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 L1- L2 Maximal volumes: Intumescentia cervicalis: 38mm Intumescentia lumbalis: 35 mm

Gross anatomy of spinal cord

Spinal ganglion Pseudounipolar neurons in the spinal ganglion (HE)

Neuronal architecture of spinal cord Cervical nerves 1-8 Thoracic nerves 1-12 Lumbar nerves 1-5 Sacral nerves 1-5 Coccygeal nerve 1 C3 C6 Th6 L3 n. S2 S2 n. L3

Neuronal architecture of spinal cord White matter Dorsal funiculus Ventral funiculus Lateral funiculus Anterior fissure Dorsal median sulcus Dorsal septum Sulcus dorsolateralis:Radices dorsales Sulcus ventrolateralis:radices ventrales Ventral white comissure Dorsolateral tract of Lissauer cervical segment thoracic segment sacral segment

White matter: Dorsolateral tract of Lissauer

Ascending pathways: White matter: Descending pathways:

White matter: Fasciculus proprius: proriospinal fibers

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) lateral horn (visceromotor neurons) Neuronal architecture of spinal cord- gray matter

Neuron types: 1. radicular 2. funicular 3. internuncial 4. interneurons: f.i. Renshaw cells 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 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 hereEfferent 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 skinSpinothalamic 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 -tr.corticospinalis, tr. Reticulospinalis Dorsal spinocerebellar tract (Flechsig) -preganglionic sympathetic neurons -preganglionaris parasympathicus neurons 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

Cervical segment: 1. Phrenic nucleus (C3-C5): Phrenic nerve 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 Bronislaw Onuf-Onufrowicz ( ) Additional nuclei of lamina IX.:

Gray matter: 1.: Cajal-Ag impregnation II. lamina

Gray matter: 2.: VII. lamina X. lamina

Schematic representation of motor neurons 1.Nucleus retrodorsolateralis: kis ujjizmok 2.Nucleus dorsolateralis: alkar és kéz izmai 3.Dorsalisan: hajlító izmok 4.N. ventromedialis et dorsomedialis:tarkó- és hátizmok, bordaközi és hasizmok 5.N. ventrolateralis: vállöv és felkar izmai 6.Ventralisan: feszítő izmok

Ramus anterior Plexuses Ramus communicans albus Ramus communicans griseus Ramus posterior Spinal nerve Ramus meningeus

Typical arrangement of the spinal nerves

Reflexes of the spinal cord 1. Proprioceptive, monosynaptic reflex

3. 1.Receptor : Annulospiral endings of neuromuscular spindle 2. Afferent nerve: 1 st neuron from spinal ganglion Iα type sensory fibere its collaterals terminate on the same segment’s motoneuron, and more caudal segments’ inhibiting neurons 3. Central connections: monosynaptic 4. Efferent nerve: 2 nd 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 Reflexes of the spinal cord

6. Additional connections : a., reciprok inhibition b., gamma-loop 1. Proprioceptive, monosynaptic reflex specific inhibitory neuron Antagonist muscle group is inhibited

6. Additional connections : a., reciprok inhibition b., gamma-loop gamma-loop 1.Descending axon (pl. tr. reticulospinalis, tr. vestibulospinalis) 2. Aγ neuron (innervation intrafusal fibers) 3. Neuromuscular spindle: anulospiral receptor 4. Iα sensory neuron‘s fiber for the muscle spindle 5.Aα motoneuron (innervation of the extrafusal musclefiber) 1. Proprioceptive, monosynaptic reflex Function: Regulating muscle tone

Clinical importance of monosynaptic reflexes: Clinical tendon jerks DIMINISHED Lesion of „lower motoneurons” (trauma, degeneration, demyelination disorder, infections, impairment of blood supply, tumors) Flaccid paralysis of affected muscles: segmantal localization Examples: patella-reflex L2-4, biceps-reflex C5-6, triceps-reflex C6-7, gastrocnemius-reflex S1-2 EXAGGERATED Lesion of „upper motoneurons” - lack of inhibitory pathways results in spastic palsy

Reflexes of the spinal cord 2. Polysynaptic, nociceptive (withdrawal) reflex arc

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: 2 nd or 3 rd neuron: Interneurons, funicular neurons: among many segments, Renshaw-inhibition 4. Efferent nerve : at least the 3 rd 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. Reflexes of the spinal cord

Polysynaptic, nociceptíve (withdrawal) reflex arc