3 Outline________________________________________________________________________IntroductionDevelopmentBasal and Alar Plates____________________________________________________________________External FeaturesAnterior, Lateral & Posterior MedullaVasculatureInternal Anatomy of the MedullaAscending Pathways Summary / Descending Pathways SummaryCaudal Medulla: Levels of the Motor (Pyramidal) & Sensory DecussationsMidmedullary LevelRostral Medulla and Pons-Medulla JunctionInternal Vasculature of the Medulla and Medullary SyndromesTonsillar Herniation_________________________________________________________________________
4 The Medulla Oblongata Myelencephalon Caudal Brainstem.Foramen Magnum - Pons.Cavity of the Medulla consists ofa Narrow, caudal part = continuation of the central canal of the cervical spinal cord,a Flared, rostral portion, which is the medullary part of the fourth ventricle.The blood supply from the vertebral arteries.
5 WHY MEDULLA IS IMPORTANT?? Though its size is modest(0.5% of total brain weight)All the tracts passing to or from the spinal cord traverse the medulla,7/12 cranial nerves (VI to XII) are associated with the medulla or the pons-medullary junction.Also, the medullary reticular formation contains cell groups that influence heart rate and respiration.
6 Development1The basic structural plan of the medulla is an elaboration of that seen in the spinal cord.
8 The Obex2The obex (from the Latin for barrier) is the point in the caudal medulla posteriorly b/w fourth ventricle & the central canal of the spinal cord.The decussation of sensory fibers happens at this point.
10 3 Development The Basal and Alar plates give rise to specific nuclei each brainstem level is characterized by appearance of specific structures
11 3 Basal plate the basal plate give rise to hypoglossal nucleus ([GSE] cells)dorsal motor vagal nucleus ( [GVE] cells)inferior salivatory nucleus ( [GVE] cells)nucleus ambiguus ( [SVE] cells).
12 3 Alar plate Gives rise to: the vestibular / cochlear nuclei [SSA]the solitary nucleus [GVA] [SVA])the spinal trigeminal nucleus [GSA]caudal to the obex give rise to the gracile and cuneate nuclei.Rostral to the obex, form the nuclei of the inferior olivary complex.
13 3 ascending and descending fibers are traversing the medulla. the pyramids prominent bundle of axons ventrally.
15 External Features Anterior Medulla 4characterized by ananterior median fissure, two laterally adjacent longitudinal ridgesthe pyramids, corticospinal fibersthe olive (inferior olivary eminence)the preolivary sulcus (shallow groove b/w the pyramid and the olive.hypoglossal nerve (XII) Rootlets exit the medulla via preolivary sulcusThe abducens nerve (VI) emerges at the pons-medullary junction, generally in line with XII rootlets.
17 Lateral Medulla shallow trough 5On the lateral aspect of the medulla, a, thepostolivary sulcus, is located betweenRestiform body andOLIVE = large eminence formed by the underlying inferior olivary nucleus
18 Lateral Medulla shallow trough 5emerge from the pons-medulla jun.(CP angle) as clinically regarded posterolaterally7th VII (Facial nerve)8th VIII (Vestibulocochlear nerve)Indeed, a vestibular schwannoma (incorrectly, referred to as an acoustic neuroma) is a tumor of the vestibular portion of the 8th CN at the CP angle.emerge from the postolivary sulcus Laterally9th IX (glossopharyngeal), 9th10th X (vagus), 10th11th XI (accessory) 11th the so-called medullary part of11th is made up from cells in the upper cervical spinal cord, ascend through the foramen magnum, exit skull via the jugular foramen along with the 9th & 10th
20 Lateral Medulla6Fibers of the spinal trigeminal nucleus and tract with superficial location and formthe trigeminal tubercle (tuberculum cinereum)Rostral to the obex, these fibers are deeper & internal to a progressively enlarging restiform body.
22 7 Posterior Medulla characterized by the restiform body Gracile & Cuneate fasciculiGracile & Cuneate tubercles formed by underlying nuclei.the restiform bodyprominent elevation Rostrolateral to the gracile and cuneate tuberclesjoin the juxtarestiform body In the base of the cerebellum, to form the inferior cerebellar peduncle.
