The Brain

THE BRAIN
Mr. Binu Babu
Asst. Professor
Mrs. Jincy Ealias
Asst. Professor

• The brain is one of the most complex and
magnificent organs in the human body.
Brain gives us awareness of ourselves and
our environment, processing a constant
stream of sensory data.
• It controls muscle movements, the
secretions of glands, and even breathing and
internal temperature.

The Brain: Embryonic development
• Embryonic development of the human
brain.
– Formed by week 4, the neural tube quickly
subdivides into the primary brain vesicles,
which subsequently form the secondary brain
vesicles by week 5. These five vesicles
differentiate into the adult brain structures. The
adult structures derived from the neural canal.

• The brain and spinal cord begin as an embryonic
structure
• called the neural tube. The neural tube forms, its
anterior (rostral) end begins to expand and
constrictions
• appear that mark off the three primary brain
vesicles
– Prosencephalon or forebrain
– Mesencephalon or midbrain
– Rhombencephalon or hindbrain
• The remaining caudal (“toward the tail”), or
posterior, portion of the neural tube becomes the
spinal cord.

Human Brain
• The major components
of the brain are
– The cerebrum
– The cerebellum
– The brainstem

Cerebrum
• The cerebrum is the largest and most
developmentally advanced part of the
human brain. It is responsible for several
higher functions, including higher
intellectual function, speech, emotion,
integration of sensory stimuli of all types,
initiation of the final common pathways for
movement, and fine control of movement.

Cerebrum Cerebrum
Cerebellum
Cerebrum

Cerebral hemispheres
• The cerebrum is divided into a
right and a left hemispheres.
• The left hemisphere controls the
majority of functions on the right
side of the body, while the right
hemisphere controls most of
functions on the left side of the
body
• The crossing of nerve fibers takes
place in the brain stem. Thus,
injury to the left cerebral
hemisphere produces sensory and
motor deficits on the right side,
and vice versa.

Lobes of the Cerebrum
 Fissures (deep
grooves) divide the
cerebrum into lobes
 Cerebrum is
composed of pairs of
 Frontal lobe
 Parietal lobe
 Occipital lobe
 Temporal lobe

External features:
Gyri – Elevated ridges “winding” around the brain.
Sulci – Small grooves dividing the gyri
– Central Sulcus – Divides the frontal lobe from the parietal
lobe.
– Lateral sulcus - outlines the flaplike temporal lobe and
separates it from the parietal and frontal lobes.
Fissures – Deep grooves, generally dividing large
regions/lobes of the brain
• Transverse Fissure – Separates the cerebrum from the
cerebellum.
• Longitudinal Fissure – Divides the two cerebral
hemispheres
• Sylvian/Lateral Fissure – Divides the temporal lobe from
the frontal and parietal lobes

Boarders of cerebral hemispheres

Regions of cerebral hemisphere
Cerebral hemisphere has three basic regions:
1. A superficial cerebral cortex of gray matter,
which looks gray in fresh brain tissue
2. Internal white matter
3. Basal nuclei, islands of gray matter situated
deep within the white matter

Grey matter
• It is a major component
of the central nervous
system consisting
of neuronal cell
bodies, neuropil
(dendrites and myelinat
ed as well as
unmyelinated axons)
glial cells (astrocytes
and oligodendrocytes)
synapses and capillaries.

Grey matter in the spinal cord
• Grey matter in the spinal cord is known as the grey
column which travels down the spinal cord
distributed in three grey columns that are presented
in an "H" shape.
• The forward-facing column is the anterior grey
column
• The rear-facing one is the posterior grey column
• The interlinking one is the lateral grey column.
• The grey matter on the left and right side is
connected by the grey commissure.
• The grey matter in the spinal cord consists
of interneurons, as well as cell bodies.

Cerebral cortex
• The cerebral cortex is the “executive suite” of the
nervous system.
• It enables us to be aware of ourselves and our
sensations, to communicate, remember, understand
and initiate voluntary movements.
• The cerebral cortex is composed of gray matter:
neuron cell bodies, dendrites, associated glia and
blood vessels, but no fiber tracts.
• It contains billions of neurons arranged in six layers.
• 2–4 mm (about 1/8 inch) thick
• It accounts for roughly 40% of total brain mass.

