Ganglia

_____________ mediates smooth transitions between commands for movement initiation and/or movement termination

Basal Ganglia

The functions of Basal Ganglia are disrupted by _________ ______ and ________ ________

Parkinson’s disease
Huntington’s disease

What is the corpus striatum?

• Receives cortical input

• Consists of the caudate and putamen

Caudate

• Eye/head movement and body movements

• sensory input from cortex

• Motor input from eye areas in frontal lobe and motor cortex

Putamen

• Body movements

• Sensory input from cortex

• Motor input from premotor and motor cortex

• Topological map of body

What is the Globus Pallidus

• Receives input from the corpus striatum

• Inhibits the thalamus

• Must be “turned of” for movement

What is the Thalamus?

• Relays Basal Gnglia output to motor cortex

• Receives inhibition from the internal Globus Pallidus (iGP)

• Provides excitatory drive to motor cortex

• Must be disinhibited. for movement

What is the Basic Loop (Direct pathway through Basal Ganglia)

1) Cortical Input “Motor Plan”

2) Modulation by Basal Ganglia “Go/Stop”

3) Thalamic integration & relay

4) Cortical integration & execution

_________ ______ ________ in the caudate and putamen receive cortical input

Medium spiny neurons

_________ _________ __________ do NOT fire action potentials easily, require many cortical inputs

GABAergic Inhibitory Neurons

_________ _________ _________ Code a “decision to move toward a goal” rather than movement itself

Basal Ganglia Neurons

A ______ _______ neuron receives input from ~ 100 medium spiny neurons

Globus Pallidus

_______ make a small number of synapses with many globus pallidus neurons (GPNs)

Medium Spiny Neurons (MSNs)

Explain the Basal Nerual Circuit of the Basal Ganglia

1) MSNs of the caudate and putamen receive excitatory input from the cortex

2) MSNs inhibit GPNs

3) GPNs inhibit thalamic neurons

4) GPNs control thalamic responses to excitatory inputs

5) Thalamic neurons excite upper motor neurons

If there is no input from the cortex, there is no (or aberrant) movement because….

1) MSN neurons are inactive

2) GPNs are not inhibited by MSNs

3) GPNs inhibit thalamic neurons

4) Motor cortex is not excited

Cortical input excites the MSNs and there is correct movement because….

1) MSN neurons are active

2) GPNs are inhibited by MSNs

3) Thalamic neurons are disinhibited

4) Motor cortex is excited

Explain the Basal Ganglia Projections: Direct Pathway

Explain the Basal Ganglia Circuitry: Direct Pathway Movement

Cortical input to the basal ganglia excites MSNs in the Caudate and Putamen which ______ neurons in the Globus Pallidus or Pars Reticulata and ________ the thalamus or superior colliculus to ________ movement

Cortical input to the basal ganglia excites MSNs in the Caudate and Putamen which inhibit neurons in the Globus Pallidus or Pars Reticulata and disinhibit the thalamus or superior colliculus to promote movement

What does the Motor Nuclei contain?

• Caudate

• Putamen

• Globus Pallidus

• Substantia Nigra Pars Reticulata

What does the Modulatory Nuclei contain?

• Subthalamic Nucleus

• Substantia Nigra

What is the Subthalamic Nucleus (STN)- Hyper-Direct Pathway?

• Receives excitation from cortex

• Role: Provide excitatory drive globus pallidus internal (GPI)

• Must be inhibited for movement

Explain the Direct Pathway in the Basal Ganglia

Explain Hyperdirect pathway in Basal Ganglia Projections

Explain the Indirect pathway in the Basa Ganglia Projections

The _______ pathway counteracts the ______ pathway to terminate movement or suppress unwanted movements by ________ the inhibitory influence of the internal globus pallidus.

The indirect pathway counteracts the direct pathway to terminate movement or suppress unwanted movements by increasing the inhibitory influence of the internal globus pallidus.

The external segment of the globus pallidus projects to the internal segment and the

_________ in the ___________

pathway.

A. subthalamic nucleus; indirect

B. thalamus; indirect

C. caudate; indirect

D. caudate; direct

E. subthalamic nucleus; direct

E. subthalamic nucleus; direct

Increased activity from the ________ to the subthalamic nucleus increases the

________ input to the thalamus.

A. GP external; excitatory

B. GP internal; inhibitory

C. cortex; excitatory

D. GP internal; excitatory

E. cortex; inhibitory

E. cortex; inhibitory

What is the Substantia Nigra and what does it do?

