1. PowerPoint ® Lecture Slides prepared by Karen Dunbar Kareiva Ivy Tech Community College © Annie Leibovitz/Contact Press Images Chapter 12 Part D The Central Nervous System © 2016 Pearson Education, Inc.

2. 12.10 Spinal Cord Gross Anatomy and Protection Spinal cord is enclosed in vertebral column –Begins at the foramen magnum –Ends at L 1 or L 2 vertebra Functions –Provides two-way communication to and from brain and body –Major reflex center: reflexes are initiated and completed at spinal cord © 2016 Pearson Education, Inc.

3. Gross Anatomy and Protection (cont.) Protected by bone, meninges, and CSF Spinal dura mater is one layer thick –Does not attach to vertebrae Epidural space –Cushion of fat and network of veins in space between vertebrae and spinal dura mater CSF fills subarachnoid space between arachnoid and pia maters Dural and arachnoid membranes extend to sacrum, beyond end of cord at L 1 or L 2 –Site of lumbar puncture or tap © 2016 Pearson Education, Inc.

4. Figure 12.27a Gross structure of the spinal cord, dorsal view. © 2016 Pearson Education, Inc. Cervical spinal nerves Cervical enlargement Lumbar spinal nerves Sacral spinal nerves Thoracic spinal nerves Dura and arachnoid mater Lumbar enlargement Conus medullaris Filum terminale The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Cauda equina

5. Figure 12.28 Diagram of a lumbar puncture. © 2016 Pearson Education, Inc. Lumbar puncture needle entering subarachnoid space Ligamentum flavum Supra- spinous ligament Filum terminale Cauda equina in subarachnoid space Dura mater Arachnoid mater Inter- vertebral disc S1S1 L5L5 L4L4 L5L5 T 12

6. Gross Anatomy and Protection (cont.) Spinal cord terminates in cone-shaped structure called conus medullaris Filum terminale extends to coccyx –Fibrous extension of conus covered with pia mater –Anchors spinal cord Denticulate ligaments –Extensions of pia mater that secure cord to dura mater –Cervical and lumbar enlargements: areas where nerves servicing upper and lower limbs arise from spinal cord © 2016 Pearson Education, Inc.

7. Gross Anatomy and Protection (cont.) Spinal nerves –Part of PNS –Attach to spinal cord by 31 paired roots Cervical and lumbosacral enlargements –Nerves serving upper and lower limbs emerge here Cauda equina –Collection of nerve roots at inferior end of vertebral canal © 2016 Pearson Education, Inc.

8. Figure 12.27a Gross structure of the spinal cord, dorsal view. © 2016 Pearson Education, Inc. Cervical spinal nerves Cervical enlargement Lumbar spinal nerves Sacral spinal nerves Thoracic spinal nerves Dura and arachnoid mater Lumbar enlargement Conus medullaris Filum terminale The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally. Cauda equina

9. Figure 12.27b Gross structure of the spinal cord, dorsal view. © 2016 Pearson Education, Inc. Terminus of medulla oblongata of brain Foramen magnum Sectioned pedicles of cervical vertebrae Spinal nerve rootlets Dorsal median sulcus of spinal cord Cervical spinal cord.

10. Figure 12.27c Gross structure of the spinal cord, dorsal view. © 2016 Pearson Education, Inc. Spinal cord Dorsal root ganglion Vertebral arch (cut) Cut edge of dura mater Dorsal root Thoracic spinal cord. Dorsal median sulcus

11. Figure 12.27d Gross structure of the spinal cord, dorsal view. © 2016 Pearson Education, Inc. First lumbar vertebral arch (cut across) Spinal cord Conus medullaris Cauda equina Filum terminale Inferior end of spinal cord, showing conus medullaris, cauda equina, and filum terminale.

12. Spinal Cord Cross-sectional Anatomy Two lengthwise grooves that run length of cord partially divide it into right and left halves –Ventral (anterior) median fissure –Dorsal (posterior) median sulcus Gray matter is located in core, white matter outside Central canal runs length of cord –Filled with CSF © 2016 Pearson Education, Inc.