• Based on the differences in lamination the
cerebral cortex can be classified into two
parts
– The large area of neocortex
– The smaller area of allocortex

Neocortex
• The neocortex (also known as the isocortex or
neopallium) is the part of the mature cerebral
cortex with six distinct layers.

Allocortex
• The allocortex is the part of the cerebral
cortex with less than six layers and has
three regions,
– The paleocortex with three cortical laminae
– The archicortex which has four or five cortical
laminae
– The periallocortex – a transitional zone
between the neocortex and the allocortex

White matter
• The white matter is a
network of fibers that
enables regions of the
brain to communicate
with each other.

• White matter consists largely of myelinated
fibers bundled into large tracts. These fibers
and tracts are classified according to the
direction in which they run as
– Association Fibers
– Projection Fibers
– Commissural Fibers

• Association fibers: Connects different cortical
areas of the same hemisphere to one another.
– Eg:- superior longitudinal fasciculus
• Projection fibers: Connects cerebral cortex to
other parts of CNS like brain stem and spinal
cord.
– Eg: corona Radiata,internal capsule
• Commissural fibers: Connects the
corresponding parts of two hemispheres

White Matter of Cerebral
hemisphere
• Association tracts (fibers)- different regions
in cerebral cortex.
• Projection tracts (fibers)- cerebral cortex
other masses of gray matter.
• Commissures fibers - R L.

Internal capsule
• Internal capsule is
located between the
lentiform nucleus
laterally and
the thalamus and
caudate nucleus
medially.
• In a horizontal section of
cerebral hemisphere, the
internal capsule appears
as a V-shaped bundle of
fibers with the apex
directed medially.

The internal capsule is divided into five parts.
– Anterior limb: part of the internal capsule that lies between the
anterior part of lentiform nucleus laterally and head of caudate
nucleus medially.
– Genu: It is the bend between the anterior and posterior limb of
internal capsule. The concavity of the bend faces laterally.
– Posterior limb: is that part of internal capsule which lies
between the thalamus medially and the posterior part of
lentiform nucleus laterally.
– Retrolentiform part: is located posterior to the lentiform
nucleus.
– Sublentiform part: is located inferior to the lentiform nucleus.

Internal capsule contains both the motor
fibers and sensory fibers
Motor/Descending Fibers in Internal capsule
• Corticopontine :originate from all the lobes of cerebrum and relay
in ipsilateral pontine nuclei.
• Pyramidal fibers:
– Corticospinal: originate mainly in primary motor cortex and
relay in contralateral anterior horn of spinal cord.
– Corticonuclear: originate mainly in primary motor cortex
and relay usually in contralateral (some bilateral) motor
nuclei of cranial nerves.
• Extrapyramidal fibersCoticorubral, corticostriate, corticonigral
fibers etc.: these fibers originate in the motor and premotor areas of
cerebral cortex relay in subcortical nuclei viz. red nucleus, corpus
stiatum and substantia nigra respectively.

Internal Capsule -
Sensory/Ascending Fibers
• Thalmocortical and corticothalamic fibers: The
thalamocortical fibers are the 3rd order neurons of ascending
pathways.
• The four thalamic radiation bands are:
– Anterior thalamic radiation: Pass anteriorly to connect the
anterior and dorsomedial nucleus of thalamus to the frontal
lobe.
– Superior thalamic radiation: Pass superiorly to connect the
ventral tier of nucleus of thalamus to primary and premotor
areas of frontal lobe and sensory areas of parietal lobe.
– Posterior thalamic radiation (Optic radiation): pass
posteriorly to connect the lateral geniculate body to the
primary visual cortex.
– Inferior thalamic radiation (Auditory radiation): pass
inferiorly and laterally to connect the medial geniculate body
to the primary auditory area.

