YR1 Lecture 1H - Sensory and Motor Pathways - Dr Yossi Buskila 2021 PDF

synaptic proces ↓ New muscular junction el e ct r o chemi c All t signals I e potentials action Postsynaptpotenti ic a l Sensory & motor pathways a ↳ Dr Yossi Buskila by to generated neurones and propagateirateme School of Medicine Email – [email protected] contraction 1 Learning object...

synaptic proces ↓ New muscular junction el e ct r o chemi c All t signals I e potentials action Postsynaptpotenti ic a l Sensory & motor pathways a ↳ Dr Yossi Buskila by to generated neurones and propagateirateme School of Medicine Email – [email protected] contraction 1 Learning objectives Describe the anatomical pathways in the somatosensory system, and explain the concept of Dermatomes skin stripes that send We to - sensory information Spinal coral - -. Describe the anatomical pathways in the motor system, and how knowledge of Myotomes and motor axon conduction pathways is used to define the level of spinal cord lesions 2 The somatosensory system A complex sensory system consisting of a specialized sensory receptors (mechanoreceptors, thermoreceptors, chemoreceptors and nociceptors) in the skin, muscles, tendons and joints that provide information about changes to the surface or internal state of the body. Can be divided to three subsystems: A tactile system that mediate the sensation of fine touch, vibration and pressure from cutaneous mechanoreceptors A proprioceptive system that mediate proprioception (sense of position and movement) from specialized receptors associated with muscles, tendons and joints A nociception system that mediate the sensation of pain and temperature. 3 The somatosensory system So, where the signal in the somatosensory system start? 4 The somatosensory system Sensory transduction - the process of converting the energy of a stimulus into an electrical concert signal is similar in all sensory afferents energy of the - sensory signals receptors starts in the -> in skin & muscle fibres Stimula they receive electricial signals is a > - into A stimulus alters the permeability of cation channels in the afferent nerve endings, generating a I process that is depolarizing current called receptor (generator) potential. called ↳Proe s ↳ Then the action working d as a postsynaptic potential senool. transduction potential will andgenerated the information neme ending. to the Drain be will more at the ① Pressure ② FORMATION ③ / ↓ Capable vibration signal pres influx & (Pacinian corpuscle) to induce and sodium Production of a generator. potential into electrochemical. signals 5 The somatosensory system Once the receptor potential pass threshold, it leads to action potential that propagate along the axon all the way to the dorsal roots of the spinal cord. Each spinal nerve is made out of sensory afferent and motor efferent that gets into the spinal cord from a specific location along the vertebral column. · of the spinal word , spinal Each is made cord nerve up of a that -gett afferent cord spinal sensory into the. 6 The somatosensory system In total = of 31 pain spinal names 8 = Cervical ((1 C8) -. 12 5 5 = = = 2 = Thoracic (T1 T12) - Lumbar (L1 - 15). Sacral (S1-55). Coccygeal 7 The somatosensory system Each segment of the spinal cord receives cutaneous information from a single dorsal root ganglia, which transduce information from a particular strip of skin called Dermatome Dermatomes are arranged segmentally. Knowing the dermatomes is particularly important in defining the level of spinal cord injury/lesion. ↳ Every part the by body of is mapped. dermatomes 8 The somatosensory system Shingles is a reactivation of the varicella zoster (chickenpox) virus that lies dormant in the nerve roots of your body. Symptoms of shingles, such as pain and a rash, occur along dermatomes associated with the affected nerve root. T2-T3 T9-T10 webmd.com 9 Somatic sensory afferents exhibit distinct functional properties Different sense modalities are mediated by morphologically distinct fibers Axons of afferent sensory neurons can be classified by conduction velocity. The larger diameter axons have higher conduction velocity. 10 The somatosensory system Primary sensory afferents are anatomically segregated Sensory tactile information is conveyed by large, rapidly-conducting myelinated sensory axons (afferents) latural pathway - enterior Unmyelinated, slowly-conducting afferents sensory axons can also provide tactile sensations, but mostly provide heat or nociceptive information 11 Central pathways conveying sensory information from the body Two primary sensory pathways The Dorsal Column-Medial Lemniscal pathway (DCML)–Convey tactile information from the body (FAST-TRACK PATHWAY). The Spinothalamic tract – convey information about crude touch, pain and temperature (SLOWER) s ↓ Both pathways transmit information via 3 types of neurones = ④ Primary - ② Secondary. ③. nes Tatian Anterior-lateral 12. Dorsal Column-Medial Lemniscal Pathway The DCML pathway transmits information from mechanoreceptors and proprioceptors and consist three orders of neurons: First order neurons- transmit information from the periphery and enters the spinal cord through the dorsal root. They travel along the ipsilateral dorsal column and end in the dorsal column nuclei in the medulla oblongata where they synapse with second-order neurons. Second order neurons start from the medulla, cross over to the contralateral side of the medulla in the medial lemniscus and ascend to the thalamus. Third order neurons transmit information from the thalamus to the somatosensory cortex. 