Hemispheres

Brain divisions
Cerebrum - largest part of the brain;
- composed of right and left hemispheres
- performs higher functions like interpreting touch, vision,
hearing, as well as speech, reasoning, emotions, learning,
and fine control of movement.

Diencephalon - located between the cerebrum and brainstem

Cerebellum - located under the cerebrum

- function - to coordinate muscle movements, maintain
posture, and balance.

Brainstem - composed of the midbrain, pons, and medulla.

- acts as a relay center connecting the cerebrum and
cerebellum to the spinal cord.
- performs automatic functions such as breathing, heart
rate, body temperature, wake and sleep cycles, digestion,
sneezing, coughing, vomiting, and swallowing.
- Ten of the twelve cranial nerves originate from it.
 Brain divisions
Telencephalon Cerebral cortex
Cerebral white matter
Basal ganglia

Diencephalon Thalamus
Hypothalamus
Subthalamus
Epithalamus
Mesencephalon
midbrain

Metencephalon Cerebellum
Pons

Myelencephalon
Medulla oblongata
 Cerebral Cortex
The outermost layer of gray matter making up the superficial aspect of the cerebrum.
 Cerebral Cortex
Main Terms used:
Gyri (Gyrus) – Elevated ridges “winding” around the brain.
Sulci (Sulcus) – Small grooves dividing the gyri
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
 Cerebral Cortex
Gyri (ridge)

Sulci
(groove)

Fissure
(deep groove)
 Cerebral Cortex
Cerebral Cortex Lobes

Frontal Lobe - involved with decision-making,

problem solving, and planning.

Parietal Lobe - involved in the reception and

processing of sensory
information from the body.

Occipital Lobe - involved with vision.

Temporal Lobe - involved with memory,

emotion, hearing, and
language.
 Frontal Lobe
The Frontal Lobe of the brain is located deep to the Frontal Bone of the
skull and divided
Parietal lobe via Central Sulcus
Temporal lobe via Sylvian/Lateral Fissure

It plays an integral role in the following functions/actions:

- Memory Formation

- Emotions

- Decision Making/Reasoning

- Personality
 Frontal lobe
Lateral Surface
✓ Precentral Gyrus is located anterior
to the central sulcus. It is primary motor area
(pyramidal tracts starts) Anterior to precentral
gyrus is precentral sulcus.

✓ Superior Frontal Gyrus

✓ Middle Frontal Gyrus
✓ Inferior Frontal Gyrus
Pars Opercularis ] Broca’s area (dominant hemisphere)
Pars Triangularis
Pars Orbitalis

Between superior, middle and

inferior gyri are superior frontal
sulcus and inferior frontal sulcus.
On the inferior surface of the
frontal lobe is olfactory sulcus,
which separates rectus gyrus from
Orbital gyri.
Frontal lobe
 Frontal lobe
Medial Surface
Medial Frontal Gyrus
Paracentral Lobule

Inferior Surface
Rectus Gyrus
Orbital Gyrus

*
Frontal lobe - Motor Homunculus
 Parietal Lobe
The Parietal Lobe of the brain is located
deep to the Parietal Bone of the skull.

It plays a major role in the following

functions/actions:

- Senses and integrates sensation(s)

- Spatial awareness and perception
(Proprioception - Awareness of body/
body parts in space and in relation to
each other)
 Parietal Lobe
Lateral Surface
Postcentral Gyrus is located posterior to the central sulcus. It is primary somatosensory
area. Posterior to Postcentral Gyrus is postcentral sulcus.
Parietal lobe has intraparietal sulcus, which separates
Superior Parietal Lobule from
Inferior Parietal Lobule ---- Wernicke’s area
Supramarginal Gyrus
Angular Gyrus
Medial Surface
Paracentral Lobule
Precuneus
 Parietal Lobe
Primary
Somatosensory Cortex/
Postcentral Gyrus
– Site involved with
processing of tactile and
proprioceptive information.