Arrangement of Descending (Motor)
and Ascending (Sensory) Fibers
Anterior limb:
Motor
• Frontopontine fibers
Sensory
• Anterior thalamic radiation
Genu
Motor
• Frontopontine fibers,
• Corticonuclear
• Corticospinal fibers for head
and neck
Sensory
• Superior thalamic radiation
Retorlentiform part
Motor
• Parietopontine
• Occipitopontine fibers
Sensory
• Posterior thalamic ( Optic)
radiation
Sublentiform part
Motor
• Parietopontine
• Occipitopontine fibers
Sensory
• Inferior thalamic ( Auditory)
radiation

Basal Nuclei
• Deep within the cerebral white matter is the
third basic region of each hemisphere, a group
of subcortical nuclei called the basal nuclei or
basal ganglia.
• Basal nuclei include the
– Caudate nucleus
– Putamen
– Globus pallidus
• The comma-shaped caudate nucleus arches
superiorly over the diencephalon. Together
with the putamen, it forms the striatum

• The putamen and globus pallidus together
form a lens-shaped mass, sometimes called the
lentiform nucleus.
• The basal nuclei are functionally associated
with the subthalamic nuclei of the diencephalon
and the substantia nigra of the midbrain.
• The basal nuclei receive input from the entire
cerebral cortex, as well as from other
subcortical nuclei

The substantia nigra
• It is a brain structure
located in the
midbrain, and forms
part of the basal
ganglia. It is the largest
nucleus in the
midbrain.
• The substantia nigra
also plays an
important role in
reward and addiction.

Amygdaloid nucleus
• A small oval structure in the temporal
lobe of the brain that is closely connected to
the hypothalamus, the hippocampus, and
the cingulate gyrus.
• The amygdaloid nucleus is part of the
olfactory and limbic systems and plays a
role in the sense of smell, motivation, and
emotional behavior.

Ventricles
• The ventricles are structures that
produce cerebrospinal fluid, and transport
it around the cranial cavity. They are lined
by ependymal cells, which form a structure
called the choroid plexus. It is within
the choroid plexus that CSF is produced.
• Embryologically, the ventricular system is
derived from the lumen of the neural tube.
• There are four ventricles; right and left lateral
ventricles, third ventricle and fourth ventricle.

Lateral Ventricles
• The left and right lateral ventricles are located
within their respective hemispheres of the
cerebrum. They have ‘horns’ which project into the
frontal, occipital and temporal lobes.
• The paired lateral ventricles, one deep within each
cerebral hemisphere, are large C-shaped chambers
that reflect the pattern of cerebral growth.
• Anteriorly, the lateral ventricles lie close together,
separated only by a thin median membrane called
the septum pellucidum.
• The volume of the lateral ventricles increases with
age.

Third Ventricle
• The lateral ventricles are connected to
the third ventricle by the foramen of Monro.
The third ventricle is situated in between
the right and the left thalamus. The anterior
surface of the ventricle contains two
protrusions:
– Supra-optic recess – located above the optic
chiasm.
– Infundibular recess – located above the optic
stalk.

Fourth Ventricle
• The fourth ventricle is the last in the system – it
receives CSF from the third ventricle via
the cerebral aqueduct. It lies within the
brainstem, at the junction between
the pons and medulla oblongata. From the 4th
ventricle, the fluid drains into two places:
– Central spinal canal – Baths the spinal cord
– Subarachnoid cisterns – Baths the brain, between
arachnoid mater and pia mater. Here the CSF is
reabsorbed back into the circulation.

CORPUS CALLOSUM
• It is the largest collection
of commissural fibers of
the cerebrum.
• It located in the floor of
the median longitudinal
fissure and connects two
cerebral hemisphere
except lower and anterior
part of the temporal lobe.
• Corpus callosum closely
related to lateral ventricle.

PARTS OF CORPUS
CALLOSUM
• 4 parts
• Anterior end called genu
• Central part is the Trunk
• Posterior bulbous part
called Splenium
• Rostrum is the
prologation from the
upper part of the genu to
the upper end of the
lamina terminals

FIBERS OF CORPUS
CALLOSUM
• Rostrum connects orbital
surfaces of frontal lobe.
• Forceps minor is made up
of fibers of genu that
connects the 2 frontal lobes.
• Forceps major is made up of
fibers of splenium that
connects the 2 occipital
lobes.
• The tapetum formed by
some fibers of the trunk
and splenium of corpus
callosum
FUNCTION OF CORPUS
CALLOSUM
COORDINATES THE ACTIVITIES
OF THE TWO CEREBRAL
HEMISPHERES

Diencephalon
• The diencephalon consists largely of three
paired structures:- the thalamus,
hypothalamus, and epithalamus.
• These gray matter areas collectively enclose
the third ventricle

Thalamus
• The thalamus consists of bilateral egg-shaped nuclei,
which form the superolateral walls of the third
ventricle.
• The thalamus is the relay station for information
coming into the cerebral cortex.
• Large mass of grey matter, lies immediately lateral to
third ventricle
Two poles
 Anterior pole(or end)
 Lies behind the interventricular foramen
 Posterior pole(or end also called pulvinar lies just
above and lateral to superior colliculus.

