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Putamen and globus pallidus are separated by the external medullary lamina.

From deep to superficial, the order of structures of basal ganglia in horizontal section is as follows:

• Caudate nucleus (innermost)
• Internal capsule
• Globus pallidus internal (GPi)
• Internal medullary lamina
• Globus pallidus external (GPe)
• External medullary lamina
• Putamen
• External capsule
• Claustrum
• Extreme capsule
• Insular cortex (outermost)

A lesion in the subthalamic nucleus causes sudden, violent, involuntary movements confined to one side of the body, commonly affecting the proximal extremity musculature, a condition called hemiballismus. The movements are seen contralateral to the side of the lesion, i.e., involuntary movements of the right arm and leg are seen in the lesion of the left subthalamic nucleus and vice versa.

The medial surface of the thalamus does not form the inferior boundary of the third ventricle. It forms the lateral wall of the IIIrd ventricle.

The thalamus is an ovoid shape mass of grey matter that forms a relay station for all information passing to the cerebral cortex, basal ganglia, hypothalamus, and brainstem.

Relations of the thalamus:

• Anteriorly: Interventricular foramen
• Superiorly: It is covered by a sheet of white matter called stratum zonale. Above the stratum zonale lies the body of fornix and the ventricle
• Posteriorly: The posterior end is expanded to form the pulvinar, which overhangs above the superior colliculus.
• Inferiorly: Plane connecting the hypothalamic sulci
• Medially: Lateral wall of the third ventricle
• Laterally: Posterior limb of the internal capsule

The image below demonstrates the lateral and medial relations of the thalamus.

The marked structure ‘X’ is thalamus. Internal medullary lamina is a Y-shaped sheet of white matter dividing the thalamus to 3 parts:

• Anterior nuclear groups
• Medial nuclear groups
• Lateral nuclear groups

External medullary lamina is a sheet of white matter on the lateral surface of the thalamus that separates the thalamus from the reticular nucleus.

The intralaminar nuclei lie embedded within the internal medullary lamina and the midline nuclei lie close to the lateral walls of the third ventricle.

The thalamus plays an important role in sensory and motor integration. Input and output of the thalamus:

• Pre-cortical input- All sensory system (except olfactory system)
• Cerebral cortex input- Largest input (from modified pyramidal cells of layer VI )
• Projection fibers to other areas-
• Cerebral cortex (most fibers)
• Basal nuclei and hypothalamus (few fibers)

The largest subdivision of anterior thalamic nuclei is the anteroventral nucleus (and not the anteromedial nucleus).

The anterior thalamic nuclei have 3 subdivisions—anteroventral nucleus, anteromedial nucleus and anterodorsal nucleus.

• Major input: Mamillothalamic tract from the mammillary nuclei of the hypothalamus.
• Major cortical output: Anterior limbic area, cingulate, and the parahippocampal gyrus
• Major function:
• Regulation of alertness and attention
• Acquisition of memory

The largest division of the affected structure i.e. the thalamus is the lateral thalamic nuclei.

The lateral thalamic nuclei are further divided into the dorsal and ventral nuclei, as shown below.

The ventral posteromedial nucleus receives inputs from the trigeminothalamic pathway.

The medial geniculate body receives auditory input from both the ears, but predominantly from the contralateral ear (not ipsilateral ear).

The marked structure is the thalamus. The reticular nucleus of the thalamus does not project to the neocortex. Its output is mainly to the other thalamic nuclei.

All other thalamic nuclei send output to the neocortex.

Lesion of the supraoptic nucleus of the hypothalamus causes inhibition of the synthesis of vasopressin leading to diabetes insipidus.

The hypothalamus is a part of the diencephalon that lies below the thalamus.

• Anteriorly, the preoptic area is included in the hypothalamus.
• Posteriorly, it merges with the tegmentum of the midbrain.
• Laterally, it is bounded by the internal capsule.

Microscopically, the hypothalamus is divided into multiple nuclei.

Tuber cinereum is not a part of the epithalamus. It is a part of the hypothalamus. The epithalamus consists of:

• Anterior and posterior paraventricular nuclei
• Medial and lateral habenular nuclei
• Stria medullaris thalami
• Posterior commissure
• Pineal gland

The red nucleus is situated at the level of the superior colliculus in the midbrain.

