The diencephalon includes structures like the thalamus, hypothalamus, epithalamus, and subthalamus. The thalamus relays sensory and motor signals to the cerebral cortex. It contains nuclei that relay specific sensations like vision, hearing, and somatosensation. The hypothalamus controls autonomic functions and regulates behaviors related to hunger, thirst, temperature, sleep, and reproduction. It also controls the pituitary gland. The epithalamus includes the pineal gland and habenular nucleus. The subthalamus contains the subthalamic nucleus and is involved in motor control.

1. The diencephalon
Made by
SURBHI
Physiotherapist
physiosurbhi28@gmail.com
AIIMS
New Delhi

2. The diencephalon includes:
The diencephalon ("interbrain") is the region of the
vertebrate neural tube which gives rise to posterior
forebrain structures. In development, the forebrain
develops from the prosencephalon, the most anterior
vesicle of the neural tube which later forms both the
diencephalon and the telencephalon
the thalamus.
the hypothalamus.
the subthalamus.
the epithalamus.
The third ventricle lies between the halves of the
diencephalon.

4. THALAMUS IN HORIZONTAL
SECTION
The anterior end with anterior nucleus & forms the posterior
boundary of the interventricular foramen
• Thalami form the lateral walls of the third ventricle.
• Posterior limb of the internal capsule separates thalamus
from the lentiform nucleus.
• Pulvinar is demonstrated in the artwork below

7. Thalamus
It is a large ovoid mass of grey matter that forms major
part of diencephalon.
It is a station for all main sensory systems.
Its anterior end forms the posterior boundary of
interventricular foramen.
Its posterior end forms pulvinar.
Its medial surface forms the lateral wall of the third
ventricle.& 2 surfaces are interconnected by an
interthalamic adhesion
Inferior surface rests on the subthalamus

9. Its lateral surface separated from lentiform nucleus by internal
capsule.
It is sub-divided into anterior, medial and lateral parts, in each
we have a group of thalamic nuclei.
Function:-
Relaying sensation, spatial sense and motor signals to the
cerebral cortex, along with the regulation of consciousness,
sleep and alertness

11. Organization oftheDorsalThalamus
The thalamus is the largest component of the
diencephalon. It is the primary site of relay for all of the
sensory pathways except olfaction on their way to the
cerebral cortex. Even olfactory signals reach the thalamus
via indirect connections with the cortical regions initially
receiving the olfactory signal.
Thalamic nuclei contain many inhibitory interneurons
(GABAergic and peptidergic) that can modulate the
transmission of signals through the thalamus. Additionally,
many neuromodulatory neurotransmitter systems (such as
serotonin and norepinephrine systems) have terminations
within thalamic nuclei.

12. There are three basic types of thalamic nuclei:
i) relay nuclei;
ii) association nuclei; and
iii) nonspecific nuclei.
Relay nuclei receive very well defined inputs and project this
signal to functionally distinct areas of the cerebral cortex.
These include :
The nuclei that relay primary sensations (the ventral
posterolateral - VPL,
ventral posteromedial - VPM,
medial geniculate and lateral geniculate nuclei) and also the
nuclei involved in feedback of cerebellar signals (ventral
lateral - VL) and in feedback of basal gangliar output (part of
the VL and the ventral anterior nucleus - VA).

13. The association nuclei are the second type of thalamic
nuclei and receive most of their input from the cerebral
cortex and project back to the cerebral cortex in the
association areas where they appear to regulate activity.
The third type of thalamic nuclei are the Nonspecific
nuclei, including many of the intralaminar and midline
thalamic nuclei that project quite broadly through the
cerebral cortex, may be involved in general functions
such as alerting.

14. Relay Thalamic Nuclei
The VPL and VPM nuclei are part of the somatosensory
system. The VPL relays medial lemniscal and spinothalamic
connections to the cerebral cortex. The VPM receives
trigeminothalamic input and relays to the inferior portion of
the postcentral gyrus.
The lateral and medial geniculate nuclei are specific nuclei
that relay vision and hearing, respectively. The lateral
geniculate receives retinotopic input via the optic tract from
the contralateral homonomous visual world. This projects in
a topographic manner to the primary visual cortex via the
optic radiations

15. The optic radiations from the upper visual world loop
through the temporal lobe white matter on the way to the
visual cortex (Meyer's loop), while optic radiations from
the lower visual world pass just deep to the parietal lobe.
The medial geniculate receives tonotopically organized
auditory afferents from the inferior colliculus via the
brachium of the inferior colliculus. This projects to the
primary auditory cortex on the superior temporal gyrus
(transverse gyrus of Heschel).

16. The VL receives input from the cerebellum, mainly from
the dentate nucleus. There is a small input from the
basal ganglia to the rostral part of the VL, as well. The VL
projects to the primary motor area, area 4, of the
precentral gyrus and also has a smaller projection to
premotor areas. The VL is thus involved in motor
feedback from the cerebellum and basal ganglia to the
cerebral cortex.

18. The VA nucleus receives most of its input from the basal
ganglia especially the medial globus pallidus and
substantia nigra, parts reticulata. This projects to
premotor cortex including the supplementary motor
area of the frontal lobes and is involved in planning and
initiating movements. The centromedian nucleus (one of
the intralaminar nuclei) has reciprocal connections with
the globus pallidus and with the premotor cortex. It
appears to function as part of the basal gangliar
feedback system.

