Spinal Cord Anatomy PDF

Spinal Cord Anatomy Dr. Cristian Martonos DVM, MSc, PhD Dr. Brady Little, DVM, MSc  Spinal cord Facts: Continuation of the CNS out of the foramen magnum In dogs, it travels down to the level of the 6th/7th lumbar vertebrae Segments are defined by the attachment...

Spinal Cord Anatomy Dr. Cristian Martonos DVM, MSc, PhD Dr. Brady Little, DVM, MSc  Spinal cord Facts: Continuation of the CNS out of the foramen magnum In dogs, it travels down to the level of the 6th/7th lumbar vertebrae Segments are defined by the attachment of the dorsal and ventral roots of the spinal nerves There are 36 pairs of nerve root. One pair for every vertebra plus one more - C1. These pairs do NOT always mirror the exact level of the same # vertebrae. The more you move caudally within the vertebral canal, the spinal nerves must extend further caudally in order to pass through their designated intervertebral foramina. Filum terminale- is a narrow cord of meninges. Terminal tapering of the cord is the conus medullaris (sacral and caudal segments) - Level of termination varies among species Nerves caudal to the conus medullaris are collectively called the cauda equina There are six regional divisions of the spinal cord based on structures supplied a. Cranial cervical region L4-S2 b. Cervicothoracic f Cd1-5 region c. Thoracolumbar region d. Lumbosacral region e. Sacral region f. Caudal region It will be your job to decide which segments of spinal cord is affected by the lesion We can make these diagnosis based on clinical signs  Cervicothoracic intumescence DON’T Memorize Individual nerve origins Lubosacral intumescence Source: de Lahunta et al. Veterinary Neuroanatomy and Clinical Neurology, 4th Edition.  Spinal Cord Regions a. Cranial cervical region (C1-5) Innervation to axial muscles and skin of cranial cervical region b. Cervicothoracic region (C6-T2) Cervical intumescence (enlargement) supplies the brachial plexus, hence innervation of the thoracic limb muscles and skin Innervation of regional axial muscles and skin Sympathetic innervation to the head/eye (T1-T2)  Spinal Cord Regions c. Thoracolumbar region (T3-L3) Innervation of regional muscles and skin Also contains preganglionic sympathetic neurons (“thoracolumbar”) d. Lumbosacral region (L4-S2) Lumbar intumescence (enlargement) supplies the lumbosacral plexus, hence innervation to the skin and muscles of the pelvic limb Innervation of regional axial muscles and skin Partial supply to the bladder and perineum  Spinal Cord Regions e. Sacral region (S1-S3) Innervation to the perineum muscles and skin as wells as external anal sphincter and urethral sphincter (pudendal nerve) Parasympathetic innervation to the viscera of the pelvis and urinary bladder (pelvic nerve) f. Caudal region (Cd1-5) Innervation of muscles and skin of the tail e. f. Conus Medularis: Narrowing of the spinal Column at the caudal aspect. Cauda Equina: Where the Spinal “Cord” no longer exists and there are only individual nerves within the Spinal canal (looks like a horse’s tail). Cranial Caudal L5 L6 L7 L4 Sacrum Conus Medularis Cauda Equina Dorsal View  Knowing the location of the conus medullaris is clinically relevant. When withdrawing CSF fluid, or application of an “epidural” anesthetic, we often insert the needle caudal to the conus medullaris to avoid puncturing the spinal cord. Cat: Tapers at L7 – S3 Dog: Tapers at L6 – L7 Pig: Tapers at S1 – S2 Ox: Tapers at L6 – S1 Horse: Tapers at S2  Spinal cord anatomy Dorsal median sulcus Dorsolateral sulcus Ventrolateral Ventral median fissure. sulcus.  