Neuroscience of Movement Control

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Questions and Answers

What role do the basal ganglia play in movement control?

They initiate movement commands.

They help in the refinement of movement. (correct)

They are solely responsible for muscle contraction.

They process visual sensory input.

Which areas of the brain are primarily responsible for executing movement?

Cerebellum and occipital lobe

Frontal cortex and motor cortex (correct)

Basal ganglia and sensory cortex

Prefrontal cortex and brainstem

What is the primary function of the cerebellum in relation to movement?

Generating movement commands

Initiating motor neuron activation

Refining timing and accuracy of movement (correct)

Processing sensory information

How do sensory feedback loops contribute to movement management?

They are involved in refining and optimizing movements. Signup and view all the answers

What is the primary relationship between upper motor neurons and lower motor neurons?

Upper motor neurons send signals to lower motor neurons to generate movement. Signup and view all the answers

What is a primary role of the motor cortex?

To plan and execute movement. Signup and view all the answers

What influences the grasp force during movement?

The basal ganglia Signup and view all the answers

Which statement is true regarding the relationship between sensory and motor systems?

They must work together to facilitate smooth movement. Signup and view all the answers

What is the main responsibility of the lateral corticospinal tract?

Fine motor control of distal muscles Signup and view all the answers

Where does the medial corticospinal tract decussate?

At the spinal cord level Signup and view all the answers

Which cortico-spinal tract is responsible for innervating the muscles of the head and face?

Corticobulbar tract Signup and view all the answers

What is the role of the posterior parietal cortex in motor control?

Integrating sensory input Signup and view all the answers

In the motor cortex, areas responsible for greater motor control are represented how?

In disproportionately larger regions Signup and view all the answers

What is the function of the premotor area (PMA)?

Planning sensory-guided movements Signup and view all the answers

What consequences arise from lesions in area 6 of the motor cortex?

Apraxia, impairing complex movements Signup and view all the answers

Which tract originates at the red nucleus and is responsible for supplying distal muscles?

Rubrospinal tract Signup and view all the answers

What is the main activation pattern of the primary motor cortex (M1)?

Activated when executing movements Signup and view all the answers

What defines the somatotopic organization in the motor cortex?

Body parts with greater fine motor control occupy larger cortical areas Signup and view all the answers

What is a common symptom associated with lower motor neuron lesions?

Flaccid paralysis Signup and view all the answers

Which symptom is indicative of upper motor neuron lesions in the long term?

Hyperreflexia Signup and view all the answers

What occurs during spinal shock following an upper motor neuron lesion?

Areflexia and hypotonia Signup and view all the answers

What effect does a unilateral upper motor neuron lesion above the decussation have on the body?

Spasticity on the opposite side Signup and view all the answers

Which of the following symptoms is associated with lower motor neuron injury over time?

Muscle atrophy Signup and view all the answers

What is the characteristic reflex response for upper motor neuron lesions indicated by the Babinski sign?

Toes fanning out Signup and view all the answers

Which type of neuron damage leads to hyporeflexia and weakness?

Lower motor neurons Signup and view all the answers

What is a key distinguishing feature of upper motor neuron lesions compared to lower motor neuron lesions?

Spasticity and hyperreflexia Signup and view all the answers

Which statement correctly explains the role of the corticospinal tract?

It mediates voluntary movement from the brain to the spinal cord. Signup and view all the answers

What might cause loss of reflexes in lower motor neuron lesions?

Damage to the reflex arc circuitry Signup and view all the answers

What is the primary function of lower motor neurons?

To directly innervate skeletal muscles for voluntary and reflexive movements Signup and view all the answers

Which statement best describes the size principle in muscle recruitment?

Motor units are activated from small to large in order of their size. Signup and view all the answers

What role do upper motor neurons play in the motor system?

They synapse with lower motor neurons and provide voluntary control. Signup and view all the answers

What is one primary source of input for lower motor neurons?

Inputs from upper motor neurons in the brain Signup and view all the answers

What allows for the graded force production in muscles?

Modulating the number of motor neurons activated based on task demands. Signup and view all the answers

Which statement about the corticospinal tract is true?

90% of its fibers decussate at the level of the medulla. Signup and view all the answers

What defines a motor unit?

A lower motor neuron and all the muscle fibers it innervates. Signup and view all the answers

What phenomenon occurs during fused tetanus?

