Anatomy of brain discussing abouts parts of the brain and lobes basal, nuclei and other parts with the blood supply to the brain

1. BRAIN

2. BRAIN
The brain is that part of the CNS which lies within the cavity of the skull. It consists of
the following parts:
Forebrain Cerebrum
Diencephalon
Midbrain
Pons
Medulla oblongata
Cerebellum
Midbrain
Hindbrain
Midbrain, pons and medulla together constitute the brainstem.

5. Cerebrum
 The cerebrum is the largest part of the brain.
 It consists of right and left cerebral hemispheres, which are partially separated by a
sickle-shaped fold of dura, the falx cerebri.
 The median longitudinal fissure of cerebrum intervenes between the medial surfaces of
the right and left hemispheres.
 At the bottom of the fissure lies the corpus callosum, which is a connecting bond
between the two hemispheres.
 The contents of the longitudinal fissure are falx cerebri and the accompanying arachnoid
mater, pia mater covering the medial surfaces of the hemispheres, anterior cerebral
vessels.

6. External Features
 The surfaces of the cerebral hemispheres are not smooth.
 They show a series of grooves or sulci, which are separated by intervening areas
that are called gyri.
 The sulci vary in depth from slight grooves to deep fissures.
 The gyri consist of a central core of white matter (nerve fibers running to and from
the overlying cerebral cortex) covered by a layer of gray matter, the cerebral cortex.
 The cortex extends as a continuous sheet over the whole surface of the
hemisphere

7. Each cerebral hemisphere has three poles and three surfaces.
Poles
They are the pointed ends anterior frontal pole, posterior occipital pole and the temporal pole
lying between frontal and occipital, pointing forwards and downwards.
Surfaces
Superolateral surface
Medial surface
Inferior surface: It is divided into:
An anterior orbital surface, and A posterior tentorial surface.

11. Lobes
There are four lobes namely (i) frontal, (ii) parietal, (iii) occipital, and (iv) temporal.
1.Frontal Lobe: Located at the front of the brain, this lobe is involved in executive
functions such as planning, decision making, problem-solving, and motor control.
It also plays a role in speech production (Broca's area) and aspects of personality
and social behavior.
2. Parietal Lobe: Positioned behind the frontal lobe, the parietal lobe processes
sensory information from the body, including touch, pressure, temperature, and
pain. It's also involved in spatial awareness, perception, and integration of sensory
input.

12. 3.Temporal Lobe: Found on the sides of the brain, beneath the temples, the
temporal lobe is primarily responsible for processing auditory information
(including language comprehension) and certain aspects of memory, such as the
formation and retrieval of long-term memories. The hippocampus, a structure
within the temporal lobe, is crucial for memory formation.
4.Occipital Lobe: Located at the back of the brain, the occipital lobe is primarily
responsible for processing visual information from the eyes. It interprets visual
stimuli, allowing us to perceive shapes, colors, and motion, and plays a role in
visual memory and object recognition.

13. The lobes of each hemisphere are demarcated by some important landmarks:
 Central sulcus or Rolandic fissure between frontal and parietal lobes.
 Parieto-occipital sulcus between parietal and occipital lobe.
 Sylvian fissure or lateral sulcus between parietal and temporal lobes.
 Preoccipital notch.
Structures within the Cerebral Hemisphere
The surface of the cerebral hemisphere is covered by a thin layer of gray matter called
the cerebral cortex.

14. The cortex follows the irregular contour of the sulci and gyri of the hemisphere and extends
into the depths of the sulci. As a result of this folding of the cerebral surface, the cerebral
cortex acquires a much larger surface area than the size of the hemispheres would
otherwise allow.
The greater part of the cerebral hemisphere deep to the cortex is occupied by white matter,
within which are embedded certain important masses of gray matter.
Immediately lateral to the third ventricle, there are the thalamus and hypothalamus.

16. More laterally, there is the corpus striatum. It consists of two masses of gray matter, the
caudate nucleus and the lentiform nucleus, which consists of two functionally distinct parts,
the putamen and the globus pallidus.
A little lateral to the lentiform nucleus, we see the cerebral cortex in the region of the insula.
Between the lentiform nucleus and the insula, there is a thin layer of gray matter called the
claustrum.
The caudate nucleus, the lentiform nucleus, the claustrum, and some other masses of gray
matter are referred to as basal nuclei or basal ganglia.

