1 / 52

The Somatosensory System CH7 Blumenfield

The Somatosensory System CH7 Blumenfield. By: Laurence Poliquin-Lasnier R2 neurology. Outline. Sensory neuron Main somatosensory pathways Posterior column-medial lemniscus Spinothalamic tract Somatosensory cortex Central modulation of pain Thalamus Spinal cord syndromes

kura
Download Presentation

The Somatosensory System CH7 Blumenfield

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. The Somatosensory SystemCH7 Blumenfield By: Laurence Poliquin-Lasnier R2 neurology

  2. Outline • Sensory neuron • Main somatosensory pathways • Posterior column-medial lemniscus • Spinothalamic tract • Somatosensory cortex • Central modulation of pain • Thalamus • Spinal cord syndromes • Bladder, bowel and sexual function

  3. Main somatosensory pathways • Posterior column-medial lemniscus • Proprioception, vibration, fine discriminative touch • Spinothalamic tract • Pain, temperature, crude touch • Via unipolar sensory neuron

  4. Unipolar sensory neuron

  5. Sensory neuron fiber types

  6. Sensory neuron • Sensory neuron cell body located in dorsal root ganglia • A peripheral region innervated by sensory fibers from a single nerve root = dermatome

  7. Outline • Sensory neuron • Main somatosensory pathways • Posterior column-medial lemniscus • Spinothalamic tract • Somatosensory cortex • Central modulation of pain • Thalamus • Spinal cord syndromes • Bladder, bowel and sexual function

  8. Posterior column-Medial lemniscus

  9. Posterior column-Medial lemniscus • Large myelinated axons • Proprioception, vibration, fine touch

  10. Posterior column-Medial lemniscus Ascend through: • Gracile Fasciculus: legs + lower trunk • Cuneate Fasciculus: arms, neck, trunk above T6 • 1st order sensory neuron synapses synapse onto 2nd order neurons in the nucleus gracilis and nucleus cuneatus at th level of the medulla • Axons of these 2nd order neurons decussate as internal arcuate fibers and form the medial lemniscus on the other side of the medulla

  11. Posterior column-Medial lemniscus • 2nd order neurons synapse into the ventral posterior lateral (VPL) nucleus of the thalamus • 3rd order neurons then project to the posterior limb of the internal capsule to reach the primary somatosensory cortex in the post-central gyrus

  12. Sensory homunculus

  13. Outline • Sensory neuron • Main somatosensory pathways • Posterior column-medial lemniscus • Spinothalamic tract • Somatosensory cortex • Central modulation of pain • Thalamus • Spinal cord syndromes • Bladder, bowel and sexual function

  14. Spinothalamic tract

  15. SpinothalamicTract • Small diameter • Unmyelinated • Pain and temperature

  16. Spinothalamic tract • Enter spinal cord via dorsal root ganglia • 1st order neuron synapse in the grey matter of the dorsal horn marginal zone (lamina1) and deeper in the dorsal horn (lamina 5) • Some axon collaterals ascend or descend for a few segments in lissauer tract before entering the central gray • 2nd order neuron cross over in the spinal cord anterior commissure to ascend in the anterolateral white matter • It takes 2-3 spinal segments for the decussating fibers to reach the opposite side ( so sensory level of spinal cord lesion starts a few levels below the lesion)

  17. Spinothalamic tract • Anterolateral pathway reaches medulla • Run between the olives and the inferior cerebellar peduncles • Enters pontinetegmentum • 2nd order neuron synapses in the thalamus to 3rd order neuron • 3rd order neuron to somatosensory cortex in the postcentralgyrus • Secondary somatosensory association cortex in parietal operculum (somatotopic organization) and association area in posterior parietal lobule

  18. Anterolateral pathway: 3 tracts • Spinothalamic (I, V) • Discriminative aspects of pain, location, intensity • Synapse on VPL (different area than DCML), relay to specific SSC target (Brodmann 3,1,2) • Spinoreticular (VI, VII, VIII) • Emotional and arousal aspects of pain • Reticular formation projects to intralaminar thalamic nuclei (centromedian), which then project diffusely to the entire cerebral cortex (behavioural arousal) • Spinomesencephalic (I, V) • To periaqueductal grey and superior colliculi • Pain modulation