13 Dorsal Column-Medial Lemniscal Pathway Rapidly-conducting sensory axons (myelinated afferents) travel in the dorsal columns (cuneate and gracile fasciculi) all the way to the Gracile nucleus and Cuneate nucleus in the medulla Pathways from lower body Pathways from upper body - 14 Spinothalamic tract The spinothalamic tract consists of two adjacent pathways: anterior and lateral. The anterior spinothalamic tract carries information about crude touch The lateral spinothalamic tract conveys pain and temperature signals First order neurons- transmit information from the periphery and enters the spinal cord through the dorsal root. They ascend/descend 1-2 vertebras and synapse with second-order neurons ipsilaterally. Second order neurons start from the nucleus proprius or substantia gelatinosa, cross over to the contralateral side of the spinal cord and ascend to the thalamus. Third order neurons transmit information from the thalamus to the somatosensory cortex. Me Ipsilated e contra 15 Spinothalamic tract Pathway pain Crude touch 16 The somatosensory components of the Thalamus all - Relay station of senses coming to the brain. except offaction The Thalamus is the relay station in the brain. All somatosensory pathways coming through the spinal-cord and the brainstem converge on the Ventral posterior complex (VP) of the Thalamus in organized fashion The VPL (lateral) receive information from the body, while the VPM (medial) relay info information from the head face a structure a paired ventricles - - - side Sits either of the Collection of nuclei- from 3rd organized trad ↑ into discrete groups information the body ↳ & - Somatosensory pathways coming Spina cord ↳ Throughthe on-ventral me m complex of a the organized posterior ge thalamus fashion. 17./ The somatosensory components of the Thalamus The thalamus project afferent axons to the primary (SI) and secondary (SII) somatosensory cortices 18 Primary somatosensory cortex The cerebral cortex is anatomically segregated to 6 layers, and the main input from the thalamus is getting to layer 4 The primary somatosensory cortex is located in the postcentral gyrus, comprises four brodmann’s areas (1, 2, 3a and 3b), and form a somatotopic map of the body called homunculus ↑ Somatosensory anatomically segregrated into& Layers) morphology and density of the cells that reside cortex ↳ cellular is ↳ - , in each layer - "Little men" in lation. 19 Homunculus Cortical homunculus is a neurological "map" of the anatomical divisions of the body. There are two types of cortical homunculus: sensory and motor The presentation of the body parts is not proportional to the real organ size, why? The density of receptors in some body parts (lips, hands) is much greater, hence they are more sensitive 20 The somatosensory system The homunculi (sensory and motor homunculus) were discovered by Wilder Penfield, by stimulating the cortex in human patients undergoing brain surgery, however these days we can study the brain using functional Magnetic Resonance Imaging (fMRI) 21 Studying the brain using fMRI ↓ By recording the responses to brushing different parts of the body we can map the cortical representation of somatosensory inputs Acting are regions of applying the cortex , while stimuli to > - we brush movements different body parts , 22 Studying the brain using fMRI The primary somatosensory cortex (S1) is organised somatotopically 23 Somatotopic maps Does the somatotopic maps are uniquely expressed in humans? 24 Somatotopic maps apparent in other animals C mous , rats , mockcys etc. The star-nosed mole is blind and uses its highly specialized nose to feel for food 25 Somatotopic maps apparent in other animals It has 11 pairs of tendrils located around its nostrils (N), with ~25,000 highly sensitive mechanoreceptors The cortical representation is greater for the nose and forepaws than for any other part of the body ↓ larger , 4 density of receptors. 26 Somatotopic maps are plastic * Important to know ↓ somatotopic maps functional are ↓ very Law Change following or plastic & lesions experince. 27 The somatosensory system: Summary Afferent axons enter the dorsal roots of the spinal cord The cell bodies of the primary afferent neurones reside in the dorsal root ganglia Large-diameter myelinated axons travel up the dorsal columns and synapse in the cuneate and gracile nuclei in the medulla Secondary afferents project to and synapse in the ventral posterolateral nucleus (VP) of the thalamus, and then project to the primary somatosensory cortex in the post-central gyrus 28 The somatosensory system: Unmyelinated pain afferent axons enter the dorsal roots of the spinal cord, and synapse ipsilaterally in the dorsal horn of the spinal cord. The secondary afferents cross over and travel in the spinothalamic tract, terminating in the posterior complex of the thalamus Third-order neurons project to the primary and secondary somatosensory cortices 29 The motor system The motor system is the part of the central nervous system that involve with planning, controlling and executing movement. from all sensory information , One movements gathered ↳ I execute te - me environment D lan our them & The primary motor cortex (M1) lies along the precentral gyrus, and generates the signals that E prim any control the execution of movement. M1 is arranged somatotopically Moley - cottex Secondary motor areas are involved in motor planning. 