The Central Nervous SystemNeuroanatomy Chapter 2 Section 2 Brain stemThe cranial nerves are designated by Roman numerals and names. The Roman numerals refer to the order in which the nerves are positioned from the superior to the inferior.Cranial nerves III through XII emerge from the brain stem.Brain stem Cranial nerves from rostral to caudalThe oculomotor nerve (n.III) emerges from the interpeduncular fossa located between the crus cerebri of the cerebral peduncles of the midbrain. The n.IV (trochlear) emerges from the posterior surf. of the midbrain caudal to the inferior colliculus. Brain stem Cranial nerves cranial nerve V (trigeminal) emerges laterally from the midpons, cranial nerves VI (abducent), VII (facial), and VIII (vestibulocochlear) emerge from medial to lateral along the junction between the pons and medulla, Brain stem Cranial nerves cranial nerves IX (glossopharyngeal), X (vagus), and XI (cranial root of spinal accessory nerve) emerge in a rostral to caudal continuum dorsal to the olive, cranial nerve XII (hypoglossal) emerges between the olive and pyramid.Brain stem Cranial nerves from the surface slightly lateral to the midlinen.III (oculomotor) from the interpeduncular fossa, n.IV (trochlear) emerges from the posterior surf. of the midbrain.n.VI (abducent) at the ponsmedulla junction, n.XII (hypoglossal) locates between the olive and pyramid. Brain stem Cranial nerves from the lateral surface n.V (trigeminal) from the midpons, n.VII (facial) and n.VIII (vestibulocochlear) from the ponsmedulla junction, n.IX (glossopharyngeal), n.X (vagus) and n.XI (cranial root of accessory nerve) as nerve filaments from the postolivary sulcus. The spinal root of n.XI arises as filaments emerging laterally between the dorsal and ventral roots of spinal cord levels C1 to C6Brain stem Cranial nerves The brainstem nuclei of the motor cranial nerves are arranged in three discontinuous columns.General somatic columnSpecial visceral columnGeneral visceral (parasympathetic) columnMotor Nerves and Their Nuclei of Origin Within BrainstemNucleus of oculomotor nerve IIINucleus of trochlear nerve IVNucleus of abducent nerve VI, Nucleus of hypoglossal nerve XIIMotor Nerves and Their Nuclei of Origin Within Brainstem1. General somatic columnIt associated with cranial nerves III, IV, VI, and XII. These motor nuclei are located in the posteromedial tegmentum. General somatic motor nuclei nNucleus of oculomotor n.nNucleus of trochlear n. nNucleus of abducent n. nNucleus of hypoglossal n.Those of nerves III and IV are in the midbrain, that of n.VI in the lower pons, and that of n.XII extends the length of the medulla. General somatic motor nuclei nNucleus of oculomotor n.nNucleus of trochlear n. nNucleus of abducent n. nNucleus of hypoglossal n. NucleusSiteCranial n.FunctionNucleus of oculomotor n.MidbrainSupreior, inferior,and medial recti, inf. obliquus, levator palpebrae superiorisNucleus oftrochlear n.MidbrainSuperior obliquusNucleus of abducent n.PonsLateral rectusNucleus of hypoglossal n.MedullaMuscles of tongueGeneral somatic motor nucleiInnervate striated muscles that are derived from the somites and are involved with movements of the tongue and eyeballsMotor nucleus of trigeminal nerveNucleus of facial nerveNucleus ambiguusAccessory nucleusMotor Nerves and Their Nuclei of Origin Within Brainstem2. Special visceral columnIt consists of 4 nuclei associated with cranial nerves V, VII, IX, X, and XI. Special visceral motor nucleinMotor nucleus of trigeminal n.nNucleus of facial n. nNucleus ambiguus nAccessory nucleusThe motor nucleus of n.V locates in the lateral tegmentum of the pons, the motor nucleus of n.VII is in the caudal pontine tegmentum, and that of IX, X, and XI, known as the nucleus ambiguus, is within the central tegmentum throughout the medulla.The spinal root of n.XI arises from the accessory nucleus which locates from caudal medulla to the spinal cord levels C1 to C6 Special visceral motor nucleinMotor nucleus of trigeminal n.nNucleus of facial n. nNucleus ambiguusnAccessory nucleusSpecial visceral motor nucleiNucleusSiteCranial