Diencephalon

Hypothalamus

General information

• Part of diencephalon

• Weighs about 4 grams

The whole brain weighs 1 400 grams

• Occupies the bottom and infero-lateral walls of the III ventricle

Topography

• In the center of the limbic system. • At the crossing of numerous nerve pathways.

• Surrounded by the circle of Willis.

Boundaries

Anterior Lamina terminalis Posterior Corpora mammillaria Dorsal Sulcus hypothalamicus Medial ІІІ стомахче Lateral Subthalamus & capsula interna Ventral Chiasma opticum, tuber

cinereum, corpora mammillaria & neurohypophysis

• Chiasma opticum

• Infundibulum

• Tuber cinereum

• Corpus mamillare

• Tractus opticus

Anatomy

Organization

• Composed of lateral and medial zones divided by fornix.

• Nuclei of the lateral zone concerned with feeding (center of hunger) and drinking (center of thirst).

• Nuclei of the medial zone grouped in 3 regions: regio anterior, tuberalis and posterior.

Хипоталамични области и ядра

• Латерална област • Nucl. preopticus lateralis • Nucl. hypothalamicus lateralis

• Медиална област • Regio preoptica

• Nucl. preopticus medialis • Полово диморфично ядро

• Regio supraoptica • Nucl. suprachiasmatis • Nucl. anterior • Nucl. paraventricularis • Nnucl. supraopticus

• Regio tuberalis • Nucl. dorsomedialis • Nucl. ventromedialis • Nucl arcuatus

• Regio mamillaris • Nucll. mamillares • Nucl. posterior

Crossed by fasciculus prosencephalicus medialis

Contains two nuclei:

1. Nucleus preopticus lateralis

2. Nucleus hypothalamicus lateralis - when stimulated feeling of hunger

- when destroyed anorexia nervosa and fast

Lateral zone

Nucleus preopticus Control of parasympathetic function

Nucleus supraopticus Synthesis and secretion of vasopressin. Damage causes diabetes insipidus.

Nucleus suprachiasmaticus Fibers from the retina; fibers to the pineal body. Controls circadian rhythms.

Nucleus anterior Controls temperature and sexual behavior.

Nucleus paraventricularis Synthesis and secretion of oxytocin (milk secretion & uterine contraction). Controls food intake

Regio anterior

Hypothalamus

Nucleus dorsomedialis

- center of hunger - on stimulation rage, cruelty Nucleus ventromedialis

- center of satiety - on stimulation depression of apetite Nucleus arcuatus

- periventricular in tuber cinereum - secretes releasing-factors - dopaminergic neurons, inhibit release of prolactin

Regio tuberalis

Nucleus mamillaris

- impulses from hippocampal formation via fornix

- impulses from tegmental nuclei, nuclei raphae via pedunculus mamillaris

- projections to nucleus anterior thalami via tractus mamillothalamicus

Nucleus posterior

- controls thermoregulation (съхранение и образуване на топлина)

- damage causes poikilothermia – inability of thermoregulation

Regio posterior

Connections

Connections

Extensive and complex, can be summarized in 3 categories:

➢Connections with the limbic system

➢Connections with the pituitary gland

➢Connections with somatic and visceral nuclei

1) Fasciculus prosencephalicus medialis: visceral

function

2) Tractus supraopticohypophysialis: neurosecretion

3) Tractus tuberoinfundibularis: liberins & statins

4) Afferents from corpora mamillaria: visceral function

5) Efferents to brainstem & spinal cord: autonomous

function

Connections

Afferents

- nucleus tractus solitarii – visceral information via vagus.

- formatio reticularis –various information from spinal cord.

- retina – to nucl. suprachiasmaticus. Circadian rhythm.

- circumventricular organs – lacks blood-brain bareer. Control of substances isolated from the CNS, e.g., toxins.

- limbic and olfactory system –controls behavior reactions.- intrinsic receptors, monitor temperature and water balance.

Main afferentsFrom most parts of brain. Most pathways are non-myelinated and small.

Fasciculus prosencephalicus medialis •From area septalis & area olfactoria lateralis to hypothalamic nuclei. •Integrates olfaction with emotions and feeding. Stria terminalis •From corpus amygdaloideum and area septalis to regio preoptica and nuclei hypothalamici anteriores. • Controls physiological response to emotions and sexual arousal. Fornix •From formatio hippocampalis to corpora mammillaria. •Integrates memory, emotions and visceral reactions.

Main efferents

Fasciculus mammillothalamicus • From nuclei mamillares to nucleus anterior of

thalamus. • Creating and coding memory traces. Hypothalamo-reticular pathway • Connects the hypothalamus with parasympathetic

and sympathetic nuclei.

Efferents: To autonomous nervous system medulla: а) parasympathetic nucleus of n. vagus б) cells projecting to sympathetic nuclei in the spinal cord. Control of heart rate, vasoconstriction, digestion, sweating etc..

Endocrine signals to/through pituitary gland а) axons to neurohypophysis to release oxitocin & vasopressin; б) releasing factors into the vessels of adenohypophysis.

Hypoth can control any endocrine gland, change blood pressure (vasopressin and vasoconstriction), body temperature, metabolism (TSH) and epinephrine level (ACTH).

Blood pressure, temperature, water and electrolyte balance, weight are maintained within optimal values.

Hypothalamus = Homeostasis

• Autonomous, endocrine, emotional and somatic functions

• Serves three basic systems:

– Autonomic nervous system

– Endocrine system

– Lymbic system

• Maintains homeostasis of the body

Controls

Function 1. Autonomous control - anterior region stimulates parasympathetic function - posterior region stimulates sympathetic function

2. Thermoregulation - anterior region maintains bogy temperature - posterior region stimulates production and preserving heat

3. Maintaining water balance а. Nucleus ventromedialis – center of satiety б. Nucleus hypothalamicus lateralis – center of hunger 4. Liberins and statins - produced from nucleus arcuatus - transported to the portal system of adenohypophysis - control hormon production in the adenohypophysis

Functional characteristics

Subthalamus

General characteristics

• Vaguely delineated area between midbrain, thalamus,

hypothalamus, capsula interna and ІІІ ventricle.

• Contains fibers and nuclear structures - zona incerta, nucleus

subthalamicus, Forel fields, nuclei reticulares

• Connected mainly with somatomotor functions

http://www.bartleby.com/107/189.html

Nuclear structures

• Nucleus subthalamicus (Luys) – Well defined lying on capsula interna – Rostral penetration of sustantia nigra – Connected bilaterally with globus pallidus

• Nuclei reticulares – Small groups and extensions of cells

• Zona incerta - continuation of nucleus reticularis thalami • Fields H of Forel (prerubral):

– H1 of Forel - between thalamus and zona inserta – H2 of Forel - between nucl. subthalamicus and zona

inserta

A. Fasciculus thalamicus (in H1 field of Forel) 1. Lemniscus medialis 2. Tractus dentatothalamicus 3. Tractus pallidothalamicus 4. Bundle of reticular fibers connecting brainstem with

diencephalon B. Fasciculus lenticularis (in H2 field of Forel)

- Pallidothalamic fibers through capsula interna C. Ansa lenticularis

- Fibers from globus pallidus (mainly pallidothalamic) beneath capsula interna

D. Fasciculus subthalamicus – bidirectional fibers between globus pallidus and nucleus subthalamicus

Fibers