Level Cavity Nuclei

Motor tract

Sensory tra ct

Inferior colliculus Cerebral aqueduct

Inferior colliculus, substantia nigra, trochlear nucleus, mes encephalic nucleus of V nerv e

Corticospinal and corticonucl ear tracts, temporopontine, fr ontopontine, medial longitud inal fasciculus

Lateral, trigeminal spinal, an d medial lemnisci, decussatio n of superior cerebellar pedu ncles

Superior colliculus Cerebral aqueduct

Superior colliculus, substanti a nigra, trochlear nucleus, m esencephalic nucleus of V ner ve, oculomotor nucleus, Edin ger- Westphal nucleus, red n ucleus

Corticospinal and corticonucl ear tracts, temporopontine, fr ontopontine, medial longitud inal fasciculus, decussation o f rubrospinal tract

Trigeminal spinal and medial lemnisci

Lateral lemniscus is not seen at the level of the superior colliculus, therefore it is not susceptible to injury in this case. It is a part of the auditory pathway and ends at the level of the inferior colliculus of the midbrain.

Level Cavity Nuclei

Motor tract

Sensory tra ct

Superior colliculus Cerebral aqueduct

Superior colliculus, substatia nigra, oculomotor nucleus, E dinger- Westphal nucleus, m esencephalic nucleus of V ner ve

Corticospinal and corticonucl ear tracts, temporopontine, fr ontopontine, medial longitud inal fasciculus, decussation o f rubrospinal tract

Trigeminal, spinal and media l lemnisci

Inferior colliculus Cerebral aqueduct

Inferior colliculus, substatia nigra, trochlear nucleus, mes encephalic nucleus of V nerv e

Corticospinal and corticonucl ear tracts, temporopontine, fr ontopontine, medial longitud inal fasciculus

Lateral, trigeminal spinal and medial lemnisci, decussation of superior cerebellar pedun cles

The ventral tegmental decussation in the midbrain is due to the rubrospinal tract. The red nucleus is situated at the level of superior colliculus.

• It receives afferents from the corticorubral fibers in the cortex and the cerebellorubral fibers
• in the cerebellum.
• It sends out efferent fibers as the rubrospinal tract.
• It decussates as ventral tegmental decussation at the level of the superior colliculus and
• descends to the spinal cord.

The midbrain has four decussations:

• At the level of the superior colliculus
• Ventral tegmental decussation of the rubrospinal tract
• Dorsal tegmental decussation of the tectospinal tract
• At the level of the inferior colliculus
• Decussation of superior cerebellar peduncles
• Decussation of trochlear nerve

Fibres passing through the most medial part of crus cerebri are frontopontine fibers. The crus cerebri contains important descending tracts:

• Middle two-thirds: Corticospinal and corticonuclear fibers
• Medial part: Frontopontine fibers
• Lateral part: Temporopontine fibers

The given clinical scenario is suggestive of paralysis agitans(parkinsonism). The structure marked in the image is the substantia nigra in the coronal section of the midbrain.

The ophthalmic nerve is not a content of the interpeduncular fossa.

The floor of the interpeduncular fossa anteriorly to posteriorly contains - tuber

cinerum, infundibular stalk, mamillary bodies, and posterior perforated substance. The posterior perforated substance is pierced by the posterior cerebral arteries. The oculomotor nerve emerges between the superior cerebellar and posterior cerebral arteries in the interpeduncular fossa.

The image given below shows the interpeduncular fossa.

The marked structure i.e. olive is seen in the medulla. The external features of medulla oblongata are:

Anteriorly, the anterior median fissure is continuous with the anterior median fissure of the spinal cord. On either side of the fissure are pyramids containing the corticospinal tracts. Posterolateral to the pyramids are olives. Olives are elevations produced by the underlying inferior olivary nuclei. Posterior to the olives, the inferior cerebellar peduncles connect the medulla with the cerebellum.

