Podcast
Questions and Answers
What is the primary role of upper motor neurons (UMNs) in motor pathways?
What is the primary role of upper motor neurons (UMNs) in motor pathways?
- Producing the neurotransmitters required for muscle contraction.
- Directly innervating skeletal muscles.
- Regulating autonomic nervous system activity.
- Controlling the function of lower motor neurons (LMNs). (correct)
- Relaying sensory information to the brain.
Where are the cell bodies of lower motor neurons (LMNs) that innervate the trunk and limbs located?
Where are the cell bodies of lower motor neurons (LMNs) that innervate the trunk and limbs located?
- Ventral root ganglia.
- Dorsal root ganglia.
- Lateral horn of the spinal cord.
- Posterior horn of the spinal cord.
- Anterior horn of the spinal cord. (correct)
Which of the following describes the somatotopic organization of lower motor neurons (LMNs) in the anterior horn of the spinal cord?
Which of the following describes the somatotopic organization of lower motor neurons (LMNs) in the anterior horn of the spinal cord?
- The somatotopic organisation changes randomly.
- Proximal limb muscles are represented medially, while distal limb muscles are represented laterally. (correct)
- Distal limb muscles are represented medially, while proximal limb muscles are represented laterally.
- Trunk muscles are represented dorsally, while limb muscles are represented ventrally.
- LMNs are organized randomly with no specific somatotopic arrangement.
What is the role of supraspinal centers in the regulation of lower motor neurons (LMNs)?
What is the role of supraspinal centers in the regulation of lower motor neurons (LMNs)?
Which of the following is a characteristic of upper motor neuron (UMN) pathways?
Which of the following is a characteristic of upper motor neuron (UMN) pathways?
Which motor pathway is responsible for voluntary movements?
Which motor pathway is responsible for voluntary movements?
The cell bodies of the LMN of muscles innervated by cranial nerves are located in the...
The cell bodies of the LMN of muscles innervated by cranial nerves are located in the...
Which of the following most accurately describes the function of the lateral corticospinal tract?
Which of the following most accurately describes the function of the lateral corticospinal tract?
After a stroke, a patient exhibits increased tone in extensor muscles of the upper and lower limbs. This is most likely due to damage to which of the following?
After a stroke, a patient exhibits increased tone in extensor muscles of the upper and lower limbs. This is most likely due to damage to which of the following?
A lesion in the internal capsule affects the posterior limb. This lesion would most likely impact what?
A lesion in the internal capsule affects the posterior limb. This lesion would most likely impact what?
Which of the following is a sign of lower motor neuron lesions?
Which of the following is a sign of lower motor neuron lesions?
The anterior corticospinal tract is distinguished from the lateral corticospinal tract by?
The anterior corticospinal tract is distinguished from the lateral corticospinal tract by?
Following a spinal cord injury, a patient exhibits paralysis and loss of fine motor control in the left arm and leg. Sensation is mostly intact. Lesion most likely affects which of the following?
Following a spinal cord injury, a patient exhibits paralysis and loss of fine motor control in the left arm and leg. Sensation is mostly intact. Lesion most likely affects which of the following?
What is the result of a complete lesion of the spinal cord?
What is the result of a complete lesion of the spinal cord?
A patient presents with weakness in proximal muscles of both arms and legs, but normal strength in the hands and feet. Sensation is intact. In which spinal cord tract is the lesion MOST likely to be found?
A patient presents with weakness in proximal muscles of both arms and legs, but normal strength in the hands and feet. Sensation is intact. In which spinal cord tract is the lesion MOST likely to be found?
If a patient exhibits deficits in posture and balance, which descending motor pathway is MOST likely involved?
If a patient exhibits deficits in posture and balance, which descending motor pathway is MOST likely involved?
What is the function of the rubrospinal tract?
What is the function of the rubrospinal tract?
Decorticate posture, characterized by flexion of the upper limbs and extension of the lower limbs, suggests a lesion where?
Decorticate posture, characterized by flexion of the upper limbs and extension of the lower limbs, suggests a lesion where?
Which of the following cranial nerves is NOT involved in innervating muscles of the head and neck?
Which of the following cranial nerves is NOT involved in innervating muscles of the head and neck?
