Neuroanatomy i

THE REGULAR NURSING , MLS , ANATOMY AND PHYSIOLOGY STUDENT OF BABCOCK UNIVERSITY

1. NEUROANATOMY - I BABCOCK UNIVERSITY BENJAMIN CARSON (Snr.) SCHOOL OF MEDICINE Lecturer: ADETUNJI O.A B.Tech., M.Sc., Mphil ., Ph.D.

2. Divisions of the Nervous System 2 main subdivisions: Central Nervous System the brain & spinal cord Peripheral Nervous System - groups of neurons called ganglia and peripheral nerves provides pathways to & from the central nervous system for electrochemical signals (impulses) 2

3. The Peripheral Nervous System Composed of 2 divisions: Somatic Provides sensory information (voluntary) Transmits impulses to and from skeletal muscles - usually conscious actions Autonomic motor system for viscera (smooth muscles & glands-involuntary) Autonomic is further divided into 2 subdivisions 3

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5. The Autonomic Nervous System 2 subdivisions of Autonomic: Sympathetic participates in body’s response to stress; fight or flight Parasympathetic returns body to resting state & conserves resources 5

6. Orientation of the PNS Dorsal roots carry sensory info to the spinal cord Ventral roots carry outgoing motor axons Peripheral nerves formed from dorsal & ventral roots Symmetry of PNS Arranged on 2 axis: longitudinal: rostral to caudal ( head to tail) dorsal to ventral (back to front) Segmented: 31 pairs of spinal nerves 12 pairs of cranial nerves 6

7. Neurons The basic and functional unit of the nervous system. Consist of a cell body ( perikaryon ) and processes arising from it. The processes arising from the cell body of a neuron are called neurites . Several short branching processes called Dendrites One longer process called an Axon 7

8. Types of Neuron 8

9. Synapse Synapses are sites of junction between neurons . Types axosomatic synapse axoaxonal synapse dendro-axonic or dendro -dendritic somato -dendritic 9

10. NEUROGLIAS: Supporting cells of nervous system Non conducting cells of the nervous systems. Classification of Neuroglia Astrocyte Microglia Schwann cells Oligodentrocytes They provide mechanical support to neurons S erve as insulators and prevent neuronal impulses from spreading in unwanted directions. 10

11. The Central Nervous System Consists of following Regions : Spinal Cord Brain Cerebrum Cerebellum Diencephalon: the caudal (posterior) part of the forebrain, containing the epithalamus , thalamus, hypothalamus, and ventral thalamus and the third ventricle. Brain Stem Midbrain Medulla Pons 11

12. Protection of the Brain & CNS The skull & spinal column The Meninges 3 layers of tissue protecting brain Dura mater outer tough layer Subdural space – normally small Arachnoid membrane next to dura mater Subarachnoid space - spongy layer filled with cerebrospinal fluid and blood vessels Pia mater membrane that covers the brain Cerebrospinal fluid (CSF) - cushions brain; circulates around the brain & spinal cord 12

13. VENTRICULAR SYSTEM 13 The ventricles are a communicating network of cavities. The adult derivatives of the open space or lumen of the embryonic neural tube

14. LATERAL VENTRICLE 14  The largest of these spaces  One within each of the cerebral hemispheres) Volume increases with age Best seen in frontal sections, where their ventral  surface is usually defined by the basal ganglia, dorsal  surface by the corpus callosum , and medial  surface by the septum pellucidum

15. 15 Projection of the horns

16. THIRD VENTRICLE 16  Forms a narrow midline space between the right and left thalamus Runs through the midbrain The anterior surface contains two protrusions: Supra-optic recess  Infundibular recess 

17. FOURTH VENTRICLE 17 The last in the system It lies within the brainstem, at the junction between the pons and medulla oblongata.

