DPT 735 Neuroscience Lecture PDF

DPT 735 Neuroscience Lecture Sensory Systems Discriminative touch and Proprioception DPT 735 Somatosensation - Touch 1  Objectives Discuss the process of musculoskeletal innervation, including: – Sensory modalities, – Type and locatio...

DPT 735 Neuroscience Lecture Sensory Systems Discriminative touch and Proprioception DPT 735 Somatosensation - Touch 1  Objectives Discuss the process of musculoskeletal innervation, including: – Sensory modalities, – Type and location of receptors associated with each modality; Define the anatomy of the ascending vertical tracts (location in spinal cord, and throughout the entire neural axis) – Dorsal Column Medial Lemniscus Fasciculus gracilis Fasciculus cuneatus – Posterior Spinocerebellar – Cuneocerebellar – Trigeminothalamic tract For each ascending pathway listed above: – State the modality subserved by the pathway and function of the pathway, – State the location of cell bodies and all relevant synapses (1st, 2d, 3rd order, etc), – Describe the somatotopy throughout the neural axis, – Identify the cortical areas receiving the input; Discuss the clinical significance of the organization of the sensory DPT 735 Somatosensation - Touch 2 systems;  Tactile Sensation & Proprioception Tactile sensation can be classified into: – Crude touch (non- discriminative) – e.g. gentle stroking of the skin with a fine cotton strand – Fine touch (discriminative) – enables detection of fine detail regarding location, size, shape, texture of an object even with eyes closed ConsciousDiscriminative proprioception: (fine) touch, – Comprises pressure, static and vibratory dynamic sense, and position sense DPT 735 Somatosensation proprioception are transmitted via - Touch 3 Dorsal Column Pathway An ascending fiber tract or pathway that transmits fine touch, pressure, proprioception sensations Also called Dorsal Column Medial Lemniscal Pathway (DCML) DPT 735 Somatosensation - Touch 4  Dorsal 3 Column Pathway: Component Neurons 1 1st Order Neuron: 2 Cell body in the DRG; Synapses with the 1 nucleus cuneatus and gracilis in the medulla 2 2nd Order Neuron: Synapses in the ventral postero lateral (VPL) nucleus of the thalamus 3 3rd Order Neuron: Synapses in the DPT 735 Somatosensation - Touch 5  Dorsal Column Pathway: Order 1 Neuron st Peripheral sensory receptors respond to fine touch, pressure, conscious proprioception Peripheral receptors consist of Merkel’s discs, Meissner’s, and Pacinian corpuscles Peripheral afferent from the receptor travels toward the spinal cord Cell bodies of the peripheral afferent axon are located DPT 735in the dorsal Somatosensation - Touch root ganglion 6  Dorsal Column Pathway: Order 1 Neuron st - The axon of the 1st order neuron enters the spinal cord through the dorsal root entry zone - Forms the dorsal funiculus or dorsal column - Remember that all these neurons and tracts are bilateral - At this location, these tracts are carrying fine touch and DPT 735 Somatosensation - Touch 7 Dorsal Column Pathway: Order 1 Neuron st The ascending tracts in the dorsal columns comprise of 2 distinct parts: -Fasciculus Gracilis (gracilis = slender) - include afferent processes that enter the cord at the lower thoracic, lumbar, and sacral levels - present throughout the length of the cord - Fasciculus Cuneatus (cuneus = wedge) - only present above T6 - include DPT 735 Somatosensation - Touch afferents that 8  Dorsal Column Pathway: Order 2 Neuron nd - 1st order neurons of the Nucleus Gracilis & Cuneatus in fasiculi gracilis and cuneatus the Medulla synapse with 2nd order neurons whose cell bodies are housed within nuclei of the same name(s) (in the medulla) - 2nd order fibers cross over (decussate) at the medulla as internal arcuate fibers - Reach ventromedial medulla and form the medial DPT 735 Somatosensation - Touch lemniscus 9  Dorsal Column Pathway: Order 3 Neuron rd Nucleus Gracilis - Medial lemniscus fibers & Cuneatus in the Medulla synapse in the VPL of the thalamus - Ascend via the internal capsule to terminate in the primary somatosensory area of the cortex (post central gyrus) - Initial cortical processing of tactile discrimination occurs here DPT 735 Somatosensation - Touch 10 Dorsal Column Pathway 3 2 1 DPT 735 Somatosensation - Touch 11 Trigeminothalamic Pathway Transmits discriminative touch sensation from the face ‘Joins’ the dorsal column pathway at the Pons 1st Order neuron: Trigeminal nerve; cell bodies