BRAINSTEM
Structural Overview
of Brainstem
• Midbrain, pons,
medulla
• functions
BRAINSTEM
VENTRAL SURFACE
DORSAL SURFACE
medulla
• Connects pons superiorly with spinal cord
inferiorly
• Conical in shape
• The Central canal continues upward into
the lower half of medulla, in the upper half
of medulla it expands as the cavity of
fourth ventricle
• two parts: open and closed
• an open part (close to the pons)
• a closed part (further down towards
the spinal cord).
Gross Anatomy Review
Medulla - ventral
Anterior median fissure
Pyramids
Pyramidal decussation
Olive
Inferior cerebellar peduncle
Gross Anatomy Review
Dorsal medulla
• Posterior median
sulcus
• Gracile tubercle
• Cuneate tubercle.
Brainstem X-sections
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Caudal medulla
Rostral medulla
Caudal pons
Rostral pons
Caudal midbrain
Rostral midbrain
medulla
• 3 sections inside the medulla:
I. Pyramidal decussation
II.Sensory decussation
III.Level of olive
Caudal medulla
pyramidal decussation
CAUDAL MEDULLA
(LEVEL OF PYRAMIDAL DECUSSATION)
FG
DMS
FC
GN
ST5
Central grey
matter
CN
SN5
Central canal
DSC
PD
VSC
P
VMF
CAUDAL MEDULLA
(LEVEL OF PYRAMIDAL DECUSSATION)
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DMS: Dorsal median sulcus
FG: fasciculus gracilis
GN: Gracile nucleus
FC: Fasciculus cuneatus
CN: Cuneate nucleus
SN5: Spinal nucleus of trigeminal nerve
ST5: Spinal tract of trigeminal nerve
P: Pyramid
PD: Pyramidal decussation
DSC: Dorsal spinocerebellar tract
VSC: Ventral spinocerebellar tract
VMF: Ventral median fissure
CAUDAL MEDULLA
(LEVEL OF PYRAMIDAL DECUSSATION)
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GREY MATTER:
Sensory nuclei: Gracile, cuneate,
spinal nucleus of trigeminal
• WHITE MATTER:
1. Ascending tracts: Gracile, cuneate,
spinal tract of trigeminal, dorsal &
ventral spinocerebellar, spinal
leminiscus
2. Descending tracts: Pyramidal &
extrapyramidal tracts
CAUDAL MEDULLA
(LEVEL OF PYRAMIDAL DECUSSATION)
• Pyramidal decussation: Most of the fibers
of pyramid decussate then pass laterally &
dorsally to form the lateral corticospinal tract
that descend in the lateral white column of
spinal & terminate in ventral horn cells of
opposite side
• Spinal nucleus of trigeminal: It lies in the
lower part of pons, the whole medulla &
extends to the 2nd cervical segment of spinal
cord where it is continuous with substantia
gelatinosa. It receives pain & temperature
sensations from the face along trigeminal
nerve
CAUDAL MEDULLA
(LEVEL OF PYRAMIDAL DECUSSATION)
• Dorsal & ventral spinocerebellar tracts:
They carry proprioceptive fibers to the
cerebellum through inferior cerebellar
peduncle (dorsal) & superior cerebellar
peduncle (ventral)
• Gracile &Cuneate tracts: They carry
proprioceptive sensations & end in
Gracile & Cuneate nuclei (2nd order
neurones in dorsal column tract)
MID MEDULLA
(LEVEL OF SENSORY DECUSSATION)
DMS
FG
FC
GN
CN
Central grey
matter
Central canal
ST5
SN5
DSC
M
L
VSC
Internal
Arcuate Fibers
Sensory
Decussation
P
VMF
MID MEDULLA
(LEVEL OF SENSORY DECUSSATION)
• Gracile & cuneate nuclei: They are
more prominent. Axons of cells of
gracile & cuneate nuclei curve around
the central canal as internal arcuate
fibers then decussate forming the
sensory decussation & ascend in the
brain stem as medial leminiscus that
end in the ventral posterolateral
nucleus of thalamus
• Pyramid: They are more prominent
MID MEDULLA
(LEVEL OF SENSORY DECUSSATION)
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GREY MATTER:
Sensory nuclei: Gracile, cuneate,
spinal nucleus of trigeminal
• WHITE MATTER:
1. Ascending tracts: gracile, cuneate,
spinal tract of trigeminal, dorsal &
ventral spinocerebellar, spinal
leminiscus
2. Descending tracts: Pyramidal &
extrapyramidal tracts
Caudal medulla
int arcuate fibers
•gracile & cuneate nuc &
fasc
•Int arcuate fibers – ML
•MLF
•Nucleus of spinal tract of
trigeminal nerve
•Inferior olivary nuc
•Pyramids
•Hypoglossal nuclei
Rostral medulla
inf olivary nuc
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olivary nuclear complex
Vestibulocochlear nuclei
Nucleus ambiguus
Hypoglossal nerve, dorsal
nucleus of vagus,
vestibulocochlear,
glossopharyngeal and
accessory nuclei
ROSTRAL MEDULLA
DCN
4TH V
MV
LV
VH
S
VCN
ICP
A
D
Vagus
Nerve
Hypoglossal
Nerve
I.O.
