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Somatosensory Systems Proprioception

Somatosensory Systems Proprioception. Modalities Touch (and Pressure), Vibration Sense, Proprioception, Kinesthesia, Stereognosis Proprioception - sense of static and dynamic position of limbs and body Kinesthesia - the ability to feel movements of the limbs and body

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Somatosensory Systems Proprioception

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  1. Somatosensory Systems Proprioception Modalities Touch (and Pressure), Vibration Sense, Proprioception, Kinesthesia, Stereognosis Proprioception - sense of static and dynamic position of limbs and body Kinesthesia - the ability to feel movements of the limbs and body Stereognosis – ability to recognize objects based on touch alone • Today – Proprioception • Dorsal Column-Medial Lemniscus Pathway –Fine Touch from Body • Main Trigeminal Nucleus – Fine Touch from Head • Cerebellar Pathways – Non-Conscious Proprioception

  2. o Quaternary (4 ) Action Potential Initiation Site The Basic Plan for Somatosensory Information to Consciousness 4 • Adequate Stimulus – The stimulus modality to which a sense organ responds optimally. • Generator Potentials are depolarizations in receptors that are graded relative to the intensity and form of the stimulus. 3 2 1 Serial Path to consciousness involves 4 neurons and 3 synapses Result of a lesion at each level Outside the CNS!

  3. Sensory information from the body to Consciousness: 2 Systems Spinal Lemniscus Medial Lemniscus 1 An important anatomical difference is where they cross (spinal cord vs brainstem). AnterolateralDorsal Column pain & temp, fine touch discrimination gross touch anterolateral dorsal protopathic epicritic primitive recent Spinal Lemniscus Medial Lemniscus Dorsal / Posterior Lateral 1 Ventral / Anterior

  4. Key Elements - Divisions Dorsal Column – FAST and Discrete allowing fine discrimination. Modality is Fine Discrimination Touch (vibration, pressure, conscious proprioception) Anterolateral System = Lateral and Anterior Spinothalamic Tracts – Slow and Crude. Modalities are Pain, Temperature and Course Touch.

  5. Afferent Fiber Types – vary in conduction speed and modality Entire Peripheral Nerve FAST SLOW Haines, p42.

  6. Haines, Fundamental Neuroanatomy, p254 Afferent Fiber Types – also vary in myelination and point of entry into the spinal cord

  7. Somatosensory Information from the Body to Consciousness

  8. Dorsal Column – Medial Lemniscus Pathway QUATERNARY 4o Primary Somatosensory Cortex synapse 4 TERTIARY 3o synapse Thalamus - VPL Internal Arcuate Fibers = Sensory Decussation: Crosses the midline SECONDARY 2o Medulla synapse Spinal Cord Dorsal Funiculus DRG PRIMARY 1o MIDLINE Receptorskin/muscle/tendon High degree of spatial and temporal resolution. Modalities: tactile (2-point discrimination), vibration, pressure, position sense. 3 Medial Lemniscus 2 1

  9. Posterior Intermediate Sulcus Sensory Decussation T6+ Gracile * Cuneate sup * inf Colliculi Pons Spinal Trigeminal Nucleus * Pyramidal Tract Gracilius and Cuneatus: Lower body and Upper Body Aspects of the Dorsal Columns * Central processes of the primary afferent’s axon are located in the dorsal funiculus of the spinal cord. Lower body is represented Medially = Gracilius Upper body is represented laterally = Cuneatus

  10. Key Questions for the Touch Pathway from the Body The second order neuron crosses the midline. Where does the crossing occur for the Dorsal Column-Medial Lemniscus System? Second order neuron is located in the brainstem. Therefore the CROSSING occurs in the brainstem Medial Lemniscus – Cells of origin? - Contralateral brainstem: Gracile Nucleus - Lower Body; Cuneate Nucleus – Upper Body) Medial Lemniscus – projects to (terminates in): - Ipsilateral VPL of thalamus

