Neuroscience Chapter on Basal Ganglia Movement

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Questions and Answers

What role do the basal ganglia (BG) primarily serve in movement?

They act as a funnel and filter for movement. (correct)

They solely receive sensory input.

They inhibit all movement activities.

They initiate movements directly.

What happens to BG neurons at rest?

They increase stimulation of the thalamus.

They are completely inactive.

They tonically inhibit the thalamus. (correct)

They only fire during specific phases of movement.

During which phase do BG neurons fire to facilitate movement?

Rest phase

Execution phase

Planning phase (correct)

Recovery phase

Which structures are influenced by the output of the basal ganglia?

Upper motor neurons via the thalamus Signup and view all the answers

What is the impact of lesions in the basal ganglia on movement?

They lead to disturbances in initiation of movements. Signup and view all the answers

What is the primary function of the globus pallidus internal segment?

To inhibit the thalamus Signup and view all the answers

Which of the following is a cardinal motor feature of Parkinsonism?

Resting tremor Signup and view all the answers

What occurs to striatal neurons at rest?

They are hyperpolarized Signup and view all the answers

What type of neurons are primarily affected by degeneration in Parkinson's disease?

Dopaminergic neurons in the substantia nigra Signup and view all the answers

What results from the loss of stimulation from the substantia nigra to the striatum?

Hypokinetic syndromes Signup and view all the answers

What is one predominant symptom of akinesia?

Difficulty initiating movements Signup and view all the answers

How does the direct pathway affect movement initiation?

Removes inhibition from the thalamus Signup and view all the answers

What is a significant postural change associated with Parkinson's disease?

Flexed posture Signup and view all the answers

What is one of the main functions of the basal ganglia in motor output modulation?

Improving movement efficiency by performing only wanted movements Signup and view all the answers

Which statement best describes a motor program as understood in movement theory?

Stored sequences of movements activated by the stimulation of upper motor neurons. Signup and view all the answers

What role does the basal ganglia play in relation to competing movements?

It selects and initiates movements while inhibiting competing movements. Signup and view all the answers

Which of the following is a function of the basal ganglia related to eye movements?

Controlling saccadic eye movements Signup and view all the answers

What is the significance of the body motor loop associated with the basal ganglia?

It governs the direct and indirect pathways and their abnormalities. Signup and view all the answers

What does the term 'adaptive movements' imply in the context of the basal ganglia's function?

Movements that can be modified in real-time based on environmental feedback. Signup and view all the answers

Which structure does the basal ganglia primarily influence to modulate motor actions?

Upper motor neurons to enhance movement control. Signup and view all the answers

What is an expected outcome when there are abnormalities in the direct motor pathway of the basal ganglia?

Difficulty in initiating desired movements. Signup and view all the answers

What is the role of the internal segment of the globus pallidus (GPi)?

To inhibit the thalamus in a resting state Signup and view all the answers

Which segment of the globus pallidus contributes to modulatory projections to the subthalamic nucleus?

External segment (GPe) Signup and view all the answers

What happens when the GPi is transiently inhibited during motor program activation?

It allows the thalamus to stimulate the cerebral cortex Signup and view all the answers

Which of the following accurately describes the subthalamic nucleus?

It is located inferior to the thalamus Signup and view all the answers

Which structure has a characteristic black appearance and is located in the midbrain?

Substantia nigra Signup and view all the answers

What is the underlying mechanism for direct pathway activation in the basal ganglia?

Inhibition of GPi leading to thalamic activation Signup and view all the answers

What occurs to the striatum in response to stimulation from the cerebral cortex?

It inhibits the GPi Signup and view all the answers

What effect does the tonic action of the GPi have at rest?

It prevents excessive motor output Signup and view all the answers

Which statement about the external segment (GPe) is correct?

It has modulatory effects but no direct projections. Signup and view all the answers

Which structure is primarily responsible for facilitating movement by affecting thalamic excitability?

Striatum Signup and view all the answers

What type of mutation is associated with Huntington's Disease?

