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Neuronal architecture of the spinal cord: prorioceptive and nociceptive (withdrawal) reflex arcs Viktória Vereczki M.D., PhD. Department of Anatomy, Histology and Embryology Semmelweis University Gross anatomy of spinal cord •45 cm lon from the atlas to L1L2 •Maximal volumes: Intumescentia cervicalis: 38mm Intumescentia lumbalis: 35 mm Gross anatomy of spinal cord Gross anatomy of spinal cord Spinal ganglion Pseudounipolar neurons in the spinal ganglion (HE) Neuronal architecture of spinal cord C3 C6 Cervical nerves 1-8 C3 Thoracic nerves 1-12 C6 Th6 Th6 Lumbar nerves 1-5 L3 L3 S2 Sacral nerves 1-5 Coccygeal nerve 1 n. L3 n. S2 S2 Neuronal architecture of spinal cord White matter •Dorsal funiculus cervical segment •Ventral funiculus •Lateral funiculus •Anterior fissure •Dorsal median sulcus •Dorsal septum thoracic segment •Sulcus dorsolateralis:Radices dorsales •Sulcus ventrolateralis:radices ventrales •Ventral white comissure •Dorsolateral tract of Lissauer sacral segment White matter: Dorsolateral tract of Lissauer White matter: Ascending pathways: Descending pathways: White matter: Fasciculus proprius: proriospinal fibers Neuronal architecture of spinal cord- gray matter •Posterior gray column dorsal horn( viscerosensory (enteroception) and somatic sensory neurons) •Anterior gray column ventral horn(somatomotor neurons) •Lateral gray column( only at thoracic segments) horn (visceromotor neurons) lateral Neuronal architecture of spinal cord- gray matter Rexed laminae of spinal cord ( at the level of Th10) 1. Dorsal nucleus of Clarke-Stilling 2. Proper nucleus of dorsal comumn Neuron types: 1. radicular 2. funicular 3. internuncial 4. interneurons: f.i. Renshaw cells 3. Substantia gelatinosa (Rolandi) 4. Marginal zona 5.Intermediolateral cell column 6. Intermediomedial cell collumn 7. Motor neurons of ventral horn Laminae of Rexed Afferent fibers, terminating here Efferent fibers , originating here lamina I. –marginal zone Marginal neurons (Waldeyer-neurons): pain - and temperature sensory neurons, visceral afferents, from brain stem: monoaminoergic descending fibers Tr. spinothalamicus Dorsolateral tract of Lissauer lamina II. -substantia gelatinosa (Rolandi) From the skin nociceptive fibers: unmyelinated os myelinated, from brain stem: monoaminoergic descending fibers The unmyelinated axons of substantia gelatinosa cels ascend or descend for up to four segments of the spinal cord; their branches synapse within the dorsal horn lamina III-IV. nucleus proprius columnae dorsalis Mechanoreceptors of skin Spinothalamic tract lamina V-VI. Transmitting touch , pain and visceral signals Spinothalamic tract Fibers associating within the spinal cord lamina VII. -nucleus dorsalis seu nucleus thoracicus (Clarke-Stilling nucleus) Th1-L3:cornu laterale: • nucleus intermediolateralis • nucleus intermediomedialis sacral part: Proprioceptive and epicritic sensation of the skin of the lower part of the body -internuntial neurons among the descending pathways and motoneurons, Renshaw cells Dorsal spinocerebellar tract (Flechsig) lamina VIII. -comissural nucleus of Lenhossek crossing fiber in the comisssura alba lamina IX. –motor nuclei of ventral horn Aα-motoneurons Aγ- motoneutons lamina X.