The document provides an overview of the diencephalon, which is the region of the brain between the cerebral hemispheres and below the thalamus. It describes the gross topography and borders of the diencephalon. The diencephalon includes the epithalamus, thalamus, metathalamus, subthalamus, and hypothalamus. Details are given on the structures and functions of these regions, including the thalamic nuclei and their connections. Clinical notes discuss lesions of the thalamus and how they can cause sensory loss or pain.

1. By
Dr.Faris Al-Haddad
M.B.Ch.B, PhD Anatomy
College of Medicine,
Hawler Medical University
Arbil, Iraq
e-mail: farisurgeon@gmail.com
Diencephalon

2. Diencephalon

3. GROSS TOPOGRAPHY OF
DI ENCEPHALON,
“or in-bet ween br ain,”
• is complet ely sur rounded by
t he cer ebral hemispher es
except at it s vent ral
surf ace.
Borders :
• Ant er ior ly :
Foramen of Monro
Lamina t er minalis
• Post erior ly :
Post erior commissur e

4. • Super ior ly :
f or ms f loor of
lat er al vent ricle
• Medially :
f or ms lat eral wall
of
3rd
vent r icle.
• lat er ally :
Post er ior limb of
int er nal capsule
Lat er al and 3rd
vent r icles

5. Diencephalon is also
mar ked medially by :
St ria medullaris
t halami

6. • A groove ext ending
bet ween t he f oramen
of Monro and t he
aqueduct of Sylvius
(The Hypot halamic
Sulcus)
t hat divides
diencephalon int o
1. A vent ral port ion,
The

7. • The t wo t halami are
connect ed acr oss
t he midline in about
70% of humans
t hrough t he
(int ert halamic
adhesion)

8. Diencephalon
includes :
(1) Epit halamus,
(2) Thalamus and
Met at halamus,
(3) Subt halamus,
(4) Hypot halamus.

9. Epit halamus

10. Epithalamus :
The epit halamus occupies a
posit ion dorsal t o t he t halamus and
includes t he f ollowing st ruct ures :
A. STRIA MEDULLARIS THALAMI
This band of nerve f ibers connect s
t he sept al (medial olf act ory) area
wit h t he habenular nuclei.
B. HABENULAR NUCLEI
are part of a net work t hat
includes t he limbic and olf act ory
syst ems, concerned wit h
mechanisms of emot ion & behavior .
C. PINEAL GLAND
I t s an endocrine gland. The
f unct ions of t he pineal gland are not
well underst ood. I t may have roles
in gonadal f unct ion and circadian
rhyt hm.

11. Thalamus

12. Thalamus :
General Appearances
• The t halamus is a large,
egg-shaped mass of gr ay
mat t er t hat f or ms t he
maj or par t of t he
diencephalon.
• Ther e ar e t wo t halami, and
one is sit uat ed on each side
of t he t hir d vent r icle.

13. • Ant er ior end
of t he t halamus is
nar row and r ounded
• Post er ior end
is expanded t o f or m
t he pulvinar , which
overhangs t he
super ior colliculus .
• Usually connect ed t o
t he opposit e t halamus
by int er t halamic
adhesion

14. Relat ions :
• Ant erior ly: int ervent ricular
f oramen
• Post eriorly : expand as Pulvinar
• Superiorly : f loor of lat eral
vent ricle & Tela choroidae of
3rd
vent ricle
• I nf erior ly : I t rest s on
subt halamus & hypot halamus.
Midbrain.
• Medially : f orms part of lat eral
wall of t he 3rd
vent ricle. St ria
medullaris t halami

15. Subdivisions of t he Thalamus
The gr ay mat t er of t he
t halamus is divided by a
ver t ical sheet of whit e
mat t er,
int er nal medullar yint er nal medullar y
laminalamina,
int o medial and lat er al
halves. t halamus t hus is
subdivided int o t hree main
part s;
1. Ant er ior part : lies bet ween
t he limbs of t he Y.
2. Medial part : on medial side
of Y st em.
Anterior
Medial
Lateral

16. • Each of t he t hree par t s of t he t halamus cont ains
a gr oup of :
THALAMI C NUCLEI .
• Ot her smaller nuclear groups are :
1. Wit hin int ernal medullar y lamina ( int r alaminar ),
2. On medial surf ace of t he t halamus
3. On lat er al sur f ace of t he t halamus.
4. Ret icular nucleus.

