446
UNIT 3
Regulation and Integration of the Body
12
of the
vestibulocochlear nerves
(ves-tib
0
u-lo-kok
9
le-ar) synapse
with the
cochlear nuclei
(auditory relays), and with numerous
vestibular nuclei
in both the pons and medulla. Te vestibular
nuclei mediate responses that maintain equilibrium.
Also housed in the medulla are several nuclei associated with
ascending sensory tracts. Te most prominent are the dorsally
located
nucleus gracilis
(grah-sĭ
9
lis) and
nucleus cuneatus
(ku
9
ne-āt-us), associated with a tract called the
medial lemnis-
cus
(Figure 12.14). Tese serve as relay nuclei in a pathway by
the
olives
are oval swellings (which
do
resemble olives) (Fig-
ure 12.13b). Tese swellings are caused mainly by the wavy
folds of gray matter of the underlying
inferior olivary nuclei
(Figure 12.14c). Tese nuclei relay sensory information on the
degree of stretch in muscles and joints to the cerebellum. Te
rootlets of the
hypoglossal nerves
emerge from the groove be-
tween the pyramid and olive on each side of the brain stem.
Other cranial nerves associated with the medulla are the
glos-
sopharyngeal nerves
and
vagus nerves
. Additionally, the fibers
Dorsal
Cerebral
aqueduct
Superior
colliculus
Reticular
formation
Crus cerebri
of cerebral
peduncle
Ventral
Fibers of
pyramidal tract
Substantia
nigra
(a) Midbrain
Red
nucleus
Medial lemniscus
Oculomotor nucleus (III)
Periaqueductal gray
matter
Tectum
Reticular
formation
Trigeminal
nerve (V)
Pontine
nuclei
Fibers of
pyramidal tract
Middle
cerebellar
peduncle
Trigeminal
main sensory
nucleus
Trigeminal
motor
nucleus
Superior cerebellar
peduncle
Medial lemniscus
Fourth
ventricle
(b) Pons
Choroid
plexus
Fourth ventricle
Reticular formation
Pyramid
Medial lemniscus
Inferior
olivary
nucleus
Nucleus
ambiguus
Inferior cerebellar
peduncle
Cochlear
nuclei
(VIII)
Vestibular
nuclei
(VIII)
Solitary
nucleus
Dorsal motor nucleus
of vagus (X)
Hypoglossal nucleus (XII)
(c) Medulla oblongata
Lateral
nuclear
group
Medial
nuclear
group
Raphe
nucleus
Figure 12.14
Cross sections through different regions of the brain stem.
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