Gross Anatomy of the Brain

1
Organization of the Brain
 The basic parts of the brain are as follows:
 The cerebrum
 The diencephalon
 The brain stem
 The cerebellum
 The brain is organized into groupings of cell bodies (the gray
matter) and fibers (the white matter).
 The cerebrum and the cerebellum contain gray matter on the
outer edges with white matter below this surface.
 While the diencephalon and brain stem have the white matter
superficially surrounding internal pockets of gray matter 2
Cerebrum
 Largest portion of brain (>=80% mass) and responsible
for higher mental functions.
 Divided into left and right hemispheres by the longitudinal
fissure.
 The cell bodies in the outer cortex require more surface
area than the underlying white matter which results in
much folding.

3
The upfoldings are called gyri (gyrus, singular).
The infoldings are called sulci (sulcus, singular).
4
General Appearance:
 Separated by a deep midline sagittal
fissure –longitudinal cerebral fissure
 The fissure contains falx cerebri and
the anterior cerebral arteries
 In the depth of the fissure, the corpus
callosum connects the hemispheres
across the midline
 Gyri – the folds of the surface of
hemispheres
 Sulci – the fissures separating the
gyri
5
6
The Brain
 The brain, a bilaterally symmetric, soft, gelatinous structure
surrounded by its meninges and enclosed in its bony cranium, is
continuous with the spinal cord at the foramen magnum at the
base of the skull.
 At birth the brain weighs less than 400 g, but by the beginning
of the second year of life it has more than doubled in weight to
900 g.
 The adult brain weighs between 1,250 and 1,450 g, and
demonstrates a gender differential, since brains of males
generally weigh more than those of females.
7
Cerebral cortex -functions
 The is particularly well developed in humans is
responsible for many higher brain functions,
 including manual dexterity (e.g. to move the fingers
individually so as to play the piano);
 conscious, discriminative aspects of sensation;
 cognitive activity, including language, reasoning, and
 many other aspects of learning and memory.

8
Exterior of the Cerebral
Hemispheres
 The cerebral hemispheres are
narrower posteriorly, at the
occipital pole, than anteriorly,
at the frontal pole.
 Gyri – Elevated ridges
“winding” around the brain.
 Sulci – Small grooves dividing
the gyri

9
Exterior of the Cerebral Hemispheres
 Central Sulcus: Divides the Frontal Lobe from the Parietal Lobe
 Fissures – Deep grooves, generally dividing large regions/lobes
of the brain
 Longitudinal Fissure – Divides the two Cerebral Hemispheres
 Transverse Fissure – Separates the Cerebrum from the
Cerebellum
 Sylvian/Lateral Fissure – Divides the Temporal Lobe from the
Frontal and Parietal Lobes

10
Exterior of the Cerebral Hemispheres
 The main sulci include
 1. Central sulcus: Indents
the superior medial border
of the hemisphere, 1 cm
behind the mid-point
 It runs downward, forward
and toward the lateral
sulcus across the lateral
aspect of the hemisphere
 It separates the frontal lobe
from the parietal lobe.

11
 2. Lateral sulcus: Deep cleft on the
inferior and lateral surfaces of the
cerebral hemisphere
 It separates the temporal lobe from the
frontal and parietal lobes.
 3. Parieto-occipital sulcus: Begins on
the superior medial border of the
hemisphere, about 5 cm anterior to the
occipital pole.
 It passes downward and anteriorly on
the medial surface to meet the calcarine
sulcus
 The parieto-occipital fissure separates
the parietal lobe from the occipital lobe.
12
 Calcarine sulcus:
 Found on the medial
surface of the
hemisphere
 It begins under the
posterior end of the
corpus callosum
 It ascends upward and
backward to reach the
occipital pole

13
Exterior of the Cerebral Hemispheres
 The floor of the cerebral
fissure is formed by the
corpus callosum, a large
myelinated fiber tract that
forms an anatomical and
functional connection
between the right and left
hemispheres.

