Neuroscience Movement Control Quiz

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Questions and Answers

What is the primary role of the premotor cortex?

Planning movement (correct)

Executing movement

Judging grasp force

Refining movement

Which structure is responsible for regulating the timing and accuracy of movements?

Basal ganglia

Spinal cord

Motor cortex

Cerebellum (correct)

What do lower motor neurons primarily innervate?

Thalamus

Basal ganglia

Skeletal muscles (correct)

Cerebellum

What main function do the basal ganglia serve in the context of movement?

Refining movement Signup and view all the answers

Which area processes visual sensory input before it reaches the motor regions?

Visual cortex Signup and view all the answers

What is the relationship between the sensory and motor systems regarding movement?

They work together to ensure smooth movements. Signup and view all the answers

In addition to lower motor neurons, which other structures receive input for movement execution?

Brainstem and cortex Signup and view all the answers

What aspect of movement is NOT primarily a function of the basal ganglia?

Executing movement commands Signup and view all the answers

What is the primary effect of injury to the descending tracts on muscle signals?

It prevents signals from the brain from reaching the muscles. Signup and view all the answers

Which symptom is characteristic of a lower motor neuron lesion?

Flaccid paralysis Signup and view all the answers

How do upper motor neuron lesions manifest after prolonged muscle contraction?

Hypertonia Signup and view all the answers

Which symptom would be least associated with a lower motor neuron lesion?

Spasticity Signup and view all the answers

What is the main cause of hyperreflexia in upper motor neuron lesions?

Damage to descending pathways affecting reflex response. Signup and view all the answers

Lesions above the pyramidal decussation produce effects on which side of the body?

Contralateral side. Signup and view all the answers

What condition can result from lower motor neuron damage over time?

Muscle atrophy Signup and view all the answers

Which symptom is NOT typically associated with spinal shock in upper motor neuron lesions?

Hypertonia Signup and view all the answers

What condition can occur as a result of lower motor neuron lesion?

Hemiplegia Signup and view all the answers

What is the Babinski sign indicative of?

Corticospinal tract health. Signup and view all the answers

Which motor tract is primarily responsible for fine motor control of the fingers and hand?

Lateral corticospinal Signup and view all the answers

What is the function of the reticulospinal tract?

Maintain antigravity posture Signup and view all the answers

Which area of the brain is involved in the planning of motor actions from memory?

Supplementary motor area Signup and view all the answers

What do the findings from Fritsch and Hitzig's stimulation studies indicate about motor control?

Contralateral movements are elicited from stimulating one side of the brain. Signup and view all the answers

Which of the following best describes the organization of the somatotopic motor map in the cortex?

Certain body areas requiring greater motor control have disproportionately larger representations. Signup and view all the answers

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

Corticobulbar Signup and view all the answers

What is the primary role of the primary motor cortex (M1)?

To execute movement through muscle contraction Signup and view all the answers

Damage to the premotor cortex is most likely to result in which condition?

Apraxia or impairment of complex movements Signup and view all the answers

Which motor tract is associated with head and eye orientation to objects of interest?

Tectospinal Signup and view all the answers

The dorsal regions of the motor cortex primarily control which of the following?

Torso and limbs Signup and view all the answers

What is the primary role of lower motor neurons?

Connect upper motor neurons to skeletal muscle Signup and view all the answers

What is meant by the 'size principle' in motor unit recruitment?

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

Which of the following structures is primarily responsible for voluntary movement control?

Upper motor neurons Signup and view all the answers

What distinguishes pyramidal descending tracts from extrapyramidal tracts?

Pyramidal tracts are responsible for voluntary control Signup and view all the answers

How do motor nerves reach muscle fibers?

Through mixed spinal nerves Signup and view all the answers

What occurs during rate coding in muscle contraction?

The frequency of action potentials is varied Signup and view all the answers

Which neurotransmitter is primarily released at the neuromuscular junction?

Acetylcholine Signup and view all the answers

What is a motor unit composed of?

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

What happens to the fibers in the corticospinal tract at the level of the medulla?