17. White Matter of Cerebrum
The interior of each cerebral hemisphere consists of a core of white matter, which is
composed of myelinated nerve fibers.
These fibers can be classified into three groups:
1.Association fibers .
2. Projection fibers
3.Commissural fibers.

19. Association Fibers
Association fibers connect different cortical areas of the same hemisphere to one
another.
For example, superior longitudinal fasciculus. It connects the frontal, parietal, occipital
and temporal lobes of the same hemisphere.
Projection Fibers
Projection fibers connect the cerebral cortex to other parts of CNS like brainstem and
spinal cord.

20. Examples of Projection Fibers
The corona radiata is a mass of white matter composed of the projection fibers, which
converge from the cerebral cortex to the internal capsule and fan out from the internal capsule
towards the cortex
The internal capsule transmits the projection fibers like corticospinal, corticonuclear and
corticopontine fibers. These fibers arise in the cerebral cortex and terminate on the lower
neurons. The internal capsule also gives passage to thalamic radiations.
Commissural Fibers
Commissural fibers are fibers which connect corresponding parts of two hemispheres. Largest
commissural fibers of the cerebrum form the corpus callosum.

21. INTERNAL CAPSULE
 The internal capsule is a large band of projection fibers, situated in the
inferomedial part of each cerebral hemisphere.
 In horizontal sections of the brain, it appears V-shaped, with its concavity directed
laterally.
 This concavity is occupied by the lentiform nucleus.
 The internal capsule is composed of fibers going to and coming from the cerebral cortex.
 When traced upward, the fibers of the capsule diverge and form the corona radiata.
 When traced downward, these fibers form a compact bundle and continue as the crus of
midbrain.

25. Parts of Internal Capsule
 Anterior limb-short
 Posterior limb-long
 Genu-junction of anterior and posterior limbs
 Retrolentiform part (i.e. behind the lentiform nucleus)
 Sublentiform part (i.e. below the lentiform nucleus).
Anterior limb lies between the head of caudate nucleus and lentiform nucleus. It
contains thalamocortical, frontopontine and corticobulbar (cortex to medulla
oblongata) fibers.

26. Posterior limb lies between the thalamus and lentiform nucleus. It contains mainly
corticospinal fibers.
Genu (bend) lies between anterior and posterior limbs; contains corticospinal and
corticonuclear (nuclei of cranial nerves) fibers, mainly for the head and neck.
Retrolentiform part lies behind the lentiform nucleus; composed of optic radiations
(fibers from lateral geniculate body to visual cortex).
Sublentiform part lies below the lentiform nucleus, contains auditory radiations (from
medial geniculate body to auditory cortex).

27. BASAL NUCLEI (GANGLIA)
The basal nuclei or basal ganglia are large masses of gray matter situated deep in the
cerebral hemispheres.
The basal nuclei are:
 Caudate nucleus Lentiform nucleus
 Corpus striatum
 Amygdaloid nucleus
 Claustrum.

29. Caudate Nucleus
 It is a C-shaped nucleus, which is surrounded by and closely related to the lateral
ventricle.
 The concavity of the caudate nucleus encloses the thalamus and internal capsule.
 The caudate nucleus has a head, body and tail.

30. Lentiform Nucleus
 Lentiform nucleus is a large, biconvex lens-shaped nucleus forming the lateral
boundary of internal capsule.
 Subdivisions: The lentiform nucleus is divided into two parts by a thin lamina of
white matter.
 The larger, lateral part is called the putamen and the medial part is called the
globus pallidus.

31. Amygdaloid Nucleus
Amygdaloid body or amygdala lies in the temporal lobe close to the tip of the tail of
caudate nucleus.
Claustrum
Claustrum is a thin, irrregular sheet of neurons that is attached to the underside of the
neocortex in the center of the brain

32. Functions of Basal Ganglia
 Along with prefrontal cortex, cerebellum and thalamus, basal ganglia play an
important role in planning and programming of motor activities. Voluntary motor
activities are initiated by cerebral cortex. However, these movements are
controlled by basal ganglia. During lesions of basal ganglia, the control mechanism
is lost and so the movements become inaccurate and awkward.
 Corpus striatum regulates the muscle tone and makes the voluntary movements
smooth.

