Motor cortex connections

Corticospinal neuron subpopulation-specific developmental genes prospectively indicate mature segmentally specific axon projection targeting

“…The corticospinal system is essential for skilled movements ( Martin, 2005 ); fine motor control relies on corticospinal neurons (CSN) projecting axons to appropriate and specific segmental targets. CSN in multiple cortical areas, beyond the primary motor cortex (M1), form corticospinal circuitry with distinct functional outputs, including spinal motor neuron excitation and inhibition by direct and indirect pathways, descending control of ascending inputs, and autonomic control ( Lemon, 2008 ; Lemon and Griffiths, 2005 ; Sahni et al, 2020 ; Welniarz et al, 2017 ). Such diverse functional output, especially for precise motor control, requires distinct CSN subpopulations to project to segmentally specific targets in the pons, medulla, and cervical, thoracic, and lumbar cord for head, forelimb, trunk, and hindlimb motor control.…”

Crim1 and Kelch-like 14 exert complementary dual-directional developmental control over segmentally specific corticospinal axon projection targeting

“…The corticospinal system is the principal spinal-projecting pathway controlling performance of highly skilled and complex movements ( Martin, 2005 ). In addition, the corticospinal circuit exerts critical control over sensory modulation and autonomic functions ( Lemon, 2008 ; Lemon and Griffiths, 2005 ; Liu et al, 2018 ; Sahni et al, 2020 ; Welniarz et al, 2017 ). For this precise top-down sensorimotor and autonomic control, distinct corticospinal neurons (CSN) extend axons to, and innervate, distinct subcerebral targets: rostral targets in the brainstem and cervical cord to caudal targets in the thoracic and lumbar cord.…”

“…In particular, specification and differentiation of CSN is regulated first by controls over broad corticofugal projection neuron differentiation, then by controls over all subcerebral projection neurons, and then by CSN-subtype-specific molecular controls ( Arlotta et al, 2005 ; Cederquist et al, 2013 ; Chen et al, 2005a , 2005b ; Galazo et al, 2016 ; Greig et al, 2016 ; Han et al, 2011 ; Joshi et al, 2008 ; Kwan et al, 2008 ; Lai et al, 2008 ; Lodato et al, 2014 ; McKenna et al, 2011 ; Molyneaux et al, 2005 ; Ozdinler and Macklis, 2006 ; Shim et al, 2012 ; Tomassy et al, 2010 ; Woodworth et al, 2012 , 2016 ). Guidance molecules direct CSN axons at specific choice points, including in the spinal cord (e.g., EphA4; reviewed by Canty and Murphy 2008 ; Sahni et al 2020 ; Welniarz et al 2017 ). Further, specific signaling mechanisms promote CSN axon extension into the cord (e.g., insulin growth factor [IGF]-I [ Ozdinler and Macklis, 2006 ] and Wnt-Ryk signaling [ Liu et al, 2005 ]).…”

Lumican regulates cervical corticospinal axon collateralization via non-autonomous crosstalk between distinct corticospinal neuron subpopulations

“…Corticospinal neurons (CSN, and related cortico-brainstem neurons; together “CSN”) extend axon projections to subcerebral targets, and make synaptic connections with circuits in the brainstem and spinal cord (Kalil and Dent, 2014; Levine et al, 2012; Sahni et al, 2020). CSN axons thus form the corticospinal tract (CST), the major motor output pathway from the cerebral cortex, essential for voluntary motor control, and the principal circuit underlying skilled movement (Lemon, 2008; Martin, 2005).…”