90% decussate to form the lateral corticospinal tract Signup and view all the answers

What defines a motor pool?

A collection of motor units within a single muscle Signup and view all the answers

Which of the following statements about muscle fiber innervation is correct?

One motor neuron can innervate multiple muscle fibers. Signup and view all the answers

How does the body control the amount of force generated by a muscle?

By controlling the activity of motor neurons and recruitment of motor units Signup and view all the answers

What type of movement do the corticobulbar tracts primarily control?

Musculature of the head and neck Signup and view all the answers

What initiates the knee jerk reflex when the patella tendon is tapped?

Stretching of the quadriceps Signup and view all the answers

Which part of the cerebellum is primarily responsible for maintaining balance and posture?

Vestibulocerebellum Signup and view all the answers

What is the main function of the spinocerebellum?

Real-time error correction in ongoing movements Signup and view all the answers

Which of the following statements best describes how cerebellar lesions affect movement?

They result in uncoordinated or inaccurate movements. Signup and view all the answers

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

Modulation of descending commands Signup and view all the answers

Which functional division of the cerebellum is involved in planning and modifying movements based on learnings?

Cerebrocerebellum Signup and view all the answers

What physiological change occurs due to UMN lesions affecting the lateral corticospinal tract?

Increased reflex sensitivity Signup and view all the answers

Why does the cerebellum not initiate motor commands directly?

Its main role is in modifying and refining movements. Signup and view all the answers

Which condition indicates damage to the spinocerebellum?

Coordination issues resulting in dysmetria Signup and view all the answers

How do cerebellar hemispheres exhibit ipsilateral control over body movements?

Double decussation of input and output pathways Signup and view all the answers

What is an effect of lesions in the vestibulocerebellum?

Inability to compensate for body position shifts Signup and view all the answers

Which of the following best describes the processing role of the cerebrocerebellum?

Assessment of movement errors for refining learned skills Signup and view all the answers

Which basal ganglia structure is involved in modulating motor commands back to the cortex?

Globus pallidus Signup and view all the answers

What is the consequence of an acute cerebellar lesion?

Dysfunction in coordinating rapid movements Signup and view all the answers

What role does the globus pallidus play in the motor output circuit?

It inhibits the thalamus, reducing cortical activity. Signup and view all the answers

Which pathway does the D1 receptor primarily influence?

Direct pathway to enhance movement. Signup and view all the answers

What is the effect of dopamine on the indirect pathway?

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

Which of the following is a symptom of Parkinson's disease?

Increased muscle tone and rigidity. Signup and view all the answers

What differentiates hypokinetic symptoms from hyperkinetic disorders?

Hypokinetic symptoms involve less motor activity. Signup and view all the answers

What is the primary output from the striatum to the basal ganglia?

Primarily inhibitory projections. Signup and view all the answers

In Huntington's disease, which pathway is primarily underactive?

Indirect pathway, resulting in excessive movements. Signup and view all the answers

What physiological change is primarily responsible for the symptoms in Parkinson's disease?

Loss of dopaminergic neurons in the substantia nigra. Signup and view all the answers

What does increased cortical activity represent in the context of motor plans?

A facilitated initiation of movement. Signup and view all the answers

Which receptor activation is primarily involved in facilitating the direct pathway?

D1 receptor activation. Signup and view all the answers

What symptom is NOT typically associated with Parkinson's disease?

Chorea. Signup and view all the answers

How does the direct pathway affect the likelihood of enacting a motor plan?

Increases the likelihood of enactment. Signup and view all the answers

What is a characteristic movement symptom of Parkinson's disease?

Shrunken steps, or shuffling gait. Signup and view all the answers

What is one of the non-motor symptoms associated with Parkinson's disease?

Sensory and sleep issues. Signup and view all the answers

What is the consequence of loss of neurons in the substantia nigra pars compacta?

Difficulty with movement facilitation Signup and view all the answers

Why is levodopa (L-dopa) used in the treatment of Parkinson's disease?

