Neuroanatomy: Spinal Cord and Motor Control

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Questions and Answers

Which area of the motor cortex is primarily responsible for the innervation of the arms and trunk?

Midsagittal area

Upper motor cortical region (correct)

Lower third of the motor cortex

Precentral gyrus

What is the role of the prefrontal cortex in the motor cortex system?

Refines movements by suppressing competing actions

Serves as the primary output for cranial nerves

Regulates planning and implementation of movement

Adds quality of judgment and cognitive accountability (correct)

Which artery supplies the lateral cortical surface of the motor cortex?

Middle cerebral artery (correct)

Basilar artery

Vertebral artery

Anterior cerebral artery

What happens when a lesion occurs above the point of decussation in the descending fibers?

Motor signs appear contralateral to the lesion Signup and view all the answers

Which cortical area is involved in regulating higher-order spatial aspects of the movement plan?

Somatosensory association cortex Signup and view all the answers

What are the clinical signs of Lower Motor Neuron Syndrome?

Muscular fibrillation and absent reflexes Signup and view all the answers

Which cerebellar lobe is mainly responsible for muscle tone and walking posture?

Anterior lobe Signup and view all the answers

What is the primary characteristic of cerebellar damage indicated by ataxia?

Lack of order and coordination in muscle activities Signup and view all the answers

What function does the superior cerebellar peduncle serve?

Transmits outputs to the motor cortex and spinal cord Signup and view all the answers

Which of the following best describes intention tremor?

A tremor that worsens with movement towards a target. Signup and view all the answers

Which region of the cerebellum is most medial and contributes to body posture?

Vermal region Signup and view all the answers

What type of gait is characterized by broad-based stance and inability to complete tandem tasks?

Ataxic gait Signup and view all the answers

Which aspect of cognitive function is associated with the cerebellum?

Emotional control Signup and view all the answers

What happens to patients with cerebellar pathology regarding motor memory?

They lose movement automaticity and revert to conscious control. Signup and view all the answers

Which cerebellar lobe is concerned with sequential planning and coordination of skilled movements?

Posterior lobe Signup and view all the answers

What percentage of the motor fibers are contained in the corticospinal tract?

30% Signup and view all the answers

Which area is responsible for the majority of the motor fibers that originate in the corticospinal tract?

Primary Motor Cortex Signup and view all the answers

In the corticonuclear/corticobulbar tract, which cranial nerve is associated with facial muscle control?

Facial (CN VII) Signup and view all the answers

What characterizes Pseudobulbar Palsy?

Bilateral involvement of corticonuclear pathways Signup and view all the answers

What is the primary effect of a brainstem lesion in terms of motor function?

Ipsilateral cranial nerve motor nucleus impact Signup and view all the answers

Which of the following describes spastic hemiplegia?

Paralysis with increased muscle tone and hyperreflexia Signup and view all the answers

What type of paralysis affects both lower limbs?

Paraplegia Signup and view all the answers

Which symptom is NOT typically associated with Pseudobulbar Palsy?

Loss of voluntary movement of limbs Signup and view all the answers

Which condition is characterized by alternating patterns of symptoms affecting both LMN and UMN systems?

Alternating/Crossed Hemiplegia Signup and view all the answers

Which reflex is commonly assessed in UMN syndrome?

Positive Babinski reflex Signup and view all the answers

What is the primary function of the dorsal horns in the spinal cord?

Transmit sensory information Signup and view all the answers

Which tract is responsible for regulating voluntary muscle activity of the limbs?

Lateral corticospinal tract Signup and view all the answers

What occurs with a lesion in the lateral corticospinal tract?

Profound, bilateral weakness Signup and view all the answers

Which of the following is a component of a motor unit?

Motor cell body Signup and view all the answers

How does damage to the lower motor neuron (LMN) manifest in clinical findings?

Ipsilateral findings at the damage site Signup and view all the answers

What type of reflex is referred to as a stretch reflex?

Knee jerk reflex Signup and view all the answers

Which motor neurons control muscle contraction in response to external forces?

γ-motor neurons Signup and view all the answers

Hyporeflexia is commonly associated with which type of disorder?

Lower motor neuron disorders Signup and view all the answers

What role do extrapyramidal tracts play in the motor system?

Influence muscle tone and posture Signup and view all the answers

What is a critical characteristic of segmental injuries in the spinal cord?

Sensory and motor functions are impaired below the lesion Signup and view all the answers

Which could be a consequence of releasing spinal reflexes from higher levels of control?

