ascending tract of the spinal cord
TRANSCRIPT
ASCENDING TRACTS (SENSORY PATHWAY)
Submitted under the guidance of : Dr. Sachin Shris, MBBS, MS
Submitted by : Nibedita Ayan
PATHWAY:• There is a continuous flow of information between the brain, spinal
cord, and peripheral nerves. • A group of neurons connecting two masses of grey matter is called a
tract.• Generally the pathways:
Consists of a chain of tracts, associated nuclei and varying number of relays (synapses)
Consist of two or three neurons Exhibit somatotopy (precise spatial relationships) Decussate Involve both the brain and spinal cord Are paired (bilaterally and symmetrically)
SOMATOSENSORY PATHWAY: When a tract relays sensory information from the receptors (peripheral nerve endings) to the brain , the tract is the Ascending (somatosensory) tract .• Monitor conditions both inside the body and in the external environment• Sensation-stimulated receptor passes information to the CNS via
afferent (sensory) fibers• Most sensory information is processed in the spinal cord , thalamus, or
brain stem. Only 1% reaches the cerebral cortex and our conscious awareness
• Processing in the spinal cord can produce a rapid motor response (stretch reflex)
• Processing within the brain stem may result in complex motor activities (positional changes in the eye, head, trunk)
ASCENDING TRACTS:• LATERAL SPINOTHALAMIC TRACT• ANTERIOR SPINOTHALAMIC TRACT• FASCICULUS GRACIALIS• FASCICULUS CUNEATUS• DORSAL (post.) SPINOCEREBELLAR TRACT• VENTRAL (ant.) SPINOCEREBELLAR TRACT• SPINO-OLIVARY TRACT• SPINOTECTAL TRACT
• Three major pathways carry sensory informationPosterior/Dorsal
column pathway (gracile & cuneate fasciculi)
Anterolateral pathway (spinothalamic)
Spinocerebellar pathway
All these three pathways involve a sequence of three neurons each.
>> First-order neuron • Delivers sensations to the CNS • The cell body is in the dorsal or cranial root ganglion
>> Second-order neuron • An interneuron with the cell body in the spinal cord or brain
>> Third-order neuron • Transmits information from the thalamus to the cerebral cortex
Based on the perception • For conscious perception:
Spinothalamic system• For unconscious perception:
SpinocerebellarSpino-olivarySpinotectalSpinoreticular
Dorsal Column• Contains two tracts, Fasciculus gracilis (FG) & fasciculus cuneatus (FC)
• Carry impulses concerned with proprioception and discriminative touch from ipsilateral side of body
• Contain the axons of primary afferent neurons that have entered cord through dorsal roots of spinal nerves
FG contains fibers received at sacral, lumbar and lower thoracic levels, FC contains fibers received at upper thoracic and cervical levels.
Fibers ascend without interruption where they terminate upon 2nd order neurons in nucleus gracilis and nucleus cuneatus
The axons of the 2nd order neurons decussate in the medulla as internal arcuate fibers and ascend through the brain stem as medial lemniscus.
The medial lemniscus terminates in the ventral posterior nucleus of the thalamus upon 3rd order neurons, which project to the somatosensory cortex (thalamocortical fibers)
Spino-thalamic Tracts
• Located lateral and ventral to the ventral horn
• Carry impulses concerned with pain and thermal sensations (lateral tract) and also non- discriminative touch and pressure (medial tract)
• Fibers of the two tracts are intermingled to some extent
• Fibers are highly somato-topically arranged, with those for the lower limb lying most superficially and those for the upper limb lying deeply
Information is sent to the primary sensory cortex on the opposite side of the body
Spinocerebellar Tracts• The spinocerebellar system
consists of a sequence of only two neurons
• Two tracts: Posterior & Anterior
• Located near the dorsolateral and ventrolateral surfaces of the cord
• Contain axons of the second order neurons
• Carry information derived from muscle spindles, Golgi tendon organs and tectile receptors to the cerebellum for the control of posture and coordination of movements
Spinotectal Tract• Ascends in the anterolateral
part in close association with spinothalamic system
• Primary afferents reach dorsal horn through dorsal roots and terminate on 2nd order neurons
• The cell bodies of 2nd order neuron lie in base of the dorsal horn
• Axons of 2nd order neuron cross to opposite side, and project to the superior colliculus in the midbrain
Spino-olivary Tract• Indirect spinocerebellar pathway (spino-olivo-
cerebellar)• Impulses from the spinal cord are relayed to
the cerebellum via inferior olivary nucleus• Conveys sensory information to the
cerebellum• Fibers arise at all level of the spinal cord
TRACT SENSATION FIRST ORDER
SECOND ORDER THIRD ORDER FINAL DESTINATION CROSS-OVER SITE
POSTERIOR COLUMNSFASCICULUS GRACIALIS Proprioception; inferior to T6 Dorsal root
gangliaNucleus Gracialis Posteriolateral ventral
nucleus of thalamusPrimary Sensory Cortex on opposite side (contralateral)
Uncrossed
FASCICULUS CUNEATUS Proprioception; superior to T6
Dorsal root ganglia
Nucleus Cuneatus Posteriolateral ventral nucleus of thalamus
Primary Sensory Cortex on opposite side (contralateral)
Uncrossed
SPINOTHALAMIC TRACTSLATERAL SPINOTHALAMIC Pain and temperature Dorsal root
gangliaSubstantia Gelatinosa
Posteriolateral ventral nucleus of thalamus
Primary sensory cortex ;contralaterally
Crosses in the same segment
ANTERIOR SPINOTHALAMIC Crude touch and pressure Dorsal root ganglia
Nucleus Proprius Posteriolateral ventral nucleus of thalamus
Primary sensory cortex ;contralaterally
Ascends 2-3 segments and then crosses
SPINOCEREBELLAR TRACTSPOSTERIOR SPINOCEREBELLAR Proprioception Dorsal root
gangliaClark’s Column NIL Cerebellar cortex ;
ipsilaterallyUncrossed
ANTERIOR SPINOCEREBELLAR Proprioception Dorsal root ganglia
Neurons of Posterior Horn
NIL Cerebellar cortex ; ipsilaterally
Crosses twice;-spinal cord-midbrain
NON SPECIFICSPINO-OLIVARY Proprioception - - - Olivary nuclei UncrossedSPINOTECTAL Afferent limb of reflex
movement of eyes and head- - - Tectum or superior colliculus Crossed
CLINICAL CO-RELATESTRACT CLIINICAL TEST RELATED DISORDERS
LATERAL SPINOTHALAMIC
Pain with pin prick Temperature test Brown Sequard’s
Syndrome (due to hemisection of spinal cord)
Syringomyelia
ANTERIOR SPINOTHALAMIC
Joint sense Vibration Tactile localization Romberg's test Stereognosis Crude touch Crude pressure
FASCICULUS GRACIALIS
FASCICULUS CUNEATUS
DORSAL SPINOCEREBELLAR Cerebellar tests (finger ,nose, heel-
knee tests)VENTRAL SPINOCEREBELLARSPINO-OLIVARY
Visual and proprioception testsSPINOTECTAL
th@nkU