24 Bran. from AICA (bran. from basilar artery) Vasculature8In general, the entire blood supply arises from branches of the vertebral arteries.The exceptions arethe choroid plexus out of the foramen of Luschkaand the adjacent cochlear nucleiserved byBran. from AICA (bran. from basilar artery)
25 8 Vasculature Medially by Anterolaterally by Posterolaterally by (ASA) anterior spinal arteryAnterolaterally by(VA) vertebral small branches from thePosterolaterally by(PSA) posterior spinal artery Caudal to the obex(PICA) posterior inferior cerebellar artery rostral to the obex
27 Internal Anatomy of the Medulla Ascending Pathways Summary 9the spinal cord GM (anterolateral system, posterior and anterior spinocerebellar tracts, and so on)posterior root ganglion cells (gracile and cuneate fasciculi) continue into the medullaanterolateral systemspinoreticular fibers,spinomesencephalicspinothalamic fibers convey pain and temperature input.Posterior columns (synapse in the medulla), but medial lemniscus continues rostrally to carry the tactile and vibratory information.
31 11 ~ 90% of corticospinal fibers cross the anterior midline to form Caudal Medulla: Level of the Motor Decussation (Pyramidal Decussation) 1/611~ 90% of corticospinal fibers cross the anterior midline to formthe contralateral lateral corticospinal tract of the cord
34 12Caudal Medulla: Level of the Motor Decussation (Pyramidal Decussation) 2/6Posteriorly, at this levelthe Gracile and Cuneatenuclei first appear in their respective fasciculifasciculi = the posterior (or dorsal) columns,their nuclei = the posterior column nuclei.
36 Caudal Medulla: Level of the Motor Decussation (Pyramidal Decussation) 3/6 13Laterally, at this levelthe spinal trigeminal tractvisible trigeminal tubercle or tuberculum cinereum) is located on the lat. medullary surface.Internal to the spinal trigeminal tract is the spinal trigeminal nucleus, pars caudalis (Fig. 11-6).composed of primary sensory fibers that enter the brain mainly in the trigeminal nerve.This tract also receives fibers that originate from cranial nerves VII, IX, and X. (5,7,9,10)terminate on the spinal trigeminal nucleus, which, in turn, projects to the contralateral thalamus as the ventral trigeminothalamic tract.
38 14Caudal Medulla: Level of the Motor Decussation (Pyramidal Decussation) 4/6Laterally, at this levelthe anterolateral system ( spinoret./spinomesen./spinothal.)rubrospinal tractare found medial to the superficially locatedAnterior spinocerebellar tractsPosterior spinocerebellar tracts (Fig. 11-6).It is important to emphasize thatanterolateral system fibers (conveying pain and temperature input from the contralateral body)and spinal trigeminal tract fibers (conveying pain and temperature from the ipsilateral face)are located adjacent to each other throughoutthe lateral medulla.
40 The anterior medulla contains 15Caudal Medulla: Level of the Motor Decussation (Pyramidal Decussation) 5/6The anterior medulla containsthe most rostral part of the accessory nucleus (cranial nerve XI),the medial motor cell column of C1,and the medial longitudinal fasciculus and tectobulbospinal system.1 & 2 are seen at this level but do not extend into the medulla.At this level, the tectospinal fibers in the tectobulbospinal system are incorporated into the MLF & displaced laterally by the motor decussation compared with more rostral levels.
42 16Caudal Medulla: Level of the Motor Decussation (Pyramidal Decussation) 6/6The central gray surrounds the central canal of the medulla and containsthe caudal extremes ofthe hypoglossal (XII)and dorsal motor vagal nuclei (X)
44 Caudal Medulla: Level of the Sensory Decussation 1/11 17Cells of the posterior column nuclei(gracile and cuneate nuclei)give rise to axons that swing anteromedially, asinternal arcuate fibers,to cross the midline immediately rostral to the motor decussation (Fig. 11-5).This crossing of fibers at the midline constitutesthe sensory decussation,so named because it is the point at whicha major ascending sensory pathway(posterior column-medial lemniscus)crosses the midline.
