Download The Brain

The Brain
Chao-Ying Wang
102.9.12
Outline
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The Organization of brain
Meninges
Ventricular System: Ventricles and Cisterns
Cerebrum: Lobes and Basal ganglion
Diencephalon: Thalamus, Epithalamus, Hypothalamus
, Pituitary gland
Limbic System
Brain Stem: Midbrain, Pons and Medulla Oblongata
Cerebellum
Cerebral Vascular system: Arterial and Venous System
Superior
(Cranial)
Sagittal
Anterior
(Ventral)
Posterior
(Dorsal)
(Transverse, tranaxial)
(Coronal)
Inferior
(Caudal)
Imaging Planes
Transverse
Axial
Sagittal
Coronal
The organization of brain
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An adult brain weighs between 1.35 and 1.4 kilograms
(kg) (around 3 pounds) and has a volume of about 1200
cubic centimeters (cc). Cerebrum is 83% of brain volume;
cerebellum contains 50% of the neurons
Brain size is not directly correlated with intelligence
It is not the physical size of the brain that determines
intelligence—it is the number of active synapses.
Embryonic development:neural tube
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Pros-encephalon(forebrain)
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Mes-encephalon(midbrain)
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Telencephalon: cerebrum
Diencephalon: epithalamus, thalamus,hypothalamus
Mesencephalon: cerebral peduncles, colliculi
Rhomb-encephalon(hindbrain)
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Metencephalon: pons, cerebellum
Myelencephalon: medulla oblongata
The Brain’s 4 Major Regions
Cerebrum, diencephalon, brainstem, and cerebellum.
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The cerebrum is divided into two halves, called the left and right
cerebral hemispheres.
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Each hemisphere is subdivided into five functional areas called lobes.
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Outer surface of an adult brain exhibits folds called gyri (gyrus) and
shallow depressions between those folds called sulci (sulcus).
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The brain is associated with 12 pairs of cranial nerves.
Support and Protection of the Brain
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The brain is protected and isolated by multiple structures:
 Bony cranium
 Meninges:
 Protective connective tissue membranes
 surround and partition portions of the brain.
 Cerebrospinal fluid (CSF)
 acts as a cushioning fluid.
 Blood-brain barrier:
 prevents entry of harmful materials from the
bloodstream.
Brian Cushing
Brain Cushing
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Three dense regular connective tissue layers:
 Separate the soft tissue of the brain from the bones of the
cranium.
 Enclose and protect blood vessels that supply the brain.
 Contain and circulate cerebrospinal fluid(CSF).
 Parts of the cranial meninges form some of the veins that
drain blood from the brain.
From superficial to deep, the cranial meninges are the dura
mater, the arachnoid, and the pia mater.
Cranial Meninges
Dura mater
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Strongest of the meninges.
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Dura mater is composed of two layers.
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periosteal layer, attaches to the periosteum of the cranial bones
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meningeal layer lies deep to the periosteal layer
Arachnoid
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Lies immediately internal to the dura mater.
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Composed of a delicate web of collagen and elastic fibers(arachnoid
trabeculae).
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Between the arachnoid and the overlying dura mater is the subdural space.
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Immediately deep to the arachnoid is the subarachnoid space.
Pia mater
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The innermost of the cranial meninges.
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Thin layer of delicate connective tissue that tightly adheres to the brain
Cranial Dural Septa
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The meningeal layer of the dura mater extends as flat
partitions (septa) deep into the cranial cavity;
 at four locations
 called cranial dural septa.
Membranous partitions separate specific parts of the
brain and provide additional stabilization and support to
the entire brain.
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1. falx cerebri
2. tentorium cerebelli
3. falx cerebelli
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4. diaphragma sellae
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MRI of the brain, T1-weighted coronal cut.
1, Sulcus. 2, Gyrus. 3, Falx cerebri. 4, Temporal
lobe (Left side). 5, Temporal lobe (Right side).
1, Tentorium cerebelli. 2, Gyrus. 3, Sulcus. 4,
Cerebellum.
MRI of the brain, T1-weighted sagittal cut.
1, Occipital lobe. 2, Tentorium cerebelli. 3,
Cerebellum. 4, Midbrain.
Brain Ventricles
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Cavities or expansions within the brain that are derived from the
lumen (opening) of the embryonic neural tube.
Continuous with one another as well as with the central canal of the
spinal cord.
Four ventricles in the brain.
 two lateral ventricles are in the cerebrum, separated by a thin
medial partition called the septum pellucidum
 within the diencephalon is a smaller ventricle called the third
ventricle
 each lateral ventricle communicates with the third ventricle
through an opening called the interventricular foramen
The fourth ventricle is located within the pons and cerebellum.