  11. Dorsal Column System – Symptoms Associated with Lesions What is the symptom associated with the lesion?

  12. Lesions and Clinical Deficits - Syringomyelia Gliosis and cavitation in midline of the spinal cord – CSF enters the cord. The larger the cavitation, the more tracts affected. One possible cause is a Chiari Malformation. Other causes include trauma, infection. (anything that compresses the CSF) Symptoms: Bilateral loss of pain and temperature at the level of the lesion (segments involved). Area of lesion http://www.asap4sm.com/

  13. Spinal Trigeminal Tract Trigeminal Nucleus Dorsal Spinocerebellar Tract Ventral Spinocerebellar Tract ALS (lateral spinothalamic tract) Lesions and Clinical Deficits - Wallenberg’s Lateral Medullary (Wallenberg’s) Syndrome – Symptoms include loss of pain and temperature on the ipsilateral head/face, contralateral loss of pain and temperature in the body, and ataxia.

  14. Area of Lesion Lesions and Clinical Deficits – Tabes Dorsalis Degeneration of myelinated afferent fibers in the dorsal columns, (destroys large diameter axons), is a late stage of syphilis. Symptoms: Severe deficits in touch and position sense but often little loss of temperature perception and of nociception. Bilateral lesion = bilateral effects.

  15. LESIONS and Clinical Deficits – Brown-Sequard Syndrome Hemisection of the spinal cord, often in the cervical spinal cord – (it is rare for the entire hemisection to be affected, but this does occur, more often incomplete hemisection is found). Symptoms: a) Loss of fine discrimination touch, vibration, and position sense ipsilaterally for body regions from affected dermatome and down b) Loss of pain and temperature contralaterally for body regions from affected dermatome and down (small region of bilateral loss of pain and temp at level of lesion and 2 segments below) c) Motor Effects: – Ipsilateral Spasticity and Weakness DC Arch Neurol (2001) 58: 1470.

  16. Conscious Somatosensation Non-conscious Proprioception Spinocerebellar Tracts (IPSILATERAL) BODY HEAD Trigeminal System PAIN & Temp Fine Touch Pain Touch Lateral Spino-Thalamic Dorsal Column System Spinal Principal (Main)

  17. Opthalmic Maxillary Mandibular TRIGEMINAL NUCLEUS Mesencephalic Nucleus (Proprioceptive) Main Sensory Nucleus (fine touch, pressure) Spinal Trigeminal Nucleus (pain, temp) Trigeminal Nerve – Sensory Component – pain, temperature, touch, position sense Trigeminal Ganglion

  18. Trigeminal System: Touch Component

  19. Principal or Main Trigeminal Nucleus – Touch Sensation from the Face SI Cortex SI Cortex Contralateral VPM VPM synapse synapse Dorsal Ventral Trigemino- Trigemino- thalamic thalamic cross midline Tract Tract m Principal Sensory i Mid Pons d Nucleus l i n e Second Order Neurons

  20. Similarities Between Body and Head Pathways The trigeminal ganglion is functionally similar to what in the body representation pathway? Both contain cell bodies of the ? order neurons of what morphological cell type? The Mesencephalic Nucleus of V is a special case why? Answer: Dorsal Root Ganglion first Answer: pseudounipolar neurons Answer: It is the only place within the CENTRAL nervous system that contains primary afferent cell bodies.

  21. Key Questions for the Ventral Trigeminal Thalamic Tract What sensory modalities are associated with the Ventral Trigeminal Thalamic Tract at the level of the pons? Touch (conscious proprioception), Pain & Temperature Where are the cell bodies of origin of the Ventral Trigeminal Thalamic Tract? Contralateral Trigeminal Nucleus (Spinal & Main Components) Where does the VTT terminate? Ipsilateral Ventral Posterior MEDIAL (VPM) Nucleus of the Thalamus

  22. Trigeminal System – Symptoms Associated with Lesions VPM

  23. Non-conscious Proprioception Conscious Somatosensation Spinocerebellar Tracts (IPSILATERAL) BODY HEAD Trigeminal System PAIN & Temp Fine Touch Pain Touch Lateral Spino-Thalamic Dorsal Column System Spinal Principal (Main)