47 Caudal Medulla: Level of the Sensory Decussation 2/11 18At this levelThe posterior columns = gracile and cuneate fasciculiare largely replaced by the gracile and cuneate nucleiFibers conveyingtactile and vibratory sensationsfrom lower (the gracile n.) and upper (cuneate n.) levels of the body terminate, respectively, in these nuclei.The axons of these cells, in turn, form theinternal arcuate fibers,which cross the midline as thesensory decussation to formthe medial lemniscus on the contralateral side
48 Caudal Medulla: Level of the Sensory Decussation 3/11 18The posterior columns =gracile and cuneate fasciculinucleiinternal arcuate fibers,(sensory decussation)the medial lemniscuson the contralateral side
50 Caudal Medulla: Level of the Sensory Decussation 4/11 19At this levelInformation from lower extremities (gracile cell axons) is conveyed in the anterior part of the medial lemniscusinformation from the upper extremities (cuneate cell axons) is conveyed in the posterior part of the medial lemniscus (see Fig ).GMLA vs CLUP :GMLA = Gracille Medial in cord senses Lower extr. Being Ant. In medial lemn.CLUP = Cuneate Lateral in cord senses Upper extr. Being Post. In medial lemn.
52 Caudal Medulla: Level of the Sensory Decussation Lateral 5/11 20The spinal trigeminal tract and nucleus (pars caudalis) maintain their position in the lateral medulla.caudalis = located caudal to the level of the obex.
54 Caudal Medulla: Level of the Sensory Decussation Lateral 6/11 21Just medial to the spinal trigeminal nucleus, a small column of motor neurons, the nucleus ambiguus, appears (Fig. 11-8).The axons of these SVE cells travel in the glossopharyngeal (IX) and vagus (X) nerves. 9 & 10Fibers of the anterolateral system and rubrospinal tract are located in the anterolateral medulla (Fig. 11-8).The lateral reticular nucleus, a distinct cell group adjacent to the anterolateral system, receives spinal input and projects to the cerebellum.
56 Caudal Medulla: Level of the Sensory Decussation Anterior 7/11 22Structures at this level includethe pyramid,fibers of the hypoglossal nerve,the caudal end of the inferior olivary complexprincipal,medial accessory,posterior accessory nuclei.
57 Caudal Medulla: Level of the Sensory Decussation Anterior 8/11 22Hypoglossal (GSE) XIImotor neurons innervatethe ipsilateral half of the tongue.These course anterolaterallyalong the lateral edge ofthe medial lemniscus and pyramid.The inferior olivary nucleibecome larger at more rostral levels,receive input from a variety of areasproject primarily to the cerebellum.
59 Caudal Medulla: Level of the Sensory Decussation Anterior 9/11 23Internal to the pyramid, and along the midline from anterior to posterior, arethe medial lemniscus,tectobulbospinal fibers,medial longitudinal fasciculus (MLF)At this level, MLF are characteristically foundadjacent to the midlineanterior to structures of the central gray.
61 Caudal Medulla: Level of the Sensory Decussation 10/11 24Vagus (GVE )Xthe dorsal motor vagal nucleusProvidepreganglionic parasympathetic fibers tovisceromotor ganglia (autonomic ganglia),the postganglionic fibers of which innervate viscera in the thorax and abdomen.The solitary tract and nucleus (7,9,10)receive GVA and SVA (taste) input from cranial nervesVII, IX, and X.
63 Caudal Medulla: Level of the Sensory Decussation 11/11 25The 4th ventricle flares open at the level of the obex.The area postrema is an emetic (vomiting) center located in the wall of the ventricle at this level.Especially noticeable changes are enlargement of the inferior olivary complex and restiform body.
