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Brain stem 1
Medulla Oblongata
Development of the brain
Brain Stem
• Located :
between the cerebrum and
the SC
• Consists of :the
midbrain, pons, and
medulla oblongata.
• Each region is about an
inch in length.
Microscopically, it
consists of deep grey
matter surrounded by
white matter fiber tracts
CONNECTIONS WITH
CEREBELLUM:
• Each part of brain stem
is connected to
cerebellum by cerebellar
peduncles (superior,
middle & inferior).
FUNCTIONS OF BRAIN STEM
1. Pathway of tracts between
cerebral cortex & spinal
cord.
2. Site of origin of nuclei of
cranial nerves (from 3rd to
12th).
3. Site of emergence of
cranial nerves (from 3rd to
12th).
4. Contains groups of nuclei
& related fibers known as
reticular formation
responsible for: control of
level of consciousness,
perception of pain,
regulation of
cardiovascular &
respiratory systems.
Medulla Oblongata
External structure of the medulla
Most inferior region of the brain
stem.
Becomes the spinal cord at the
level of the foramen magnum.
Medulla is broad above: joins with pons
& narrow below: continuous with spinal
cord
Length is about 3cm, width is about 2cm
at its upper end
Surfaces shows series of fissures
Anterior median fissure
Spinal cord
Posterior median fissure
Medulla oblongata
External features
• It is divided into right & left halves by anterior &
posterior median fissures
• Each half again into ant, post , lat region by
anterolateral & posterolateral sulci
• The ant. region in the form of a longitudinal
elevation called pyramid
• Anterior external arcuate fibres run transversely
across upper part of the pyramid
• Lateral region shows an oval elevation, the olive.
• It is produced by a mass of greymater- inferior
olivary nucleus
Pyramid
Olive
Anterolateral fissure
Anterior median fissure
MEDULLA – VENTRAL SURFACE
 Ventral median fissure:
•
•
•
Continuation of ventral median
fissure of spinal cord
Divides the medulla into 2
halves
Its lower part is masked by
decussation of most of
pyramidal (corticospinal) fibers
(75%-90%).
 Pyramid:
•
•
An elevation, lies on either side
of ventral median fissure
Produced by corticospinal
tract.
 Olive:
• An elevation, lies lateral to
the pyramid.
• Produced by inferior olivary
nucleus (important in
control of movement).
 Nerves emerging from
Medulla (4 nerves):
• Hypoglossal (12th): from
sulcus between pyramid &
olive
• Glossopharyngeal (9th),
vagus (10th) & cranial part
of accessory (11th): from
sulcus dorsolateral to olive
(from above downwards)
MEDULLA – DORSAL SURFACE
• The features
differ in the
caudal part
(closed
medulla) and
the cranial
part (open
medulla)
open medulla
closed medulla
 Cavity: central canal.
 Composed of:
1-Dorsal median sulcus: divides
the closed medulla into 2 halves.
2-Fasciculus gracilis: on either side
of dorsal median sulcus.
3-Gracile tubercle: an elevation
produced at the upper part of
fasciculus gracilis, marks the site
of gracile nucleus.
4-Fasciculus cuneatus: on either
side of fasciculus gracilis.
5-Cuneate tubercle: an elevation
produced at the upper part of
fasciculus cuneatus, marks the
site of cuneate nucleus.
CLOSED
MEDULLA
 Cavity: 4th ventricle
 On either side, an
inverted V-shaped sulcus
divides the area into 3
parts (from medial to
lateral):
1. Hypoglossal triangle:
overlies hypoglossal
nucleus.
2. Vagal triangle: overlies
dorsal vagal nucleus.
3. Vestibular area: overlies
vestibular nuclei.
OPEN MEDULLA
Internal features



Closed Medulla
Traversed by the Central
Canal.
Includes the Motor
Decussation.
Includes the Spinal
Nucleus of Trigeminal
(Trigeminal sensory
nucleus) :
It is a large sensory
nucleus.
It is the brain stem
continuation of the
Substantia Gelatinosa of
spinal cord.
Substantia
Gelatinosa
TRIGEMINAL SENSORY NUCLEUS & TRACT
• The Nucleus Extends :
• Through the whole length of
the brain stem and into upper
segments of spinal cord.