  19. Outline • Sensory neuron • Main somatosensory pathways • Posterior column-medial lemniscus • Spinothalamic tract • Somatosensory cortex • Central modulation of pain • Thalamus • Spinal cord syndromes • Bladder, bowel and sexual function

  20. Central modulation of pain • Gate control theory • Sensory input from large diameter non pain A-β fibers reduce pain transmission through the dorsal horn • Periaqueductal gray receives input from: hypothalamus, amygdala, cortex • Inhibits pain transmission in the dorsal horn via relay in rostral ventral medulla (RVM) • RVM includes serotonergic neurons of the raphe nuclei that project to the spinal cord and modulate pain • RVM sends input (via substance P) to the locus ceruleus to spinal cord dorsal horn (via NE)

  21. Central modulation of pain • Opiate receptors and endogenous opiate peptides located at key points in the pain modulatory pathways • Enkephalin and dynorphin -> PAG, RVM, dorsal column • β-endorphin -> hypothalamus

  22. Outline • Sensory neuron • Main somatosensory pathways • Posterior column-medial lemniscus • Spinothalamic tract • Somatosensory cortex • Central modulation of pain • Thalamus • Spinal cord syndromes • Bladder, bowel and sexual function

  23. Thalamus • Major sensory relay station • Deep gray matter structure part of the diencephalon • Convey different types of input to the cortex • Sensory • Motor from cerebellum and basal ganglia • Limbic • Modulatory inputs involved in aroual and sleep-wake cycle

  24. Thalamus • Divided by internal medullary lamina (a Y shaped structure) into: • Medial nuclear group • Lateral nuclear group • Anterior nuclear group • Nuclei within internal medulary lamina called intralaminar nuclei

  25. Thalamus

  26. Thalamus • 3 categories of nuclei: • Relay nuclei • Intralaminar nuclei • Reticular nucleus

  27. Thalamus: Relay nuclei • Lie mainly in lateral thalamus • All primary sensory modalities have relays in the lateral thalamus en route to their specific cortical target, with one exception -> olfaction • Reciprocal innervationw/ cortex

  28. Thalamus: Relay nuclei -> Lateral nuclear group

  29. Thalamus: Relay nuclei -> other groups

  30. Thalamus

  31. Clinical concept: dysfunction in pain pathways • Negative symptom = sensory loss • Positive symptoms = paresthesias = added sensation • Dysesthesia = unpleasant abnormal sensation • Allodynia = painful sensation provoked by minor stimulus eg.: light touch • Posterior column: tingling, numb, tight band, walking on clouds • Anterolateral: sharp, burning pain

  32. Outline • Sensory neuron • Main somatosensory pathways • Posterior column-medial lemniscus • Spinothalamic tract • Somatosensory cortex • Central modulation of pain • Thalamus • Spinal cord syndromes • Bladder, bowel and sexual function

  33. Spinal cord lesions Spinal shock: • Flaccid paralysis below the lesion • Loss of DTR • Autonomic dysfunction • Decreased sympathetic outflow to vascular smooth muscles -> Hypotension • Absent sphincter tone • Over weeks to months, spasticity and UMN signs develop Cord compression: • If non-ambulatory at tx, 80% remain so • If ambulatory at tx, 80% will remain mobile

  34. Sensory loss: patterns and localization • Primary somatosensory cortex • Contralateral face, arm, leg, trunk • Two point discrimination, extinction, stereognosis, graphestesia • Thalamus (VPL or VPL) • Contralateral face, arm, leg, trunk • Relative preservation of cortical features • Lateral pons and medulla • Pain and temperature • Ipsi face and contra hemibody • Medial medulla • Medial lemniscus = vibration, position sense

  35. Spinal cord syndromes • Transverse cord syndrome • Sensory level with loss of all sensory modalities • DDx: trauma, tumor, MS, transverse myelitis

