Tracts Flashcards
Epicritic carries what?
- fine/discriminatory touch (texture, slippage, position)
- vibration
- proprioception
Epicritic runs where?
- dorsal/posterior column in spinal cord - afferents add laterally as it ascends: fasciculus cuneatus (cervical/above T6) is lateral and fasciculus gracilis (lumbar/below T6) is medial
- synapse in dorsal nuclei in medulla (cuneatus and gracilis)
- secondary neuron decussates in caudal medulla, crossing in the internal arcuate fibers
- becomes medial lemniscus which begins ascending anterior midline but gradually moves away from midline through brainstem
- synapse in VPL nucleus of thalamus
- tertiary neuron projects via posterior limb of internal capsule to synapse in S1
Epicritic also called
lemniscal pathway
Epicritic afferent fiber type
large, rapidly conducting, myelinated fibers:
- A-beta Ib run from GTO, carry sensation and muscle force info
- A-beta II run from skin receptors (Pacinian, Ruffini [skin/joint], Meissner’s, Merkel’s), carry sensation
Protopathic carries what?
- pain (fast [Adelta] and slow [C fibers])
- temperature
- crude touch
Protopathic runs where?
- into dorsal horn, up/down Lissauer tract, synapse in layer I/V
- from dorsal horn (V), secondary neuron crosses midline in the anterior white commissure; as they ascend new fibers are added medially (legs lateral, arms medial)
- ascends spinal cord and brainstem in the anterolateral tract; runs lateral through brainstem but then moves more dorsal while staying lateral when going from medulla to pons to midbrain
- synapses in VPL of thalamus, with collaterals to the intralaminar (projects diffusely throughout cortex for general arousal) and dorsomedial nuclei (for projects to prefrontal cortex)
- tertiary neuron projects to S1
Protopathic also called
lateral spinothalamic
Protopathic afferent fiber type
small, slowly conducting, lightly myelinated or unmyelinated fibers:
- A-delta (lightly myelinated) run from free nerve endings, carry fast pain/temp
- C fibers (unmyelinated) run from free nerve endings, carry second pain/temp
Vestibulospinal
- mediates reflex to catch yourself in a fall*
- falling sensed by vestibular system
- from vestibular nuclei
- innervates neck and trunk muscles
- integrates/coordinates movements of head/trunk based on balance
Reticulospinal
- from reticular formation (in pons/medulla)
- innervates neck and trunk muscles
- coordinates movements of head and trunk
Rubrospinal
- from red nucleus
- travels closely with corticospinal tract and participates in control of arm muscles
Colliculospinal/Tectospinal
- turns head/eyes when your attention is caught in the periphery*
- from superior colliculus
- to cervical spinal cord to innervate neck muscles
- coordinates head/neck movements with eye movements and attention
Corticobulbar
motor cortex to brainstem to innervate ipsi/contralateral brainstem motor nuclei - 3, 4, 5, 6: ipsi and contra - 7 - upper face: ipsi and contra 7 - lower face: contra only - 9, 10, 11, 12: ipsi and contra
Somatotopy of corticospinal and corticobulbar tracts in: cortex, IC, and spinal cord
- cortex: face is lateral, leg/foot is medial
- internal capsule: corticospinal is posteromedial, corticobulbar is anteromedial
- spinal cord/LMNs: extremities are lateral, trunk is medial
Pyramidal tract
aka corticospinal
- runs from motor cortex (pre-central gyrus)
- descends via corona radiata, posterior limb of internal capsule, then through the crus cerebri in anterior midbrain then start to break up in pons
- 85-90% of fibers decussates at the pyramidal decussation in the lower anterior medulla and form the lateral CS tract
- the remaining 10-15% of fibers descend ipsilaterally and are called the anterior CS tract
- Spinal cord to LMNs:
lateral CS tract –> synapses in anterior horn
anterior CS tract –> crosses midline at level and then synapses on LMN in anterior horn
Dorsal spinocerebellar tract
carries unconscious proprioceptive input from periphery to the cerebellum
A alpha afferents
- Epicritic information on touch and pressure*
- (Ia and Ib) mostly carry info from muscles - spindles and GTOs, resp.
- these synapse in deep dorsal horn layers, as well as directly in ventral horn on alpha motoneurons for monosynaptic reflex
A beta afferents
- Epicritic information on touch and pressure*
- carry cutaneous and joint sensations
- synapse in deep dorsal horn
A delta and C fibers
- Protopathic information on pain and temp*
- first synapse in Substantia gelatinosa (Rexed layers I and II) for modulation
- can also synapse first in layer V
- interneuron can project up/down in Lissauer tract
- second-order neuron gets input in the ipsilateral dorsal horn, then decussates and ascends in the anterolateral spinothalamic tract
Spinoreticular tract
- division of the spinothalamic tract but terminates in the reticular formation in the pons (instead of thalamus)
- neurons come from all layers of the dorsal horn
- for general arousal, emotional aspects of pain
Spinomesencephalic tract
- division of the spinothalamic tract but terminates in the periaqueductal gray in the midbrain (instead of thalamus)
- neurons come from layer I and V of the dorsal horn
- important for activating descending efferent pathways that modulate pain
Trigeminal epicritic input
- cell body in trigeminal ganglion
- synapse in chief/principal sensory nucleus of V
- some decussate and ascend in ATT; some don’t decussate and ascend in PTT
- all go to VPM to synapse and then project to lateral S1
Trigeminal protopathic input
- cell body in trigeminal ganglion
- descend in spinal trigeminal tract
- synapse in spinal trigeminal nucleus
- decussate
- ascend in ATT/ventral trigeminal lemniscus
- synapse in VPM, project to lateral S1
Dorsal spinocerebellar tract
- afferents from spindles and GTOs from leg and body
- afferents ascend via fasciculus gracilis
- synapse in Clarke’s nucleus
- project to cerebellum with synapse in inferior cerebellar peduncle
