Where do projections that control reflexive control of head position arise from?
Neurons in the medial vestibular nucleus give rise a medial vestibulospinal tract that terminates bilaterally in the medial ventral horn of the cervical cord, where it regulates head position by reflex activation of neck muscles in response to the stimulation of the semicircular canals.
Where do projects that reflexively maintain stable balance and upright posture arise from?
Neurons in the lateral vestibular nucleus are the source of the lateral vestibulospinal tract, which courses through the anterior white matter in a slightly more lateral position than the medial vestibulospinal tract. The lateral vestibulo spinal tract terminates among medial lower motor neuron pools that govern proximal muscles of the limbs. This tract responds to stimulation of the otolith organs.
What is the reticular formation?
A complicated network of circuits in the core of the brainstem that extends from the rostral midbrain to the caudal medulla; it is similar in structure and function to circuitry in the intermediated gray matter of the spinal cord. Its descending motor control pathways to the spinal cord are similar to the vestibular nuclei's, they terminate on the medial parts of the gray matter
What are some of the functions of the neurons in the reticular formation?
Cardiovascular and respiratory control, the governance of myriad sensory sensory motor reflexes, the coordination of eye movements, regulation of sleep and wakefulness, and the temporal and spatial coordination of limb and trunk movements
What is the primary purpose of the reticular formation in motor control?
Predicting and adjusting for postural instability caused by volitional movements
Where do the projections that control axial musculature of the neck arise from?
The superior colliculus via the colliculospinal tract terminating on medial cell groups of the cervical cord and in non-humans, the red nucleus via the rubrospinal tract in the lateral white matter, terminating in the lateral regions of the ventral horn and intermediate zones
Describe the descending pathways from the primary motor and premotor cortex.
The axons of these motor neurons descend in the corticobulbar ("bulbar" refers to brainstem nuclei) and corticospinal tracts. They pass through the posterior limb of the internal capsule in the forebrain to enter the cerebral peduncle at the base of the midbrain. They run through the base of the pons and coalesce on the ventral surface of the medulla where they form the medullary pyramids. Here the corticobulbar tract that innervates cranial nerve nuclei (reticular formation, red nucleus, basilar pontine nuclei) leave the pathway at appropriate levels of the brainstem. At the caudal end of the medulla, 90% of the axons in the pyramidal tracts decussate as they enter the lateral corticospinal tract. The remaining 10% constitute the ventral corticospinal tract and terminate ipsilaterally or bilaterally (crossing the midline via the ventral white commissure).
Where do axons of the lateral corticospinal tract terminate?
Lateral portions of the ventral horn and intermediate gray matter, with some axons synapsing directly on some of the α motor neurons that control the forearm and hand
What is the functional distinction between the premotor cortex and the primary motor cortex?
The primary motor cortex has more monosynaptic connections with α motor neurons.
What distinguishes the lateral premotor cortex?
The lateral premotor cortex is more involved in closed loop motor programs and the selection of movements (as opposed to directly causing the movements) based on external events. Mirror motor neurons and Broca's area are also located in the lateral premotor cortex
What part of the brain is most involved in open loop motor programs?
The medial premotor cortex