n.FunctionMotor nucleus of trigeminal n.PonsMasticatory muscles, anterior belly of digastric, mylohyoid Nucleus of facial n.PonsFacial m., platysma, posterior belly of digastric, stylohyoid, stapediusNucleus ambiguusMedulla, Skeletal m. of pharynx, larynx and upper part of esophagusAccessory nucleusMedulla-cervical cordSternocleidomastoid, trapezius(innervate muscles that are derived form the brachial arches)Accessory nucleus of oculomotor nerveSuperior salivatory nucleusInferior salvatory nucleusDorsal nucleus of vagus nerveMotor Nerves and Their Nuclei of Origin Within Brainstem3. General visceral (parasympathetic) columnIt emits preganglionic fibers that are part of cranial nerves III, VII, IX, and X., which provide autonomic innervation of smooth muscles and the glands in the head, neck and torso.General visceral motor nucleinAccessory oculomotor nucleusnSuperior salivatory nucleusnInferior salivertory nucleusnDorsal nucleus of vagus n. The parasympathetic nucleus associated with n.III is the accessory nucleus of n.III (nucleus of E-W) in the midbrain; that associated with n.VII is the superior salivatory nucleus in the lower pons; that associated with n.IX is the inferior salivatory nucleus located in the rostral medulla; and that associated with n.X is the dorsal vagal nucleus located in the medullaGeneral visceral motor nucleiNucleusSiteCranial n.FunctionAccessory oculomotor nucleusMidbrainSphincter pupillae and ciliary m.Superior salivatory nucleusPonsSubmandibular, sublingual and lacrimal glandsInferior salivertory nucleusMedullaParotid glandDorsal nucleus of vagus n.medullaMany cervical, thoracic and abdominal visceraprovide autonomic innervation of smooth muscles and the glands in the head, neck and torsoThe sensory cranial nerves (equivalent to dorsal root) include the following:trigeminal nerve (n.V), facial nerve (n.VII), vestibulocochlear (acoustic/vestibular) nerve (n.VIII),glossopharyngeal nerve (n.IX),vagus nerve (n.X). Sensory Nerves and their Nuclei of TerminationThe brainstem nuclei of sensory cranial nerves are arranged in continuous columns as follows:1.General somatic column2.Visceral column3.Special somatic columnthe mesencephalic nucleus of n.V, located lateral to the ventricular canal in the upper pons and midbrain, the principal sensory nucleus of n.V, located in the lateral tegmentum in the midpons, and the spinal nucleus of n.V, located laterally in the lower pontine, medulla, and first two cervical spinal cord levels.Sensory Nerves and their Nuclei of Termination1. General somatic columnassociated with cranial nerves V, VII, IX, and X. nMesencephalic nucleus of trigeminal n. nprincipal sensory nucleus of trigeminal n. nSpinal nucleus of trigeminal n. General somatic sensory nucleiNucleusSiteCranial n.FunctionMesencephalic nucleus of trigeminal n.MidbrainProprioception of headprincipal sensory nucleus of trigeminal n.PonsTactile sensation of headSpinal nucleus of trigeminal n.MedullaPain and temperature sense of headReceive and relay sensory stimuli from the skin and mucosa of most of the headnNucleus of solitary tractassociated with cranial nerves VII, IX, and X. This column, known as the nucleus solitarius, is located in the posterior tegmentum of the medulla. 2. Visceral columnSensory Nerves and their Nuclei of TerminationRelay sensory stimuli from the viscera and more specialized taste stimuli from the tongue and epiglottisVisceral sensory nuclei ( general and special )NucleusSiteCranial n.FunctionNucleus of solitary tractMedulla,Taste and visceral sensationassociated with cranial nerve VIII. The vestibular nuclei are located in the posterolateral tegmentum of the lower pons and upper medulla; the paired cochlear nuclei are located on the outer surface of the inferior cerebellar peduncle.3. Special somatic columnSensory Nerves and their Nuclei of TerminationnCochlear nucleinVestibular nucleiSpecial somatic sensory nucleiNucleusSiteCranial n.FunctionCochlear nucleiPons and medulla Sense of hearingVestibular nucleiPons and medullaSense of equilibriumNucleusSiteSuperior colliculusMidbrain