M
L
F
M ML
P
VMF
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ROSTRAL MEDULLA
H: Hypoglossal nucleus
V: Dorsal vagal nucleus
S: Nucleus solitarius
A: nucleus ambiguus
MV: Medial vestibular nucleus
LV: Lateral vestibular nucleus
DCN: Dorsal cochlear nucleus
VCN: Ventral cochlear nucleus
ICP: Inferior cerebellar peduncle
I.O.: Inferior olive
D: Dorsal accessory olive
M: Medial accessory olive
MLF: Medial longitudinal fascisulus
ML: Medial leminiscus
P: Pyramid
VMF: Ventral median fissure
ROSTRAL MEDULLA
• GREY MATTER:
1.Motor nuclei: Hypoglossal, dorsal
vagal, nucleus ambiguus
2.Sensory nuclei: Nucleus solitarius,
medial & lateral vestibular nuclei,
dorsal & ventral cochlear nuclei, spinal
nucleus of trigeminal
3.Extrapyramidal nuclei: Inferior olive,
medial & dorsal accessory olive
ROSTRAL MEDULLA
• WHITE MATTER:
1.Ascending tracts: Medial leminiscus,
spinal leminiscus, spinal tract of
trigeminal, ventral spinocerebellar tract
2.Descending tracts: Pyramidal &
extrapyramidal tracts
3.Both ascending & descending tract:
Medial longitudinal fasciculus
4.Inferior cerebellar peduncle: fibers
connecting medulla to cerebellum
ROSTRAL MEDULLA
• Hypoglossal nucleus: It lies in the medial
part of floor of 4th ventricle. It contains motor
neurones innervating muscles of tongue
(except palatoglossus) through hypoglossal
nerve
• Dorsal vagal nucleus: It lies in the floor of
4th ventricle , lateral to hypoglossal nucleus.
It contains preganglionic parasympathetic
neurones running in the vagus nerve
• Nucleus Solitarius: It lies ventrolateral to
dorsal vagal nucleus. It receive taste fibers
from facial, glossopharyngeal & vagus
nerves
ROSTRAL MEDULLA
• Nucleus ambiguus: It lies dorsal to inferior
olivary nucleus. It contains motor neurones
innervating muscles of pharynx, palate &
larynx through glossopharyngeal, vagus &
cranial part of accessory nerves
• Medial & lateral vestibular nuclei: They
lie in the floor of 4th ventricle, lateral to dorsal
vagal nucleus. They receive afferent fibers
from vestibular nerve
• Dorsal & ventral cochlear nuclei: They
lie dorsal (dorsal nucleus) & lateral (ventral
nucleus) to ICP. They receive afferent fibers
from cochlear nerve
ROSTRAL MEDULLA
• Olivary nuclear complex: It is
formed of a large nucleus (inferior
olive) & 2 smaller nuclei (medial &
dorsal accessory olive).
1. Afferents: From cerebral and
cerebellar cortex & spinal cord
2. Efferents: To cerebellum through ICP
3. Function: They are concerned with
control of movement
ROSTRAL MEDULLA
• Medial longitudinal fasciculus: It
consists of both ascending & descending
fibers:
1. Ascending fibers: connect vestibular nuclei
to nuclei supplying extraoccular muscles
(occulomotor, trochlear & abducent nuclei).
