Spinal Cord Disease
Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw in Hankey's Clinical Neurology, 2020
Macroscopically, brain and spinal cord often appear normal; the precentral gyrus and corticospinal tracts may show atrophy (Figures 23.28–23.32). Microscopic findings (Figures 23.33, 23.34) are: Loss of Betz’ cells of the motor cortex.Degeneration and gliosis of the corticospinal tracts.Degeneration of lower brainstem motor nuclei (not oculomotor nuclei) in most cases.Cytoplasmic eosinophilic inclusions (Bunina's bodies) and ubiquitin immunoreactive inclusion bodies (containing TAR DNA binding protein 43 [TDP-43]) in degenerating cranial motor nuclei, anterior horn cells, and Betz’ cells.Muscle shows features of denervation.Nonmotor pathways also demonstrate pathologic changes, including sensory pathways and peripheral sensory nerves.
The Consciousness of Muscular Effort and Movement
Max R. Bennett in The Idea of Consciousness, 2020
Figure 4.7 A shows how the sensation of the heaviness of an object held in the hand is generated by a collateral effect. The pathway from the motor cortex to the alpha motor neurons is shown to give off a collateral branch at the level of the basal ganglia (depicted at this particular level for definiteness only). It is hypothesized that the associated corollary discharge generates a sensation in the cortex of the degree of heaviness of an object by firing impulses in proportion to those that are being propagated down the motor pathway. The neurons in the motor cortex that project to the motor neurons in the spinal cord to contract muscles involved in lifting an object are called Betz cells. When these are activated a collateral signal is sent which gives rise to the perception of heaviness of the object being lifted (the collateral effect). It follows that when a muscle is weakened by fatigue, such as when holding a heavy suitcase, a greater number of impulses are required by the non-fatigued component of the muscle in order for the muscle to continue lifting the suitcase, and so more impulses are being propagated down the motor pathway. The collateral branch then receives a greater number of impulses and so a greater sensation of heaviness is experienced.
ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
Betz cells, named after Vladimir Betz (1834-1894) who discovered them, are giant (5080 m) PYRAMIDAL NEURONS in layer 5 of the primary MOTOR CORTEX. There are about 30000 Betz cells in the human motor cortex. Their axons contribute to the CORTICOSPINAL TRACT, which contains the axons of about a million neurons. See also: agranular cortex; cytoarchitecture
The Role of Primary Motor Cortex: More Than Movement Execution
Published in Journal of Motor Behavior, 2021
Sagarika Bhattacharjee, Rajan Kashyap, Turki Abualait, Shen-Hsing Annabel Chen, Woo-Kyoung Yoo, Shahid Bashir
Early investigation of the motor cortex in humans (Penfield & Boldrey, 1937; Woolsey, 1952) had functionally divided the motor cortex into two major areas: the primary motor cortex (M1) and premotor area (PMA; Fulton, 1935). M1 is located in the precentral gyrus of the frontal lobe that plays a crucial role in the execution of voluntary movements (Pearson, 2000). Histological examination of M1 has revealed the presence of giant pyramidal neurons called Betz cells. Betz cells are also known as upper motor neurons because they send axons to the lower motor neurons situated in the gray column of the spinal cord. The upper motor neuron contributes to the corticospinal pathway, whereas the lower motor neurons innervate the skeletal muscle fibers situated at the periphery (Porter & Lemon, 1993). With this structural construct, M1 is predominantly considered to only have a role in motor execution.
Better understanding the neurobiology of primary lateral sclerosis
Published in Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration, 2020
P. Hande Ozdinler, Mukesh Gautam, Oge Gozutok, Csaba Konrad, Giovanni Manfredi, Estela Area Gomez, Hiroshi Mitsumoto, Marcella L. Erb, Zheng Tian, Georg Haase
In an effort to better understand the mechanisms of neurodegeneration in PLS, numerous mouse models were generated based on PLS-linked mutations, such as ALS2/Alsin, C9Orf72, DCTN/Dynactin 1, FIG4/Phosphoinositide 5-phosphatase, OPTN/Optineurin, SETX/Senataxin, SPG7/Paraplegin or UBQLN2/Ubiquilin 2 (17). However, generation and characterization of a mouse model for an UMN disease is challenging. Humans heavily depend on their Betz cells for the initiation and modulation of voluntary movement and there are direct projections from Betz cells to the spinal motor neurons. In mice, in addition to the corticospinal tract, the rubrospinal tract also plays an important role and the circuitry within the spinal cord includes an interneuron component (24). Therefore, when humans have defects in their corticospinal tract, they may be paralyzed, whereas mice will be able to move, albeit with loss of their ability for fine movement. During evolution, humans have become more specialized in fine movement in the expense of making themselves vulnerable to significant spinal cord injuries. Rodents, however, have better capabilities to recover from an injury, but they are not as skilled as humans when it comes to dexterity (24,44). Moreover, there are no good outcome measures, which can quantitatively assess the timing and the extent of UMN degeneration in mouse models of PLS. Despite these two limitations the UMNs in mice and human share many common cell biological features and display similar pathologies at a cellular level (26,27,45). Hence, many different labs generated mouse models for genes that had been found mutated in PLS patients. Albeit most mouse lines did not have a prominent phenotype at a species level (46), detailed cellular investigations of their UMNs began to reveal the underlying problems.
Neurophysiological features of primary lateral sclerosis
Published in Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration, 2020
Mamede de Carvalho, Matthew C. Kiernan, Seth L Pullman, Kourosh Rezania, MR Turner, Zachary Simmons
Overall, markers of cortical hyperexcitability can be observed early in the disease course of PLS, but with disease progression, the motor cortex becomes progressively inexcitable, corresponding to a severe loss of motor neurons, typically with a greater level of dysfunction involving excitatory pathways compared to inhibitory synapses. In support, neuropathological and imaging studies have identified severe atrophy of the cortical motor strip and selective depletion of Betz cells in layer V, changes which likely contribute to the neurophysiological abnormalities (21).
Related Knowledge Centers
- Axon
- Central Nervous System
- Primary Motor Cortex
- Pyramidal Cell
- Pyramidal Tracts
- Synapse
- Upper Motor Neuron
- Spinal Cord
- Neuron
- Grey Matter