• It lies in all levels of M.O, medial
to the spinal tract of the
trigeminal.
• It receives pain and
temperature from face,
forehead.
• Its tract is present in all levels of
M.O. is formed of descending
fibers that terminate in the
trigeminal nucleus.
PYRAMIDAL DECUSSATION
• It is the Motor
Decussation.
• Formed by pyramidal
fibers, (75-90%) cross
to the opposite side
• They descend in the
lateral white column
of the spinal cord as
the lateral
corticospinal tract.
• The uncrossed fibers
form the ventral
corticospinal tract.
MID MEDULLA
 Traversed by the Central Canal.
 Larger size Gracile & Cuneate nuclei, concerned
with proprioceptive deep sensations of the
body.
 Axons of Gracile & Cuneate nuclei form the
internal arcuate fibers; Sensory Decussation.
 Pyramids are prominent ventrally.
SENSORY DECUSSATION
• Formed by the crossed
internal arcuate fibers
• Medial Leminiscus:
– Composed of the
ascending internal
arcuate fibers after
lemniscus = ribbon
their crossing.
– Lies adjacent to the
middle line ventral to
the central canal
– Terminates in thalamus.
Open Medulla
On the ventral aspect :
 The pyramid is clear, with
medial lemniscus on either
sides of middle line dorsal
to the pyramid
 Inferior Olivary Nucleus:
– A convoluted mass of
gray matter. Has a
hilum directed
medially, lies
posterolateral to the
pyramids & lateral to
the medial leminiscus.
– It is concerned with the
control of movement.
Open Medulla
Its dorsal surface forms:
The lower part of the floor
of the 4th ventricle.
• The Inferior Cerebellar
Peduncle is dorsolateral in
position, connecting M.O.
with cerebellum.
• Dorsal and lateral to the
Inferior cerebellar
peduncle lie the Cochlear
nuclei (dorsal and ventral).
 Beneath the floor of 4th
ventricle lie :
1. Hypoglossal Nucleus lies just
lateral to the midline.
2. Dorsal Nucleus of Vagus
lateral to the hypoglossal
nucleus, contains preganglionic
parasympathetic fibers.
Medial longitudinal fasciculus
lies close to the midline,
ventromedial to the
hypoglossal nucleus, dorsal to
the medial lemniscus. It links
the vestibular nuclei with
nuclei of extraocular ms.
(3,4&6) to help coordination of
head & eye movements.
3. Vestibular nuclei complex
: is composed of medial,
lateral, inferior & superior
nuclei, concerned with
equilibrium.
4. Nucleus Ambiguus: lie
deep to the floor and dorsal
to olivary nucleus gives
motor fibers to constrictors
of the pharynx & intrinsic
muscles of the larynx.
5. Solitary nucleus: lie
ventrolateral to dorsal
nucleus of vagus, receive
taste sensation from the
tongue along the facial (VII),
glossopharyngeal (IX) and
vagus (X) cranial nerves.
Cranial Nerves of the Medulla
Vestibular nuclei
N. solitarious
Sensory nucleus for
CN VII, IX, X
Dorsal motor
nucleus of X
Posterior 1/3 of the tongue
N. ambiguus
Spinal
trigeminal tract
CN V, VII, IX, X
Sensation behind ear
Motor nucleus for CN IX,
X & XI
Stylopharyngeus (lifts
pharynx)
CN X: Vagus Nerve
Dorsal motor nucleus
of X
Parasympathetic,
preganglionic
N. solitarious
Sensory nucleus for
CN VII, IX, X
Taste, epiglottis
Cardiorespiratory
N. ambiguus
Spinal trigeminal tract
CN V, VII, IX, X
Ear
Motor nucleus for CN
IX, X & XI
Pharynx
Larynx
• Nuclei in the medulla are associated with
autonomic control, cranial nerves, and
motor/sensory relay.
• Autonomic nuclei:
1-Cardiovascular centers
Alter the rate and force of cardiac contractions
Alter the tone of vascular smooth muscle
2-Respiratory rhythmicity centers
Receive input from the pons
3-Additional Centers
Emesis, deglutition, coughing, hiccupping, and
sneezing