13. Figure 12.29a Anatomy of the spinal cord. © 2016 Pearson Education, Inc. Epidural space (contains fat) Subdural space Subarachnoid space (contains CSF) Cross section of spinal cord and vertebra Pia mater Spinal meninges Arachnoid mater Dura mater Bone of vertebra Dorsal root ganglion Body of vertebra

14. Figure 12.29b Anatomy of the spinal cord. © 2016 Pearson Education, Inc. The spinal cord and its meningeal coverings Dorsal funiculus Ventral funiculus Lateral funiculus White columns Dorsal root ganglion Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Spinal nerve Dorsal median sulcus Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater Gray commissure Dorsal horn Gray matter Lateral horn Ventral horn

15. Spinal Cord Cross-sectional Anatomy (cont.) Gray matter and spinal roots –Cross section of cord resembles butterfly or letter “H” –Three areas of gray matter are found on each side of center and are mirror images: Dorsal horns: interneurons that receive somatic and visceral sensory input Ventral horns: some interneurons; somatic motor neurons Lateral horns (only in thoracic and superior lumbar regions): sympathetic neurons © 2016 Pearson Education, Inc.

16. Spinal Cord Cross-sectional Anatomy (cont.) Gray matter and spinal roots (cont.) –Gray commissure: bridge of gray matter that connects masses of gray matter on either side Encloses central canal –Ventral roots: bundle of motor neuron axons that exit the spinal cord –Dorsal roots: sensory input to cord –Dorsal root (spinal) ganglia: cell bodies of sensory neurons –Spinal nerves: formed by fusion of dorsal and ventral roots © 2016 Pearson Education, Inc.

17. Spinal Cord Cross-sectional Anatomy (cont.) Gray matter and spinal roots (cont.) –Gray matter divided into four groups based on of somatic or visceral innervation Somatic sensory (SS), visceral sensory (VS), visceral (autonomic) motor (VM) and somatic motor (SM) © 2016 Pearson Education, Inc.

18. Figure 12.30 Organization of the gray matter of the spinal cord. © 2016 Pearson Education, Inc. Spinal nerve Dorsal horn (interneurons) SS VS VM SM Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons SS VS VM SM Ventral root (motor) Ventral horn (motor neurons) Dorsal root (sensory) Dorsal root ganglion Somatic sensory neuron Visceral sensory neuron Visceral motor neuron Somatic motor neuron

19. Spinal Cord Cross-sectional Anatomy (cont.) White matter –Myelinated and nonmyelinated nerve fibers allow communication between parts of spinal cord, and spinal cord and brain –Run in three directions Ascending: up to higher centers (sensory inputs) Descending: from brain to cord or lower cord levels (motor outputs) Transverse: from one side to other (commissural fibers) © 2016 Pearson Education, Inc.

20. Spinal Cord Cross-sectional Anatomy (cont.) White matter (cont.) White matter is divided into three white columns (funiculi) on each side –Dorsal (posterior) –Lateral –Ventral (anterior) Each spinal tract is composed of axons with similar destinations and functions © 2016 Pearson Education, Inc.

21. Figure 12.29b Anatomy of the spinal cord. © 2016 Pearson Education, Inc. The spinal cord and its meningeal coverings Dorsal funiculus Ventral funiculus Lateral funiculus White columns Dorsal root ganglion Dorsal root (fans out into dorsal rootlets) Ventral root (derived from several ventral rootlets) Spinal nerve Dorsal median sulcus Central canal Ventral median fissure Pia mater Arachnoid mater Spinal dura mater Gray commissure Dorsal horn Gray matter Lateral horn Ventral horn

22. Figure 12.31 Major ascending (sensory) and descending (motor) tracts of the spinal cord, cross-sectional view. © 2016 Pearson Education, Inc. Ascending tractsDescending tracts Fasciculus gracilis Dorsal white column Fasciculus cuneatus Dorsal Lateral Rubrospinal tract Medial Tectospinal tract Lateral Ventral Spinocerebellar tracts Spinothalamic tracts Ventral white commissure Corticospinal tracts (pyramidal tracts) Reticulospinal tracts Vestibulospinal tract

23. Spinal Cord Trauma and Disorders Spinal cord trauma –Localized injury to spinal cord or its roots leads to functional losses Paresthesias: caused by damage to dorsal roots or sensory tracts –Leads to sensory function loss Paralysis: caused by damage to ventral roots or ventral horn cells –Leads to motor function loss –Two types of paralysis: flaccid or spastic © 2016 Pearson Education, Inc.

