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

The Basic Plan for Somatosensory Information to Consciousness Quaternary (4 ) o 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 Sensory responses involved in unconscious proprioception respond in similar ways at the receptor level – the receptors include muscle spindles and golgi-tendon organs, and some of this information is transmitted to the ipsilateral cerebellum, and these will be presented at the end of this lecture. Action Potential Initiation Site 2 1 Serial Path to consciousness involves 4 neurons and 3 synapses Result of a lesion at each level Outside the CNS!

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

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.

Conduc-tion Speed (m/sec) Afferent Fiber Types – vary in conduction speed and modality Entire Peripheral Nerve Group Fiber Type Fiber Diameter (mm) Conduc-tion Speed (m/sec) Receptor Type Modality I A alpha 12 - 22 80 – 120 Spindles & GTO Conscious and NonconsciousProprioception II A beta 5 - 12 35 – 75 Spindles & Cutaneous Mechanoreceptors Touch, Pressure, and Vibration A delta 1 - 5 5 – 30 Free Nerve Endings, noci-, thermo-, & other mechano-receptors Fast Pain, Temp, Touch IV C 0.1 – 1.5 0.5 – 2.0 Slow Pain, Temp, Touch, itch FAST They will already have had much of this info from Rich’s lecture the day before!! SLOW 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 MIDLINE Internal Arcuate Fibers = Sensory Decussation: Crosses the midline QUATERNARY 4o 4 High degree of spatial and temporal resolution. Modalities: tactile (2-point discrimination), vibration, pressure, position sense. Primary Somatosensory Cortex synapse TERTIARY 3o Thalamus - VPL synapse 3 SECONDARY 2o Medial Lemniscus Medulla synapse 2 Receptor skin/muscle/tendon PRIMARY 1o DRG Spinal Cord Dorsal Funiculus Click for Slide Animation 1

Gracilius and Cuneatus: Lower body and Upper Body Aspects of the Dorsal Columns Pons sup inf Colliculi Posterior Intermediate Sulcus T6+ Cuneate Gracile Spinal Trigeminal Nucleus Pyramidal Tract Sensory Decussation * * Click for Slide Animation Posterior funiculus is divided by a posterior intermediate sulcus into medial fasciculus gracilis and a lateral fasciculus cuneatus. Posterior intermediate septum divides these two – becomes discernable at T6. * * 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

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) Click for Slide Animation 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. ALS (lateral spinothalamic tract) Trigeminal Nucleus Spinal Trigeminal Tract Dorsal Spinocerebellar Tract Ventral Lateral Medullary (Wallenberg’s) Syndrome- lesion of the dorsolateral medulla (occlusion of posterior inferior cerebellar artery); produces ipsilateral loss of pain and temperature in the head/face (spinal tract & nucleus of V) and contralateral loss of pain and temperature in the body due to interruption of spinal lemniscus. Now this commonly occurs with occlusion of the posterior inferior cerebellar artery, which as you can see here essentially wraps around the medulla.

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 Click for Slide Animation DC Arch Neurol (2001) 58: 1470.

Spinocerebellar Tracts 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)

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

Trigeminal System: Touch Component Click for Slide Animation

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 Tract cross midline Tract m Principal Sensory i Mid Pons Nucleus d l i n Second Order Neurons e

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.

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 This is a diagram or cartoon of the brain stem, a little bit of the spinal cord down here and not shown are the thalamus and cortex, up here.

Spinocerebellar Tracts 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)

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 Click for Slide Animation The general rule is that the cerebellum receives information from the ipsilateral side of the body

Cerebellar Tracts: Non-Conscious Proprioception Flocculonodular Lobe Receptor DRG Spinal Cord: Dorsal Nucleus of Clarke Restiform Body s y n a p e Primary 1 o Secondary 2 Dorsal Spinocerebellar Tract Anterior Lobe Posterior Lobe Paramedian Lobule Cerebellar Nuclei Dorsal Spino- Cerebellar Tract T1 to L2 Inferior Cerebellar Peduncle Spinocerebellum Click for Slide Animation Cerebellar Nuclei: fastigial, globose, emboliform, dentate For Dorsal Spinocerebellar, fibers entering dorsal roots below (caudal to) L2 ascend in dorsal funiculus to reach the nucleus. Kandel and Schwartz 1985, p506.

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 Flocculonodular Lobe Receptor DRG Spinal Cord: Dorsal Nucleus of Clarke Restiform Body s y n a p e Primary 1 o Secondary 2 Dorsal Spinocerebellar Tract Anterior Lobe Posterior Lobe Paramedian Lobule Cerebellar Nuclei Dorsal Spino- Cerebellar Tract T1 to L2 Inferior Cerebellar Peduncle Cuneo- Cerebellar Tract Cuneocerebellar Tract C2 to T4 Dorsal root fibers in spinal segments C2 to T4 carry muscle spindle and exteroceptive information in the ipsilateral cuneate fasciculus to the main cuneate nucleus 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 Spinal border cells Ventral Spinocerebellar Tract Ventral Spinocerebellar Tract Afferents TO the ventral spinocerebellar Tract are group I flexor reflex afferents and group II and III mechanoreceptors. Ventral Spinocerebellar and Rostral Spinocerebellar – cutaneous tactile information from Meissner’s, Merkel’s and Pacinian mechanoreceptors, group II and III afferents to cerebellum L3 to S1

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. ALS (lateral spinothalamic tract) Trigeminal Nucleus Trigeminal Tract Dorsal Spinocerebellar Tract Ventral

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 Click for Slide Animation DC Arch Neurol (2001) 58: 1470.