Anatomy of brainstem

BrainstemByDr Manah Chandra Changmai IMS

BrainstemLocated between the cerebrum and the spinal cord Provides a pathway for tracts running between higher and lower neural centers.

Consists of the midbrain, pons, andmedulla oblongata.

Each region is about an inch in length.Microscopically, it consists of deep gray matter surrounded by white matter fiber tracts.Produce automatic behaviors necessary for survival.Midbrain PonsMedullaobongata

Ventral surface of brain stemMidbrainPons Medullaoblongata

Ventral – Lateral ViewMidbrainCerebral pedunclesPonsBasis pontisMedulla

Vertical Columns of Cranial Nerves

Subdivisions of Vertical ColumnsMotor nucleiSomatic motorclosest to midlineeyes, tongueCN III, IV, VI, XIIBranchial motorLateral positionBranchial arches: chewing, expression, middle ear, pharynx, larynx, sternomastoic, trapeziusCN V, VII, XIN. ambiguus (IX, X)Visceral motorventral / ventrolateralParasympathetic: glands, smooth muscle, heart, lungs, GI above splenic flexureEdinger-Westfall (III)Sup. & Inf. salivatorySensory nucleiGeneral sensorylateral to branchial motorFace, sinuses, meningesAll modalitiesCN V mainlyAlso CN VII, IX, XVisceral sensorylateral to visceral motorTaste; cardiorespiratory, GI infoN. of the solitary tract (CN VII, IX, X)Special sensoryfurthest lateralBalance; hearingCN VIII (vestibular)CN VIII (cochlear)

MidbrainConnects pons and cerebrum with forebrainCruscerebriShortest brain stem,not more than2cm in length,lies in the posterior cranial Fossa.For descriptive purpose,divided intoDorsal tectum and right and left cerebralPeduncles.Each cerebral peduncles divide furtherinto ventral cruscerebri and a dorsalTegmentum by a pigmented lamina“ Substantianigra”Cerebral peduncles contains:-Descending fibers that go to the cerebellum via the pons-Descending pyramidal tractsRunning through the midbrain is the hollow cerebral aqueduct which connects the 3rd and 4th ventricles of the brain.Ventral – Dorsal OrganizationTectumBasisTegmentum

Superior colliculiThe roof of the aqueduct ( the tectum) contains the corpora quadrigemina2 superior colliculithat control reflex movements of the eyes, head and neck in response to visual stimuli2 inferior colliculithat control reflex movements of the head, neck, and trunk in response to auditory stimuliInferior colliculiCorpora quadregeminaSuperior and inferior colliculiseperated by cruciform sulcusSuperior colliculi larger and darker than inferior colliculi,the difference In colour due to superficial neurons inSuperior colliculi

Internal Structure of MidbrainCross section at two levelsLevel of inferior colliculus

Level of superior colliculusInternal structure Transverse section of midbrainCommon to both at inferior and superior colliculus:Cruscerebri (or basis pedunculi):- Consists of fibres descending from cerebral cortex. - Its medial one-sixth is occupied by coticopontinefibres from frontal lobe,lateral one-sixth fibres from temporal,occipital and parietal lobes,the intermediate two third by corticospinal and cortico- nuclear fibres.Substantianigra:- Present immediately behind and medial to basispedunculi. - It appears dark as neuron within it contain pigment. ( neuromelanin )

Cerebral aqueductBasis pedunculiSubstantianigraCruscerebri(cerebral peduncle)

Internal Structure of MidbrainCross section at inferior colliculus

Section at the level of inferior colliculusInferior colliculusInferior colliculus - large mass of grey matter lying in the tectum - Forms cell station in auditory pathway.Trochlear nucleus: - Lies in the ventral part of central grey matterMesencephalic nucleus of trigeminal nerve: - Lies in lateral part of the central grey matterMedial leminiscus: - Fibres of ventral spinothalamic tractSpinal leminiscus: - Fibres of lateral spinothalamic and spinotectal tract.Trigeminal leminiscusInferior colliculusTrochlear nerve(N)Mesencephalic nucleus of V cranial nerveMedial longitudinal fasciculus