17. 1. Ant er ior par t :
• Ant er ior t halamic nuclei
2. Medial par t :
• Dor somedial nucleus
• Sever al smaller nuclei
3. Lat er al par t :
A. Dorsal Tier of t he Nuclei :
• Lat eral dorsal nucleus
( LD ),
• Lat eral post erior nucleus (
LP ),
• Pulvinar
B. Vent ral Tier of t he Nuclei :
• Vent ral ant erior nucleus
( VA )
• Vent ral lat eral nucleus ( VL
)
• Vent ral post erior nuclei
( VP ):
1. Vent ral post eromedial ( VPM
Thalamic Nuclei :

18. Ant erior
VA
VL
VI
VPM
VPL
VP
LD
LP
Pulvinar
MGB
LGB
lamina
I nt ernal medullary lamina
Median
Medial
I nt ert halamic
adhesion
THALAMI C NUCLEI

19. Funct ion of t he Thalamus
Alt hough an enormous amount of research has
been devot ed t o t his area, we st ill know very
lit t le about t he f unct ional signif icance of many
of t he nuclei.
1. A vast amount of sensory inf ormat ion of all
t ypes (except smell t hat inegrat ed wit h t ast e
t hen) converges on t he t halamus and presumably
is int egrat ed t hrough t he int erconnect ions
bet ween t he nuclei. The result ing inf ormat ion
pat t ern is dist ribut ed t o ot her part s of t he
cent ral nervous syst em.
2.The t halamus possesses cert ain very import ant
nuclei whose connect ions have been clearly
est ablished. These include t he ventralventral
posteromedialposteromedial nucleus, t he ventralventral
posterolateralposterolateral nucleus, t he medial geniculatemedial geniculate
body, and t he lateral geniculatelateral geniculate body. Their

20. 3. Anat omically and f unct ionally, t he
t halamus and t he cerebral cort ex are
closely linked. The f iber connect ions
have been est ablished, and it is known
t hat f ollowing removal of t he cort ex,
t he t halamus can appreciat e crude
sensat ions. However, t he cerebral
cort ex is required f or t he
int erpret at ion of sensat ions based on
past experiences. For example, if t he
sensory cort ex is dest royed :
• one can st ill appreciat e t he presence
of a hot obj ect in t he hand;
• appreciat ion of t he shape, weight , and
exact t emperat ure of t he obj ect

21. Connect ions And Funct ion
Of Thalamic Nuclei

22. Thalamic
Nucleus
Af f er ent
Neuronal Loop
Ef f er ent
Neur onal Loop
Funct ion
Ant er ior
Nucleus
Cingulat e gyr us,
Hypot halamus
• Emot ional
t one
• Recent
memor y

23. Thalamic
Nucleus
Af f er ent
Neur onal
Loop
Ef f er ent
Neur onal Loop
Funct ion
Medial
Nuclei:
Dor somedial
Pr ef r ont al cor t ex,
hypot halamus,
ot her t halamic nuclei
I nt egr at ion
of somat ic,
viscer al, &
olf act or y
inf or mat ion
and
r elat ion t o
emot ional
f eelings and
subj ect ive
st at es

24. Thalamic
Nucleus
Af f er ent
Neur onal
Loop
Ef f er ent
Neur onal
Loop
Funct ion
Dor sal Tier of
t he Nuclei :
Lat er al
dorsal,
Lat er al
post erior,
Pulvinar
Cerebral cor t ex,
ot her t halamic nuclei
Unknown?

25. Thalamic
Nucleus
Af f er ent
Neur onal
Loop
Ef f er ent
Neur onal Loop
Funct ion
Vent ral Tier
of t he
Nuclei :
1. Vent r al
ant erior N.
Ret icular f or mat ion,
subst ant ia nigr a,
cor pus st r iat um,
pr emot or
cor t ex,
ot her t halamic nuclei
I nf luences
act ivit y of
mot or
cor t ex
2. Vent r al
lat eral N.
As in VA, but also has :
• maj or input f r om
cerebellum

26. Thalamic
Nucleus
Af f er ent
Neuronal
Loop
Ef f er ent
Neur onal
Loop
Funct ion
3. Vent r al
post er omedia
l (VPM)
Trigeminal
lemniscus,
gust at or y
f iber s
Pr imar y
somat ic
sensor y
(areas 3,1,
2)
in
cor t ex
Relays
common
sensat ions t o
consciousness4. Vent r al
post er olat era
l (VPL)
Medial and
spinal
lemnisci