-substantia grisea centralis -tr.corticospinalis, tr. Reticulospinalis -preganglionic sympathetic neurons -preganglionaris parasympathicus neurons Additional nuclei of lamina IX.: Cervical segment: 1. Phrenic nucleus (C3-C5): Phrenic nerve Bronislaw Onuf-Onufrowicz (1863-1928) 2. spinal accessory nucleus (C1-C5): spinal root of accessory nerve innervating sternocleidomastoid adn trapezius muscle S2 segment: 3. nucleus Onuf (motor nucleus of pudendal nerve: urinary and fecal continence, innervating ischiocavernosus, bulbospongiosus muscles and pelvic floor 4. Lateral central nucleus Gray matter: 1.: Cajal-Ag impregnation II. lamina Gray matter: 2.: VII. lamina X. lamina Schematic representation of motor neurons 1. 2. 4. 6.3. 5. 1. Nucleus retrodorsolateralis: kis ujjizmok 2. Nucleus dorsolateralis: alkar és kéz izmai 3. Dorsalisan: hajlító izmok 4. N. ventromedialis et dorsomedialis:tarkóés hátizmok, bordaközi és hasizmok 5. N. ventrolateralis: vállöv és felkar izmai 6. Ventralisan: feszítő izmok Spinal nerve Ramus posterior Ramus meningeus Ramus communicans griseus Ramus anterior Plexuses Ramus communicans albus Typical arrangement of the spinal nerves Reflexes of the spinal cord 1. Proprioceptive, monosynaptic reflex Reflexes of the spinal cord 1. Proprioceptive, monosynaptic reflex 1. Receptor : Annulospiral endings of neuromuscular spindle 2. Afferent nerve: 1st neuron from spinal 2. ganglion Iα type sensory fibere its collaterals terminate on the same segment’s motoneuron, and more caudal segments’ inhibiting neurons 1. 3. 4. 5. 3. Central connections: monosynaptic 4. Efferent nerve: 2nd neuron Aα motoneuron innervating its own extrafusal fibers 5. Effector: Its own muscle fiber 6. Additional connections: a., reciprok inhibition b., gamma-loop 1. Proprioceptive, monosynaptic reflex 6. Additional connections : a., reciprok inhibition b., gamma-loop specific inhibitory neuron Antagonist muscle group is inhibited 1. Proprioceptive, monosynaptic reflex 6. Additional connections : a., reciprok inhibition b., gamma-loop 1. gamma-loop 4. 1.Descending axon (pl. tr. reticulospinalis, tr. vestibulospinalis) 2. 5. 3. 2. Aγ neuron (innervation intrafusal fibers) 3. Neuromuscular spindle: anulospiral receptor 4. Iα sensory neuron‘s fiber for the muscle spindle Function: Regulating muscle tone 5.Aα motoneuron (innervation of the extrafusal musclefiber) Clinical importance of monosynaptic reflexes: Clinical tendon jerks DIMINISHED Lesion of „lower motoneurons” EXAGGERATED (trauma, degeneration, demyelination disorder, infections, impairment of blood supply, tumors) Lesion of „upper motoneurons” - Flaccid paralysis of affected muscles: segmantal localization lack of inhibitory pathways results in spastic palsy Examples: patella-reflex L2-4, biceps-reflex C5-6, triceps-reflex C6-7, gastrocnemius-reflex S1-2 Reflexes of the spinal cord 2. Polysynaptic, nociceptive (withdrawal) reflex arc Reflexes of the spinal cord 2. Polysynaptic, nociceptíve (withdrawal) reflex arc 1. Receptor: Nociceptors in skin , mucosa 2. Afferent nerve: 1st neuron from spinal ganglion Aδ, C rostok (Lissauer –zone) 3. Central connections: 2nd or 3rd neuron: Interneurons, funicular neurons: among many segments, Renshaw-inhibition 4. Efferent nerve : at least the 3rd neuron Aα motoneuron 5.Effector: Flexor muscles of the same side , and extensor muscles of the opposite side Examples: abdominal-reflex, cremasteric-reflex, cornea-reflex. 2. Polysynaptic, nociceptíve (withdrawal) reflex arc 2. 3. 1. 4. 5.