Posteriorly, the superior half forms the floor of the fourth ventricle. Inferiorly, there is a posterior median sulcus. On either side of this sulcus, the nucleus gracilis is situated. The nucleus cuneatus lies lateral to nucleus gracilis.

The anterolateral sulcus lies in the groove between the pyramid and the olive and the XII cranial nerve emerges from there. The posterolateral sulcus lies in the groove between the olives and the

inferior cerebellar peduncles. The IX, X, and XI cranial nerves emerge from here.

The dorsal nucleus of vagus is present through the floor of the fourth ventricle seen in a cross-section of the medulla at the level of olives.

The following table describes major structures seen in cross-sections at different levels in the medulla oblongata:

The trapezoid body and the superior vestibular nucleus are seen in the section of lower pons.

Level Cavity

Just inferior to the po ns

Fourth ventricle

Olives, inferior cerebe llar peduncle

Fourth ventricle

Decussation of medial lemnisci

Central canal

Decussation of the pyr amids

Central canal

Level Just inferior to the po ns

Nuclei Arcuate nucleiInferior

olivary nucleusSpinal nucleus of V nerveDo rsal nucleus of vagusV III, XI nerve nucleiNu cleus ambiguus

Olives, inferior cerebe llar peduncle

Arcuate nucleiInferior olivary nucleusSpinal nucleus of V nerveDo rsal nucleus of vagusV III, IX, X, XII nerve n ucleiNucleus ambiguu sNucleus tractus solita rius

Decussation of medial lemnisci

Inferior olivary nucleu sNucleus gracilisNucle us cuneatusSpinal nuc leus of V nerveAcceso ry nucleusHypoglossal nucleus

Decussation of the pyr amids

Nucleus gracilisNucle us cuneatusSpinal nuc leus V nerveAccesory nucleus

Motor tr acts

Sensory t racts

Pyramid

Medial longitudinal fa sciculusTectospinal tr actMedial lemniscusS pinal tract of V nerve Anterior spinocerebell ar tractLateral spinoth alamic tract

Pyramids

Same as at the section just inferior to pons

Pyramids

Medial longitudinal fa sciculusDecussation o f medial lemnisciFasci culus gracilis and cun eatusSpinal tract of V nerveAnterior and pos terior spinocerebellar tractLateral spinothal amic tract

Decussation of cortico spinal tracts, pyramid s

Spinal tract of V nerve Anterior and posterior spinocerebellar tractL ateral spinothalamic t ract

The given clinical scenario is suggestive of Wallenberg syndrome. The symptoms of dysphagia and dysarthria are due to the involvement of nucleus ambiguus. Ataxia is a feature of inferior cerebellar peduncle involvement.

Option A: Medial medullary syndrome is also known as Dejerine's anterior bulbar syndrome. Option B: Lateral medullary syndrome is also known as Wallenberg syndrome.

Option C: Medullary tegmental paralysis is also known as Babinski-Nageotte syndrome. Option D: Midbrain stroke syndrome is also known as Weber syndrome.

The arrangement of cerebellar nuclei from lateral to medial is dentate, emboliform, globose, and fastigial.

Ataxia-telangiectasia is characterized by progressive neuronal degeneration with a loss of Purkinje and granule cells in the cerebellum. The granule cells are the only excitatory cells in the cerebellar cortex.

The tremors are caused due to progressive degeneration of the Purkinje cells that form the output of the cerebellar cortex. They form the only output neurons of the cerebellar cortex.

The output of the whole cerebellum is from the deep cerebellar nuclei namely fastigial, globose, emboliform and dentate.

The incorrect statement is that the accessory middle meningeal artery lies under it. It is the anterior branch of the middle meningeal artery that lies deep to the pterion, making it vulnerable to epidural hematomas upon lateral skull trauma.

The structure marked A is ventral mesentery. The falciform ligament is a derivative of the ventral mesentery.

Mesenteries are double layers of the peritoneum that enclose an organ and connect it to the body wall. Only the foregut has a ventral mesentery. When the liver grows into the mesenchyme of the septum transversum, it divides the ventral mesentery into 2 parts: Lesser omentum and Ligaments of the liver (falciform ligament, right and left triangular ligaments, and coronary ligaments).