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Brain Motor Centers and Pathways
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
The reticulospinal tract, through its two subdivisions, controls the activity of extensor and flexor muscles of the trunk and proximal limbs and plays a prominent role in the regulation of muscle tone, locomotion, and control of posture, particularly in reactive postural adjustments.
Back and central nervous system
Published in Aida Lai, Essential Concepts in Anatomy and Pathology for Undergraduate Revision, 2018
Reticulospinal tract– coordinates posture, fine control of voluntary movement, and spinal reflexes– reticular formation → cross at variable levels → alpha/gamma motor neurons– pontine reticular formation (excites extensor motoneurons)– medullary reticular formation (inhibits extensor motoneurons)
Clinical Management of Spasticity and Contractures in Stroke
Published in Anand D. Pandyan, Hermie J. Hermens, Bernard A. Conway, Neurological Rehabilitation, 2018
Judith F. M. Fleuren, Jaap H. Buurke, Alexander C. H. Geurts
Spasticity is probably the result of an imbalance of inputs from central motor pathways, such as the (cortico-)reticulospinal and other descending pathways, to the interneuronal circuits of the spinal cord. Via corticobulbar tracts, motor areas of the cortex project on the ventromedial reticular formation, the brain stem area where sensory information is being processed (Sheean, 2002). The main supraspinal inhibitory tract arising from the ventromedial reticular formation is the lateral reticulospinal tract, which runs very close to the lateral corticospinal (pyramidal) tract with overlap of their spinal targets (Lemon, 2008). The lateral reticulospinal tract is under facilitatory control of corticobulbar tracts, thereby augmenting the inhibitory drive to the upper and lower limbs in healthy subjects. The main excitatory pathway, also arising in the brainstem, is the medial reticulospinal tract, which facilitates the maintenance of anti-gravity tone in muscles situated around the longitudinal axis of the body. The medial reticulospinal system is, however, not under cortical control. Damage to the corticobulbar fibres – in the cortex or lower down the tract – will thus primarily lead to decreased facilitation of inhibition of limb reflexes at brain stem level. Consequently, (sub)cortical lesions involving the corticobulbar tracts give rise to a net loss of inhibitory control at brain stem level, leading to increased alpha motoneuron excitability at the cervical and lumbar spinal cord levels and, subsequently, increase in limb muscle tone.
Anodal Contralesional tDCS Enhances CST Excitability Bilaterally in an Adolescent with Hemiparetic Cerebral Palsy: A Brief Report
Published in Developmental Neurorehabilitation, 2023
Rodrigo G. Delatorre, Ellen N. Sutter, Samuel T. Nemanich, Linda E. Krach, Gregg Meekins, Timothy Feyma, Bernadette T. Gillick
Our results are similar to and build upon previous work in the adult stroke population. A study by McCambridge and colleagues used anodal tDCS to stimulate the contralesional hemisphere in adults with stroke and found a trend for increased excitability in the paretic (ipsilateral) biceps brachii.24 Furthermore, a recent paper showed that anodal contralesional tDCS can modulate spinal motor networks for controlling arm movement in adults with stroke.20 However, in adult stroke, other ipsilaterally descending pathways, like the reticulospinal tract, may support recovery after unihemispheric injury.25 In this brief report, our findings and prior literature suggest that changes in excitability arose from CST pathways rather than another descending pathway. First, responses were recorded from intrinsic hand muscles necessary for fine motor control, which are primarily innervated by descending fibers in the CST.26 Second, closer inspection of individual MEP traces showed that the ipsilateral and contralateral MEPs were similar in latency (19–21 ms) and morphology (Figure 2). Third, reticulospinal projections, for example, are linked to upper-limb synergies, and these synergies are absent in children with hemiparesis with prenatal injuries.27 Still, because we did not directly measure other pathways in this study, we cannot rule out their contributions to the MEPs.
Split phenomenon of antagonistic muscle groups in amyotrophic lateral sclerosis: relative preservation of flexor muscles
Published in Neurological Research, 2021
Jingwen Liu, Zhili Wang, Dongchao Shen, Xunzhe Yang, Mingsheng Liu, Liying Cui
The pattern of split phenomena in our study is consistent with the weak distribution that occurs as the pyramidal tract is damaged, suggesting that pyramidal tract impairment due to UMN lesions may play a role to some extent. Besides the corticospinal tract, there are other indirect pathways, including the reticulospinal tract and the rubrospinal tract that control movement [24]. Experiments with macaques confirmed that after lesioning the corticospinal tract, the connection strength from the brainstem to motor neurons (probably due primarily to the reticulospinal tract) that innervate the forearm flexors is increased significantly, but the path innervating the forearm extensors does not change. This imbalance reflects the phenomenon that the extensor is weaker than the flexor following pyramidal tract lesioning [25]. For example, the flexor predominates over the extensor in patients during the recovery phase after stroke. Moreover, the lower limb is typically held in extension with predominant plantar flexion at the ankle following UMN injury, which makes the patient appear as the foot drop posture (a common symptom of ALS) [10]. In ALS, when both UMN and LMN degeneration is observed, and the split phenomenon appears, the flexor was stronger than the extensor, which conforms to the general manifestation of cortical motor neuron pathway damage.
The comparison of recovery patterns between ischemic spinal cord injury and traumatic spinal cord injury from acute to chronic phase
Published in The Journal of Spinal Cord Medicine, 2021
Jin Young Ko, Hyunsu Choi, Jee Hyun Suh, Kyung Seok Park, Joon Woo Lee, Ju Seok Ryu
With respect to bladder dysfunction, the ISCI group had a significantly worse bladder function than the TSCI group at each time point. The ISCI group showed a similar recovery pattern to the TSCI group, considering the time-and-group interaction, so that the earlier worse function was maintained until the outpatient follow-up period (Table 5, Figure 4). We found a significant improvement in the late phase in the ISCI group, as in previous studies.7 In previous studies, 86% needed a catheter for voiding initially. However, at the outpatient follow-up, those needing a catheter decreased to 45.1%.7,18 Our study obtained similar figures; 85.2% of ISCI patients needed a catheter at admission, and by the final follow-up, only 50.0% used a catheter (Table 5). The reason for the more severe bladder dysfunction in the ISCI group is may be related to the different location of the lesion in the spinal cord compared with the TSCI group. Ischemic injury involves the anterior two-thirds of the spinal cord3,4; contrastingly, traumatic spinal cord injury tends to involve the central cord first8–10. Descending tracts that are involved in detrusor and sphincter function are located in the anterolateral white matter of the spinal cord. This pathway is known to be a part of or an adjacent structure to the lateral reticulospinal tract, located anterior to the lateral corticospinal tract.19–21 Our results seem to contribute to the understanding of the natural course of neurologic and bladder impairments. In addition, these results can be used to estimate the prognosis and establish a treatment plan for patients with ISCI.