Podcast
Questions and Answers
Which of the following structures does the corticospinal tract pass through in the midbrain?
Which of the following structures does the corticospinal tract pass through in the midbrain?
Which of these is a characteristic of the anterior limb of the internal capsule?
Which of these is a characteristic of the anterior limb of the internal capsule?
What does the term "somatotopic distribution" refer to in relation to upper motor neurons?
What does the term "somatotopic distribution" refer to in relation to upper motor neurons?
What is the function of the corona radiata?
What is the function of the corona radiata?
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Where are upper motor neurons primarily located?
Where are upper motor neurons primarily located?
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What is the location of the pyramids in the central nervous system?
What is the location of the pyramids in the central nervous system?
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Which of the following statements about corticospinal tracts is true?
Which of the following statements about corticospinal tracts is true?
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What is the name of the structure that connects the thalamus and the basal nuclei in the brain?
What is the name of the structure that connects the thalamus and the basal nuclei in the brain?
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What percentage of fibers decussate at the pyramidal decussation to form the lateral corticospinal tract?
What percentage of fibers decussate at the pyramidal decussation to form the lateral corticospinal tract?
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Where do the fibers of the anterior corticospinal tract synapse?
Where do the fibers of the anterior corticospinal tract synapse?
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Which tract is responsible for controlling gait and posture?
Which tract is responsible for controlling gait and posture?
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Which of the following motor tracts begins in the midbrain from the red nucleus?
Which of the following motor tracts begins in the midbrain from the red nucleus?
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How are the axons arranged in the lateral corticospinal tract with respect to their target areas?
How are the axons arranged in the lateral corticospinal tract with respect to their target areas?
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Study Notes
Motor Tracts
- Motor tracts are pathways that transmit signals from the cerebral cortex to the spinal cord controlling contralateral movement
- These tracts are influenced by feedback loops involving basal nuclei, cerebellum, thalamus, and pons
- Motor tracts involve two types of neurons: upper motor neurons (UMN) and lower motor neurons (LMN)
- UMNs originate in the cortex and project to the spinal cord
- LMNs originate in the spinal cord and project to muscles
- Motor tracts run in either lateral or anterior white columns of the spinal cord
- Key tracts include the lateral corticospinal tract and anterior corticospinal tract
Upper Motor Neurons
- Originate primarily in the primary motor cortex and sometimes in the premotor area
- Arranged in a somatotopic distribution (organized according to the body part they control)
- Large pyramidal neurons located in layer V of the cerebral cortex
Upper Motor Neuron Axons in the Cerebrum
- Axons leave the cortex and enter the corona radiata (radiating crown)
- The corona radiata contains axons ascending or descending from the cortex, sometimes also known as projection fibers
- Axons in the corona radiata form the internal capsule as they pass between the thalami and basal nuclei
- The internal capsule has distinct sections: anterior limb, genu, and posterior limb
Internal Capsule
- Maintains the somatotopic organization of the motor tracts (e.g. leg, trunk, arm, face representation)
Motor Tracts in the Midbrain
- Corticospinal tracts condense in midbrain, becoming the crus cerebri
- Situated anterior to the substantia nigra
Motor Tracts in the Pons
- Corticospinal fibers descend from the crus cerebri and pass through the basilar portion of the pons
Motor Tracts in the Medulla Oblongata
- Corticospinal fibers converge in the pons and form pyramids
- Most fibers (85%) decussate (cross over) at the pyramidal decussation, becoming lateral corticospinal tract
- Remaining 15% become the anterior corticospinal tract
Motor Tracts in the Spinal Cord
- Anterior corticospinal tracts descend through anterior white columns
- They synapse with lower motor neurons (LMNs), controlling trunk and girdle muscles (ipsilateral and contralateral)
- Lateral corticospinal tracts descend through contralateral lateral white columns
- They synapse with LMNs, controlling musculature
- Both tracts show somatotopic organization, with distal upper extremity axons centralized relative to lower extremity neurons
Other Motor Tracts
- Corticobulbar tract: parallels the corticospinal tract but only reaches the brainstem, controlling head & neck muscles
- Rubrospinal tract: originates in midbrain's red nucleus, controlling contralateral muscles
- Tectospinal tract: originates in superior colliculus, controlling head and eye movements
- Vestibulospinal tract: originates in brainstem vestibular nuclei, positioning head and neck/maintaining balance
- Reticulospinal tract: originates in reticular formation, controlling gait and posture
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Description
This quiz explores the key concepts of motor tracts and upper motor neurons, detailing their pathways and functions. Learn about their roles in controlling movement and the feedback loops involved in signal transmission. Understand the structure and organization of upper motor neurons within the cerebral cortex.