A complete summation of force generates a smooth contraction. Signup and view all the answers

Which type of movements do larger motor units primarily facilitate?

Coarse, powerful movements such as running. Signup and view all the answers

What is the main purpose of sensory receptors in the motor system?

To send feedback to enhance movement coordination. Signup and view all the answers

How does the motor system facilitate smooth movements?

By precisely timing and coordinating inputs from various neurons. Signup and view all the answers

How does rate coding contribute to muscle force production?

By increasing the frequency of action potentials to enhance force. Signup and view all the answers

What is the impact of asynchronous firing of motor units?

It allows for smooth and continuous force generation. Signup and view all the answers

What primarily occurs in the neuromuscular junction?

Neurotransmitters like acetylcholine are released to activate muscles. Signup and view all the answers

What is the primary mechanism of action for leflunomide?

Inhibits pyrimidine synthesis. Signup and view all the answers

What effect does rituximab have on CD20+ cells?

It causes cell death through antibody-dependent processes. Signup and view all the answers

What is the main action of basiliximab in the immune system?

Blocks IL-2 receptors to prevent T cell activation. Signup and view all the answers

How does aldesleukin enhance immune responses?

By enhancing Th-cell proliferation. Signup and view all the answers

What is the role of ipilimumab and nivolumab in cancer treatment?

They expand and prolong existing T cell responses. Signup and view all the answers

What happens to the tongue when there is hypoglossal nerve impingement?

It deviates to the affected side. Signup and view all the answers

What is the typical response of the uvula when one side of the soft palate elevates?

The uvula will point towards the unaffected side. Signup and view all the answers

Which nerve is responsible for the parasympathetic innervation to the lacrimal gland?

Facial nerve via the chorda tympani. Signup and view all the answers

What is the primary function of mycophenolate in the immune system?

Inhibits inosine monophosphate dehydrogenase. Signup and view all the answers

Which of the following is NOT a mechanism of action for cyclophosphamide?

Blocking purine synthesis. Signup and view all the answers

What triggers the knee jerk reflex?

Tapping of the patella tendon Signup and view all the answers

What is the primary role of the vestibulocerebellum?

Maintaining balance and posture Signup and view all the answers

Which cerebellar division is responsible for real-time error correction during limb movements?

Spinocerebellum Signup and view all the answers

What happens when there is damage to the lateral corticospinal tract?

Exaggerated reflexes Signup and view all the answers

What best describes the primary function of the cerebrocerebellum?

To aid in planning and modifying learned movements Signup and view all the answers

Which of the following is a symptom of spinocerebellar damage?

Dysmetria Signup and view all the answers

How does the cerebellum coordinate movements?

By modulating commands from the primary motor cortex Signup and view all the answers

What impact does a vestibulocerebellum lesion have on a person's balance?

Requires conscious effort to maintain balance Signup and view all the answers

What are the main components of the basal ganglia?

Striatum and globus pallidus Signup and view all the answers

Which pathway is primarily excitatory within the basal ganglia?

Direct pathway Signup and view all the answers

How does the cerebellum receive sensory information?

Through the vestibular system and sensory cortex Signup and view all the answers

What is the significance of cerebellar ataxia?

It results in lack of coordination and accuracy Signup and view all the answers

What is the primary role of the basal ganglia in movement control?

Feedback modulation on thalamus and cortex Signup and view all the answers

Which feature allows the cerebellum to efficiently pack neurons?

Folded surface with grey matter Signup and view all the answers

What is the primary reason dopamine cannot be directly administered for Parkinson's treatment?

It cannot cross the blood-brain barrier. Signup and view all the answers

What is the main effect of levodopa in treating Parkinson's disease?

It increases the synthesis of dopamine in neurons. Signup and view all the answers

What potential complication arises from excessive removal of subthalamic nucleus neurons during surgery for Parkinson's?

Hyperkinesia leading to unwanted movements. Signup and view all the answers

How does deep brain stimulation function as a treatment for Parkinson's disease?

It inhibits activity in selected brain regions. Signup and view all the answers

Which area of the brain is primarily responsible for planning movements?

Premotor cortex. Signup and view all the answers

What outcome is typically seen after an upper motor neuron lesion following the initial phase?

Loss of voluntary control and spasticity. Signup and view all the answers

What does the surgical treatment for Parkinson's aim to modify in the basal ganglia pathways?