Hyperactive reflexes Signup and view all the answers

Which motor nucleus innervates the diaphragm?

C3-C5 nuclei Signup and view all the answers

What is the function of the rubrospinal tract?

Support the body against gravity Signup and view all the answers

What is a key characteristic of spasmodic torticollis?

Fixation of the neck Signup and view all the answers

Which of the following is NOT a characteristic of Parkinson's disease?

Increased muscular rigidity Signup and view all the answers

Huntington disease primarily presents with which symptom?

Dysarthria Signup and view all the answers

What is the main cause of Wilson's disease?

Copper metabolism disorder Signup and view all the answers

Which type of treatment is shown to improve motor performance in Parkinson's disease patients?

L-Dopa (Sinemet) Signup and view all the answers

What is a prominent diagnostic feature of Wilson's disease?

Kayser-Fleischer ring Signup and view all the answers

How does tardive dyskinesia typically present?

Facial grimacing and tongue thrust Signup and view all the answers

Which of these symptoms is commonly seen in Progressive Supranuclear Palsy?

Dysarthria Signup and view all the answers

At what age do symptoms of Huntington disease typically begin to manifest?

Around age 30 Signup and view all the answers

What causes the motor symptoms in Parkinson's disease?

Degeneration of substantia nigra cells Signup and view all the answers

Which cognitive symptoms are associated with Progressive Supranuclear Palsy?

Slow thinking and inattention Signup and view all the answers

What is a primary characteristic of myoclonus?

Sudden, lightning-like jerks Signup and view all the answers

What is a common associational feature found in patients with Parkinson's disease?

High rates of depression Signup and view all the answers

Which type of tremor is specifically associated with Parkinson's disease?

Tremor at rest Signup and view all the answers

What is the term used to describe decreased muscle tone associated with cerebellar damage?

Hypotonia Signup and view all the answers

Which of the following is NOT a task used to assess cerebellar function?

Pushing against resistance Signup and view all the answers

What symptom is associated with Friedreich ataxia?

Loss of proprioception Signup and view all the answers

Which structure is NOT part of the basal ganglia anatomy?

Thalamus Signup and view all the answers

What is the primary function of the basal ganglia?

Refinement of motor movements Signup and view all the answers

Which of the following characterizes bradykinesia?

Slowness of movement Signup and view all the answers

What describes a resting tremor?

Associated with Parkinson's disease Signup and view all the answers

What symptom is indicative of dystonia?

Involuntary muscle contractions Signup and view all the answers

What is the typical outcome for patients with unilateral cerebellar lesions?

Ipsilateral motor signs Signup and view all the answers

Which condition is NOT typically associated with progressive cerebellar degeneration?

Cerebellar tumors Signup and view all the answers

Which symptom would most likely be present with dysmetria?

Impaired movement accuracy Signup and view all the answers

What effect does a lesion in the basal ganglia have on motor control?

Loss of inhibitory influence Signup and view all the answers

Which characteristic is associated with athetosis?

Slow, involuntary twisting Signup and view all the answers

Study Notes

Innervation Pattern

Brainstem and spinal cord injuries damaging lower motor neurons (LMNs) result in ipsilateral findings.
The spinal cord has an outer ring of white matter containing ascending and descending fibers.

Anatomical Marking - Internal Anatomy

The spinal cord has a butterfly-shaped central gray area.
Dorsal horns contain sensory nerve cells receiving bodily sensory information.
Ventral horns contain motor neurons sending motor impulses to muscles from the central nervous system (CNS).
Fibers from dorsal and anterior roots merge to form spinal tracts.

Tracts of the Spinal Cord - Ascending (Sensory)

Transmit sensory information from various body parts.
Sensory impulses include pain, thermal sensation, touch, proprioception, and kinesthesia.

Spinal Motor Control Circuitry

Lower motor neurons are the output pathway to skeletal muscles.
Called the final common pathway.
Efferent impulses from the motor cortex pass through these neurons before muscle movement.

Tracts of the Spinal Cord - Descending (Motor)

Composed of pyramidal and extrapyramidal tracts.
Pyramidal tracts (corticospinal tracts) control voluntary limb movements.
Lateral corticospinal tract constitutes 90% of corticospinal fibers, crossing the medulla.
Anterior corticospinal tract constitutes 10% of corticospinal fibers, also crossing the medulla.

Tectospinal Tract

Regulates neck and body movements for startle reflexes.

Rubrospinal Tract

Regulates muscle tone supporting the body against gravity.