27. Thalamic
Nucleus
Af f er ent Neur onal
Loop
Ef f er ent
Neur onal
Loop
Funct ion
Ret icular
Cer ebr al cor t ex,
r et icular f or mat ion
Ot her
t halamic
nuclei
Cer ebral
cor t ex
r egulat es
t halamus
I nt r alamina
r
Ret icular
f or mat ion,
spinot halamic and
t r igeminot halamic
t r act s
To
cer ebr al
cor t ex via
ot her
t halamic
nuclei,
cor pus
I nf luences
levels of
consciousne
ss and
aler t ness

28. METATHALAMUS

29. METATHALAMUS
The t erm met at halamus ref ers t o t wo t halamic nuclei : t he
medial geniculat e and lat eral geniculat e.
1. Medial Geniculate Nucleus
This is a relay t halamic nucleus in t he audit ory syst em. I t
receives :
• Audit ory f ibers reach t he medial geniculat e body via
inf erior brachium of t he inf erior colliculus.
• Af f erent f eedback f ibers comes f rom t he primary audit ory
cort ex in t he t emporal lobe.
• Ef f erent out f low f orms t he audit ory radiat ion of t he
int ernal capsule t o t he primary audit ory cort ex in t he
t emporal lobe (areas 41 and 42).
• have roles in :
1. spectral analysis of sound,
2. sound pattern recognition,
3. auditory memory,
4. localization of sound in space,

30. 2. Lateral Geniculate Nucleus
This is a r elay nucleus in t he visual syst em. I t
receives :
• Visual f iber s f r om t he opt ic t ract conveying
impulses f r om bot h r et inae.
• Af f erent Feedback f ibers also reach t he nucleus
f rom t he primar y visual cort ex (ar ea 17) in t he
occipit al lobes.
• Ef f erent out f low f or ms t he opt ic radiat ion of t he
int er nal capsule t o t he primar y visual cort ex in t he
occipit al lobe.
• Some of t he ef f erent out f low pr oj ect s t o t he
pulvinar nucleus and t o t he secondar y visual cort ex
(areas 18 and 19)

31. Clinical Not es About Thalamus
• Since t he t halamus is such an import ant
relay and int egrat ive cent er, so f ollowing
disease of t his area t here will be prof ound
ef f ect s.
• The t halamus may be invaded by neoplasm,
undergo degenerat ion f ollowing disease of it s
art erial supply, or be damaged by
hemorrhage.

32. Lesions of t he Thalamus
Sensory Loss
• These lesions usually result f rom t hrombosis
or hemorrhage of one of t he art eries
supplying t he t halamus. Damage t o t he
vent ral post eromedial nucleus and t he
vent ral post erolat eral nucleus will result inresult in
the loss of all forms of sensationthe loss of all forms of sensation,
including light t ouch, t act ile localizat ion and
discriminat ion, and muscle j oint sense f rom
t he opposit e side of t he body.

33. • Surgical Relief of Pain by Thalamic
Caut erizat ion :
Caut erizat ion of some nuclei has been shown
t o relieve severe and int ract able pain
associat ed wit h t erminal cancer.
• Thalamic Pain:
Thalamic pain may occur as t he pat ient is
recovering f rom a t halamic inf arct .
Spont aneous pain, which is of t en excessive
(t halamic overreact ion), occurs on t he
opposit e side of t he body. The painf ul
sensat ion may be aroused by light t ouch or
by cold and may f ail t o respond t o powerf ul

34. Subt halamus
The subt halamus is a mass of gray and whit e
subst ance in t he caudal diencephalon. I t is
bor dered :
• Medially by t he hypot halamus,
• Lat er ally by t he int ernal capsule,
• Dor sally by t he t halamus,
• Vent r ally by t he int ernal capsule.
The subt halamus consist s of t hr ee main st ruct ur es;
t hese ar e :
1. Subt halamic Nucleus,
2. Fields Of For el,
3. Zona I ncert a.
Funct ion : has wide connect ions, t hat engage it in

36. Hypot halamus

37. Hypot halamus
Lies in t he diencephalon vent r al t o t he
hypot halamic sulcus .
Relat ions:
1. Ant er ior ly : Lamina t er minalis
2. Post er ior ly : Midbrain.
3. I nf er ior ly : Ant ropost er iorly :
• Opt ic chiasma,
• I nf undibulum f orms pit uit ary st alk.
• Floor slopes upwards and backwar ds t o aqueduct ,
• Floor is mar ked by t he pair of mamillar y bodies and
behind t hem by t he post erior per f or at ed
subst ance.
• Floor bet ween opr ic chiasma & mamillary bodies is
Tuber Cinereum.
4 Medially : 3rd
vent r icle

38. • The f ornix divides t he hypot halamus
1. The Lat eral Zone :
cont ains mainly t he medial
f orebr ain bundle which connect s t he sept al
area, hypot halamus & midbrain. Among
which are scat t ered neurons of lat eral
hypot halamic nuclei which are :
• part of t he preopt ic nucleus,
• part of t he suprachiasmat ic nucleus,
• Supraopt ic nucleus,
• Lat eral nucleus,
• Tuberomammillary nucleus,
• Lat eral t uberal nuclei.

