MEDULLA OBLONGATA AND PONS

MEDULLA OBLONGATA AND PONS
form lower part of brainstem (oblongata, pons, midbrain)
Medulla oblongata
- is uper continuation of the spinal cord
Its caudal part is alike the spinal cord, while
- its cranial half is split open to form lower part of the floor of the 4 th ventricle
External features of oblongata
the sulci and funiculi of spinal cord are continuous on the oblongata
- anterior median fissure
is crossed by
pyramidal decussation - marks the point of transition from the spinal cord to the oblongata
- anterior funiculi terminate in
pyramids of oblongata (contain corticospinal tracts)
- anterolateral sulcus – 12 th cranial n. emerges from it
- olive (elevated by underlying olivary nucleus) lies behind the anterolateral sulcus
- lateral funiculus is continuous into the inferior cerebellar peduncle (joins with the cerebellum)
- posterolateral sulcus – here the 11 th , 10 th and 9 th cranial nerves emerge from the oblongata
- gracile and cuneate fasciculi are continuous from the spinal cord to the oblongata and terminate
in :
- the gracile tubercle elevated by the gracile nucleus
- the cuneate tubercle elevated by the cuneate nucleus
- posterior median sulcus is continuous from the spinal cord to the oblongata
D o r s a l d i s t r i c t of upper half of oblongata
forms lower part of floor of the 4 th ventricle
The bulbopontine sulcus separates oblongata and pons ventrally
the 6 th, the 7 th and the 8 th cranial nerves arise from the bulbopontine sulcus
Pons
- v e n t r a l s u r f a c e is prominent convex and marked by
sulcus basilaris occupied by basilar artery
- laterally pons narrows to form middle cerebellar peduncles terminating in the cerebellum
- the 5 th cranial nerves emerge from the anterolateral parts of the pons
d o r s a l s u r f a c e of pons forms upper part of the floor of the 4 th ventricle
the 4 th ventricle
- is upper expanded continuation of the central canal of oblongata
- pyramidal in shape
- laterally projects into the lateral recesses
the floor of the 4 th ventricle is named
6

the rhomboid fossa
– this is formed by dorsal surface of the pons and open upper half of the oblongata
rhomboid fossa is marked by:
- median sulcus
- limitans sulci
- median eminences
on the median eminence some elevations are found:
- hypoglossal triangle - elevated by underlying hypoglossal nerve nucleus
- vagal triangle – (in lower part) elevated by vagus nerve nucleus
- facial coliculus (in upper part of the eminence) overlies abducent nerve nucleus and facial
nerve fibres
- vestibular area and acoustic tubercle – are placed in the lateral recess
- striae medullares – the strips of white matter running from the lateral recesses towards the
median sulcus
INTERNAL STRUCTURE OF OBLONGATA AND PONS
under the floor of the 4 th ventricle the oblongata and pons contain
CRANIAL NERVES NUCLEI arranged in four lines in each half
medial and lateral lines of motor nuclei and
medial and lateral lines of sensory nuclei
MOTOR nuclei
medial line of motor nuclei:
1. hypoglossal nucleus – is located in the oblongata in lower part of rhomboid fossa
2. abducent nucleus – in pontine part of rhomboid fossa
lateral line of motor nuclei:
1. 1a: nucleus ambiguus - – (placed lateral to the hypoglossal)
is a motor nucleus of the 9 th , the 10 th and the 11 th nerves
1b: dorsal (PS) nucleus of vagus n.
1c: inferior salivary nucleus – parasymp. ncl. of the 9 th n.
2. 2a: facial nerve nucleus (motor) - its fibres loop around the 6 th n. nucleus to form internal
genu facial n.
2b: superior salivary nucleus – parasympathetic ncl. of facial n. for the nerve supply of
salivary glands – submandibular and sublingual
2c: lacrimal nucleus – parasympathetic ncl. of facial n. for nerve supply of the lacrimal
gland
3. masticatory nucleus - motor ncl. of the trigeminal n.
SENSORY nuclei
are placed laterally to the motor nuclei
1. nucleus of the tractus solitarius is located lateral to the dorsal nucleus of vagus n.
receives:
- gustatory fibres via the 7 th , the 9 th and the 10 th cranial nerves and
- visceral sensory fibres from the 9 th and the 10 th nerves (gastropulmonary system)
7

