ANATOMY OF THE

BY L. S. K

( Ph.D. In View)

DEPARTMENT OF HUMAN ANATOMY Brainstem Located between the cerebrum and the  Provides a pathway for tracts running between higher and lower neural centers. Pons Consists of the midbrain, pons, and . Each region is about an inch in Medulla length. oblongata  Microscopically, it consists of deep gray matter surrounded by fiber tracts. Produce automatic behaviors necessary for survival.

Vertical Columns of Cranial Nerves Roots DEVELOPMENT DEVELOPMENT of the brain stem

Midbrain: The midbrain develops from mesencephalon. Cells within the midbrain multiply continually and be compressed to form cerebral aqueduct. Pons: The pons develops from the anterior part of the , but it also receives a cellular contribution from alar part of the myelencephalon. Medulla: develops from the caudal myelencephalic part of the rhombencephalic vesicle

Midbrain

 Connects the pons and with the forebrain.  It is about 0.8 inch(2cm) in length  The midbrain is traversed by a narrow channel called cerebral aqueduct filled with CSF.  Passes through the tentorial notch. RELATIONS  Laterally are  Parahippocampal gyri, Optic tracts, Posterior cerebral artery, Basal vein, Trochlear nerve and Geniculate bodies  Anteriorly to interpeduncular structures  Posteriorly  To the splenium of corpus callosum, great cerebral vein, pineal body, posterior ends of the right and left thalami. STRUCTURE OF MIDBRAIN EXTERNAL FEATURES

Structure of Midbrain EXTERNAL FEATURES

 The midbrain comprises two lateral halves called- Cerebral peduncles; which is again divided into 1. anterior part- Crus cerebri 2. posterior part -Tegmentum by a pigmented band of gray matter, substantia nigra

 The central narrow cavity is called the cerebral aqueduct or aqueduct of Sylvius, which connects the 3rd and 4th ventricles.

 The tectum is the part of the midbrain posterior to the cerebral aqueduct; it has four small surface swellings referred to previously; these are two superior and two inferior colliculi.

TECTUM & TEGMENTUM ANTERIOR SURFACE  Anteriorly, it presents two large bundles of fibers, one on each side of the midline, called crus cerebri.

 The oculomotor nerve emerges from the medial aspect of the crus of the same side

 The crus cerebri bounds the interpeduncular fossa (posterior perforated substance ) on either side.

POSTERIOR SURFACE  Posteriorly, the midbrain presents four rounded swellings called colliculi- One Superior and inferior colliculi one on each side.  Each colliculus is laterally related to a ridge called brachium. o Superior and inferior brachium arises from respective colliculi o Superior brachium connects the to lateral geniculate body and the optic tract o Inferior brachium connects the inferior colluculus to medial geniculate body o In the midline below the inferior colliculus, the trochlear nerve emerges which then winds round the side of the midbrain to reach its ventral aspect

Lateral view INTERNAL STRUCTURE Transverse section at the level of Superior Colliculi  Superior colliculi  Substantia nigra  Oculomotor nucleus  Pretecta nucleus   Mesencephalic nucleus of trigeminal n.  Edginger-westphal nucleus Tracts Motor  Corticospinal  Corticonuclear  Temporopontine  Frontopontine  Medial longitudinal fasciculas  Decussation of

Sensory  Trigeminal  Spinal  Medial

Transverse Section at the level of Inferior Colliculi

 Substantia nigra- lamina of made up of deeply pigmented cells, concerned with muscle tone  Troclear nucleus  Mesencephalic nucleus of trigeminal nerve- receives proprioceptive mpulses from muscles of mastication, facial and ocular muscles and the teeth  Inferior colliculus

Tracts Motor  Corticospinal  Corticonuclear  Temporopontine, parietopontine & occipitopontine  Frontopontine  Medial longitudinal fasciculus Sensory  Lateral  Trigeminal  Spinal  Medial lemnisci  Decussation of superior cerebellar peduncles

Blood Supply

 Artery –  posterior cerebral artery  superior cerebellar artery  basilar artery  Veins – Drained by basal or great cerebral veins

