Understanding Spinal Cord and Nerves

1. BIOL 2401 Fundamentals of Anatomy and Physiology Mrs. Willie Grant wgrant4@alamo.edu 210-643-8968

2. 13 The Spinal Cord, Spinal Nerves, and Spinal Reflexes

3. An Introduction to the Spinal Cord, Spinal Nerves, and Spinal Reflexes Learning Outcomes 13-1 Describe the basic structural and organizational characteristics of the nervous system. 13-2 Discuss the structure and functions of the spinal cord, and describe the three meningeal layers that surround the central nervous system. 13-3 Explain the roles of white matter and gray matter in processing and relaying sensory information and motor commands. 13-4 Describe the major components of a spinal nerve, and relate the distribution pattern of spinal nerves to the regions they innervate. 13-5 Discuss the significance of neuronal pools, and describe the major patterns of interaction among neurons within and among these pools. 13-6 Describe the steps in a neural reflex, and classify the types of reflexes. 13-7 Distinguish among the types of motor responses produced by various reflexes, and explain how reflexes interact to produce complex behaviors. 13-8 Explain how higher centers control and modify reflex responses.

4. Figure 13-1 An Overview of Chapters 13 and 14 CHAPTER 14: The Brain Motor output overcranial nerves Sensory input over cranial nerves Effectors Reflexcentersin brain Sensoryreceptors Muscles CHAPTER 13: The Spinal Cord Glands Motor output overspinal nerves Sensory input over spinal nerves Reflexcentersin spinalcord Sensoryreceptors Adipose tissue

5. 13-2 Spinal Cord • Gross Anatomy of the Spinal Cord • About 18 inches (45 cm) long • 1/2 inch (14 mm) wide • Ends between vertebrae L1 and L2 • Bilateral symmetry • Grooves divide the spinal cord into left and right • Posterior median sulcus – onposterior side • Anterior median fissure – deeper groove on anterior side

6. 13-2 Spinal Cord • Enlargements of the Spinal Cord (expanded amount of gray matter in segments of the spinal cord and motor control of the limbs) • Cervical enlargement • Nerves of shoulders and upper limbs • Lumbar enlargement • Nerves of pelvis and lower limbs • The distal end • Conus medullaris • Thin, conical spinal cord below lumbar enlargement • Filum terminale • Thin thread of fibrous tissue at end of conus medullaris • Attaches to coccygeal ligament • Cauda equina • Nerve roots extending below conus medullaris

7. Figure 13-2 Gross Anatomy of the Adult Spinal Cord Posterior median sulcus Dorsal root Dorsal rootganglion White matter Graymatter Centralcanal C1 C2 C3 Cervical spinalnerves C4 C5 Spinalnerve Ventralroot C6 Anterior median fissure Cervicalenlargement C7 C3 C8 T1 T2 T3 T4 T5 T6 T7 T8 Thoracicspinalnerves Posteriormedian sulcus T9 T10 T3 Lumbarenlargement T11 T12 Conusmedullaris L1 L2 Inferiortip ofspinal cord L3 Lumbarspinalnerves L4 Cauda equina L5 L1 S1 Sacral spinalnerves S2 S3 S4 S5 S2 Filum terminale(in coccygeal ligament) Coccygealnerve (Co1)

8. 13-2 Spinal Cord • 31 Spinal Cord Segments • Based on vertebrae where spinal nerves originate • Positions of spinal segment and vertebrae change with age • Cervical nerves • Are named for inferior vertebra • All other nerves • Are named for superior vertebra

9. 13-2 Spinal Cord • Roots • Two branches of spinal nerves • Ventral root • Contains axons of motor neurons • Dorsal root • Contains axons of sensory neurons • Dorsal root ganglia • Contain cell bodies of sensory neurons

10. 13-2 Spinal Cord • The Spinal Nerve • On each side of spine • Dorsal and ventral roots join to form a spinal nerve • Mixed Nerves • Carry both afferent (sensory) and efferent (motor) fibers

12. 13-2 Spinal Cord • The Spinal Meninges • Specialized membranes isolate spinal cord from surroundings • Functions of the spinal meninges include: • Protecting spinal cord • Carrying blood supply • Continuous with cranial meninges • Meningitis • Viral or bacterial infection of meninges

13. BIOL 2401 Meningitis is an inflammation of the meninges or the three membranes that surround and protect the brain and spinal cord. In most cases, the condition is caused by a viral or bacterial infection. Meningitis can afflict children and adults. Today vaccinations are offered by most of the educational institues to curtail the spread of the condition through teens and young adults. In addition, vaccines are available for travelers visiting foreign countries where the prevalence of meningitis may be higher. Meningitis is extremely contagious and can spread from person to person through coughing and sneezing. Symptoms of meningitis: severe headache, back ache, neck ache, pain in the eyes, especially around light, nausea, fever, vomiting, confusion, sleepiness, lethargy and fatigue.