40. 1. Medial Zone :
has a clust er of
nuclei organized int o maj or groups. From
ant erior t o post erior :
• Preopt ic nucleus;
• Ant erior nucleus,
• Suprachiasmat ic nucleus;
• Paravent ricular nucleus;
• Dorsomedial nucleus;
• Vent romedial nucleus;
• I nf undibular (arcuat e) nucleus

42. AI N AFFERRENT CONNECTI ONS OF HYPOTHALAMU

43. Or igin Pat hway Dest inat ion
Viscer a and
somat ic
st r uct ur es
Medial and spinal
lemnisci, t r act us
solit ar ius,
r et icular
f or mat ion
Hypot halamic
nuclei
Ret ina Visual f ibers
Supr achiasmat ic
nucleus
Olf act ory mucous
membr ane
Medial f or ebr ain
bundle
Hypot halamic
nuclei
I nner ear Audit or y f ibers
Hypot halamic
nuclei

44. Or igin Pat hway Dest inat ion
Hippocampus
Hippocampo-
hypot halamic f iber s
( main out put of
limbic syst em)
Nuclei of
mammillar y body
Fr ont al lobe of
cer ebr al cor t ex
Cor t icohypot halamic
f iber s
Hypot halamic
nuclei
Amygdaloid
complex
Amygdalohypot hala
mic f iber s
Dor somedial and
midline nuclei of
t halamus
Thalamohypot halami
c f iber s
Tegment um of
midbr ain
Tegment al f iber s

45. MAIN EFFERRENT CONNECTIONS OF HYPOTHALAMUS

46. Or igin Pat hway Dest inat ion
Pr eopt ic,
ant erior,
post er ior and
lat er al nuclei of
hypot halamus
Descending f ibers
in r et icular
f ormat ion t o
br ainst em and
spinal cor d
Par asympat het ic
& Sympat het ic
out f lows
Nuclei of
mammillary body
Mammillo
t halamic t r act
Ant erior nucleus
of t halamus;
relayed t o
cingulat e gyr us
Mammillo
t egment al t r act
Ret icular
f or mat ion in
t egment um of
midbr ain
Hypot halamic
Mult iple pat hways Limbic syst em

47. ConneCtions of the hypothalamus With the
hypophysis Cerebri
The hypot halamus is connect ed t o t he hypophysis
cerebri (pit uit ary gland) by t wo pat hways:
(1) nerve f ibers t hat t ravel f rom t he supraopt ic and
paravent ricular nuclei t o t he posterior lobe
of t he hypophysis
(2) long and short portal blood vessels
t hat connect sinusoids in t he median eminence and
inf undibulum wit h capillary plexuses in anterior
lobe of t he hypophysis.
• These pat hways enable t he hypot halamus t o
inf luence t he act ivit ies of t he endocrine glands.

48. Hypophyseal Port al Syst emHypophyseal Port al Syst em
is f ormed on each side f rom
t he
• Superior hypophyseal ar t er y,
which is a branch of t he
int ernal car ot id art ery.
• The art er y divides int o t uf t s
of capillar ies.
• These capillar ies drain int o
long and shor t descending
vessels t hat end in t he
ant erior lobe of t he
hypophysis by dividing int o
vascular sinusoids t hat pass

49. Hypot halamic
Releasing and I nhibit ory
Hormones and
Their Ef f ect s on
Ant erior Lobe of
Hypophysis (Pit uit ar y)

50. Hypot halami
c Regulat ory
Hor mone
Pr esumed
nuclei of
origin
Ant er ior
Pit uit ar y
Hor mone
pr oduces
Funct ional
Result
Growt h
Hor mone–
Releasing
Hor mone
(GHRH)
I nf undibular
(ar cuat e
nucleus)
Gr owt h
hor mone
(GH)
St imulat es
linear gr owt h
in epiphyseal
car t ilages
Growt h
Hor mone–
I nhibit ing
Hor mone
(GHI H) or
Supr achiasma
t ic nucleus
Gr owt h
hor mone
(r educed
pr oduct ion)
Reduces
linear gr owt h
in epiphyseal
car t ilages