Two thalami on each side of slit like cavity of 3rd ventricle
3 cms length x 1.5 cms breadth Long axis 300 oblique to
midline.
Interthalamic adhesion

Superior surface
Superior surface
• The superior (dorsal)
surface of the thalamus
is covered by a thin layer
of white matter, the
stratum zonale
• It extends laterally and
forms the roof of the
third ventricle
• More laterally it forms
part of the floor of the
lateral ventricle.
• Related laterally to
caudate nucleus

Medial surface
The medial surface
• The medial surface of the
thalamus is the superior
(dorsal) part of the lateral
wall of the third ventricle.
• It is usually connected to the
contralateral thalamus by an
interthalamic adhesion
behind the interventricular
foramina.
• The thalamus is continuous
with the midbrain
tegmentum, the subthalamus
and the hypothalamus

Inferior surface of thalamus
• Inferior surface of the tegmentum is related
to hypothalamus anteriorly and to ventral
thalamus posteriorly.
• The ventral thalamus seperates the
thalamus from tegmentum of midbrain.

Internal structure of the
thalamus
• Thalamus consists of mainly of grey matter
• Superior surface is covered by a thin layer of white
matter called stratum zonale
• Lateral surface is covered by a similar layer called
externalmedullary layer.
• Internally, the thalamus is divided into anterior, medial
and lateral nuclear groups by a vertical Y-shaped sheet
of white matter, the internal medullary lamina
• Nuclei of the anterior part.
• Anterior nucleus.
• Nuclei in the medial part
• Largest nuclei among them medial dorsal nucleus.

Blood supply of thalamus
• Perforating branches of the posterior cerebral
artery
• Posteromedial group (thalamo - perforating
arteries) supply medial and anterior part.
• Posterolateral group (thalamo-geniculate
branches) supply
• posterior and lateral part of thalamus.
• Also recieves branches from posterior
communicating anterior choroidal,posterior
choroidal and middle cerebral artery.

Hypothalamus
• Hypothalamus which lies below the thalamus. It
the floor and lower parts of the lateral walls of the
3rd ventricle.
• The hypothalamus caps the brain stem and forms
the inferolateral walls of the third ventricle.
• The hypothalamus extends from the optic chiasma
(crossover point of the optic nerves) to the posterior
margin of the mammillary bodies.
• The mammillary bodies paired pea like nuclei that
bulge anteriorly from the hypothalamus, are relay
stations in the olfactory pathways.

• The hypothalamus is the main visceral
control center of the body.
• Small in size weighing only4gm, forms only
0.3 % of total brain mass.
• Mainly acts through 3 systems.
a. Autonomous nervous system
b. Endocrine system
c. The limbic system

Boundaries
• Anteriory - lamina
terminalis
• Posteriorly -subthalamus
• Inferiorly - structures in
the floor of the 3rd
ventricle.ie, tuber
cinereum, infundibulam
and mammillary bodies.
• Superiorly – thalamus
• Lateral boundary -
internal capsule.
• Medially - bounded by the
cavity of 3rd ventricle.

Anteroposteriorly divided into
• Preoptic region - area adjoining
the lamina terminalis.
• Supra optic region - above the
optic chiasma
• Tubreal region includes the tuber
cinereum,infundibulam and area
around it.
• Mammillary region - includes the
mammillary bodies and area
around it.

Hypothalamic nuclei
• Hypothalamus is made up of numerous small nuclear
masses called hypothalamic nucleus.
• They are divided into groups according to their regional
distribution and they differ in their functions also.

The subthalamic nuclei
• The subthalamic nuclei are
small paired structures that
are part of the
functional basal ganglia.
• They are located ventral to
the thalamus, dorsal to
the substantia nigra and
medial to the internal
capsule.
• The subthalamic nucleus
receives its main input from
the lateral pallidum (external
segment of the globus
pallidus). Excitatory,
glutamatergic inputs come
from the cerebral cortex.