15. 13-2 Spinal Cord • The Three Meningeal Layers • Dura mater • Outer layer of spinal cord • Arachnoid mater • Middle meningeal layer • Pia mater • Inner meningeal layer

16. 13-2 Spinal Cord • The Dura Mater • Tough and fibrous • Cranially • Fuses with periosteum of occipital bone • Is continuous with cranial dura mater • Caudally • Tapers to dense cord of collagen fibers • Joins filum terminale in coccygeal ligament

17. 13-2 Spinal Cord • The Dura Mater • The Epidural Space • Between spinal dura mater and walls of vertebral canal • Contains loose connective and adipose tissue • Anesthetic injection site

18. 13-2 Spinal Cord • The Arachnoid Mater • Middle meningeal layer • Arachnoid membrane • Simple squamous epithelia • Covers arachnoid mater

19. 13-2 Spinal Cord • The Interlayer Spaces of Arachnoid Mater • Subdural space • Between arachnoid mater and dura mater • Subarachnoid space • Between arachnoid mater and pia mater • Contains collagen/elastin fiber network (arachnoid trabeculae) • Filled with cerebrospinal fluid (CSF) • Cerebrospinal Fluid (CSF) • Carries dissolved gases, nutrients, and wastes • Lumbar puncture or spinal tap withdraws CSF

20. 13-2 Spinal Cord • The Pia Mater • Is the innermost meningeal layer • Is a mesh of collagen and elastic fibers • Is bound to underlying neural tissue

21. 13-2 Spinal Cord • Structures of the Spinal Cord • Paired denticulate ligaments • Extend from pia mater to dura mater • Stabilize side-to-side movement • Blood vessels • Along surface of spinal pia mater • Within subarachnoid space Figure 13-4 The Spinal Cord and Associated Structures

22. 13-3 Gray Matter and White Matter • Sectional Anatomy of the Spinal Cord • White matter • Is superficial • Contains myelinated and unmyelinated axons • Gray matter • Surrounds central canal of spinal cord • Contains neuron cell bodies, neuroglia, unmyelinated axons • Has projections (gray horns)

23. 13-3 Gray Matter and White Matter • Organization of Gray Matter • The gray horns • Posterior gray horns contain somatic and visceral sensory nuclei • Anterior gray horns contain somatic motor nuclei • Lateral gray horns are in thoracic and lumbar segments; contain visceral motor nuclei • Gray commissures • Axons that cross from one side of cord to the other before reaching gray matter

24. 13-3 Gray Matter and White Matter • Organization of Gray Matter • The cell bodies of neurons form functional groups called nuclei (masses of gray matter within the CNS) • Sensory nuclei • Dorsal (posterior) • Connect to peripheral receptors • Motor nuclei • Ventral (anterior) • Connect to peripheral effectors • Sensory or motor nucleus location within the gray matter determines which body part it controls

25. 13-3 Gray Matter and White Matter • Organization of White Matter • Posterior white columnslie between posterior gray horns and posterior median sulcus • Anterior white columnslie between anterior gray horns and anterior median fissure • Anterior white commissure area where axons cross from one side of spinal cord to the other • Lateral white columns located on each side of spinal cord between anterior and posterior columns

26. BIOL 2401 What is the difference between a horn and a column in the spinal cord? A HORN is an area of gray matter. A COLUMN is a region of white matter.

27. 13-3 Gray Matter and White Matter • Organization of White Matter • Tracts or fasciculi (a bundle of axons in the white columns that relay the same information in the same direction). • Ascending tracts • Carry information to brain • Descending tracts • Carry motor commands to spinal cord

29. 13-3 Gray Matter and White Matter • Spinal Cord Summary • Spinal cord has a narrow central canal surrounded by gray matter • Containing sensory (dorsal) and motor nuclei (ventral) • Gray matter • Is covered by a thick layer of white matter • White matter • Consists of ascending and descending axons organized in columns • Contains axon bundles with specific functions • Spinal cord is so highly organized • It is possible to predict results of injuries to specific areas

30. 13-4 Spinal Nerves and Plexuses • Anatomy of Spinal Nerves • Every spinal cord segment • Is connected to a pair of spinal nerves • Every spinal nerve • Is surrounded by three connective tissue layers • That support structures and contain blood vessels

31. 13-4 Spinal Nerves and Plexuses • Three Connective Tissue Layers of Spinal Nerves • Epineurium • Outer layer • Dense network of collagen fibers • Perineurium • Middle layer • Divides nerve into fascicles (axon bundles) • Endoneurium • Inner layer • Surrounds individual axons

32. Figure 13-6 A Peripheral Nerve Blood vessels Connective TissueLayers Epineurium coveringspinal nerve Perineurium (aroundone fascicle) Endoneurium Myelinated axon Fascicle Schwann cell