It is synthesized into dopamine after administration. Signup and view all the answers

What can occur if too many subthalamic nucleus neurons are removed during surgery for Parkinson's disease?

Hyperkinesia and unwanted movements Signup and view all the answers

What effect does deep brain stimulation have on the targeted areas of the brain?

It suppresses their activity. Signup and view all the answers

Which area of the brain generates a motor plan based on memory of past movements?

Supplementary motor area Signup and view all the answers

How can an examiner differentiate between upper motor neuron (UMN) and lower motor neuron (LMN) lesions in a patient?

By observing for hyperreflexia after spinal shock resolves. Signup and view all the answers

What are the long-term symptoms associated with upper motor neuron lesions?

Spasticity and loss of voluntary control. Signup and view all the answers

In a case of middle cerebral artery infarction, which movements are primarily affected?

Fine movements of the upper limb and face. Signup and view all the answers

What is the result of activating the premotor area while observing a dance video?

Planning a sensory-guided movement. Signup and view all the answers

What is a typical short-term symptom for lower motor neuron lesions?

Areflexia and muscle wasting. Signup and view all the answers

During which procedure is the patient awake to determine optimal stimulation patterns?

Deep brain stimulation Signup and view all the answers

What impact does peripheral administration of dopamine have?

It produces unwanted side effects. Signup and view all the answers

What is the main action of leflunomide in relation to cell proliferation?

Blocks pyrimidine synthesis Signup and view all the answers

Which of the following accurately describes the effect of cyclophosphamide?

Blocks DNA synthesis Signup and view all the answers

What is the primary mechanism of action of mycophenolate?

Blocks inosine monophosphate dehydrogenase Signup and view all the answers

Which symptom is associated with cerebellar damage?

Overstepping during reaching movements Signup and view all the answers

What is the primary function of the cerebrocerebellum?

Fine motor control and planning complex movements Signup and view all the answers

What role does rituximab play in relation to B cells?

Anergizes CD20+ B cells Signup and view all the answers

What would likely occur if the glossopharyngeal nerve is impinged?

Decreased salivation from the parotid gland Signup and view all the answers

What is the effect of basiliximab on T cell activation?

Inhibits IL-2 receptor activity Signup and view all the answers

Which type of muscle is innervated by the nerve to mylohyoid?

Anterior belly of digastric Signup and view all the answers

How does aldesleukin enhance immune response?

Augments Th-cell proliferation Signup and view all the answers

Ipilimumab and nivolumab primarily work by which mechanism?

Preventing T cell deactivation Signup and view all the answers

Which symptom would NOT be associated with cerebellar dysfunction?

Severe spasms in arms Signup and view all the answers

What characteristic deviation is observed when the hypoglossal nerve is impinged?

Tongue deviates to the affected side Signup and view all the answers

Which of the following best describes dysdiadochokinesia?

Inability to perform rapid alternating movements Signup and view all the answers

What role does the vestibulocerebellum play?

Compensatory postural adjustments and eye movements Signup and view all the answers

Which cranial nerve is responsible for the parasympathetic innervation of the ciliary muscle?

Oculomotor nerve Signup and view all the answers

Which of the following ganglia is involved in parasympathetic innervation to the parotid gland?

Otic ganglion Signup and view all the answers

Which vessel contributes to the arterial anatomy of the thyroid gland?

Superior thyroid artery Signup and view all the answers

Which option describes the consequence of an arch aneurysm?

Dilated pupil and 'down and out' gaze in the affected eye Signup and view all the answers

How do calcineurin inhibitors function in the immune response?

Block IL-2 signal transduction Signup and view all the answers

What does the cortex of the cerebellum primarily manage?

Coordination of intricate movements Signup and view all the answers

Which structure primarily facilitates movement planning and control?

Cerebrocerebellum Signup and view all the answers

What is NOT a characteristic of calcineurin inhibitors?

