presentation about the diencephalon

1. DIENCEPHALON
(& RETICULAR FORMATION)
By Dr Catherine Mwesigwa Lutalo
Facilitated by Dr Joseph Ochieng
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2. EMBRYOLOGY recap
• Neurulation – week 3-4
• Formation of 3 primary vesicles – week 4
• Including Prosencephalon
• Formation of 5 secondary vesicles – week 6
• Telencephalon and DIENCEPHALON
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3. ADULT DERIVATIVES OF DIENCEPHALON
(included in presentaion) (covered elsewhere)
• Thalamus
• Hypothalamus
• Epithalamus
• Subthalamus
• Mamillary bodies
• Neurohypophysis (post
pituitary gland)
• Pineal gland
• Globus pallidus
• Retina
• Iris
• Ciliary body
• Optic nerve
• Optic chiasma
• Optic tract
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4. Diencephalon
• Paired structure
• Central core of cerebrum
• Located between the brain stem
and the cerebral hemisphere
• Continuous with the rostral part
of the midbrain
• Forms the lateral wall of the 3rd
ventricle
• Extends from interventricular
foramina till where 3rd ventricle
is continous with cerebellar
aqueduct
C
mo
mb
p
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5. • Surrounded by the
cerebral hemispheres
• A little part seen
externally on the base
of the brain caudal to
optic chiasma,
includes:
• Infundibulum
• Tuber cinerium
• Mamillary bodies
• Other parts seen on
sagittal & coronal
sections
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6. • On the medial
surface, the
diencephalon is
subdivided, by
hypothalamic
sulcus
(indicated by
black line) into:
 Dorsal part
 Ventral part
Cerebral
aqueduct
Dorsal
Fornix
Optic chiasma
Ventral
Midbrain
CC
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7. Diencephalon
 Made of four parts
Thalamus
Hypothalamus
Epithalamus
Subthalamus
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8. Dorsal part
Thalamus & Epithalamus
Subthalamus & Hypothalamus
Ventral part
H
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9. Relations
Lateral:
Internal
capsule
Medial: 3rd
ventricle
Dorsal:
Lateral
ventricle
Ventral: Exposed on
the base of the brain
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10. BLOOD SUPPLY
• Posterior cerebral, terminal branch of Basilar
artery
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11. THALAMUS
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12. Thalamus
• Large mass of grey matter, in shape and size, resembles
small hen’s egg
• Forms the lateral wall of the 3rd ventricle
• Separated from hypothalamus by hypothalamic sulcus
• May be connected to opposite thalamus by
interthalamic adhesion (massa intermedia)
thalamus
Interthalamic
adhesion
Hypothalamic
sulcus
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13. Thalamus has a narrow
anterior end called
tubercle of thalamus,
that lies in the posterior
boundary of the
interventricular
foramen
The expanded posterior end,
called pulvinar, lies above the
superior colliculi
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14. Relations
Medial: 3rd
ventricle
Dorsal: lateral ventricle
Ventral: Subthalamus & Hypothalamus
Lateral:
Internal
capsule
Caudal: midbrain
Anterior:
interventricular
foramen
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15. Surfaces
4 Surfaces:
Superior
Inferior
Medial
Lateral
S
l
M
L
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16. Superior Surface
• Bounded laterally by
caudate nucleus,
thalamostriate vein
and a nerve fiber
bundle called stria
terminalis
• Lateral part lies in the
floor of the lateral
ventricle & is covered
by ependyma
• Medial part is related
to the choroid plexus
of the 3rd ventricle
caudate nucleus
LV
ependyma
choroid plexus
thalamo-
striate vein
stria terminalis
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17. Lateral Surface
• Related to the
internal capsule
Inferior Surface
• Rests on the
subthalamus &
hypothalamus
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18. Medial Surface
• Stria medullaris thalami
(a fascicle of nerve
fibers) courses along its
dorsomedial margin
• Below is limited by
hypothalamic sulcus
• Forms the upper part
of the lateral wall of
the 3rd ventricle
Stria medullaris thalami
Hypothalamic sulcus
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19. Blood supply
• Perforating branches of the posterior cerebral artery
• Thalamoperforating artery supplies the
anterior dorsal and medial thalamus ie posteromedial
group
• Thalamogeniculate artery supplies the
posterior and lateral thalamus and geniculate bodies
• Also branches from posterior communicating anterior
choroidal,posterior choroidal & middle cerebral artery.
• Venous ; Thalamostriate veins → Internal cerebral
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20. Internal Organization
• Thalamus is composed
of gray matter,
interrupted by two
vertical sheaths of white
matter called medullary
laminae.