33. Note: Basal ganglia decrease muscle tone by inhibiting the gamma motor neurons.
 Basal ganglia forms the integral part of extrapyramidal system through which it
controls posture and equilibrium.
 It controls associated automatic movements like swinging of hands while walking,
facial expressions and emotions.
 Through its connections to limbic system, basal ganglia is involved in cognition
(initiation to do something) and affection

34. Added Information
CEREBRAL DOMINANCE
It is defined as the dominance of one cerebral hemisphere over the other in the control
of cerebral functions. The two cerebral hemispheres are not functionally equivalent.
Cerebral dominance is related to handedness, i.e. preference of the individual to use
right or left hand. More than 90% of people are right-handed. In these individuals, the
left hemisphere is dominant and it controls the analytical process and language- related
functions such as speech, reading and writing. Hence, the left hemisphere of these
persons is called dominant or categorical hemisphere.

35. FUNCTIONAL AREAS OF CEREBRAL CORTEX
Brodmann has given different numbers to different functional areas of the brain. We
will consider these areas here, lobe wise
Frontal Lobe
The frontal lobe of cerebral cortex is divided into three parts:
1. Primary motor area
2. Premotor area
3. Motor speech area.

38. Primary Motor Area
It extends throughout the precentral gyrus and the adjoining lip of central sulcus. Area
4 is located in the precentral gyrus of frontal lobe. It is the center for movement, as it
sends efferent fibers of primary motor area. Through the fibers of corticospinal tracts;
area 4 activates the lower motor neurons in the spinal cord.
Function
Primary motor areas' function is to control the voluntary movements in the opposite
side of the body.

39. Premotor Area
This has area 6 (main) and 8. The premotor area is anterior to primary motor area in
the precentral cortex.
Function
The premotor area is responsible for acts producing orderly series of movements, e.g.,
combing of hair.

40. Motor Speech Area (areas 44 and 45)
It is situated in the inferior frontal gyrus. It is present unilaterally in the dominant
hemisphere, i.e., in the left cerebral hemisphere in right-handed individuals. A
destructive lesion in this area (e.g. total loss of blood supply) causes motor aphasia, in
which the patient loses his speech.
Two other areas concerned with speech are:
1. Speech area of Wernicke
2. Supplementary motor area (M11)

41. Prefrontal Cortex
It is the anterior part of frontal lobe of cerebral cortex in front of areas 8 and 44.
Areas present in prefrontal cortex are 9, 10, 11, 12, 13, 14, 23, 24, 29 and 32. Area 13
is concerned with emotional reactions.
Functions
 It forms the center for the higher functions like emotion, learning, memory and
social behavior. It is the seat of intelligence. Short-term memories are registered
here.
 It is the center for planned actions.
 It is responsible for the personality of the individuals

42. Parietal Lobe
Parietal lobe has sensory areas of cerebral cortex. First
Somatosensory Area (SI)
It corresponds to areas 3, 1 and 2 of Brodmann and is located in postcentral gyrus.
The different sensory areas of the body are represented in postcentral gyrus (primary sensory
area) in an inverted manner as in the motor area. This miniature human is called a sensory
homunculus. The toes are represented in lowest part of medial surface, legs at the upper border
of hemispheres, then from above downward knee, thigh, hip, trunk, upper limb, neck and face.
The representation of face is not inverted. The representation of parts of face from above
downward is eyelids, nose, cheek, upper lip and lower lip.

44. Second Somatosensory Area (S II)
It is situated in postcentral gyrus below the area of face of somatosensory area I.
This area receives sensory impulses from somesthetic area I and from thalamus directly.
Though the exact role of this area is not clear, it is concerned with perception of sensation.
Thus, the sensory parts of body have two representations-in somesthetic area I and area II.
Functions
Both the areas are responsible for perception and integration of cutaneous sensations. Area I
is basically concerned with sensory perception. Area II is concerned with integration of those
senses

45. Temporal lobe
Temporal lobe of cerebral cortex includes three functional areas
 Primary auditory area
 Auditopsychic area
 Area for equilibrium
Primary Auditory Area
Primary auditory area includes:
Area 41
Area 42
Wernicke's area

46. Areas 41 and 42 are situated in anterior transverse gyrus and lateral surface of superior
temporal gyrus. Wernicke's area is in upper part of superior temporal gyrus posterior to areas
41 and 42.
Functions
 Primary auditory area is concerned with perception of auditory impulses, analysis of pitch
and determination of intensity and source of sound.
 Areas 41 and 42 are concerned only with the perception of auditory impulses. Wernicke's
area is responsible for the interpretation of sound. It carries out this function with the
help of auditopsychic area (area 22).