It coordinates movements of head & eyes
2. Descending fibers: connect vestibular
nuclei to nuclei of ventral horn of spinal
cord (medial vestibulospinal tract). It
control body posture & balance
ROSTRAL MEDULLA
• Spinal leminiscus: It carries pain,
temperature & touch sensations
from the opposite side of body to
ventral posterolateral nucleus of
thalamus
• Inferior cerebellar peduncle: It is
formed of fibers connecting
medulla to cerebellum
Level of Inferior Olives
Vestibular nuclei
Hypoglossal nucleus
CN XII
Inferior cerebellar
peduncle =
Restiform body
Medial
Inferior
MLF
Inferior olivary
nuclei
Arcuate nuclei  pontine nuclei
Rostral medulla
N. solitarious
Dorsal motor
nucleus of X
Spinal trigeminal
tract
CN V, VII, IX, X
Sensory nucleus
for
CN VII, IX, X
N. ambiguus
Motor nucleus for
CN IX, X & XI
Cranial Nerves of the Medulla
Vestibular nuclei
CN XII
Cranial Nuclei of the Medulla
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Cranial Nuclei of the Medulla
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Spinal trigeminal
tract
Cranial Nuclei of the Medulla
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Spinal trigeminal
tract
N. ambiguus
Motor nucleus for
CN IX, X & XI
Cranial Nuclei of the Medulla
N. solitarious
Dorsal motor
nucleus of X
Spinal trigeminal
tract
CN V, VII, IX, X
Sensory nucleus
for
CN VII, IX, X
N. ambiguus
Motor nucleus for
CN IX, X & XI
CN IX: Glossopharyngeal Nerve
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Spinal trigeminal
tract
CN V, VII, IX, X
N. ambiguus
Motor nucleus for
CN IX, X & XI
CN IX: Glossopharyngeal Nerve
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Posterior 1/3 of
the tongue
Spinal trigeminal
tract
CN V, VII, IX, X
N. ambiguus
Motor nucleus for
CN IX, X & XI
CN IX: Glossopharyngeal Nerve
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Posterior 1/3 of
the tongue
Spinal trigeminal
tract
CN V, VII, IX, X
Sensation behind
ear
N. ambiguus
Motor nucleus for
CN IX, X & XI
CN IX: Glossopharyngeal Nerve
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Posterior 1/3 of
the tongue
Spinal trigeminal
tract
CN V, VII, IX, X
Sensation behind
ear
N. ambiguus
Motor nucleus for
CN IX, X & XI
Stylopharyngeus
(lifts pharynx)
CN IX: Glossopharyngeal Nerve
N. solitarious
Inf. salivatory
nucleus
Parotid gland,
parasympathetic
Spinal trigeminal
tract
CN V, VII, IX, X
Sensation behind
ear
Sensory nucleus
for
CN VII, IX, X
Posterior 1/3 of
the tongue
N. ambiguus
Motor nucleus for
CN IX, X & XI
Stylopharyngeus
(lifts pharynx)
CN X: Vagus Nerve
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Spinal trigeminal
tract
CN V, VII, IX, X
N. ambiguus
Motor nucleus for
CN IX, X & XI
CN X: Vagus Nerve
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Taste, epiglottis
Cardiorespiratory
Spinal trigeminal
tract
CN V, VII, IX, X
N. ambiguus
Motor nucleus for
CN IX, X & XI
CN X: Vagus Nerve
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Taste, epiglottis
Cardiorespiratory
Spinal trigeminal
tract
N. ambiguus
CN V, VII, IX, X
Motor nucleus for
Ear
CN IX, X & XI
CN X: Vagus Nerve
N. solitarious
Sensory nucleus
for
CN VII, IX, X
Taste, epiglottis
Cardiorespiratory
Spinal trigeminal
tract
N. ambiguus
CN V, VII, IX, X
Motor nucleus for
Ear
CN IX, X & XI
Pharynx
Larynx
CN X: Vagus Nerve
N. solitarious
Dorsal motor
nucleus of X
Sensory nucleus
for
CN VII, IX, X
Taste, epiglottis
Cardiorespiratory
Spinal trigeminal
tract
N. ambiguus
CN V, VII, IX, X
Motor nucleus for
Ear
CN IX, X & XI
Pharynx
Larynx
CN X: Vagus Nerve
N. solitarious
Dorsal motor
nucleus of X
Parasympathetic,
preganglionic
Spinal trigeminal
tract
Sensory nucleus
for
CN VII, IX, X
Taste, epiglottis
Cardiorespiratory
N. ambiguus
CN V, VII, IX, X
Motor nucleus for
Ear
CN IX, X & XI
Pharynx
Larynx
Pons
• Lies anterior to cerebellum
• Connects medulla to midbrain
• 1 inch long
Pons
Landmarks
4th ventricle
Cerebellum and Middle
cerebellar peduncle
Basilar groove
Cranial Nerves
Abducent, facial,
vestibulocochlear,
Trigeminal nerves
Ventral – Lateral View
Midbrain
Cerebral peduncles
Pons