(Foramen of Monro)
Frontal(anterior) horn
Occipital(Post.) horn
Temporal(Inferior) horn
(Foramen of Luschka)
(Foramen of Magendie)
Cistern
Magna
Cerebellopontine angle cistern
Cerebrospinal Fluid
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A clear, colorless liquid that circulates in the ventricles and
subarachnoid space. Is similar to blood plasma.
Made in choroid plexuses (roofs of ventricles)
 Filtration of plasma from capillaries through ependymal cells
(electrolytes, glucose)
500 ml/d; total volume 100-160 ml (1/2 c)
Performs several important functions.
 buoyancy
 protection
 environmental stability
 nourishes brain
Assayed in diagnosing meningitis, bleeds, MS
Hydrocephalus: excessive accumulation
Subarachnoid cisterns
• Areas within the subarachnoid space where the pia mater and arachnoid
membrane are not in close approximation.
• Subarachnoid space and CSF gathers to form pools or cisterns.
• Some major subarachnoid cisterns:
1. cisterna magna (cerebellomedullary cistern): the largest of the
subarachnoid cisterns
2. pontine cistern
3. suprasellar cistern
4. interpeduncular cistern
5. quadrigeminal cisterns (superior cistern or cistern of the great cerebral
vein)
6. ambient cistern
7. Cerebellopontine angle(CPA) cistern
Subarachnoid cisterns
Cerebral hemispheres: note lobes
• Divided by longitudinal fissure into
right & left sides
• Central sulcus divides frontal from
parietal lobes
• Lateral sulcus separates temporal lobe
from parietal lobe
• Parieto-occipital sulcus divides
occipital and parietal lobes (not seen
from outside)
• Transverse cerebral fissure separates
cerebral hemispheres from cerebellum
• Insula – deep within the lateral sulcus
Organization of Brain Tissue
• During brain development, an outer, superficial region of gray matter
forms from migrating peripheral neurons.
• External sheets of gray matter, called the cortex, cover the surface of
most of the adult brain (the cerebrum and the cerebellum).
• Gray matter: outer
– motor neuron and interneuron cell bodies, dendrites, axon terminals
– unmyelinated axons.
• White matter: inner
– composed primarily of myelinated axons.
• Within the white matter:
– discrete innermost clusters of gray matter called cerebral nuclei (or
basal nuclei).
– are oval, spherical, or sometimes irregularly shaped clusters of
neuron cell bodies.
Cerebral cortex
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Composed of gray matter-- 3 mm thick
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Neuronal cell bodies, dendrites, and
short axons
Folds in cortex – triples its size
2 types of cells
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stellate cells
 have dendrites projecting
in all directions
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pyramidal cells
 have an axon that passes
out of the area
Functional areas of the cortex
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Three kinds of functional areas
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Motor areas
Sensory areas
Association areas
Motor areas
Anterior to central sulcus
• Primary motor area
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Precentral gyrus of frontal lobe (4)
Conscious or voluntary movement of skeletal muscles
Large neurons called pyramidal cells
Their axons: form massive pyramidal or corticospinal tracts
• Decend through brain stem and spinal cord
• Cross to contralateral (the other) side in brainstem
• Therefore: right side of the brain controls the left side of the body, and the left
side of the brain controls the right side of the body
Motor areas – continued
• Broca’s area (44): specialized motor speech area
– Base of precentral gyrus just above lateral sulcus in only one
hemisphere, usually left
– Word articulation: the movements necessary for speech
– Damage: can understand but can’t speak; or if can still speak,
words are right but difficult to understand
Motor areas – continued
• Premotor cortex (6): complex movements associated with highly
processed sensory info; also planning of movements
• Frontal eye fields (inferior 8): voluntary movements of eyes
Sensory areas
Posterior to central sulcus
• Primary somatosensory cortex:
postcentral gyrus of parietal
lobe (allows conscious awareness of
sensation and the ability to localize it:
where the sensation is from)
• Somatosensory association
area: behind it
(understanding of what is being felt: the
meaning of it)
From special sense organs
• Occipital lobe: visual
– Primary visual cortex (17)
– Visual association area (18 & 19)
• Face recognition is usually on
the right side
• Hearing: temporal lobe
– Primary auditory area (41)
– Auditory association area (22)
• Smell (olfactory sense): uncus
– Deep in temporal lobe along medial surface
Homunculus – “little man”
• Body map: human body spatially represented
– Where on cortex; upside down
Refer back to this labeled version as needed
Auditory Association Area
• The auditory association area contains two special regions.
• BROCA'S AREA is a region of the brain that allows for speech.
• WERNICKE’S AREA is the region of the brain that allows understanding of
words.
• Arcuate Fasciculus - A white matter tract that connects Broca’s Area and
Wernicke’s Area through the temporal, parietal and frontal Lobes. Allows
for coordinated, comprehensible speech.