They promote DNA synthesis Signup and view all the answers

Study Notes

Introduction

Sensory information is processed through the visual cortex and then the frontal cortex
Sensory input is received through sensory receptors and neurons via ascending pathways
The premotor cortex (planning movement) and motor cortex (executing movement) plan and execute movements
The basal ganglia and cerebellum refine movements
Descending motor tracts are responsible for transmitting signals to skeletal muscles
Sensory and motor systems work in tandem to enable smooth and coordinated movements

How We Control Movement

Involves a complex process beyond simple muscle contractions
Key steps include planning, initiating, coordinating, refining, and optimizing movements

Diagram Explanation

Muscles are innervated by lower motor neurons (LMNs) in the spinal cord.
The spinal cord (and its LMNs) receive input from the brainstem and cortex.
The basal ganglia and cerebellum play a role in movement refinement and coordination.
Both the basal ganglia and cerebellum activate the thalamus, highlighting feedback loops.

Lower Motor Neuron Functions

Directly innervate muscles, involved in both voluntary and reflexive movements.
Their cell bodies are located in the spinal cord, particularly in the ventral horn.
Motor nerves travel within mixed spinal nerves (containing both sensory and motor components).
Motor nerves synapse onto skeletal muscle at the neuromuscular junction, releasing neurotransmitters (e.g., acetylcholine).
One motor neuron can innervate multiple muscle fibers, while each muscle fiber receives input from only one motor neuron

Example of Lower Motor Neuron Function

Sensory receptors transmit sensory input via sensory neurons, which synapse with alpha motor neurons (LMNs).
The LMNs then innervate muscles, triggering muscle contractions.

Lower Motor Neuron Structure & Inputs

Multipolar neurons connecting upper motor neurons (UMNs) to the skeletal muscle they innervate.
Receive input from three sources:
- Spinal interneurons
- Sensory input from muscle spindle stretch receptors
- Upper motor neurons from the brain (primarily the primary motor cortex)

Motor Unit and Motor Unit Pool

A motor unit consists of a single motor neuron and all the muscle fibers it innervates.
A motor pool is a group of motor units within a muscle.
The ventral horn of the spinal cord houses different motor neurons. Their axons travel through mixed spinal nerves, innervating specific muscle fibers.
Motor neurons collectively innervate a diverse number of muscle fibers.

Grading of Muscle Force Production

Recruitment: Increasing the number of active motor neurons (and consequently, muscle fibers).
- Size Principle: Orderly recruitment of motor neurons based on size, from smallest to largest (Henneman Size Principle).
- Small neurons, innervating fewer muscle fibers, are recruited first, followed by larger neurons.
Rate Coding: Varying the frequency of excitation by adjusting the firing rate of motor neurons.
- Increasing the frequency of action potentials in a motor neuron leads to increased force production by individual muscle fibers.
- This helps to reduce fatigue and distribute contractile work among muscle fibers.

The Size Principle

Motor units are activated from small to large.
Motor neurons and their axons innervate specific sets or types of muscle fibers within a muscle.
Different motor neurons (e.g., axons B, green, blue) innervate different sets of fibers within a single muscle.
The number of activated muscle fibers determines the force generated within that muscle.
Different tasks require varying levels of muscle tension.
- Fine, delicate movements (e.g., fingers, eyes) utilize smaller motor units.
- Coarse, powerful movements (e.g., hip, thigh) utilize larger motor units.

Rate Coding

A motor neuron innervates a set of muscle fibers, forming a single motor unit.
The frequency of action potentials in a motor neuron determines the rate of force generation within the motor unit.
Muscle contraction duration is longer than the duration of a single action potential.
Increasing the frequency of action potentials increases force generation through summation of force.
- Low frequencies (e.g., 5Hz) result in oscillations without significant force summation.
- High frequencies (e.g., 40Hz) result in complete force summation.
Unfused tetanus produces oscillating force generation, showing individual contractions.
Fused tetanus creates smooth force summation, blurring individual contractions.
Real-life movements are smooth, not jerky, due to tetanus and asynchronous firing of multiple motor units, leading to combined force generation.

