the midline and instead form the anterior corticospinal tract that innervates motor neurons that project to midline muscles. The direct cortical corticospinal system consists of direct fibers that project through the internal capsule crus cerebri (cerebral peduncles) and then in the medulla of the spinal cord 90% of these fibers will crossto the opposite side obviously because the right hand side of the cerebral cortex controls the left hand side of the body 10% of the fibers do not cross and they form a bilateral system which innervates midlinemusculature midline musculature doesn't have the left and right categorization The Indirect Pathway– send axons from the motor and premotor cortex to nuclei in the brainstem which then send projections down the spinal cord to motor neurons in the ventral horn (and brainstem motor neurons). This system covers coarse motor control – piano moving. It makes up 50% of descending motor control. You might think that these pathways could be activated under conditions of stroke damage which damages the cerebral cortex in that the direct pathways are no longer functional but also the indirect pathways are no longer functional either as for voluntary motor activity the cortex is critically responsible for indirect motor pathway activation alsoThe motor and pre-motor cortex are responsible for executing motor activity however these neurons areunder the influence of other brain regions such as the basal ganglia which initiate motor function choosing the motor actions that will be executed and also under the executive activity of the cerebellar cortex which dictates how these motor functions are carried out.The motor cortex is not the boss of motor function, it receives what to do information from the basal ganglia and how to do information from the cerebellum.
The cortex sends direct (corticospinal) and indirect (corticobulbar/bulbospinal) projections to the spinal cord - lesion: paralysisMovement is initiated in the basal ganglia which then projects to the motor cortex – lesions : akinesia (Parkinson’s)Movement is regulated by the cerebellum which then projects to the motor cortex – lesions : dyskinesiaDescending Motor PathwaysDescending tracts deliver efferent impulses from the brain to the spinal cord, and are divided into two groups-Direct pathways equivalent to the pyramidal tracts-Indirect pathways, essentially all othersMotor pathways involve two neurons (upper and lower)-The upper motor neuron is in the motor cortex-The lower motor neuron is a spinal motor neuron or a cranial nerve motor neuronDirect SystemIndirect SystemIncludes the brain stem, motor nuclei, and all motor pathways not part of the pyramidal systemThis system includes the rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts
These motor pathways are complex and multisynaptic, and regulate:Axial muscles that maintain balance and postureMuscles controlling coarse movements of the proximal portions of limbsHead, neck, and eye movementReticulospinal tracts – maintain balance