47. Auditopsychic Area
It is the area 22 and it occupies the superior temporal gyrus. This area is concerned with
interpretation of auditory sensation along with Wernicke's area.
Occipital Lobe
Occipital lobe is also called the visual cortex.
Areas of Occipital Lobe
The occipital lobe consists of three functional areas:
1. Primary visual area-area 17
2. Visual association area-area 18
3. Occipital eye field-area 19.

48. Functions
 Primary visual area-area 17 is concerned with perception of visual impulses
 Visual association area-area 18 is concerned with interpretation of visual impulses
 Occipital eye field-area 19 is concerned with movement of eyes.

49. DIENCEPHALON
We have seen that the forebrain has two parts, the cerebrum and the diencephalon.
Diencephalon is a midline structure, which is largely embedded in the cerebrum and,
therefore, hidden from the surface view. Its cavity is the third ventricle.
SUBDIVISIONS
The hypothalamic sulcus extending from interventricular foramen to the cerebral aqueduct
divides each half of the diencephalon into dorsal and ventral parts.

50. Dorsal part of diencephalon:
Thalamus
Metathalamus
 Medial geniculate body (concerned with hearing)
 Lateral geniculate body (concerned with vision) Epithalamus.
Ventral part of diencephalon:
 Hypothalamus
 Subthalamus.
The subthalamic nucleus is included with the basal ganglia to which it is closely related
functionally.

52. THALAMUS
 Thalamus is a large egg-shaped mass of grey matter, situated one on either side of the
lateral wall of the 3rd ventricle in the diencephalon.
 Both thalami form 80% of diencephalon.
 It is a sensory relay station with afferent fibers reaching it from the spinal cord and the
brainstem.
 Medial surfaces of the two thalami are connected across the midline by the
interthalamic adhesion;
 But fibers from one thalamus never cross the midline.
 The lateral surface of the thalamus is related to the internal capsule which separates it
from the lentiform nuclei.

55.  The gray matter of the thalamus is subdivided into three main parts by a Y-shaped sheet of
white matter, which is called the internal medullary lamina.
 This lamina is placed vertically. It divides the thalamus into lateral, medial and anterior
parts situated between the two limbs of the 'Y.
Anatomical Classification of Thalamic Nuclei
Nuclei in the Anterior Part
A number of nuclei can be distinguished, but we shall refer to them collectively as the anterior
nucleus.
Nuclei in the Medial Part
The largest of these is the medial dorsal nucleus. It is divisible into a magnocellular part
(anteromedial) and a parvocellular part (posterolateral).

56. Nuclei in the Lateral Part
The nuclei in the lateral part can be subdivided into a ventral group and a lateral group.
The nuclei in the ventral group are as follows (in anteroposterior order):
 Ventral anterior nucleus
 Ventral lateral nucleus (also called the ventral intermediate nucleus)
 Ventral posterior nucleus, which is further subdivided into a lateral part, called the
ventral posterolateral nucleus, and a medial part, called the ventral posteromedial
nucleus.

57. The nuclei of the lateral group are as follows (in anteroposterior order):
 Lateral dorsal nucleus (or dorsolateral nucleus)
 Lateral posterior nucleus
 Pulvinar.
Connections
Affferent fibers from different parts of CNS reach the thalamus. It is regarded as a great
integrating center where information from different parts of brain and spinal cord are
brought together. This information is projected to all parts of the cerebral cortex through
thalamocortical projections or thalamic radiations.