Control the direct and indirect pathway balance. Signup and view all the answers

Which symptom is NOT typically associated with lower motor neuron lesions?

Spasticity. Signup and view all the answers

What is one of the main roles of the spinocerebellum?

Regulating movements in progress. Signup and view all the answers

The inability to perform rapid alternating movements in a patient indicates potential damage to which part of the brain?

Cerebellum. Signup and view all the answers

In terms of movement control, what primarily happens during an injury to the spinal cord affecting the lateral corticospinal tract?

Leads to ipsilateral flaccid paralysis. Signup and view all the answers

What characterizes intention tremors seen in motor coordination disorders?

Tremors that increase during purposeful movement. Signup and view all the answers

What type of reflex is absent when a patient cannot move their toes and shows a lack of myotatic reflex?

Patellar reflex. Signup and view all the answers

What is the role of the globus pallidus in the motor circuit?

It inhibits the thalamus, reducing thalamic effects on the motor cortex. Signup and view all the answers

Which neurotransmitter is crucial for modulating the functions of the striatum in the basal ganglia?

Dopamine Signup and view all the answers

How does the direct pathway impact motor output?

It enhances the excitatory effect of the thalamus on the motor cortex. Signup and view all the answers

What is the primary effect of dopamine on the indirect pathway?

It increases the inhibition of the globus pallidus external segment. Signup and view all the answers

What characterizes Parkinson’s disease with respect to motor symptoms?

Impaired initiation of movement and rigidity. Signup and view all the answers

Which condition is associated with excessive uncontrollable movements due to underactivity of the indirect pathway?

Huntington's disease Signup and view all the answers

In the direct pathway, what role do D1 receptors primarily play?

They enhance excitation of striatal neurons. Signup and view all the answers

What happens to the cortical output in the indirect pathway?

It decreases due to increased inhibitory effects. Signup and view all the answers

What effect does the thalamus have when disinhibited by the basal ganglia circuitry?

It excites the motor cortex, enhancing movement output. Signup and view all the answers

Which of the following describes the primary action of the subthalamic nucleus in the motor circuitry?

To stimulate the globus pallidus internal segment. Signup and view all the answers

What is the impact of increased activity in the indirect pathway on motor plans?

It reduces the likelihood of enacting motor plans. Signup and view all the answers

What characterizes the tremors associated with Parkinson's disease?

They are maximal at rest and disappear with voluntary movement. Signup and view all the answers

How is the balance between the direct and indirect pathways important in the basal ganglia?

It regulates motor output and movement selection. Signup and view all the answers

What are common non-motor symptoms of Parkinson’s disease?

Autonomic dysfunction and cognitive issues. Signup and view all the answers

What happens due to the degeneration of dopaminergic neurons in Parkinson’s disease?

Difficulty in facilitating movement. Signup and view all the answers

Which cerebellar region is primarily responsible for movement coordination, potentially affected in Adam’s symptoms?

Cerebrocerebellum Signup and view all the answers

What type of ataxia might be observed if there is a lesion in the cerebellar vermis?

Uncoordinated limb movements Signup and view all the answers

Dysdiadochokinesia is associated with dysfunction in which aspect of movement?

Smoothness and speed of alternating movements Signup and view all the answers

Which of the following symptoms is NOT typically associated with cerebellar damage?

Flaccid paralysis Signup and view all the answers

What is the primary function of the spinocerebellum?

Coordination of ongoing movements Signup and view all the answers

Which statement about the vestibulocerebellum is correct?

It regulates compensatory postural changes and eye movements. Signup and view all the answers

If the glossopharyngeal nerve is damaged at the jugular foramen, what symptom is likely present?

Reduction in salivation from the parotid gland Signup and view all the answers

Corticosteroids primarily inhibit which enzyme related to inflammation?

Phospholipase A2 Signup and view all the answers

Calcineurin inhibitors are used for organ transplantation due to their effect on which cytokine?

IL-2 Signup and view all the answers

Which statement about m-TOR inhibitors is correct?

They prevent the signal transduction of IL-2. Signup and view all the answers

Which artery does NOT contribute to the vascular supply of the thyroid gland?

Superficial cervical artery Signup and view all the answers

Past-pointing behavior can indicate a lesion in which cerebellar area?