The tectospinal tract is primarily associated with:
The tectospinal tract is primarily associated with:
In somatotopic organization of the lateral corticospinal tract in the spinal cord, where are the upper limb neurons located relative to the lower limb neurons?
In somatotopic organization of the lateral corticospinal tract in the spinal cord, where are the upper limb neurons located relative to the lower limb neurons?
What is the functional consequence of the anterior corticospinal tract NOT decussating in the medulla?
What is the functional consequence of the anterior corticospinal tract NOT decussating in the medulla?
Which of the following best represents the pathway for voluntary motor control, beginning in the cerebral cortex and ending with muscle contraction?
Which of the following best represents the pathway for voluntary motor control, beginning in the cerebral cortex and ending with muscle contraction?
In a rare neurological condition, damage occurs precisely at the decussation of the pyramids. What specific motor deficit would be expected?
In a rare neurological condition, damage occurs precisely at the decussation of the pyramids. What specific motor deficit would be expected?
Flashcards
What are Lower Motor Neurons (LMNs)?
What are Lower Motor Neurons (LMNs)?
Neurons that control skeletal muscles through cranial and spinal nerves.
What are Upper Motor Neurons (UMNs)?
What are Upper Motor Neurons (UMNs)?
Neurons that regulate LMN activity. They originate in the brainstem and cerebral cortex.
How do cranial and spinal nerves relate to LMNs?
How do cranial and spinal nerves relate to LMNs?
Cranial nerves innervate head and neck muscles. Spinal nerves innervate trunk and limb muscles.
Where are LMNs located in the spinal cord?
Where are LMNs located in the spinal cord?
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Where do UMNs originate?
Where do UMNs originate?
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What are the types of UMN origin?
What are the types of UMN origin?
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What structures indirectly control LMNs?
What structures indirectly control LMNs?
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What does the Lateral Corticospinal Tract (LCST) control?
What does the Lateral Corticospinal Tract (LCST) control?
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What does the Anterior Corticospinal Tract (ACST) control?
What does the Anterior Corticospinal Tract (ACST) control?
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Where does decussation occur in the LCST?
Where does decussation occur in the LCST?
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What is the LCST Pathway?
What is the LCST Pathway?
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Why dual cortical innervation for trunk/proximal limbs?
Why dual cortical innervation for trunk/proximal limbs?
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What type of movement deficit is caused by a unilateral LCST lesion?
What type of movement deficit is caused by a unilateral LCST lesion?
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What is the result of lesion above posterior limb internal capsule?
What is the result of lesion above posterior limb internal capsule?
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Study Notes
Clinical Neuroanatomy of Motor Disorders: Motor Pathways
- The main anatomical pathways, key regions, and functions related to voluntary movements and motor control are discussed
Objectives
- The main anatomical pathways responsible for voluntary movements are understood
- UMN (Upper Motor Neuron) and LMN (Lower Motor Neuron) roles are clear
- The anatomical regions associated with motor pathways are understood
- Motor dysfunction's anatomical basis can be explained
- Signs of LMN vs. UMN lesions are understood and can be localized
- A general understanding about movement control is developed
Motor Pathways
- The motor pathway consists of 2 sets of neurons: UMN and LMN
- The motor pathway is responsible for control of skeletal muscles for voluntary movements and control of balance and posture
- UMNs control the LMN function
- LMNs directly innervate the skeletal muscles and is the final common pathway
Lower Motor Neurons
- Cranial motor nerves innervate the skeletal muscles of the head and neck
- Spinal motor nerves innervate the trunk and limbs
Location of LMN in Spinal Cord
- The cell bodies of LMN for spinally innervated muscles are in the anterior horn
- Cell bodies of distal limb muscles are placed laterally
- Lower limb UMNs are located more peripherally
- Proximal limb and trunk muscles are placed medially
Arrangement of LMN of Cranial Nerves in Brainstem
- LMN cell bodies for muscles innervated by cranial nerves are in the motor nuclei of respective cranial nerves