  36. Spinal cord syndromes • Hemicord syndrome • “Brown-Sequard” • Damage to lateral corticospinal tract = ipsi UMN weakness • Damage to post. column = ipsi loss of vibration and position sense • Damage to anterolateral system = contra pain and temperature • May have a strip of 1-2 segments of ipsi loss of pain and temp caused by damage to post horn cell before their axons have crossed over

  37. Spinal cord syndromes • Central cord syndrome • Suspended sensory loss to pain and temp • Cape-like pattern if cervical cord • Suspended dermatomes if at other level • LMN deficit if damage to anterior horn cells

  38. Spinal cord syndromes • May get sacral sparing as spinothalamic tract = more medial cervical region and more lateral sacral region • Causes of central cord syndrome: • Spinal cord contusion, post-traumatic syringomyelia, intrinsic spinal cord tumor

  39. Spinal cord syndromes • Posterior cord syndrome • Loss of vibration and position sense below the lesion • May get UMN weakness if it encroaches lateral corticospinal tract • Causes: trauma, extrinsic compression, MS, Vitamin B12 deficiency, tabesdorsalis (tertiary syphilis), HTLV-1

  40. Spinal cord syndromes • Anterior cord syndrome • Damage to anterolateral pathway = loss of pain and temp below lesion • Damage to anterior horn cell may produce LMN weakness at the level of the lesion • If larger lesion, corticospinal tract involved -> UMN weakness

  41. Spinal cord syndrome Anterior spinal artery syndrome: • Back of neck pain of sudden onset • Rapidly progressive flaccid and areflexic paraplegia • Loss of pain and temperature to a sensory level • Preservation of JPS and vibration sensation • Urinary incontinence

  42. Outline • Sensory neuron • Main somatosensory pathways • Posterior column-medial lemniscus • Spinothalamic tract • Somatosensory cortex • Central modulation of pain • Thalamus • Spinal cord syndromes • Bladder, bowel and sexual function

  43. Anatomy of bowel, bladder and sexual function • Complex interplay between sensory, motor (voluntary and involuntary) and autonomic pathways at multiple levels of the nervous system • Frontal “micturition inhibiting area”, sensorimotor sphincter control area, BG, vermis, pontinemicturition center • S2-S4 • Sensory (bladder, rectum, urethra, genitalia) • Ascends via posterior & anterolateral columns • Motor • ant. horn cell  pelvic floor • Onuf’s nucleus =sphincteromotor nucleus  urethral and anal sphincters contraction • Parasympatheticsdetrusor contraction • Sympathetics T11-L1 (intermediolateral cell column)detrusor relaxation, bladder neck contraction • Need bilateral pathways involved to get clinical syndrome

  44. Bladder function: detrusor reflex (voiding) and urethral reflex (storage) • Voluntary relaxation of external urethral sphincter • Inhibition of sympathetics to bladder neck (relaxes) • Parasympathetic activation for detrusor (dome) contraction • Self-perpetuate as long as urine flows • When urine stops, , urethral sphincters contract triggering detrusor relaxation Detrusor reflex mediated by intrinsic spinal cord circuits, pontinemicturition center, cerebellar and BG pathways

  45. Incontinence • Lesions affecting bilateral medial frontal micturition centers result in reflex activation of pontine and spinal micturition centers when the bladder is full • Normal emptying but not under voluntary control • Causes of frontal type incontinence: hydrocephalus, parasagittalmeningioma, traumatic brain injury, neurodegenerative disorders

  46. Incontinence • Lesion below pontinemicturition center but above conus (S2-S4) • Flaccid, acontractile (atonic) bladder ->retention • Evolves over months into hyperreflexic spastic bladder -> retention 2ary dyssynergia and feeling of urgency 2ary reflex bladder contractions • Peripheral nerve lesion or lesion at S2-S4 • Flaccid atonic bladder ->overflow incontinence • Loss of parasympathetic outflow to detrusor or loss of afferent sensory information

  47. Bowel function • Also mediated by medial frontal lobes • 3 components: • Internal smooth muscle sphincter + GI motility (parasympathetics) • External striated sphincter (Onuf) • Pelvic floor muscles (S2-S4 anterior horn cells) • Etiologies: damage at any level • Acute lesions flaccid sphincter and loss of sacral PS  constipation

More Related