Nucleus of inferior colliculusMidbrain Red nucleusMidbrain Substantia nigraMidbrain Pretectal areaMidbrain Superior olivery nucleusPons Pontine nucleusponsNucleus ceruleus ponsGracile nucleusMedulla (underneath gracile tubercle)Cuneate nucleusMedulla (underneath cuneate tubercle)Inferior olivary nucleus MedullaNon-cranial nerve nucleiAscending and Descending Fiber TractsAscending tractsPyramidal tractCorticospinal tractCorticonuclear tract1.Medial Lemniscus2.Spinothalamic tract3.Trigeminothalamic tract4.Lateral lemniscusDescending Fiber Tracts1. Medial LemniscusThe fasciculi gracilis and cuneatus terminate in the nucleus gracilis and nucleus cuneatus. Fibers from these nuclei decussate in the lower medulla to form the medial lemniscus, which ascends through the tegmentum and terminates in the ventral posterolateral nucleus of the thalamus(VPL). Ascending tractsThis pathway transmits exteroceptive and proprioceptive impulses.exteroceptive, information on localization and quality of tactile sensation, such as well-localized sensations of fine touch, vibration, two-point discrimination; proprioceptive, information on limb position and body posture). Ascending tractsSpinal ganglion 1neuron Fasciculus gracilis Fasciculus cuneatus Gracile and cuneate nuclei2neuron Decussation of medial lemniscusMedial lemniscusVPL 3neurons Central thalamic radiation T4Medial lemniscus 2. Spinothalamic tract（Spinal lemniscus）This pathway ascends from the spinal cord and continues within the lateral aspect of the tegmentum as the spinothalamic tract until it terminates in the ventral posterolateral nucleus of the thalamus.Ascending tractsThe pathway transmits pain, temperature sensation, crude touch and pressure sensations. Spinal ganglia1neuron Lamina, 2neuron Lateral spinothalamic tract anterior spinothalamic tract Spinal lemniscusVPL 3neurons Central thalamic radiationAscending tractsSpinothalamic tract （Spinal lemniscus）3. Trigeminothalamic tract The trigeminal nerve enters the brainstem laterally in the midpons. Some of its primary fibers descend as the spinal tract of n.V. Some second-order fibers arising from the principal sensory nucleus and spinal nucleus of n.V decussate to form the anterior trigeminothalamic tract, which is located between the medial lemniscus and the spinothalamic tract in the pons and midbrain; nondecussating fibers form the posterior trigeminothalamic tract, located posterolaterally in the tegmentum. Both tracts of trigeminothalamic fibers terminate in the ventral posteromedial nucleus (VPM)of the thalamus.Ascending tracts Trigeminal ganglion1neuron Pontine nucleus of V 2neuronSpinal nucleus of V 2neuronTrigeminal lemniscus Spinal tract of trigeminal n. VPM 3neurons Central thalamic radiation Ascending tractsTrigeminothalamic tract （Trigeminal lemniscus）It conveys tactile, pain, and temperature impulses from the skin of the face, the mucous membranes of the nasal and oral cavities, and the eye, as well as proprioceptive information from the facial and masticatory muscles. 4. Lateral lemniscusIt is the auditory pathways receive afferent input from the cochlear nuclei located on the surface of the inferior cerebellar peduncle in the rostral medulla. It ascends as the lateral lemniscus. The fibers of the lateral lemniscus terminate in the inferior colliculus, which gives rise to the brachium of the inferior colliculus. The brachium terminates in the medial geniculate body of the thalamus.Ascending tractsIt transmits auditory impulses of both sides.The pyramidal tractIt originates from the cerebral cortex, descend successively through the internal capsule, crus cerebri, and basilar pons, terminate in the motor nuclei of the brain stem or the ventral horn and intermediate zone of the spinal cord. Descending tractsThe corticonuclear fibersThe corticospinal fibers The corticonuclear fibers terminate in the motor nuclei, influencing cranial nerve nuclei located within the brain stem. (1). The corticonuclear fibers(Corticonuclear tract)Nucleus of oculomotor nerve （III）Nucleus of trochlear nerve （IV）Nucleus of abducent nerve （VI） Nucleus of hypoglossal nerve （XII）Nucleus of facial nerve （）Nucleus ambiguus（, ）Accessory nucleus （）Nucleus of hypoglossal nerve （XII）It originates from the cerebral cortex, descend successively through the internal capsule, crus cerebri, and basilar pons. It continues as the pyramids of the medulla and cross the midline as the decussation at the junction between the brainstem and spinal cord, and then, enter the spinal cord.