Upper and Lower motor neurons Németh Orsolya

Carry motor informations to lower motor neurons Upper motor neuron: Carry motor informations to lower motor neurons Originates in primary motor cortex Pass through the brainstem Decussates in medulla oblongata decussate → lateral corticospinal tract do not decussate → ventral corticospinal tract Terminate in spinal cord

Upper motor neuron pathways: Corticobulbar tract

Innervate muscle fibers (link between upper neurons and muscle fibers) Lower motorneuron: Recieves motor commands from upper motor neuron, send them to muscle fibers Innervate muscle fibers (link between upper neurons and muscle fibers) 3 types : α-motor neuron: extrafusal muscle → initiating contraction β-motor neuron: intrafusal fibers with collaterals to extrafusal fibers γ-motor neuron: intrafusal muscle fiber → forming muscle spindle with sensory afferents

Deseases: Upper motor neuron lesions: „pyramidal insufficiency” stroke, multiple sclerosis, traumatic brain injury, cerebral palsy, Amyotrophic lateral sclerosis (ALS) sympthoms: muscle weakness, decreased motor controll, increased deep tendon,Clasp-knife response, Babinski sign Lower motor neuron lesions: affect nerve fibers from ventral horn of SC sympthoms: muscle paralysis, fasciculations, fibrillation hypotonia, hyporeflexia, decreased strength