14
Exterior of the Cerebral Hemispheres

15
Exterior of the Cerebral Hemispheres

16
Exterior of the Cerebral Hemispheres
 Poles, Surfaces, and Borders
 The cerebrum consists of two cerebral hemispheres that are
partially connected with each other
 Three somewhat pointed ends or poles can be recognized.
These are the frontal pole anteriorly, the occipital pole
posteriorly, and the temporal pole that lies between the
frontal and occipital poles, and points forwards and somewhat
downwards.

17
Poles, Surfaces,
and Borders
 Each hemisphere has
three borders:
 Superomedial,
 Inferolateral and
 Inferomedial.

18
Surfaces
 These borders divide the
surface of the hemisphere into
three large surfaces:
 Superolateral,
 Medial and
 Inferior.

19
 Lobes
 Each cerebral hemisphere is
divided into four (five) major
subdivisions or lobes.
 To consider the boundaries of
these lobes reference has to
be made to some sulci and
other features to be seen on
each hemisphere

20
 Lobes of the cerebral hemispheres
 The four (five) lobes of the
cerebral hemispheres are the
 Frontal,
 Parietal,
 Temporal, and
 Occipital lobes, and the insula

21
Lobes of the cerebral hemispheres

22
 Structure of cerebrum
 The surface few millimeters of the
cerebral hemisphere are
composed of a highly folded
collection of gray matter, known
as the cerebral cortex.
 Deep to the cortex is a central
core of white matter that forms
the bulk of the cerebrum and
represents fiber tracts, supported
by neuroglia.
23
 Structure of cerebrum
 Buried within the mass of
white matter are
collections of neuron cell
bodies, some of which are
lumped together under
and termed basal ganglia,
even though, technically,
they are nuclei.

24
 Structure of cerebrum
 The cerebrum is a hollow
structure and the cavities within
the cerebral hemispheres are
called the right and left lateral
ventricles,
 It communicates with the third
ventricle via the interventricular
foramen (foramen of Monroe)

25
 Structure of cerebrum
 The two lateral ventricles
are separated from one
another by two closely
adjoined non-nervous
membranes, each known
as a septum pellucidum.

26
 Structure of cerebrum
 Ependymal cells line
each lateral ventricle,
and protruding into
each ventricle is a
choroid plexus that
functions in the
manufacture of
cerebrospinal fluid

Choroid plexus are found in certain locations within

28
Lobes of the cerebral hemispheres
 In each hemisphere of the
mammalian brain the insular
cortex (also insula and insular
lobe) is a portion of the
cerebral cortex folded deep
within the lateral sulcus (the
fissure separating the
temporal lobe from the
parietal and frontal lobes

29
 Lobes of the cerebral hemispheres
 Additionally, the cortical
constituents of the limbic
system are also considered
to be a region of the
cerebral hemisphere and
some consider it to be the
sixth lobe, the limbic
lobe.
The limbic lobe is an arc-shaped region of cortex on the medial surface of
each cerebral hemisphere of the mammalian brain, consisting of parts of the
frontal, parietal and temporal lobes.
30
Frontal lobe
 The frontal lobe extends from
the frontal pole to the central
sulcus, constituting the
anterior one-third of the
cerebral cortex.

31
 Frontal lobe.
 The frontal lobe is located in the
anterior cranial fossa. The central
sulcus divides the frontal lobe
from the parietal lobe in a
coronal plane.
 Its posteriormost gyrus, the
precentral gyrus, consists of the
primary motor area and is
bordered anteriorly by the
precentral sulcus
32
 Frontal lobe.
 The region of the frontal lobe
located anterior to the
precentral sulcus is subdivided
into the superior, middle, and
inferior frontal gyri.
 This subdivision is due to the
presence, though inconsistent,
of two longitudinally disposed
sulci, the superior and
inferior frontal sulci.
33
Frontal lobe.
 The inferior frontal gyrus is
demarcated by extensions of the
lateral fissure into three sub regions:
1. Pars opercularis,
2. The pars triangularis and
3. Pars orbitalis.
 In the dominant hemisphere, a region
of the inferior frontal gyrus is known as
Broca’s area, which functions in the
production of speech.

