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Questions and Answers
What is the primary function of the pyramidal tract?
Where do the fibers of the pyramidal tract pass through?
What is the term 'somatotopic' referring to in the context of the motor homunculus?
Which area of the motor homunculus is responsible for controlling the tongue and larynx?
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What is the term for the collective areas from which the pyramidal tract fibers arise?
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What is the function of the neurons in the dorsolateral area of the motor homunculus?
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How many areas contribute to the origin of the pyramidal tract fibers?
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What is the arrangement of CST fibers in the internal capsule?
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What percentage of anterior CST fibers are uncrossed?
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Where do the lateral CST fibers terminate?
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What is the result of lesions within the cerebral cortex above the pyramidal decussations?
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What is the characteristic of the pyramidal tract?
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Where do the anterior CST fibers eventually cross?
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What is the location of the pyramidal decussation?
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What is the primary region of termination for pyramidal tract fibers?
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What is the role of corticospinal tracts in voluntary movements?
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What is the effect of a lesion on the upper motor neuron (UMN)?
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What is the effect of a lesion on the lower motor neuron (LMN)?
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Which type of tracts are inhibitory?
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What is the role of impulses from the pyramidal tract in muscle tone?
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Which of the following tracts is responsible for maintenance of upright posture and balance?
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What type of motor neurons are innervated by the lateral vestibulospinal tract in the cervical and lumbosacral levels?
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Where do the fibers of the lateral vestibulospinal tract terminate?
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What is the characteristic of the fibers of the pontine reticulospinal tract?
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Which of the following tracts is longer than the medial vestibulospinal tract?
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What is the primary function of the neurons excited by the lateral vestibulospinal tract?
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What is the necessary position to maintain balance, according to the lateral vestibulospinal tract function?
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Which part of the body is affected by a lesion in the lateral funiculus of the RIGHT cervical spinal cord?
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What is the characteristic of a Lower Motor Neuron Lesion?
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A patient with a lesion involving the dorsolateral portion of the LEFT sensorimotor cortex will present with weakness of which of the following?
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What is the characteristic of a fasciculation?
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Which of the following is a manifestation of an Upper Motor Neuron Lesion?
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A patient with a lesion of the LEFT lateral funiculus of the lumbar segment of the spinal cord will present with weakness of which of the following?
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Which of the following is NOT a manifestation of a Lower Motor Neuron Lesion?
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A lesion in the anterior horn cells will result in which of the following?
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What is the result of a lesion in the RIGHT cervical spinal cord affecting the descending tracts?
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Which of the following is a characteristic of the corticospinal tract?
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Study Notes
Pyramid Tract Overview
- The pyramid tract is the longest and largest descending fiber tract in the human CNS.
- It is concerned with voluntary, discrete, and skilled movements.
- It controls muscles involved in speech and vocalization.
- Fibers pass through the medullary pyramids, located in the upper medulla.
Motor Homunculus
- The motor homunculus is a somatotopic representation of the body on the primary motor and premotor cortex.
- Each part of the body is represented on each portion of the primary and premotor cortex.
- The area at the lowest lateral portion to the Sylvian fissure features neurons for the tongue and larynx.
- The ventral part represents the face and lips, while the dorsolateral part represents the fingers and hands.
- The superior part represents the arms and trunk, and the medial part represents the arms, trunk, perineal muscles, and feet.
Origin of the Tract Fibers
- Fibers arise from the sensorimotor cortex, which includes three areas.
- The three areas constitute the sensorimotor cortex, which gives rise to the pyramidal tract.
Parts of the Internal Capsule
- The internal capsule has three parts: anterior limb, genu, and posterior limb.
- The posterior limb is where the corticospinal tract (CST) fibers would pass through.
- Fibers follow a somatotopic arrangement, with anterior fibers controlling the upper limbs and posterior fibers controlling the lower extremities.
Pyramidal Tract Fiber Distribution
- Pyramidal tract fibers terminate mostly on cervical spinal levels.
- This allows for better motor control in the upper extremities.
- Corticospinal tracts are not the sole pathways for voluntary movements.
- They form a pathway that confers speed and agility to voluntary movements.
- They contribute more to controlling prime mover muscles, while other tracts control simple basic movements.
Termination of Pyramidal Tract Fibers
- 55% of pyramidal tract fibers terminate on cervical spinal levels.
- 20% terminate on thoracic spinal levels.
- 25% terminate on lumbar and sacral spinal levels.
Points to Remember
- Extrapyramidal tracts are inhibitory and flexor.
- Pyramidal tracts are excitatory and extensor.
- Pyramidal tracts increase muscle tone and initiate impulses to skeletal muscles.
Upper and Lower Motor Neurons
- Upper motor neurons (UMNs) transmit signals from the brain to the spinal cord.
- Lower motor neurons (LMNs) transmit signals from the spinal cord to muscles.
- UMN lesion causes contralateral defects.
- LMN lesion causes ipsilateral defects.
Reticulospinal Tracts
- The lateral vestibular nucleus is the origin of the reticulospinal tract.
- The tract is uncrossed and descends in the anterolateral funiculus of the spinal cord.
- It terminates on Rexed laminae VII and VIII.
- It functions to maintain upright posture and balance by exciting extensor motor neurons.
Pontine (Medial) Reticulospinal Tract
- The pontine reticulospinal tract is almost entirely ipsilateral.
- It descends chiefly in the anterior funiculus of the spinal cord.
- It terminates on Rexed laminae VII and VIII.
Lesions
- A lesion in the lateral funiculus of the spinal cord affects the descending tracts and produces weakness on the same side.
- A lesion in the sensorimotor cortex affects the contralateral side.
- Fasciculations are seen in cases where there is slow destruction of the anterior horn cells, which is a characteristic of LMN lesions.
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Description
This quiz covers the pyramidal tract, its function in controlling voluntary movements and speech, and the concept of motor homunculus. Test your knowledge of the human central nervous system and its role in muscular control.