Region Nucleus Functions
Preotic region Preoptic nucleus
Contains the sexually
dimorphic nucleus, which
releases GnRH
Supraoptic region
Supra optic nucleus Vassopressin release
Anterior nucleus Thermo regulation, sweating
Paraventricular nucleus
TRH, CRH Corticotropin &
Oxytocin release
Tuberal region
Arcuate (infundibular
nucleus)
GHRH, feeding and
Dopamine release
Ventromedial nucleus Satiety centre
Dorsomedial nucleus
Controls BP, HR and GI
stimulation

Autonomic control of body
• Hypothalamus controls autonomic functions of body
through sympathetic as well as parasympathetic
fibres including cardiac, and respiratory activity,
vasomotor tone of blood vessels ,digestive process .

Part of limbic system
The limbic system is a complex
set of structures that lies on both
sides of the thalamus, just under
the cerebrum. It includes the
hypothalamus, the hippocampus,
the amygdala, and several other
nearby areas. It appears to be
primarily responsible for our
emotional life, and has imp. Role
in formation of memories.

Regulation of sleep
• Ventro lateral preoptic area

Regulation of Food & water intake
• The extreme lateral part of
the ventromedial nucleus of the
hypothalamus is responsible for
the control of food intake.
Stimulation of this area causes
increased food intake.
Bilateral lesion of this area
causes complete cessation of
food intake.
•

Temperature regulation
• The cold and heat sensors
located in the hypothalamus
respond appropriately to
maintain the body
temperature at optimum level
in diverse conditions.
• The ant. Portion of
hypothalamus prevents the
rise in body temperature
while,
• Posterior portion promotes
heat conservation and heat
production.

Circadian rhythm
• Hypothalamus regulates the
cyclic activities of the body
,viz sleeping and waking cycle
but itself affected by diurnal
rhythm.
• The circadian rhythm for
many body functions is of
about 24 hours.

Sexual dimorphism
• Several hypothalamic nuclei are sexually dimorphic i.e.
there are clear differences in both structure and function
between males and females.

Other functions
• EMOTIONAL EXPRESSION:_
Hypothalamus regulates the
expression of emotions through
its control over the ANS
(laughting,crying,sweating,cryi
ng etc.)
• Fear processing:_The medial
zone of hypothalamus is part of
a circuitry that controls
motivated behaviors, like
defensive behaviors.

APPLIED ANATOMY
• Lesions in the hypothalamus will cause one of the
following syndromes;
• Obesity
• Diabetes insipidus
• Sexual disturbance
• Disturbance in sleep: somnolence,narcolepsy
• Hyperglycemia and glycosuria
• Diencepahlic autonomic epilepsy : characterized by
flushing,sweating,salivation,lacrimation,tacycardia,r
etardation of respiartory rate,unconsciousness etc.

Epithalamus
• The most dorsal portion of the diencephalon
• The epithalamus forms the roof of the third
ventricle. Extending from its posterior border
and visible externally is the pineal gland or
body.
• The pineal gland secretes the hormone
melatonin and, along with hypothalamic nuclei,
helps regulate the sleep-wake cycle.
• The posterior commissure forms the caudal
border of the epithalamus.

The brain stem
• The brain stem regions are
– Midbrain
– Pons
– Medulla oblongata

Midbrain
• Connects the pons and cerebellum with
the forebrain.
• It is about 0.8 inch in length
• The midbrain is traversed by a narrow
channel called cerebral aqueduct filled with
CSF.

Anterior Surface
 Anteriorly, it presents
two large bundles of
fibers, one on each side
of the midline, called
crus cerebri.
 The oculomotor nerve
emerges from the
medial aspect of the crus
of the same side
 The crus cerebri bounds
the interpeduncular
fossa on either side.

Posterior Surface
 Posteriorly, the midbrain presents
four rounded swellings called
colliculi- One Superior and
inferior colliculi one on each side.
 Each colliculus is laterally related to
a ridge called brachium.
 Superior and inferior brachium
arises from respective colliculi
 Superior brachium connects the
superior colliculus to lateral
geniculate body.
 Inferior brachium connects the
inferior colluculus to medial
geniculate body
 In the midline below the inferior
colliculus, the trochlear nerve
emerges which then winds round
the side of the midbrain to reach its
ventral aspect.