18. BOUNDARIES 18 Lateral boundary- superior and inferior cerebellar peduncles Roof- Superior part is formed by medial superior cerebellar peduncle, inferior part by inferior medullary velum. Floor- Formed by posterior surface of pons and cranial halves of medulla. Divided by median sulcus

19. COMMUNICATION 19 Lateral Ventricle Lateral Ventricle Third ventricle Fourth ventricle Cisterna Magna Median aperture ( Magendie ) Intervertebral foramen of Monro Intervertebral foramen of Monro Lateral aperture ( Lushka ) Lateral aperture ( Lushka ) Cerebral aqueduct

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21. ASSOCIATION WITH BRAIN REGIONS 21

22. CHOROID PLEXUS 22 Lined by ependymal cells Located in the ventricles produce Cerebrospinal fluid (CSF), which fills the ventricles and subarachnoid space, following a cycle of constant production and reabsorption . It forms the barrier between blood and CSF

23. CEREBROSPINAL FLUID 23 Found in the ventricles of the brain and in the subarachnoid space around the brain and spinal cord The circulation is aided by the arterial pulsations of the choroid plexuses and by the cilia on the ependymal cells lining the ventricles. The main sites for the absorption of the cerebrospinal fluid are the arachnoid villi that project into the dural venous sinuses, especially the superior sagittal sinus Functions…….

24. CLINICAL RELEVANCE 24 Hydrocephalus is defined as an abnormal collection of CSF within the ventricles of the brain. Chronic hydrocephalus causes raised intracranial pressure, and consequently cerebral atrophy There are 2 basic clinical classifications COMMUNICATING (NON-OBSTRUCTIVE HYDROCEPHALUS ) NON-COMMUNICATING (OBSTRUTIVE HYDROCEPHALUS)

25. 25 COMMUNICATING (NON-OBSTRUCTIVE HYDROCEPHALUS) Abnormal collection of CSF in the absence of any flow obstruction in the ventricles. Common causes usually involve the functional impairment of the arachnoid granulations, such as fibrosis of the subarachnoid space following a haemorrhage .

26. 26 NON-COMMUNICATING (OBSTRUTIVE HYDROCEPHALUS) Abnormal collection of CSF, with flow obstructed within the ventricular system. The most common site of obstruction is the cerebral aqueduct, connecting the third and fourth ventricles. Causes

27. 27 BLOCKAGE OF CSF CIRCULATION Obstruction can arise in the interventricular foramen, median aperture or cerebral aqueduct. Occurs due to tumor Causes distention of the ventricles

28. 28 HYDROCEPHALUS EX VACUO Refers to ventricular expansion, secondary to brain atrophy. Occur due to loss of adjacent brain parenchyma Often seen in patients with neurodegenerative conditions, such as Alzheimer’s disease.

29. 29 INCREASED CSF PRESSURE Caused by an intracranial tumor Compresses the thin walls of the retinal vein as it crosses the extension of the subarachnoid space to enter the optic nerve. Results in congestion of the retinal vein, bulging forward of the optic disc, and edema of the disc; the last condition is referred to as papilledema . Both eyes exhibits papilledema . Persistent papilledema leads to optic atrophy and blindness.

30. The Spinal Cord- gross anatomy and internal structure   The spinal cord is roughly cylindrical in shape.   It begins superiorly at the foramen magnum in the skull.   It terminates inferiorly in the adult at the level of the lower border of the L1.    In the young child, it usually ends at the upper border of L3. 30

31. Spinal Cord (cont’d) ENLARGEMENTS  Cervical & lumbar enlargements In the cervical region, it gives origin to the  brachial plexus  In the lower thoracic and lumbar regions, it gives origin to the  lumbosacral plexus CONUS MEDULLARIS: Inferiorly, the spinal cord tapers off into the conus medullaris . 31

32. FILUM TERMINALE: From the apex of conus medullaris Prolongation of the pia mater, descends to be attached to the posterior surface of coccyx. FISSURE & SULCI In the midline anteriorly , the anterior median fissure.  On the posterior surface, a shallow furrow, the posterior median sulcus . 32

