Diencephalon – Thalamus, Hypothalamus, Epithalamus & Subthalamus (Dr Venu Madhav Nelluri)

These flashcards cover anatomy, nuclei, connections, functions, blood supply and clinical correlations of the diencephalon with emphasis on the thalamus and hypothalamus.

What five major components make up the diencephalon?

Thalamus, Hypothalamus, Epithalamus, Subthalamus and Metathalamus.

Which three structures together form the thalamencephalon?

Thalamus, Metathalamus and Epithalamus.

Where is the thalamus situated anatomically?

In the lateral wall of the third ventricle, forming the central core of the inter-brain and enclosed by the cerebral hemispheres.

What is the principal function of the thalamus?

It acts as the main relay station for all sensory impulses (except olfaction) and channels them to the appropriate cortical areas.

Which thalamic end forms the posterior boundary of the interventricular foramen?

The anterior end of the thalamus.

What structure overhangs the medial and lateral geniculate bodies?

The posterior end (pulvinar) of the thalamus.

To which ventricular structure is the superior surface of the thalamus related?

The floor of the lateral ventricle and the tela choroidea of the third ventricle.

Name the three broad functional classes of thalamic nuclei.

Specific sensory relay nuclei, Motor nuclei and Nonspecific (association) nuclei.

Which nuclei comprise the anterior nuclear group of the thalamus?

Anterior ventral (AV), Anterior dorsal (AD) and Anterior medial (AM) nuclei.

Lesion of which thalamic nucleus produces Korsakoff’s syndrome with recent-memory loss?

Lesion of the anterior nuclei of the thalamus.

Which thalamic nucleus interconnects cerebellum and basal ganglia with frontal cortices?

The Ventral Lateral nucleus (motor thalamus).

Into what two parts is the ventral posterior nucleus divided and what do they relay?

VPL (ventral posterolateral) relays body somatosensation; VPM (ventral posteromedial) relays face and taste sensation.

Which thalamic nuclei serve as auditory and visual relay nuclei respectively?

Medial geniculate body – auditory; Lateral geniculate body – visual.

What is the main functional role of the pulvinar nucleus?

Integration of visual stimuli and higher-order sensory association.

What is the chief role of the intralaminar nuclei (e.g., centromedian)?

Regulation of levels of consciousness and cortical arousal.

Which three laminae/tracts constitute the white matter of the thalamus?

External medullary lamina, Internal medullary lamina and Thalamic radiations.

List the four named thalamic radiations.

Anterior, Superior, Posterior and Inferior (via the corona radiata/pedicles).

Name four arterial sources supplying the thalamus.

Posterior communicating artery (central branches), Posterior cerebral artery, Basilar artery and Anterior & Posterior choroidal arteries (plus lateral striate branches of MCA).

What clinical triad characterises classical Dejerine-Roussy (thalamic pain) syndrome?

Contralateral sensory disturbance, motor deficit and psychological disturbances following VPL/VPM infarction or haemorrhage.

Describe the posture called the ‘thalamic hand’.

Wrist pronated and flexed, metacarpophalangeal joints extended, interphalangeal joints flexed owing to thalamic lesion.

Which grey-matter structures are included in the subthalamus?

Subthalamic nucleus, cranial ends of red nucleus and substantia nigra, and zona incerta.

Why is the subthalamic nucleus clinically important?

It integrates motor signals; its lesion produces hemiballismus, and it is a target for deep-brain stimulation in Parkinson’s disease.

What is the Field of Forel (H1 & H2)?

White-matter region containing ansa lenticularis and lenticular fasciculus linking globus pallidus to thalamus.

Which structures form the floor and anterior wall of the third ventricle (i.e., the hypothalamus)?

Optic chiasma, tuber cinereum, infundibulum, median eminence and hypophysis.

Give six key homeostatic functions regulated by the hypothalamus.

Autonomic control, Endocrine control, Temperature regulation, Food & water intake, Sex & reproduction, Circadian rhythm/emotions.

Where is the feeding (hunger) centre located?

In the lateral hypothalamic area.

Which hypothalamic nucleus acts as the satiety centre?

Ventromedial nucleus.

Which hypothalamic area functions as the arousal centre of the brain?

Posterior hypothalamus.

What hormone is produced by neurons of the supraoptic nucleus?

Antidiuretic hormone (vasopressin, ADH).

Which hypothalamic nucleus contains corticotropin-releasing hormone (CRH) and projects via the hypothalamo-hypophysial tract?

Paraventricular nucleus.

What is the prime biological clock of the brain and where is it located?

The suprachiasmatic nucleus (SCN) of the hypothalamus, regulating circadian rhythms.

Which hypothalamic nucleus degeneration results in diabetes insipidus?

Destruction of the supraoptic nucleus or interruption of the hypothalamo-hypophysial tract.

Hyperthermia results from lesions in which part of the hypothalamus?

