The document provides information on the nervous system, including its main divisions and components. It discusses: 1) The central nervous system (CNS) which includes the brain and spinal cord, and the peripheral nervous system (PNS) which connects the CNS to the rest of the body and is divided into somatic and autonomic systems. 2) The autonomic nervous system has two divisions - the sympathetic and parasympathetic systems which work in opposition to activate the body during stress and restore it to resting state. 3) The brain is the control center of the body and is made up of the cerebrum, cerebellum, and brain stem. It is protected by meninges and

1. NEUROANATOMY - I
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

4. 4

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
1. UNIPOLAR 3. MULTIPOLAR
2. BIPOLAR 4. PSEUDOUNIPOLAR
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
Serve 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

20. 20

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

38. 38

39. Clinical Anatomy of spinal cord
Developmental anomalies: Spinal bifida
–meningomyelocoele, meningomyelocoele,
rachischisis
39

40. 40
•Tabes dorsalis (syphilitic myelopathy)
–complication of advanced syphilis (Treponema
pallidum)
•Damage to dorsal root ganglion (or spinal ganglion)
•degeneration (demyelination) of dorsal column fibres
•Loss of proprioceptive sense (position sense), and
discriminative touch

41. 41
Lumbar puncture
•Gives access to the spinal subarachnoid space
•Needle inserted between L3/L4 or L4/L5
•Structures traversed during lumbar puncture:
–Skin
–Subcutaneous tissue
–Supraspinous ligament
–Interspinous ligament
–Ligamentum flavum
–Epidural tissue
–Spinal dura
–Arachnoid mater

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

43. 43
Amyotrophic Lateral Sclerosis, ALS (or
Lou Gehrig’s Disease
• Upper and lower motor
neuron disease
– with gradual degeneration of
motor neurons
– Progressive weakening of
skeletal muscles occurs
• atrophy and fasciculation (fine
twitching) occur
• May involve genetic factor
– Mutation of SOD1 gene (on
xsome 21) reported
– FALS runs in family
• Symptoms starts around 40-
60 years (more in men)
• Patient may die from
respiratory failure
– due to paralysis of diaphragm

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 106 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. Temporal
◦ 4. Occipital
49

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

51. The Frontal Lobe
Intellectual functioning
Reasoning
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

77. 77

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

100. 100

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

102. 102

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

104. 104

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

106. 106

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
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

115. 115