58. The most important connections of the thalamus are those of the ventral posterior
nucleus (VPN), which receives terminations of the major sensory pathways coming
from the brainstem and spinal cord. All these sensations are carried to areas 3, 1 and 2
of the cerebral cortex

59. HYPOTHALAMUS
 The hypothalamus is a part of the diencephalon.
 It lies in the floor and lateral wall of the 3rd ventricle.
 It has been described as the chief ganglion of autonomic nervous system because of its role
in the control of many metabolic activities of the body.
Nuclei
The hypothalamus has many nuclei but the two most important are:
 The supraoptic nucleus lies above the optic chiasma; secretes Anti Diuretic
Hormone(ADH)
 Paraventricular nucleus lies just above the supraoptic nucleus and secretes
oxytocin.

60. BRAIN STEM
The brain stem connects forebrain and spinal cord. It consists of three parts:
1. Midbrain
2. Pons
3. Medulla oblongata

63. MIDBRAIN
 Midbrain or Mesencephalon is the shortest segment of the brainstem, connecting the pons
and cerebellum with the forebrain.
 Its cavity, the cerebral aqueduct, connects the 3rd ventricle to the 4th ventricle.
 The midbrain contains nuclei of origin for cranial nerves III (oculomotor) and IV (trochlear).
 Apart from the cranial nerve nuclei, the midbrain also has nuclei that coordinate the
movement of eyeball in response to visual stimuli located in superior colliculi. Nuclei, which
coordinate movements of head and trunk in response to auditory stimuli, are located in
inferior colliculi.

64. Parts
 The midbrain is traversed by the cerebral aqueduct of Sylvius, which connects the 3rd and 4th
ventricles.
 The part of the midbrain lying behind an imaginary transverse line drawn through the cerebral
aqueduct is called the tectum.
 The part lying in front of the transverse line is made up of right and left cerebral peduncles.
Each peduncle consists of three parts. From anterior to posterior, they are:
The crus cerebri
The substantia nigra
The tegmentum

66. The aqueduct is surrounded by gray matter which contains the nuclei of trochlear nerve (IV cranial
nerve) and oculomotor nerve (III cranial nerve).
The tectum is made up of a pair of superior colliculi (right and left) and a pair of inferior colliculi.
The superior colliculus, connected to the lateral geniculate body by a brachium, is concerned with
visual pathway.
The inferior colliculus, connected to the medial geniculate body, is concerned with the auditory
pathway.
The crus cerebri is made up of descending fibers (tracts); the most important among these is the
pyramidal tract (corticospinal tract).

67. The substantia nigra is a thin layer of deeply staining gray matter; the neurons contain a pigment
called neuromelanin. It has important connections with striatum (caudate nucleus and
putamen). Dopamine produced by neurons in the substantia nigra passes along their axons into
the striatum. A reduction in the Dopamine level results in Parkinsonism (already described
under "Basal nuclei").
The tegmentum contains ascending (sensory) fibers-mainly spinothalamic tract.

68. PONS (BRIDGE)
 The pons lies between the midbrain and the medulla oblongata.
 On each side, it is connected to the cerebellum by the middle cerebellar peduncle.
 Pons is made up of gray and white matter.
 Pons is important physiologically, as the center of respiration is present in it.
 Nuclei of the cranial nerves, V (trigeminal), VI (abducent), VII (facial), and VIII
(vestibulocochlear) are situated in the pons.

69. External Features
 Pons shows a convex anterior surface, marked by prominent transversely running fibers.
 Laterally, these fibers collect to form a bundle, the middle cerebellar peduncle.
 The trigeminal nerve emerges from the anterior surface and the point of its emergence is
taken as a landmark to define the plane of junction between the pons and the middle
cerebellar peduncle.
 The line of junction between the pons and the medulla is marked by a groove through
which a number of cranial nerves emerge.
 The posterior aspect of the pons forms the upper part of the floor of the fourth ventricle.

70. MEDULLA OBLONGATA
 The medulla, a part of the brainstem, is about 3 cm in length; it is continuous above with the
pons and below with the spinal cord.
 The junction of the medulla and cord lies at the level of the upper border of the atlas
vertebra. The transition is, in fact, not abrupt but occurs over a certain distance.
 The medulla is divided into a lower closed part, which surrounds the central canal and an
upper open part, which is related to the lower part of the fourth ventricle.
Externally medulla has (i) an anterior median fissure, (ii) posterior median sulcus, (iii)
anterolateral sulcus,and(iv) posterolateral sulcus.