• External medullary
lamina:
 Located laterally,
separates reticular
nucleus from the rest of
the thalamic mass
 Contains
thalamocortical &
corticothalamic fibers
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21. • Internal medullary
lamina
 Y- shaped band, divides
thalamus into Anterior,
Medial & Lateral nuclear
groups
 Contains:
 Fibers connecting
thalamic nuclei with
one another
 Intralaminar nuclei
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22. Nuclear Groups
• Anterior
• Lateral divided into:
 dorsal &
 ventral tiers
• Medial nuclear group
• Intralaminar nuclei
• Reticular nucleus
• Midline nuclei
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23. Functional Organization
• All the nuclei of the
thalamus except
reticular nucleus,
project to ipsilateral
cerebral cortex
• The whole of the
cerebral cortex
receives input from
the thalamus
• All thalamic nuclei
receive corticofugal
fibers in a basically
reciprocal fashion
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24. • Based on their connection with the
cerebral cortex, the thalamic nuclei are
divided into:
Specific nuclei
Nonspecific nuclei
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25. • Specific nuclei:
Have well-defined
sensory and motor
functions
Have highly organized
point-to-point connection
with sensory & motor
regions of cerebral cortex
Lie within the ventral tier
of the lateral nuclear
group
• Non-specific Nuclei:
Receive less functionally
distinct afferent input
Connect with wider area
of cortex, including
associative and limbic
regions
 Include nuclei of the
dorsal tier of lateral
group (LD,LP,pulvinar),
and whole of the
anterior and medial
group
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26. SUMMARY OF LATERAL(SPECIFIC) NUCLEI, CONNECTIONS & FUNCTIONS
Function Afferents Efferents
Ventral Anterior Influences motor activity Ipsilateral globus pallidus &
substantia nigra
Motor cortex
Premotor &
supplementary motor
cortex
Ventral Lateral Influences motor activity Ipsilateral globus pallidus &
substantia nigra
Contralateral dentate nucleus
Primary motor cortex
Primary motor cortex
Ventral Posterior
VPL & VPM
Chief sensory relay station General sensory afferents from the
contralateral half of the Head & neck
;VPM-trigeminal &gustatory
Body; VPL-ascending sensory tracts
Primary
somatosensory cortex
Lateral Geniculate Part of the Visual Pathway
(visual information from
opp field of vision)
Ipsilateral temporal hemiretina
Contralateral nasal hemiretina
Optic radiation to the
primary visual cortex
Medial Geniculate Part of the Auditory
Pathway (
Inferior colliculus
Contralateral auditory( lateral
lemniscus from both ears)
Auditory radiation to
the primary auditory
cortex
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27. SUMMARY OF NON-SPECIFIC NUCLEI, CONNECTIONS & FUNCTIONS
Function Afferents Efferents
Anterior
3 parts:
Anteroventral
Anteromedial
Anterodorsal
Functionally part of the
limbic system. Involved in
control of instinctive
drives, emotional aspect
of behaviour and in recent
memory
Cingulate gyrus,
Mammillary body of
hypothalamus
Cingulate gyrus
Hypothalamus
Medial Group
(Mediodorsal & Nucleus
reuniens)
Integrates emotion,
thought & judgment
Hypothalamus, amygdala,
other thalamic nuclei,
prefrontal cortex
Prefrontal cortex & limbic
structures
Lateral dorsal,lateral
posterior,pulvinar
Unknown Cerebral cortex, other
thalamic nuclei
Cerebral cortex, other
thalamic nuclei
Intralaminar Influences levels of
consciousness and
alertness
Reticular formation,
spinothalamic &
trigeminothalamic
systems
Widespread regions of
cerebral cortex, caudate &
putamen of the basal
ganglia
Midline Important in visceral
functions
Brainstem reticular
formation
Cingulate gyrus and
hypothalamus
Reticular ? Cerebral cortex
regulates thalamus
Cerebral cortex, reticular
formation
Other thalamic nuclei
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28. Functions of the thalamus
• Receives and analyses all the sensory information
(except olfactory) from the body
• Having extensive connections with the basal ganglia and
the motor cortices, it plays a pivot role in voluntary
motor activity. Thalamotomy (VA, VL) was once used to
treat basal ganglia disorders
• Connections with the limbic system makes it important
in the control of mood, emotional and sexual behavior,
and memory
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29. Thalamic Lesions
• Due to neoplasms, degeneration from poor B/S or
hemorrhage
• Cerebrovascular lesions (post cerebral a.) or tumors of
thalamus lead to:
 Loss of sensation in the contralateral side of face and
body followed by distressing discomfort, & burning and
diffuse pain in the anaesthetic areas (thalamic pain)
Thalamic syndrome: Abnormal voluntary movements
(chorea or hemiballismus) with hemisensory disturbance.
Also body becomes hypersensitive to pain as a result of
damage to the thalamus
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30. • Central location – lesion affects adjascent
structures hence signs/symptoms overshadowing
thalamic
Eg midbrain - coma, internal capsule - extensive
motor and sensory deficits.