PONS

 It is situated anteriorly to the cerebellum measuring about 1 inch in length.  Connects the medulla oblongata to the midbrain.  Its also connects two cerebellar hemispheres and its name comes from this bridge like appearance. FUNCTIONS OF PONS Arousal Controls autonomic functions Relays sensory information between the cerebrum and cerebellum Sleep Maintaining posture

24 External Features

 Has 2 surfaces,  VENTRAL and  DORSAL Anterior surface of Pons Pons has a convex anterior surface marked by transversely running fibers which laterally form a bundle called middle .

Main Features:  The trigeminal nerve (has 2 roots, motor and sensory) emerges from the anterolateral surface at its junction with middle cerebellar peduncle.  Presents a basilar sulcus in the midline which lodges basilar artery  In the groove between Pons and the medulla oblongata, there emerge, from medial to lateral, abducent, facial and vestibulocochlear nerves.

Posterior Surface  Triangular in shape and form the superior ½ of the floor of the fourth ventricle.  Laterally bounded by the Superior cerebellar peduncles.  Posterior surface contains median sulcus which is bounded by madial eminence on both sides.  Inferior end of medial eminence is slightly expanded to form facial colliculus, which is produced by facial nerve root.  The upper end of sulcus limitans presents a bluish-gray coloration called substantia ferruginosa.  Area vestibule lies lateral to sulcus limitans. Structure of Pons

 Posterior part- Tegmentum

 Anterior part- Basis pontis traversed by running fibers of Trapezoid body. Transverse Section Through the Cranial Part Transverse Section Through the Cranial Part  - It is situated in the most anterior part of the tegmentum  THE LATERAL and SPINAL LEMNISCI lie at the lateral extremity of the medial lemniscus  MOTOR NUCLEUS OF TRIGEMINAL N.- situated beneath the lateral part of the fourth ventricle within the  SENSORY NUCLEUS OF TRIGEMINAL N.- situated on the lateral side of the motor nucleus and is continuous inferiorly with the nucleus of the spinal tract.   TRAPEZOID BODY- made up of fibers derived from the cochlear nuclei and the nuclei of the trapezoid body. They run transversely in the anterior part of the tegmentum Tracts Motor  Corticospinal  Corticonuclear  Transverse pontine fibers  Medial longitudinal fasciculas Sensory  Lateral  Spinal  Medial lemnisci

Transverse section through the Caudal part Transverse section through the Caudal part

 Medial lemniscus (accompanied by the spinal and lateral lemnisci)  Facial nucleus-lies posterior to the lateral part of the medial lemniscus. The fibers of the facial nerve wind around the nucleus of the abducent nerve  Abducent nucleus  Medial longitudinal fasciculus- situated beneath the floor of the fourth ventricle on either side of the midline  the main pathway that connects the vestibular and cochlear nuclei with the nuclei controlling the extraocular muscles (oculomotor, trochlear, and abducent nuclei).  Medial vestibular nucleus- lateral to the abducent nucleus and is in close relationship to the inferior cerebellar peduncle  Spinal nucleus of trigeminal nerve- and its tract lie on the anteromedial aspect of the inferior cerebellar peduncle  Trapezoid body- made up of fibers derived from the cochlear nuclei and the nuclei of the trapezoid body. They run transversely in the anterior part of the tegmentum  Pontine nuclei Tracts Motor  Corticospinal  Corticonuclear  Transverse pontine fibers  Medial longitudinal fasciculas

Sensory  Spinal tract of trigemial nerve  Lateral  Medial lemnisci

Blood Supply MEDULLA OBLONGATA External structure of medulla

Most 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 cord

Length is about 3cm, width is about 2cm at its upper end

Surfaces shows series of fissures .Anterior median fissure .Posterior median fissure Medulla oblongata. A: Anterior view. B: Posterior view EXTERNAL FEATURES VENTRAL DORSAL  Pyramid  Posterior median sulcus  Olive  Postrolateral sulcus  Anterior median fissure.  Gracilis tubercle  Anterolateral/pre-olivary  Cuneate tubercle sulcus  Fasciculus gracilis  Post olivary sulcus  Fasciculus cuneatus  Rootlets of CN IX-XII External surface of medulla

