The Pons Neurological System > Brainstem & Cranial Nerve Anatomy > Brainstem & Cranial Nerve Anatomy THE PONS OVERVIEW Here, we'll learn about the pons. • Start a table. • Denote that, from a clinician's perspective, the pons is, most notably, the neurobiological site of injury that produces locked-in syndrome. • Start a mid-sagittal section. First, draw the different brainstem levels, from superior to inferior: • Midbrain • Pons • Medulla KEY SURROUNDING STRUCTRES Label the anterior/posterior orientational plane of our diagram. • Include the key structures that border the brainstem: • The hyopthalamus, superiorly. • The cerebellum, posteriorly. • The cervical spinal cord, inferiorly. • And the temporal lobe, laterally. • Now, point out the pontine basis, which comprises pontine nuclei and pontocerebellar fiber tracts. • Shade in the CSF and indicate that the 4th ventricle lies at the level of the pons. RADIOGRAPHIC AXIAL SECTION • Before we draw a detailed anatomical section, let's review an axial section in radiographic perspective, which is the 1 / 4 common clinical perspective. • Show its anterior/posterior orientational plane. • Draw the pons. • Demarcate the pontine basis, anteriorly. • In this view, show its representative pontine nuclei. • And show its pontocerebellar fibers, which cross the pons and pass into the middle cerebellar peduncle as an important step in the corticopontocerebellar pathway. Clinical Correlation: central pontine myelinolysis ANATOMIC AXIAL SECTION Now, let's draw an anatomic axial outline of the pons. • Indicate the anterior–posterior axis of our diagram. • Label the left side of the page as nuclei and the right side as tracts. • Then, label the fourth ventricle — the cerebrospinal fluid space of the pons. • Next, distinguish the large basis from the comparatively small tegmentum. • Now, in the basis, draw representative corticonuclear (aka corticobulbar) tracts. • Lateral to them, draw representative corticospinal tracts. • Next, draw representative pontine nuclei within the pontine basis. • Now, draw the middle cerebellar peduncle (aka brachium pontis) in the dorsal pons. • Show that the pontine nuclei project pontocerebellar fibers via the middle cerebellar peduncle as part of the corticopontocerebellar pathway. • Next, draw the inferior cerebellar peduncle. • Adjacent to it, draw the superior cerebellar peduncle (aka brachium conjunctivum). • Importantly, show that the middle and inferior cerebellar peduncles are the main inflow pathways into the cerebellum and that the superior cerebellar peduncle is the main outflow pathway from the cerebellum. - The inferior cerebellar peduncle comprises the restiform and juxtarestiform bodies. - Spinocerebellar, reticulocerebellar, and olivocerebellar fibers pass through the restiform body, whereas the juxtarestiform body primarily comprises fibers that pass between the vestibular nucleus and vestibulocerebellum. - The superior cerebellar peduncles attach to the upper pons and midbrain; the middle cerebellar peduncle attaches to the pons and extends to the pontomedullary junction; and the inferior cerebellar peduncle attaches to the lower pons and medulla. • Next, show that in the pons, the medial lemniscus lies medially (unlike in the midbrain, where the red nuclei push the medial lemniscus out laterally). • Then, show that the spinothalamic tract lies lateral to it. 2 / 4 • Along the posterior wall of the medial lemniscus, draw the anterior trigeminothalamic tract (TTT). • Far lateral from it, draw the anterior spinocerebellar tract. - Different portions of the spinocerebellar and trigeminothalamic tracts are variably found at different brainstem levels due to their complex anatomy. • Next, show that the medial longitudinal fasciculus descends through the dorsal midline tegmentum (as it does throughout the brainstem). Clinical Correlation - Internuclear ophthalmoplegia (MLF syndrome) PONTINE FUNCTIONS Now, start another table, so we can keep tract of details of pontine functions. • Label the locus coeruleus in the posterior tegmentum. • Indicate that locus coeruleus nuclei are most heavily concentrated in the pons and are concentrated most significantly with noradrenalin (aka norepinephrine). • Given their noradrenergic make-up and widespread connections, the locus coeruleus most likely plays a role in attention and arousal. - Note that although most heavily concentrated in the pons, the locus coeruleus actually spans from the caudal end of the periaqueductal gray area in the lower midbrain to the facial nucleus in the mid-pons. • Now, in the ventral tegmentum label the reticular formation, which most notably functions in wakefulness. - The reticular formation divides into lateral, medial, and median zones. Indicate that the raphe nuclei populate the median zone. - Denote that they are primarily serotinergic and are modulated by psychotropic medications. CRANIAL NERVE NUCLEI • Next, let's include the cranial nerve nuclei in axial view, which is the opposite orientation of our radiographic diagram. Medially, draw the motor nuclei: • In midline, draw the abducens nucleus of CN 6. • Lateral to it, draw the motor trigeminal nucleus of CN 5. • Then, the facial nucleus of CN 7. • Next, the superior salivatory nucleus of CN 7. Laterally, draw the sensory nuclei: • The principal sensory nucleus of CN 5. 3 / 4 • The vestibulocochlear nucleus of CN 8. Clinical Correlation - Cranial Neuropathies: 5, 6, 7 8 ADVANCED STRUCTURES • Now, show that the tectospinal tract continues to descend through the dorsal midline tegmentum; it produces contralateral head turn. • It originates in the superior colliculus of the midbrain, decussates in the dorsal midbrain tegmentum, and innervates the upper cervical spinal segments. • Then, show that the central tegmental tract descends through the dorsal, central tegmentum. - Indicate that it carries ascending reticular fibers to the rostral intralaminar nuclei of the thalamus as part of the ascending arousal system and descending fibers from the red nucleus to the inferior olive as part of the triangle of Guillain-Mollaret, which is a network involved in movement. Clinical Correlation - Oculopalatal Myoclonus • Next, include the rubrospinal tract just posterior to the anterolateral system; indicate that it produces upper extremity flexion. - It originates from the red nucleus in the midbrain, crosses in the ventral tegmental area of the brainstem, and innervates the upper cervical spinal cord. • Next, list the pontine components of the auditory system: the lateral lemniscus, trapezoid body, and superior olivary complex. Show: • The lateral lemniscus tract in the lateral tegmentum. • The trapezoid body: a conglomeration of auditory fibers that lie between the lateral and medial leminscuses. • The superior olivary complex in the anterolateral tegmentum. - It comprises three separate nuclei: the nucleus of the trapezoid body, medial superior olivary nucleus, and lateral superior olivary nucleus. Powered by TCPDF (www.tcpdf.org) 4 / 4.