Cerebrocerebellum Signup and view all the answers

What type of damage is most likely associated with dysmetria?

Lesion in the cerebrocerebellum. Signup and view all the answers

What muscle is innervated by the nerve to mylohyoid?

Digastric (anterior belly) Signup and view all the answers

Study Notes

Motor Neuron Organisation and Clinical Signs of Lesions

Upper Motor Neurons (UMNs): Originate in the motor cortex or brainstem and terminate within the brainstem or spinal cord (ventral horn). They control voluntary movements and do not directly innervate muscles, instead, they synapse with lower motor neurons.
Lower Motor Neurons (LMNs): Directly innervate muscles, involved in voluntary and reflexive movements. Cell bodies located in the spinal cord, particularly in the ventral horn.
LMN Lesions: Cause flaccid paralysis, paresis, muscle atrophy, and areflexia.
UMN Lesions: Cause spasticity, hyperreflexia, and a positive Babinski reflex.
Spinal Shock: Immediate consequence of UMN lesions, characterised by flaccidity, hypotonia, and areflexia.
Hyperreflexia: Exaggerated reflexes caused by damage to descending pathways that normally modulate reflexes.
Clonus: Rhythmic cycles of reflexive contraction and relaxation due to sustained stretch.
Hypertonia: Increased resistance to passive muscle stretch due to ongoing contractile activity.

Cortical Areas Involved in Motor Control

Posterior Parietal Cortex: Sensory integration center providing sensory input to the premotor cortex.
Prefrontal Cortex: Decision making center for executing actions.
Premotor Cortex (PMA): Plans movement sequences based on sensory input from the posterior parietal cortex and receives information from the prefrontal cortex.
Primary Motor Cortex (M1): Executes movement based on motor plans received from the premotor cortex. It directly innervates lower motor neurons in the spinal cord via the corticospinal tract.
Supplementary Motor Area (SMA): Involved in planning motor actions, especially based on memory and learning new motor sequences.

Descending Motor Tracts

Pyramidal Tracts: Originate in the cerebral cortex, responsible for voluntary control of muscles in the body and face.
- Corticospinal Tract: Contributes to the movement of the body.
  - Lateral Corticospinal Tract: Carries signals from the primary motor cortex to the spinal cord, controlling distal muscles (fine motor control of fingers/hand).
  - Medial Corticospinal Tract (Anterior Corticospinal Tract): Carries signals to axial muscles, proximal segments of arms/legs.
- Corticobulbar Tract: Carries signals controlling muscles of the head and face.
Extrapyramidal Tracts: Originate in the brainstem, involved in involuntary/autonomic control of musculature.

The Cerebellum and Movement

Cerebellum: Involved in refining and coordinating movements, and receives input from both the cerebral cortex and brainstem.
Functional Subdivisions of the Cerebellum:
- Cerebrocerebellum: Responsible for coordination and planning of voluntary movements.
- Spinocerebellum: Regulates muscle tone and coordination.
- Vestibulocerebellum: Maintains balance and posture.

The Basal Ganglia and Movement

Basal Ganglia: A group of nuclei that are involved in planning and executing movement, learning new motor skills, and controlling muscle tone.
- The Functional Circuitry of the Basal Ganglia:
  - Direct Pathway: Promotes movement.
  - Indirect Pathway: Inhibits movement.

Movement Coordination

Sensory Feedback: Sensory information from muscles and joints is crucial for the brain to monitor and adjust movement.
Motor Unit: One motor neuron and all the muscle fibers it innervates.
Motor Pool: A group of motor units that work together to control a muscle.
Size Principle: Motor units are recruited from smallest to largest to control the amount of force generated.
Rate Coding: Varying frequencies of excitation by motor neurons influences force production.### Knee-Jerk Reflex
Tapping the patellar tendon stretches the quadriceps muscle.
Stretch receptors in the muscle sense the change in muscle length, triggering an increased firing rate of sensory neurons.
This signal travels to the ventral horn of the spinal cord, causing motor neurons to fire more frequently and contract the muscle.
The reflex is dampened by descending pathways from the lateral corticospinal tract.
Damage to this tract (UMN lesion) leads to exaggerated reflexes, a sign of reduced descending inhibition.

Cerebellum

It is located on the back of the brain, below the cerebrum and above the brainstem.
It plays a critical role in coordinating and refining movements, but does not directly execute them.
The cerebellar hemispheres are connected by the vermis, and together they contain 50% of the brain's neurons.