Upper Motor Neurons

Innervate lower motor neurons.
Give rise to descending motor tracts, with cell bodies originating in the motor cortex or brainstem and terminating in the brainstem or spinal cord (ventral horn).
Control voluntary movements, but do not directly innervate muscle.
They synapse with LMNs in the brainstem or spinal cord, which then form the somatic motor part of the peripheral nervous system.

Descending Pathways

Transmit motor signals from the brain (descending motor tracts originating from motor neurons).
These axonal tracts form descending pathways.
An example is an upper motor neuron in the primary motor cortex traveling down and synapsing with a LMN, which then innervates muscles to produce movement.

Pyramidal vs. Extrapyramidal Pathways

Pyramidal: Originate in the cerebral cortex, carrying motor fibers to the spinal cord and brainstem. They control voluntary movement of the body and face.
Extrapyramidal: Originate in the brainstem, carrying motor fibers to the spinal cord. They control involuntary/autonomic movement.

Corticospinal Tract

Carries motor signals from the motor cortex to the spinal cord, responsible for voluntary control of the body's musculature.
90% of fibers decussate (cross over) at the medulla, forming the lateral corticospinal tract.
The remaining 10% of fibers travel ipsilaterally, forming the anterior corticospinal tract (also known as the ventral or medial corticospinal tract).

Organisation of Descending Tracts within the Spinal Cord

Different descending motor tracts have specific locations within the spinal cord, often organized based on the areas of the body they control.
The lateral corticospinal tract, responsible for distal muscle control, occupies the dorsolateral region of the ventral horn.
The medial corticospinal tract, responsible for axial muscle control, terminates in the ventral horn.
The corticobulbar tract, innervating the head and face muscles, terminates in cranial nerve nuclei.

Organisation of the Motor Cortex

The motor cortex, located in the frontal lobe of the brain, controls voluntary movement.
Different areas of the motor cortex are responsible for controlling movement of specific parts of the body.
The concept of a somatotopic map represents the mapping of the body onto the motor cortex.

Somatotopic Motor Map

Body areas requiring finer motor control (e.g., fingertips, hands, lips, tongue) are represented by disproportionately larger regions on the homunculus.
Ventral areas control head movements, while more dorsal areas control torso and limbs.
Key regions within the motor cortex:
- Face area
- Arm area
- Leg area

Cortical Areas Involved in Motor Control

Several hierarchically organized brain regions contribute to motor control.
Posterior Parietal Cortex: Sensory integration center providing sensory input to the premotor cortex.
Prefrontal Cortex: Decision-making center for selecting actions.
Premotor Cortex: Plans movements and motor sequences, receiving input from the prefrontal cortex and posterior parietal cortex.
Primary Motor Cortex (M1): Executes movement through muscle contraction and relaxation, receiving information from the premotor area.

Primary Motor Cortex (M1)

Activated specifically during movement execution.
Upper motor neurons in M1 project down the corticospinal tract.
Lowest electrical thresholds for stimulating movement, resulting in simple movements.
Lesions impair simple movements.
Receives input from areas 6 (pre-motor) and sensory areas 1, 2, and 3 (posterior to the central sulcus).

Pre-Motor and Supplementary Motor Areas (Area 6)

Premotor Area (PMA): Involved in sensory-guided movements.
Supplementary Motor Area (SMA): Responsible for planning motor actions, especially those based on memory and new motor sequences.
Electrical stimulation results in complex movements.
Lesions can cause apraxia (difficulty performing complex movements).
They receive input from the posterior parietal cortex (sensory areas 5, 7) and prefrontal cortex.
Some motor neurons from these areas contribute to the corticospinal tract, though most originate from M1.

Clinical Relevance of Upper Motor Neuron Lesions

Upper motor neuron lesions disrupt communication between the brain and muscles, as UMNs synapse onto LMNs, which directly innervate muscles.
Conditions like spinal muscular atrophy (SMA), where motor neuron axons degenerate, impede signals from the brain to muscles, resulting in impaired movement.

