Motor Pathways Flashcards
Organization of motor pathways
. Organized hierarchically and in parallel
Origin of descending pathways
. Origin is cerebral cortex
. Called corticospinal pathways and are efferent projections from the cerebral cortex
Pyramidal system
. Pathway devoted to the voluntary motor control has fibers coursing int hr ventral medulla that then form the pyramids
. Term applied to corticospinal tracts together w/ the functionally equivalent corticonuclear fibers
. Also known as corticobulbar
. Pathways in charge of realization of movement
Characteristics of motor pathways
. Monosynaptic (bineuronal): pyramidal cell located in the cortex synapses directly w/ lower motor neurons
. Communication is fast and uninterrupted, it is not modulated
. Pathways end contralat.
. Some fibers may end bilaterally. So that a movement generated from lower motor neurons is controlled from both hemispheres
Corticospinal tract
. Originate from large pyramidal neurons in layer V of the M-1 and PMC, SMA, and S-1 and parietal assoc. cortex
. Fibers course somatotopically through post. Limb of internal capsule, the muddle of crus cerebri in midbrain, and the pyramids
. 95-90% of fibers decussate at pyramid and enter lat. funiculus of spinal cord to become the lat. corticospinal tract
. Remaining fibers stay ipsilateral. And enter ventral funiculus of the spinal cord to become ant. Corticospinal tract and ultimately decussate in the ant. Commissure of the spinal cord synapsing w/ contralateral lower motor neurons
Lateral corticospinal tract
. Located in lat. funiculus of the spinal cord
. Projects somatotopically to all levels of spinal cord
. Terminate in ventral horn of all levels
. Functions: activation of neurons in the ventral horn that innervate distal musculature, particularly neurons that innervate mm. Of hands and fingers
Ventral (ant.) corticospinal tract (ACST)
. Small tract located in med. aspect of ant. Funiculus of spinal cord
. Consists of 10-15% of corticospinal tract that does not decussate at pyramidal decussation
. Fibers ipsilateral until leve at which they will terminate where they decussate in ant. White commissure to get to contralateral ventral horn where they terminate
. Function: mostly unknown but it could activate neurons in ventral horn that innervate axial musculature
Corticonuclear tract
. Fibers originate from large pyramidal neurons in layer V of M-1, PMC, SMC, S-1, and parietal assoc. cortex
. Fibers directly synapse w/ neurons in motor nuclei of cranial nn.
. Course somatotopically through post. Limb of the internal capsule and the middle of the crus cerebri of midbrain
. Some fibers terminate in midbrain (III, IV) while the rest descend in pons
. In pons fibers are dispersed in basilar pons and some terminate in pontine nuclei (V, VI, VII)
. Projections primarily bilat. Except CN VII and XII
Descending tracts that play role in involuntary movements and their adjustment and synchronization
. Rubospinal tract
. Vestibulospinal tract
. Reticulospinal tracts
. Tectospinal tract
Rubrospinal tract
. Fibers of tract arise from neurons in red nucleus in midbrain. Decussate in midbrain and will course in the late. Funiculus of spinal cord and terminate in synapses w/ lower motor neurons in ventral horn
. Red nucleus receives direct cortical inputs from the ipsilateral motor cortices
. Influences flexors and supplements corticospinal system ( CN compensate for loss in corticospinal tract)
Vestibulospinal tract
. Med. and lat. tracts that arise in vestibular nuclei in brainstem
. Descend in ventral funiculus of spinal cord and terminate in ventral horn
. Mediators of postural adjustment and head movements
. Activated in response to vestibular stimulation
Lateral reticulospinal tract
. Originates from neurons in med. aspect of medullary reticular formation
. Axons descend bilaterally in lat. funiculus
. Projects to all spinal cord levels
. Functions to inhibit motor neurons in ventral horn
. Innervate extensor mm.
Medial reticulospinal tract
. Originates from neurons in lat. aspect of pontine reticular formation
. Axons descend ipsilateral in ventral funiculus
. Project to alls pineal cord levels
. Excite motor neurons in ventral horn
. Innervate extensor mm.
Tectospinal tract
. In ventral funiculus of cervical spinal cord levels only
. Originates from neurons in sup. Colliculus
. Decussate in midbrain tegmentum
. Descend as tectospinal tract through pons and medulla
. Terminate in ventral horn of cervical spinal cord
. Functions: reflex control and coordination of head, neck, and eye movements in response to visual and auditory stimuli and to voluntary motor commands
Extrapyramidal system
. Motor output arises from motor, sensory, assoc. cortices
. Motor info enters complex and reverberating circuits that imply many reaches he lower motor neurons of brainstem and spinal cord and through lower motor neuron, the mm.
. Multineuronal/multisynaptic pathway
. All different stops are a chance for more stimuli arising from other area of brain that are not the cerebral cortices
. Allows info to be richer when reaching lower motor neuron allowing complexity of a movement
. Structures: cerebral cortex, basal ganglia, some thalamus nuclei, subthalamus, and some nuclei of brainstem
