Upper Motor Neurons in Balance and Posture

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Questions and Answers

What are the two sets of upper motor neurons that control the local circuitry in the brainstem and spinal cord?

The reticular formation and the vestibular nuclei.

What type of control does the reticular formation play in posture?

Feedforward control

What type of control does the vestibular nuclei play in posture?

Feedback control

What part of the brain is responsible for movement execution?

The primary motor cortex Signup and view all the answers

What part of the brain is responsible for planning and selecting movements?

The premotor cortices Signup and view all the answers

What are the two ways that the motor cortex influences movements?

Directly by contacting lower motor neurons and local circuit neurons, and indirectly by innervating neurons in brainstem centers. Signup and view all the answers

What are the two types of tracts that make up the pyramidal tract?

Corticospinal and corticobulbar tracts Signup and view all the answers

What are the four types of tracts that make up the extrapyramidal tracts?

Reticulospinal, vestibulospinal, and rubrospinal tracts Signup and view all the answers

The brainstem pathways can independently organize gross motor control.

True Signup and view all the answers

What are the distal parts of the limbs that are crucial for everyday life?

The tongue and face Signup and view all the answers

What are the two groups of muscles that are affected by damage to the descending motor pathways?

Damage to the descending motor pathways can affect the control of these groups of muscles. Signup and view all the answers

Where do the projections from the vestibular nuclei that control axial muscles originate?

The medial and lateral vestibulospinal tracts Signup and view all the answers

Where do the projections from the vestibular nuclei that influence proximal limb muscles originate?

The medial and lateral vestibulospinal tracts Signup and view all the answers

What type of response do direct projections from the vestibular nuclei to the spinal cord ensure?

A rapid compensatory response Signup and view all the answers

What is the reticular formation similar in structure and function to?

The intermediate gray matter in the spinal cord Signup and view all the answers

What are some of the functions of neurons within the reticular formation?

Cardiovascular and respiratory control, governance of sensory motor reflexes, the organization of eye movements, regulation of sleep and wakefulness Signup and view all the answers

What is the function of the skeletomotor control by the reticular formation?

Temporal and spatial coordination of movements Signup and view all the answers

The descending motor control pathways from the reticular formation to the spinal cord are similar to those of the vestibular nuclei.

True Signup and view all the answers

What are the motor centers in the reticular formation largely controlled by?

Other motor centers in the cortex or brainstem. Signup and view all the answers

What mechanism does the reticular formation use to stabilize posture during ongoing movements?

Feedforward mechanism Signup and view all the answers

Where do the upper motor neurons in the cerebral cortex reside?

In several adjacent and highly interconnected areas in the frontal lobe Signup and view all the answers

What type of regulatory input do the cortical areas receive?

Regulatory input from the basal ganglia and cerebellum via relays in the ventrolateral thalamus, and inputs from the somatic sensory regions of the parietal lobe Signup and view all the answers

Which cortical layer has the pyramidal cells of the primary motor cortex?

Cortical layer V Signup and view all the answers

What two tracts do the axons of the pyramidal cells descend in?

The corticobulbar and corticospinal tracts Signup and view all the answers

What structure do the tracts pass through before entering the cerebral peduncle?

The internal capsule of the forebrain Signup and view all the answers

Where are the axons located as they pass through the base of the pons?

Scattered among the transverse pontine fibers and nuclei of the pontine gray matter. Signup and view all the answers

Where do the axons coalesce again as they pass through the brainstem?

On the ventral surface of the medulla Signup and view all the answers

What structure do the axons form on the ventral surface of the medulla?

The medullary pyramids Signup and view all the answers

Where do the components of the upper motor neuron pathway that innervate cranial nerve nuclei, the reticular formation, and the red nucleus leave the pathway?

At the appropriate levels of the brainstem Signup and view all the answers

What happens to most of the axons in the pyramidal tract at the caudal end of the medulla?

They decussate to enter the lateral columns of the spinal cord Signup and view all the answers

Where does the lateral corticospinal tract form the direct pathway to the spinal cord?

From the cortex Signup and view all the answers

Where does the lateral corticospinal tract terminate primarily?

In the lateral portions of the ventral horn and intermediate gray matter in the spinal cord Signup and view all the answers

What are the axons that enter the spinal cord without crossing called?

The ventral corticospinal tract Signup and view all the answers

Where do the axons of the ventral corticospinal tract terminate?

