Download Brain stem - DENTISTRY 2012

Brain stem
Brain stem
1. Medulla oblongata
2. Pons
3. Midbrain
Brainstem
• Stalk like in shape
• Connects spinal cord to higher centers of
forebrain
Functions
1. Conduit for ascending and descending tracts
connecting spinal cord and cortex
2. Contains reflex centers (cardiac and
respiratory centers) levels of consciousness
3. Contains important nuclei of cranial nerves
(3rd to 12th cranial nerves)
Origin of the 12 cranial
nerves
CEREBRUM
1&2
BRAINSTEM
MIDBRAIN
3&4
PONS
5, 6, 7, & 8
MEDULLA
9, 10, 11 & 12
Accessory nerve (11th) has dual origin
– Cranial & spinal root
Only one nerve arise from dorsal aspect
– Trochlear nerve (4th)
Medulla oblongata
 Most caudal level of the brain stem
 Continuous with the spinal cord
 Connects pons to spinal cord
 Conical in shape
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Cranial nerves VIII–XII attach to the medulla
 Central canal of spinal cord continues into the
lower medulla (close medulla)
 Upper medulla contains cavity of 4th
ventricle(open medulla)
Medulla Oblongata
• Along with the pons, forms the ventral wall of
the fourth ventricle
• Contains a choroid plexus on the roof of the
fourth ventricle
• Pyramids – two longitudinal ridges formed by
corticospinal tracts
• Decussation of the pyramids – crossover points
of the corticospinal tracts
Gross appearance (ant. surface)
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Anterior median fissure
Pyramid – pyramidal decussation
Olives
Groove bt pyramid and olive (12th emerges)
Inferior cerebellar peduncle
Groove bt olive and ICP (10th 9th & cranial 11th
emerge)
Gross appearance(post. Surface)
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Floor of 4th ventricle (upper 1/2)
Posterior median sulcus
Gracile tubercle
Cuneate tubercle
Medulla ( post. View)
10: Gracile tubercle
9: Cuneate tubercle
12: Posterior median sulcus
Internal structure
1. Level of decussation of pyramids(motor /
close medulla)
2. Level of decussation of leminisci (sensory/
close medulla)
3. Level of olives (open medulla)
Level of decussation of pyramids
• 85% of Corticospinal
fibers decussate and
continue downward
as lat. Corticospinal
tract
Level of decussation of leminsci
• Sensory decussation
• Leminisci are formed by internal arcuate fibers
• internal arcuate fibers emerge from anterior
aspect of nucleus gracilis and nucleus
cuneatus
• Decussation takes place posterior to pyramids
Level of sensory
decussation
1----ant. Median fissure
2-----post. Median sulcus
6-----nucleus gracile
7-----nucleus cuneatus
8-----int. arcute fibers
9---- decussation of medial
leminiscus
10----pyramids
Medial
leminiscus
Level of olives (open medulla)
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Passes across the inferior part of 4th ventricle
Nuclei of 12th 11th 10th & 9th
Inf Olivary nucleus
Pyramids
ICP
Medial leminiscus
RF
Spinal nucleus of trigeminal and its tract
Medulla Oblongata
Figure 12.16c
Olivary nuclear complex
 Mainly Inf. Olivary nucleus
 Gray matter is shaped like a crumpled bag
with its mouth directed medially
 Responsible of the elevation olive
 Has communications with spinal cord,
cerebellum & cortex
 Function is associated with voluntary muscle
movement
Medulla oblongata at the level of olives
Nucleus ambiguus
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Large motor neurons
Situated deep in RF
Emerging fibers join 9th 10th cranial accessory
an elongated nucleus in the medulla
oblongata that gives rise to the motor fibers of
the glossopharyngeal, vagus, and accessory
nerves supplying striated muscle of the larynx
and pharynx
Central gray matter
 Lies beneath the floor of 4th ventricle
 Passing from M to L:
1. Hypoglossal nucleus
2. Dorsal nucleus of vagus
3. Solitary nucleus
4. Vestibular nuclei
Others
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Pyramids (corticospinal&corticonuclear fibers)
Medial leminiscus
Medial longitudinal fasciculus
Inferior cerebellar peduncle
Reticular formation
9th 10th cranial 11th & 12th emerge at this
section
Medial
leminiscus
is a pathway in the
brainstem that
carries sensory
information from
the gracile and
cuneate nuclei to
the thalamus.
Medial longitudinal fasciculus
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Small tract of nerve fibers
situated on each side of the midline
Posterior to med. Leminiscus
Anterior to 12th nucleus
It is composed largely of ascending fibers from
the vestibular nuclei and cochlear nuclei
ascending to the motor nuclei (third, fourth
and sixth)
MLF
Spinal nucleus of trigeminal and its
tract
• Its found anteriomedial to ICP
• Seen in all 3 levels of medulla
Level of olives
1--Inferior
cerebellar
peduncle
2--Floor of fourth ventricle
3---Hypoglossal nucleus
4---Medial longitudinal
fasciculus
5---Reticular formation
6---Medial lemniscus
8---Inferior olivary nucleus
9----Pyramids
The Brain Stem – The Medulla
Oblongata
• The core of the medulla contains:
– Much of the reticular formation
• Nuclei influence autonomic functions
– Visceral centers of the reticular formation
include:
• Cardiac center and Vasomotor center (adjusts force
and rate of heart contraction)
• The medullary respiratory center (control rate and
depth of breathing)
• Centers for hiccupping, sneezing, swallowing, and
coughing
Reticular Formation
•Widespread connections
•Arousal of the brain as
a whole
•Reticular activating
system (RAS)
•Maintains
consciousness and
alertness
Open medulla
Exam 1
Ventricles of Brain
 Hollow chambers filled with CSF
 Four ventricles:
(2) Lateral
(1) third ventricle
(1) fourth ventricle
 Each lateral ventricle communicates with the third ventricle via a channel
called an interventricular foramen (foramen of Monro)
 Third ventricle is continuous with the fourth ventricle via the cerebral aqueduct
 The central canal is the cerebrospinal fluid filled space that runs longitudinally through
the length of the entire spinal cord
 The central canal is continuous with the ventricles of the brain