Ascending Tracts
Ascending tractsTasneem25-10-2021DPT
TractsBundle of fibers having the same origin, termination andcarry the same function. These occupy almost a definiteposition in the white matterAscending tractsconvey sensory information from spinal cord to brainDescending tractsconvey motor information from brain to spinal cord Most exhibit somatotopy (precise spatialrelationships) All pathways are paired , Right and left
The four ascending (sensory) tracts Dorsal columnSpinothalamic tractSpinocerebellar tractTrigeminothalamic tract
Dorsal Column Tract(Medial lemniscal pathway)Fibers run only in dorsal columnTransmit impulses from receptors in skinand jointsDetect discriminative touch andbody position sense consciousproprioception1st order neuron – Dorsal root / sensoryneuron synapses with2nd order neuron – Fasciculus gracilis(Sacral/lumbar) to nucleus gracilisFasciculus cuneatus (thoracic/cervical) tonucleus cuneatus in the medulladecussate (internal arcuate fibers) andascend to contralateral thalamus3rd-order neuron - VPL (thalamicneurons)transmits impulse to somato- sensorycortex (postcentral gyrus)
The lateral and anteriorspinothalamic tracts Lateral: transmits impulsesconcerned with pain and temp. toopposite side of brain Anterior: transmits impulsesconcerned with crude touch andpressure to opposite side of brain 1st order neuron: DR sensoryneuron 2nd order neuron: interneurons ofdorsal horn; decussate & ascend 3rd order neuron: VPL inthalamus; carry impulse fromthalamus to postcentral gyrus
Spinocerebellar tractsAnterior & PosteriorUnconscious proprioception frommuscle spindle & Golgi tendonorgans ; position of joint andpostural movementPrimary neuron DRS neuronsSecondary neurons Dorsal columnof Clark C8 –L2 segment SPC. Post Sp. Cerebl. Tract do notdecussate pass through theInf. Cerebl. Peduncle tocerebellum Ant. Sp. Cerebl. Tractdecussate at the level ofantery. Fibers (Clarke’scolumn) pass though sup.Cerebl. Peduncle tocerebellumV,VI,VIIBoth the ventral and dorsal spinocerebellartracts are concerned mainly with the lowerlimbs and trunk.
The Cuneocerebellar tractThe cuneocerebellar tract carries impulses from the upper limb First order neurons: some of the central processes of DRG(related to cervical segments) reach the accessory cuneatenucleus in the medulla. Second order neurons in accessory cuneate nucleus formthe posterior external arcuate fibres which via the inferiorcerebellar peduncle (of the same side) reach the cerebellum.
Trigeminothalamic tractReceives sensory impulses from several cranialnerves:CNV : receives general afferents from the skin ofthe face/head/neckSynapse in trigeminal ganglionCNVII, CNIX, CNX (visceral afferents from the restof the body) via the spinal nucleusSynapse at parasympathetic nuclei in medullaTrigeminal nerve has 3 sensory nuclei Mesencephalic nucleus (proprioception) Chief/primary nucleus (pressure, touch) –Spinal nucleus (pain, temp)
Primary neurone trigeminal ganglion (like DRG)(except Mesencephalic nuclei)Synapses in the trigeminal nucleus inbrainstem according to sensation (e.g.pain in the spinal nucleus)Pain/temp in spinal nucleusTouch/pressure in chief nucleusProprioception in mesencephalicnucleus itselfSecondary neurone Decussates at level of entry intobrainstemTravel up (trigeminal lemniscus)Synapses in the VPM of thalamusTertiary neurone FromVPM via internal capsuleSynapses in primary sensory cortex (toface division – more lateral than limbs)
Spinal Cord injury and DisordersVentral root lesion (LMN) results inflaccid paralysis (limp and unresponsive)Skeletal muscles cannot move either voluntarily or involuntarilyWithout stimulation, muscles atrophy.Primary motor cortex damage (UMN lesion)spastic paralysis occurs - muscles affected by persistentspasms and exaggerated tendon reflexesTransection /cross section of cord at any level results intotal motor and sensory loss in body regions inferior to site of damage.If injury in cervical region, all four limbs affected (quadriplegia)If injury between T1 and L1, only lower limbs affected (paraplegia)
Results after damage toone side of the spinal cordonly (hemisection),typically in the neck(cervical spinal cord), orthoracic spinal cordCharacterized by a lesionin the SC results inweakness or paralysis(hemiparaplegia) on oneside of the body and a lossof sensation(hemianesthesia) on theopposite side.Brown-Séquard syndrome:
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Tracts Bundle of fibers having the same origin, termination and carry the same function. These occupy almost a definite position in the white matter Ascending tracts convey sensory information from spinal cord to brain Descending tracts convey motor information from brain to spinal cord
Indicate on a diagram of a cross-section of the spinal cord, the ascending and descending tracts. List any three of each of the following: ascending tracts descending tracts characteristics of conscious ascending tracts. Desc
Spinal Tracts Ascending tracts Descending tracts (Crossman & Neary, 2019) Ascending tracts Dorsal columns fasiculus gracilis fasciculus cuneatus Spinothalamic tracts lateral . spinal cord and terminates by synapsing with the lower motor neurone in spinal cord Lo
18. In general, _?_ spinal cord tracts carry sensory information and _?_ tracts carry motor information. (a) ascending, descending (b) descending, ascending (c) projection, commisural (d) commissural, association (e) none of these 19. Most ascending spinal cord tracts _?_ . (a) are crossed (b) involve three sets of synapses (c) have connections
(contralateral) sides of the brain or spinal cord. Projection: Tracts that run longitudinally through the CNS, connecting “higher” and “lower” areas. Ascending or Afferent: Projection tracts carrying sensory information “up” through the CNS. Descending or Efferent: Projection tracts carrying motor information “down” through the CNS.
functions. Sensory information from ascending tracts is also essential for posture, balance, and coordination of movements. Here, the main projections from the brain to the spinal cord and vice versa are summarized. 2.1. Descending motor tracts The descending tracts in the spinal cord (Figure 1, left-hand side) run from the brain and
The white matter of the spinal cord is composed of ascending and descending fiber tracts. These are arranged into six columns of white matter called funiculi. The fiber tracts within the white matter of the spinal cord are named to indicate whether they are ascending (sensory) or
Spinal tract, any one of the ascending (sensory) and descending (motor) pathways for sensory or motor nerve impulses that is found in the white matter of the spinal cord. Twenty-one different tracts lie within the dorsal, ventral, and lateral funiculi of the white substance. Ascending tracts conduct impu
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