Spinal cord segment (color coded) Dorsal and ventral roots join to produce spinal nerves Cord segment is the region of the spinal cord where the ONE set of dorsal and ventral rootlets attach Dorsal roots bring sensory fibers into the spinal cord Dorsal root ganglia (DRG) contain cell bodies of sensory (afferent) neurons Ventral roots bring motor (efferent) nerve fibers from cell bodies in the spinal cord to the effector structures (organs, muscles and glands)  REVIEW TOPIC CSN 1 C1 The first pair of cervical spinal nerves (CSNs) emerge through the lateral vertebral foramina of the atlas. CSN 2 C2 The remaining CSNs emerge cranial to CSN 3 their correspondent cervical vertebrae, with CSN 8 emerging caudal to C7. C3 CSN 4 The thoracic spinal nerves and lumbar spinal nerves will emerge caudal to their C4 correspondent vertebrae. CSN 5 C5 The first two sacral spinal nerves (dog) CSN 6 emerge through the sacral foramina (dorsal and pelvic sacral foramina). C6 CSN 7 The third sacral spinal nerve (dog) C7 emerges between the intervertebral CSN 8 foramen between the sacrum and the first caudal vertebra. T1 TSN 1  REVIEW: The number of vertebrae varies among species, thus the number of spinal cord segments must also vary The number of thoracic, lumbar, and sacral spinal cord segments is consistent with the number of vertebrae in these regions. Spinal cord segments in different species: Dog: 8 cervical; 13 thoracic; 7 lumbar; 3 sacral; 5 caudal = 36 total Cat: 8 cervical; 13 thoracic; 7 lumbar; 3 sacral; 5 caudal = 36 total Horse: 8 cervical; 18 thoracic; 6 lumbar; 5 sacral; 5 caudal = 42 total Ox: 8 cervical; 13 thoracic; 6 lumbar; 5 sacral; 5 caudal = 37 total Human: 8 cervical; 12 thoracic; 5 lumbar; 5 sacral; 1 caudal = 31 total *Recall that mammals have 7 cervical vertebrae and 8 cervical spinal segments/nerves. FYI sloth and manatee have 6  Arterial supply to the spinal cord Longitudinal ventral spinal artery (VSA) One or two dorsal spinal arteries (DSA) Source: De Risio, L., & Platt, S. R. (2010). Fibrocartilaginous Embolic Myelopathy in Small Animals. Veterinary Clinics of North America: Small Animal Practice, 40(5), 859– 869. doi:10.1016/j.cvsm.2010.05.0 03 Arterial supply to the lumbar spinal cord. C, central artery; DRA, dorsal radicular artery; DSA, dorsal spinal artery (paired); L, lumbar artery; LaDbch, lumbar artery dorsal branch; LaSbch, lumbar artery spinal branch; VSA, ventral spinal artery; VR, ventral radicular artery.  Venous drainage of the spinal cord Ventral spinal vein (VS) Dorsal spinal vein (DS) Venous drainage of the lumbar spinal cord. BV, basivertebral vein; DEVP, dorsal external vertebral venous plexus; DL, dorsolateral vein (paired); DRV, dorsal radicular vein; DS, dorsal spinal vein; IVbch, intervertebral vein branch; Source: De Risio, L., & Platt, S. R. (2010). Fibrocartilaginous Embolic VEVP, ventral external vertebral venous plexus; VIVP, ventral internal vertebral Myelopathy in Small Animals. Veterinary Clinics of North America: Small venous plexus; VL, ventrolateral vein (paired); VRV, ventral radicular vein; VS, Animal Practice, 40(5), 859–869. doi:10.1016/j.cvsm.2010.05.003 ventral spinal vein.  Spinal cord histology Dorsal horn Grey commissure -Sensory neurons- White matter Lateral horn -Motor sympathetic neurons- Central canal Ventral horn Grey matter -Motor neurons- White commissure Source: Yale’s University Image, Histology Source: GDD 8th edition FIG. 6-40 Transverse section of spinal cord: second cervical segment (C2), eighth cervical segment (C8), twelfth thoracic segment (T12), and sixth lumbar segment (L6). 1. Dorsal median sulcus 2. Ventral median fissure 3. Central canal 4. Dorsal funiculus 5. Lateral funiculus 6. Ventral funiculus 7. Dorsal gray horn 8. Ventral gray horn 9. Lateral gray horn 10. Dorsal rootlets 11. Ventral rootlets  Rexed’s laminae I Marginal nucleus (Superficial sensation). Source: Morriss-K, Spinal cord and PNS, 2016 II Substantia gelatinosa of Rolando (Superficial sensation). III &IV Nucleus proprius (Deep sensation / deep DH Pain). V&VI Visceral sympathetic stimulus. VII interneurons IX Motor neurons for axial and limb muscles VH DH- dorsal horn of gray substance; VH- ventral horn of gray substance; X Comissural nucleus VIII Motor neurons for axial muscles (neck, shoulders and trunk).  