Somatosensory
Association Cortex
Assists with the integration
and interpretation of
sensations relative to body
position and orientation in
space. May assist with visio-
motor coordination.

Primary
Gustatory Cortex
Primary site involved with the interpretation of the sensation of Taste.
Parietal Lobe
Parietal lobe
 Temporal Lobe
The Temporal Lobes are located on the sides of the brain, deep to the
Temporal Bones of the skull; divided vial lateral (Sylvian) fissure(sulcus)
from parietal and frontal lobes

They play an integral role in the following functions:

- Hearing

- Organization/Comprehension of
language

- Information Retrieval (Memory

and Memory Formation)
 Temporal Lobe
Lateral Surface
Superior Temporal Gyrus
Middle Temporal Gyrus
Inferior Temporal Gyrus
They are separated by the superior
And inferior sulci.
Basal(inferior) Surface has occipitotemporal sulcus and colateral sulcus.
Parahypocampal Gyrus - olfactory center
Medial Occipitotemporal Gyrus
Lateral Occipitotemporal Gyrus
 Temporal Lobe
Primary Auditory Cortex – Responsible for hearing is in the superior
temporal gyrus.
Primary Olfactory Cortex – Interprets the sense of smell once it reaches the
cortex via the olfactory bulbs. (Not visible on the superficial cortex) is in the
Parahypocampal Gyrus
Wernicke’s Area – Language comprehension. Located on the Left Temporal
Lobe.
 Temporal Lobe

Primary
Auditory Cortex

Wernike’s Area

Primary Olfactory
Cortex (Deep)
Conducted from Olfactory Bulb
Temporal lobe
 Wernicke’s and Broca’s areas
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, clear
speech. Damage may result in:
- Conduction Aphasia - Where auditory comprehension and speech articulation are
preserved, but people find it difficult to repeat heard speech.
 Occipital Lobe
The Occipital Lobe of the Brain is located deep to the Occipital Bone of the Skull.
Its primary function is the processing, integration, interpretation, etc. of VISION
and visual stimuli.
It has transversus and lateral sulci. The occipital lobe contains sulcus calcarinus,
which contains Primary Visual center.
Lateral Surface
Lateral Occipital Gyrus
Superior Occipital Gyrus
Inferior Occipital Gyrus

Medial Surface
Cuneus
Lingual Gyrus

Basal Surface
Lingual Gyrus
Occipitotemporal Gyrus
 Occipital Lobe
Primary Visual
Cortex
This is the primary area of the
brain responsible for sight -
recognition of size, color, light,
motion, dimensions, etc.