in the trigeminal ganglion (like the DRG); 2nd Order neuron: Axons end in trigeminal main sensory nucleus; cross the midline in pons 3rd Order neuron: Synapse at the VPM of thalamus; terminate in cerebral cortex DPT 735 Somatosensation - Touch 12 Another way to depict the Dorsal Column Pathway DPT 735 Somatosensation - Touch 13 ‘Tracts within Tracts’ Interfasciular fascicularis Lies btw fasiculus gracilus and cuneatus. Septomarginalis Lies btw the 2 fasiculi gracilis These ‘tracts ‘stay within the cord Enable intra- and inter-segmental communications within the cord DPT 735 Somatosensation - Touch 14  Clinical correlate: Tabes Dorsalis Neurosyphyllitic condition characterized by sensory ataxia due to impairment of 2-point discrimination, vibratory sense, position sense. Romberg Sign: difficulty maintaining standing balance with eyes closed and feet approximated How can the patient compensate? – Rely heavily on vision (i.e. look at legs while walking) DPT 735 Somatosensation - Touch 15  Clinical correlate: Selective Dorsal Rhizotomy Transection of dorsal roots in children with spastic CP Performed to reduce afferent input to the CNS, and thereby reduce efferent motor output (spasticity) DPT 735 Somatosensation - Touch 16  ‘Secondary’ or ‘Minor’ Pathways Major Pathways = Conscious, Contralateral/crossed, terminate in the contralateral cerebral sensory cortex (Post Central Gyrus) Minor Pathways= ‘Unconscious’, Ipsilateral (uncrossed), AKA “reflex,” do not terminate in the cortex; may terminate in the ipsilateral cerebellar hemisphere or brain stem; may be bilateral as well DPT 735 Somatosensation - Touch 17 Spinocerebellar Pathways Only a small portion of proprioceptive info reaches consciousness, most is transmitted to the cerebellum via ascending somatosensory cerebellar pathways without projecting to the thalamus or cortex. Two pathways take information from receptors in muscles, tendons, joints to the cerebellum Posterior or Dorsal Spinocerebellar Cuneocerebellar Two others transmit info from spinal interneurons and descending motor DPT 735 Somatosensation - Touch 18 pathways to cerebellum  Posterior Spinocerebellar tract Relays neuromuscular info from GTOs and muscle spindles from the ipsilateral trunk and lower limb to the cerebellum Also relays touch and pressure 1st Order Neuron : peripheral 2 afferent with cell body in the DRG synapses in the nucleus dorsalis (Clarke’s column) of the spinal cord ; 2nd Order Neuron: Tract 1 ascends ipsilaterally inDPT lateral 735 Somatosensation - Touch 19  Cuneocerebellar tract Relays neuromuscular info from GTOs and muscle spindles from the neck, upper limb, upper trunk Is the neck and upper limb counter part of the dorsal spinocerebellar tract 2 1st Order Neuron : peripheral afferent with cell body in the DRG ascend with Fasciculus 1 Cuneatus and terminate in the nucleus cuneatus of the cervical spinal cord 2nd Order Neuron: Tract DPT 735 Somatosensation - Touch 20  Clinical correlate: Friedreich’s Ataxia Hereditary disorder Degeneration of spinocerebellar tracts and dorsal columns Progressive ataxia DPT 735 Somatosensation - Touch 21  Active Tactile Exploration Is needed for tactile discrimination Using hands to grasp and manipulate objects, running fingers over surface to establish sequence of contacts between fingers and object Texture – determined through relative movement of skin over a surface DPT 735 Somatosensation - Touch 22  Functions: Touch + Proprioception Stereognosis – Ability to use touch and proprioception to identify an object Important pathway for: – Recognizing objects – Controlling movements DPT 735 Somatosensation - Touch 23  Functions: Touch+Proprioception Kinesthesia – Use tactile and proprioceptive input to yield awareness of body location in space Emanates from the following inputs: – Skin stretch Cutaneous receptors – Muscle & tendon information stretch receptors in the muscle – Joint information Encapsulated mechanoreceptors 24 DPT 735 Somatosensation - Touch Spinal Cord: Transverse Section DPT 735 Somatosensation - Touch 25 Clinical correlate: Dorsal Column Pathway- Effects of Lesion Location 26 DPT 735 Somatosensation - Touch  Review Questions Where would the sensory loss be if you transect/lesion: 1. The left fasciculus gracillis? 2. The left dorsal columns (gracile & cuneate)? 3. The right medial lemniscus, in the medulla? 4. The left posterior limb of the internal capsule? DPT 735 Somatosensation - Touch 27