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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 The Basic Plan for Somatosensory Information to Consciousness Quaternary (4o ) 4 C o rte x : rig h t le ft Te r t ia r y o (3 ) 3 Thalamus: left • right • R e c e p to r S e c o n d a ry o (2C r o s s e s ) o Primary (1 ) 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. 2 1 S k in Serial Path to consciousness involves 4 neurons and 3 synapses Result of a lesion at each level Spinal Cord Dorsal Root Ganglion Action Potential Initiation Site left Midline Outside the CNS! right Sensory information from the body to Consciousness: 2 Systems Anterolateral pain & temp, gross touch Dorsal Column fine touch discrimination 4th Ventricle Spinal Lemni scus Superior Middle Cerebellar Peduncle V Medial Lemniscus anterolateral dorsal protopathic epicritic primitive recent Spinal Lemniscus Pontocerebellar Fibers Medial Lemniscus Dorsal / Posterior midline 1 Ventral / Anterior Lateral 1 An important anatomical difference is where they cross (spinal cord vs brainstem). 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. Afferent Fiber Types – vary in conduction speed and modality Gr oup FAST I II II SLOW IV Fiber Type A alpha A beta A delta C Fiber Diamet er (mm) 12 - 22 5 - 12 1-5 0.1 – 1.5 Conduction Speed (m/sec) Entire Peripheral Nerve Receptor Type Modality 80 – 120 Spindles & GTO Conscious and Nonconscious Proprioception 35 – 75 Spindles & Cutaneous Mechanorecepto rs Touch, Pressure, and Vibration 5 – 30 Free Nerve Endings, noci-, thermo-, & other mechanoreceptors Fast Pain, Temp, Touch 0.5 – 2.0 Free Nerve Endings, noci-, thermo-, & other mechanoreceptors Slow Pain, Temp, Touch, itch Haines, p42. Afferent Fiber Types – also vary in myelination and point of entry into the spinal cord Haines, Fundamental Neuroanatomy, p254 Somatosensory Information from the Body to Consciousness Dorsal Column – Medial Lemniscus Pathway QUATERNARY 4o Primary Somatosensory Cortex High degree of spatial and temporal resolution. 4 Modalities: tactile (2-point discrimination), vibration, pressure, position sense. TERTIARY 3o 3 SECONDARY 2o 2 Internal Arcuate Fibers = Sensory Decussation: Crosses the midline Medulla Dorsal Funiculus DRG 1 PRIMARY 1o Receptor skin/muscle/tendon MIDLINE Spinal Cord Thalamus - VPL Medial Lemniscus osum all nx For Co rpus C Gracilius and Cuneatus: Lower body and Upper Body Aspects of the Dorsal Columns i T h a l a m u s sup inf Colliculi T6+ Posterior Intermediate Sulcus o live Pons Sensory Decussation Gracile Cuneate * Spinal Trigeminal Nucleus 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 * * * Pyramidal Tract 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 Dorsal Column System – Symptoms Associated with Lesions What is the symptom associated with the lesion? 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/ 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. Spinal Trigeminal Tract Trigeminal Nucleus Dorsal Spinocerebellar Tract Ventral Spinocerebellar Tract ALS (lateral spinothalamic tract) 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. Area of Lesion 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. Non-conscious Proprioception Conscious Somatosensation Spinocerebellar Tracts BODY HEAD Trigeminal System PAIN & Temp Fine Touch Pain Lateral SpinoThalamic Dorsal Column System Spinal Touch Principal (Main) (IPSILATERAL) Trigeminal Nerve – Sensory Component – pain, temperature, touch, position sense Trigeminal Ganglion Opthalmic Maxillary Mandibular TRIGEMINAL NUCLEUS Mesencephalic Nucleus (Proprioceptive) Main Sensory Nucleus (fine touch, pressure) Spinal Trigeminal Nucleus (pain, temp) Trigeminal System: Touch Component C o rte x Tr igeminal NUCLEUS Mesencepahl ic VPM PONS 1 Mandibular MEDULLA 2 2 2 SPINAL CORD 3 3 Pain & Temp Main MIDLINE Maxillary 1 2 2 2 T h a la m u s Touch 1 Spinal Opthalmic Br anches of t he Tr igeminal (V) Ner ve Tr igeminal Gangl ion 1 1 1 VPL Tr igeminal Ner ve 4 4 VENTRAL TRIGEMIN0THALAMIC TRACT Principal or Main Trigeminal Nucleus – Touch Sensation from the Face SI Cortex SI Cortex VPM Contralateral VPM synapse synapse Dorsal Trigeminothalamic Tract Principal Sensory Nucleus Second Order Neurons midline Mid Pons cross midline Ventral Trigeminothalamic Tract Similarities Between Body and Head Pathways The trigeminal ganglion is functionally similar to what in the body representation pathway? Answer: Dorsal Root Ganglion Both contain cell bodies of the first ? order neurons of what morphological cell type? Answer: pseudounipolar neurons The Mesencephalic Nucleus of V is a special case why? Answer: It is the only place within the CENTRAL nervous system that contains primary afferent cell bodies. 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 Trigeminal System – Symptoms Associated with Lesions VPM Non-conscious Proprioception Conscious Somatosensation Spinocerebellar Tracts BODY HEAD Trigeminal System PAIN & Temp Fine Touch Pain Lateral SpinoThalamic Dorsal Column System Spinal Touch Principal (Main) (IPSILATERAL) Cerebellar Tracts: Non-Conscious Proprioception Cerebellum – Master coordinator of movement, does not initiate. Limb position, joint angles, muscle tension, muscle length. 1. Dorsal Spinocerebellar Tract - coordination of individual muscles of the lower trunk and lower extremity during postural adjustments and movements. 2. Ventral Spinocerebellar Tract - general coordination of muscles of the lower part of the body during movement (walking). 3. 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 Cerebellar Tracts: Non-Conscious Proprioception Dorsal Spinocerebellar Tract Spinocerebellum Anterior Lobe Posterior Lobe Paramedian Lobule Flocculonodular Lobe Cerebellar Nuclei Dorsal SpinoCerebellar Tract Inferior Cerebellar Peduncle Restiform Body Kandel and Schwartz 1985, p506. Secondary 2 T1 to L2 DRG o Spinal Cord: Dorsal Nucleus of Clarke o Primary 1 Receptor 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 Cerebellar Tracts: Non-Conscious Proprioception Dorsal Spinocerebellar Tract Cuneocerebellar Tract Anterior Lobe Posterior Lobe Paramedian Lobule Flocculonodular Lobe Cerebellar Nuclei Dorsal SpinoCerebellar Tract CuneoCerebellar Tract Inferior Cerebellar Peduncle Restiform Body Restiform Body DRG Secondary 2o Lateral Cuneate Nucleus Spinal Cord: Dorsal Nucleus of Clarke o Primary 1 Receptor DRG o Primary 1 Receptor C2 to T4 ps e T1 to L2 o sy na Secondary 2 Medulla 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). Cerebellar Tracts: Non-Conscious Proprioception Ventral Spinocerebellar Tract Recrosses in Cerebellum Superior Peduncle Ventral Spinocerebellar Tract Ventral Spinocerebellar Tract L3 to S1 DRG Spinal Cord: Lamina V-VII + border Primary 1o Receptor ps e Secondary 2o sy na midline Crosses in a nterior white commissure Spinal border cells 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. Trigeminal Tract Trigeminal Nucleus Dorsal Spinocerebellar Tract Ventral Spinocerebellar Tract ALS (lateral spinothalamic tract) 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. 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.