Sensory Ascending Tracts PDF

Sensory System -Ascending Tracts Ekman Ch 6,7 Dr. Meeyoung Kim Neurosciences Physiotherapy Dept. University of Sharjah  - specialised (smell, vision, hearing, taste) Sensory - visceral (viscera, smooth muscle Receptors - unconscious or autonomic) - soma...

Sensory System -Ascending Tracts Ekman Ch 6,7 Dr. Meeyoung Kim Neurosciences Physiotherapy Dept. University of Sharjah  - specialised (smell, vision, hearing, taste) Sensory - visceral (viscera, smooth muscle Receptors - unconscious or autonomic) - somatic (skin, striated muscle, joints) Characteristics of sensory neurons Shape suited to function Receptor type specific to sense GRADED receptor potential Not all-or-nothing action potential  Sense of Touch Mechanoreceptors in the skin and viscera detect varying degrees of pressure. Free nerve endings have pain receptors and thermoreceptors.  Cutaneous receptors Muscle, tendon receptors There are various types of nerve fibres (axons) whose free endings form nociceptors.  Ascending tracts Watch the video before you come to the next lecture: https://www.youtube.com/watch?v=fnpSz8NaZSA The White matter of the spinal cord consists of Ascending and Descending Nerve Fibers. It is divided into Dorsal, Lateral & Ventral Columns or Funiculi. 9 very imp Ascending tracts ( lemniscus medialis) graphaesthesia ! stereoaesthesia !  (a) Ascending (sensory or afferent). (b) Descending (motor or efferent). They serve to join the brain to the spinal cord. fine touch conscious proprioception works for prox part of UL reticulo and vestibulo spinal tracts have 2 tracts -> medial and latera, working close to each other for balance  The main fiber remains on the ipsilateral side of the cord and terminates in synaptic contact with the second order neuron which lies either in the spinal grey matter or in t he medulla oblongata of the brain stem. does decussation at medulla level The first-order neuron or primary afferent neuron) enters the spinal cord through the dorsal root of a spinal nerve and its cell body lies in the dorsal root ganglion.  The axon of the second order neuron crosse s over (decussates) to the opposite side of the CNS and ascends to the thalamus, where it ter minates. The third-order neuron has its cell body in th e thalamus. Its axon passes to the somatosensory cortex o f the parietal lobe of the cerebral hemisphere. Spinothalamic Tracts (STT) no need all these * Rexed’s laminae are 10 laminae in grey matter  Lateral Spinothalamic Tract Function: Carries pain & Temperature to thalamus and sensory area of the cerebral cortex. neurons: 3 neurons Neuron I: Small cells in the dorsal root ganglia. Neuron II: Cells of substantia gelatinosa of Rolandi in the posterior horn. Neuron III: Cells of (VP) nucleus of the thalamus. The spinothalamic tract contains second-order neurons , the cell bodies of which lie in the contralateral dorsal horn.  Spinothalamic Tracts Located lateral and ventral to the ventral horn. Carry impulses concerned with; pain and therm al sensations (Lateral tract) and non- discrimi native touch and pressure (Anterior tract). In brain stem, constitute the spinal lemniscus. Information is sent to the primary sensory corte x on the opposite side of the body  Anterior Spinothalamic Tract Function: Carries crude touch & pressure to thalamus and sensory cor tex. Neurons: 3 Neurons Neuron I: Medium sized cells in the dorsal root ganglia. Neuron II: Cells of main sensory nucleus or (nucleus proprius). Neuron III: Cells of VP nucleus of thalamus.  Effect of lesion: Loss of crude touch sensation below the level of the lesion. decussation of spinothalamic tract there is decussation while they are crossing over problem in middle part of spinal cord  Syringomyelia, (widening of the central canal) leads to Loss of pain & temperature below the level of the lesion because the spinothalamic axons decussate to the opposite side of the cord by passing through the ventral white commissure, which lies ventral to the central canal of the cord,. Central canal enlarged ->cavity compress the adjacent nerve fibers (which are 2nd order neurons decussate in this place) ->selective loss of pain and temp. sensation in upper limb –>Joints of the limbs become disorganized without discomfort (Charcot's joint) ->Dorsal columns function is normal. Syringomyelia problem in commisure area bilateral problem mostly UL spinothalamic fibers crossing at cervical level are affected first dissociated sensory loss: temperature, pain disturbance on both