65 Midmedullary Level = Rostral to the obex 1/4 26dorsally4th ventricle medial floor structuresthe hypoglossal nucleusdorsal motor vagal nucleusthe vestibular nuclei ( lateral to the sulcus limitans) medial and inferior (or spinal) They receive input from cranial nerve VIII and interconnect with areas of the brain concerned with balance and eye movement.The solitary tract and nucleus characteristic position immediately inferior to the vestibular nuclei.
67 27 Midmedullary Level 2/4 Laterally Restiform Body a prominent elevation on the posterolateral aspect of the medullacontains posterior spinocerebellar, cuneocerebellar, olivocerebellar, reticulocerebellar, and other cerebellar afferents.join the juxtarestiform body In the base of the cerebellum, to form the inferior cerebellar peduncle.spinal trigeminal tract and nucleus (pars interpolaris / rostral to the obex) are internal to the restiform body
69 28 Midmedullary Level 3/4 Laterally Other structures are those seen more caudally.the nucleus ambiguus (9 & 10)the lateral reticular nucleusthe anterolateral system,anterior spinocerebellar tract,rubrospinal tractthe nucleus ambiguus contribute axons to cranial nerves IX and X, which innervate pharyngeal and laryngeal muscles, including those of the vocal folds.
71 29 Midmedullary Level 4/4 Anterolaterally the inferior olivary complex prominent at midmedullary levelscomposed of aprincipal olivary nucleus (large, saccular)medial accessory olivary nuclei (diminutive)posterior accessory olivary nuclei (diminutive)receive input from a variety of CNS nucleiproject primarily to the contralateral cerebellum (as olivocerebellar fibers) through the restiform body.
73 Rostral Medulla and Pons-Medulla Junction mid medulla structures + 30In the floor of the 4th ventricle,the prepositus (hypoglossal) nucleusthe inferior salivatory nucleusReplacing hypoglossal and dorsal motor vagal nucleiThe prepositus nucleus issmall, flattened cell groupeasily distinguished from the hypoglossal nucleus.The GVE cells of the inferior salivatory nucleus are located immediately inferior tothe medial vestibular nucleusand medial to the solitary tract and nucleus.
74 Rostral Medulla and Pons-Medulla Junction mid medulla structures + 30The medial and inferior (or spinal) vestibular nuclei are prominent at this level and are joined, in this plane of section, bythe posterior and anterior cochlear nucleithe restiform body withthe spinal trigeminal tract and the pars oralis Medial to it (rostral to the level of the hypoglossal nucleus)
76 Rostral Medulla and Pons-Medulla Junction 31Facial motor nucleus (SVE cells) appears anterolaterallytrapezoid body and superior olivary nucleus (auditory information) appear adjacent to the facial nucleus and the spinal trigeminal tract and nucleus.
77 Rostral Medulla and Pons-Medulla Junction 31The inferior olivary complex disappears, and the central tegmental tract, one source of input to the inferior olive, appears about where the latter cell group was located (Fig ).medial lemniscusshift anterolaterallyposteroanterior orientationAt the pons-medulla junction, oriented obliquelyAt the mid pons, it is horizontal
79 Reticular and Raphe Nuclei 32Reticulum = Latin word "little net" denotes mesh-like structures, diffuse and ill definedRaphe is a Greek word for "suture" or "seam." Thus, bilaterally symmetrical cell groups located directly adjacent to the midline.
80 Reticular and Raphe Nuclei Medullary RF function in the control of heart rate and respiration.Consequently,a sudden onset of central apnea,indicating damage to these respiratory areas,is often a prime early sign of medullary compression.32
81 Reticular and Raphe Nuclei Raphespinal fibersare especially important for the inhibition of pain transmission in the posterior horn of the spinal cord.Serotonin is the principal neurotransmitter? cholecystokinin-containing cells? enkephalin32
83 Internal Vasculature of the Medulla and Medullary Syndromes 33from branches of theVAASA ( all Ant.med. struct.)PICA (Rostral post.lat.)& its branch PSA (Caudal post) .
84 ASA & the medial medullary syndrome. 33ASA serves Medial structures of the medulla at all levels, includingthe pyramid,medial lemniscus,hypoglossal nucleus and rootsOcclusion of these to one side of the medial medulla may result in a pattern of deficits characteristic of the medial medullary syndrome.
