Descending Spinal Tracts

Question 1

Tectospinal Tract

Answer 1

• Medial UMN Tract
• Postural control and Gross motor movements. Coordinates head and eye Turns head toward visual/auditory stimulus. innervates mm on other side, contralateral to origin.
• 1. starts in superior colliculus in midbrain. Crosses SC immediately.
• 2. synapses in ventral horn with lower motor neurons that control cervical muscles.

Question 2

Medial (Pontine) Reticulospinal Tract

Answer 2

• Medial UMN Tract
  • Responsible for: controlling axial and extensor motor neurons e.g enable extension of the legs to maintain postural support. refine voluntary movement by preventing unnecessary contractions (inhibitory effect on stretch reflexes. Control muscle tone and muscle reflex activity. role in maintaining balance and making postural adjustments.
  • facilitate extensors and inhibit flexors.
  • 1. starts in reticular formation in pons, descends ipsilaterally through anterior funiculus in SC.
  • 2. synapses at all levels of SC in medial ventral horn, terminates in alpha and gamma MNs.

Question 3

Lateral (Medullary) Reticulospinal Tract

Answer 3

• Medial UMN Tract
  • Facilitates flexors of extremities and inhibits extension of extremities.
  • Modulation of the stretch reflex. Control muscle tone and muscle reflex activity. role in maintaining balance and making postural adjustments.
  • 1. starts in reticular formation of medulla, descends bilaterally. Predominantly ipsilateral control. Majority of fibers do not cross and descend in the anterior funiculus of SC.
  • 2. synapses at all levels of SC in dorsal side of the ventral horn, terminates on alpha and gamma MNs.

Question 4

Lateral Vestibulospinal Tract

Answer 4

• Medial UMN Tract
  • Receives information from vestibular apparatus in regards to gravity. facilitates extensors and inhibits flexors for trunk and lower extremity control. when a person is upright this tract is continuously working to maintain center of mass over base of support – very sensitive
  • 1. originates in lateral vestibular nucleus in lower pons and upper medulla. Descends through anterior funiculus.
  • 2. synapses in medial ventral horn of thoracic and lumbar levels. Ipsillateral input to LMNs.

Question 5

Medial Vestibulospinal Tract

Answer 5

• Medial UMN Tract
  • Affect activity of MNs that control neck and upper back musculature. Bilateral segments. Most do not cross.
  • 1. originates in medial and inferior vestibular nucleus in lower pons/upper medulla. Runs with the medial longitudinal fasciculus.
  • 2. synapse with MNs in ventral horn of cervical and thoracic segments.

Question 6

Medial (anterior) Corticospinal Tract

Answer 6

• Medial UMN Tract
  • Convey information to lower motor neurons that control axial mm: neck, shoulder, and proximal trunk muscles. Prepares motor system to respond to perturbations (postural adjustments). influence the motor neurons innervating the muscles of the upper extremities and neck. involved in motor control of proximal muscles
  • 1. starts in cortex, descends through internal capsule and anterior brainstem. Fibers cross the anterior spinal commissure of SC.
  • 2. synapses with LMNs on ventral horn of SC only in the cervical and thoracic SC (does not reach lumbar).

Question 7

Lateral Corticospinal Tract

Answer 7

• Lateral UPN Tract
  • Control limb function and fine motor control. Allows for Fractionation of movement, the ability to isolate individual muscles independently
  • 1. starts in primary motor cortex through internal capsule and cerebral peduncles, runs through the lateral midbrain, medial pons and medulla and crosses midline at the pyramids of the lower medulla.
  • 2. synapses in lateral ventral horn of SC with LMNs. (fibers to the UEs are more medial, fibers to the LEs are more lateral)

Question 8

Rubrospinal Tract

Answer 8

• Lateral UMN Tract
  • Primary role is with control of Mm tone: Facilitate flexion of neck, trunk and inhibit extension. May facilitate flexion of upper limb muscles and inhibition of extensors during gait.Very strong modulator if tone - affects force, velocity and direction of movement
  • 1. originates in red nucleus in midbrain, crosses immediately. Starts medially then migrates laterally as it runs down brainstem and into SC.
  • Synapses with LMNs within cervical and thoracic cord which control upper limb flexion.

Question 9

Corticobulbar Spinal Tract

Answer 9

-Lateral Upper Motor Neuron Tract
-Extension of the Corticospinal Tract
• Voluntary control muscles of the face, tongue, larynx, pharynx, and SCM/traps. Lower face is controlled by contralateral fibers, upper face controlled by both fibers that do cross and do not cross (bilaterally).
• 1. starts in motor cortex, travels to cranial nerve nuclei in brainstem.
• 2. synapse on motor nuclei of CNs V, VII, X, XI, and XII in the brainstem. LMNs carry efferent signals to muscles in the face, head, and neck. Some fibers cross in medulla.