Medulla - Part 1 Flashcards
Connects the pons superiorly with the spinal cord inferiorly
Medulla
Where is the junction of medulla and spinal cord?
at the origin of the anterior and posterior roots of the first cervical spinal nerve, which corresponds approximately to the level of the foramen magnum.
Blood supply of medulla
posterior inferior cerebellar artery (lateral part) vertebral artery (medial)
Continuous inferiorly with the anterior median fissure of the spinal cord
Anterior median fissure
Swelling on each side of the median fissure
o Composed of bundles of nerve fibers called corticospinal fibers, which originate in large nerve cells (pyramidal/Betz cells) in the precentral gyrus of the cerebral cortex
Pyramids
o Few nerve fibers that emerge from the anterior median fissure above the decussation
o Pass laterally over the surface of the medulla oblongata to enter the cerebellum
Anterior external arcuate fibers
o Posterolateral to the pyramids
o Oval elevations produced by the underlying
inferior olivary nuclei
Olives
Emerges in the groove between the pyramid
and the olive
Hypoglossal nerve
Roots of these nerves emerge in the groove
between the olive and the inferior cerebellar
peduncle
Glossopharyngeal
Vagus
Accessory
Forms the lower part of the floor of the fourth
ventricle
Superior half of the medulla oblongata
Continuous with the posterior aspect of the spinal cord and possesses a posterior median sulcus
Inferior half
o Elongated swelling located on each side of the
median sulcus
o Produced by the underlying gracile nucleus
Gracile tubercle
o Lateral to the gracile tubercle
o Produced by the underlying cuneate nucleus
Cuneate tubercle
Its extensive lateral spread resulted in an
alteration in the position of the derivatives of the
alar and basal plates of the embryo
Fourth ventricle
Alar and basal plates: situated lateral and medial to the sulcus limitans respectively (vs. in
the spinal cord, wherein the alar and basal plates are situated posterior and anterior to the sulcus limitans)
Fourth ventricle
Four levels of medulla
o Level of decussation of pyramids
o Level of decussation of lemnisci
o Level of the olives
o Level just inferior to the pons
o Seen in a transverse section through the inferior half of the medulla oblongata
o Also known as the decussation of pyramids
Great motor decussation
Part of the medulla where corticospinal fibers occupy and form the pyramid
Superior part of the medulla
About three-fourths of the fibers cross the median plane continue down the spinal cord in the lateral white column as the __________
lateral corticospinal tract
Continue to ascend superiorly posterior to the central gray matter
Fasciculus gracilis and fasciculus cuneatus
Appear as posterior extensions of the centralgray matter
Nucleus gracilis and nucleus cuneatus
Found in the posterior gray column of the spinal cord, which becomes continuous with the inferior end of the nucleus of the spinal tract of the trigeminal nerve (CN V)
Substantia gelatinosa
o Seen in the transverse section through the inferior half of the medulla oblongata
o Also known as the decussation of lemnisci
o Found a short distance above the level of the decussation of the pyramids
Great sensory decussation
o Where the lemnisci have been formed, which
have emerged from the anterior aspects of
nucleus gracilis and nucleus cuneatus
o First travel anteriorly and laterally around the
central gray matter
o They then curve medially toward the midline
where they decussate with the corresponding
fibers of the opposite side
Internal arcuate fibers
Lies lateral to the internal arcuate fibers
Nucleus of the spinal tract of the trigeminal nerve
Lies lateral to the trigeminal nucleus
Spinal tract of the trigeminal nerve
Composed of the lateral and anterior spinothalamic tracts and the spinotectal tract; Occupy an area lateral to the decussation of the lemnisci
Spinal lemniscus
Situated in the anterolateral region of the medulla oblongata
Spinocerebellar, vestibulospinal and rubrospinal tracts
largest nucleus of
this complex
Inferior olivary nucleus
elevation on the surface of the medulla
Olive
Gray matter is shaped like a crumpled bag with
its mouth directed medially
Olivary nuclear complex
Cells of the inferior olivary nucleus send fibers ______ across the midline to enter through cerebellum through the inferior cerebellar peduncle
medially
Function of the olivary nuclei
voluntary muscle movement
Made up of medial vestibular nucleus, inferior
vestibular nucleus, lateral vestibular nucleus,
and superior vestibular nucleus
Vestibulocochlear nuclei
situated on the anterolateral aspect of the inferior cerebellar peduncle
Anterior cochlear nucleus
situated on the posterior aspect of the peduncle lateral to the floor of the fourth ventricle
Posterior cochlear nucleus
o Consists of large motor neurons
o Situated deep within the reticular formation
o Emerging nerve fibers join the glossopharyngeal, vagus, and cranial part of the accessory nerve and are distributed to voluntary skeletal muscle
Nucleus ambigous
o Lies beneath the floor of the fourth ventricle
o (Medial to lateral): hypoglossal nucleus, dorsal
nucleus of the vagus, nucleus of the tractor
solitaries, medial and inferior vestibular nuclei
Central gray matter
o Thought to be inferiorly displaced pontine nuclei
o Situated on the anterior surface of the pyramids
o Receive nerve fibers from the cerebral cortex
o Send efferent fibers to the cerebellum through
the anterior external arcuate fibers
Arcuate nuclei
o Contain the corticospinal and some corticonuclear fibers situated in the anterior part
of the medulla, separated by the anterior median fissure
o Corticospinal tract: descend to the spinal cord
o Corticonuclear tract: distributed to the motor nuclei of the cranial nerves situated within themedulla
Pyramids
o Forms a flattened tract on each side of the midline posterior to the pyramid
o Emerge from the decussation of the lemnisci
o Convey sensory information to the thalamus
Medial lemniscus
Forms a small tract of nerve fibers situated on each side of the midline posterior to the medial lemniscus and anterior to the hypoglossal nucleus
o Consists of ascending and descending fibers
Medial longitudinal fasciculus
Situated in the posterolateral corner of the section on the lateral side of the fourth ventricle
Inferior cerebellar peduncle
Situated on the anteromedial aspect of the inferior cerebellar peduncle
Spinal tract of trigeminal nerve and its nucleus
Situated near the surface in the interval between the inferior olivary nucleus and the nucleus of the spinal tract of the trigeminal nerve
Anterior spinocerebellar tract
o Consists of diffuse mixture of nerve fibers and small groups of nerve cells
o Deeply placed posterior to the olivary nucleus
o Also present in the pons and midbrain
Reticular formation
