DIENCEPHALON MIDDLE STRUCTURE LARGELEY EMBEDDED IN THE CDEREBRUM,

DIENCEPHALON DETAIL

1. DIENCEPHALON

2. DIENCEPHALON Ms.R.SIVA ANANDHI ASSISTANT PROFESSOR VISTAS CHENNAI

3. T h e d i e n c e p h a l o n i s a m i dd l e s t r u c t u r e w h i c h i s largely embedded in the cerebrum Its cavity forms the greater part of third ventricle The hypothalamic sulcus extending from interventricular foramen to the cerebral aqueduct divides each half of the dienchephalon into dorsal and ventral parts INTRODUCTION

4. D O R S A L P A R T O F D I E N C E P H A L O N Thalamus Metathalamus - including medial and lateral geniculate bodies Epithalamus - including the pineal body and habenula V E N T R A L P A R T O F D I E N C E P H A L O N Hypothalamus Subthalamus

5. T H A L A M U S Thalamus is a large mass of grey matter situated in the lateral wall of the third ventricle and floor of central part of lateral ventricle Measurements Anteroposterior- 4cm Vertical- 4cm Transverse- 4cm Ends- Anterior and Posterior Surfaces- Superior, Inferior, Medial and Lateral

6. Anterior end - with anterior nucleus- narrow and forms p osterior boundary of interventricular foramen Posterior end - expanded- known as pulvinar overhangs lateral and medial geniculate bodies Superior surface - divided into lateral ventricular part which forms the floor of central part of the lateral ventricle medial extraventricular part which is covered by tela choroidea of third ventricle by free margin of body of fornix limited laterally by caudate nucleus, stria terminalis, thalamostriate vein medially by habenular stria Inferior surface - rests on subthalamus and hypothalamus

7. S T R U C T U R E A N D NUCLEI O F T H A L A M U S White matter External medullar y lamina covers lateral surface Internal medullar y lamina divides thalamus into three parts- anterior, medial and lateral Grey matter a . A n t e r i o r n u c l e u s b . M e d i a l n u c l e u s c. Lateral part of thalamus- largest- Neothalamus d . I n t r a l a m i n a r n u c l e i

8. Afferent impulses from a large number of subcortical centres converge on the thalamus Exteroce p tive and proprioceptive impulses ascend to it through the medial leminiscus, spinothalamic tracts and trigeminothalamic tracts Visual and auditor y impulses reach the medial and lateral geniculate bodies Great integrating centre - information is projected to cerebral cortex through profuse thalamocortical projections C O NN E C T I O N S & F U N C T I O N S O F T H A L A M U S

9. METATHALAMUS Metathalamus consists of medial and lateral geniculate bodies, which are situated on each side of midbrain, below the thalamus Medial geniculate body Oval elevation situated just below the pulvinar lateral to superior colliculus inferior brachium connects medial geniculate body to inferior colliculus

10. Connections Afferents lateral leminiscus fibres from both inferior colliculi ascending reticular pathway Efferents acoustic radiation going to auditory area of cortex to secondary somatosensory area Function - last relay station on the pathway of auditory impulses to cerebral cortex

11. Lateral geniculate body Small oval elevation situated anterolateral to medial geniculate body, below thalamus Overlapped by medial part of temporal lobe Connected to superior colliculus by superior brachium Connections Afferents- optic tract Efferents- optic radiation going to visual area of cortex Function - last relay station on the visual pathway to occipital cortex

12. EPITHALAMUS Epithalamus occupies caudal part of the roof of the diencephalon and consists of right and left Habenular nuclei Pineal body or epiphysis cerebri Habenular commissure Posterior commissure

13. H A B E N U L A R N U C L E U S Nucleus lies beneath the floor of the habenular trigone Trigone is a small, depressed triangular area, situated above superior colliculus and medial to pulvinar of thalamus Medially- bounded by stria terminalis thalami and stalk of pineal body A ff erents - hypothalamus, amygdaloid body, hippocampus E ff erents - interpedencular nucleus Functions - acts as a nodal point for convergence of basic emotional drives

14. P I N E A L B O D Y Pineal body is a small, conical organ, projecting downwards and backwards between two superior colliculi Consists of a conical bod y and a stalk or peduncle which divides into two laminae seperated by the pineal recess of the third ventricle Superior lamina of stalk - contains habenular commissure Inferior lamina - contains posterior commissure

15. P I N E A L B O D Y Structure Composed of two types of cells- pinealocytes and neuroglial cells Functions endocrine gland- produces hormones that may have an important regulatory influence on other endocrine glands Melatonin- causes changes in skin colour

16. HYPOTHALAMUS Hypothalamus is a part of the diencephalon Lies in the floor and lateral wall of the third ventricle Boundaries Anteriorly- posterior perforated substance each side- optic tract and crus cerebri Saggital section anteriorly- lamina terminalis inferiorly- floor of third ventricle posterosuperiorly- hypothalamic sulcus

17. Parts o f hypothalamus Optic part Preoptic and supraoptic nuclei Paraventricular nucleus Suprachiasmatic nucleus Tuberal part Ventromedial nucleus Dorsomedial nucleus Mammillary part Posterior nucleus Lateral nucleus

18. Im p ortant connections Afferents receives visceral sensations through spinal cord and brainstem Efferents Supraoptico- hypophyseal tract Mammillothalamic tract Mammillotegmental tract Tubero-infundibular tract

19. Functions o f Hypothalamus Endocrine control forms releasing hormones or release inhibiting hormones regulates secretion of TSH, ACTH, STH, LH, FSH and melanocyte stimulating hormone by the pars anterior of hypohysis cerebri Neurosecretion Oxytocin and vasopressin are secreted by hypothalamus and transported to infundibulum and posterior lobe of hypophysis cerebri

20. Functions of Hypothalamus General autonomic effect anterior part- parasympathetic activity posterior part- sympathetic activity Temperature regulation maintains balance between heat production and heat loss of the body Regulation of food and water intake hunger or feeding centre- laterally satiety centre- medially

21. Functions of Hypothalamus Sexual behaviour and reproduction controls gametogenesis, reproductive cycles Biological clocks Sleep is produced by hypogenic zones, mainly of thalamus and hypothalamus Emotion, fear, rage, aversion, pleasure and reward controlled by hypothalamus, limbic system and prefrontal cortex.

22. SUBTHALAMUS Subthalamus lies between midbrain and thalamus, medial to internal capsule and globus pallidus It consists of Grey matter cranial ends of red nucleus and SN extend into it Subthalamic nucleus Zona incerta White matter Cranial ends of leminisci, lateral to red nucleus Ansa lenticularis

23. C L I N I C A L A N A T O M Y Lesions of thalamus- impairments of all types of sensibilities; joint sense being most affected Thalamic syndrome- disturbances of sensations, hemiplegia, hemiparesis together with hyperaesthesia and pain Damage to medial nucleus of thalamus- forgetfullness Lesions of hypothalamus Obesity- Frolich syndrome Diencephalic autonomic epilepsy Hyperglycemia Acute ulcerations in upper part of GIT