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Postgraduate Medical Journal Nov 1995The plantar response is a reflex that involves not only the toes, but all muscles that shorten the leg. In the newborn the synergy is brisk, involving all flexor muscles...
The plantar response is a reflex that involves not only the toes, but all muscles that shorten the leg. In the newborn the synergy is brisk, involving all flexor muscles of the leg; these include the toe 'extensors', which also shorten the leg on contraction and therefore are flexors in a physiological sense. As the nervous system matures and the pyramidal tract gains more control over spinal motoneurones the flexion synergy becomes less brisk, and the toe 'extensors' are no longer part of it. The toes then often go down instead of up, as a result of a segmental reflex involving the small foot muscles and the overlying skin, comparable to the abdominal reflexes. With lesions of the pyramidal system, structural or functional, this segmental, downward response of the toes disappears, the flexion synergy may become disinhibited and the extensor hallucis longus muscle is again recruited into the flexion reflex of the leg: the sign of Babinski. A true Babinski sign denotes dysfunction of the pyramidal tract, and should be clearly distinguished from upgoing toes that do not belong to the flexion synergy of the leg. Correct interpretation of the plantar response depends only to a minor degree on the method or site of stimulation of the foot. It is therefore most important to assess the response in the entire leg.
Topics: Humans; Muscle Contraction; Physical Stimulation; Pyramidal Tracts; Reflex, Babinski; Spinal Cord Diseases
PubMed: 7494766
DOI: 10.1136/pgmj.71.841.645 -
Journal of Neurophysiology Sep 2014Small axons far outnumber larger fibers in the corticospinal tract, but the function of these small axons remains poorly understood. This is because they are difficult...
Small axons far outnumber larger fibers in the corticospinal tract, but the function of these small axons remains poorly understood. This is because they are difficult to identify, and therefore their physiology remains obscure. To assess the extent of the mismatch between anatomic and physiological measures, we compared conduction time and velocity in a large number of macaque corticospinal neurons with the distribution of axon diameters at the level of the medullary pyramid, using both light and electron microscopy. At the electron microscopic level, a total of 4,172 axons were sampled from 2 adult male macaque monkeys. We confirmed that there were virtually no unmyelinated fibers in the pyramidal tract. About 14% of pyramidal tract axons had a diameter smaller than 0.50 μm (including myelin sheath), most of these remaining undetected using light microscopy, and 52% were smaller than 1 μm. In the electrophysiological study, we determined the distribution of antidromic latencies of pyramidal tract neurons, recorded in primary motor cortex, ventral premotor cortex, and supplementary motor area and identified by pyramidal tract stimulation (799 pyramidal tract neurons, 7 adult awake macaques) or orthodromically from corticospinal axons recorded at the mid-cervical spinal level (192 axons, 5 adult anesthetized macaques). The distribution of antidromic and orthodromic latencies of corticospinal neurons was strongly biased toward those with large, fast-conducting axons. Axons smaller than 3 μm and with a conduction velocity below 18 m/s were grossly underrepresented in our electrophysiological recordings, and those below 1 μm (6 m/s) were probably not represented at all. The identity, location, and function of the majority of corticospinal neurons with small, slowly conducting axons remains unknown.
Topics: Animals; Axons; Macaca fascicularis; Macaca mulatta; Male; Nerve Fibers, Myelinated; Neural Conduction; Pyramidal Tracts; Reaction Time
PubMed: 24872533
DOI: 10.1152/jn.00720.2013 -
Scientific Reports Jan 2020Motor function after hemispheric lesions has been associated with the structural integrity of either the pyramidal tract (PT) or alternate motor fibers (aMF). In this...
Motor function after hemispheric lesions has been associated with the structural integrity of either the pyramidal tract (PT) or alternate motor fibers (aMF). In this study, we aimed to differentially characterize the roles of PT and aMF in motor compensation by relating diffusion-tensor-imaging-derived parameters of white matter microstructure to measures of proximal and distal motor function in patients after hemispherotomy. Twenty-five patients (13 women; mean age: 21.1 years) after hemispherotomy (at mean age: 12.4 years) underwent Diffusion Tensor Imaging and evaluation of motor function using the Fugl-Meyer Assessment and the index finger tapping test. Regression analyses revealed that fractional anisotropy of the PT explained (p = 0.050) distal motor function including finger tapping rate (p = 0.027), whereas fractional anisotropy of aMF originating in the contralesional cortex and crossing to the ipsilesional hemisphere in the pons explained proximal motor function (p = 0.001). Age at surgery was found to be the only clinical variable to explain motor function (p < 0.001). Our results are indicative of complementary roles of the PT and of aMF in motor compensation of hemispherotomy mediating distal and proximal motor compensation of the upper limb, respectively.
Topics: Adolescent; Brain Injuries; Child; Diffusion Tensor Imaging; Female; Hemispherectomy; Humans; Male; Motor Activity; Motor Cortex; Pyramidal Tracts; White Matter; Young Adult
PubMed: 31974395
DOI: 10.1038/s41598-020-57504-x -
NeuroImage. Clinical 2020Underlying neural factors contribute to poor outcomes following anterior cruciate ligament reconstruction (ACLR). Neurophysiological adaptations have been identified in...