  24. Cerebellar Tracts: Non-Conscious Proprioception Cerebellum – Master coordinator of movement, does not initiate. Limb position, joint angles, muscle tension, muscle length. • Dorsal Spinocerebellar Tract - coordination of individual muscles of the lower trunk and lower extremity during postural adjustments and movements. • Ventral Spinocerebellar Tract - general coordination of muscles of the lower part of the body during movement (walking). • Cuneocerebellar Tract - coordination of individual muscles in the upper trunk and upper extremity. C2 – T4 The general rule is that the cerebellum receives information from the ipsilateral side of the body

  25. Cerebellar Tracts: Non-Conscious Proprioception Spinocerebellum DorsalSpinocerebellarTract Anterior Lobe Posterior Lobe Paramedian Lobule Flocculonodular Lobe Cerebellar Nuclei Dorsal Spino- CerebellarTract Inferior Cerebellar Peduncle Restiform Body o Secondary 2 e s p T1 to L2 a Spinal Cord: n y Dorsal Nucleus of Clarke s o DRG DRG DRG Primary 1 Receptor Receptor Receptor Kandel and Schwartz 1985, p506.

  26. Key Elements for Dorsal Spinocerebellar Tract The dorsal spinocerebellar tract carries information from the lower part of the body and synapses within the cerebellum in such a way to maintain the somatotopic map of the body within the cerebellum. Key Questions for the Dorsal Spinocerebellar Tract Where are the Cells of Origin for the Dorsal Spinocerebellar Tract? Ipsilateral Spinal Cord: Dorsal Nucleus of Clarke Where does the tract terminate? Ipsilateral Spinocerebellum

  27. DorsalSpinocerebellarTract CuneocerebellarTract Anterior Lobe Posterior Lobe Paramedian Lobule Flocculonodular Lobe Cerebellar Nuclei Dorsal Spino- CerebellarTract Cuneo- CerebellarTract Inferior Cerebellar Peduncle Restiform Body o Secondary 2 e s p T1 to L2 a Spinal Cord: n y Dorsal Nucleus of Clarke s C2 to T4 o DRG DRG DRG Primary 1 Receptor Receptor Receptor Cerebellar Tracts: Non-Conscious Proprioception Medulla

  28. Key Elements for the Cuneocerebellar Tract The Cuneocerebellar tract originates in the brainstem and ascends ipsilaterally to the cerebellum, carrying information from the upper body (C2-T4).

  29. Cerebellar Tracts: Non-Conscious Proprioception Ventral Spinocerebellar Tract Spinal border cells Ventral SpinocerebellarTract Ventral Spinocerebellar Tract L3 to S1

  30. Trigeminal Tract Trigeminal Nucleus Dorsal Spinocerebellar Tract Ventral Spinocerebellar Tract ALS (lateral spinothalamic tract) Lateral Medullary (Wallenberg’s) Syndrome – Symptoms include loss of pain and temperature on the ipsilateral head/face, contralateral loss of pain and temperature in the body, and ataxia. Lesions and Clinical Deficits - Wallenberg’s

  31. Lesions and Clinical Deficits – Tabes Dorsalis Degeneration of myelinated afferent fibers in the dorsal columns, (destroys large diameter axons), is a late stage of syphilis. Symptoms: Severe deficits in touch and position sense but often little loss of temperature perception and of nociception. Bilateral lesion = bilateral effects.

  32. LESIONS and Clinical Deficits – Brown-Sequard Syndrome Hemisection of the spinal cord, often in the cervical spinal cord – (it is rare for the entire hemisection to be affected, but this does occur, more often incomplete hemisection is found). Symptoms: a) Loss of fine discrimination touch, vibration, and position sense ipsilaterally for body regions from affected dermatome and down b) Loss of pain and temperature contralaterally for body regions from affected dermatome and down (small region of bilateral loss of pain and temp at level of lesion and 2 segments below) c) Motor Effects: – Ipsilateral Spasticity and Weakness DC Arch Neurol (2001) 58: 1470.

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