Functional Neuroanatomy of Spinal Cord

1. Functional Neuroanatomy of Spinal Cord 蔡昀岸 台北榮民總醫院神經醫學中心 神經修復科

2. 重點 • Function of the spinal cord • Spinal motor control • Tracts evaluated in International Standard Neurological Classification of Spinal Cord Injury (ASIA) • Special SCI syndromes • Lumbar locomotor center • Discomplete syndrome

3. Figure 10-3 Longitudinal relationships between spinal cord and vertebral column. A, Posterior surface of a spinal cord within a vertebral canal dissected from the back. B, How the anterior surface of the same spinal cord would look after removal of dura, arachnoid, and spinal nerves. C, Spinal cord exposed from the lateral direction, showing that the cord ends at about the L1-L2 level and spinal nerves travel progressively longer distances in the cauda equina to reach their exits from the vertebral canal. (From Mettler FA: Neuroanatomy, ed 2, St. Louis, 1948, Mosby.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

4. Function of the Spinal Cord • The Major Roles of the Spinal Cord • Connection • Processing information (spinal cord brain)

5. Spinal Motor Control • Three levels of motor control • 1. Motor neuron activated by peripheral sensory input • 2. Plurisegmental activation • Interneuron and propriospinal interneuronal circuits • Synergistic activation, transmidline activation • 3. Supraspinal control • Repeating cyclic output (reticulospinal) • Posture and balance (reticulospinal and vestibulospinal) • Skillful goal-directed movements (corticospinal)

6. Figure 10-1 Segmentation of the spinal cord. The portion in color, giving rise to a single spinal nerve on each side, represents a single segment. (From Mettler FA: Neuroanatomy, ed 2, St. Louis, 1948, Mosby.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

7. Figure 10-4 Cutaneous territories innervated by spinal nerves (dermatomes) and the trigeminal nerve (V1, V2, V3). Co, coccygeal segment. (Based on Bonica JJ: Applied anatomy relevant to pain. In Bonica JJ, editor: The management of pain, ed 2, Philadelphia, 1990, Lea & Febiger.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

8. Figure 10-5 Formation of the cauda equina. A to E, Cross sections from progressively more caudal levels of a vertebral column in which the subarachnoid space was filled with dyed gelatin (C3, T3, L1, L2, and L3 vertebrae, respectively). The C3 and T3 vertebrae encase spinal cord segments C4 and T4-T5, each adjacent to the dorsal and ventral roots of these segments and suspended by denticulate ligaments. The L1 and L2 vertebrae encase the sacral spinal cord (S) together with a collection of dorsal and ventral roots from lumbar and sacral segments. By the level of the L3 vertebra, the spinal cord has ended and only the cauda equina remains. F, Actual-size view of the caudal end of the spinal cord and the cauda equina, seen from the posterior side after the arachnoid and dura were spread apart. * in A, foramen for the vertebral artery; arrow in C, spinal nerve emerging from the intervertebral foramen. (A to E, from Key A, Retzius G: Studien in der anatomie des nervensystems und des bindegewebes, vol 1, Stockholm, 1875, Norstad. F, courtesy Dr. Norman Koelling, University of Arizona College of Medicine. Adapted from Nolte J, Angevine JB Jr: The human brain in photographs and diagrams, ed 3, St. Louis, 2007, Mosby.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

9. Figure 10-7 General cross-sectional anatomy of the spinal cord, represented in this case by the eighth cervical segment. A, Cross section of C8. B, Laminae of Rexed are indicated on the right, and the general kinds of cells and connections in these different areas are indicated on the left. Large-diameter, heavily myelinated afferents (1) enter medially through the posterior funiculus, whereas small-diameter afferents (2) enter laterally near the substantia gelatinosa. This corresponds to the way tactile and proprioceptive information is processed, relative to pain and temperature information. These afferents then contact interneurons (3) and, in some cases, motor neurons (4) directly. AF, anterior funiculus; AH, anterior horn; IG, intermediate gray matter; LF, lateral funiculus; PF, posterior funiculus; PH, posterior horn; asterisks indicate the substantia gelatinosa. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