2. trigeminal nerve nucleus
long nucleus traversing all the brainstem, extends from the upper cervical segments of spinal
cord to the midbrain
trigeminal nucleus is subdivided into:
the spinal, pontine and mesencephalic parts
the axons of trigeminal n. nucleus ascend in the trigeminothalamic tract (trigeminal lemniscus)
to reach special thalamic nuclei
3. vestibular nuclei – inferior, medial, superior and lateral
are contained in the lateral recesses of rhomboid fossa
receive afferents from vestibular apparatus and send efferents to the cerebellum and spinal cord
-vestibulocerebellar tract, vestibulospinal tract – related to maintaining of equilibrium
4. cochlear nuclei – ventral and dorsal (ant. and post.)
placed lateral to the vestibular nuclei
receive acoustic nerve fibres and send efferents to the diencephalon – the tract is named the
lateral lemniscus (a part of auditory path)
Except the cranial nerves nuclei the grey matter of oblongata and pons includes:
1. gracile nucleus and
2. cuneate nucleus
- two nuclei receive nerve fibres from the spinobulbar tract – fasciculus gracilis and cuneatus
- the axons of gracile and cuneate nuclei cells cross median plane as lemniscal decussation
and
- ascend upwards to form bulbothalamic tract- medial lemniscus terminating in
the special thalamic nuclei
3. olivary nucleus (inferior)
is a folded mass of grey matter, open medially as hilum
axons cross midline to form olivocerebellar tract interconnecting cerebellum with the spinal
cord, red nucleus and reticular formation
accessory olivary nuclei are found near the hilum of main olivary nucleus
4. reticular formation
is represented by a numerous nerve cells located near the midline
receiving afferent fibers from
and sending efferent fibers to all parts of CNS
5. arcuate nuclei
- are placed under the surface of pyramids
represent caudally displaced pontine nuclei - send efferents to the cerebellum
6. pontine nuclei
- scattered in the ventral part of pons among the corticospinal tract fibres
- are relay stations in the cortico-ponto-cerebellar path
8

THE WHITE SUBSTANCE OF THE OBLONGATA AND PONS
is composed of ascending and descending tracts
ASCENDING TRACTS:
are coming from the spinal cord:
1. spinothalamic tract (spinal lemniscus)
2. spinotectal tract
3. spinoreticular tract
4. spinocerebellar tracts
starting in the oblongata and pons:
5. medial lemniscus (bulbothalamic tract)
contains crossed axons of gracile and cuneate nuclei cells ascending to the thalamic nuclei
6. trigeminothalamic tract (trigeminal lemniscus)
7. solitariothalamic tract – begins in the ncl. of the tractus solitarius (gustatory pathway)
8. lateral lemniscus – starts in the cochlear nuclei (auditory pathway)
DESCENDING TRACTS:
1. corticospinal tract
2. corticonuclear tract – terminate on the motor nuclei of cranial nerves
3. tectospinal
4. rubrospinal
5. reticulospinal and
6. vestibulospinal tract
7. medial longitudinal fascicle contains ascending and descending fibres connecting
some nuclei of cranial nerves, upper cervical segments and midbrain
motor fibres of cranial nerves
SM (somatomotor) – supply voluntary muscles developed from the somites
VM ( visceromotor) – supply inner organs
Special VM – supply voluntary muscles developed from the branchial arches
General VM = PS – supply involuntary muscles and glands
sensory fibres of cranial nerves
VS (viscerosensory) - sensations from the inner organs
Special VS – carry special sensations from the inner organs - taste
General VS – carry general sensations from the inner organs - mainly pain
SS (somatosensory) – carry informations from skin, mucous membranes, muscles,
General SS – convey general sensations (temperature, touch, pain…)
Special SS – convey auditory
9

