Descending motor pathways Flashcards
levels of motor hierarchy
the highest level - precommand level
middle level - projection level
lowest level - segmental level
precommand level
involves the premotor cortex, basal ganglia and cerebellum
what is the premotor cortex role at the precommand level?
responsible for initiating a plan for the next intended movement
what is the role of the basal ganglia at the precommand level?
release brake to start a specific movement
what is the role of the cerebellum at the precommand level?
precisely calculates the best way to achieve coordinates synergistic across multiple limb joints, as well as monitoring muscle tone and balance
projection level
involves the primary motor cortex and the brainstem
what is the role and location of upper motor neurons?
directly control the spinal cord. they are located in the primary cortical motor areas and brainstem
what is the role and location of the pyramidal tracts?
they originate from the primary motor cortex, synapse either with interneurons or with ventral horn motor neurons in the spinal cord. they are concerned with voluntary, discrete, skilled movements
what is the role and location of the command neurons?
they are located in the brainstem nuclei. they function to start, stop or modify the basic rhythm of CPGs of the spinal cord through the indirect pathways.
segmental level
the spinal cord
reflex arcs
are composed of afferent axons, which synapse onto interneurons in the spinal cord, which relay the information back to efferent neurons. these axons go onto effector organs to initiate a command
What is the role of lower motor neurons?
their axons synapse onto the skeletal muscles, creating motor units
central pattern generators (CPGs)
the segmental circuits in the spinal cord that control locomotion and other specific and often-repeated motor activity. it consists of a network of neurons, on both sides of the spinal cord, that work together to generate a rhythmic pattern of motor activity. CPGs are initiated and generated by brainstem command neurons.
the direct (pyramidal) system
origin in from the primary motor cortex. axons go down via the internal capsule, and decussate at the pyramid. axons largely cross over, but not all together. 90% decussate at the lateral corticospinal tract. 8% cross over at the anterior corticospinal tract. 2% are uncrossed and pass through the corticospinal tract.
stroke at the internal capsule
the face, upper extremity, trunk and lower extremity all sit at the internal capsule. stroke can result in paralysis in any of these regions
the corticospinal (pyramidal) tract (function)
involved with regulating fast and skilled movements, and controlling reflex motor output and modifying sensory input.
the lateral corticospinal tract
crosses over at the lateral part of the pyramid
the anterior corticospinal tract
crosses over at the anterior part of the pyramid
damage to the corticospinal tract
leads to paralysis of the target muscles.
if the lesion is above pyramidal decussation, paralysis occurs on the opposite side to the lesion in upper and lower limb muscles.
if the lesion is below pyramidal decussation in the lateral T10, paralysis is on the same side lower limb muscles.
the corticobulbar tracts
part of the direct system. the have bilateral synapses, but are mainly contralateral.
the tract goes from the cortex → brainstem → cranial nerve nuclei
the indirect (extrapyramidal) system
motor axons arise from several brainstem nuclei
what are the four major tracts of the indirect system?
- tectospinal tracts
- rubrospinal tracts
- reticulospinal tracts
- vestibulospinal tracts
tectospinal tracts
move the head and back, and provide visual input. are formed by the superior colliculus on the tectum or roof of the midbrain
rubrospinal tracts
maintains muscle tone. formed by the red nucleus in the midbrain
