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DIENCEPHALON Dr. Ifeanacho ABIREH

MBBS, MSc, PGDE, MWACS

3/4/2019 www.abireh.com 1

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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