BACKGROUND
Underlying neural factors contribute to poor outcomes following anterior cruciate ligament reconstruction (ACLR). Neurophysiological adaptations have been identified in corticospinal tract excitability, however limited evidence exists on neurostructural changes that may influence motor recovery in ACLR patients.
OBJECTIVE
To 1) quantify hemispheric differences in structural properties of the corticospinal tract in patients with a history of ACLR, and 2) assess the relationship between excitability and corticospinal tract structure.
METHODS
Ten participants with ACLR (age: 22.6 ± 1.9 yrs; height: 166.3 ± 7.5 cm; mass: 65.4 ± 12.6 kg, months from surgery: 70.0 ± 23.6) volunteered for this cross-sectional study. Corticospinal tract structure (volume; fractional anisotropy [FA]; axial diffusivity [AD]; radial diffusivity [RD]; mean diffusivity [MD]) was assessed using diffusion tensor imaging, and excitability was assessed using transcranial magnetic stimulation (motor evoked potentials normalized to maximal muscle response [MEP]) for each hemisphere. Hemispheric differences were evaluated using paired samples t-tests. Correlational analyses were conducted on structural and excitability outcomes.
RESULTS
The hemisphere of the ACLR injured limb (i.e. hemisphere contralateral to the ACLR injured limb) demonstrated lower volume, lower FA, higher MD, and smaller MEPs compared to the hemisphere of the non-injured limb, indicating disrupted white matter structure and a reduction in excitability of the corticospinal tract. Greater corticospinal tract excitability was associated with larger corticospinal tract volume.
CONCLUSIONS
ACLR patients demonstrated asymmetry in structural properties of the corticospinal tract that may influence the recovery of motor function following surgical reconstruction. More research is warranted to establish the influence of neurostructural measures on patient outcomes and response to treatment in ACLR populations.
Topics: Adult; Anterior Cruciate Ligament Reconstruction; Cross-Sectional Studies; Diffusion Tensor Imaging; Evoked Potentials, Motor; Female; Functional Laterality; Humans; Lower Extremity; Male; Pyramidal Tracts; Quadriceps Muscle; Transcranial Magnetic Stimulation; White Matter; Young Adult
PubMed: 31901791
DOI: 10.1016/j.nicl.2019.102157 -
Journal of Applied Physiology... Sep 2022Resistance training increases volitional force-producing capacity, and it is widely accepted that such an increase is partly underpinned by adaptations in the central... (Review)
Review
Resistance training increases volitional force-producing capacity, and it is widely accepted that such an increase is partly underpinned by adaptations in the central nervous system, particularly in the early phases of training. Despite this, the neural substrate(s) responsible for mediating adaptation remains largely unknown. Most studies have focused on the corticospinal tract, the main descending pathway controlling movement in humans, with equivocal findings. It is possible that neural adaptation to resistance training is mediated by other structures; one such candidate is the reticulospinal tract. The aim of this narrative mini-review is to articulate the potential of the reticulospinal tract to underpin adaptations in muscle strength. Specifically, we ) discuss why the structure and function of the reticulospinal tract implicate it as a potential site for adaptation; ) review the animal and human literature that supports the idea of the reticulospinal tract as an important neural substrate underpinning adaptation to resistance training; and ) examine the potential methodological options to assess the reticulospinal tract in humans.
Topics: Adaptation, Physiological; Animals; Humans; Muscle Strength; Muscle, Skeletal; Pyramidal Tracts; Resistance Training
PubMed: 35834623
DOI: 10.1152/japplphysiol.00264.2021 -
Current Biology : CB Apr 2022During motor learning, as well as during neuroprosthetic learning, animals learn to control motor cortex activity in order to generate behavior. Two different...
During motor learning, as well as during neuroprosthetic learning, animals learn to control motor cortex activity in order to generate behavior. Two different populations of motor cortex neurons, intra-telencephalic (IT) and pyramidal tract (PT) neurons, convey the resulting cortical signals within and outside the telencephalon. Although a large amount of evidence demonstrates contrasting functional organization among both populations, it is unclear whether the brain can equally learn to control the activity of either class of motor cortex neurons. To answer this question, we used a calcium-imaging-based brain-machine interface (CaBMI) and trained different groups of mice to modulate the activity of either IT or PT neurons in order to receive a reward. We found that the animals learned to control PT neuron activity faster and better than IT neuron activity. Moreover, our findings show that the advantage of PT neurons is the result of characteristics inherent to this population as well as their local circuitry and cortical depth location. Taken together, our results suggest that the motor cortex is more efficient at controlling the activity of pyramidal tract neurons, which are embedded deep in the cortex, and relaying motor commands outside the telencephalon.