• Receives excitation from the corpus striatum

• Provide dopaminergic input tot the corpus striatum

• Excites the direct pathway, inhibits the indirect pathway

The substantia nigra pars compacta provides __________ to the MSNs of the __________________. Dopamine increases the activity of the _______ pathway but suppresses the ________ pathway

The substantia nigra pars compacta provides dopamine to the MSNs of the corpus striatum (caudate/putamen). Dopamine increases the activity of the direct pathway but suppresses the indirect pathway

What is the cause of Parkinson’s disease?

Loss of doapmine neurons in the substantia nigra

What happens in the Basal Ganglia projections in Parkinson’s disease?

The loss of dopamine to the MSNs of increases the activity of the indirect pathway but suppresses the direct pathway

What is Huntington’s Disease?

• Atrophy of cerebral nerve tissue and Basal Ganglia

• Increased inhbition of GP internal

• Too much ballistic movement

What occurs in the Basal Ganglia projections in Huntington’s disease?

The connection between the caudate and GP-External is degenerated

What are the inputs to the cerebellum?

• Cortex - vid the pons (movement information)

• Spinal cord (sensory input)

• Vestibular Nuclei (sensory input)

• Olive (sensory and modulatory input)

What are the parts of the cerebellar cortex?

• Cerebrocerebellar

• Spinocerebellar

• Vestibulocerebellum

What is the fucntional organization of cerebellar outputs? (from Cerebellar cortex to Pathways to upper motor neurons)

What is the Cerebrocerebellum?

• Gets input from cerebral cortex

• Skilled movements

• Planning and execution of movement sequences in time and space

What is Dysmetria?

Errors in smoothness and direction of targeting movements due to cerebro-cerebellar pathway

• Patients tend to over or undershoot objections

• The closer the movement gets to the target, the more irregular the movement (intention tremor)

What is the Spinocerebellum?

• Gets input from the spinal cord

  • Sensory

• Has somatotopic maps

• Two zones

  • Median

  • Paramedian

What is the Vestibulocerebellum?

• Input from Vestibular Nuclei

• Coordinate Posture, Balance

• Coordinate eye-body movements- i.e. Vestibular ocular reflex (VOR)

What are Cerebellar Nuclei?

• Receive inhibitory input

  from the cerebellar cortex

• Sole source of output from the cerebellum

• Project to the thalamus (which projects to motor cortex)

• Project to the brainstem upper motor neurons

What is the Motor Planning Pathway?

Cerebrocerebellum > Dentate Nucleus > Thalamus/Premotor Cortex

What is the Motor Execution Pathway?

Spinocerebellum > Fastigial/Interposed Nuclei > Thalamus/Brainstem

Explain the following in the Vestibulo-verebellar, Spino-cerebellar, and Cerebro-cerebellar pathways:

• Input From

• Region of Cerebellar Cortex

• Deep nuclei

• Function(s)

Vestibulo-cerebellar Pathway

• Input from: Vestibular system

• Region of Cerebellar cortex: Vestibulo-cerebellum

• Deep Nuclei: Vestibular nuclei

• Function(s): Balance and reflexive eye movements

Spinocerebellar pathway

• Spinal Cord

• Spinocerebellum

• Fastigial nuclei/interposed nuclei

• Error Correction for movements

Cerebro-cerebellar Pathway

• Cerebral cortex

• Lateral hemisphere

• Dentate Nuclei

• Motor planning

Crossing over Coordinates ________ input from the cortex and ________ input from the spinal cord and brainstem. In the cortex, ipsilateral muscle movements are represented in the _________ hemisphere. At the spinal cord, the muscle movements are driven by _______ neurons. The cerebellum has an _______ representation of muscle movement (like the spinal cord).

Crossing over coordinates descending input from the cortex and ascending input from the spinal cord and brainstem. In the cortex ipsilateral muscle movements are represented in the contralateral hemisphere. At the spinal cord, the muscle movements are driven by ipsilateral neurons. The cerebellum has an ipsilateral representation of muscle movement (like the spinal cord).

What is Ataxia? What are the causes?

• A neurological disorder consisting of lack of voluntary coordination of muscle movements

• Causes

  • Cerebrellar Dysfunction

  • Could be due to environmental factors (alcohol, trauma)

  • Also caused by genetic disorders (e.g. spinocerebellar ataxia)

What are the effects of alcohol (short term & long term)

Short term

• Lack of coordination

• Unsteady gait

• Slurred speech

Long term

• Damage to anterior portion of cerebellar cortex (anterior vermis in fig) affects movement in lower limbs

• Wide and staggering gait

• Little impairment of arm or hand movements

• No disruption of speech