hands Dorsal Column-Medial Lemniscal (DCML) Pathways  Three major pathways carry sensory information: Posterior column (Gracile & Cuneate fasciculi) Anterolateral pathway (Spinothalamic) Spinocerebellar pathway Dorsal Column-Medial Lemniscal Pathways Posterior Column: Contains two tracts; Fasciculus Gracilis (FG) & Fasciculus Cuneatus (FC) Carry impulses concerned with proprioception conscious and discriminative touch, vibrations from ipsilateral side of the body decussation happening second order neuron at Contain the axons of primary afferent neurons that hav medulla level e 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 cervi cal levels (T6 and above)  Fibers ascend without interruption where they terminate upon 2nd order neurons i n nucleus gracilis and nucleus cuneatus The axons of the 2nd order neurons dec ussate in the medulla as internal arcuate fibers and ascend through the brain ste m as medial lemniscus. The medial lemniscus terminates in the v entral posterior nucleus of the thalamu s (3rd order neurons), which project to t he somatosensory cortex (thalamocortic making a curve al fibers) Lesions in Dorsal columns Tabes dorsalis syphilitic infection, Affects: lumbosacral dorsal spinal roots and dorsal columns of the spinal cord. ->high step page and unsteady gait (sensory ataxia) Subacute Combined Degeneration of the spinal cord B12 deficiency ->Affects: Dorsal columns = Sensory ataxia. And Lateral columns (Lateral corticospinal tracts) = Weak & spastic limbs. Multiple sclerosis at T6 , above affects specifically fasciculus Cuneatus of the cervical region ->loss of proprioception in hands and fingers (Astereognosis) The difference between the routes of the lemniscal pathway (for touch and proprioception) and the spinothalamic pathway (for pain) the woman injured on the left side of her spinal cord, at the 10th thoracic vertebra. She will experience a reduced sense of touch on the left side of her body below the level of the injury, because the lemniscal pathway runs up the same (ipsilateral) side. She will also experience a reduced sense of pain below the injury, but on the right side of her body, because the spinothalamic pathway runs up the opposite (contralateral) side. As a result of this sensory dissociation, she will same side dorsal be able to feel it when a mosquito lands on her column pathway, information not right leg, but not if the mosquito then bites it. delivered opposite side spinothalamic tract not deliver informaion Spinocerebellar Tracts (SCT)  The spinocerebellar system consists of a seq uence of only two neurons; Spinocerebellar Tracts neuron I:Large cells of dorsal root ganglia. neuron II: cells of the nucleus dorsalis (Clark's nucleus. Two tracts: Dorsal &Ventral 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 tactile receptors to the cerebellum for the control of posture and coordination of movements  Posterior Spinocerebellar Tract Present only above level L3 The cell bodies of 2nd order neuron lie in Clark’s column Axons of 2nd order neuron terminate ipsilaterally (uncrossed) in the cerebellar cortex 3 peduncles connecting pons to cerebellum by entering through the inferior cerebellar peduncle. Posterior spinocerebellar tract convey sensory information to the same side of cerebellum no decussation  Ventral (Anterior)Spinocerebellar Tract The cell bodies of 2nd order neuron lie in base final destination of spinocerebellar -> cerebellum of the dorsal horn of the lumbosacral segments Axons of 2nd order neuron cross to opposite side, ascend as far as the midbrain, and then make a sharp turn caudally and enter superior cerebellar peduncle The fibers cross the midline for a second time within the cerebellum before terminating in the cerebellar cortex Ventral spinocerebellar tract convey sensory information to the same side of the cerebellum there is decussation twice Lesions in SCT Friedrichs ataxia inherited degenerated disease, affect SCT, affect childhood - >incoordination of arms, intense tremor, wide base reeling gait ataxia ->wheelchair in 20yrs.  only know the function (what I highlighted) 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 dorsal horn. Axons of 2nd order neuron cross to opposite side, and project to the periaquiductal gray matter and superior colliculus in the midbrain. Involved in reflexive turning of the head and eyes toward a point of cutaneous stimulation. only know the function (what I highlighted) Spinoreticular Tract only know the function (what I highlighted) Any questions?