Dominant mutation Signup and view all the answers

Which of the following is a symptom of Huntington's Disease?

Chorea Signup and view all the answers

What part of the brain is primarily affected in Huntington's Disease?

Striatum Signup and view all the answers

What neurotransmitter is primarily used by neurons of the substantia nigra?

Dopamine Signup and view all the answers

In Huntington's Disease, what happens to the inhibition of the thalamus?

Decreased inhibition Signup and view all the answers

What genetic sequence is repeated abnormally in the Huntington gene?

CAG Signup and view all the answers

What is the typical age range for the onset of Huntington's Disease symptoms?

30s-40s Signup and view all the answers

Which dopamine receptors are associated with the indirect pathway in the striatum?

D2 receptors Signup and view all the answers

What effect does dopamine have on neurons in the direct pathway of the striatum?

Depolarizes the cell Signup and view all the answers

What is a common characteristic of the movements caused by Huntington's Disease?

Uncontrolled jerking Signup and view all the answers

What type of input does the globus pallidus internal segment provide to the thalamus within the direct pathway?

Inhibitory Signup and view all the answers

What role does the subthalamic nucleus (STN) play in the indirect pathway?

It enhances the inhibitory drive of the globus pallidus internal. Signup and view all the answers

Which statement correctly describes the function of the indirect pathway?

It represses movement by enhancing inhibition of the thalamus. Signup and view all the answers

In terms of neural circuitry, what is the effect of the striatum on the globus pallidus external (GPe)?

The striatum inhibits the GPe to release the STN. Signup and view all the answers

What initiates the indirect pathway at the cortical level?

Excitation of the striatum Signup and view all the answers

What is the final outcome of the indirect pathway's influence on the thalamus?

Inhibition of the thalamus leading to no unwanted movement. Signup and view all the answers

What happens when the striatum inhibits the globus pallidus external segment?

The STN is released to fire excitatory signals. Signup and view all the answers

Which pathway is primarily responsible for suppressing unwanted movements?

Indirect pathway Signup and view all the answers

How does the indirect pathway modify the activity of the thalamus?

By reinforcing inhibitory control. Signup and view all the answers

The inhibition of the globus pallidus external by the striatum has what effect on the subthalamic nucleus?

It allows the STN to provide excitatory signals. Signup and view all the answers

Study Notes

Motor Modulation: Basal Ganglia and Cerebellum

The basal ganglia and cerebellum modulate motor output by influencing upper motor neurons
This improves movement efficiency by performing only intended movements, and not unintended ones
Motor learning also improves movements with practice
Timing between muscle groups is coordinated to produce fluid movements
Movements are also adaptable in real time

Basal Ganglia

A group of nuclei that function to select and initiate the collection of relevant movements for a given task (motor programs)
Inhibit competing movements for a task
Control saccadic eye movements
Process social cues
Includes the caudate nucleus, putamen, globus pallidus, subthalamic nucleus, and substantia nigra

Learning Objectives (Basal Ganglia)

Describe the general function of the basal ganglia
Recognize input, output, and modulatory nuclei and their projection patterns
Explain the function of the body motor loop, specifically describe the direct and indirect motor pathways and associated pathologies.
Analyze motor deficits in a case study and propose a diagnosis

Input Nuclei ('Striatum')

Certain nuclei in the BG receive the initial stimulus from the cerebral cortex (input nuclei)
Include the caudate and putamen, also collectively called the striatum
Caudate and putamen are heavily interconnected by axons, making them appear 'striped' in certain sections

Caudate Nucleus

C-shaped nucleus, curving into multiple cerebral lobes

Putamen Nucleus

Primary input nucleus for motor movement
Most lateral structure in the basal ganglia, adjacent to the lateral fissure and insula

Output - the Globus Pallidus (GP)