Vestibulospinal Tract

Regulates reflexive adjustments of body posture.

Reticular Descending Tracts

Regulate respiration, vomiting, and cough reflexes.
Involves motor nuclei from C3 to C5.
Phrenic nerve innervates the diaphragm (C3-C5).
Other motor nuclei (T1-T2) innervate the internal and external intercostal muscles (T6-T12) and abdominal muscles.

Motor Nuclei of the Spinal Cord

Spinal gray matter contains motor nerve cells.
Anterior α-motor neurons control voluntary muscle contraction.
Anterior γ-motor neurons regulate muscle contraction in response to external forces.

Motor Functions of the Spinal Cord

Reflexive motor responses are stereotyped, involuntary reactions to sensory stimulation.

Spinal Reflexes

Reflexes are independent of cortical voluntary control.
Input from higher motor centers ensures a homeostatic state for smooth motor movements.
If higher motor control is released, spinal reflexes become hyperactive.
Stretch reflexes include tendon-jerk reflexes (such as knee jerk) and reflexes of biceps, triceps, quadriceps, and ankle muscles.
Withdrawal/Flexor reflex.
Crossed Extensor reflex.

Clinical Correlates - Altered Reflexes

Three patterns: hyperreflexia (common in upper motor neuron (UMN) disorders), clonus, and hyporeflexia/areflexia (common in lower motor neuron (LMN) disorders).

Types of Spinal Cord Disorders

Segmental lesions affect a specific spinal level, impairing sensory, and motor functions below the lesion level.
Complete spinal transection results in bilateral loss of sensory and motor functions below the lesion.
Longitudinal lesions selectively impact specific nerve cells, possibly affecting both sensory and motor systems.
Spinal hemisection affects both sensory and motor systems on the ipsilateral side.

Lower Motor Neuron Syndrome

Muscle fibers are disconnected from motor efferents, resulting in progressively worsening atrophy.
Signs include flaccid paralysis, absent reflexes, and muscular fibrillation.

Cerebellar Anatomy

The cerebellum is composed of two hemispheres, internal white matter, and four pairs of embedded nuclei.
Three cerebellar peduncles (superior, middle, inferior) connect to the brainstem.
The cerebellum is divided into three transverse lobes (anterior, posterior, flocculonodular).
The anterior lobe (paleocerebellum) controls muscle tone and posture.
The posterior lobe (neocerebellum) plans and coordinates skilled movements.
The flocculonodular lobe (archicerebellum) regulates equilibrium and posture.

Cerebellar Pathologies

Cerebrovascular accidents (CVAs) can damage the cerebellar arteries (posterior inferior cerebellar artery and anterior inferior cerebellar artery), leading to cerebellar pathologies.

Cerebellar Damage

Ataxia: Lack of order/coordination in muscle activities, resulting from dysmetria, dysdiadochokinesis, and decomposition of movement, and ataxic gait.
Ataxic dysarthria: speech characterized by slow, poorly coordinated movements of the articulators.
Intention tremor: intentional movements that create tremors that increase as the target is approached.
Hypotonia/impaired check and rebound: reduced muscle tone, difficulty controlling movement amplitude and speed, and excessive rebounding.

Basal Ganglia Anatomy

Basal ganglia structures include the striatum (caudate nucleus and putamen), globus pallidus, and claustrum.
Related structures include the substantia nigra and subthalamic nucleus.

Function of the Basal Ganglia

Motor regulation: Basal ganglia (BG) nuclei refine and suppress competing movements, promoting precise and focused target-directed motor activity, automatic motor movements, emotional expression, and vocalization.
Higher mental functions: BG nuclei also contribute to processing higher mental functions.

Innervation Pattern (Basal Ganglia)

BG motor organization is contralateral to sensory input and motor output.
BG nuclei communicate to and from the motor cortex on the ipsilateral side, influencing the opposite side's brainstem and spinal cord motor nuclei activity.

Signs of Basal Ganglia Dysfunction

Bradykinesia: slowness of movement.
Hypokinesia: reduced movement.
Akinesia: absence of movement.
Dyskinesia: abnormal involuntary movements (athetosis, ballism, chorea).
Tremor: involuntary shaking movement.
Dystonia: sustained or intermittent muscle contractions causing abnormal postures or twisting movements.
Torticollis: abnormal neck posture.
Myoclonus: sudden, brief, involuntary muscle contractions.

