Unit 3: ascending tracts Flashcards
what are the ascending tracts?
neural pathways by which sensory info from peripheral nerves is transmitted to cerebral cortex
what stimulus do meissner’s corpuscles detect?
fine touch and pressure
what stimulus do pacinian corpuscles detect?
vibration
what stimulus do free nerve endings detect?
pain and temperature
what stimulus do ruffini endings detect?
skin stretch, shear stress, deformation in joints
what stimulus do merkel’s endings detect?
crude touch (discriminative) and pressure
what stimulus do hair follicles detect?
light touch (fine touch/ non-discriminative)
what are the two conscious tracts?
dorsal column medial leminiscus pathway
anterolateral system
which pathway is initiated by fine touch, vibration and proprioception?
dorsal column medial leminiscus pathway
how many neurones are involved in the dorsal column medial leminiscus pathway?
3 - first, second, third order
what are the two types of first order neurones in the dorsal column pathway?
upper limb (t6 and above) travel in fasciculus cuneatus and synapse in nucleus cuneatus in the medulla oblongata (lateral) lower limb (below t6) travel in fasciculus gracilis and synpase in nucleus gracilis in the medulla oblongata (medial)
what do the second order neurones do in the dorsal column pathway?
carry information from the medulla oblongata to the ventral posterolateral nucleus in the thalamus
internal arcuate fibres decussate in the medulla and ascend the medial leminiscus to the thalamus
what is the medial leminiscus?
decussation of the internal arcuate fibres
what do the third order neurones do in the dorsal column pathway?
ascend from ventral posterolateral nucleus through the internal capsule to the sensory cortex
what are the two tracts of the anterolateral system?
anterior spinothalamic: crude touch
lateral spinothalamic: pain and temperature
what do the first order neurones do in the anterolateral system?
neurones arise from sensory receptors and enter spinal cord ascending 1-2 vertebral levels and synapse onto tip of dorsal horn = substantia gelatinosa
what do the second order neurones do in the anterolateral system?
fibres decussate in the spinal cord through the anterior white commissure and ascend the medulla synapsing onto the ventral posterolateral nucleus of the thalamus
what do the third order neurones do in the anterolateral system?
fibres ascend from the ventral posterolateral nucleus of the thalamus, through the internal capsule to the primary sensory cortex
what is brown sequard syndrome? what is its effect on the dorsal column and spinothalamic tracts?
hemisection of spinal cord (one-sided lesion)
dorsal column = ipsilateral sensory loss of fine touch, vibration and proprioception
spinothalamic = contralateral sensory loss of crude touch, pain and temperature
what are the unconscious tracts and what is their function?
spinocerebellar tracts - transmits information about propioception
what are the two type of spinocerebellar tracts?
dorsal - carries information from upper limb to ipsilateral cerebellum
ventral - carries information from lower limb to ipsilateral cerebellum
explain the two neurone pathway of the dorsal spinocerebellar tract
1) fibres enter spinal cord from dorsal root ganglion and synapse at thoracic nucleus
2) fibres ascend medulla along dorsal lateral funiculus and connects to cerebellum at inferior cerebellar peduncle
explain the two neurone pathway of ventral spinocerebellar tract
1) fibres synapse onto dorsal horn cells in lumbral/ sacral segments
2) fibres immediately decussate and ascend to midbrain along ventral aspect of lateral funiculus, then descends to superior peduncle decussating at the midline
what is the effect on the spinocerebellar tracts if there is a lesion in spnal cord?
ipsilateral loss of muscle coordination - spastic paralysis
accompanied by damage to descending motor tracts - muscle weakness/ paralysis