72. Anterior (Ventral) Aspect
 Pyramid: The region between the anterior median sulcus and the anterolateral sulcus is
occupied (on either side of the midline) by an elevation called the pyramid. The elevation is
caused by a large bundle of fibers that descend from the cerebral cortex to the spinal cord
(the pyramidal tract/corticospinal tract)
 Olive: In the upper part of the medulla, the region between the anterolateral and
posterolateral sulci shows a prominent, elongated, oval swelling, named the olive. This
swelling is about half-an-inch long. It is produced by a large mass of gray matter called the
inferior olivary nucleus. (Resembles the seed of olive tree).
 Rootlets of the hypoglossal nerve: These emerge from the anterolateral sulcus between the
pyramid and the olive.

73.  Inferior cerebellar peduncles of the left and right side attach the medulla with the
cerebellum.
 Rootlets of the IX, X and XI (cranial part) cranial nerves: These emerge through the
posterolateral sulcus separating the olive from the inferior cerebellar peduncle.

74. Posterior (Dorsal) Aspect
The posterior surface of the lower part (closed part) medulla, between the posterior median
sulcus and the posterolateral sulcus, contains tracts that enter from the posterior funiculus of
the spinal cord. These are the fasciculus gracilis, next to the midline, and the fasciculus
cuneatus, placed laterally. These fasciculi end in rounded elevations called the gracile and
cuneate tubercles. These tubercles are produced by masses of gray matter called the nucleus
gracilis and the nucleus cuneatus, respectively.

75. The lower part of the medulla, immediately lateral to the fasciculus cuneatus, is marked by
another longitudinal elevation called the tuberculum cinereum. This elevation is produced by
an underlying collection of gray matter of the spinal nucleus of the trigeminal nerve.
The posterior surface of the upper medulla (open part) forms the lower part of the floor of the
fourth ventricle.

76. Vital Centers of the Body
The medulla is the seat for many vital centers of the body.
 The respiratory center: Respiratory centers are group of neurons, which control the rate,
rhythm and force of respiration. These centers are bilaterally situated in reticular formation
of the brainstem. Depending upon the situation in the brainstem, the respiratory centers
are classified into two groups:
1.Medullary centers which are made up of: Dorsal respiratory group of neurons, Ventral
respiratory group of neurons
2.Pontine centers which are: Pneumotaxic center, Apneustic center.
 The cardiovascular center: This area located in the medulla controls the rate and force of
uterine contraction and blood pressure.

77. RETICULAR FORMATION
 It is a diffuse network of nerve fibers and neurons which occupy the ventral part of the
entire brainstem (midbrain, pons and medulla).
 It occupies the area between the cranial nerve nuclei, sensory and motor nuclei and the
named long and short white tracts.
 It is considered as the most ancient part of the central nervous system in vertebrate
phylogeny. However, now it is believed that the highly specific pyramidal and extrapyramidal
systems and the nonspecific network of reticular formation are both indispensable and have
evolved as interdependent paths which contribute to the total response of the organism.

78. Characteristics of Reticular Formation
Reticular formation consists of deeply placed ill-defined collection of neurons and fibers. It has
diffuse connections. This system contains serotonergic, cholinergic and catecholamine group of
neurons. It consists of two pathways:
Ascending reticular pathway
It is also called reticular activating system. It receives inputs from all sensory
pathways, visceral afferents and from auditory and visual pathway.
The fibers ascend from pons to thalamus and have multisynaptic connections with cerebral
cortex.
It is the pathway for alertness and conscious state of body.

79. Descending reticular pathway
It is both inhibitory and facilitatory
The inhibitory fibers project to motor cortex, cerebellum, medulla and via
reticulospinal tract to spinal neurons. They inhibit movements.
The facilitatory fibers descend on spinal neurons and produce movements.
CEREBELLUM (LITTLE BRAIN)
 The cerebellum is the largest part of the hindbrain.
 It is situated in the posterior cranial fossa.
 It lies below the occipital lobe of cerebrum, from which it is separated by the tentorium
cerebelli (a fold of dura).