Structure of Midbrain
• The midbrain comprises two lateral halves called the
Cerebral peduncles;
• The Cerebral peduncles are separated in to two parts by a
pigmented band of gray matter called substantia nigra
– Anterior part - crus cerebri
– Posterior part - tegmentum
The central narrow cavity is called the cerebral aqueduct
or aqueduct of Sylvius, which connects the 3rd and 4th
ventricles.
 The tectum is the part of the midbrain posterior to the
cerebral aqueduct; it has four small surface swellings
referred to previously; these are two superior and two
inferior colliculi.

Blood Supply
Artery –
• posterior cerebral
artery
• superior cerebellar
artery
• basilar artery
Veins –
• Drained by basal or
great cerebral veins

PONS
• It is situated anteriorly to the cerebellum
measuring about 1 inch in length.
• Connects the medulla oblongata to the
midbrain.
• Its also connects two cerebellar
hemispheres and its name comes from this
bridge like appearance.

Anterior surface of Pons
Pons has a convex anterior surface marked by
transversely running fibers which laterally form a bundle
called middle cerebellar peduncle.
Main Features:
• The trigeminal nerve emerges from the anterior surface at
its junction with middle cerebellar peduncle.
• Presents a basilar sulcus in the midline which lodges
basilar artery
• In the groove between Pons and the medulla oblongata,
there emerge, from medial to lateral, abducent, facial and
vestibulocochlear nerves.

Posterior Surface
• Posterior surface contains
median sulcus which is
bounded by medial eminence
on both sides.
• Inferior end of medial
eminence is slightly expanded
to form facial colliculus, which
is produced by facial nerve
root.
• The upper end of sulcus
limitans presents a bluish-gray
coloration called substantia
ferruginosa.

• Respiratory nuclei:
• Apneustic & pneumotaxic centers work with
the medulla to maintain respiratory rhythm
• Nuclei & tracts that process and relay info
to/from the cerebellum
• Ascending, descending, and transverse
tracts that interconnect other portions of
the CNS

Structure of Pons
Posterior Part
• Tegmentum
Anterior part
• Basis pontis traversed
by running fibers of
Trapezoid body.

APPLIED ANATOMY
• Unilateral lesions in the lower part of the
pons results in paralysis of facial nerve in
the same side and limbs in the opposite side.

Medulla Oblangata
• The medulla oblongata (medulla) is one of
the three regions that make up the
brainstem. It is the most inferior of the three
and is continuous above with the pons and
below with the spinal cord. The medulla
houses essential ascending and descending
nerve tracts as well as brainstem nuclei

• Relays ascending sensory pathway impulses
from skin and proprioceptors through nuclei
cuneatus and gracilis
– Contains visceral nuclei controlling heart rate,
blood vessel diameter, respiratory rate, vomiting,
coughing, etc.
– Relays sensory information to the cerebellum
through inferior olivary nuclei
– Contains nuclei of cranial nerves VIII–XII
– Contains projection fibers
– Site of decussation of pyramids

Structures of the Medulla
Oblongata
• Flanking the midline on the medulla’s
ventral aspect are two longitudinal ridges
called pyramids, formed by the large
pyramidal (corticospinal) tracts descending
from the motor cortex most of these fibers
cross over to the osite side before
continuing into the spinal cord.
• This crossover point is called the
decussation of the pyramids

• The olives are oval swellings. These
swellings are caused mainly by the wavy
folds of gray matter of the underlying
inferior olivary nuclei. These nuclei relay
sensory information on the degree of
stretch in muscles and joints to the
cerebellum.

External Anatomy of the Medulla
• The superior margin of the medulla is located at the
junction between the medulla and pons
• The inferior margin is marked by the origin of the first pair
of cervical spinal nerves. This occurs just as the medulla
exits the skull through the foramen magnum.
• Length is about 3 cm, width is about 2 cm
• Surfaces shows series of fissures
– Anterior median fissure
– Posterior median fissure

Anterior median fissure
Pyramid
Anterolateral fissure
Olive

Anterior Surface
• There are several structures visible on the anterior surface of
the medulla – namely the three fissures/sulci, the pyramids, the
olives, and five cranial nerves.
– Anterior median fissure, which is continuous along the
length of the spinal cord. Two sulci are visible –
the ventrolateral sulcus and the posterolateral sulcus.
– The pyramids are paired swellings found between the
anterior median fissure and the ventrolateral sulcus.
– The olives are another pair of swellings located laterally to
the pyramids – between the ventrolateral and posterolateral
sulci.
• Arising from the junction between the pons and medulla is the
abducens nerve (CN VI). Extending out of the ventrolateral
sulcus is the hypoglossal nerve (CN XII). In the posteriolateral
sulcus, three more cranial nerves join the medulla (CN IX, CN X,
and CN XI).

