Find the substantia gelatinosa which is continuos caudally with the spinal nucleus of the trigeminal CN V
On the ventral side of the medulla find the pyramids which contain the decussating motor axons.
Olivary nuclei
are lateral to pyramids
More rostrally the, 4th ventricle widens
(2) Pons
is characterized in cross section by striped appearance caused by pontine axons crossing the midline to enter the cerebellum laterally as the middle cerebellar peduncle; 4th ventricle begins to reduce in size
(3) Midbrain
– cross section is characterized by pairs of dorsal rounded eminencies = inferior and superior colliculi
all 4 colliculi = tectum = roof of the midbrain; inferior receives auditory inputs and superior receives visual
cerebral peduncles
– most ventral part of midbrain.
Consist of: descending cortocopontine, corticobulbar and corticospinal axons
Substantia Niagra
rests on dorsal surface of each cerebral peduncle
Aqueduct of Sylvius
(cerebral aqueduct) is caudal continuation of 4th Ventricle
Tegmentum
is below aqueduct in ventral aspect of midbain, and includes:
Reticular formation
, some CN nuclei, the red nuclei, and decussating axons of the superior cerebellar peduncles
Middle and inferior peduncles
are also found here.
Brainstem Structures
(1) Proprioception, fine touch and vibration
Fasiculis gracilis:
tract in the medial dorsal column that carries axons of these sensory primary dorsal root ganglions of the sacral and lumbar regions ipsolaterally to the gracilis nucleus in the medulla
Fasiculis cuneatus:
tract in the upper lateral dorsal column that carries axons of sensory primary dorsal root ganglions of the thoracic and cervical regions ipsolaterally to the cuneatus nucleus in the medulla
gracilis nucleus and cuneatus nucleus
contain secondaryneuron cell bodies that send decussating axons in the medulla to the contralateral medial lemniscus (a tract) which ascends to the ventral posterolateral nucleus (VPL)
Medial lemniscus
contain axons of secondary neuron described above. The headless man standing on a pyramid. Starts medial in the medulla separated from the Anteriolateral system and rotates out laterally to join the ALS as it ascends rostrally in the brain stem
(2) Trigeminal pathway
Spinal tract of V
: located in the pons and medulla carrying axons of primarysensory neurons from ganglions of CN’s V, VII, IX and X that descend to the base of the medulla along the spinal nucleus of V into which then enter and synapse. The tract and nucleus are located laterally in the brain stem and run dorsal to the ALS. Secondaryaxons from the nucleus cross the midline all along its length and ascend to the Ventral Posteromedial Nucleus of the Thalamus (VPM) in the Ventral Tigeminothalamic Tract.
(3) Tracts
Pyramidal tracts:
white matter tracts that lie on the ventral surface of the medulla and contains upper motor neuron axons decending from the motor cortex to the spinal cord.
Medial Longitudinal Fasiculus (MLF)
: axon tract that carries excitatory projections from the abducens nucleus to the contralateral oculomotor nucleus; important in coordinating conjugate eye movements.
Cerebellar peduncles
: three bilateral pairs of axon tracts on the dorsal surface of the pons that carry information to and from the cerebellum
Middle cerebellar peduncle
lies between the superior cerebellar peduncle and inferior cerebellar peduncle ( = restiform body). They are associated with the pontine relay nuclei
Cerebral peduncles
: carries axons running between cerebrum and spinal cord; continuous with the pyramidal tract
Inter peduncular fossa
: area between the peduncles that gives rise to CN III.
Solitary tract
is located along the solitary nucleus containing axons from both primary Sensory gustatory and visceral neurons from ganglion of CN VII (geniculate ganglion of facial), CN IX (inferior ganglion of glossopharyngeal) and CN X (inferior ganglion of Vagus)
The tract and nucleus are located in the dorsal medulla ventral to the vestibular nucleus. The secondary neurons project to the hypothalamus and the VPM.
The gustatory fibers are carrying taste info from all over the tongue and epiglottis
Visceral sensory fibers carry cardiorespiratory info from carotid and aortic bodies as well as from the thoracic and abdominal viscera.
(4) Midbrain
Red nucleus
plays a role in motor feedback pathways by processing input from the dentate nucleus of the cerebellum by sending info to the thalamus which originally stimulated the dentate; or discharging down to the lower motor neurons by means of the rubrospinal tract; therefore, it influences the corticospinal impulses at the spinal level.
Reticular formation
: a network of neurons and fibers (evolutionarily primitive) that occupies the core of the brain stem, giving a reticulated appearance in myelin stained cross section.
Its major functions include control of heart and respiration rate, posture, and state of consciousness
Neurons of reticular formation are scattered among axon bundles that course through medial portion of midbrain, pons, and medulla
Reticulospinal tract
is a component of the medial brain stem pathways which contains the descending projections from the reticular formation and terminate primarily in the medial part of the spinal cord gray matter; thus influencing limb muscles
Functions of Brainstem Nuclei
Nucleus ambiguus
– striated muscles from branchial arches (the other branchial motor nuclei are Motor Nucleus of V, and Motor Nucleus of VII)
Spinal Trigmenial Tract
– all general sensory stuff of the face
Nucleus Solitarius
– Rostral – special sensory, Caudal – general sensory
Arranged by Cranial Nerve
:
CN I – Olfactory Neurosensory cells – direct projection from telencephalon!!!
CN II – Ganglion cells in neuroepithelium of retina
CN III
(1) Somatic Oculomotor Nucleus
Þ oculomotor nerve
(2) Edinger-Westphal Nucleus
Þ parasympathetic to Ciliary Ganglion Þ pupil sphincter
CN IV – Trochlear nerve nucleus Þ motor to Superior Oblique muscle
CN V – primary neurons are in trigeminal ganglion and mesencephalic nucleus
(1) Motor Nucleus of V
– motor Þ muscles of mastication (4), tensor tympani, tensor veli palatini, Anterior belly digastric, mylohyoid
(2) Chief Sensory Nucleus
– light touch, vibration from face
(3) Mesencephalic Nucleus
– Proprioception from jaw and jaw reflex
(4) Spinal Trigeminal Tract
– pain and temperature from face
CN VI – Nucleus of Abducent Nerve – motor to Lateral Rectus Muscle
CN VII – facial movements, taste, salivation, lacrimation
(1) Facial Motor Nucleus
– motor Þ facial expressions
(2) Nucleus Solitarius
– taste buds from anterior 2/3 of tongue via Chordae Tympani N.)
(3) Spinal Trigeminal Tract and Nucleus
– sensory Þ posterior surface of the external ear via posterior auricular branch of the facial nerve
– striated motor from branchial archesÞ pharyngeal arch muscles of the larynx and pharynx, striated muscle of the upper esophagus, muscle of the uvula, levator veli palatini, palatoglossus muscles
(2) Nucleus Solitarius
:
Caudal (GVA) – innervates mucous membrane of the pharynx, larynx, esophagus, trachea, and thoracic and abdominal viscera.
Rostral (SVA) – innervates taste buds in epiglottis
(3) Dorsal Nucleus of the Vagus
– motor Þ parasympathetic
(4) Spinal Trigeminal Tract and Nucleus
– sensory Þ posterior surface of the external ear, external auditory meatus, and tympanic membrane
CN XI
Nucleus Ambiguus
(cranial root) Þ motor to intrinsic muscles of the larynx (BUT WE SHOULD JUST KNOW THAT ALL THESE MUSCLES ARE INNERVATED BY VAGUS)