Ventral surface of medulla oblongata contains Pyramid •Elevation between anterior median and anterolateral sulcus •Formed due to decussation of corticospinal fibres. Olive •Oval swelling between anterolateral posterolateral sulcus,half an inch long •Produced by large mass of gray matter called

The posterior part of medulla contains Fasciculus gracilis medially ending in rounded elevation ,called nucleus gracilis

Fasciculus cuneatus laterally ending in rounded elevation,called nucleus cuneatus Posterior part of the medulla forms the floor of the fourth ventricle

Tuberculum cinereum, longitudinal elevation in the lower part of medulla, lateral to fasciculus cuneatus.

Internal Structure of Medulla

Cross section at three levels

Level of pyramidal decussation

INTERNAL FEATURES Internally, the medulla is generally studied at the following levels;

 At the level of the pyramidal decussation  At the level of the  At the level of the olivary nucleus  At level just below the pons LEVEL OF PYRAMIDAL DECUSSATION

Ascending tract Descending tract

 Fasciculus gracilis  Corticospinal tract Fasciculus cuneatus  Rubrospinal tract   Olivospinal tract  Spinotectal tract   Spino-olivary tract Transverse sections of the medulla oblongata. Level of decussation of the pyramids. LEVEL OF SENSORY DECUSSATION Features  Nucleus gracilis & cuneatus are much larger, no longer continuous with central grey matter.  Internal arcuate fibre crossing, constituting the lemniscal decussation.  Lowest part of inferior olivary nucleus  Medial accessory olivary nucleus  Lateral olivary nucleus  Arcuate nuclei lying anterior to pyramids

Transverse sections of the medulla oblongata. Level of decussation of the medial lemnisci. LEVEL OF OLIVARY NUCLEUS FEATURES  Medial lemniscus very prominent, pyramids, spinal nucleus, trigeminal & reticular formation.  Inferior cerebellar peduncle connect medulla to cerebellum. Posteriorly, medulla forms floor of 4th ventricle  CN nuclei in relation to the floor of 4th ventricle  Pontobulbar body lies on dorsolateral aspect of the inferior cerebellar peduncle. LEVEL OF OLIVARY NUCLEUS(CONT’D) Ascending Tracts Descending Tracts  Medial lemniscus, which  Pyramids forms an anteroposterior  Tectospinal tract L-shaped band next to  Vestibulosinal tract midline  Rubrospinal tract  Spinothalamic tract  Spinal tract of trigeminal  Spinocerebellar tract nerve  Spinotectal tract A

Transverse sections of the medulla oblongata at the level of the middle of the olivary nuclei(A) and the superior part of the olivary nuclei just inferior to the pons (B). CONNECTIONS OF THE INFERIOR OLIVARY COMPLEX Afferent Fibres Efferent Fibres  The main afferents of  Efferents are to the inferior olivary cerebellar cortex nucleus are from the through cerebral cortex and olivocerebellar tract. the spinal cord  Nucleus of olivospinal tract is a relay station on cortico- olivocerebellar & spino-olivo- cerebellar pathways CONNECTIONS OF ARCUATE NUCLEI AND PONTOBULBAR BODY  Arcuate nuclei are regarded as displaced pontine nuclei, cortical fibres reach them through Pyramids.  They relay to the cerebellum by fibres via anterior external arcuate fibres to the ICP and fibres of Striae medullares to the floor of 4th ventricle  Fibres from arcuate nuclei end in the of the cerebellum  Fibres from pontobulbar body form the circumolivary bundle & join the arcuate nuclei to ICP of opposite side level cavity nuclei Motor tract Sensory tract