Anterior hypothalamus (heat-loss centre).

Hypothermia results from lesions in which part of the hypothalamus?

Posterior hypothalamus (heat-gain centre).

Name the four antero-posterior subdivisions of the hypothalamus.

Preoptic, Supraoptic, Tuberal (infundibulotuberal) and Mammillary regions.

What is the main afferent tract reaching the mammillary bodies and what efferent tract leaves them?

Afferent – fornix; Efferent – mammillothalamic tract.

Which hypothalamic lesion is associated with narcolepsy and cataplexy?

Generalised hypothalamic disorder affecting sleep–wake regulation centres.

State the mnemonic for metathalamic nuclei functions.

‘Lateral for Look, Medial for Music’ – Lateral geniculate (visual), Medial geniculate (auditory).

Which arteries provide thalamo-perforating branches?

Posterior cerebral and posterior communicating arteries.

Which veins drain the thalamus?

Thalamostriate, internal cerebral, basal vein and great cerebral vein of Galen.

What are the three zones of the hypothalamus in the coronal plane?

Periventricular, Medial and Lateral zones.

Which hypothalamic region secretes gonadotropin-releasing hormone to influence reproduction?

The tuberal region (particularly arcuate/infundibular nucleus).

Which nucleus integrates visceral and emotional information and connects to the frontal cortex (limbic relay)?

Mediodorsal (dorsomedial) nucleus of the thalamus.

What is the thalamic ‘pacemaker’ and why is it important?

Intralaminar nuclei modulate cortical electrical activity and maintain wakefulness.

Which lamina separates the thalamus from the internal capsule laterally?

External medullary lamina.

Name two degenerative diseases affecting basal ganglia pathways that relay via the thalamus.

Parkinson’s disease (dopamine neuron loss) and Huntington’s chorea (GABA/ACh neuron loss).

What movement disorder results from a lesion of the subthalamic nucleus?

Contralateral hemiballismus.

Which nuclei form the metathalamus?

Medial and Lateral geniculate bodies.

Which transmit visual information from the lateral geniculate body to the visual cortex?

Optic radiations (geniculocalcarine tract).

Which thalamic nuclei are classified as ‘association’ nuclei?

Ventral anterior, Dorsal medial (mediodorsal) and Pulvinar nuclei.

Which thalamic nucleus receives the dentatothalamic tract from the cerebellum?

Ventral lateral nucleus (pars oralis).

Which part of the hypothalamus houses the neurosecretory cells for oxytocin?

Paraventricular nucleus.

What is the main neurotransmitter of the reticular thalamic nucleus and what is its role?

GABA; it modulates activity of other thalamic nuclei (inhibitory gating).

Describe the boundaries of the subthalamus.

Lies between thalamus and midbrain, medial to internal capsule and globus pallidus.

Which fibres compose the hypothalamo-hypophysial tract?

Axons from supraoptic and paraventricular nuclei terminating in the posterior pituitary.

What hypothalamic lesion may produce obesity?

Bilateral lesion of the ventromedial (satiety) nucleus.

Which nucleus is the ‘thirst centre’ and where is it located?

Osmoreceptive neurons in the lateral hypothalamus/tuberal region.

Which thalamic nucleus is the principal relay for taste?

Ventral posteromedial (VPM) nucleus.

Which thalamic nucleus receives the trigeminothalamic tract?

Ventral posteromedial (VPM) nucleus.

Which nucleus of the thalamus is the largest specific somatosensory relay nucleus?

Ventral posterior nucleus (VPL + VPM).

What is the major function of the lateral dorsal (LD) and lateral posterior (LP) nuclei?

Integration of sensory information for limbic and parietal association cortices.

Which arteries supply the geniculate bodies (thalamo-geniculate branches)?

Posterior choroidal branches of the posterior cerebral artery.

What are the principal functions of the pineal gland within the epithalamus?

Synthesis and secretion of melatonin, regulation of circadian rhythms.

Which nucleus is a luminance detector responding to light onset and offset?

Suprachiasmatic nucleus (SCN).

Name the three main efferent fibre bundles emerging from the mammillary bodies.

Mammillothalamic tract, Mammillotegmental tract and Post-commissural fornix continuation.

How does the hypothalamus influence sympathetic activity?

Via descending fibres from the lateral hypothalamic nucleus to brainstem autonomic centres.

What is the principal connection between the hippocampus and the hypothalamus?

The fornix terminating in the mammillary bodies.

Which thalamic nuclei are considered ‘midline nuclei’ and what is their function?

Paraventricular and paratenial nuclei; they maintain alertness and receive limbic inputs.

Which thalamic nucleus’s lesion is linked to Parkinsonism when damaged?

Ventro-anterior nucleus.

Give two common pathological causes of thalamic syndromes.

Haemorrhage or infarction affecting thalamic perforating vessels.