Ventral surface of medulla oblongata contains
• Pyramid
• It is an elevation between anterior median and
anterolateral sulcus
• Formed due to decussation of corticospinal fibres.
Pyramid
Olive
Olive
• Oval swelling between anterolateral
posterolateral sulcus,half an inch
long
• Produced by large mass of gray
matter called inferior olivary
nucleus

The posterior surface
• The posterior surface has a midline structure –
the posterior median sulcus – which is
continuous below as the posterior median
sulcus of the spinal cord. Above, the sulcus
ends at the point in which the fourth ventricle
develops.
• As we move lateral from the midline,
the fasciculus gracilis and fasciculus
cuneatus are seen, separated by the posterior
intermediate sulcus.

Internal Anatomy of the Medulla
• The internal structures of the medulla must
be viewed in cross section to understand the
layout. Three levels of the medulla are
typically discussed (inferior – superior):
– Level of decussation of the pyramids
– Level of decussation of the medial lemnisci
– Level of the olives

• The medulla contains gray matter, while
the outer portions consist
of white matter. The posterior white matter
contains the fasiculus gracilis and the
more lateral fasiculus cuneatus.
Corresponding portions of gray matter
extend to these regions and are the nucleus
gracilis and nucleus cuneatus associated
with a tract called the medial lemniscus.

Functions of the Medulla
Oblongata
• The small size of the medulla belies its crucial role as an
autonomic reflex center involved in maintaining body
homeostasis. The medulla contains these important
functional groups of visceral motor nuclei:
Cardiovascular center. Adjusts the force and rate of heart
contraction to meet the body’s needs, and the vasomotor
center, which changes blood vessel diameter to regulate
blood pressure.
Respiratory centers. These generate the respiratory
rhythm and control the rate and depth of breathing.
Various other centers. Additional centers regulate such
activities as vomiting, hiccuping, swallowing, coughing, and
sneezing

The Limbic System
• The limbic system is a group of structures
located on the medial aspect of each
cerebral hemisphere and diencephalon.
• These functional system:
– Includes cerebral and diencephalon structures
(e.g., hypothalamus and anterior thalamic
nuclei)
– Mediates emotional response
– Involved in memory processing

• The limbic system is our emotional, or affective
(feelings), brain.
• Amygdaloid body is critical for responding to
perceived threats such as angry or fearful facial
expressions with fear or aggression.
• The cingulate gyrus plays a role in expressing
our emotions through gestures and in resolving
mental conflicts when we are frustrated.
• Rhinencephalon helps the brain in responds to
odors.

Reticular Formation
• The reticular formation is a
set of interconnected nuclei
that are located throughout
the brainstem. The reticular
formation is not anatomically
well defined because it
includes neurons located in
diverse parts of the brain.
• A functional system:
– Maintains cerebral cortical
alertness (reticular activating
system)
– Filters out repetitive stimuli
– Helps regulate skeletal and
visceral muscle activity

Reticular Activating System
• The neurons of the part of the reticular
formation known as the reticular activating
system (RAS).
• Reticular activating system send a
continuous stream of impulses to the cerebral
cortex, keeping the cortex alert and conscious
and enhancing its excitability. Impulses from all
the great ascending sensory tracts synapse
with RAS neurons, keeping them active and
enhancing their arousing effect on the
cerebrum.

• The reticular formation is divided into three
columns:
– Raphe nuclei (median),
– Magnocellular red nucleus (medial zone),
– Parvocellular reticular nucleus(lateral zone).

• The raphe nuclei is the place of synthesis of
the neurotransmitter serotonin, which plays
an important role in mood regulation.
• The magnocellular red nucleus is involved in
motor coordination.
• The parvocellular nucleus
regulates exhalation.

The Brain

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