Topics: Animals; Brain-Computer Interfaces; Learning; Mice; Motor Cortex; Motor Neurons; Pyramidal Tracts
PubMed: 35219429
DOI: 10.1016/j.cub.2022.02.006 -
Journal of Rehabilitation Medicine Mar 2014The corticospinal tract, a major neural tract in the human brain for motor function, is concerned mainly with movement of the distal extremities. Preservation or... (Review)
Review
The corticospinal tract, a major neural tract in the human brain for motor function, is concerned mainly with movement of the distal extremities. Preservation or recovery of the corticospinal tract is essential for good recovery of impaired motor function in patients with brain injury. Therefore, thorough and precise knowledge of the corticospinal tract is necessary for successful brain rehabilitation. Many studies have reviewed the corticospinal tract; however, review articles from the rehabilitative viewpoint are lacking. Therefore, the aim of this paper was to review the corticospinal tract from the rehabilitative viewpoint with regard to classification, cerebral origin, collaterals and development.
Topics: Adolescent; Adult; Aged; Aged, 80 and over; Aging; Brain Injuries; Child; Child, Preschool; Diffusion Tensor Imaging; Female; Humans; Infant; Infant, Newborn; Male; Middle Aged; Movement; Pyramidal Tracts; Young Adult
PubMed: 24531325
DOI: 10.2340/16501977-1782 -
Acta Neuropathologica Communications Jan 2021Transactive response DNA-binding protein 43 kDa (TDP-43) has been identified as the major component of ubiquitinated inclusions found in patients with sporadic...
Transactive response DNA-binding protein 43 kDa (TDP-43) has been identified as the major component of ubiquitinated inclusions found in patients with sporadic amyotrophic lateral sclerosis (ALS). Increasing evidence suggests prion-like transmission of TDP-43 aggregates via neuroanatomic connection in vitro and pyramidal tract in vivo. However, it is still unknown whether the spreading of pathological TDP-43 sequentially via pyramidal tract can initiate ALS-like pathology and phenotypes. In this study, we reported that injection of TDP-43 preformed fibrils (PFFs) into the primary motor cortex (M1) of Thy1-e (IRES-TARDBP) 1 mice induced the spreading of pathological TDP-43 along pyramidal tract axons anterogradely. Moreover, TDP-43 PFFs-injected Thy1-e (IRES-TARDBP) 1 mice displayed ALS-like neuropathological features and symptoms, including motor dysfunctions and electrophysiological abnormalities. These findings provide direct evidence that transmission of pathological TDP-43 along pyramidal tract induces ALS-like phenotypes, which further suggest the potential mechanism for TDP-43 proteinopathy.
Topics: Amyotrophic Lateral Sclerosis; Animals; Axonal Transport; DNA-Binding Proteins; Humans; Mice; Mice, Transgenic; Motor Cortex; Protein Aggregates; Protein Aggregation, Pathological; Pyramidal Tracts
PubMed: 33461623
DOI: 10.1186/s40478-020-01112-3 -
Frontiers of Neurology and Neuroscience 2013Stroke is a leading cause of long-term disability with early accelerated followed by gradual recovery during the first 6 months after the ictus. The most important... (Review)
Review
Stroke is a leading cause of long-term disability with early accelerated followed by gradual recovery during the first 6 months after the ictus. The most important mechanism concerning early recovery is thought to be brain plasticity provided by anatomical and functional reorganization of the central nervous system after injury. Recent advances in noninvasive, functional brain imaging techniques provided some insight indicating the contribution of ipsilateral uncrossed corticospinal tracts in motor recovery after stroke. Since motor tracts vary considerably among subjects, the ratio of contralateral corticospinal tract fibers and their interhemispheric control versus the amount and function of ipsilateral corticospinal tract fibers may affect the scale of motor recovery after stroke. Further studies are needed to clarify the mechanisms of motor recovery after stroke in humans.
Topics: Adaptation, Physiological; Animals; Brain; Efferent Pathways; Humans; Neuronal Plasticity; Paresis; Pyramidal Tracts; Recovery of Function; Stroke
PubMed: 23859962
DOI: 10.1159/000348821 -
F1000Research 2019The last few years have seen major advances in our understanding of the organisation and function of the corticospinal tract (CST). These have included studies... (Review)
Review
The last few years have seen major advances in our understanding of the organisation and function of the corticospinal tract (CST). These have included studies highlighting important species-specific variations in the different functions mediated by the CST. In the primate, the most characteristic feature is direct cortico-motoneuronal (CM) control of muscles, particularly of hand and finger muscles. This system, which is unique to dexterous primates, is probably at its most advanced level in humans. We now know much more about the origin of the CM system within the cortical motor network, and its connectivity within the spinal cord has been quantified. We have learnt much more about how the CM system works in parallel with other spinal circuits receiving input from the CST and how the CST functions alongside other brainstem motor pathways. New work in the mouse has provided fascinating insights into the contribution of the CM system to dexterity. Finally, accumulating evidence for the involvement of CM projections in motor neuron disease has highlighted the importance of advances in basic neuroscience for our understanding and possible treatment of a devastating neurological disease.
Topics: Animals; Humans; Mice; Motor Cortex; Primates; Pyramidal Tracts; Species Specificity
PubMed: 30906528
DOI: 10.12688/f1000research.17445.1