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