• Damage may result in Conduction Aphasia - Where auditory
comprehension and speech articulation are preserved, but people find it
difficult to repeat heard speech.
Cerebral White Matter
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Extensive communication
 Areas of cortex with each other
 Areas of cortex with brain stem and spinal cord
Via (mostly) myelinated axon fibers bundled into
tracts
 Commissures
 Association fibers
 Projection fibers
Cerebral White Matter
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Types of tracts or fibers
 Commissures – composed of commissural fibers
 Allows communication between cerebral
hemispheres
 Corpus callosum – the largest commissure
 Association fibers
 Connect different parts of the same hemisphere
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Projection tracts
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Projection fibers run vertically
 Cerebral cortex running down (with motor instructions)
 Or ascend to cerebral cortex from below (sensory info
to cortex)
 Internal capsule – projection fibers form a compact
bundle
 Passes between the thalamus and basal nuclei
 Corona radiata – superior to the internal capsule
 Fibers run to and from the cerebral cortex
• Projection fibers
_________________
– Corona radiata: fanning
out of the fibers
– Internal capsule: bundled, ___________________
pass down
• Commisure
– Corpus callosum: connects
right and left hemispheres
• Decussation: crossing of
pyramidal tracts
_____________________
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White Matter-Fractional Anisotropy map of DTI
White Matter Fiber Tracts
Association
Projection
Callosum
Wakana S, Jiang H, Nagae-Poetscher LM, van Zijl PC, Mori S. Fiber tract-based atlas of human white matter
anatomy. Radiology. 2004 Jan;230(1):77-87. Epub 2003 Nov 26.
Basal nuclei
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A group of nuclei deep within the cerebral white matter
 Caudate nucleus – arches over the thalamus(head, body and tail)
 Lentiform nucleus – “lens shaped”
 Amygdala – sits on tail of the caudate nucleus
 Functionally belongs with the limbic system
Lentiform nucleus
 Divided into two parts
 Globus pallidus
 Putamen
Basal nuclei
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Cooperate with the cerebral cortex in controlling movements
Receive input from cortical areas, send most of output back to
motor cortex through thalamus
Involved with stopping/starting & intensity of movements
“Dyskinesias”-bad movements
 Parkinson’s disease: loss of inhibition from substantia nigra
of midbrain – everything slows down
 Huntington disease: overstimulation (“choreoathetosis”) degeneration of corpus striatum which inhibits; eventual
degeneration of cerebral cortex
The Diencephalon
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Border the third ventricle
Surrounded by the cerebral hemispheres
Primarily composed of gray matter
Forms the center core of the forebrain
Composed of three paired structures:
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Thalamus, hypothalamus, and epithalamus
The Thalamus
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Two large lobes of gray matter
Laterally enclose the 3rd ventricle
Gateway to cerebral cortex: every part of brain
that communicates with cerebral cortex relays
signals through a nucleus in the thalamus
Processing (editing) occurs also in thalamus
(Mass intermedia)
The Diencephalon – The
Hypothalamus
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Lies between the optic chiasm and the
mammillary bodies
Pituitary gland projects inferiorly
Contains approximately a dozen nuclei
Main visceral control center of the body
The Hypothalamus
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Functions include the following:
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Control of the autonomic nervous system
Control of emotional responses
Regulation of body temperature
Regulation of hunger and thirst sensations
Control of behavior
Regulation of sleep-wake cycles
Control of the endocrine system
Formation of memory
Mammillary Bodies
• A pair of small round bodies at the anterior end of the fornix
• Part of the diencephalon; they form part of the limbic system.
• They relay information (recognition memory) from the
hippocampus. They also add the element of smell to memories.