11. Figure 10-9 A single motor neuron from the lumbar spinal cord of an adult cat. A marker substance (horseradish peroxidase) was injected from the intracellular tip of a microelectrode, and the neuron was subsequently reconstructed from a series of sections. The extent and complexity of the dendritic trees of real neurons are obviously different from those of the "cartoon" neurons in most of the diagrams in this book. (Modified from Ulfhake B et al: J Comp Neurol 278:69, 1988.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

12. Figure 10-10 Clusters of motor neurons (arrows) in the anterior horn at S4. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

13. LEVEL 1 MOTOR CONTROL

14. Figure 10-11 Stretch reflex. Striking the patellar tendon activates muscle spindle primary endings, which then monosynaptically excite alpha motor neurons that innervate the stretched muscle. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

15. Figure 10-12 Reflex connections of Golgi tendon organs. Contraction of a muscle activates the Golgi tendon organ (GTO) in its attached tendon. Under some conditions, the Ib afferents then activate inhibitory interneurons that inhibit the motor neurons to that muscle (autogenic inhibition). Under other conditions, the opposite effect is noted, mediated by excitatory interneurons. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

16. LEVEL 2 MOTOR CONTROL

17. Figure 10-13 Flexor reflex. This reflex involves several segments, and all connections are polysynaptic. In the example shown, a nociceptive fiber from the foot enters the spinal cord at S1 and activates (through at least one interneuron) motor neurons to iliopsoas and hamstring muscles. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

18. Figure 10-14 Reciprocal inhibition. Striking the patellar tendon initiates a stretch reflex, as in Figure 10-11. It also causes inhibition, through an interneuron, of the motor neurons to the antagonist hamstring muscles. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

19. Figure 10-15 Crossed extension. Stepping on a tack initiates a flexor reflex, as in Figure 10-13. It also causes excitation, through an interneuron, of the contralateral antagonist muscles. In this case, contraction of the contralateral quadriceps helps the leg with the nonpunctured foot to support the body. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

20. LEVEL 3 MOTOR CONTROL

21. Figure 10-18 Dorsal root entry zone, using C8 as an example. Small-diameter fibers enter the cord laterally and join Lissauer's tract (L) before terminating in the substantia gelatinosa (SG) and other superficial laminae of the posterior horn. Large-diameter fibers enter the spinal cord through the medial division, forming a large-fiber entry zone medial to Lissauer's tract and joining the posterior columns. Collaterals of many of these fibers sweep over the medial surface of the posterior horn (arrows) to reach deeper laminae. (From Nolte J, Angevine JB Jr: The human brain in photographs and diagrams, ed 3, St. Louis, 2007, Mosby.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

22. Figure 10-19 Posterior column-medial lemniscus pathway. Primary afferents carrying tactile and proprioceptive information synapse in the posterior column nuclei of the ipsilateral medulla. The axons of second-order cells then cross the midline, form the medial lemniscus, and ascend to the ventral posterolateral (VPL) nucleus of the thalamus. Third-order fibers then project to the somatosensory cortex of the postcentral gyrus. A somatotopic arrangement of fibers is present at all levels. The beginnings of this somatotopic arrangement, as a lamination of fibers in the posterior columns, is indicated in the inset to the right. FC, fasciculus cuneatus; FG, fasciculus gracilis. (Inset, redrawn from Mettler FA: Neuroanatomy, ed 2, St. Louis, 1948, Mosby.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