MESENCEPHALON – MIDBRAIN
- joins pons with the diencephalon and hemispheres
- is connected with cerebellum through the superior cerebellar peduncles
- v e n t r a l p a r t -
crura cerebri – emerge from the hemispheres and enter the pons
- anteriorly crura are crossed by optic tracts
crura cerebri border interpeduncular fossa - interpeduncular perforate substance marked by
minute openings (for passage of central branches of circulus arteriosus)
- oculomotor nerves emerge on the medial border of crura
d o r s a l s u r f a c e
tectum - consists of
superior colliculi
inferior colliculi
colliculi are connected with diencephalon (metathalamus)
by brachium of superior colliculus
brachium of inferior colliculus
- trochlear nerves emerge below the inferior colliculi
Internal structure of the midbrain
on the cross section midbrain consists of:
- tectum
- tegmentum
- crura cerebri
TECTUM
contains visual and auditory reflex centres
superior colliculi
contained grey matter is a centre of visual reflexes
receives afferent fibres from: retina and visual cortex
spinal cord (spinotectal tract)
inferior colliculi
sends efferent fibres to: the oblongata, pons (motor nuclei of cranial nerves) - tectonuclear tract
the spinal cord (motor nuclei in the anterior horns) – tectospinal tract
pretectal nucleus
lies cranial to the superior colliculi
is a centre for the light reflex
receives afferent fibres: from the retina - optic tract
sends efferent fibres: to the Edinger-Wesphal nucleus
(parasympathetic nucl. of oculomotor n.)
inferior colliculi
grey matter of inf. colliculi represents auditory reflex centres
10

afferent fibres: lateral lemniscus (auditory pathway)
efferent fibres: to the superior colliculi
to thespinal cord – tectospinal tract
to the nuclei of cranial nerves – tectonuclear tracts
TEGMENTUM
cerebral aquaeduct indicates subdivision of the midbrain on the tectum and tegmentum
grey matter of tegmentum:
1. red nucleus
is an important part of the extrapyramidal system (belongs to the subcortical motor centres)
receives afferents from:
cerebellum
basal nuclei
thalamus
sends fibres to:
spinal cord
reticular formation
nuclei of the 3 rd , 4 th , 6 th and 11 th cranial nerves
thalamus
2. substantia nigra
is a lamina of grey matter (contained cells are pigmented)
substantia nigra is also a part of extrapyramidal system
connected with:
cerebral cortex
basal nuclei
reticular formation
3. nucleus of oculomotor n. – motor nucl.
lies in the tegmentum at the level of the superior colliculus
accessory nucleus of oculomotor n. – Edinger-Westphal nucl.
is a parasympathetic nucleus supplying fibres for the sphincter pupillae
and ciliaris muscles
4. nucleus of trochlear n.
is located in tegmentum at the level of the inf. colliculus
trochlear nerves emerge on the dorsal side of midbrain
5. mesencephalic part of trigeminal n. nucleus
6. interstitial nucleus
lies near the oculomotor nucl.
is an reflex centre sending fibres to the medial longitudinal fascicle
11

7. reticular formation
groups of nerve cells placed near the midline
8. interpeduncular nucleus – mediates autonomic response on the olfactory stimuli
white matter of tegmentum:
1. medial lemniscus – bulbothalamic tract
2. trigeminal lemniscus – trigeminothalamic tract
3. lateral lemniscus – auditory path
4. spinal lemniscus – spinothalamic tract
5. spinotectal tract
6. tectospinal and tectobulbar tracts
7. tracts to and from the cerebellum
8. medial longitudinal fasciculus – contains ascending and descending fibres connecting:
- interstitial nucleus – main reflex centre
- vestibular nuclei
- nuclei of the 3 rd , 4 th , 6 th , 7 th , 11 th cranial nerves
- motoneurons of the spinal cord
med. long. fasciculus coordinates movement of eyes and head in
response to the stimulation of the vestibular apparatus
CRURA CEREBRI
consist of white matter – fibres descending from the cortex
1. corticospinal fibres
2. corticonuclear fibres
3. frontopontine fibres
parietotemporopontine fibres
12