Visual
Association Area

– Interprets information
acquired through the
primary visual cortex.
Occipital lobe
Insular lobe is located in the lateral fissure of the
hemispheres. It is separated by sulcus circularis. Consists
of one long and three short gyri.
 Cerebral White Matter
The cerebral white matter consists primarily of myelinated axons in
three types of tracts: 1. Association tracts contain axons that conduct
nerve impulses between gyri in the same hemisphere. 2.
Commissural tracts contain axons that conduct nerve impulses from
gyri in one cerebral hemisphere to corresponding gyri in the other
cerebral hemisphere. Three important groups of commissural tracts
are the corpus callosum (the largest fiber bundle in the brain,
containing about 300 million fibers), anterior commissure, and
posterior commissure. Corpus callosum is the largest commissure,
which consists of 4 parts: splenium, truncus, genu, rostrum 3.
Projection tracts contain axons that conduct nerve impulses from
the cerebrum to lower parts of the CNS (thalamus, brain stem, or
spinal cord) or from lower parts of the CNS to the cerebrum. An
example is the internal capsule, a thick band of white matter that
contains both ascending and descending axons. The internal capsule
consists of anterior crus, genu, posterior crus.
 Basal ganglia
Deep within each cerebral hemisphere are three nuclei (masses of gray
matter) that are collectively termed the basal ganglia. They are: corpus
striatum, claustrum and amigdala.
The term corpus striatum refers to the striated appearance of the
internal capsule as it passes among the basal nuclei. Corpus striatum
consists of 2 nuclei: Lentiform nucleus and caudate nucleus. Lentiform
nucleus consists of the globus pallidus, which is closer to the thalamus,
and the putamen , which is closer to the cerebral cortex.
The caudate nucleus has a large “head” connected to a smaller “tail” by
a long comma-shaped “body.”
The claustrum is a thin sheet of gray matter situated lateral to the
putamen.
The amygdala is composed of several groups of neurons located close
to the tail of the caudate nucleus, in the temporal lobe. It is part of the
limbic - “emotional brain” because it plays a primary role in a range of
emotions.
Basal ganglia
Limbic system
 Ventricular System and Cerebrospinal Fluid//CSF
• The brain and spinal cord are suspended in cerebrospinal fluid (CSF). The
buoyant environment created by the CSF reduces the pressure of the brain
on the nerves and vessels on its inferior surface.
– CSF is produced in the choroid plexuses, vascular networks within four
ventricles (spaces) of the brain. The first two of these ventricles are large
and paired; the third and fourth are smaller and lie in the midline.
– The 1st and 2nd (lateral) ventricles, paired cavities that occupy a large
portion of each cerebral hemisphere, communicate with the 3rd ventricle
through the interventricular foramina (of MONRO).
– The 3rd ventricle, a slitlike space between the two halves of the
diencephalon, communicates posteriorly with the 4th ventricle through a
narrow passage, the cerebral aqueduct (of SYLVIUS), which passes
through the mesencephalon.
– The 4th ventricle, a pyramidally shaped space that extends from the
pons to the medulla oblongata, is continuous with the spinal canal
inferiorly and with the subarachnoid space through the median and
lateral apertures in its roof (MAGENDIE AND LUSCHKA).
– CSF circulates through the ventricles and passes into the subarachnoid
space and subarachnoid cisterns through the median and lateral
apertures of the 4th ventricle. It flows superiorly through the fissures and
sulci of the cerebrum and is reabsorbed into the venous circulation
through the arachnoid granulations that protrude into the superior sagittal
sinus.
 The lateral ventricles
• The 1st and 2nd (lateral) ventricles, paired cavities that
occupy a large portion of each cerebral hemisphere. The lateral
ventricle consists of central part (parietal lobe) and three horns
– anterior horn is in the frontal lobe, posterior horn in the
occipital lobe, inferior - in the temporal lobe. Wall of the lateral
ventricles is formed by the corpus calossum, thalamus, caudate
nucleus. The lateral ventricles communicate with the 3rd
ventricle through the interventricular foramina (of MONRO),
which is located on the medial wall of the anterior horn.
• Internal carotid
arteries
(right and left)
• Vertebral arteries
(right and left)
circle of Willis
• Circle of Willis
• Anterior cerebral artery
• Anterior communicating
artery
• Internal carotid artery
• Posterior cerebral
artery
• Posterior
communicating
artery
• The cranial meninges, coverings that protect the brain,
consist of the external fibrous dura mater, the thin
intermediate arachnoid mater, and the delicate inner
pia mater - PAD
