BRAIN DAYS PART III DIENCEPHALON Kaan Ycel M

BRAIN DAYS PART III DIENCEPHALON Kaan Yücel M. D. , Ph. D. IN 10 QUESTIONS

Learning Objectives Explain the components of the diencephalon Explain the anatomical features of the structures in diencephalon

1. Diencephalon Prosencephalon [Forebrain] 1. Telencephalon 2. Diencephalon

2. Diencephalon is composed of… (1) thalamus (2) subthalamus [-sub: 'inferior to”] (3) epithalamus [-epi: “superior to”] (4) hypothalamus [-hypo: “under” ]

2. Diencephalon extends. . . posteriorly where 3 rd ventricle becomes continuous with the cerebral aqueduct anteriorly interventricular foramina A midline structure with symmetrical right and left halves

2. Diencephalon’s inferior surface • Only area exposed to the surface in the intact brain. • Formed by hypothalamic and other structures, which include, from anterior to posterior: o optic chiasma o infundibulum with the tuber cinereum [x] o mammillary bodies [x]

2. Diencephalon’s superior surface • Concealed by the fornix. • The actual superior wall of the diencephalon is formed by roof of the third ventricle A pair of vascular processes, choroid plexuses of the third ventricle, project downward from the midline into the cavity of the third ventricle and CSF is produced here. •

2. Diencephalon’s lateral surface Bounded by the internal capsule oconsists of nerve fibers oconnect the cerebral cortex with parts of the brainstem and spinal cord. MRI of the brain, T 1 -weighted axial cut 1. Insula 2. Internal capsule 3. Caudate nucleus 4. Putamen 5. Internal capsule Posterior limb 6. Splenium, corpus callosum 7. Thalamus

2. Diencephalon’s medial surface a. k. a. Lateral wall of the third ventricle Superior part by medial surface of thalamus hypothalamic sulcus Inferior party by hypothalamus stria medullaris thalami • Afferent fibers to the habenular nucleus • Forms a ridge along the superior margin of the medial surface of the diencephalon

3. Thalamus L. thalamus "inner chamber, " from Gk. thalamos "inner chamber, bedroom" Large ovoid mass of gray matter that forms the major part of the diencephalon. On each side of the third ventricle.

3. Thalamus The superior surface of the thalamus is covered medially by the tela choroidea and the fornix The inferior surface is continuous with the tegmentum of the midbrain.

3. Thalamus The medial surface of the thalamus forms the superior part of the lateral wall of the third ventricle Usually connected to the opposite thalamus by a band of gray matter, interthalamic connection (interthalamic adhesion- adhesio interthalamica- massa interrmedia) Found in 70 -80% of humans Axial T 2 -weighted MR image C = caudate nucleus G = globus pallidus L = lentiform nucleus (G+P) P = putamen T = thalamus

§ Important station that receives the main sensory tracts (except the olfactory pathway). § A station where much of the information is integrated and relayed to the cerebral cortex and many other subcortical regions. § A key role in the integration of visceral and somatic functions.

3. Thalamus Anterior thalamic nuclei, which receive the mammilothalamic tract from the mammillary nuclei. Associated with of that of the limbic system and is concerned with emotional tone and the mechanisms of recent memory.

3. Thalamus Medial part of the thalamus large dorsomedial nucleus and several smaller nuclei. 2 connections with the whole prefrontal cortex and hypothalamic nuclei. Responsible for integration of a large variety of sensory information relation of this information to one’s emotions

3. Thalamus

Stria terminalis: Runs @ lateral margin of thalamus From amygala to hypothalamus Major output of amygdala

4. Hypothalamus CHIEF OF THE HORMONES from the region of the optic chiasma to the caudal border of the mammillary bodies

4. Hypothalamus four distinct groups in the rostral-caudal plane of the third ventricle: 1. preoptic (above and in front of the optic chiasm - telencephalic extension of the basal forebrain, but functionally diencephalonic) 2. chiasmatic (above and around the optic chiasm) 3. tuberal (above and around the "tuber cinereum", i. e. pituitary stalk) 4. posterior region which includes the mammillary bodies.