Either ipsilaterally or contralaterally Signup and view all the answers

What are the two sources of upper motor neurons in the brainstem that the indirect pathway to lower motor neurons in the spinal cord runs to?

The red nucleus and the reticular formation Signup and view all the answers

Where do the axons to the red nucleus originate?

From the parts of the motor cortex that project to the lateral region of the spinal cord gray matter Signup and view all the answers

Where do the axons to the reticular formation originate?

From the parts of the motor cortex that project to the medial region of the spinal cord gray matter Signup and view all the answers

The premotor cortex is rostral to the primary motor cortex.

True Signup and view all the answers

What are the two components of the premotor region?

The lateral and medial components Signup and view all the answers

What function does the lateral premotor cortex seem to be involved in?

The selection of movements based on external events Signup and view all the answers

What do patients with frontal lobe damage have difficulty learning to do?

Select a particular movement to be performed in response to a visual cue or heard verbal command Signup and view all the answers

What function does the medial premotor cortex mediate?

The selection of movements Signup and view all the answers

What type of cues does the medial premotor cortex appear to be specialized for initiating movements in response to?

Internal cues Signup and view all the answers

What is the effect of injury to the medial premotor area on the number of self-initiated or spontaneous movements?

It reduces the number of self-initiated or spontaneous movements Signup and view all the answers

What ability remains largely intact after injury to the medial premotor area?

The ability to execute movements in response to external cues Signup and view all the answers

What is the main symptom that occurs when upper motor neurons in the motor cortex or descending motor axons in the internal capsule are damaged?

Immediate flaccidity of the muscles on the contralateral side of the body and face. Signup and view all the answers

What term is used to describe the immediate flaccidity that occurs after upper motor neuron injury?

Spinal shock Signup and view all the answers

What is spinal shock a reflection of?

The decreased activity of spinal circuits suddenly deprived of input from the motor cortex and brainstem Signup and view all the answers

Where are the acute manifestations of upper motor neuron injury most severe?

In the arms and legs Signup and view all the answers

What is the typical condition of trunk muscles after upper motor neuron injury?

Control of trunk muscles is preserved Signup and view all the answers

What is the normal response in an adult when the sole of the foot is stroked?

Flexion of the big toe Signup and view all the answers

What is the abnormal plantar reflex seen after damage to descending upper motor neuron pathways called?

The Babinski sign Signup and view all the answers

What is the primary symptom of spasticity?

Increased muscle tone Signup and view all the answers

Spasticity is probably caused by the removal of inhibitory influences exerted by the cortex on the postural centers of the vestibular nuclei and reticular formation.

True Signup and view all the answers

Spasticity can be eliminated by sectioning the dorsal roots.

True Signup and view all the answers

What is another symptom that may occur with spasticity?

Clonus Signup and view all the answers

What happens to the ability to perform fine movements when the lesion involves the descending pathways that control the lower motor neurons to the upper limbs?

The ability to execute fine movements is lost. Signup and view all the answers

What is the effect of damage to the facial motor nucleus or its nerve on the muscles of facial expression?

It affects all the muscles of facial expression on the side of the lesion Signup and view all the answers

What is the effect of unilateral injury to the motor areas in the lateral frontal lobe on facial expression?

Difficulty controlling the contralateral muscles around the mouth but retain the ability to symmetrically raise their eyebrows and wrinkle their forehead. Signup and view all the answers

What is the recent interpretation of the reason why strokes involving the middle cerebral artery spare the superior aspect of the face?

The relevant upper motor neurons are in the cingulum Signup and view all the answers

Superior facial sparing in strokes involving the middle cerebral artery may arise because the cingulate motor area sends descending projections through the corticobulbar pathway that bifurcate and innervate dorsal facial motor cell columns on both sides of the brainstem.

True Signup and view all the answers

What type of paralysis is often associated with an upper motor neuron lesion?

Spastic type of paralysis Signup and view all the answers

Superficial reflexes are often lost in both upper and lower motor neuron lesions.

True Signup and view all the answers

The plantar reflex is present in upper motor neuron lesions.

False Signup and view all the answers

Deep reflexes are often exaggerated in upper motor neuron lesions.

True Signup and view all the answers

Clonus is often present in upper motor neuron lesions.

True Signup and view all the answers

Electrical activity is often normal in upper motor neuron lesions.

True Signup and view all the answers

Groups of muscles are often affected in upper motor neuron lesions.

True Signup and view all the answers

Individual muscles are often affected in lower motor neuron lesions.