85 ASA & the medial medullary syndrome. 33also known as the Dejerine syndrome.The deficits and corresponding structures damaged in this syndrome include acontralateral hemiparesis (pyramidal and corticospinal damage),contralateral loss of proprioception and vibratory sense (medial lemniscus),deviation of the tongue to the ipsilateral side when protruded (hypoglossal root or nucleus injury).
86 PSA & Posterior medullary syndrome 33The posterior medulla caudal to the obex served by branches of the PSAMajor structures in this area includethe posterior column (gracile and cuneate) nucleiand the spinal trigeminal tract and nucleus.Although rare, may producean ipsilateral loss of proprioception and vibratory sense on the body (posterior columns and nuclei)ipsilateral loss of pain and temperature sensation from the face (spinal trigeminal tract).
88 PICA and Lateral medullary syndrome 34PICA serves the entire posterolateral medulla Rostral to the obexIncluded in the territory served by this vessel areAnterolateral system,Spinal trigeminal tract and nucleus,Vestibular nuclei,Solitary tract and nucleus,Nucleus ambiguus.
89 PICA and Lateral medullary syndrome 34Vascular insufficiency of PICA (or blockage of one VA) gives rise to a characteristic set of sensory and motor deficits commonly calledlateral medullary syndrome,PICA syndrome, orWallenberg syndrome.
90 PICA and Lateral medullary syndrome 34PICA and Lateral medullary syndromeThe deficitscontralateral loss of pain and temperature sensation from the body (anterolateral system),ipsilateral loss of pain and temperature sensation from the face (spinal trigeminal tract and nucleus),some vertigo and nystagmus (vestibular nuclei),loss of taste from the ipsilateral half of the tongue (solitary tract and nucleus), andhoarseness and dysphagia (nucleus ambiguus or roots of cranial nerves IX and X) .? Horner syndrome (injury to hypothalamospinal fibers descending through the lateral medulla).
92 Tonsillar Herniation 1/3 it may have a profoundly negative impact on the medulla.The causes vary, examples includeposterior fossa mass: tumor / hrgposterior fossa surgery.lumbar puncture in a pt with a mass lesion.
93 Tonsillar Herniation 2/3 cerebellar tonsil downward extrusion into, and through, the foramen magnum rapid ICP.two mechanisms.mechanical injury ( compression)Vascular injury (infarction)
94 Tonsillar Herniation 3/3 The major concern in acute herniation isdamage to the ventrolateral reticular area of the medulla, which contains neurons that influence and control heart rate and respiration.Acute Manifestations:a sudden change in heart rate and respiration (Cheyne-Stokes with intermittent apnea),increase in blood pressure (hypertension),hyperventilation,rapidly decreasing levels of consciousness,and death.chronic Manifestations:slowly the patient suffers minimal neurologic consequences.
95 Synopsis of Clinical Points 1 7/12 cranial nerves exit from the medulla or medulla-pons junction; tumors in this confined space usually affect these nerves .Lesions of the motor (pyramidal) decussation may result in bilateral weakness of the extremities .Deficits in the medial medullary (or Dejerine) syndrome reflect damage to the structures in this area; these deficits are:ipsilateral deviation of the tongue,contralateral weakness of the extremities,and contralateral loss of proprioception/position sense .Occlusion of the anterior spinal artery or its penetrating branches may result in different patterns of deficits .
96 Synopsis of Clinical Points 2 the lateral medullary (or Wallenberg) syndromeHas characteristic Deficits.an alternating hemianesthesia,vertigo,nystagmus,dysarthria,and dysphagia .may be seen following occlusion ofthe vertebral arteryits major branch, the PICA .Tentorial herniation may result from:rapidly expanding lesion in the fourth ventriclelumbar puncture in a pt with a supratentorial mass .Tonsillar herniationcompresses the medulladamages cardiac and respiratory centers .Cheyne-Stokes respiration and apnea .
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