30. ( The motor system The largest areas of primary motor cortex are dedicated to the hands and face, why? The circuitry required for facial expression and speech is very large, involving many neurons 31 Motor neurons e primary reurones - 2 that types originate compassion Motor * - from the to ene less system cortex and descend to the simues > - Spinal transmit signal cord much h faster. , to innovate lower the motor hecones. ④ Upper motor neurons (UMN) – are neurons that originate from the motor cortex and innervate. directly the LMN’s within the ventral horn of the spinal cord (first order neurons) ② Lower motor neurons (LMN)- are the neurons that originate from the spinal cord and innervate the muscle fibers (second order neurons) 32 The motor system The motor cortex project information through upper motor neurons (UMN), that descend through the corticospinal and corticobulbar tracts, which form the main pathways for control of voluntary movements Axons of the corticobulbar tract terminate in the brainstem and innervate cranial nerves, while axons of the corticospinal tract terminate in the spinal cord. corticobulbar tract - via ; the Brain stem. 33 The corticospinal tract - Layer 5 of the motor cortex. Most Layer V pyramidal axons from the corticospinal tract descend through the internal capsule to the pyramidal decussation in the medulla, where they cross over to the contralateral side. After crossing, the fibers continue to descend through the lateral column of the spine, terminating at the appropriate spinal levels and forming a synapse with lower motor neurons (LMN). ↓ ↓ ↓ ↓ d Innovation of neurons low motor. 34 The corticospinal tract fibres 10-20% of the axons from the corticospinal tract do not cross over and travel through the ventral columns of the spinal cord and terminate bilaterally (majority), ipsilateral or contralaterally. This pathway is called the anterior corticospinal tract. - ↑ Pyramidal ventral column tract. 35. The corticospinal tract 36 The motor system – descending pathways Rapidly-conducting corticomotoneuronal axons travel in the lateral (90%) and anterior (10%) corticospinal tracts in the Fibres - , originated LCST · in the contrakteral hemisphere the from generated same ipsilateral hemisphere ; ↑ fibres seen in CST the anterior 37. Lower Motoneurons ~> originate from the ventral horn of the spinal. cord There are three types of somatic lower motoneurons involved in muscle contraction: a, β and γ motoneurons. All of them have myelinated axons and they are classified based on the type of muscle fibre they innervate. Skeletal muscle consist of two types of fibres: ④ Extrafusal fibres – compose the majority of the muscle and are responsible for its contractile function & produce force ② Intrafusal fibres – embedded deep in the extrafusal fibres, forming the muscle spindle ↑ - 38 Lower Motoneurons Alpha (a) motoneurones, also known as skeletomotor neurones, as they innervate skeletal muscle. They have the largest diameter axons and thus the fastest conducting ↳ velocity. large diameter Gamma (γ) motoneurons, also called fusimotor motoneurones, as they innervate specialized sensory endings in skeletal muscle - the muscle spindles. They have small diameter axons, and therefore conduct slower than (a) motoneurones. Beta (β) motoneurons innervate both intrafusal fibres of muscle spindles and extrafusal fibres. 39 Somatotopic organization of the ventral horn The spinal motoneurones are arranged somatotopically within the ventral horn, forming clusters (pools) that supply a given muscle and form motor units The proximal muscles are innervated by the ventral tract, while the distal muscles are innervated by the lateral tract Innervated by the Ventral corticospinal tract Innervated by the Lateral corticospinal tract Innovated Innovated ↳ by medialthe region of horn of Region By Lateral ventral t - work.. 40 The motor system Motor axons of lower motor neurons leave the ventral horn via the ventral roots Ventral root 41 The motor system The muscles supplied by each spinal nerve are arranged segmentally as myotomes. ↓ which correlates of in dermatomes the motor. system 42 Myotoms A myotome is the group of muscles that a single spinal nerve root innervates. The muscle and its nerve make up a myotome. It is the motor equivalent of a dermatome, and as such they are organized segmentally. knowledge of the myotomes is clinically important for defining the level of spinal cord injury 43 Summary Rapidly-conducting sensory axons (afferents) project to the cortex in the dorsal columns of the spinal cord, synapsing first in the medulla (cuneate & gracile nuclei), then to the thalamus Slowly-conducting afferents project to the cortex via the lateral and anterior spinothalamic tracts, synapsing first in spinal cord and then in the thalamus Rapidly-conducting motor axons (efferents) travel from the primary motor cortex via the pyramidal tract (lateral corticospinal tract) and the extra-pyramidal tract (ventral corticospinal tract) 44 Further reading “Neuroscience”,fifth edition -Chapters 9, 10, 16 and 17 45