CEREBELLUM
1. takes part in maintenance of the muscular tone
2. co-ordinates the various groups of muscles
3. helps to maintain the balance and equilibrium
receives impulses mainly from:
muscles and joints
vestibular apparatus
cortex
cerebellum is placed in the posterior cranial fossa
connected with oblongata, pons and midbrain by
the cerebellar peduncles – superior, middle, inferior
cerebellum has superior and inferior surfaces – separated by horizontal fissure
superior surface is separated from the occipital lobes by the tentorium cerebelli
cerebellum is subdivided into:
vermis - central part
hemispheres - lateral parts
THE SURFACE OF CEREBELLUM
is grooved by sulci separating folia, and fissures which separate lobules and lobes
lobules and lobes of cerebellum
Vermis (lobules) Hemispheres (lobules) LOBES
lingula vinculum lingulae anterior lobe
(central) lobule ala of central lobule
culmen
quadrangular lobule
Fissura prima
declive simplex lobule posterior lobe
folium
superior semilunar
Horizontal fissure
tuber
inf. semilunar
pyramis
biventer lobule
uvule
tonsil
nodule flocculus noduloflocular lobe
FYLOGENETICAL AND FUNCTIONAL SUBDIVISION OF THE CEREBELLUM
archicerebellum - noduloflocular lobe
the oldest part – vestibular in connections (receives vestibulocerebellar tracts)
paleocerebellum – anterior lobe
phylogenetically following (next) part – spinocerebellar in connections (receives spinocerebellar
tracts)
13

neocerebellum - posterior lobe
the youngest part – corticocerebellar in connections (receives cortico-ponto-cerebellar tracts)
INTERNAL STRUCTURE OF THE CEREBELLUM
grey matter – cortex and nuclei
white matter – central core, laminae – arbor vitae
cerebellar nuclei:
- dentate nucleus – is a folded plate of grey matter open medially as the hilum
- embolifom nucleus – elongated nucleus placed near the hilum
- globose nuclei – small nuclei also placed near the hilum
- fastigial nucleus – located in vermis (the oldest of all the nuclei)
efferent tracts begin in cerebellar nuclei
White matter of the cerebellum
1. fibrea propriae (do not leave cerebellum)
- commissural fibres
- association fibres
2. projection fibres – connect the cerebellum with the other parts of CNS (afferent and efferent
fibres)
AFFERENT FIBRES - TRACTS
1. vestibulocerebellar tract comes from the vestibular nuclei and vestibular apparatus
2. spinocerebellar tract ant. and post.- carries the impulses from the muscles – essential for
the muscle tonus
3. bulbocerebellar tract – from gracile and cuneate nuclei – brings the impulses from the
exteroreceptors – necessary for the muscular coordination
4. nucleocerebellar tract – contains fibres from the nuclei of some cranial nerves – mainly
trigeminal
5. tectocerebellar tract – for passage of auditory and visual impulses
6. rubrocerebellar tract – is a part of extrapyramidal connections
7. olivocerebellar tract – similar than the preceding
8. reticulocerebellar tract
9. (cortico)pontocerebellar tract
EFFERENT FIBRES
1. cerebellothalamic tract
2. cerebellorubral tract
3. cerebellovestibular tract
4. cerebelloreticular tract
5. cerebelloolivary tracts
all the tracts serve for performing of crebellar functions – maintaining of muscle tonus,
equilibrium and muscular coordination
14