34
 Parietal lobe.
 The parietal lobe is interposed
between the frontal and
occipital lobes and is situated
above the temporal lobe.
 The parietal lobe interprets
sensations from the body. The
gyrus posterior to the central
sulcus, the postcentral gyrus, is
the primary area for receipt of
these sensations.
35
 Parietal lobe
 Primary somatosensory
information is channeled from the
contralateral half of the body.
 The remainder of the parietal lobe,
separated from the postcentral
gyrus by the postcentral sulcus, is
subdivided by the inconsistent
intraparietal sulcus, into the
superior and inferior parietal
lobules.
36
 Parietal lobe. (medial aspect)
 The parietal lobe is separated from
the occipital lobe by the parieto-
occipital sulcus and its inferior
continuation, the calcarine fissure.
 This region of the parietal lobe is
subdivided into two major structures,
the anteriorly positioned posterior
paracentral lobule (a continuation of
the postcentral gyrus) and the
posteriorly situated precuneus.
37
Occipital lobe.
 The occipital lobe is located
superior to the tentorium
cerebelli, in the posterior
cranial fossa, and is primarily
concerned with vision.
 The occipital lobe extends
from the occipital pole to the
parieto-occipital sulcus.

38
 Occipital lobe
 On its medial aspect, the occipital lobe
is subdivided into the superiorly
located cuneate gyrus (cuneus) and
the inferiorly positioned lingual gyrus,
separated from each other by the
calcarine fissure.
 The cortical tissue on each bank of this
fissure is known collectively as the
striate cortex (calcarine cortex), and
forms the primary visual cortex.

39
 Temporal lobe.
 The temporal lobe is located in the
middle cranial fossa and is primarily
concerned with hearing.
 The temporal lobe is separated from
the frontal and parietal lobes by the
lateral fissure and from the occipital
lobe by an imaginary plane that
passes through the parieto-occipital
sulcus.

40
Temporal lobe.
 On its lateral aspect, the
temporal lobe exhibits three
parallel gyri, the superior,
middle, and inferior temporal
gyri, separated from each
other by the inconsistently
present superior and inferior
temporal sulci.

41
 Temporal lobe.
 The superior temporal gyrus of
the dominant hemisphere
contains Wernicke’s area, which
is responsible for the individual’s
ability to speak and
understand the spoken and
written word

42
 Temporal lobe
 The inferior aspect of the temporal
lobe is grooved by the inferior
temporal sulcus that is interposed
between the inferior temporal
gyrus and the lateral
occipitotemporal gyrus (fusiform
gyrus).
 The collateral sulcus separates
the fusiform gyrus from the
parahippocampal gyrus of the (fusiform gyrus)
limbic lobe. inferior temporal gyrus
43
 Insula
 The insula forms the floor of the
lateral sulcus
 In order to view the insula the
frontal, orbital, temporal, and
parietal opercula have to be
pulled apart.
 It is completely circumscribed by
the circular sulcus.

44
Insula
 During development of the
cerebral hemisphere this area
grows less than surrounding
areas which, therefore, come
to overlap it and occlude it
from surface view.
 These surrounding areas
are called opercula (= lids).

45
Insula
 The lateral surface of the
insula is subdivided into
several short and long gyri,
the most prominent of which is
located posteriorly.
 The insula is believed to be
associated with taste, and
perhaps other visceral
functions.

46
The limbic lobe
 The limbic lobe is not a single brain structure, but rather
an interacting group of brain structures that includes
portions of each lobe of the cerebral cortex.
 This C-shaped brain region is vital for the functioning of
memory, learning, motivation, and emotion, as well as
endocrine functions and some autonomic—
automatic, unconscious—bodily functions.

47
 The limbic lobe
 Phylogenetically, a primitive
part of brain
 Diseases: Epilepsy,
congenital anomalies,
dementias & psychiatric
disorders

48
The limbic lobe
 The limbic system was once thought to be a discrete set
of brain structures, but now we know that the limbic
system involves a complex range of brain structures, as
well as the hormones that affect these structures.
 The limbic lobe, by contrast, is a discrete set of brain
structures—the same structures once thought to
constitute the entirety of the limbic system.

49
 The limbic lobe
 The limbic lobe is a C-shaped
region that crosses brain
hemispheres within the
cortex, including portions of
the temporal, parietal, and
frontal lobes.
 All mammals have a limbic
lobe.

