Download 04-brain stem

POSITION & SHAPE
It is stalk like in shape . 
It connects the narrow
spinal cord with the
expanded fore brain.
It occupies the posterior 
cranial fossa of the skull
against the basal portion
of the occipital bone.
It is largely covered by 
the cerebellum.
PARTS
It is made up of: 
Medulla oblongata.
Pons. 
Midbrain. 
FUNCTIONS
(1) A conduit for the 
ascending and
descending tracts
connecting the spinal
cord to the higher
centers in the
forebrain.
(2) It contains the 
important cranial
nerve nuclei (111x11).
FUNCTIONS
(3) It contains 
important reflex
centers that control
respiration and
cardiovascular
systems.
(4) It controls over 
the level of
consciousness
through the reticular
formation .
CLINICAL NOMENCLATURE
It is named BULB. 
The entering fibers 
are Cortico Bulbar.
The syndromes 
associated with the
medulla are pseudo
Bulbar palsy and
Bulbar palsy.
VENTRAL ASPECT OF THE
MEDULLA
It is divided by the 
ventral median
fissure into two
halves.
Each half has the 
following features:
PYRAMID
It is a longitudinal 
elevation along the side of
the fissure.
The pyramids are 
composed of bundles of
nerve fibers (Corticospinal)
that originate from large
nerve cells in the cerebral
cortex.
PYRAMID
The pyramids taper 
inferiorly where the
majority of the
descending fibers (7590%) cross over to the
opposite side forming
the Decussation of the
pyramids.
This partially obscures 
the ventral fissure.
OLIVE
It is an oval elevation
lateral to the upper part
of the pyramid.
It is produced by the
underlying Inferior
Olivary Nucleus (which is
connected to the
cerebellum)
It is important in the
control of movement.

ROOTLETS OF CRANIAL
NERVES
TH)
A. hypoglossal (12

nerve. It emerges
between the pyramid and
olive.
B. Glossopharyngeal, 
Vagus and cranial part of
the Acessory (9, 10
and11TH) nerves.
They emerge in the groove 
between the olive and the
inferior cerebellar
peduncle.
PONS
It has a median groove 
(basilar sulcus) which lodges
the basilar artery.
Its anterior surface is convex 
from side to side and shows
many transverse
Pontocerebellar fibers which
are collected laterally to form
the Middle Cerebellar
Peduncles.
PONS
Four cranial nerves are 
attached to its anterior
surface.
1. Trigeminal (5th) nerve: 
It is attached to the side of 
the pons near its upper
border by two roots .
A large sensory and a small 
motor. The motor root is
located antero medial to
the sensory root.
PONS
2. Abducent (6th) nerve : 
It is located in the groove 
between the lower border
of the pons and the
pyramid.
PONS
3. Facial (7th) nerve : 
It is found between the 
lower border of the pons
and the inferior
cerebellar peduncle.
4. Vestibulo cochlear 
(8th) nerve :
It is lateral to the facial . 
The vestibular nerve is
anterior and the cochlear
nerve is posterior.
MID BRAIN
It is formed by the 
Massive Basis Pedunculi 
(Crura Cerebri).
The crura are formed by 
the descending
Corticobulbar and
Corticospinal fibers.
The cerebral peduncles 
are separated by the
Interpeduncular Fossa.
Interpeduncular Fossa.
Boundaries: 
Inferiorly :pons. 
Anteriorly :optic 
chiasma.
Laterally: optic tracts . 
Posterolaterally: 
cerebral peduncles.
MID BRAIN
Oculo motor (3rd) 
nerve :
Emerges through a 
groove at the
medial sides of the
cerebral peduncles.
DORSAL SURFACE OF THE
MEDULLA
Closed medulla 
It is the 
continuation of the
posterior surface of
the spinal cord.
It is divided by the 
posterior median
sulcus into two
halves.
Each half has the 
following features:
LOWER MEDULLA
A. GRACILE tract: 
It is a longitudinal 
column on both
sides of the median
sulcus.
It expands 
superiorly where it
ends in the Gracile
Tubercle (produced
by the Gracile
Nucleus).
LOWER MEDULLA
B. CUNATE tract and 
tubercle :
Are lateral to the 
gracile tract and
tubercle respectively.
OPEN MEDULLA
It forms the lower 
third of the floor of the
fourth ventricle.
It is divided by the 
median sulcus into
two halves.
Each half has an 
inverted (v) shaped
depression (Inferior
Fovea).
It separates the motor 
from the sensory
nuclei
OPEN MEDULLA
Medial : the hypoglossal 
nucleus.
Lateral : the vestibular 
nerve nucleus.
At the fovea : the nuclear 
complex of the
glossopharyngeal and
vagus nerves.
PONS
It is hidden by the 
cerebellum.
It forms the upper two 
thirds of the floor of the
fourth ventricle.
It is widest at the 
pontomedullary junction.
At this point, the lateral 
aperture (foramen of
Luschka) is found to allow
passage of CSF from the
fourth ventricle to the
subarachnoid space around
PONS
The posterior surface is limited 
laterally by the superior
cerebellar peduncles and
divided into symmetrical
halves by the median
sulcus.Lateral to the sulcus is
an elongated elevation (Medial
Eminence).
Its inferior end is expanded to 
form the Facial Colliculus
produced by the fibers of the
facial nerve winding around
the nucleus of the abducent
nerve.
PONS
Lateral to the 
medial eminence is
the vestibular area
produced by the
underlying
vestibular nuclei.
MID BRAIN
It has four Colliculi 
(Corpora Quadregimina)
which are rounded
eminences that are
divided into superior and
inferior pairs.
Superior Colliculi: centers 
for visual reflexes.
Inferior Colliculi: lower 
auditory centers.
MID BRAIN
Trochlear nerve (the only 
cranial nerve that can be
identified in the dorsal
aspect)
It emerges in the midline 
immediately caudal to the
inferior colliculi.
The cerebral aqueduct 
traverses through the
length of the mid brain.
CEREBELLAR PEDUNCLES
The superior and 
inferior peduncles 
appear on the dorsal
aspect of the brain
stem.
They form the lateral 
walls of the upper part
of the floor of the 4th
ventricle.
They connect the mid 
brain and medulla to the
cerebellum
respectively.
LATERAL ASPECT OF THE
BRAIN STEM
The middle 
cerebellar peduncle
can be
distinguished on
the ventral, dorsal
and lateral aspects
of the brain stem.