True Signup and view all the answers

Fascicular twitch is present in upper motor neuron lesions.

False Signup and view all the answers

Study Notes

Upper Motor Neurons Maintaining Balance and Posture

Vestibular nuclei are upper motor neurons in the brainstem
Projections from vestibular nuclei control axial and proximal limb muscles, using medial and lateral vestibulospinal tracts
Other vestibular nuclei project to cranial nerves (3, 4, and 6) for eye movements during head movement
Direct projections from vestibular nuclei to spinal cord allow rapid compensatory responses to postural instability sensed by inner ear.

Reticular Formation as Upper Motor Neurons

Reticular formation is a complex network in the brainstem
Similar in structure and function to spinal cord's intermediate gray matter
Involved in numerous functions (cardiovascular, respiratory, sensory-motor reflexes, eye movements, sleep-wake cycles)
Reticular formation coordinates movements temporally and spatially.
Descending motor control pathways from reticular formation target gray matter, impacting axial and proximal limb muscles
Reticular formation is controlled by other motor areas (cortex/brainstem) to make adjustments for maintaining posture during movement

Origin of Pyramidal Tract

Upper motor neurons in cerebral cortex initiate complex movements
These cortical areas receive input from basal ganglia, cerebellum, and the parietal lobe's somatic sensory regions
Primary motor cortex (Brodmann's area 4) is in precentral gyrus and has pyramidal cells (Betz cells) as upper motor neurons
Axons descend to brainstem (corticobulbar tract), then spinal cord (corticospinal tract) through internal capsule and cerebral peduncle
Axons run through pons, then form medullary pyramids
Corticobulbar tract innervates cranial nerves, reticular formation, and red nucleus; leaving before reaching the spinal cord

Course of Pyramidal Tract

Most pyramidal tract axons cross (decussate) into lateral corticospinal tract in the caudal medulla then spinal cord
Smaller number of axons enter spinal cord uncrossed, forming ventral corticospinal tract, which targets axial and proximal muscles
Axons project to red nucleus and reticular formation via an indirect pathway

The Premotor Cortex

Lies rostral to primary motor cortex; interconnected frontal lobe areas
Influences motor behaviour through connections with primary motor cortex and directly through corticobulbar/corticospinal pathways
Lateral premotor cortex: involved in selecting movements based on external cues (e.g., visual, auditory)
Medial premotor cortex: involved in selecting movements based on internal cues (self-initiated), reducing spontaneous movement in response to external stimuli

Summary

Two sets of upper motor neurons contribute to brainstem and spinal cord control
One set (reticular formation/vestibular nuclei) controls posture (feedforward/feedback)
Other set (primary motor cortex/premotor areas) controls movement execution/planning
Motor cortex influences movement by direct (corticospinal/corticobulbar) and indirect pathways (via brainstem centers) to lower motor neurons

Damage to Upper Motor Neuron Pathways

Upper motor neuron damage causes symptoms like hypotonia, hyporeflexia and later, signs/symptoms like spasticity, abnormal reflexes (babinski)
Gradual recovery of function generally occurs, but fine motor skills and some reflexes may not return

Patterns of Facial Weakness

Lower motor neuron facial weakness affects all facial muscles on the affected side
Upper motor neuron facial weakness affects contralateral facial muscles below the eyebrows/eyes/forehead, but superior muscles are unaffected

Upper vs Lower Motor Neuron Lesions

Symptoms differ: Upper motor neuron lesions lead to hypertonia/spasticity, whereas lower neuron lesions result in hypotonia/flaccidity
Reflexes (superficial and deep) differ/ abnormalities

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Description

This quiz explores the role of upper motor neurons in maintaining balance and posture, focusing on vestibular nuclei and the reticular formation. Learn how these areas of the brainstem control muscle movements and respond to postural challenges for efficient body positioning and coordination.

Upper Motor Neurons in Balance and Posture

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Podcast

Questions and Answers

What are the two sets of upper motor neurons that control the local circuitry in the brainstem and spinal cord?

What type of control does the reticular formation play in posture?

What type of control does the vestibular nuclei play in posture?

What part of the brain is responsible for movement execution?

What part of the brain is responsible for planning and selecting movements?

What are the two ways that the motor cortex influences movements?

What are the two types of tracts that make up the pyramidal tract?

What are the four types of tracts that make up the extrapyramidal tracts?

The brainstem pathways can independently organize gross motor control.

What are the distal parts of the limbs that are crucial for everyday life?