Cross section atLevel of superior colliculusSection at the level of superior colliculusTwo large masses of grey matter seen at this levelSuperior colliculus in the tectum– Receives visual input from retina and frontaland occipital eye fields– Receives auditor input from inferior colliculus– Mediates audiovisual refflexesCommissure of superior colliculus– Connects two superior colliculusBrachium of superior colliculus– Pathway for fibres from superior colliculus toCortex

Section at the level of superior colliculus……contd.Cerebral aqueduct and periaqueductalgray matterRed nucleus in the tegmentum - Lies in the anterior part of the tegmentum,dorsomedial to the substantianigra- It is called because of reddish colour which is due to the presence of iron pigment in its neurons.Oculomotor nucleus - Related to the ventral part of central grey matterMedial longitundinal fasciculus– Vestibular fibres that coordinate eyemovements– Interconnects ocular motor CN 3, 4, 6Central tegmental tractSection at the level of superior colliculus……contd.Medial lemniscus– Spinal afferent tractSpinal lemniscus– Spinal afferent tractSubstantianigra– Receives GAGAergic input from caudate putamen– Projects dopaminergicfibres to caudate putamen– Projects nondopminergicfibres to thalamusCruscerebriSuperior colliculus

Superior colliculusEdingerwestfalnucleusOcculomotor nucleusRed nucleus– relay from cortex and cerebellum to spinal cord, inferior olive, reticular formation, cerebellumControls arm movement

Corticobulbar Fibers– Arise from precentral and postcentralGyri– May synapse directly on motor neuronsor indirectly via interneurons(corticoreticular fibers)– Innervate sensory relay nuclei– Innervate cranial nerve motor nucleibilaterally, with the exception of upperface division of the facial nucleus– Innervates the ipsilateral spinal nucleusof CN 11, which supplies thesternocleidomastoid muscle and thecontralateral spinal nucleus of CN 11,which innervates the trapezius muscle

PonsThe pons shows a convex anterior surface with prominent transversely running fibres. These fibres collect to form bundles,the middle cerebellar peduncles.Trigeminal nerve emerges from the anterior surface,at the junction between pons and middle cerebellar peduncle.The anterior surface of pons is marked in the midline by a shallow groove,thesulcusbasilariswhich lodges the basilar artery.PonssSulcusbasilaris

Subdivided into ventral and dorsal partVentral part of the pons containsPontine nuclei:

Recievescorticopontinefibres from frontal,temporal,parietal and occipital lobes of cerebrumThe efferent fibres form the transverse fibres of pons.It has been estimated that there are about twenty million neurons in pontinenuclei.Most of them are glutaminergic.Vertically running corticospinal and corticopontinefibres.Transversely running fibres arising in pontine nucleiPontine nuclei

Dorsal part of ponsMidponsThe dorsal part of the pons may be regarded as continuation of the part of the medulla behind the pyramids.Superiorly continous with the tegmentum of the midbrain.

Occupied predominately by reticular formation

Posterior surface help to form floor of fourth ventricle

The dorsal part is bounded laterally by inferior cerebellar peduncle in the lower part of the pons and superior cerebellar peduncle in upper part.DORSAL PARTUpper pons

Dorsal surface of ponsSix ascending tract1 Dorsal and ventral cochlear nuclei – Receives auditory input from the cochlea through CN 82 Trapezoid body – Formed by decussating fibres of the ventral cochlear nuclei3 Superior olivary nucleus – Auditory relay nucleus that receives input from the cochlear nuclei and contributes to lateral lemniscus 4 Lateral lemniscus» Auditory pathway that conducts mostcontralateral cochlear input 5 Medial lemniscus» Spinal afferent pathway 6 Spinal lemniscus» Spinal afferent pathway

