Download Neuro Anatomy Lec.5 د.عبد الجبار الحبيطي The medulla oblongata

Neuro Anatomy
‫عبد اجلبار احلبيطي‬.‫د‬
Lec.5
The medulla oblongata: Is the part of the brain stem (also part of the hind brain)
extending from the foramen magnum below; to lower border
of the pons above, it is 2.5cm long which lies against the basilar
part of the occipital bone, being wider above & narrower
below. It consists of 2 parts; a closed lower ½ (traversed by the
central canal) & opened upper 1/2, which has no central canal
& forms the lower ½ of the floor of 4th ventricle, it show the
following features: Anterior median fissure which continues below with the
anterior median fissure of the spinal cord, this fissure is
interrupted inferiorly by the motor decussation (pyramided
decussation).
On each side of the fissure we can see a vertical band of
elevated area known as pyramid, which is formed by the
descending motor fibers (cortico-spinal) coming from the precentral gyrus, 80-85% of these fibers decussate to the opposite
side forming the lateral cortico-spinal tract (descends to the
white mater of spinal cord), while the remaining 15-20% of
fibers descends as uncrossed fibers to form anterior corticospinal tract (also descend to the white mater of the spinal
cord).
Just lateral to the pyramid, there is an olive like elevation
known as olive (it is produced by the underlying inferior olivary
nucleus). The hypoglossal nerve (rootlets) emerges from the
groove between the pyramid & olive.
Just lateral to olive there is inferior cerebellar peduncle,
connecting the medulla oblongata with the cerebellum. In the
groove between the olive & inferior cerebellar peduncle 3
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cranial nerves emerge the glossopharyngeal, vagus & cranial
part of accessory nerve. The inferior cerebellar peduncle is a
route of communication between the cerebellum & both the
medulla oblongata & spinal cord.
Note: - Between the inferior border of the pons & upper part of
medulla oblongata 3 cranial nerves emerges (Abducent, Facial
& Vestibulocochlear nerves) the Abducent emerges between
the pons & upper border of the pyramid.
The posterior surface of the medulla oblongata: I- On the upper half (open medulla) which forms the lower
part of the floor of the 4th ventricles. It shows the
following features: V shaped depression called inferior fovea with the
following triangles & areas: i-
Hypoglossal triangle lies adjacent to the posterior
median sulcus; it overlies the nuclei of both the
hypoglossal & the glossopharyngeal nerves.
ii-
Vestibular area produced by vestibular nuclei.
iii-
Vagal triangle: - a depressed area between the
hypoglossal triangle & the vestibular area, it overlies
the dorsal nucleus of the vagus nerve.
II- On the lower half (closed medulla) we see: i-
Gracile tubercle & its associated tract or fasiculus.
The fibers of the gracile tract arise in the cells of the
dorsal root ganglia of the spinal nerves of the same
side (first order neurones) carry proprioceptive
sensation as well as fine touch from lower 1/2 of the
body.
ii-
Cuneate tubercle & its associated fasculus contains
fibers from dorsal spinal root ganglia which carry
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proprioceptive and fine touch sensation of the upper
1/2 of the body.
Nuclei in the M.O.
I-
inferior olivery nucleus gives rise to: i- Olivo-cerebellar tract.
ii- Olivo-spinal tract.
II- Gracile & cuneate nuclei: The fibers of both fasciculi terminate at these
ganglia,then internal arcuate fibers passes up ward from
here,they decussate (forming sensory decussation) and
after the decussation continues as the medial lemniscus
(2nd order neurons) which relay (terminates) in the
thalamus.
III- Spinal nucleus of trigeminal nerve which lies medial
to spinal tract of trigeminal, it carries pain &
temperature sensations from the same side of the
face.
It also receives general sensation via the 9th & 10th cranial
nerves.
IV- Nucleus ambigues which is amotor nucleus which
give rise to the motor fibers joining the emerging
9th-11th cranial nerve to supply the ms of pharynx,,
larynx & soft palate.
V- Dorsal nucleus of vagus which is a parasympathetic
nucleus gives rise to the secretomotor fibers of the
vagus n.
VI- Inferior salivary nucleus gives rise to secretomotor
of glossopharyngeal which relays in otic ganglion to
reach the parotid gland.
VII- Nucleus solitarius:-receive taste sensations from 7th,
9th & 10th cranial n.
VIII- Hypoglossal nucleus & glossopharyngeal n.
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