Motor Tracts Flashcards
Lower vs upper motor neurons
Upper:
- responsible for controlling the firing rates of lower motor neurons
- are located in the cerebral cortex or the brainstem ONLY
- note that upper motor neuron nuclei are only found in the cortex, any upper motor neurons located in the brainstem are parts of tracts*
Lower:
- interconnection between the upper motor neuron and the muscle that is designated to be innervated
- are located in the ventral horn of the spinal cord or the cranial nerve nuclei in the brainstem ONLY
Spinal cords functions in motor functions
Contains the reflex motor centers
Final common path for neurons that innervate skeletal muscles
Cerebral cortex functions in motor functions
Most important source of upper motor neuron nuclei
Basal nuclei functions in motor functions
Modulate activity of upper motor neurons in the cerebral cortex
Cerebellum functions in motor functions
Principal integrator of motor function
- intakes a lot of motor inputs and generates smooth motions from choppy inputs
Brainstem functions in motor functions
Upper motor neurons generate motor spinal tracts that exert influences on spinal motor neurons
Thalamus functions in motor functions
Is the relay center of information to motor regions fo the cerebral cortex
Descending motor tracts
Includes lateral corticospinal and anterior corticospinal tracts
Which spinal tracts make up the lateral motor system?
Lateral corticospinal tract
Rubrospinal tract
- these tracts travel in posterolateral columns of the spinal cord and synapse on the lateral ventral horn neurons/interneurons*
- these neurons focus more on lateral extremities and the more distal portions of them. Also more flexor innervation vs extensor *
Which spinal tracts make up the medial motor system
Anterior corticospinal tract
Vestibulospinal tract
Reticulospinal tract
Tectospinal tract
- these tracts travel anteriomedial columns of the spinal cord and synapse on the medial ventral horn motor neurons/interneurons*
- these focus more on axial/limb girdle musculature and the more proximal portions of the extremities. Also focus more on extensor actions vs flexor actions*
Corticospinal (pyramidal) tract
Involved in the control of movement on the contralateral side of the body
Pathway:
- starts in upper motor nuclei in the cerebral cortex
- descends into the internal capsule of telencephalon, the cerebral peduncle and the base of the brainstem to the medullary pyramids
- almost all fibers (roughly 90%) in this tract decussate at the medulla-spinal cord junction to form the lateral corticospinal tracts
- uncrossed fibers form the anterior/ventral corticospinal tract (these fibers then decussate at the spinal levels they get off at)
What are the 3 cortical regions in the telencephalon that the upper motor neuron nuclei originate from?
Primary motor cortex
(Precentral)
Primary somatosensory cortex (postcentral)
Supplementary motor area (SMA)and pre motor area (PMA)
The Posterior parietal cortex (PPC) does not have upper motor nuclei and instead help modulate the corticospinal tract
How specifically does the upper motor neurons leave the cortex?
They enter the corona radiata into the internal capsule
They travel through the internal capsule as follows:
Anterior limb -> genu -> posterior limb
Corticobulbar fibers are found in the genu (the corticospinal tract just passes through)
Corticospinal fibers are found in the posterior limb
Somatotopic organization of the corticospinal tract in the internal capsule and cerebral peduncle of the midbrain of
Internal capsule (from anteromedial -> posterolateral)
- face
- arm
- trunk
- leg
Cerebral peduncle (from most medial -> lateral
- face
- arm
- trunk
- leg
Where in the brainstem does the corticospinal fibers specifically travel through to get to the next part?
Midbrain = middle 1/3 of cerebral peduncle
Basilar pons = between pontine nuclei
Medulla = aggregate on ventral surface and course within the pyramids
- medial fibers in pyramids = cervical fibers*
- lateral fibers in pyramids = thoracic/lumbar fibers*