23. Figure 10-22 Spinothalamic tract. Pain, temperature, and some touch and pressure afferents end in the posterior horn. Second- or higher-order fibers cross the midline, form the spinothalamic tract, and ascend to the ventral posterolateral (VPL) nucleus of the thalamus (and also to other thalamic nuclei not indicated in this figure). Thalamic cells then project to the somatosensory cortex of the postcentral gyrus, to the insula, and to other cortical areas (also not indicated in this figure). Along their course through the brainstem, spinothalamic fibers give off many collaterals to the reticular formation (RF). The inset to the left shows the lamination of fibers in the posterior columns and the spinothalamic tract in a leg-lower trunk-upper trunk-arm sequence. The inset to the right shows the longitudinal formation of the spinothalamic tract. Primary afferents ascend several segments in Lissauer's tract before all their branches terminate; fibers crossing to join the spinothalamic tract do so with a rostral inclination. As a result, a cordotomy incision at any given level will spare most of the information entering the contralateral side of the spinal cord at that level, and to be effective, the incision must be made several segments rostral to the highest dermatomal level of pain. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

24. Figure 10-24 Corticospinal tracts. Fibers from the precentral gyrus and other nearby cortical areas descend through the cerebral peduncles, pons, and medullary pyramids; most cross in the pyramidal decussation to form the lateral corticospinal tract. Those that do not cross in the pyramidal decussation form the anterior corticospinal tract; most of these fibers cross in the anterior white commissure before ending in the spinal gray matter. Most corticospinal fibers do not synapse directly on motor neurons; they are drawn that way here for simplicity. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

25. AUTONOMIC NERVOUS SYSTEM

26. Figure 10-25 Parallels between somatic and autonomic parts of the nervous system. Both involve specialized afferents and efferents, reflex connections, and ascending and descending pathways to and from higher levels of the CNS. In the case of the sympathetic and parasympathetic systems, however, the hypothalamus rather than the thalamus receives much of the ascending information, and the hypothalamus rather than the cerebral cortex is a major source of descending pathways. In addition, sympathetic and parasympathetic transmission to the periphery involves an intermediate synapse in an autonomic ganglion (AG). Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

27. Figure 10-26 One major difference between somatic and autonomic efferents. The myelinated axons of lower motor neurons leave the spinal cord through ventral roots (A), or leave the brainstem through cranial nerves (B), and reach skeletal muscle directly. The autonomic system, in contrast, uses a two-neuron path. The thinly myelinated axons of preganglionic neurons leave through ventral roots or cranial nerves and end on postganglionic neurons in autonomic ganglia outside the CNS. Unmyelinated axons of postganglionic neurons then innervate smooth muscle, cardiac muscle, and glands. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

28. Figure 10-27 Major differences between the sympathetic and parasympathetic systems. The axons of preganglionic sympathetic neurons end in ganglia relatively close to the spinal cord, whereas those of preganglionic parasympathetic neurons travel a longer distance and reach ganglia near the innervated organ. The preganglionic neurons of both systems use acetylcholine as a neurotransmitter, but at the synapses of postganglionic neurons, the parasympathetic system uses acetylcholine and the sympathetic system typically uses norepinephrine. M, muscarinic synapse; N, nicotinic synapse. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

29. Figure 10-28 Origin and distribution of sympathetic (left) and parasympathetic (right) efferents. Postganglionic neurons that live in sympathetic chain ganglia and project to the body wall and upper extremity are omitted from the diagram to avoid excessive complexity; their axons travel in spinal nerves in a way analogous to that indicated for the lower extremity supply. Although the cranial nerves have distinct and separate parasympathetic contents, there is substantial overlap in the contents of ventral roots S2 to S4. CeG, celiac ganglion; CG, ciliary ganglion; D, pupillary dilator; IMG, inferior mesenteric ganglion; LG, lacrimal gland; OG, otic ganglion; PaG, parotid gland; PG, pterygopalatine ganglion; S, pupillary sphincter; SaG, submandibular and sublingual salivary glands; SCG, superior cervical ganglion; SG, submandibular ganglion; SMG, superior mesenteric ganglion. (Modified from Mettler FA: Neuroanatomy, ed 2, St. Louis, 1948, Mosby.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