Output nuclei deliver the final signal to the thalamus
Composed of the internal and external segments (GPi and GPe)
Internal segment (GPi) is most medial, and has output to motor information (also for direct and indirect pathways).
External segment (GPe) is more lateral, and has modulatory projections to the subthalamic nucleus (indirect pathway only)
The GPi has high tonic inhibitory activity, suppressing the thalamus during rest

Modulatory Nuclei

Communicate only with other nuclei in the basal ganglia – either reinforcing or inhibiting (modulatory)
Include the globus pallidus external (GPe) and the subthalamic nucleus
The substantia nigra is a midbrain nucleus, with a dark appearance, adjacent to the crus cerebri

Direct Pathway Flowchart

The direct pathway's goal is to excite the cortex
At rest, the thalamus is inhibited by the globus pallidus internal (GPi).
Stimulation of the cortex causes the striatum to inhibit the GPi, thus freeing the thalamus, allowing excitation of the cortex

Direct Pathway Modulation from the SN (Substantia Nigra)

The substantia nigra is another important source of stimulation for the striatum
At rest, striatal neurons are hyperpolarized, requiring multiple excitatory inputs to reach firing threshold.
Loss of stimulatory drive from the substantia nigra can cause hypokinetic syndromes, such as Parkinson's disease

Parkinson's Disease

A neurodegenerative disease that causes slowness or absence of movement
Associated with the degeneration of dopaminergic neurons in the substantia nigra
Neurodegeneration preferentially affects neurons of the direct pathway, resulting in a loss of stimulation to the striatum and hence a loss of the 'go' signal.
- Typical symptoms include: tremor, rigidity, akinesia/bradykinesia, and postural changes.

Indirect Pathway

Reinforces the inhibitory drive to the thalamus, suppressing movements (especially unwanted ones or competing motor programs)

Indirect Pathway Flowchart

One way to increase the inhibitory drive to the thalamus is to provide greater stimulus to the GPi
The subthalamic nucleus (STN) has excitatory synapses on the GPi

Huntington's Disease

A neurodegenerative disease causing unwanted movements due to degeneration of neurons in the striatum (preferentially indirect pathway neurons)
- Typical symptoms include: chorea, rigidity, and problems with movement

Summary Slide - Direct Pathway

Cortical neurons excite the striatum
Striatum inhibits the globus pallidus internal segment
Thalamus, now released from GPi inhibition, can fire and excite the motor cortex
Net effect: Two inhibitory synapses can cause net excitation.

Summary of Indirect Pathway

Cortical neurons excite the striatum
Striatum inhibits globus pallidus external
Subthalamic nucleus excites globus pallidus internal
Globus pallidus internal inhibits the thalamus.
Thalamus is inhibited, resulting in the absence of unwanted movements.
Net effect: Three inhibitory synapses cause net inhibition.

Nigrostriatal Pathway

Neurons use dopamine as a neurotransmitter
Striatal neurons in the direct pathway have D1 dopamine receptors, causing depolarization in response to dopamine
Striatal neurons in the indirect pathway have D2 dopamine receptors, causing hyperpolarization in response to dopamine
Thus, the substantia nigra can both excite the direct pathway and inhibit the indirect pathway

Case Study

A man, 63 years old, has generalized body stiffness and tremors, which have worsened over the last 3 years.
Moves slowly, shuffles feet, has a stooped posture, and mask-like facial expression.
His tremor stops only when he performs a voluntary movement.

Resources

Worksheets (with information on direct and indirect pathways)
3D models of the brain (links to online resources).
Links to videos about Parkinson's disease, Huntington's disease and the basal ganglia.

Check-in Question 1

Which nuclei of the basal ganglia receive direct cortical input?
Caudate and putamen

Check-in Question 2

Within the direct pathway, the globus pallidus internal segment provides input to the thalamus.
Inhibitory

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Description

Test your knowledge on the role of the basal ganglia in movement. This quiz covers essential functions, neuron activity at rest and during movement, and the effects of Parkinson's disease on motor control. Understand the key structures influenced by the basal ganglia and their significance in neuroanatomy.