Tracts Flashcards
Corticospinal tract
The corticospinal tract controls voluntary fine motor control and has a slight flexor bias (connects with motorneurons that innervate flexor muscles).
Overview of tract - begins in the primary motor cortex (BA4) and descends through the posterior limb of the internal capsule, through the cerebral peduncles and continues through the longitudinal fibers of the pons. When the axons reach the pyramids, 90% of them decussate in the medullary pyramids to form the lateral corticospinal tract (LCST - associated with distal musculature or arms/legs, you can move one arm independent of the other and in specific ways, so this is contralateral and this requires more axons) and the other 10% continue ipsilaterally to form the anterior corticospinal tract (ACST - associated w axial muscles, think about moving your back, you can’t move half independent of the other so it is bilateral and requires less axons as its a more general movement).
The LCST synapses on the ventral horn contralaterally, whereas the ACST synapses on the ventral horn bilaterally
Corticobulbar tract
The corticobulbar tract is responsible for voluntary movement of the face/neck - it contains LOTS OF TERMINATIONS
Overview of tract - begins in the primary motor cortex (BA 4) OR the frontal eye fields (follows a SLIGHTLY different path). Signals from the primary motor cortex follow axons through the genu of the internal capsule, continue through the cerebral peduncles to the longitudinal fibers of the pons, and to the pyramids. Along this pathway, axons leave the larger bundle and synapse in their respective motor cranial nerve nuclei, as well as the red nucleus.
CN V - trigeminal nucleus - associated with chewing - bilateral
CN VII - facial motor nucleus - associated with facial expression
UPPER face - bilateral
LOWER face - contralateral
Nucleus ambiguus - speaking/swallowing (CN IX, X, and XI) - bilateral
CN XII - hypoglossal nucleus/ nucleus of XII - associated with the tongue - contralateral
Red Nucleus directs what signals get sent to proximal limbs - ipsilateral
Signals from the frontal eye field axons descend through the anterior limb of the internal capsule and synapse at the paramedian pontine reticular formation (PPRF) to influence CN III, IV, and VI indirectly.
PPRF - I believe it is bilateral but I need to ask - i’ve been told eye movements will not be on the exam :)
Vestibulospinal tract
Originates in the vestibular nuclei of brain stem (6&7, 8&9, and 10&12) and can be medial or lateral. Medial (rotation head and neck): travels within medial longitudinal fasciculus below VI then to ventromedial spinal cord. Decussates at the brain stem in sensory decussation. Bilateral to origin. Terminates in the ventral horn (cervical and high thoracic)
Lateral (balance of trunk, proximal limbs): travels in brainstem then ventrolateral spinal cord. ipsilateral (does not decussate) terminates at all levels of the ventral horn
Tectospinal tract
In charge of reflexes for head and neck and eye movements. Starts in the superior colliculus then travels ventral to MLF then ventromedial spinal cord. Decussates immediately in dorsal tegmental decussation (contralateral to origin) terminates in the ventral horn (cervical)
Reticulospinal tract
Ponto-reticulospinal (extensor, limp): starts in pontine reticular formation, travels via anterior funiculus, ipsilateral (no decussation) terminates in the ventral horn
Medullary reticulospinal tract (flexor, limp): starts in medullary reticular formation via anterolateral funiculus, bilateral (medullary cross) terminates in the ventral horn
Rubrospinal tract
Gross movements of upper body (flexor). Starts in the red nucleus, travels dorsolateral in white mater with LCST in spinal cord (cerebral peduncles). Decussates at ventral tegmental decussation (contralateral) and terminates in the ventral horn (cervical). Location: dorsolateral
Dorsal Column Medial Lemniscal system
Fine touch and proprioception. Sensory transduction in the periphery, cell body in dorsal root ganglion. Enter spinal ford and travel in dorsal fascicule (cuneate arms, gracile legs). Synapse in dorsal fascicule in the caudal medulla at sensory decussation (across midline as arcuate fibers). Synapse in VPL then sends axons through posterior limb of internal capsule to the primary somatosensory cortex.
Anterolateral system (ALS)
Pain and temperature. Complex nociception (dimensions, reflex, autonomic, affective, behavioral).
Neuron 1: DRG, terminates in substantia gelatinosa (L3/5)
Neuron 2: decussates at ventral white commissure (immediate) and terminates in VPL
Neuron 3: terminates in postcentral gyrus
