Transcript pons
Pons The base of the pons (basis pontis) contains three components: fiber bundles of the corticospinal tracts, pontine nuclei that have received input from the cerebral cortex by way of the corticopontine pathway, pontocerebellar fibers from the pontine nuclei, which cross and project to cerebellum by way of the large middle cerebellar peduncle. Along the midline of the pons and part of the medulla lie the raphe nuclei. Serotonin-containing neurons in these nuclei project widely to the cortex and hippocampus, basal ganglia, thalamus, cerebellum, and spinal cord. These cells are important in controlling the level of arousal and modulate the sleep–wake cycle. They also modulate sensory input, particularly for pain Caudal pons Caudal pons Tegmentum The lower pons contains the nucleus of nerve VI (abducens nucleus) and the nuclei of nerve VII (the facial, superior salivatory, and gustatory nuclei). The branchial motor component of the facial nerve loops medially around the nucleus of nerve VI. The upper half of the pons harbors the main sensory nuclei of nerve V Mid pons medial lemniscus assumes a different position (lower body, medial; upper body, lateral) the spinothalamic tract courses even more laterally as it travels through the pons. Rostral pons The central tegmental tract contains descending fibers from the midbrain to the inferior olivary nucleus and ascending fibers that run from the brain stem reticular formation to the thalamus, and runs dorsolateral to the medial lemniscus. The tectospinal tract (from midbrain to cervical cord) and the medial longitudinal fasciculus are additional components of the pontine tegmentum. Rostral pons- near pons-midbrain junction Middle cerebellar peduncle The middle cerebellar peduncle is the largest of the three cerebellar peduncles. It contains fibers that arise from the contralateral basis pontis and end in the cerebellar hemisphere. Auditory system The auditory system from the cochlear nuclei in the pontomedullary junction includes fibers that ascend ipsilaterally in the lateral lemniscus It also includes crossing fibers (the trapezoid body) that ascend in the opposite lateral lemniscus. A small superior olivary nucleus sends fibers into the cochlear division of nerve VIII as the olivocochlear bundle this pathway modifies the sensory input from the organ of Corti in the cochlea Trigeminal pathway The three divisions of the trigeminal nerve project to the brain stem. Fine touch function is relayed by the main sensory nucleus pain and temperature are relayed into the descending spinal tract of V proprioceptive fibers form a mesencephalic tract and nucleus in the midbrain. The second-order neurons from the main sensory nucleus cross and ascend to the thalamus. The descending spinal tract of V sends fibers to the pars caudalis (the spinal nucleus in the medulla), the pars interpolaris (a link between trigeminal afferent components and the cerebellum), and the pars oralis. The masticatory nucleus, which is medial to the main sensory nucleus, sends branchial efferent fibers into the mandibular division of nerve V to innervate most of the muscles of mastication and the tensor tympani of the middle ear. Brainstem syndromes Name of Syndrome Site of Lesion Clinical Features Medial medullary syndrome Ventromedial medulla, including pyramid and axons of hypoglossal nerve Ipsilateral hypoglossal palsy with contralateral hemiplegia/hemiparesis, contralateral impairment of sense of position and movement+tactile discrimination Wallenberg's syndrome Site of Lesion Clinical Features Lateral medulla (territory of posterior inferior cerebellar artery), including the vestibular nuclei inferior cerebellar peduncle, nucleus ambiguus, spinal trigeminal tract and nucleus, spinothalamic tract, and fibers descending to preganglionic sympathetic neurons Vertigo, ataxia, paralysis of the ipsilateral palate and vocal cord, loss of pain and thermal sensation on the same side of face and opposite side of body, ipsilateral Horner's syndrome, and loss of facial sweating Foville syndrome Site of lesion Dorsomedial pons, including abducens nucleus, facial motor nucleus and axons, dorsal to the descending motor fibers Clinical features Ipsilateral lower motor neuron facial paralysis, ipsilateral conjugate gaze paralysis, and transient contralateral hemiparesis