What are the two groups of muscles that are affected by damage to the descending motor pathways?

Where do the projections from the vestibular nuclei that control axial muscles originate?

Where do the projections from the vestibular nuclei that influence proximal limb muscles originate?

What type of response do direct projections from the vestibular nuclei to the spinal cord ensure?

What is the reticular formation similar in structure and function to?

What are some of the functions of neurons within the reticular formation?

What is the function of the skeletomotor control by the reticular formation?

The descending motor control pathways from the reticular formation to the spinal cord are similar to those of the vestibular nuclei.

What are the motor centers in the reticular formation largely controlled by?

What mechanism does the reticular formation use to stabilize posture during ongoing movements?

Where do the upper motor neurons in the cerebral cortex reside?

What type of regulatory input do the cortical areas receive?

Which cortical layer has the pyramidal cells of the primary motor cortex?

What two tracts do the axons of the pyramidal cells descend in?

What structure do the tracts pass through before entering the cerebral peduncle?

Where are the axons located as they pass through the base of the pons?

Where do the axons coalesce again as they pass through the brainstem?

What structure do the axons form on the ventral surface of the medulla?

Where do the components of the upper motor neuron pathway that innervate cranial nerve nuclei, the reticular formation, and the red nucleus leave the pathway?

What happens to most of the axons in the pyramidal tract at the caudal end of the medulla?

Where does the lateral corticospinal tract form the direct pathway to the spinal cord?

Where does the lateral corticospinal tract terminate primarily?

What are the axons that enter the spinal cord without crossing called?

Where do the axons of the ventral corticospinal tract terminate?

What are the two sources of upper motor neurons in the brainstem that the indirect pathway to lower motor neurons in the spinal cord runs to?

Where do the axons to the red nucleus originate?

Where do the axons to the reticular formation originate?

The premotor cortex is rostral to the primary motor cortex.

What are the two components of the premotor region?

What function does the lateral premotor cortex seem to be involved in?

What do patients with frontal lobe damage have difficulty learning to do?

What function does the medial premotor cortex mediate?

What type of cues does the medial premotor cortex appear to be specialized for initiating movements in response to?

What is the effect of injury to the medial premotor area on the number of self-initiated or spontaneous movements?

What ability remains largely intact after injury to the medial premotor area?

What is the main symptom that occurs when upper motor neurons in the motor cortex or descending motor axons in the internal capsule are damaged?

What term is used to describe the immediate flaccidity that occurs after upper motor neuron injury?

What is spinal shock a reflection of?

Where are the acute manifestations of upper motor neuron injury most severe?

What is the typical condition of trunk muscles after upper motor neuron injury?

What is the normal response in an adult when the sole of the foot is stroked?

What is the abnormal plantar reflex seen after damage to descending upper motor neuron pathways called?

What is the primary symptom of spasticity?

Spasticity is probably caused by the removal of inhibitory influences exerted by the cortex on the postural centers of the vestibular nuclei and reticular formation.

Spasticity can be eliminated by sectioning the dorsal roots.

What is another symptom that may occur with spasticity?

What happens to the ability to perform fine movements when the lesion involves the descending pathways that control the lower motor neurons to the upper limbs?

What is the effect of damage to the facial motor nucleus or its nerve on the muscles of facial expression?

What is the effect of unilateral injury to the motor areas in the lateral frontal lobe on facial expression?

What is the recent interpretation of the reason why strokes involving the middle cerebral artery spare the superior aspect of the face?

Superior facial sparing in strokes involving the middle cerebral artery may arise because the cingulate motor area sends descending projections through the corticobulbar pathway that bifurcate and innervate dorsal facial motor cell columns on both sides of the brainstem.

What type of paralysis is often associated with an upper motor neuron lesion?

Superficial reflexes are often lost in both upper and lower motor neuron lesions.

The plantar reflex is present in upper motor neuron lesions.

Deep reflexes are often exaggerated in upper motor neuron lesions.

Clonus is often present in upper motor neuron lesions.

Electrical activity is often normal in upper motor neuron lesions.

Groups of muscles are often affected in upper motor neuron lesions.

Individual muscles are often affected in lower motor neuron lesions.

Fascicular twitch is present in upper motor neuron lesions.

Study Notes

Upper Motor Neurons Maintaining Balance and Posture

Reticular Formation as Upper Motor Neurons

Origin of Pyramidal Tract

Course of Pyramidal Tract

The Premotor Cortex