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MINISTRY OF HEALTH OF UKRAINE
VINNYTSIA NATIONAL MEDICAL UNIVERSITY
NAMED AFTER M.I.PIROGOV
NEUROLOGY DEPARTMENT
Stomatology Faculty
Lesson #6
Brainstem. Medulla Oblongata.
Anatomy of Cranial Nerves IX-XII.
1. Goals:
1.1. To study the anatomical fundamentals of the Brainstem,
the main Brainstem syndromes and their anatomical
localization.
1.2. To acquire the technique of the examination of the
Cranial Nerves IX-XII in normal condition and in
different pathological conditions.
2. Basic questions:
2.1. Brainstem. Anatomical Fundamentals.
2.2. Cranial Nerves IX-XII. Examination of the Cranial Nerves
IX-XII.
3. Literature:
Mathias Baehr, M.D., Michael Frotscher, M.D. Duus’ Topical
Diagnosis in Neurology. – P. 194-215
Mark Mumenthaler, M.D., Heinrich Mattle, M.D. Fundamentals
of Neurology. – P. 26-27
Surface Anatomy of the Brainstem
The three brainstem segments, i.e., the midbrain, pons,
and medulla, have clearly defined borders on the ventral
surface of the brainstem (Fig. 4.1a).
Medulla
The medulla extends from the site of exit of the roots of
the first cervical nerve (C1), at the level of the foramen
magnum, to its junction with the pons 2.53 cm more rostrally.
Dorsal view. The gracile tubercles are seen on either
side of the midline, flanked by the cuneate tubercles (Fig.
4.1b). These small protrusions are produced by the underlying
nucleus gracilis and nucleus cuneatus of both sides. These are
the relay nuclei in which the posterior column fibers of the
spinal cord form synapses onto the second neurons of the
afferent pathway, which, in turn, project by way of the medial
lemniscus to the thalamus. The rostral border of the medulla is
defined by a line drawn through the caudal portion of the
middle cerebellar peduncles. The floor of the fourth ventricle,
or rhomboid fossa, is bounded laterally by the inferior and
superior cerebellar peduncles and divided into rostral and
caudal portions by the striae medullares, which contain fibers
running from the arcuate nuclei to the cerebellum. The caudal
part of the floor contains a number of protrusions (tubercles)
produced by the underlying cranial nerve nuclei, including the
vagal triangle (or “trigone”; dorsal nucleus of the vagus
nerve), the hypoglossal triangle (nucleus of the hypoglossal
nerve), and the vestibular area (vestibular and cochlear
nuclei), while the rostral part contains the facial tubercle,
which is produced by the fibers of the facial nerve as they
course around the abducens nucleus. The roof of the fourth
ventricle is made up of the superior medullary velum, the
cerebellar peduncles, and the cerebellum itself.
Ventral and lateral views. A ventral view of the medulla
(Fig. 4.1a) reveals the pyramids, which lend their names to the
pyramidal tracts, whose fibers course through them. The
pyramidal decussation can also be seen here. Lateral to the
pyramid on either side is another protrusion called the olive,
which contains the inferior olivary nucleus. The hypoglossal
nerve (XII) emerges from the brainstem in the ventrolateral
sulcus between the pyramid and the olive. The nuclei of the
hypoglossal nerve, like those of the nerves to the extraocular
muscles, are located near the midline in the brainstem, in the
so-called basal lamina. Dorsal to the olive, the roots of the
accessory (XI), vagus (X), and glossopharyngeal (IX) nerves
emerge from the brainstem in a vertically oriented row (Fig.
4.1a and c).
Further dorsally, between the exit of these nerves and
the dorsolateral sulcus, lies the tuberculum cinereum, formed
by the nucleus of the spinal tract of the trigeminal nerve. This
is also the site of the posterior spinocerebellar tract, which
ascends to the cerebellum by way of the inferior cerebellar
peduncle (restiform body).
Cranial Nerves
The cranial nerves are examined individually. Figure
3.3 provide an overview of the anatomy and function of the 12
cranial nerves. The first two cranial nerves (the olfactory and
optic nn.) are, in reality, portions of the brain that have been
displaced into the periphery. The remaining 10 cranial nerves
structurally and functionally resemble the other peripheral
nerves of the body. They have motor, somatosensory special
sensory, and autonomic functions.
CN IX and X: Glossopharyngeal and Vagus Nn.
The efferent fibers from the nucleus ambiguus to the
muscles of the palate, larynx, and pharynx reach these
structures through the glossopharyngeal and vagus nn. The
larynx is innervated by two vagal branches, the superior
laryngeal n, and the recurrent laryngeal n. The
glossopharyngeal n. carries somatosensory fibers from the soft
palate, the posterior pharyngeal wall, the tonsillar fossa, and
the middle ear, as well as gustatory fibers from the posterior
third of the tongue. The vagus n. carries somatosensory fibers
from the external auditory canal, part of the external ear, and
the meninges of the posterior fossa. It also carries efferent
parasympathetic fibers to the thoracic and abdominal viscera.
Examination of the pharynx and larynx. The motor
function of the ninth and tenth cranial nerves is assessed by
inspection of the palate and throat and, more importantly, by
observation of the movements of these structures during
phonation (“a−aa−ah . . .”) and after induction of the gag
reflex by touching the posterior pharyngeal wall with, e. g., a
cotton swab. Unilateral weakness of the palatal veil and the
pharyngeal muscles makes these structures deviate laterally
away from the side of the lesion, as shown in Fig. 3.13.
Hoarseness due to a unilateral recurrent laryngeal nerve palsy
can sometimes be heard only when the patient sings.
CN XI: Accessory N.
Examination of the sternocleidomastoid and trapezius
mm. The external (final) branch of the purely motor accessory
n. supplies the sternocleidomastoid m. and the upper portion
of the trapezius m. To test the sternocleidomastoid m. on one
side, the examiner asks the patient to turn the head to the
opposite side against resistance, then observes and palpates the
muscular contraction at the anterior edge of the lateral triangle
of the neck (Fig. 3.14). The upper portion of the trapezius m.
is examined as follows: the examiner stands in front of the
patient, puts both hands on the patient’s shoulders, grasps the
upper edge of the trapezius m. on either side between the
thumb and index finger, and asks the patient to shrug the
shoulders against resistance. In unilateral accessory nerve
palsy, the shrug is less powerful on the affected side and the
trapezius m. is palpably thinner andweaker (Fig. 3.15).
CN XII: Hypoglossal N.
The twelfth cranial nerve is a purely motor nerve to the
muscles of the tongue. Lesions of this nerve produce atrophy
and weakness of the tongue. A unilateral lesion usually
produces a longitudinal furrow; when protruded, the tongue
deviates to the weaker side because of the predominant force
of the intact contralateral genioglossus m., which “pushes” the
tongue across the midline (Fig. 3.16).
Phonation, Articulation, and Speech
Assessment of the patient’s voice and speech is a
compulsory part of the neurological examination. The
examiner should pay attention to possible hoarseness, to the
volume of speech (e. g., hypophonia in Parkinson disease, p.
128), and to possible disturbances of articulation (dysarthria),
of the tempo of speech, and of its linguistic form and content
(aphasia, p. 41).