Functional Divisions of the Cerebellum

Vestibulocerebellum: Located in the flocculonodular lobe, it receives input from the vestibular system and is involved in maintaining balance and posture. It also receives input from the superior colliculus and visual cortex to update eye movements and maintain ocular reflexes.
Spinocerebellum: Includes the vermis and immediate hemisphere. It receives sensory input from the spinal cord and motor cortex, responsible for regulating body movements and error correction. It receives information about muscle length changes from muscle spindles and Golgi tendon organs.
Cerebrocerebellum: Located in the lateral hemispheres, it receives input from the cerebral cortex and is involved in planning and modifying learned movements. It uses sensory information from the motor cortex to refine movements based on past experiences.

Cerebellar Lesions

Vestibulocerebellar lesions impair the ability to automatically compensate for body position shifts, causing difficulty with balance and gait.
Spinocerebellar lesions affect coordination of movements, leading to cerebellar ataxia, dysmetria, and dyssenergia.
Cerebrocerebellar lesions disrupt the control of ipsilateral (same-side) movement, causing movement decomposition and deficits in motor learning, spatial cognition, and working memory.

Basal Ganglia

It is a group of interconnected nuclei located below the cerebral cortex.
The key components include striatum, globus pallidus, substantia nigra, and subthalamic nucleus.
It receives input from the motor cortex and limbic system and projects back to the cortex via the thalamus, influencing movement control.

Direct and Indirect Pathways of the Basal Ganglia

Direct pathway: Excites the thalamus, promoting cortical activity and movement initiation.
Indirect pathway: Inhibits the thalamus, suppressing cortical activity and movement initiation.
Dopamine released from the substantia nigra pars compacta plays a role in modulating both pathways, influencing movement selection and initiation.

Dopamine Circuit and its Role in Basal Ganglia Function

Dopamine activates D1 receptors in the direct pathway, promoting movement.
Dopamine activates D2 receptors in the indirect pathway, inhibiting movement.
The balance between the direct and indirect pathways, modulated by dopamine, determines the strength of basal ganglia output to the thalamus, ultimately impacting motor control.

Basal Ganglia Disorders

Hypokinetic disorders (reduced movement):
- Parkinson's disease: characterized by akinesia, bradykinesia, resting tremors, muscle stiffness, and postural instability.
Hyperkinetic disorders (increased movement):
- Huntington's disease: characterized by uncontrolled dance-like movements (chorea).
- Hemiballismus: characterized by violent and jerky movements of one side of the body.

Parkinson's Disease

This is caused by the loss of dopamine neurons in the substantia nigra pars compacta.
This leads to an imbalance between the direct and indirect pathways, with the indirect pathway becoming overactive.
Symptoms include tremors, rigidity, bradykinesia, and postural instability.

Pharmaceutical Treatment of Parkinson's Disease

L-dopa: A precursor to dopamine that can cross the blood-brain barrier and be converted into dopamine, improving movement but having potential side effects.
Dopamine agonists: Provide alternative activation for dopamine receptors.
Dopamine reuptake inhibitors: Increase dopamine levels in the synaptic cleft.

Surgical Treatment of Parkinson’s Disease

Subthalamic nucleus (STN) lesioning: Reduces the activation of the indirect pathway, improving movement but requiring careful calibration.
Deep brain stimulation (DBS): Involves implanting electrodes in specific brain regions (STN or GPi) to deliver continuous electrical stimulation, modulating neural activity and reducing symptoms.

Movement Control and the Basal Ganglia

The premotor cortex plans movements.
The supplementary motor area generates a motor plan.
The basal ganglia modulate these plans via interactions with the thalamus and motor cortex.
The direct pathway promotes the execution of the planned movement.
The indirect pathway inhibits the execution of the planned movement.
The balance between the direct and indirect pathways, influenced by dopamine, determines the likelihood of movement execution.

Lateral Corticospinal Tract

Injury to the lateral corticospinal tract results in ipsilateral flaccid paralysis due to disrupted motor signals.
The lateral corticospinal tract controls voluntary movements of the limbs.

Spinocerebellum

The spinocerebellum regulates movements in progress by modulating descending motor commands.
It receives sensory information from the spinal cord and proprioceptors.