51. Hypot halami
c Regulat ory
Hor mone
Presumed
nuclei of
or igin
Ant erior
Pit uit ary
Hor mone
Funct ional
Result
Pr olact in-
Releasing
Hor mone
(PRH)
?
Prolact in
(lut eot ropic
hor mone,
LTH)
St imulat es
lact ogenesis
Pr olact in-
I nhibit ing
Hor mone
(PI H),
Dopamine
Prolact in
(lut eot ropic
hor mone,
LTH)
(r educed
Reduces
lact ogenesis

52. Hypot halami
c Regulat ory
Hor mone
Presumed
nuclei of
or igin
Ant erior
Pit uit ary
Hor mone
Funct ional
Result
Cort icot ropi
n-Releasing
Hor mone
(CRH)
Par avent r icul
ar nuclei
Adr enocor t ic
ot r opic
hor mone
(ACTH)
St imulat es
adrenal gland
t o pr oduce
cor t icost er oi
ds and sex
hor mones
Thyr ot r opin
-Releasing
Hor mone
(TRH)
Par avent r icul
ar ,
dor somedial
nuclei and
adj acent
Thyr oid-
st imulat ing
hor mone
(TSH)
St imulat es
t hyr oid gland
t o pr oduce
t hyr oxine

53. Hypot halami
c Regulat ory
Hor mone
Presumed
nuclei of
or igin
Ant erior
Pit uit ary
Hor mone
Funct ional
Result
Lut einizing
Hor mone–
Releasing
Hor mone
(LHRH), ?
Follicle-
St imulat ing
Releasing
Hor mone
(FRH)
Pr eopt ic and
ant erior
nuclei
Lut einizing
hor mone
(LH) and
f ollicle-
st imulat ing
hor mone
(FSH)
St imulat es
ovarian
f ollicles and
product ion
of est r ogen
and
pr ogest eron
e

54. Main Funct ions of
Hypot halamus

55. Hypot halamic
Nucleus
Presumed Funct ion
Supr aopt ic Synt hesizes ant idiur et ic hormone
Par avent r icular Synt hesizes oxyt ocin
Pr eopt ic &
ant er ior
Cont rol par asympat het ic syst em
Post er ior & lat eral Cont r ol sympat het ic syst em
Ant er ior Regulat e t emper at ur e (r esponse t o
heat )
Post erior Regulat e t emper at ur e (r esponse t o
cold)
Lat er al I ncr ease f ood int ake (hunger
cent er )
Medial Reduce f ood int ake (sat iet y

56. Clinical Not es

57. General Considerat ions :
• Af f erent haypot halamic pat hways are
received f rom a. cent ral nervous syst em
(especially f rom t he limbic syst em and t he
pref ront al cort ex)
b. plasma levels of circulat ing hormones.
• I t exert s it s inf luence on bodily f unct ions
t hrough t he autonomic nervous system &
endocrine system.

58. 1. Obesit y and Wast ing :
• I t is generally associat ed wit h genit al
hypoplasia or at rophy.
• Wast ing is less common t han obesit y in
hypot halamic disease.
• Severe cachexia is suggest ive of damage t o
pit uit ary gland.
2. Sexual Disorders :
• I n children, t here may be sexual ret ardat ion.
Af t er pubert y, t he pat ient wit h
hypot halamic disease may have impot ence or
amenorrhea.

59. 3. Hypert hermia and Hypot her mia :
• The pat ient wit h hyper t hermia is ot her wise normal
and has no signs of malaise, which occur s wit h
pyr exia secondar y t o inf ect ions.
• Hypot her mia also can f ollow a lesion of t he
hypot halamus.
4. Diabet es I nsipidus :
Diabet es insipidus result s f r om a lesion of t he
supraopt ic nucleus or f r om t he int er rupt ion of t he
ner vous pat hway t o t he post er ior lobe of t he
hypophysis. Char act er ist ically, t he pat ient passes
large volumes of ur ine of low specif ic gr avit y. As a
result , t he pat ient is ext remely t hirst y and dr inks
large quant it ies of f luids. The condit ion must be

60. 1. Dist urbances of Sleep :
• Short periods of sleep during t he waking
hours
• Or insomnia has been observed in pat ient s
wit h hypot halamic lesions.
2. Emot ional Disorders :
At t acks of unexplained weeping or
laught er, uncont rollable rage, depressive
react ions, and even maniacal out burst s all
have been observed in pat ient s wit h
hypot halamic lesions.