Upper vs. Lower Motor Neuron Lesion Symptoms

Upper Motor Neuron Lesions: Symptoms include spasticity, hyperreflexia, and a positive Babinski reflex.
Lower Motor Neuron Lesions: Symptoms include hyporeflexia, atrophy, and flaccid paralysis.

Localizing Motor Neuron Damage

The lateral corticospinal tract decussates at the medullary pyramids, while the anterior corticospinal tract remains ipsilateral.
Unilateral Lesions:
- Lesions above the medullary decussation have contralateral effects.
- Lesions below the level of decussation affect the ipsilateral side of the body.
- Lower motor neuron lesions also produce ipsilateral damage, causing paralysis and atrophy.

Lower Motor Neuron Lesion Symptoms

Causes: Trauma, ischemia, infections.
Symptoms:
- Flaccid paralysis (-plegia): Loss of motor neuron function leads to muscle flaccidity, loss of motor control, and reflexes (e.g., hemiplegia, paraplegia).
- Paresis: Muscle weakness or incomplete paralysis, impairing voluntary movement.
- Muscle atrophy: Deterioration of muscle tissue due to inactivity and lack of signals from LMNs.
- Areflexia: Loss of reflexes due to disruptions in the reflex circuitry.

Upper Motor Neuron Lesion Symptoms

Short Term (Spinal Shock): Difficulty in distinguishing from LMN lesions.
- Flaccidity: Limpness and inability to contract muscles, potentially life-threatening if affecting breathing.
- Hypotonia: Reduced muscle tone due to suppressed spinal cord activity.
- Areflexia: Absence of reflexes.
Long Term:
- Spasticity: Increased muscle stiffness and hypertonia, caused by prolonged muscle contraction.
- Fractionated Movement Impairment: Difficulty controlling individual muscle movements.
- Babinski Sign: A positive Babinski reflex (toes fanning out) is a sign of damage to the corticospinal tract.

Hyperreflexia

Damage to the corticospinal tract, which normally inhibits reflex responses, results in exaggerated reflexes.
- The knee-jerk reflex is a common example.
Clonus: Sustained stretching of a muscle triggers rhythmic cycles of reflexive contraction and relaxation.
Hypertonia: Increased resistance to passive muscle stretch due to continuous muscle activity.

How Hyperreflexia Arises

Disruption of descending inhibitory pathways from the corticospinal tract leads to increased excitability of spinal cord neurons, causing heightened reflex responses and muscle stiffness, contributing to the development of hyperreflexia.

Knee Jerk Reflex

A reflex hammer taps the patella tendon, stretching the quadriceps muscle.
Stretch receptors in the muscle sense the change in length and send signals via sensory neurons to the spinal cord.
Sensory neurons fire action potentials, increasing the firing rate of motor neurons in the spinal cord's ventral horn.
This causes the muscle to contract, resulting in a knee jerk.
Descending pathways from the brain, primarily through the lateral corticospinal tract, normally dampen this reflex.
Damage to the lateral corticospinal tract results in exaggerated reflexes, as the descending inhibition is lost.

Cerebellum - Structure & Function

Located on the back of the brain, below the cerebrum and above the brainstem.
Divided into hemispheres with a central vermis connecting them.
Contains 50% of the brain's neurons.
Not directly involved in executing movements but plays a crucial role in coordination and planning.

Functional Divisions of the Cerebellum

Each division has specific functions and connections to other brain regions.
Sensory and motor components are present in all, but they don't directly control lower motor neurons.
Vestibulocerebellum:
- Located in the flocculonodular lobe.
- Receives input from the vestibular system, crucial for balance and posture.
- Receives information from the superior colliculus and visual cortex for eye movement control.
Spinocerebellum:
- Includes the vermis and immediate hemisphere.
- Receives sensory information from the spinal cord and the motor cortex.
- Responsible for regulating body movements and correcting errors based on sensory input.
Cerebrocerebellum:
- Located in the lateral hemispheres.
- Receives input from the cerebral cortex for planning and modifying learned movements.

