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DIENCEPHALON Dr. Ifeanacho ABIREH
MBBS, MSc, PGDE, MWACS
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Diencephalon Consists of: Thalamus (dorsal thalamus) Hypothalamus Epithalamus Ventral thalamus (Subthalamus) The third ventricle is a cavity in the
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Diencephalon
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Diencephalon
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Thalamus Large mass of grey matter Lies lateral to the third ventricle Two poles Anterior and posterior Four surfaces Superior, inferior, medial and lateral
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Thalamus (Relation) Anterior pole Lies behind the interventricular foramen Posterior pole (pulvinar) Lies above and lateral to superior
colliculus Separated from lateral geniculate body
by superior brachium quadrigeminum 3/4/2019 www.abireh.com 6
Thalamus (Relation) Medial surface Forms large part of lateral wall of third
ventricle The two surfaces are interconnected by
interthalamic adhesion (mass of grey matter)
Separated from the hypothalamus by hypothalamic sulcus
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Thalamus (Relation) Lateral surface Internal capsule Lentiform nucleus Superior surface Lateral part: Stria terminalis,
thalamostriate vein, Caudate nucleus Medial part: Fornix, tela choroidea (fold
of piamatter) 3/4/2019 www.abireh.com 8
Thalamus (Relation)
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Thalamus (Relation) Inferior surface Anteriorly- Hypothalamus Posteriorly- ventral thalamus
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Internal structure of the thalamus The grey matter is divided into three by
internal medullary lamina (white matter)
Anterior, medial and lateral parts Superior surface covered with stratum
zonale (layer of white matter) Lateral surface covered by external
medullary lamina 3/4/2019 www.abireh.com 11
Internal structure of the thalamus
Nuclei in the thalamus Anterior part- anterior nucleus Medial part- medial dorsal nucleus Lateral part- subdivided into ventral and
lateral groups
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Internal structure of the thalamus
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Internal structure of the thalamus • Ventral group of lateral part Ventral anterior nucleus Ventral lateral nucleus (ventral
intermediate nucleus) Ventral posterior nucleus Ventral posterolateral nucleus (lateral
part) Ventral posteromedial nucleus (medial
part) 3/4/2019 www.abireh.com 14
Internal structure of the thalamus
Lateral group of lateral part Lateral dorsal nucleus (Dorsolateral
nucleus) Lateral posterior nucleus pulvinar
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Other nuclei in thalamus Intralaminar nuclei in the internal
medullary lamina Centromedian nucleus Midline nuclei lie between the thalamus
and ependyma of third ventricle Medial and lateral geniculate bodies
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Connections of the thalamus Exteroceptive and proprioceptive
impulses Medial lemniscus Spinothalamic tracts Trigeminothalamic tract Visual and auditory impulses reach the
lateral and medial geniculate body respectively
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Connections of the thalamus
Sensation of taste through solitariothalamic fibres
Olfactory impulses through amygdaloid complex
Visceral information through hypothalamus and reticular formation
Connections from cerebral cortex, cerebellum and corpus striatum
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Connections of the thalamus
Thalamocortical fibres form large bundles called thalamic radiations or thalamic peduncles
Anterior (frontal) Posterior (caudal) Superior (dorsal) Ventral
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Connections of the thalamus
The thalamus gives efferent to corpus striatum, hypothalamus and reticular formation
Thalamus can perceive exteroceptive sensations e.g pain
The fibres from the lowest parts of the body end in the most lateral part of the ventral posterior nucleus
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Connections of the thalamus
• Those from the upper parts end in the medial part of the ventral posterior nucleus
• All the sensations are carried to the cerebral cortex through the posterior limb of internal capsule
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Medial and lateral geniculate bodies
Small oval collected of grey matters Lies below the posterior part of the
thalamus Lateral to the colliculi of the midbrain Included in the dorsal thalamus due to
relationship in function
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Medial geniculate body Relay station on auditory pathway Nuclei- medial, ventral, Dorsal nuclei Receives fibres of the lateral lemniscus Fibres from it (acoustic radiation) passes
to the cerebral cortex through internal capsule (sublentiform part)