Basal Ganglia Diseases (Parkinson's Disease)

Parkinson disease (PD): a progressive neurodegenerative disorder causing movement issues.
Cause: degeneration of cells in the substantia nigra leading to dopamine deficiency.
Characteristics include tremor at rest, cogwheel rigidity, bradykinesia, and stooped posture.
Symptoms may include masked facial expression, loss of postural reflexes, and micrographia.
Treatment: pharmacological therapies (e.g., levodopa/L-Dopa) and surgical procedures (e.g., deep brain stimulation).

Basal Ganglia Diseases (Huntington's Disease)

Huntington's disease (HD): an inherited, autosomal dominant disorder causing progressive degeneration of the brain, particularly the basal ganglia.
Cause: genetic mutation affecting the copper-transporting gene.
Progressive symptoms include chorea, dysarthria, and cognitive decline, often leading to dementia.
Characterized by involuntary, irregular movement (chorea) that gradually worsens, affecting speech, cognitive function, and gait.

Basal Ganglia Diseases (Wilson's Disease)

Wilson's disease (a progressive, autosomal recessive movement disorder), also known as hepatolenticular degeneration.
Cause: a mutation in the copper-transporting gene on chromosome 13q.
Characterized by excessive copper in the brain, liver damage, and neurological symptoms such as rigidity, tremor, dysarthria, and cognitive impairment.

Basal Ganglia Diseases (Progressive Supranuclear Palsy)

Progressive supranuclear palsy (PSP) is a neurodegenerative brain disorder.
Cause: unknown.
Characterized by progressive difficulty moving the eyes in normal directions, often to the point of fixed gaze.
Other symptoms include rigidity, difficulty swallowing (dysphagia), and a lack of balance (ataxia).

Basal Ganglia Diseases (Tardive Dyskinesia)

Tardive dyskinesia (TD) is an acquired motor disorder.
Cause: long-term use of certain medications, particularly antipsychotics.
Characterized by involuntary, repetitive, or rhythmic movements, typically affecting the face, mouth, lips, tongue, and jaw.

Cortical Motor System Connections

The primary motor cortex (PMC) receives input from other cortical areas and subcortical structures to coordinate and plan movement.
The supplementary motor cortex (SMA) and premotor cortex are involved in planning and implementing movement.
The prefrontal cortex affects judgment, cognitive awareness and spatial aspects of movement execution, and the somatosensory association cortex is important for regulating higher-order spatial planning.
Subcortical structures like the basal ganglia assist in refining movements.

Innervation Pattern (Motor Cortex)

Motor cortex efferent projections cross the midline at the medulla.
Lesions above the decussation produce contralateral motor signs, while lesions below produce ipsilateral signs.

Corticospinal Tract

Contains 30% of motor fibers mediating voluntary skeletal muscle movement through LMN connections. These fibers originate in the primary motor cortex.
Corticonuclear tract (or corticobulbar) contains 70% and regulates facial, speech, and other cranial nerve-related muscles via brainstem connections. Fibers originate from the motor cortex, passing through the brainstem and synapsing with cranial motor neurons.

Clinical Correlates - Upper Motor Neuron (UMN) Syndrome

UMN syndromes are often characterized by increased muscle tone (spastic paralysis), hyperactive reflexes, and pathological reflexes (like Babinski).
The affected muscles do not atrophy as a result of the lesion.

Clinical Correlates – Pseudobulbar Palsy

A state of paralysis of the oral-facial muscles, with symptoms such as dysphagia (difficulty swallowing) and dysarthria (difficulty speaking), resulting from bilateral lesions of the corticonuclear pathways.

Clinical Correlates - Alternating/Crossed Hemiplegia

Brainstem lesions affecting both the ipsilateral cranial nerve motor nuclei and uncrossed descending fibers of the corticospinal tract can lead to alternating symptoms, interrupting both LMN and UMN systems.
Clinical features involve both ipsilateral cranial nerve deficits and contralateral corticospinal tract deficits, highlighting the brainstem location of the lesion. Example symptoms include hemiparesis, or difficulty with chewing, speaking, and swallowing.

Clinical Correlates – Spastic Hemiplegia

A state of paralysis marked by hypertonia (increased muscle stiffness), hyperreflexia (excessive reflex responses), and spasticity in the affected limbs, arising from UMN lesions in the corticospinal tract contralateral to the site of damage. The lesion is in the UMN pathway, not LMN pathways.

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Description

Test your knowledge on the anatomy and functions of the spinal cord, including the innervation patterns and motor control circuitry. Explore key concepts such as lower motor neurons, spinal tracts, and the sensory pathways involved in bodily sensations.