Basis pontis
Medulla
Pyramid
Olive
Pons
Posterior view
• Median sulcus
• Medial eminence
• Sulcus limitans
• Facial colliculus
• Area vestibuli
Pons
• It is commonly divided
into anterior
part(basal part) and
posterior part
(tegmentum) by
transversely running
fibers of trapezoid
body
Internal Structure of the Pons
Cross section at two levels
• Level of facial nucleus (CN VII)
• Level of trigeminal nuclei
Level of facial colliculus
4th Ventricle
Pons
Connection of pons to
cerebellum
(inf. cerebellar peduncle)
Middle cerebellar peduncle
Medial lemniscus Ascending
2nd order sensory neurons
Descending upper motor neurons
Cranial Nerves of Lower Pons
Posterior view:
Cerebullum cut away
CN VIII – Vestibular Nuclei
Pure sensory  lateral location
Balance
Cranial Nerves of Lower Pons
CN VIII –
Vestibular Nuclei
(Cochlear Nuclei)
Cranial Nerves of Lower Pons
At a slightly higher level
CN VI nucleus – Abducens nerve
Abduction of eye
Longest, most vulnerable CN
CN VII nucleus – Facial nerve
Muscles of face
Cranial Nerves of Lower Pons
CN VII nucleus - Facial nerve
Muscles of face
Cranial Nerves of Lower Pons
CN VI nucleus – Abducens nerve
Abduction of eye
level of Upper Pons
Upper Pons
4th Ventricle
Middle cerebellar
peduncle
Corticospinal tract,
corticobulbar tract,
corticopontine fibers
Descending fibers
Upper Pons
4th Ventricle
Middle cerebellar
peduncle
Pontine nuclei
in basis
Upper Pons
Lateral lemniscus
Pontine nuclei
Trapezoid body – transverse fibers in pontine tegmentum
Lower PonsMedial lemniscus fibers
Lateral lemniscus
from dorsal column
(position and vibration)
Trigeminal tract
pain,
temperature,
touch from
contralateral
face
Pontine nuclei
Lemniscal sensory system – in tegmentum of the pons
Cranial Nerve of the upper
Pons
4th Ventricle
CN V
Motor trigeminal
nucleus
Cranial Nerve of the upper
Pons
4th Ventricle
CN V
Motor trigeminal
nucleus
Principal trigeminal sensory nucleus
Cranial Nerve of the upper
Pons
4th Ventricle
CN V
Motor trigeminal
nucleus
Trigeminal
fascicles
Trigeminal
nerve
Principal trigeminal sensory nucleus
Upper Pons
4th ventricle  cerebral aqueduct
Superior cerebellar peduncle
Transverse pontocerebellar fibers
Descending upper motor neurons
Upper Pons
4th ventricle  cerebral aqueduct
MLF
Midbrain
• 0.8 inch in length
• Connects Pons and cerebellum with the
forebrain
cerebral
aqueduct
EXTERNAL MORPHOLOGY
superior colliculus
EXTERNAL MORPHOLOGY
inferior colliculus
EXTERNAL MORPHOLOGY
CN.IV
EXTERNAL MORPHOLOGY
crus cerebri
EXTERNAL MORPHOLOGY
interpeduncular
fossa
EXTERNAL MORPHOLOGY
CN.III
INTERNAL MORPHOLOGY-slide 16
cerebral
aqueduc
t
External Structure of Midbrain
1.
2.
3.
4.
5.
6.
Optic chiasm
Interpeduncular fossa
Oculomotor nerve (CN III)
Trochlear nerve (CN IV)
Pons
crus cerebri
Ventral surface
(anterior)
Posterior view
Patterning of the Midbrain
Internal Structure of Midbrain
Cross section at two levels
• Level of inferior colliculus
• Level of superior colliculus
Lower Midbrain
Inferior colliculus
hearing
DORSAL
cerebral aqueduct
Crus cerebri
VENTRAL
Lower Midbrain
Inferior colliculus
Substantia
nigra
Melanin-containing cells that produce dopamine
Project to the basal ganglia, cerebral cortex,
Lower Midbrain
Inferior colliculus
Substantia
nigra
Crus cerebri
Crus
cerebri
Lower Midbrain
Inferior colliculus
CN IV
Trochlear nerve
Lower Midbrain
Inferior colliculus
CN IV
Trochlear nerve
MLF
Lower Midbrain
Inferior colliculus
CN IV
MLF
Lower Midbrain
Inferior colliculus
hearing
Mesencephalic
nucleus of V
Internal Structure of Midbrain
Cross section at two
Levels:
• Level of inferior colliculus
• Level of superior colliculus
Upper Midbrain
Superior colliculus
vision
Substantia nigra
Crus cerebri
Upper Midbrain
Vision
Superior colliculus 
Lateral geniculate body
Hearing
Inferior colliculus 
Medial geniculate body
Upper Midbrain
Superior colliculus
vision
Red nucleus – relay from cortex and cerebellum to
spinal cord, thalamus, reticular formation, substsantia nigra
Cranial Nerves of Upper Midbrain
Superior colliculus
vision
Edinger Westfal
nucleus
MLF
Red nucleus
CN III Oculomotor nucleus