24. Spinal Cord Trauma and Disorders (cont.) Spinal cord trauma (cont.) –Flaccid paralysis: severe damage to ventral root or ventral horn cells Impulses do not reach muscles; there is no voluntary or involuntary control of muscles Muscles atrophy –Spastic paralysis: damage to upper motor neurons of primary motor cortex Spinal neurons remain intact; muscles are stimulated by reflex activity No voluntary control of muscles Muscles often shorten permanently © 2016 Pearson Education, Inc.

25. Spinal Cord Trauma and Disorders (cont.) Spinal cord trauma (cont.) –Transection (cross sectioning) of spinal cord at any level results in total motor and sensory loss in regions inferior to cut Paraplegia: transection between T 1 and L 1 Quadriplegia: transection in cervical region –Spinal shock: transient period of functional loss caudal to lesion © 2016 Pearson Education, Inc.

26. Spinal Cord Trauma and Disorders (cont.) Poliomyelitis –Destruction of ventral horn motor neurons by poliovirus –Muscles atrophy –Death may occur from paralysis of respiratory muscles or cardiac arrest –Survivors often develop postpolio syndrome many years later from neuron loss © 2016 Pearson Education, Inc.

27. Spinal Cord Trauma and Disorders (cont.) Amyotrophic lateral sclerosis (ALS) –Also called Lou Gehrig’s disease –Destruction of ventral horn motor neurons and fibers of pyramidal tract –Symptoms: loss of ability to speak, swallow, and breathe –Death typically occurs within 5 years –Caused by environmental factors and genetic mutations involving RNA processing Involves glutamate excitotoxicity © 2016 Pearson Education, Inc.

28. Spinal Cord Trauma and Disorders (cont.) Amyotrophic lateral sclerosis (ALS) (cont.) –Drug riluzole interferes with glutamate signaling: only treatment © 2016 Pearson Education, Inc.

29. 12.11 Neuronal Pathways Major spinal tracts are part of multineuron pathways Four key points about spinal tracts and pathways: –Decussation: Most pathways cross from one side of CNS to other at some point –Relay: Consist of chain of two or three neurons –Somatotopy: precise spatial relationship in CNS correspond to spatial relationship in body –Symmetry: pathways are paired symmetrically (right and left) © 2016 Pearson Education, Inc.

30. Ascending Pathways Conduct sensory pathways upward through a chain of three neurons: –First-order neuron Conducts impulses from cutaneous receptors and proprioceptors Branches diffusely as it enters spinal cord or medulla Synapses with second-order neuron © 2016 Pearson Education, Inc.

31. Ascending Pathways (cont.) –Second-order neuron Interneuron Cell body in dorsal horn of spinal cord or medullary nuclei Axons extend to thalamus or cerebellum –Third-order neuron Also an interneuron Cell bodies in thalamus Axon extends to somatosensory cortex No third-order neurons in cerebellum © 2016 Pearson Education, Inc.

32. Ascending Pathways (cont.) Somatosensory signals travel along three main pathways on each side of spinal cord: –Two pathways transmit somatosensory information to sensory cortex via thalamus Dorsal column–medial lemniscal pathways Spinothalamic pathways Provide for discriminatory touch and conscious proprioception –Third pathway, spinocerebellar tracts, terminate in the cerebellum © 2016 Pearson Education, Inc.

33. Ascending Pathways (cont.) –Dorsal column–medial lemniscal pathways Transmit input to somatosensory cortex for discriminative touch and vibrations Composed of paired fasciculus cuneatus and fasciculus gracilis in spinal cord and medial lemniscus in brain (medulla to thalamus) –Spinothalamic pathways Lateral and ventral spinothalamic tracts Transmit pain, temperature, coarse touch, and pressure impulses within lateral spinothalamic tract © 2016 Pearson Education, Inc.