33. SPINAL NERVES    Along the entire length of the spinal cord are attached 31 pairs of spinal nerves Cervical …… 8 Thoracic …… 12 Lumbar …… 5 Sacral …… 5 Coccygeal …..1 Each connects to the spinal cord by 2 roots – dorsal and ventral. Each root forms from a series of rootlets that attach along the whole length of the spinal cord segment. Ventral roots are motor  while  dorsal roots are sensory. The 2 roots join to form a spinal nerve prior to exiting the vertebral column. Almost immediately after emerging from its intervertebral foramen, a spinal nerve will divide into a dorsal ramus , a ventral ramus , and a meningeal branch that re-enters and innervates the meninges and associated blood vessels. Each ramus is mixed. Joined to the base of the ventral rami of spinal nerves in the thoracic region are the rami communicantes . These are sympathetic fibers. Dorsal rami supply the posterior body trunk whereas the thicker ventral rami supply the rest of the body trunk and the limbs. 33

34. Plexuses Except for T2 to T12, all ventral rami branch extensively and join one another lateral to the vertebral column forming complicated nerve plexuses. Within a plexus, fibers from different rami criss cross each other and become redistributed. Internal Structure: The spinal cord is composed of an inner core of gray matter, which is surrounded by an outer covering of white matter. GRAY MATTER On cross section; the gray matter is seen as an H-shaped pillar with anterior and posterior gray columns, or horns, united by a thin gray commissure containing the small central canal. A small lateral gray column or horn is present in the thoracic and upper lumbar segments of the cord. The amount of gray matter present at any given level of the spinal cord is related to the amount of muscle innervated at that level. Thus, its size is greatest within the cervical and lumbosacral enlargements of the cord. 34

35. Grey and White Matter of Spinal Cord 35 WHITE MATTER The white matter, may be divided into anterior, lateral, and posterior white columns or funiculi.    The anterior column on each side lies between the midline and the anterior nerve roots;    The lateral column lies between the anterior and the  posterior nerve roots;     The posterior column lies between the posterior nerve roots and the midline.

36. Spinal Cord Nuclei and laminae 36

37. Ascending and descending tracts of spinal cord ↑ Sensory Gracile tract Leg position & vibration Cuneate tract Arm position & vibration Dorsal spinocerebellar tract Strength & muscle speed Ventral spinocerebellar tract Modulation; interneurons Lateral spinothalamic tract Pain & temperature Anterior spinothalamic tract Light touch Spinocervical thalamic tract Kinesthetic movement & discriminative touch ↓ Motor Corticospinal tract Speed & agility Reticulospinal tract Differential facilitation of motor neurons Rubrospinal tract Fix movement errors Lateral vestibulospinal tract Extensor & posture Medial vestibulospinal tract Flexor & head position Tectospinal tract Head turning 37

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39. Clinical Anatomy of spinal cord 39

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42. 42 Epidural injections   – Lumbar epidural   • (for anaesthetic /analgesic injections)   – Caudal epidural – Cervical/thoracic epidural  

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44. The Brain Remaining 6 areas of the CNS are part of the brain The control center of the body Regulates body activity; enables you to think  Surface is gray matter - 6 x 10 6 cell bodies / cc Under gray matter is white matter - formed of myelinated axons.  Surface of the brain ( neocortex ) is convoluted Increases surface area ridges = gyri grooves = sulci 44

45. Forebrain, Midbrain, Hindbrain 45

46. The Cerebral Hemispheres Largest region of brain; 7/8 by weight - Includes: Cerebral cortex – outer surface of gray matter underlying white matter 3 nuclei (clusters of related neurons): the basal ganglia the hippocampal formation the amygdala these are masses of gray matter at the base of the cerebrum that serve the motor cortex paired cavities =   lateral ventricles Divided into 2 ‘half spheres’ = hemisheres 46

47. The Cerebral Cortex The convoluted outer surface grooves = sulci elevated regions = gyri Composed of gray matter 2-5 mm thick Contains ~ 12 billion neurons Most of the cerebral cortex is concerned with processing sensory information or motor commands 2 bands of tissue – one sensory, one motor Divided into primary, secondary, & tertiary 47