80.  Cerebellum has two hemispheres joined together by a worm-like portion, the vermis.
 Each hemisphere is divided into three lobes-anterior, posterior and
flocculonodular lobes.
 These lobes are divided into numerous small parts by fissures.
 The cerebellum has an outer layer of gray matter and inner layer of white matter. Situated
deep inside the white matter, there are four pairs of nuclei. These are:
1. Dentate
2. Emboliform
3. Fastigial
4. Globose nuclei.

82. The cerebellum is connected on either side, to the brainstem, by bundles of fibers called
superior, middle and inferior cerebellar peduncles.
Phylogenetically, cerebellum can be divided into three portions:
 Archicerebellum (vestibulocerebellum): It consists of flocculonodular lobe. It is
phylogenetically the oldest part. It is concerned with maintenance of equilibrium and eye
movements.
 Paleocerebellum (spinocerebellum): It consists of vermis and adjacent medial portions of
cerebellar hemispheres. This region receives proprioceptive inputs from motor cortex and is
concerned with coordinated control of axial and proximal limb muscles, whereas
intermediate zones are concerned with control of distal limb muscles.

83.  Neocerebellum (cerebrocerebellum): This is phylogenetically the newest part. It consists of
lateral portions of cerebellar hemispheres. Through its connections to motor and premotor
cortex, it is involved in planning and programming of motor activities.
BLOOD SUPPLY OF BRAIN
The nervous system is richly supplied with blood. Interruption of blood supply even for short
period can result in damage to nervous tissue
ARTERIES SUPPLYING THE BRAIN
The brain is supplied by branches of the internal carotid and the vertebral arteries. Each internal
carotid artery gives off two major branches to the brain. These are the anterior cerebral and
middle cerebral arteries.

84. The two vertebral arteries ascend on the anterolateral aspect of the medulla. At the lower
border of the pons, they unite to form the basilar artery.
Circle of Willis (Circulus Arteriosus)
The circle of Willis is an arterial anastomotic circle present in the interpeduncular fossa. It is
polygonal in shape and extends between the superior border of pons and median longitudinal
fissure. The arterial circle is an anastomosis between the internal carotid and the
vertebrobasilar system of arteries (Fig. 16.47).
Formation
 The anterior communicating artery, which connects the right and left anterior cerebral
arteries, forms the anterior part of the circle of Willis.
 The anterior cerebral artery forms the anterolateral part on each side.

86.  The lateral part is formed by the termination of internal carotid artery on each side.
 The circle is completed posteriorly by the bifurcation of basilar artery into the right and left
posterior cerebral arteries.
 Posterolaterally, the posterior communicating artery is the connecting link
between the internal carotid and posterior cerebral arteries.
Note: The middle cerebral artery does not take part in the formation of the circle of Willis.
VERTEBROBASILAR ARTERIES
 Each vertebral artery is a branch of subclavian artery and enters the cranial cavity through
foramen magnum.

87.  The right and left vertebral arteries unite with each other at the lower margin of pons to
form the basilar artery.
 The basilar artery runs in the median sulcus on the ventral surface of pons and divides
into right and left posterior cerebral arteries at upper margin of pons.
Added Information
INTRACRANIAL BRANCHES OF VERTEBRAL ARTERY
 Anterior spinal artery
 Posterior spinal artery
 Posterior inferior cerebellar artery (largest branch of vertebral artery Or PICA)
 Medullary arteries
 Meningeal branches.

88. The branches of intracranial part of vertebral artery supply not only the hindbrain but also the
spinal cord.
BRANCHES OF BASILAR ARTERY
Superior cerebellar artery
Anterior inferior cerebellar artery or AICA Pontine
branches
Labyrinthine artery.
INTERNAL CAROTID ARTERY
The internal carotid arteries give rise to the following branches:
 Anterior cerebral artery

89.  Middle cerebral artery
Ophthalmic artery to the eyeball and structures in the orbit.
Posterior communicating artery, by which internal carotid artery is connected to the
posterior cerebral artery.
The anterior choroidal branches-to the choroid plexus of lateral and 3rd
ventricles.
VENOUS DRAINAGE
Venous drainage of brain is by cerebral veins. These veins are extremely thin due to the absence
of muscle fibers in their walls. They cross the subarachnoid spaces and finally drain into dural
venous sinuses.