33. 13-4 Spinal Nerves and Plexuses • Peripheral Distribution of Spinal Nerves • Spinal nerves • Form lateral to intervertebral foramen • Where dorsal and ventral roots unite • Then branch and form pathways to destination

34. 13-4 Spinal Nerves and Plexuses • Peripheral Distribution of Spinal Nerves • Motor nerves • The first branch • White ramus • Carries visceral motor fibers to sympathetic ganglion of autonomic nervous system • Gray ramus • Unmyelinated nerves • Return from sympathetic ganglion to rejoin spinal nerve • Dorsal and ventral rami • Dorsal ramus • Contains somatic and visceral motor fibers • Innervates the back • Ventral ramus • Larger branch • Innervates ventrolateral structures and limbs

35. Sensory input is conveyed from sensory receptors to the posterior gray horns of the spinal cord.

36. Motor output is conveyed from the anterior and lateral gray horns of the spinal cord to effectors (muscles and glands).

37. Figure 13-8 Dermatomes C2C3 N V Bilateral regions of skin monitored by specific pairs of nerves. C2C3 C2 C3 C3 C4 T2 C4 C5 T3 T1 T4 T2 T5 C5 T3 T6 T4 T7 T5 T8 T2 T9 T6 T10 T2 T7 T11 T8 T12 T9 C6 L1 T10 L2 T1 L3 T11 L4 C7 C6 L5 T12 L1 • Peripheral Neuropathy • Regional loss of sensory or motor function • Due to trauma or compression • Examples: when your leg falls asleep. S S 4 L2 3 S2 C8 C8 L3 L1 T1 S5 C7 S1 L5 L4 S2 L2 L5 L3 S1 L4 ANTERIOR POSTERIOR

38. Figure 13-9 Shingles Shingles is caused by the varicell-zoster virus (which also causes chickenpox). The herpes virus attacks neurons within the dorsal roots of spinal nerves and sensory ganglia of cranial nerves. This causes a painful rash and blisters whose distribution corresponds to that of the affected sensory nerves and follows its dermatome. Why is shingles probably NOT a problem for most people in this class?

39. 13-4 Spinal Nerves and Plexuses • Nerve Plexuses • Complex, interwoven networks of nerve fibers • Formed from blended fibers of ventral rami of adjacent spinal nerves • Control skeletal muscles of the neck and limbs • The Four Major Plexuses of Ventral Rami • Cervical plexus • Brachial plexus • Lumbar plexus • Sacral plexus

41. 13-4 Spinal Nerves and Plexuses • The Cervical Plexus • Includes ventral rami of spinal nerves C1–C5 • Innervates neck, thoracic cavity, diaphragmatic muscles • Major nerve • Phrenic nerve (controls diaphragm)

42. 13-4 Spinal Nerves and Plexuses • The Brachial Plexus • Includes ventral rami of spinal nerves C5–T1 • Innervates pectoral girdle and upper limbs • Nerves that form brachial plexus originate from: • Superior, middle, and inferior trunks • Large bundles of axons from several spinal nerves • Lateral, medial, and posterior cords • Smaller branches that originate at trunks • Major nerves • Musculocutaneous nerve (lateral cord) • Median nerve (lateral and medial cords) • Ulnar nerve (medial cord) • Axillary nerve (posterior cord) • Radial nerve (posterior cord)

44. 13-4 Spinal Nerves and Plexuses • The Lumbar Plexus • Includes ventral rami of spinal nerves T12–L4 • Major nerves • Genitofemoral nerve • Lateral femoral cutaneous nerve • Femoral nerve • The Sacral Plexus • Includes ventral rami of spinal nerves L4–S4 • Major nerves • Pudendal nerve • Sciatic nerve (Two branches: Fibular nerve and Tibial nerve)

46. 13-5 Neuronal Pools • Functional Organization of Neurons • Sensory neurons • About 10 million • Deliver information to CNS • Motor neurons • About 1/2 million • Deliver commands to peripheral effectors • Interneurons • About 20 billion • Interpret, plan, and coordinate signals in and out

47. 13-5 Neuronal Pools • Neuronal Pools • Functional groups of interconnected neurons (interneurons) • Each with limited input sources and output destinations • May stimulate or depress parts of brain or spinal cord

48. 13-5 Neuronal Pools Five Patterns of Neural Circuits in Neuronal Pools • Divergence • Spreads stimulation to many neurons or neuronal pools in CNS • Convergence • Brings input from many sources to single neuron • Serial processing • Moves information in single line • Parallel processing • Moves same information along several paths simultaneously • Reverberation • Positive feedback mechanism • Functions until inhibited

50. 13-6 Reflexes • Reflexes • Automatic responses coordinated within spinal cord • Through interconnected sensory neurons, motor neurons, and interneurons • Produce simple and complex reflexes