48. The Forebrain Telencephalon Olfactory bulb Cerebral cortex Basal telencephalon (basal ganglia) Corpus callosum commissure between cerebral hemispheres Internal capsule connections with brain stem Lateral ventricles 48

49. Lobes of the Cerebrum 2 sides called hemispheres Joined by a bridge = Corpus Callosum Separated by a deep fissure front to back Like 2 mirror images (but not quite) Divided into 4 lobes 1. Frontal 2. Parietal 3. T emporal 4. O ccipital 49

50. Lobes of the Cerebrum Parietal Lobe Temporal Lobe Frontal Lobe Limbic Lobe Occipital Lobe 50

51. The Frontal Lobe I ntellectual functioning R easoning Aggression Sexual behavior Speech Smell Voluntary movements 51

52. The Parietal Lobe Body sensory awareness (including taste) Language Abstract thought , especially math Body imaging 52

53. The Temporal Lobe Includes part of limbic system* Emotion* Interpretation of language Hearing Memory 53

54. The Occipital Lobe Receiving, interpreting, & discriminating visual stimuli Association of visual stimuli with memory 54

55. Ventral View 55

56. Sagittal Section 56

57. Superolateral surface 57

58. Superolateral surface 58

59. Medial surface 59

60. Medial surface 60

61. Inferior surface 61

62. White matter of Cerebral hemisphere The surface of the cerebral hemisphere is covered by a thin layer of grey matter called the cerebral cortex. The greater part of the cerebral hemisphere deep to the cortex is occupied by white matter within which are embedded certain important masses of grey matter . These fibres may be : Association fibres that interconnect different regions of the cerebral cortex. Projection fibres that connect the cerebral cortex with other masses of grey matter; and vice versa . Commissural fibres that interconnect identical areas in the two hemispheres. 62

63. Internal capsule The internal capsule may be divided into the following parts. The anterior limb lies between the caudate nucleus medially, and the anterior part of the lentiform nucleus laterally. The posterior limb lies between the thalamus medially, and the posterior part of the lentiform nucleus on the lateral side. In transverse sections through the cerebral hemisphere the anterior and posterior limbs of the internal capsule are seen to meet at an angle open outwards. This angle is called the genu ( genu = bend). Some fibres of the internal capsule lie behind the posterior end of the lentiform nucleus . They constitute its retrolentiform part. Some other fibres pass below the lentiform nucleus (and not medial to it). These fibres constitute the sublentiform part of the internal capsule 63

64. Functional areas 64

65. The Primary Sensory & Motor Cortex Primary Motor Cortex: controls voluntary movements of limbs & trunk contains neurons that project directly to spinal cord to activate somatic motor neurons Primary Sensory Areas receive information from peripheral receptors with only a few synaptic relays interposed 65

66. Brodmann Areas Cytoarchitectural areas of neocortex Regions with similar cell structure Numbered each represents a functionally distinct area Examples: Area 17 is the primary visual cortex at the caudal pole of the occipital lobe Area 4 is the primary motor cortex primary auditory cortex on left side of temporal lobe near language center 66

67. Secondary & Tertiary Areas Surrounding primary areas are higher order ( secondary & tertiary ) sensory & motor areas Process & integrate info coming from the primary sensory areas. Higher order motor areas send complex info required for motor actions to primary motor areas   67

68. Association Areas Three other large regions of cortex surround the primary, secondary & tertiary areas Called association areas In primates, association areas are majority of cortex 68

69. Localization of Cortical Functions 69

70. Lobes of the Brain & Associated Regions 70

71. Integration of Brain Functions Interactions of all areas sensory, motor & motivational systems is essential for behavior . Example: throw a ball - info about motion of ball, impact of ball, position of arms, legs, hands, etc. - sensory, motor, motivational systems Anatomical organization of each major functional system (sensory, motor, motivational) follows 4 principles 71