Spinal cord histology Dorsal funiculus White matter Lateral funiculus Grey matter Ventral funiculus White commissure Source: Yale’s University Image, Histology  Let’s dissect the name and dissect the tracts Ascending tracts (afferent / sensory) Descending tracts (efferent / motor) Transport sensory information from spinal Transport “commands” from brain to cord to brain spinal cord - Nomenclature usually contains - Nomenclature usually contains “spino” as prefix “spinal” as suffix Generally located in the dorsal and lateral - Initiates / regulates motor events (exterior) funiculi Generally located in the ventral and lateral (interior) funiculi  NOT only is location of neuron tracts correlated to Function but, also tolerance to compression Why does this happen? - Some tracts are deeper (more capable of tolerating compression) - Some are more myelinated (less capable of tolerating compression). * Tracts which are Most superficial and more heavily myelinated are first to manifest disease* (Proprioception: The perception of stimuli in relation to body’s position, motion, and equilibrium)  Neuroanatomic diagnosis AKA Localization of a neurologic lesion Includes a complete physical and neurologic exam to diagnose the area of neurologic damage. This often many diagnostic tests & imaging modalities - Neoplasia - Physical trauma - Vascular - Infectious - Autoimmune - Inflammatory Many spinal diseases cause compressive force on the CNS Today will focus on the anatomy needed to LOCALIZE the site of injury secondary to spinal compression  Spinal Cord Functions (3) Transmission of all information to and from the brain 1) Sensory (afferent) input from all tissue except the head. Receives information from the peripheral nerves by way of the dorsal roots. Afferent information originates from the receptors of muscles, joints, tendons, skin, and viscera. *Delivering sensation of touch, proprioception, and pain. 2) Motor (efferent) commands are sent to skeletal m., smooth m., cardiac m., organs and glands via ventral roots. * Efferent and Afferent signals travel in white matter pathways SEPARATE from one another *  Spinal Cord Functions 3) Reflexive control Unconscious reaction of a motor unit (striated muscle, smooth muscle, cardiac muscle, organ, or gland) caused by sensory input from the environment. - Often includes an Interneuron: - Interneurons (relay neuron) have 2 possible functions: 1) Integrate the afferent stimulus to induce local reflex (stimulate muscles and glands) 2) Relay the information to an afferent neuron for conscious perception Interneuron  Branches of the Spinal Nerves 1) Dorsal Branch  Epaxial sensory and motor Meningeal branch 2) Ventral Branch Hypaxial sensory and motor 3) Ramus communicans (aka 1 communicating branch)  connects to the sympathetic trunk / chain of ganglia (visceral efferent and afferent) 2 3  Key to diagram on the next slide: Dorsal roots bring sensory fibers into the spinal cord Dorsal root ganglia (DRG) contain cell bodies of sensory (afferent) neurons whose axons make up the dorsal root. Dorsal horn contains cell bodies of nerves which receive and relays afferent information from the dorsal root fibers. - Dorsal horn cell bodies have axons which ascend in the white matter of the cord to the brain (afferent for sensory perception) - Synapse may happen with an interneuron to induce simultaneous reflex Ventral roots take all efferent axons away from the spinal cord. Ventral horn contains motor (efferent) nerve cell bodies which descend to the effector structures (organs, muscles, glands) via the ventral root. Lateral horn is ONLY located in T1 – L4 spinal cord. Because this is the only area of the CNS which contains cell bodies of SYMPATHETIC pre-synaptic nerves. Axons of these neurons descend (efferent) out the ventral horn and through the communicating branch (ramus communicans) Intermediate zone is a network of interneurons. These are utilized to recruit reflex actions while at the same time allowing the stimulus to ascend in white matter to the brain for perception of the stimulus by the brain.  Intermediate zone Dorsal branch Ventral branch (visceral sympathetic) Sympathetic chain  Intermediate zone Dorsal branch Ventral branch (visceral sympathetic) Sympathetic chain  Intermediate zone Dorsal branch Ventral branch (visceral sympathetic) Sympathetic chain  Intermediate zone Dorsal branch Ventral branch (visceral sympathetic) Sympathetic chain  Thank you very much!!! Source:https://en.wikipedia.org/wiki/Nociception