(2). The corticospinal fibers(corticospinal tract)About 80% of all fibers cross in pyramidal decussation of the lower medulla oblongata to the collateral side and descend in the posterior half of the lateral funiculus as the lateral corticospinal tract, which terminates directly to the anterior horn at all spinal levels.Lateral corticospinal tractThe lateral corticospinal tract is involved with movements of the distal upper and lower extremities (hands and feet) and, thus, has a key role in the execution of skilled movements.Anterior corticospinal tractThe remaining fibers run uncrossed as anterior corticospinal tract in the anterior funiculus. This tract terminates in the medial part of the ventral horn and intermediate zone of the spinal cord bilaterally, which provides anatomic linkages for coordinated activity of the axial and limb girdle musculature during postural movements. This tract is involved with voluntary movements associated withaxial muscles of the neck and trunk. spinal cordLimb m.Trunk m.lateral corticospinal tractanterior corticospinal tractspinal cordLimb m.Trunk m.anterior corticospinal tractlateral corticospinal tractThis can account for minimal lossof motor control of axial musculature following unilateral lesions to these tracts, inwhich limb control is profoundly affected.The lateral corticospinal tractis preferentially involved with movements ofthe distal upper and lower extremities (handsand feet) and, thus, has a key role in the executionof skilled movementsThe anterior corticospinal tractis preferentially involved with control of axialmuscles (neck, shoulder, and trunk)The reticular formation (RF) consists of a complex matrix of neurons that extends throughout the length of the brain stem. It consists of a diffuse yet organized network of nuclei and tracts (hence, the term reticular). The RF network consists of multipolar neurons with long ascending and descending axons, which have highly collateralized branches synaptically linked with interneurons into complex loops of circuits.It has widespread afferent and efferent connections with other parts of the CNS, which reflect its complex and multimodal functions. Reticular formationThe ascending reticular pathways include the reticular activating system, which is involved with sleepwake cycles and in modulating awareness. Descending reticulospinal tracts originate from the medullary and pontine reticular formation. These predominantly influence muscle tone and posture. Within the reticular formation a number of individual nuclei are recognized. Some functions are subserved, however, by more dispersed networks that do not correspond exactly to anatomically identified nuclei. It applies to the so-called respiratory and cardiovascular centers, which control respiratory movements and cardiovascular function.Cranial nerves IIIXII attach to the brain stem, their fibres either originating from, or terminating in, the cranial nerve nuclei.Ascending sensory systems pass through the brain stem terminating in the thalamus. First-order proprioceptive fibres in the dorsal columns relay in the dorsal column nuclei. Second-order fibres decussate to form the medial lemniscus. Spinothalamic fibres form the spinal lemniscus.Descending fibre systems both pass through the brain stem and originate within it.The corticospinal tract runs through the crus cerebri, the basal part of the pons and the medullary pyramid; 7590% of fibres cross in the pyramidal decussation to form the lateral corticospinal tract.The reticular formation controls the level of consciousness, the cardiovascular system and the respiratory system.Internal structure of the brain stem- summary