72. Principles of Anatomical Organization Each system contains relay centers These don’t just transmit info; also modify it Most important relay center is the thalamus almost all sensory info to cerebral cortex processed by thalamus Each system is composed of several distinct pathways Example: touch & pain 72

73. Principles of Anatomical Organization (Cont.) Each pathway is topographically organized neural map - clustered functions Most pathways cross the body’s midline Thus each hemisphere controls the actions/sensations of the opposite side . Left side dominates language; right side -spatial perception, musical ability 73

74. Diencephalon Thalamus & hypothalamus taken together Important structures found in the cerebrum Between the midbrain & cerebral hemispheres Thalamus Hypothalamus Third ventricle Retina and optic nerves develop from optic vesicle that pouches off from diencephalon during development 74

75. The Thalamus & Hypothalamus Thalamus relay center - processes & distributes almost all sensory & motor info going to the cerebral cortex links nervous & endocrine system emotional control Hypothalamus under the thalamus regulates autonomic nervous system connects to thalamus, midbrain & some cortical areas Controls body temperature, thirst, hunger, emotional behavior 75

76. Cerebellum The cerebellum consists of a part lying near the midline called the vermis , and of two lateral hemispheres. two surfaces, superior and inferior Dorsal to the pons & medulla Mostly white matter covered with a thin layer of gray matter Pleated surface; divided into several lobes Receives sensory input from the spinal cord, motor info from the cerebral cortex & input about balance from receptors in the inner ear Therefore, can coordinate planning & timing of voluntary muscle movement & maintain balance . 76

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78. The Medulla Oblongata & Pons Medulla Oblongata Bottom (rostral) region of the brainstem Regulates blood pressure and respiration; controls breathing, swallowing, digestion, heart & blood vessels. Pons Above medulla links cerebellum to cerebrum; relays info from cerebral hemispheres to cerebellum 78

79. The Midbrain Mesencephalon Tectum (roof) superior colliculus + inferior colliculus Tegmentum (floor) Cerebral aqueduct Controls responses to sight (e.g. eye movements) Relay station of auditory & visual signals Motor control of some skeletal muscles 79

80. The Brainstem Anatomically, from the bottom up: Medulla Oblongata Pons Midbrain Taken together = brainstem Contains all the nerves that connect the spinal cord with the cerebrum Receives sensory info from head, face, & neck Motor neurons control muscles of head & neck 12 pairs of cranial nerves carry input & output Also involved in hearing, taste & balance 80

81. The Limbic System A functional & evolutionary division, rather than anatomical Group of structures in center of the brain above the brainstem: hypothalamus pituitary hippocampus important role in memory hippocampal gyrus amygdala coordinates actions of the autonomic & endocrine systems involved in emotions 81

82. Functions of the Limbic System Sometimes called the “mammalian brain because most highly developed in mammals One of the oldest areas of brain from an evolutionary standpoint Maintains homeostasis: e.g. helps maintain temperature, blood pressure, heart rate, blood sugar Also involved in emotional reactions needed for survival 4 F’s: fleeing, fighting, feeding. 82

83. Visualizing the Limbic System 83

84. Clinical Anatomy of Brain 84

85. Ipsilateral/Contralateral The cerebral hemispheres are involved with inputs and outputs from the contralateral side of the body Damage to neocortex causes problems on the opposite side In patients with epilepsy, surgeons occasionally cut corpus callosum to relieve seizures. Flash different pictures in each eye, patients could describe what they saw with right eye, but not left, but could pick out object - example: Heart = ART. The cerebellum is involved with the control of movement on the ipsilateral side of the body. Damage to the cerebellum causes motor deficits on the same side. 85

86. Injury Mechanisms The brain is a complex and delicate organ, and one that is vulnerable to injury from a variety of different traumas. These include: Frontal Lobe Injury Occipital Lobe Injury Temporal Lobe Injury Side Impact Injury Coup/ Contre -coup Injury Diffuse Axonal Injury Epidural Hematoma Subdural Hematoma 86