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Lateral Geniculate body Relay station on the visual pathway Receives fibres from the retinae Efferents (optic radiation) passes to the
cerebral cortex through internal capsule (retrolentiform part)
Grey matter partially split to form six lamellae separated by nerves
Laminae 1,4,6: fibres from retina of opposite side
Laminae 2,3,5: fibres from same side 3/4/2019 www.abireh.com 24
Medial and lateral geniculate bodies
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Medial and lateral geniculate bodies
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Hypothalamus • Lies below the thalamus • Forms part of lateral wall of the third
ventricle • Connects with the limbic system,
reticular formation, autonomic centres in brainstem and spinal cord
• Releases secretions into the blood stream and CSF
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Hypothalamus (Relation) • Lateral- internal capsule, ventral
thalamus • Posterior- ventral thalamus, tegmentum
of midbrain • Anterior- lamina terminalis, anterior
perforated substance • Inferior- tuber cinerum, infundibulum,
mamillary bodies 3/4/2019 www.abireh.com 28
Subdivisions of hypothalamus Regions (From medial to lateral) Periventricular zone Intermediate zone Lateral zone The periventricular and intermediate
zones are described collectively as medial zone
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Subdivisions of hypothalamus
• Regions (Anteroposteriorly) Preoptic region Supraoptic (chiasmatic) region Tuberal (infundibulotuberal) region Mamillary (posterior) region
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Hypothalamic nuclei Preoptic nucleus Mamillary nuclei
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Hypothalamic nuclei (medial zone) Paraventricular nucleus Suprachiasmatic nucleus Arcuate (infundibular) nucleus Posterior nucleus Anterior nucleus Dorsimedial nucleus Ventrimedial nucleus Premamillary nucleus 3/4/2019 www.abireh.com 32
Hypothalamic nuclei
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Hypothalamic nuclei (lateral zone) Lateral nucleus Supraoptic nucleus Tuberomamillary nucleus Lateral tuberal nuclei
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Connections of the hypothalamus Afferents Spinal cord and brainstem via reticular
formation Nucleus of solitary tract (taste and visceral) Somatic through major ascending tracts Centres connected to olfactory pathway and
limbic system Cortico-hypothalamic fibres (frontal lobe) Subthalamic nucleus and the zona incerta 3/4/2019 www.abireh.com 35
Connections of the hypothalamus
Efferents Autonomic centres in the brainstem and
spinal cord Anterior nucleus of thalamus Neocortex
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Control of neurohypophysis Vasopressin (ADH) produced mainly by
supraoptic nucleus Oxytocin produced mainly by
paraventricular nucleus These nuclei send axons into the
neurohypophysis Paraventriculo-hypophyseal tract Supraoptico-hypophyseal tract 3/4/2019 www.abireh.com 37
Control of adenohypophysis Production of releasing factors Acuate (infundibular) nucleus Releasing factors travel via
Tuberohypophyseal tract to capillaries From the capillaries through the
hypothalamohypophyseal portal system to the pars anterior of the hypophysis cerebri
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Control of the hypophysis
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Functions of the hypothalamus Regulation of eating and drinking behaviour Feeding /thirst centre-lateral hypothalamic
nucleus Satiety centre –ventromedial hypothalamic
nucleus Regulation of sexual activity and reproduction Control of autonomic activities Parasympathetic (cranial part); sympathetic
(Caudal) 3/4/2019 www.abireh.com 40
Functions of the hypothalamus
Emotional behaviour Control of endocrine activity Response to stress Temperature regulation Biological clock Sleep and waking cycle Suprachiasmatic nucleus
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Epithalamus Structures included are: Pineal body Paraventricular nuclei ( Anterior and
posterior) Habenular nuclei (medial and lateral) Stria medullaris thalami Posterior commissure 3/4/2019 www.abireh.com 42
Pineal body Related to posterior wall of third ventricle It is an endocrine gland Made up of pinealocytes Has effects on hypophysis cerebri, thyroid,
parathyroid, adrenals, gonads Secretes of melatonin Activity more in the dark; Afferents from
retina 3/4/2019 www.abireh.com 43
Ventral thalamus Lies below the posterior part of the
thalamus Behind and lateral to the hypothalamus Continuous with the tegmentum of
midbrain The nuclei include reticular nucleus,
zona incerta, perigenicular nuclei
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Acknowledgement Textbook of human neuroanatomy Last’s Anatomy Gray’s atlas of anatomy Netter’s atlas of neuroscience
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