Decussation central canal Nucleus Decussation Spinal tract of of pyramids gracilis, of corticospinal V, posterior cuneatus, tracts, spinocerebellar spinal pyramids tract, lateral nucleus of spinothalamic cranial nerve V, tract, anterior accessory spinocerebellar nucleus tract Decussation Central canal N.gracilis, pyramid Decussation of of medial n. medial lemnisci cuneatus, lemnisci, spinal F.gracilis, nucleus of F.cuneatus, cranial nerve V, spinal tract of accessory cranial nerve nucleus, V, PSC tract, hypoglossal LST, ASCT N. level cavity nuclei Motor tract Sensory tract

Olives, fourth Inferior olivary pyramid Medial inferior ventricle N, spinal longitudinal cerebellar nucleus of fasciculus, peduncle cranial nerve V, tectospinal vestibular tract, medial nucleus, lemniscus, Glossopharyng spinal tract of eal N, vagal cranial nerve N., hypoglossal V, nucleus, lateralspinothal nucleus amic ambiguus, tract, anterior nucleus of spinocerebellar tractus tract solitarius Just Fourth Lateral pyramid No major inferior to ventricle vestibular changes in pons nucleus, distribution of cochlear nuclei gray and white matter

CLINICAL ANATOMY  MILLARD GUBLER SYNDROME  A unilateral lesion in the lower part of the pons result in paralysis of the facial nerve on the side of the lesion, and paralysis of the limbs, Hemiplegia, on the opposite side.  ARGYLL-ROBERTSON PUPIL  are bilateral small pupils that reduce in size on a near object (they “accommodate”), but do not constrict when exposed to bright light (they do not “react” to light)  In general, pupils that “accommodate but do not react” are said to show light-near dissociation TUMOR OF THE MIDBRAIN BLOCKING THE CEREBRAL AQUEDUCT • Also known as dorsal midbrain syndrome and vertical gaze palsy, • Is an inability to move the eyes up or down, caused by a tumor of the pineal gland which compresses the vertical gaze center at the rostral interstitial nucleus of medial PERINAUD’S longitudinal fasciculus SYNDROME WEBER’S SYNDROME

. Weber's syndrome (superior alternating hemiplegia) is a form of stroke characterized by the presence of an ipsilateral oculomotor nerve palsy and contralateral hemiparesis or hemiplegia. . Caused by midbrain infarction as a result of occlusion of the paramedian branches of the posterior cerebral artery or of basilar bifurcation perforating arteries BENEDIKT’S SYNDROME

• Benedikt's syndrome or paramedian midbrain syndrome, is a rare type of posterior circulation stroke of the brain • It is characterized by the presence of an oculomotor nerve (CN III) palsy and cerebellar ataxia including tremor. • Structures affected include CNIII nucleus, Red nucleus, corticospinal tracts, brachium conjunctivum, and the superior cerebellar peduncle decussation.  Medulla has the locations of respiratory and vasomotor centers. Thus an injury to the medulla is therefore usually fatal.  Bulbar paralysis- xterized by paralysis of muscles supplied by last 4 CN.  Pseudobulbar palsy- a supranuclear type of paralysis of bulbar muscles as a result of cerebral arteriosclerosis.  Common vascular lesions involving the medulla are thromboses of the posterior inferior cerebellar artery and that of the vertebral artery Syndrome Affected structures Clinical effect produced

MMS(Dejerine’s anterior • Corticospinal • Contralateral hemiplegia bulbar syndrome) fibres(Pyramids) • Ipsilateral paralysis of • tongue • Medial lemnicus • Contralateral loss of sensation of fine touch,sense of movement and position PICA syndrome( Wellenberg • Inferior cerebellar Loss of equilibrium(ataxia) & syndrome) peduncle giddiness • Lateral spinothalamic tract Loss of sensation of & temp over conlateral half of the body • Spinal nucleus and tract of Loss of sensation of pain & trigerminal nerve temp over ipsilateral half of the head & face • Dysphagia, Dysarthria • Vomiting, nystamus and vertico • Descending autonomic fibres Medullary tegmental Lession at pontomedullary Combination of medial & Paralysis( Babinski-Nageotte junction involving all the lateral syndromes Syndrme) structures above Thank You