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Motor Pathways Dr Ayman G. Abu-Tabanja Upper Motor neurons: Supra spinal neurons whose axons descend in bundles (descending tracts) that innervate lower motor neurons Lower motor neurons: Motor neurons whose cell bodies are situated in the anterior horn of the spinal cord or motor nuclei of cranial nerves and whose axons innervate skeletal muscles Motor Pathways Lateral Corticospinal Tract Direct motor pathway Contralateral innervation of LMN LMN Innervates the trunk and Upper and Lower limbs Voluntary, discrete & skilled movements Posterior limb of internal capsule Cerebral peduncle in midbrain Basal part of Pons Pyramid in medulla Motor Decussation in rostral medulla Lateral Funiculus Corticobulbar Tract Direct Motor Pathway UMN innervate LMN bilaterally Exception: Facial motor nucleus which supply the muscles of the lower part of the Face Hypoglossal motor nucleus which supply genioglosus Somatotopic Representation of Corticospinal & Corticobulbar Fibers Upper & Lower Motor Neurons Lesions • Upper motor neurons lesion: Location Signs: Paralysis or paresis Hypertonia Abnormal reflexes Exaggerated reflexes Muscle atrophy is not common Plantar flexion Versus Dorsal flexion Upper & Lower Motor Neurons Lesions • Lower motor neurons lesion: Location Signs: Paralysis Hypotonia Loss of reflexes Muscular fasciculations Muscle atrophy Muscle contracture Upper & Lower Motor Neurons Lesions of the face • Upper motor neurons lesion Signs: Paralysis of Contralateral lower quadrant of face • Lower motor neurons lesion: Location: motor nucleus of facial nerve Signs: Paralysis of Ipsilateral half of face Reticulospinal tract Originate from reticular formation In brainstem Facilitate or inhibit voluntary muscle activity Tectospinal Tracts Originate from superior colliculus Upper cervical segments Cross medline (most fibers) Reflex postural movements of the head in response to visual stimuli Rubrospinal Tract Originate from red nucleus Cross medline immediately Facilitate Flexors Inhibit Extensors Vestibulotospinal Tracts Originate from vestibular nuclei Facilitate Extensors Inhibits Flexors Maintenance of balance Lesions to extrapyramidal tract • Severe Paralysis • Spasticity • Exaggerated deep muscle reflexes • Clasp knife reaction
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