 Dura mater//DURA
• A tough outer membrane surrounding
the brain
• Is composed of a periosteal layer and
a meningeal layer.
– The two layers are inseparable except
where they enclose the venous sinuses
that drain the brain (e.g., the superior
sagittal sinus).
– The outer periosteal layer
– The inner meningeal layer
 Dural Partitions
• Infoldings of the meningeal layer of the dura form incomplete
membranous partitions that separate and support parts of the
brain.
– The falx cerebri, a vertical sickle-shaped partition separating the right
and left cerebral hemispheres, is attached anteriorly to the crista galli
and the inner crest of the frontal bone and is continuous posteriorly
with the tentorium cerebelli. The inferior, free edge of the falx cerebri is
unattached.
– The tentorium cerebelli, a horizontal continuation of the falx cerebri,
separates the occipital lobes of the cerebrum from the cerebellar
hemispheres in the posterior cranial fossae.
• It is attached to the posterior clinoid processes and the petrous part of the
temporal bones anteriorly and to the parietal and occipital bones
posterolaterally.
• A U-shaped tentorial notch separates the attachments to the petrous ridge on
each side and connects the middle and posterior cranial fossae.
– The falx cerebelli, a vertical partition separating the cerebellar
hemispheres, is continuous superiorly with the tentorium cerebelli and
is attached posteriorly to the occipital crest.
– The diaphragma sellae, a small dural fold attached to the anterior and
posterior clinoid processes, forms a roof over the sella turcica, which
encloses the hypophysis (pituitary gland).
 Dural Venous Sinuses
• Dural venous sinuses are valveless venous spaces that form as a result of the
separation of the periosteal and meningeal layers of the dura. Most of the large veins
of the brain, skull, orbit, and inner ear drain through the dural sinuses and into the
internal jugular veins in the neck.
– The confluence of sinuses at the posterior edge of the tentorium cerebelli is a
junction of the superior sagittal, straight, occipital, and transverse sinuses.
– The superior sagittal sinus runs in the attached superior border of the falx
cerebri and ends in the confluence of sinuses.
– The inferior sagittal sinus runs in the free inferior edge of the falx cerebri and
ends in the straight sinus.
– The straight sinus runs in the space formed by the union of the falx cerebri and
tentorium cerebelli. It receives the inferior sagittal sinus and great cerebral vein
and drains into the confluence of sinuses.
– The paired transverse sinuses run along the attached posterolateral margins of
the tentorium cerebelli. Posteriorly, they join at the confluence of sinuses, and
anteriorly they drain into the sigmoid sinuses, forming grooves in the occipital
and parietal bones along their course.
– The paired sigmoid sinuses run in deep grooves of the occipital and temporal
bones and drain into the internal jugular veins at the jugular foramen.
– The occipital sinus runs in the free edge of the falx cerebelli and ends in the
confluence of sinuses.
 Arachnoid Mater and Pia Mater
• Arachnoid mater//arachnoid is a thin, avascular, fibrous
layer underlying the meningeal layer of the dura.
– Cerebrospinal fluid//CSF presses the arachnoid against the
dura, but the two layers are not attached.
• Weblike arachnoid trabeculae attach the arachnoid to the
underlying pia mater.
• Delicate fingers of the arachnoid layer, the arachnoid villi,
pierce the dura to allow the reabsorption of CSF into the
venous circulation and are especially numerous in the
superior sagittal sinus. They form aggregations called
arachnoid granulations that protrude into the largest dural
venous sinuses and can push the dura ahead of them into
the parietal bone, forming “pits.”
• – Pia mater, or pia, is a thin, highly vascular layer that
adheres to the surface of the brain and closely follows its
contours.
 Meningeal Spaces
• The epidural space between the cranium and dura is not a
natural space because the dura adheres to the skull.
Meningeal vessels that supply the skull and dura travel in
this space.
• The subdural space between the dura and arachnoid is a
potential space, open only in pathological conditions such
as a subdural hematoma. Superficial cerebral veins
(“bridging veins”) cross this space, connecting the venous
circulation of the brain with the dural venous sinuses.
• The subarachnoid space, between the arachnoid and pia
layers, contains cerebrospinal fluid, arteries, and veins.
– Subarachnoid cisterns are spaces that form where the
subarachnoid space enlarges around large infoldings of the
brain. The largest of these include the cerebellomedullary,
pontomedullary, interpeduncular, chiasmatic,
quadrigeminal, and ambient cisterns.
Thanks For Attantion