4th VentricleConnection of pons to cerebellumRestiform body (inf. cerebellar peduncle)Middle cerebellar peduncleMedial lemniscusAscending 2nd order sensory neuronsDescending upper motor neurons

Section through lower part of the ponsAbducent nucleus of CN 6• Lateral gazeDorsal and ventral cochlear nuclei of CN8

Medial, lateral and superior vestibularnuclei of CN 8• Receive proprioceptive input from vestibularsystems and cerebellum• Projects to cerebellum and medial longitudinalfasciculusSpinal trigeminal tract of CN 5

Facial nucleus of CN 7 • Gives rise to fibres that innervate the muscles offacial expressionSuperior olivary nucleus– Auditory relay nucleus that receives inputfrom the cochlear nuclei and contributesto lateral lemniscus

Cranial Nerves of Lower PonsVestibular Nuclei Pure sensory  lateral location Balance

Cranial Nerves of Lower PonsAt a slightly higher levelAbducens N. nucleusAbduction of eyeLongest, most vulnerable CNFacial N. nucleusMuscles of face

Mid Pons4th VentricleMiddle cerebellar peduncleCorticospinal tract,corticobulbar tract, corticopontine fibersDescending fibers

Mid PonsLateral lemniscusTrapezoid bodyfibers from dorsal column (position and vibration)Medial leminiscusfibers from dorsal column (position and vibration)Pontine nucleiTrapezoid body :transverse fibers in pontinetegmentum

Mid PonsMedial lemniscusfibers from dorsal column (position and vibration)Motor trigeminal nucleusTrigeminal tractpain, temperature, touch from contralateral facePrincipal trigeminal sensory nucleusCranial nerve nuclei and Lemniscal sensory system – in tegmentum of the pons

Section through upper part of ponsSuperior cerebellar peduncle

Principal sensory nucleus of CN 5– Receives discriminative tactile and pressuresensation from face, terminates in thalamusLateral lemniscus» Auditory pathway that conducts mostcontralateral cochlear inputTrapezoid body– Formed by decussating fibres of theventral cochlear nuclei

Upper PonsPeriaqueductal gray matterMedial longitudinal fasciculusSuperior cerebellar peduncledecussationTransverse ponto-cerebellar fibers

Upper PonsPediculopontine NucleusLocus ceruleusParabrachial NucleusSome neurons release acetylcholine Other neurons release glutamateThey assist in learning and voluntary motor control, e.g. locomotion, saccadic e

External structure of medullaMost inferior region of the brain stem.

Becomes the spinal cord at the level of the foramen magnum.

Medulla is broad above ,joins with pons narrow below, continous with spinal cordLength is about 3cm, width is about 2cm at its upper endSurfaces shows series of fissures

Posterior median fissureMedulla oblongataSpinal cord

External surface of medullaVentral surface of medulla oblongata containsPyramid

elevation between anterior median and anterolateralsulcusFormed due to decussation of corticospinalfibres.Olive

Oval swelling between anterolateralposterolateralsulcus,half an inch longProduced by large mass of gray matter called inferior olivary nucleusOlivePyramid

PyramidOlive Anterolateral fissureAnterior median fissure

Posterior part of medulla oblongataThe posterior part of medulla containsFasciculus gracilis medially ending in rounded elevation ,called nucleus gracilisFasciculus cuneatus laterally ending in roundedelevation,callednucleus cuneatusPosterior part of the medulla forms the floor of the fourth ventricleTuberculumcinereum, longitudinal elevation in the lower part of medulla lateral to fasciculus cuneatus.

DORSAL SURFACE OF MEDULLA OBLONGATAFloor of fourth ventricleObexGracile tuberclePosterior median sulcusPosterior median fissureCuneate tubercle

Anatomy of brainstem

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Anatomy of brainstem