• Surgical relief of pain by thalamic cauterization of
intralaminar nuclei ass. with relay of pain to the
cerebral cortex.
• Choreoathetosis with ataxia (???could also be
due to damage to caudate and lentiform nuclei)
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31. HYPOTHALAMUS
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32. • Small part of diencephalon
• Weighs about 4g (cm3 )
• Occupies the bottom and infero-lateral walls of
the III ventricle
• In the center of the limbic system.
• At the crossing of numerous nerve pathways.
• Surrounded by the circle of Willis.
• Part of the diencephalon that controls
visceromotor, endocrine functions & affective
(emotional) behavior.
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33. Boundaries
Anterior Lamina terminalis
Posterior Corpora mammillaria
Dorsal Sulcus hypothalamicus
Medial 3rd ventricle
Lateral Subthalamus & capsula interna
Ventral Chiasma opticum, tuber
cinereum, corpora mammillaria
& neurohypophysis
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34. • Optic chiasma
• Infundibulum
• Tuber cinereum
• Mamillary bodies
• Optic tract
Anatomy
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35. 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:
anterior, tuberal and posterior.
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37. BLOOD SUPPLY
• Circle of Willis; perforating branches
Anteromedial group
Posteromedial group
Thalamoperforating branches
• Hypophyseal portal system connects
the hypothalamus with the anterior pituitary
• Venous;
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38. Crossed by fasciculus prosencephalicus medialis
Contains several nuclei, some overlapping; (A-P)
1. Preopticus
2. Suprachiasmatic
3. Supraoptic
4. Lateral - when stimulated feeling of hunger
- when destroyed anorexia nervosa and fast (starvation)
5. Tuberomammilary
6. Lateral tuberal
Lateral zone
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39. Preoptic Control of parasympathetic function
(telencephalic) –
-Androgen and estrogen sensitivity
Supraoptic Synthesis and secretion of vasopressin.
Damage causes diabetes insipidus.
Neurones project into neurohypophysis
Paraventricular Synthesis and secretion of oxytocin (milk
secretion & uterine contraction).
Controls food intake
Neurones project into neurohypophysis
Anterior Controls temperature and sexual behavior.
Suprachiasmatic Fibers from the retina; fibers to the pineal body.
Controls circadian rhythms.
Anterior Region Nuclei
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40. Hypothalamus
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41. Dorsomedial
- center of hunger
- on stimulation rage, cruelty
Ventromedial
- center of satiety
- on stimulation depression of apettite
Arcuate
- periventricular in tuber cinereum
- secretes releasing factors
- dopaminergic neurons, inhibit release of prolactin
Tuberal Region Nuclei
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42. Mammillary- impulses from hippocampal formation via fornix and impulses from
tegmental nuclei, nuclei raphae via pedunculus mamillaris
- projections to nucleus anterior thalami via tractus mamillothalamicus
Posterior
 Anterior zone – sensitive to inc in temp thus dissipates heat by sweating via ANS
 Posterior zone – sensitive to temp dec thus conserves heat by shivering via ANS
- controls thermoregulation
- damage causes poikilothermia – inability of thermoregulation
Posterior Region Nuclei
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43. 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
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44. Connections
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
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45. 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.
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46. Efferents:
To autonomous nervous system
medulla:
а) parasympathetic nucleus of n. vagus
b) 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;
b) 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).
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47. Blood pressure, temperature, water and electrolyte
balance, weight are maintained within optimal values.
Hypothalamus = Homeostasis
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48. Functional characteristics
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49. Hypothalamic lesions
• Obesity and Wasting
• Sexual Disorders (retardation- prepubertal,
impotence/amenorrhea – postpubertal
• Head injury or surgery in adjascent structures
can cause inability to thermoregulate
• Diabetes insipidus
• Disturbances of sleep
• Emotional disorders
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50. SUBTHALAMUS
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51. 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
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52. 52
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53. 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
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54. 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
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55. EPITHALAMUS
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56. Epithalamus
• Relatively small
part, located in
most caudal and
dorsal region
• Lies immediately
rostral to superior
colliculus
• Consists of:
 Pineal gland &
 Habenular nuclei

57. Pineal Gland
• An endocrine organ
• Synthesizes
melatonin
• Controls:
 Sleep/awake
cycle
 Regulation of
onset of puberty

58. Habenular nuclei
• Located in habenular
triangle (area in the
posterior part of the
diencephalon, just
anterior to pineal gland)
• Have connections with
limbic system
 Serves autonomic
function and emotional
drives

59. FINALLY…..
The will to win, the desire to succeed, the
urge to reach your full potential... these
are the keys that will unlock the door to
personal excellence
Confucius
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60. THANK YOU FOR
LISTENING!
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