Cerebellum Lesions

Vestibulocerebellum lesions:
- Cause difficulty in automatically adjusting posture.
- Patients need to be conscious of their balance as shifts in body position cannot be automatically compensated for.
Spinocerebellum lesions:
- Affect coordination of movements.
- Cause cerebellar ataxia, dysmetria, and dyssenergia.
- Movements are typically speed-dependent, with increased disorganization at faster speeds.
- Lesions affect the ipsilateral side of the body due to double decussation.
Cerebrocerebellum lesions:
- Affect control of ipsilateral movement and movement timing and initiation.
- Can also impact cognition, specifically spatial cognition, abstract reasoning, and working memory.

Basal Ganglia

A group of interconnected nuclei located below the cerebral cortex.
Five main nuclei:
- Striatum (caudate and putamen)
- Globus pallidus (internal and external segments)
- Substantia nigra (pars reticulata and pars compacta)
- Subthalamic nucleus
Receives input from the motor cortex and limbic areas.
Projects back to the cortex via the thalamus.
Modulates descending commands from the primary motor cortex, influencing movement control.

Direct and Indirect Pathways of the Basal Ganglia

Direct Pathway:
- Excitatory pathway that enhances motor output.
- Motor cortex activates the striatum, which inhibits the globus pallidus internal segment.
- This disinhibits the thalamus, leading to increased excitation of the motor cortex.
Indirect Pathway:
- Inhibitory pathway that reduces motor output.
- Motor cortex activates the striatum, which inhibits the globus pallidus external segment.
- This reduces inhibition of the subthalamic nucleus, increasing its excitation of the globus pallidus internal segment.
- This leads to increased inhibition of the thalamus and decreased excitation of the motor cortex.

Role of Dopamine in the Basal Ganglia

Dopamine neurons project from the substantia nigra pars compacta to the striatum.
Dopamine activates D1 and D2 receptors, influencing the direct and indirect pathways.
D1 receptor activation enhances the direct pathway, promoting movement.
D2 receptor activation strengthens the indirect pathway, suppressing movement.

Basal Ganglia Disorders

Hypokinetic symptoms (too little movement):
- Parkinson's disease: characterized by akinesia, bradykinesia, resting tremors, muscle stiffness, and slowness of movements.
Hyperkinetic symptoms (too much movement):
- Huntington's disease (chorea): uncontrolled, dance-like movements.
- Hemiballismus: violent,flinging movements.
- Dyskinesias: involuntary movements.
- Hypotonia: decreased muscle tone.

Parkinson's Disease

Characterized by the loss of dopamine neurons in the substantia nigra pars compacta.
Leads to an imbalance in the basal ganglia pathways, favoring the indirect pathway and resulting in reduced movement.

Treatment of Parkinson's Disease

Pharmaceutical:
- L-dopa (levodopa), a precursor to dopamine, is administered as dopamine itself cannot cross the blood-brain barrier.
- Dopamine agonists are used as alternative treatments.
- Dopamine reuptake inhibitors prolong its effect in the synaptic cleft.
Surgical:
- Involves removing neurons from the subthalamic nucleus to reduce the indirect pathway's impact.
- This increases thalamic activation and, in turn, cortical activation.
- Requires precise calibration to avoid over-stimulation and resulting hyperkinetic movements.
Deep Brain Stimulation (DBS):
- Involves electrical stimulation of specific brain areas, like the subthalamic nucleus or globus pallidus internal segment.
- Continuous stimulation is used to modulate electrical activity and reduce symptoms.
- The exact mechanism remains unclear, but it's believed to restore balance in the basal ganglia pathways.

Movement Control and Coordination

Premotor cortex plans movements.
Supplementary motor area generates the motor plan.

Spinal Cord Injury

Injury to the lateral corticospinal tract causes ipsilateral flaccid paralysis due to interruption of motor signals.
The spinocerebellum coordinates ongoing movements by adjusting descending motor commands.
Basal ganglia refine motor commands through connections with the thalamus.