• Damage to the mammillary bodies due to thiamine deficiency
(vit B1) or alcohol causes Wernicke-Korsakoff syndrome
(anterograde amnesia)
The Diencephalon – The Epithalamus
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Forms part of the ”roof” of the third
ventricle
Consists of a tiny group of nuclei
Includes the pineal gland (pineal body)
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Secretes the hormone melatonin
Under influence of the hypothalamus
Functional Brain Systems – The Limbic System
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Location
 Medial aspect of cerebral hemispheres
 Also within the diencephalon
Composed of:
 Septal nuclei, cingulate gyrus, and hippocampal formation
 Part of the amygdala
The fornix and other tracts link the limbic system together
The “emotional brain”
 Cingulate gyrus
 Allows us to shift between thoughts
 Interprets pain as unpleasant
Hippocampal formation
 Hippocampus and the parahippocampal gyrus
The Brain Stem
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Includes the midbrain, pons, and medulla oblongata
Several general functions
 Produces automatic behaviors necessary for
survival
 Passageway for all fiber tracts running between
the cerebrum and spinal cord
 10 of the 12 pairs of cranial nerves attach to it
The Brain Stem – The Midbrain
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Lies between the diencephalon and the pons
Central cavity – the cerebral aqueduct
Cerebral peduncles located on the ventral surface of
the brain
 Contain pyramidal (corticospinal) tracts
Superior cerebellar peduncles
 Connect midbrain to the cerebellum
The Brain Stem – The Midbrain
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Corpora quadrigemina – the largest nuclei
 Divided into the superior and inferior colliculi
 Superior colliculi – nuclei that act in visual
reflexes
 Inferior colliculi – nuclei that act in reflexive
response to sound
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The Brain Stem – The Midbrain
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Two pigmented nuclei
 Substantia nigra – neuronal cell
bodies contain melanin
 Functionally linked to the basal
nuclei
 Red nucleus – lies deep to the
substantia nigra
 Largest nucleus of the reticular
formation
The Brain Stem – The Pons
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Located between the midbrain
and medulla oblongata
Contains the nuclei of cranial
nerves V, VI, and VII
Two general groups of cranial
nerve nuclei
 Motor nuclei
 Sensory nuclei
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The Brain Stem – The Medulla Oblongata
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Most caudal level of the brain stem
 Continuous with the spinal cord
 Choroid plexus lies in the roof of the fourth
ventricle
 Pyramids of the medulla – lie on its ventral
surface
 Cranial nerves VIII–XII attach to the medulla
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Functional Brain Systems
– The Reticular Formation
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Runs through the central core of the
medulla, pons, and midbrain
Forms three columns
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Midline raphe nuclei
Medial nuclear group
Lateral nuclear group
Functional Brain Systems – The
Reticular Formation
The Cerebellum
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Located dorsal to the pons and medulla
 Smoothes and coordinates body movements
 Helps maintain equilibrium
Consists of two cerebellar hemispheres
Surface folded into ridges called folia
Hemispheres each subdivided into anterior and posterior
Thick tracts connecting the cerebellum to the brain stem
 Superior cerebellar peduncles
 Middle cerebellar peduncles
 Inferior cerebellar peduncles
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The Cerebellum
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Composed of three regions
 Cortex – gray matter
 Internal white matter
 Deep cerebellar nuclei – deeply situated gray matter
Cerebellum must receive information
 On equilibrium
 On current movements of limbs, neck, and trunk
 From the cerebral cortex
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Outline
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The Organization of brain
Meninges
Ventricular System: Ventricles and Cisterns
Cerebrum: Lobes and Basal ganglion
Diencephalon: Thalamus, Epithalamus, Hypothalamus
, Pituitary gland
Limbic System
Brain Stem: Midbrain, Pons and Medulla Oblongata
Cerebellum
Cerebral Vascular system: Arterial and Venous System
Principle Brain Arteries
Internal Carotid Artery( ICA)
The segments of the internal carotid artery are as follows:
1. Cervical segment or portion, or C1
2. Petrous segment, or C2
3. Lacerum segment, or C3
• C2 and C3 compose the commonly termed Petrous portion
4. Cavernous segment, or C4, commonly used Cavernous portion
5. Clinoid segment, or C5, lies between the commonly used
Cavernous portion and Cerebral or Supraclinoid portion
6. Ophthalmic, or supraclinoid segment, or C6
7. Communicating, or terminal segment, or C7
Anterior circulation
-Internal carotid arteries
C6
C4
C2
C1
Vertebral Arteries (VA)
• The vertebral-basilar arteries supply about 20% of the blood
flow to the brain.
• Derived from subclavian arteries in the thoracic cavity.
• When they get to the atlas, they exit the spine and migrate
backwards toward the atlantooccipital membrane .
• Shortly after entering the cranial vault the vertebral arteries
unite and become the basilar artery.
• Vetebral-Basilar system include:
• Posterior inferior cerebellar artery (PICA)
• Anterior inferior cerebellar artery (AICA)
• Pontine artery
• Superior cerebellar artery(SCA)
Posterior circulation
-Vertebral arteries
Circle of Willis
The Circle of Willis is composed of the following arteries:
1. Anterior cerebral artery (ACA)
2. Anterior communicating artery(ACoA)
3. Internal carotid artery (lCA)
4. Posterior cerebral artery (PCA)
5. Posterior communicating artery (PCoA)
The basilar artery and middle cerebral arteries, supplying the
brain, are not considered part of the circle
Circle of Willis
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Lenticulostriate Arteries Supply the Basal Ganglia and Internal Capsule
Anatomy and Vascular Territories of the 3 Main Cerebral Arteries:
Middle Cerebral Artery
M3
M2
M1
Anterior Cerebral Artery and Posterior Cerebral Artery
Superficial and Deep Arterial Supply to the Cerebral Hemispheres
Coronal Plane
Superficial and Deep Arterial Supply to the Cerebral Hemisphere
Axial Plane