34. Ascending Pathways (cont.) –Spinocerebellar tracts Ventral and dorsal tracts Convey information about muscle or tendon stretch to cerebellum –Used to coordinate muscle activity © 2016 Pearson Education, Inc.

35. Figure 12.32a Pathways of selected ascending spinal cord tracts. © 2016 Pearson Education, Inc. Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Spinocerebellar pathway Cerebellum Pons Medulla oblongata Cervical spinal cord Touch receptor Nucleus gracilis Nucleus cuneatus Lumbar spinal cord Dorsal column–medial lemniscal pathway Medial lemniscus (tract) (axons of second-order neurons) Fasciculus cuneatus (axon of first-order sensory neuron) Joint stretch receptor (proprioceptor) Axon of first-order neuron Muscle spindle (proprioceptor) Dorsal spinocerebellar tract (axons of second-order neurons) Fasciculus gracilis (axon of first-order sensory neuron)

36. Figure 12.32b Pathways of selected ascending spinal cord tracts. © 2016 Pearson Education, Inc. Thalamus Cerebrum Midbrain Cerebellum Pons Medulla oblongata Cervical spinal cord Lumbar spinal cord Pain receptors Primary somatosensory cortex Axons of third-order neurons Lateral spinothalamic tract (axons of second-order neurons) Axons of first-order neurons Temperature receptors Spinothalamic pathway

37. Table 12.2-1 Major Ascending (Sensory) Pathways and Spinal Cord Tracts © 2016 Pearson Education, Inc.

38. Table 12.2-2 Major Ascending (Sensory) Pathways and Spinal Cord Tracts (continued) © 2016 Pearson Education, Inc.

39. Table 12.2-3 Major Ascending (Sensory) Pathways and Spinal Cord Tracts (continued) © 2016 Pearson Education, Inc.

40. Descending Pathways and Tracts Deliver efferent impulses from brain to spinal cord Two groups –Direct pathways: pyramidal tracts –Indirect pathways: all others Motor pathways involve two neurons: –Upper motor neurons Pyramidal cells in primary motor cortex –Lower motor neurons Ventral horn motor neurons Innervate skeletal muscles © 2016 Pearson Education, Inc.

41. Descending Pathways and Tracts (cont.) Direct (pyramidal) pathways –Impulses from pyramidal neurons in precentral gyri pass through pyramidal (lateral and ventral corticospinal) tracts –Descend directly without synapsing until axon reaches end of tract in spinal cord –In spinal cord, axons synapse with interneurons (lateral tract) or ventral horn motor neurons (ventral tract) –Direct pathway regulates fast and fine (skilled) movements © 2016 Pearson Education, Inc.

42. Figure 12.33a Three descending pathways by which the brain influences movement. © 2016 Pearson Education, Inc. Primary motor cortex Internal capsule Midbrain Cerebellum Cerebrum Medulla oblongata Cervical spinal cord Lumbar spinal cord Pons Pyramidal cells (upper motor neurons) Cerebral peduncle Ventral corticospinal tract Lateral corticospinal tract Pyramids Decussation of pyramids Skeletal muscle Somatic motor neurons (lower motor neurons) Pyramidal (lateral and ventral corticospinal) pathways

43. Descending Pathways and Tracts (cont.) Indirect pathways –Also referred to as multineuronal pathways –Complex and multisynaptic –Includes brain stem motor nuclei and all motor pathways except pyramidal pathways –These pathways regulate: Axial muscles, maintaining balance and posture Muscles controlling coarse limb movements Head, neck, and eye movements that follow objects in visual field © 2016 Pearson Education, Inc.

44. Descending Pathways and Tracts (cont.) Indirect pathways (cont.) –Consist of four major pathways: Reticulospinal and vestibulospinal tracts: –maintain balance by varying tone of postural muscles Rubrospinal tracts: control flexor muscles Tectospinal tracts: originate from superior colliculi and mediate head movements in response to visual stimuli © 2016 Pearson Education, Inc.

