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Yuniarti

Anatomy department

Faculty of Medicine

UNISBA

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Diencephalon isthe part of brain between the brainstem and the

cerebrum,surround the third ventricle

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Its main component are:

-Thalamus

-Subthalamus

-Epithalamus

-Hypothalamus

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Thalamus is a egg-shaped mass of gray matter that forms the major part of the

diencephalon.

There are two thalami, and one is situated on each side of the third ventricle

The medial surface of the thalamus forms part of the lateral wall of the thirdventricle and is usually connected to the opposite thalamus by a band of gray

matter , the interthalamic connection (interthalamic adhesion).

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The thalamus is

covered on its superior

surface by a thin layer

of white matter, calledthe stratum zonale

and on its lateral

surface by another

layer, the external

medullary lamina

The gray matter of the

thalamus is divided by a

vertical sheet of white

matter, the internal

medullary lamina, into

medial and lateralhalves

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There are two ways of dividing up the nuclei of the thalamus, namely,

topographically and functionally.

Topographically, the thalamus is subdivided by bands of white matter into a

number of component parts. The main white matter band that runs within the

thalamus is called the internal medullary lamina and it is shaped like the letter

Y. It divides the thalamus into a lateral mass, a medial mass, and an anterior

group of nuclei.

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Functionally, the thalamus has seven major group nuclei:

1. Anterior nucleus

- connect to the hypthalamus & limbic system

- it functions in emotions, regulation of alertness and memory

2. Medial nuclei

- Connect to cerebral cortex, limbic system & basal ganglia

- It function in emotions, learning, memory, awareness, and cognition

(thinking & knowing)

3. Nuclei in the lateral group

a. Lateral dorsal nucleus

function in expression of emotions

b. Lateral posterior nucleus & pulvinar nucleus

Help integrate sensory information

4. Intralaminar nuclei

- Lie within the internal medullary lamina

- Make connections with the reticular formation, cerebellum,

basal ganglia, and cerebral cortex

- Influences levels of consciousness and alertness

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5. Nuclei in ventral goup

a. Ventral anterior nucleus

contributes to motor functions, possibly movement planning

b. Ventral lateral nucleusActive during movement on the opposite side of the body

c. Ventral posterior nucleus

Relays impulses for somatic sensations such as touch, pressure,

proprioception, vibration, heat, cold and pain from the face and

body to the cerebral cortex

d. Lateral geniculate nucleusRelays visual impulses for sight from retina to the primary visual

area of the cerebral cortex

e. Medial geniculate nucleus

Relays auditory impulses for hearing from the ear to the primary auditory

area of the cerebral cortex

6. Midline nucleus

Function in memory and olfaction

7. Reticular nucleus

This nucleus monitors, filters, and integrates activities of other thalamic nuclei

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Every thalamic nucleus (except the reticular nucleus)sends axons to specific parts of the cerebral cortex andevery part of the cerebral cortex sends reciprocal fibersback to the thalamic nuclei

The thalamus is an important relay station for twosensory-motor axonal loops involving the cerebellum

and the basal nuclei:(1) the cerebellar-rubro-thalamic-cortical-ponto-cerebellar loop and

(2) the corticalstriatal-pallidal-thalamic-cortical loop,both of which are necessary for normal voluntarymovement.

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Small area below the thalamus

Have the paired subthalamic nuclei

The subthalamic nuclei, red nuclei and substansia nigra work together with

the basal ganglia, cerebellum and cerebrum in the control of body movement

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a small region superior and posterior to the thalamus

Consist of the pineal gland and habenular nuclei

The pineal gland- is about the size of a small pea

- protrudes from the posterior midline of the third ventricle

- secrete hormone melatonin to promote sleepiness, contribute to the settingof the bodys biological clock

The habenular nuclei

Involved in olfaction, especially emotional responses to odor

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The hypothalamus is a small part of the diencephalon located inferior to

the thalamus

Forms the floor and the inferior part of the lateral walls of the third ventricle

F j i f h th l

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Four major regions of hypothalamus:

1. The mammillary region

- Adjacent to midbrain, is the most posterior part of thehypothalamus

- It includes : * the mammillary bodies

* posterior hypothalamic nucleus

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2. The tubular region- The widest part of hypothalamus- It includes : *dorsomedial nucleus

*ventromedial nucleus*arcuate nucleus*infundibulum

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3. The supraoptic region

- Lies to the optic chiasm

- Contains : * paraventricular nucleus

* supraoptic nucleus

* anterior hypothalamic nucleus

* suprachiasmatic nucleus

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4. The preoptic region

- Contain :

*medial preoptic nucleus

*lateral preoptic nucleus

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Medial Zone

In the medial zone, the

following hypothalamic

nuclei can berecognized, from

anterior to posterior:

(1) preoptic nucleus;

(2) the anterior nucleus

(3) suprachiasmatic

nucleus

(4) the paraventricularnucleus

(5) the dorsomedial

nucleus

(6) the ventromedial

nucleus

(7) the infundibular(arcuate) nucleus

(8) the posterior

nucleus

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Lateral Zone

In the lateral zone, the

following hypothalamic

nuclei can berecognized, from

anterior to posterior:

(1) preoptic nucleus

(2) suprachiasmatic

nucleus

(3) supraoptic nucleus,(4) lateral nucleus,

(5) tuberomammillary

nucleus

(6) lateral tuberal nuclei.

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Nucleus Function

Supraoptic nucleus Synthesizes vasopressin (antidiuretic hormone)

Paraventricular nucleus Synthesizes oxytocin

Preoptic and anterior nuclei Control parasympathetic system

Posterior and lateral nuclei Control sympathetic system

Anterior hypothalamic nuclei Regulate temperature (response to heat)

Posterior hypothalamic nuclei Regulate temperature (response to cold)

Lateral hypothalamic nuclei Initiate eating and increase food intake (hunger

center)

Medial hypothalamic nuclei Inhibit eating and reduce food intake (satiety

center)

Lateral hypothalamic nuclei Increase water intake (thirst center)

Suprachiasmatic nucleus Controls circadian rhythms

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Hypothalamic Regulatory Hormone Functional Result

Growth hormonereleasing hormone

(GHRH)

Stimulates linear growth in

epiphyseal cartilages

Growth hormoneinhibiting hormone(GHIH) or somatostatin Reduces linear growth inepiphyseal cartilages

Prolactin-releasing hormone (PRH) Stimulates lactogenesis

Prolactin-inhibiting hormone (PIH),

dopamine

Reduces lactogenesis

Corticotropin-releasing hormone (CRH) Stimulates adrenal gland to

produce corticosteroids and

sex hormones

Thyrotropin-releasing hormone (TRH) Stimulates thyroid gland to

produce thyroxine

Luteinizing hormonereleasing hormone

(LHRH),follicle-stimulating releasing

hormone (FRH)

Stimulates ovarian follicles and

production of estrogen and

progesterone