87. Frontal Lobe Injury The frontal lobe of the brain can be injured from direct impact on the front of the head. During impact, the brain tissue is accelerated forward into the bony skull. This can cause bruising of the brain tissue and tearing of blood vessels. Frontal lobe injuries can cause changes in personality, as well as many different kinds of disturbances in cognition and memory. 87

88. Occipital Lobe Injury Occipital lobe injuries occur from blows to the back of the head. This can cause bruising of the brain tissue and tearing of blood vessels. These injuries can result in vision problems or even blindness. 88

89. Temporal Lobe Injury The temporal lobe of the brain is vulnerable to injury from impacts of the front of the head. The temporal lobe lies upon the bony ridges of the inside of the skull, and rapid acceleration can cause the brain tissue to smash into the bone, causing tissue damage or bleeding. 89

90. Side Impact Injury Injuries to the right or left side of the brain can occur from injuries to the side of the head. Injuries to this part of the brain can result in language or speech difficulties, and sensory or motor problems. 90

91. Coup/ Contre -coup Injury A French phrase that describes bruises that occur at two sites in the brain. When the head is struck, the impact causes the brain to bump the opposite side of the skull. Damage occurs at the area of impact and on the opposite side of the brain. 91

92. Diffuse Axonal Injury Brain injury does not require a direct head impact. During rapid acceleration of the head, some parts of the brain can move separately from other parts. This type of motion creates shear forces that can destroy axons necessary for brain functioning. These shear forces can stretch the nerve bundles of the brain . 92

93. Diffuse Axonal Injury The brain is a complex network of interconnections. Critical nerve tracts can be sheared and stressed during an acceleration-type of injury. Diffuse axonal injury is a very serious injury, as it directly impacts the major pathways of the brain. 93

94. Epidural Hematoma An epidural hematoma is a blood clot that forms between the skull and the top lining of the brain ( dura ). This blood clot can cause fast changes in the pressure inside the brain. When the brain tissue is compressed, it can quickly result in compromised blood flow and neuron damage. 94

95. Subdural Hematoma A subdural hematoma is a blood clot that forms between the dura and the brain tissue. The clot may cause increased pressure and may need to be removed surgically. When the brain tissue is compressed, it can quickly result in compromised blood flow and tissue damage. 95

96. Blood Supply of the Brain and Spinal Cord.

97. Introduction The brain is one of the most metabolically active organs in the body, receiving 17% of the total cardiac output and about 20% of the oxygen available in the body. The brain receives it’s blood from two pairs of arteries, the carotid and vertebral. About 80% of the brain’s blood supply comes from the carotid, and the remaining 20% from the vertebral. 97

98. These arteries arise in the neck, and ascend to the cranium. Within the cranial vault, the terminal branches of these arteries form an anastomotic circle, called the Circle of Willis . From this circle, branches arise which supply the majority of the cerebrum. Other parts of the CNS, such as the pons and spinal cord, are supplied by smaller branches from the vertebral arteries . 98

99. Internal Carotid Arteries The internal carotid arteries (ICA) originate at the bifurcation of the left and right common carotid arteries , at the level of the fourth cervical vertebrae (C4). They move superiorly within the carotid sheath, and enter the brain via the carotid canal of the temporal bone. They do not supply any branches to the face or neck. Once in the cranial cavity, the internal carotids pass anteriorly through the cavernous sinus. Distal to the cavernous sinus, each ICA gives rise to: Ophthalmic artery Posterior communicating artery Anterior cerebral artery The internal carotids then continue as the middle cerebral artery, which supplies the the lateral portions of the cerebrum. 99

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101. Vertebral Arteries The right and left vertebral arteries arise from the subclavian arteries, medial to the anterior scalene muscle. They then ascend up the posterior side of the neck, through holes in the transverse processes of the cervical vertebrae, known as foramen transversarium . The vertebral arteries enter the cranial cavity via the foramen magnum. Within the cranial vault, some branches are given off: Meningeal branch Anterior and posterior spinal arteries Posterior inferior cerebellar artery After this, the two vertebral arteries converge to form the basilar artery 101

