Neuroanatomy of human and zebrafish spinal motor system.
Similarities with human
Key differences and unknown features
Spinal cord
Spinal motor neurons
(a) Zebrafish SMN similar to human -MN.
Absence of -MN in zebrafish.
(b) Presence of different subtypes of MN, some located at specific regions of the spinal cord, with some at specific region of the cord, innervating axial and fin muscle.
have not been reported in human. Appendicular MNs in fish are not separated into a LMC.
Skeletal muscle fibres
(a) Similar morphological, molecular, and histological features like dystrophin associated glycoprotein complex, excitation-contraction coupling, and contractile machinery.
Proprioceptors like muscle spindle are absent in fish.
Brainstem
Ventromedial brainstem descending pathway
(a) Fibres from RF, VN, and nMLF descend from hind brain along with MFL through spinal cord as VMF, projecting onto interneurons and some spinal MN.
Human brainstem contains UMN. Fibres from RF, VN, and SuC descend to MMC of spinal cord projecting onto interneuron and spinal motor neuron. A direct tectospinal tract has not been identified.
Dorsolateral brainstem descending pathway
A few rubrospinal fibres present in zebrafish; a true rubrospinal tract is absent.
Motor cortex
Corticospinal tract (CST)
No CST in teleost fish.
: primary motor neuron (CaP, MiP, RoPs, and VaP); SMN: secondary motor neuron (vS: ventrally projecting SMNS); LMC: dorsal lateral motor column; RF: reticular formation; VN: vestibular nuclei; SuC: superior colliculus; nMLF: nucleus of the medial longitudinal fasciculus; VMF: ventromedial fascicle; MN: motor neuron; UMN: upper motor neuron; MMC: ventral medial motor column; CST: corticospinal tract. Adapted and modified from [41].