Cerebral Blood Supply and Motor Control

Concave hemorrhage, especially in the lateral motor cortex, often involves the middle cerebral artery (MCA).
MCA supplies the corticospinal tract responsible for fine motor control of the upper limbs and the corticoreticulospinal tract for fine hand control.
Damage to the lateral motor cortex, particularly the left side, would impact upper limb and facial movements.

Brain Activation During Movement

Premotor cortex is involved in sensory-guided movement planning and mental rehearsal of movements.
Primary motor cortex is responsible for initiating simple movements and receives sensory input from the skin and muscles.
Supplementary motor cortex is involved in complex motor tasks, particularly those involving sequencing and coordination.

Upper and Lower Motor Neuron Lesions

Upper motor neuron (UMN) lesions initially present similarly to lower motor neuron (LMN) lesions due to spinal shock.
UMN lesions eventually lead to hyperreflexia and spasticity after 1-2 weeks.
LMN lesions result in flaccid paralysis and loss of motor control.

Cerebellar Damage

Cerebellar lesions cause ataxia, dysmetria, and dysdiadochokinesia.
Damage to the right cerebellum results in ataxia with a tendency to lean towards the right side.
Cerebellar vermis is responsible for coordination, posture, and emotional changes.
Vestibulocerebellum controls balance and eye movements.
Spinocerebellum coordinates ongoing movements.
Cerebrocerebellum plans and coordinates complex movements.

Nerve Innervation

Nerve to mylohyoid, a branch of the trigeminal nerve, innervates the mylohyoid and anterior belly of digastric muscles.
Glossopharyngeal nerve innervates the stylopharyngeus muscle.
Facial nerve innervates the posterior belly of digastric, stapedius, stylohyoid, posterior auricular, and occipitalis muscles.
Infrahyoid muscles (sternohyoid, sternothyroid, thyrohyoid, and omohyoid) are innervated by the ansa cervicalis.
Suprahyoid muscles (stylohyoid, mylohyoid, geniohyoid, and digastric) are innervated by multiple cranial nerves.

Glossopharyngeal Nerve Impingement

Impingement of the glossopharyngeal nerve at the jugular foramen would affect salivation from the parotid gland.
It does not affect taste to the anterior two-thirds of the tongue.
General sensory innervation of the larynx is provided by the vagus nerve.

Cranial Nerve Function

Hypoglossal nerve (XII) innervates the genioglossus muscle, responsible for tongue protrusion.
Damage to the hypoglossal nerve causes tongue deviation towards the affected side.
Vagus nerve (X) innervates most soft palate muscles, controlling palatal elevation and uvula position.

Aortic Arch Aneurysm

Aortic arch aneurysm can cause oculomotor nerve dysfunction, leading to dilated pupil and "down and out" gaze in the affected eye.
Horner's syndrome, characterized by ptosis, anhidrosis, and miosis, is also associated with aortic arch aneurysm.
Hoarse voice can occur due to compression of the left recurrent laryngeal nerve.

Immunosuppressants

Corticosteroids inhibit phospholipase A2 activity, leading to reduced production of inflammatory mediators.
Calcineurin inhibitors, like cyclosporine, prevent IL-2 expression, thereby inhibiting T cell activation.
mTOR inhibitors block IL-2 signal transduction, preventing cell cycle progression.

Immunomodulatory Drugs

Methotrexate inhibits folic acid synthesis, affecting DNA synthesis.
Mycophenolate inhibits inosine monophosphate dehydrogenase (IMPDH), specifically affecting T and B lymphocytes.
Rituximab (anti-CD20) depletes B cells by initiating apoptosis in CD20+ cells, particularly effective in treating lymphomas.
Basiliximab blocks IL-2 receptors, preventing T cell activation.
Aldesleukin is a recombinant form of IL-2, enhancing T cell proliferation.
Ipilimumab (anti-CTLA4) and Nivolumab (anti-PD1) prolong existing T cell responses by preventing T cell deactivation.

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Description

This quiz explores key aspects of movement control within the nervous system, including the roles of various brain structures such as the premotor cortex, basal ganglia, and lower motor neurons. Test your knowledge on how these components interact and their implications for motor function and movement disorders.