50
The limbic lobe
 Key components of the limbic
lobe include
 The amygdala,
 Hippocampus,
 Mamillary body, and
 Cingulate gyrus.

51
 Medial Surface of Cerebral Hemisphere
 The structures seen are as follows.
 The corpus callosum is a
prominent arched structure
consisting of commissural fibers
passing from one hemisphere to
the other.
 It consists of a central part called
the trunk, a posterior end or
splenium, and an anterior end or
genu.
52
 Medial Surface of Cerebral Hemisphere
 A little below the corpus callosum
we see the third ventricle of the
brain.
 The interventricular foramen
through which the third ventricle
communicates with the lateral
ventricle can be seen in the upper
and anterior part.
 Posteroinferiorly, the ventricle is
continuous with the cerebral
aqueduct.
53
 Medial Surface of Cerebral Hemisphere
 The lateral wall of the ventricle is
formed in greater part by a large mass
of grey matter called the thalamus.
 The right and left thalami are usually
interconnected (across the midline) by
a strip of grey matter called the
interthalamic connexus.
 The anteroinferior part of the lateral
wall of the third ventricle is formed by
a collection of grey matter that
constitutes the hypothalamus.
54
Medial Surface of Cerebral Hemisphere
 Above the thalamus there is the
fornix. It is a commissural fiber
 Posteriorly, the fornix is
attached to the under surface of
the corpus callosum, but
anteriorly it disappears from
view just in front of the
interventricular foramen
The fornix (meaning "arch" in Latin) is a C-shaped
bundle of nerve fibers in the brain that acts as the
major output tract of the hippocampus
55
Medial Surface of Cerebral Hemisphere
 Septum pellucidum extends
between the fornix and the
corpus callosum and
separates the right and left
lateral ventricles.
 Removal of the septum
pellucidum brings the interior
of the lateral ventricle into
view.

56
 Medial Surface of Cerebral Hemisphere
 In the anterior wall of the third
ventricle there are the anterior
commissure and the lamina
terminalis.
 The anterior commissure is
attached to the genu of the corpus
callosum through a thin lamina of
fibres that constitutes the rostrum
of the corpus callosum.

57
Medial Surface of Cerebral Hemisphere
 Below, the anterior commissure
is continuous with the lamina
terminalis which is a thin
lamina of nervous tissue.
 The lower end of the lamina
terminalis is attached to the
optic chiasma.

58
Inferior Surface of Cerebrum
 Posterior to the midbrain is
seen the splenium of the
corpus callosum
 Anterior to the midbrain is a
depressed area called the
interpeduncular fossa. it is
bounded in front by the optic
chiasma and on the sides by
the right and left optic tracts.

59
Interpeduncular fossa.
 The interpeduncular fossa is a
somewhat rhomboid-shaped area of
the base of the brain, limited in front by
the optic chiasma, behind by the
antero-superior surface of the pons,
antero-laterally by the converging
optic tracts, and postero-laterally by
the diverging cerebral peduncles
 The floor of interpeduncular fossa,
from behind forward, are the posterior
perforated substance, mammillary bodies
tuber cinereum infundibulum and Pituitary
Gland.
60
Interpeduncular fossa
 Contents of interpeduncular
fossa include oculomotor
nerve, and circle of Willis.

61
 Inferior Surface of Cerebrum
 The optic tracts wind round the
sides of the midbrain to
terminate on its posterolateral
aspect.
 Two swellings, the medial and
lateral geniculate bodies, can
be seen here.

62
 Inferior Surface of
Cerebrum
 Anterior and medial to the crura of
the midbrain there are two
rounded swellings called the
mamillary bodies.
 Anterior to these bodies there is a
median elevation called the tuber
cinereum, to which the
infundibulum of the hypophysis
cerebri is attached.

63
Inferior Surface of Cerebrum
 Close to the medial border of the
orbital surface there is an
anteroposterior sulcus: it is
called the olfactory sulcus
because the olfactory bulb and
tract lie superficial to it.
 The rest of the orbital surface is
divided by an H-shaped orbital
sulcus into anterior, posterior,
medial and lateral orbital gyri.
64