45. Figure 12.33b Three descending pathways by which the brain influences movement. © 2016 Pearson Education, Inc. Midbrain Cerebellum Cerebrum Medulla oblongata Cervical spinal cord Red nucleus Pons Rubrospinal tract Rubrospinal tract

46. Table 12.3-1 Major Descending (Motor) Pathways and Spinal Cord Tracts © 2016 Pearson Education, Inc.

47. Table 12.3-2 Major Descending (Motor) Pathways and Spinal Cord Tracts (continued) © 2016 Pearson Education, Inc.

48. Developmental Aspects of Central Nervous System Starting in a 3-week old embryo: 1. Ectoderm thickens, forming neural plate Invaginates, forming neural groove flanked by neural folds 2. Neural crest forms from migrating neural fold cells 3. Neural groove deepens, edges fuse forming neural tube © 2016 Pearson Education, Inc.

49. Figure 12.34-1 Development of the neural tube from embryonic ectoderm. © 2016 Pearson Education, Inc. Head Tail Neural fold forming Neural plate Surface ectoderm The neural plate forms from surface ectoderm. It then invaginates, forming the neural groove flanked by neural folds. 1

50. Figure 12.34-2 Development of the neural tube from embryonic ectoderm. © 2016 Pearson Education, Inc. Neural crest Neural groove Neural fold cells migrate to form the neural crest, which will form much of the PNS and many other structures. 2

51. Figure 12.34-3 Development of the neural tube from embryonic ectoderm. © 2016 Pearson Education, Inc. Head Tail Surface ectoderm Neural tube The neural groove becomes the neural tube, which will form CNS structures. 3

52. Developmental Aspects of Central Nervous System Neural tube, formed by week 4, differentiates into CNS –Brain forms rostrally –Spinal cord forms caudally By week 6, both sides of spinal cord bear a dorsal alar plate and a ventral basal plate –Alar plate becomes interneurons –Basal plate becomes motor neurons –Neural crest cells form dorsal root ganglia © 2016 Pearson Education, Inc.

53. Figure 12.35 Structure of the embryonic spinal cord. © 2016 Pearson Education, Inc. Dorsal root ganglion: sensory neurons from neural crest Alar plate: interneurons Basal plate: motor neurons Axons form white matter Neural tube cells Central cavity

54. Developmental Aspects of Central Nervous System Gender-specific areas appear in both brain and spinal cord –Depends on presence or absence of fetal testosterone Maternal exposure to radiation, drugs, or infection can harm developing CNS –Example: alcohol or opiates, various infections such as rubella Smoking decreases oxygen in blood, which can lead to neuron death and fetal brain damage © 2016 Pearson Education, Inc.

55. Developmental Aspects of Central Nervous System Hypothalamus is one of last areas of CNS to develop –Premature infants have poor body temperature regulation Visual cortex develops slowly over first 11 weeks Neuromuscular coordination progresses in superior-to-inferior and proximal-to-distal directions along with myelination © 2016 Pearson Education, Inc.

56. Developmental Aspects of Central Nervous System Age brings some cognitive declines, but not significant in healthy individuals until 80s Shrinkage of brain accelerates in old age Excessive alcohol use and boxing cause signs of senility unrelated to aging process © 2016 Pearson Education, Inc.

57. Clinical – Homeostatic Imbalance 12.2 Cerebral palsy: neuromuscular disability involving poorly controlled or paralyzed voluntary muscles –Due to brain damage, possibly from lack of oxygen during birth –Spasticity, speech difficulties, motor impairments can be seen –Some patients have seizures, are intellectually impaired, and/or are deaf –Visual impairment is common © 2016 Pearson Education, Inc.

58. Clinical – Homeostatic Imbalance 12.2 Anencephaly: cerebrum and parts of brain stem never develop –Neural fold fails to fuse –Child is vegetative –Death occurs soon after birth Spina bifida: incomplete formation of vertebral arches –Spina bifida occulata: least serious, involves only one or few missing vertebrae Causes no neural problems © 2016 Pearson Education, Inc.

59. Clinical – Homeostatic Imbalance 12.2 –Spina bifida cystica: more severe and most common Saclike cyst protrudes dorsally from spine Cyst may contain CSF (meningocele) or portions of spinal cord and nerve roots (myelomeningocele) –Larger cysts cause neurological impairment Usually also see hydrocephalus –Most cases caused by lack of B vitamin folic acid U.S. incidence has dropped with mandatory supplementation © 2016 Pearson Education, Inc.