30. BLOOD SUPPLY OF SPINAL CORD

31. Figure 10-29 Arterial supply of the spinal cord, demonstrated in a beautiful series of angiograms obtained after postmortem injection of barium sulfate and gelatin. A, Anterior view, showing the anterior spinal artery joined by a large radicular artery at C7 (small arrow) and by the great radicular artery of Adamkiewicz (large arrow) at T11. Parts of posterior spinal arteries (arrowheads) can also be seen. B, Midsagittal view at C3 showing the anterior spinal artery (arrows) giving rise to many branches that run posteriorly through the anterior median fissure to reach central regions of the cord. C, Anterior and lateral (V, ventral) views of the thoracic and lumbosacral portions of a spinal cord, showing the anterior (large arrows) and posterior (small arrows) spinal arteries and the artery of Adamkiewicz (arrowhead). Near the cauda equina, anastomoses (tailed arrows) typically interconnect the anterior and posterior spinal arteries in a kind of miniature circle of Willis. D, Vertical slices of the bracketed region in C, showing the anterior spinal artery (arrow, D1), its branches to central regions of the cord (arrows, D2), branches from circumferential anterior-posterior arterial interconnections that feed parts of the cord closer to the surface (D3 and arrowheads, D2), and posterior spinal arteries medial and lateral to the dorsal root entry zone (arrow and tailed arrow, D4). (From Thron AK: Vascular anatomy of the spinal cord, Vienna, 1988, Springer-Verlag.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

32. Figure 10-30 Microangiogram of a cross section at L2. Branches (large arrow) of the anterior spinal artery run posteriorly through the anterior median fissure to reach central regions of the cord. Branches of circumferential connections between the anterior and posterior spinal arteries supply parts of the cord closer to the surface. Branches (arrowheads) of the posterior spinal artery supply the posterior columns and share with anterior spinal branches (small arrow) in the supply of the posterior horn. (From Thron AK: Vascular anatomy of the spinal cord, Vienna, 1988, Springer-Verlag.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

33. SPECIAL SYNDROME AND DISEASE

34. Figure 10-31 Brown-Séquard syndrome. Damage to the outlined area of the spinal cord (in this example at C8) would affect the indicated tracts, causing ipsilateral spastic paralysis and loss of fine touch and proprioception, and contralateral loss of pain and temperature beginning one or more segments below the level of damage. CST, corticospinal tract; PC, posterior column; STT, spinothalamic tract. Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

35. Figure 10-32 Syringomyelia. A 39-year-old man was thrown from the bed of a pickup truck in a motor vehicle accident, sustaining vertebral fractures at T5-T6 and C4-C5. About 2 years later he began to notice progressive weakness and atrophy of his hand muscles. Magnetic resonance imaging revealed a central cavity in his spinal cord (syringomyelia), extending into the caudal medulla. The cavity is somewhat irregular in shape, and damage is more extensive at some levels than at others. Typical findings in such a case would be a band of bilateral loss of pain and temperature sensation (extending into the distribution of the trigeminal nerve, in a pattern explained in Chapter 12) and weakness and atrophy at levels where the damage extends into the anterior horns (in this case, at lower cervical levels). (Magnetic resonance images, courtesy Dr. Raymond F. Carmody, University of Arizona College of Medicine.) Downloaded from: StudentConsult (on 2 August 2009 10:16 AM) © 2005 Elsevier

36. Consequence of Spinal Cord Injury (SCI)

39. Studying Spinal Cord Motor Control in Complete Spinal Cord Injury • Isolated spinal cord without the influence of the brain • Spinal cord plasticity after SCI

40. Plasticity of Spinal Cord after Injury • New reflex formation • Autonomic dysreflexia • New motor pattern with new anatomy

41. Spinal Motor Control- What we have learned from SCI • Lumbosacral locomotor center • The influence of the brain (and brainstem) on spinal cord

43. Partial Body-Weight Support Walking Training Lumbosacral locomotor center Central pattern generator Sensory input: hip flexor stretching and plantar loading Central pattern generator for UE?