Sensory Tracts PDF

Sensory TRACTS Reference: Basic & Clinical Anatomy of the Spine, Spinal Cord, & ANS by Cramer & Darby Chap. 9 • Afferent fibers travel into cord in dorsal rootlets • Each rootlet is divided into: • Lateral division • Pain and temperature fibers • Lissauer’s tract • Ascend/descend • Synapse in gra...

Sensory TRACTS Reference: Basic & Clinical Anatomy of the Spine, Spinal Cord, & ANS by Cramer & Darby Chap. 9 • Afferent fibers travel into cord in dorsal rootlets • Each rootlet is divided into: • Lateral division • Pain and temperature fibers • Lissauer’s tract • Ascend/descend • Synapse in gray • Medial division • Vibration, touch, pressure, proprioceptive fibers • Collaterals into gray and ascend or descend • Does not use Lissauer’s DORSAL ROOT ENTRY ZONE • Tract • • • • Organized bundle of axons (some overlap) Common origin Convey similar function Common destination ➢Ascending or Descending? ➢Information conveyed ➢If crossed, where? ➢Ascending tracts may convey information regarding: ⚫Type, location, intensity of stimulus ⚫Arousal, affective, motivational responses of stimulus ⚫Unconscious monitoring/control of motor activity (posture/movement) ➢NOTE: Ascending tracts are modulated by descending tracts CONCEPTS OF TRACTS Ordering of neurons First order Second order Third order Dorsal Column - Medial Lemniscus ➢Dorsal column - ipsilateral fibers in cord ➢Medial lemniscus - contralateral fibers in brain stem ➢Information conveyed: vibration, joint position sense, 2 pt (discriminatory) touch (& light touch), pressure ➢[also stereognosis & graphesthesia which needs functioning association cortex to be processed] ➢Crosses in tegmentum of caudal medulla as internal arcuate fibers Dorsal Column - Medial Lemniscus ➢1st order cell bodies are in the DRG ➢Axons of spinal nerves S5 –T7 ascend in the fasciculus gracilis. Axons of spinal nerves T6-C1 ascend in the fasciculus cuneatus ➢2nd order cell bodies are in the nuclei gracile and cuneatus ➢Axons cross as the internal arcuate fibers and ascend as the medial lemniscus ➢3rd order cell bodies are in the ventral posterior (lateral) thalamic nucleus ➢Axons course through the internal capsule to the sensory cortex (postcentral gyrus/post. paracentral lobule) (homunculus) ➢Somatotopically organized Thigh Trunk Upper extremity Head Knee Leg Foot ANTEROLATERAL SYSTEM • Anterolateral quadrant • Conveys pain and temperature (and some touch and pressure) • Nociception conveyed by A-delta and C fibers • A delta - fast conducting; localized, sharp/acute pain • C fiber - slow conducting; poorly localized; burning; aching pain • Predominantly crossed • Location - ventral white commissure ALS INCLUDES 3 TRACTS: ➢SPINOTHALAMIC (neospinothalamic, paleospinothalamic) ➢SPINORETICULAR ➢SPINOMESENCEPHALIC Spinothalamic tracts • Neospinothalamic • Courses directly to thalamus; most developed in primates • Sharp, well localized, discriminatory pain, A-delta • Terminates in primary sensory cortex (postcentral gyrus and paracentral lobule) • Paleospinothalamic • Collateral branches to Reticular F • Dull, achy, pain, C-fibers • Terminates in areas of cortex functionally associated with the motivational and affective aspect of pain • Widespread cortex Spinothalamic tract • Neospinothalamic is somatotopically organized Spinoreticular ➢Conveys cutaneous information associated with alertness, consciousness and pain (dull, achy) ➢Nociception is processed in areas involved with the affective and motivational aspects of pain ➢These result in autonomic, behavioral, and emotional responses to the painful stimuli ➢Also, part of the ascending reticular activating system (ARAS) ⚫Arouses cortex to maintain alertness and attentiveness (focus attention on painful area) Spinomesencephalic • Axons ascend to the: • Superior colliculus of the midbrain (spinotectal fibers) for reflex responses • Periaqueductal gray (PAG) of the midbrain • PAG neurons may provide descending feedback to the dorsal horn (modulates pain circuitry) via the reticular formation Indirect spinothalamic pathways. These pathways mediate the affective and arousal components of pain, temperature, and simple tactile sensations. Pain - 2 dimensions pp. 517 - 519 ➢Location, intensity, quality ⚫Neospinothalamic pathway to primary sensory cortex • Projects to posterior parietal lobe, insula then to amygdala, anterior cingulate cortex with reciprocal connections with the prefrontal cortex • These areas allow for integrating many sensory inputs to provide an overall feeling of the seriousness of the pain to the body ➢Affect and motivation to pain ⚫Spinoreticular, spinomesencephalic, spinohypothalamic pathways to brain stem nuclei, thalamus, hypothalamus • Produce elementary aspects: autonomic activation, escape responses, arousal, fear • Thalamic nuclei project to limbic (anterior cingulate cortex) system (pain is uncomfortable, aching, hurting) • Anterior cingulate cortex • Major area for processing the emotional component of pain • Connected with many other areas • • • • Amygdala - memory aspects Insula - autonomic component Parietal cortex Prefrontal cortex Pain modulation • Modulation using interneurons (substantia gelatinosa) which synapse on tract neurons • In the spinal cord • Mechanoreceptive afferents (+) synapse on interneurons (-) which inhibit tract neurons (gate control) • Supraspinal • PAG – to raphe nuclei and then to laminae I and II pp. 519 - 524 Tracts from Spinal Cord to Cerebellum • Unconscious proprioception • Mainly muscle spindles, GTO, joint capsule • Fibers are ipsilateral OR cross twice to end up reporting ipsilateral Dorsal Spinocerebellar Tract • Unconscious proprioception from the trunk and lower extremities (some touch and pressure) • 1st order cell bodies in the DRG • 2nd order cell bodies in Clarke’s nucleus (C8 - L3) • Axons ascend as the DSCT and leave the brain stem via the inferior cerebellar peduncle to terminate in the cerebellar cortex • How do fibers below L3 (L4-S3) get to Clarkes nucleus • Run in dorsal column until level L3 Cuneocerebellar Tract ➢Unconscious proprioception from the upper extremities ➢1st order cell bodies in the DRG ➢Axons ascend in the fasciculus cuneatus ➢2nd order cell bodies in the lateral/accessory cuneatus nucleus ➢Axons ascend as the CuCT and leave the brain stem via the inferior cerebellar peduncle to terminate in the cerebellar cortex Ventral Spinocerebellar Tract“rogue” • Unconscious proprioception from the trunk and lower extremities; transmits information from locomotor areas; may monitor activity of descending tracts • Input from sensory fibers and from interneuronal motor pools • 2nd order cell bodies in the ventral horn (not Clarke’s nucleus) • Axons cross, ascend as the VSCT and leave the brain stem via the superior cerebellar peduncle, recross in the cerebellum before terminating in the cerebellar cortex Spino-olivary tract • Conveys unconscious proprioception that ultimately terminates in the cerebellum; works with the cerebellum in motor learning and making corrections during on-going movements • 1st order axons terminate in dorsal horn • 2nd order axons cross and ascend to the inferior olivary nucleus and synapse • Olivocerebellar tractaxons from olive cross and travel via the inferior cerebellar peduncle into the cerebellum