- Midbrain cranial nerve nuclei contain the oculomotor and trochlear nuclei
- The pons contains the trigeminal motor nucleus and the superior oblique
- The medulla contains the hypoglossal nucleus and the nucleus ambiguus which are involved in swallowing and speech
Regulation of LMN
- LMNs are controlled by supraspinal centers with upper motor neurons
- Direct control includes:
- Brainstem level for posture and muscle tone control
- Cerebral cortex level for voluntary movements
- Indirect control includes:
- Basal ganglia for planning, supervision, and regulation
- Cerebellum for coordination
Upper Motor Neurons
- UMNs start from any supraspinal centers
- Multiple UMNs innervate the LMNs
- Primary motor cortex has Pyramidal pathways for voluntary movements
- Upper limb UMNs are located more centrally
- Brainstem Nuclei have Non-Pyramidal pathways
- These UMNs constitute the motor pathways
Motor Pathways – UMN – Non-Pyramidal / Extrapyramidal
- Non-Pyramidal pathways start from:
- Red Nucleus which carries the Rubrospinal pathway
- Vestibular Nucleus which carries the Vestibulospinal pathway
- Reticular Nucleus which carries the Reticulospinal pathway, influences the lower motor system, important for posture, balance and extensor tone, and is located in the brainstem
- Tectal Nucleus which carries the Tectospinal pathway and is for head and eye movement
Loss of Cortical Inhibition on Non-Pyramidal Pathways
- Decorticate posture: this is rigidity that results from lesions above the midbrain
- Both Rubrospinal and Vestibulospinal pathways are intact which increases tone and flexion, with increased flexion and extension in lower limbs
- Decerebrate posture: this is rigidity resulting from lesions in the lower midbrain or upper pons where Rubrospinal pathways are not intact which means legs are extended, toes are pointed away from the body and turned inward, arms are tensed, and rotated inward
Motor Pathways – UMN – Pyramidal
- Pyramidal pathways have voluntary movements
- Upper Motor Neurons terminate in the brainstem (cortical bulbar) or spinal cord (cortical spinal fibers)
- Structures include:
- Primary Motor Cortex
- Corticobulbar Pathway from cortical areas through the midbrain
- Lateral Corticospinal Pwy
- Anterior Corticospinal Pwy
- Lower Motor Neurons
Lateral Cortico-Spinal Pathway (LCSP)
- LCSP innervates distal limb muscles and controls skilled/fine movements
- LCSP starts in the UL and LL region of the motor cortex and goes through the corona radiata -> posterior limb of the internal capsule -> passes the cerebral peduncle ->anterior pons --> medullary pyramid and decussates and runs into the lateral white column of the spinal cord before synapsing with a LMN
- UL muscle axons descends to the cervical region and LL muscles descend to the lumbosacral spine
Lateral Cortico-Spinal Pathway (LCSP) - Lesions
- Medial aspect of primary motor deficit cortical area lesions on the right will result in upper motor paralysis of the left -- right side of fibers controlling the left side
- A lesion above the posterior limb of the internal capsule causes damage to cortical spinal fibers and upper MN paralysis
- disrupt motor signals to lower motor neuron paralysis on left side causes motor weakness below
Anterior Cortico-Spinal Pathway (ACSP)
- The ACSP innervates axial/trunk muscles and proximal limb girdle muscles to help to maintain posture
- The pathway starts in the trunk region of M1 --> passes through corona radiata -> posterior limb of internal capsule -> cerebral peduncle --> anterior pons -> medullary pyramid --> before passing into the anterior white column without decussating
- Anterior corticospinal tract are uncrossed - each segment, cross and synapse to contralateral side
- Dual cortical innervation is received by the trunk and proximal limb muscles because at each spinal segment the ACSP neurons synapse with LMN supplying ipsilateral and contralateral trunk and proximal limb muscles
Anterior Cortico-Spinal Pathway (ACSP) - Lesions
- Lesions on the left mean motor weakness on the right, contralateral. This affects axial and proximal muscles and leads to complete paralysis of axial and proximal sides bilaterally
Location of Motor Pathways in Spinal Cord
- The ventral corticospinal tract is a descending tract located in the ventral white commissure
- The lateral corticospinal tract and rubrospinal tract are also descending tracts
Somatotopic Organization of Lateral Corticospinal Pathway in Spinal Cord
- Motor pathway neurons (UMN) for LL are located more peripherally, while Upper limb UMNS are located more centrally
- Central lesions -> Sacral sparing (less LL muscle involvement)
- Similar to main sensory pathways
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