4. Hypothalamus When observed from below, the hypothalamus is seen to be related to the following structures, from anterior to posterior: (1) optic chiasma (2) tuber cinereum & infundibulum (3) mammillary bodies

5. Subthalamus Inferior to thalamus Between thalamus-midbrain Anteriomedially- hypothalamus Important connections with the striatum Fxn: Control of muscle activity

Adhesio interthalamica Septum pellicidum Pineal gland Anterior commissure Posterior commissure Corpora quadrigemina AC Thalamus Optic chiasm Hypothalamus Mamillary body Cerebral aqueduct Pituitary gland

6. Pituitary gland SIDEKICK OF THE HYPOTHALAMUS

Hormone Stimulated by the hypothalamic Does hormone Anterior pituitary gland (Adenohypoysis) Growth Hormone (GH) Growth Hormone-Releasing Hormone Growing (GHRH) Thyroid-stimulating Thyrotropin-Releasing Hormone (TRH) Metabolism of the body Corticotropin-Releasing Hormone (CRH) Production and release of corticosteroids from the hormone (TSH) Adrenocorticotropic hormone (ACTH) adrenal glands Prolactin (PRL) Long list of chemical substances, Stimulation of milk production in breasts Luteinizing hormone (LH) inhibited by dopamine Gonadotropin-Releasing Hormone (Gn. RH) Triggers ovulation Gonadotropin-Releasing Hormone (Gn. RH) Regulates the development, growth, pubertal Follicle-stimulating hormone (FSH) ICHS production of testosterone maturation, and reproductive processes of the body Posterior pituitary gland (Neurohypoysis) Oxytocin Secreted from the hypothalamus and Distension of the cervix and uterus during labor, carried to the pituitary gland facilitating birth, and after stimulation of the nipples, facilitating breastfeeding. Antidiuretic hormone Secreted from the hypothalamus and Increases water absorption in the kidney

7. Tuber Cinereum Interthalamic adhesion

8. Mammillary bodies Two small hemispherical bodies situated side by side posterior to the tuber cinereum. Possess a central core of gray matter invested by a capsule of myelinated nerve fibers. Korsakoff’s Syndrome Wernicle-Korsakoff Syndrome Copenhaver BR, Rabin LA, Saykin AJ, Roth RM, Wishart HA, Flashman LA, Santulli RB, Mc. Hugh TL, Mamourian AC. The fornix and mammillary bodies in older adults with Alzheimer's disease, mild cognitive impairment, and cognitive complaints: a volumetric MRI study. Psychiatry Res. 2006 Oct 30; 147(2 -3): 93 -103. Yoneoka Y, Takeda N, Inoue A, Ibuchi Y, Kumagai T, Sugai T, Takeda K, Ueda K. Acute Korsakoff syndrome following mammillothalamic tract infarction. AJNR Am J Neuroradiol. 2004; 25(6): 964 -968. Vann SD. Re-evaluating the role of the mammillary bodies in memory. Neuropsychologia. 2010; 48(8): 2316 -2327.

Septum pellicidum Fornix Thalamus Hypothalamus AC Optic chiasma Pituitary gland PC Mammillary bodies

Lamina terminalis Fornix Interthalamic adhesion Thalamus Habenula AC Hypothalamus Optic chiasm Infundibulum Pituitary gland Pineal gland Tuber cinerum PC

8. Epithalamus Pineal gland+habenular nucleus+stria medullaris thalami Pineal gland: Inhibition of hormones Circadian rhythm day & nigh time Melatonin Habenula: potential importance of the lateral habenular nucleus in regulating the dopamine reward signal Haber SN, Knutson B. The reward circuit: linking primate anatomy and human imaging. Neuropsychopharmacology. 2010; 35(1): 4 -26.

9. Third ventricle Between two thalami Lateral Ventricle Interventricular foramina (foramina of Monro) 4 th Ventricle Cerebral aqueduct (of Sylvius)

9. Third ventricle Anterior wall Lamina terminalis AC Posterior wall Cerebral aqueduct Superior to PC pineal recess Superior to pineal recess habenular commissure Lateral wall Sup: Medial surface of thalamus Inf: Hypothalamus Superiorly limited by stria medullaris thalami.

Anterior commissure (AC) Connecting temporal lobes Posterior commissure (PC) Pupillary eye reflex