Pyramidal Tract and Motor Homunculus
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Questions and Answers

What is the primary function of the pyramidal tract?

  • Control of involuntary movements
  • Transmission of sensory information
  • Regulation of blood pressure
  • Control of voluntary, discrete, skilled movements (correct)

    • Where do the fibers of the pyramidal tract pass through?

  • Pons
  • Cerebral cortex
  • Cerebellum
  • Medullary pyramids (correct)

    • What is the term 'somatotopic' referring to in the context of the motor homunculus?

  • A type of brainstem structure
  • A representation of the body on the cortex (correct)
  • A type of neuron
  • A type of muscle fiber

    • Which area of the motor homunculus is responsible for controlling the tongue and larynx?

    <p>Lateral portion to the Sylvian fissure</p> Signup and view all the answers

    What is the term for the collective areas from which the pyramidal tract fibers arise?

    <p>Sensorimotor cortex</p> Signup and view all the answers

    What is the function of the neurons in the dorsolateral area of the motor homunculus?

    <p>Control of fingers and hands</p> Signup and view all the answers

    How many areas contribute to the origin of the pyramidal tract fibers?

    <p>3</p> Signup and view all the answers

    What is the arrangement of CST fibers in the internal capsule?

    <p>Fibers follow a somatotopic arrangement, with upper limb fibers anteriorly and lower extremity fibers posteriorly</p> Signup and view all the answers

    What percentage of anterior CST fibers are uncrossed?

    <p>10-15%</p> Signup and view all the answers

    Where do the lateral CST fibers terminate?

    <p>In the anterior gray column of all spinal cord segments</p> Signup and view all the answers

    What is the result of lesions within the cerebral cortex above the pyramidal decussations?

    <p>Contralateral regions are affected</p> Signup and view all the answers

    What is the characteristic of the pyramidal tract?

    <p>It is a crossed tract</p> Signup and view all the answers

    Where do the anterior CST fibers eventually cross?

    <p>Before terminating on the anterior horn cells of the cervical and upper thoracic spinal cord segments</p> Signup and view all the answers

    What is the location of the pyramidal decussation?

    <p>At the caudal medulla</p> Signup and view all the answers

    What is the primary region of termination for pyramidal tract fibers?

    <p>Cervical spinal levels</p> Signup and view all the answers

    What is the role of corticospinal tracts in voluntary movements?

    <p>They form a pathway that confers speed and agility to voluntary movements</p> Signup and view all the answers

    What is the effect of a lesion on the upper motor neuron (UMN)?

    <p>Causes contralateral defects</p> Signup and view all the answers

    What is the effect of a lesion on the lower motor neuron (LMN)?

    <p>Causes ipsilateral defects</p> Signup and view all the answers

    Which type of tracts are inhibitory?

    <p>Extrapyramidal tracts</p> Signup and view all the answers

    What is the role of impulses from the pyramidal tract in muscle tone?

    <p>Increase muscle tone</p> Signup and view all the answers

    Which of the following tracts is responsible for maintenance of upright posture and balance?

    <p>Lateral vestibulospinal tract</p> Signup and view all the answers

    What type of motor neurons are innervated by the lateral vestibulospinal tract in the cervical and lumbosacral levels?

    <p>Alpha and gamma motor neurons</p> Signup and view all the answers

    Where do the fibers of the lateral vestibulospinal tract terminate?

    <p>Rexed laminae VII and VIII</p> Signup and view all the answers

    What is the characteristic of the fibers of the pontine reticulospinal tract?

    <p>They are almost entirely ipsilateral and descend in the anterior funiculus</p> Signup and view all the answers

    Which of the following tracts is longer than the medial vestibulospinal tract?

    <p>Lateral vestibulospinal tract</p> Signup and view all the answers

    What is the primary function of the neurons excited by the lateral vestibulospinal tract?

    <p>Innervating the muscles of the back and neck</p> Signup and view all the answers

    What is the necessary position to maintain balance, according to the lateral vestibulospinal tract function?

    <p>Extension</p> Signup and view all the answers

    Which part of the body is affected by a lesion in the lateral funiculus of the RIGHT cervical spinal cord?

    <p>RIGHT arm</p> Signup and view all the answers

    What is the characteristic of a Lower Motor Neuron Lesion?

    <p>Flaccidity</p> Signup and view all the answers

    A patient with a lesion involving the dorsolateral portion of the LEFT sensorimotor cortex will present with weakness of which of the following?

    <p>RIGHT arm</p> Signup and view all the answers

    What is the characteristic of a fasciculation?

    <p>Slow destruction of the anterior horn cells</p> Signup and view all the answers

    Which of the following is a manifestation of an Upper Motor Neuron Lesion?

    <p>Clonus</p> Signup and view all the answers

    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?

    <p>LEFT leg</p> Signup and view all the answers

    Which of the following is NOT a manifestation of a Lower Motor Neuron Lesion?

    <p>Babinski</p> Signup and view all the answers

    A lesion in the anterior horn cells will result in which of the following?

    <p>Lower Motor Neuron Lesion</p> Signup and view all the answers

    What is the result of a lesion in the RIGHT cervical spinal cord affecting the descending tracts?

    <p>Weakness of the RIGHT arm</p> Signup and view all the answers

    Which of the following is a characteristic of the corticospinal tract?

    <p>Carries motor information from the brain to the periphery</p> Signup and view all the answers

    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.

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