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103. Arterial Circle of Willis The terminal branches of the vertebral and internal carotid arteries all anastamose to form a circular blood vessel, called the Circle of Willis. There are three main (paired) constituents of the Circle of Willis: Anterior cerebral arteries : These are terminal branches of the internal carotids. Internal carotid arteries : Present immediately proximal to the origin of the middle cerebral arteries. Posterior cerebral arteries : These are terminal branches of the vertebral arteries . To complete the circle, two ‘connecting vessels’ are also present: Anterior communicating artery : This artery connects the two anterior cerebral arteries. Posterior communicating artery : A branch of the internal carotid, this artery connects the ICA to the posterior cerebral artery. 103

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105. Regional Blood Supply to the Cerebrum There are three cerebral arteries; anterior, middle and inferior. They each supply a different portion of the cerebrum. The anterior cerebral arteries supply the anteromedial portion of the cerebrum. The middle cerebral arteries are situated laterally, supplying the majority of the lateral part of the brain. The posterior cerebral arteries supply both the medial and lateral parts of the posterior cerebrum 105

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107. Anterior Spinal Artery , provides sulcal branches which penetrate the ventral median fissure and supply the ventral 2/3 of the spinal cord. Posterior Spinal Arteries , each descends along the dorsolateral surface of the spinal cord and supplies the dorsal 1/3. 107 Spinal cord blood supply

108. Ventral Dorsal 108

109. Radicular arteries, originating from segmental arteries at various levels, which divide into anterior and posterior radicular arteries as they move along ventral and dorsal roots to reach the spinal cord. Here they reinforce spinal arteries and anastomose with their branches. From these varied sources of blood supply, a series of circumferential anastomotic channels are formed around the spinal cord, called the arterial vasocorona , from which short branches penetrate and supply the lateral parts of the cord 109

110. The radicular arteries provide the main blood supply to the cord at the thorasic , lumbar and sacral segments. There are a greater number on the posterior (10-23) than anterior (6-10 only) side of the cord. One radicular artery, noticeably larger than the others, is called the artery of Adamkiewicz , or the artery of the lumbar enlargement. Usually located with the lower thorasic or upper lumbar spinal segment on the left side of the spinal cord. 110

111. The spinal cord lacks adequate collateral supply in some areas, making these regions prone to ischemia after vascular occlusions. The upper Thorasic (T1-T4 ) and first lumbar segments are the most vulnerable regions of the cord. 111

112. There are several arteries that reinforce the spinal cord blood supply and are termed segmental arteries 1. The Vertebral arteries, spinal branches which are present in the upper cervical (~C3-C5) levels 2. Ascending Cervical arteries, present in the lower cervical areas 3. Posterior Intercostal, present in the mid- thorasic region 4. First Lumbar arteries, present in the mid-lumbar regions 112

113. Clinical Relevance: Disorders of Arterial Supply Stroke The brain is particularly sensitive to oxygen starvation. A stroke is a acute development of a neurological deficit, due to a disturbance in the blood supply of the brain. There are four main causes of a cerebrovascular accident: Thrombosis – Obstruction of a blood vessel by a locally forming clot. Embolism – Obstruction of a blood vessel by an emboli formed elsewhere. Hypoperfusion – Underperfusion of the brain, due to systemically low blood pressure ( e.g shock). Haemorrhage – An accumulation of blood within the cranial cavity. Out of these four, the most common cause is embolism. In many patients, an athlerosclerotic emboli will arise from the vessels of the neck. 113

114. Clinical Relevance: Disorders of Arterial Supply Intracerebral Aneurysms An aneurysm is a dilation of an artery, which is greater than 50% of the normal diameter. They most likely to occur to occur in the vessels contributing to the Circle of Willis . They are particularly dangerous – producing no symptoms until they rupture. Once the artery wall has ruptured, it is a medical emergency , and the patient is likely to die unless treated swiftly. Treatment of an intracerebral aneurysm is surgical. 114

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