19. thalamus

22. Association Thalamic Nuclei
These nuclei receive the largest input directly from the
cerebral cortex.
The pulvinar is the largest of these association nuclei,
occupying the posterior part of the dorsal tier of the
thalamus. This receives afferent projections from the
superior colliculus as well as from the association cortex. It
projects to secondary visual areas and to association areas in
the parietotemporal region. This contributes to visual
perception and eye movements, probably relating to
attention to these stimuli.

24. ASSOCIATION THALAMICNUCLEI-
mediodorsal nucleus
The medial portion of the MD, along with the midline
nuclei, receives inputs from several brain areas including
the solitary nucleus, substantia nigra reticulata,
amygdala and ventral pallidum. It projects to limbic areas
of the cortex, including insular cortex, orbital frontal
cortex and subcallosal region. These cortical areas are
involved in autonomic regulation and emotions. Damage
to this area can also impair memory as may happen with
the amnestic syndrome due to alcoholism

26. Nonspecific Thalamic Nuclei
The reticular thalamic nucleus receives afferents from the
brain stem reticular formation as well as from the cerebral
cortex and thalamus. This makes a strongly inhibitory input
to thalamic nuclei. This nucleus may be important in sleep
wake cycles and maybe an important regulator of signals
relaying through the thalamus.
Many of the intralaminar nuclei and midline nuclei have
diffuse projections to the cortex and have been termed
"nonspecific". These nuclei are probably mostly involved in
arousal and alertness.

27. Connections of thalamus
Afferent impulses from a large number of subcortical
centres converge on thalamus.
Extroceptive and proprioceptive impulses ascend to it
through the medial lemniscus, Spinothalamic tract and
trigeminothalamic tract
Visual and auditory impulses reach the medial and lateral
geniculate bodies respectively.
Sensation of tastes are conveyed to it through
solitariothalamic fibers.
Although the thalamus does not receive direct olfactory
impulses, they reach it through the amygdaloid complex

29. Lesions of the thalamus
SENSORY LOSS
These lesions usually result from thrombosis or
hemorrhage in branches of MCA which is supplying the
thalamus.
Damage to ventral posteromedial nucleus and the
posterolateral nucleus will result in the loss of all forms of
sensation,including light touch, tactile localisation and
discrimination and muscle joint sense from the opposite
side of the body

31. Thalamic pain
It occurs when the patient is recovering from a thalamic
infarct.
Spontaneous pain i.e. excessive thalamic overreaction,
occurs on the opposite side of the body.
The painful sensation may be aroused by light touch or by
cold and may fail to respond to powerful analgesic drugs
The intralaminar nuclei of thalamus takes part in
the relay of pain to cerebral cortex. Cauterization
of these nuclei has shown to relieve severe and
intractable pain associated with terminal cancer

32. Abnormal involuntary
movements
Choreoathetosis with ataxia may follow vascular lesions
of the thalamus
The ataxia may arise as a result of loss of appriciation of
muscle and joint movement caused due to the thalamic
lesion.

33. Thalamic hand
The contralateral hand is held in an abnormal posture in some
patients with thalamic lesions.
The wrist is pronated and flexed, the metacarpophalengeal
joints are flexed and interphalangeal joints are extended
The fingers can be moved actively but slowly
The condition is due to altered muscle tone in the different
muscle groups.

37. Metathalamus
It provides the relay for special sensation of vision and
hearing :-
Lateral geniculate body for relay of visual sensation :-Part
of lateral geniculate nucleus that receives major input
from the retina & has reciprocal connections with the
primary visual cortex & the thalamic reticular nucleus
Medial geniculate body for relay of auditory sensationsit
occupies the ventro-medial quadrant, extending into the
fibers of the brachium of the inferior colliculus and
adjoining the ventral thalamic nucleus antero-medially.

39. Subthalamus
Lies inferior to thalamus.
It is situated between the thalamus and the tegmentum
of the midbrain; craniomedially it is related to the
hypothalamus.
Nerve cells found in it are cranial ends of the red nucleus
and the substantia nigra
Its structure is extremely complex.
It has subthalamic nucleus which has connection with
corpus striatum.
Subthalamus also contains many important tracts.

40. Clinical anatomy
Discrete lesions of the subthalamus nucleus result in
hemiballismus characterised by:-
Involuntary choreiform movements on the opposite side
of the body.
The condition is abolished by ablation/removal of the
globus pallidus,or of its efferent tracts, the anterior
ventral nucleus of the thalamus, area 4 of the cerebral
cortex, or of corticospinal tract.
From these facts it appears that subthalamic nucleus has
inhibitory control on the globus pallidus & on cerebral
cortex

41. Epithalamus
Consists of habenular nucleus and the pineal gland.
Pineal body or epiphysis is a small organ,projecting
backwards and downward b/w superior colliculi
It consists of a body & stalk which divides into superior
lamina that contains habenular commissure & inferior
contains the posterior commisssure
i.e. is related to gonadal functions, through secretion of
a hormone – melatonin[skin colour].

42. Habenular nucleus is the center for integration of olfactory ,
visceral and somatic pathways
Habenular complex- habenular nucleus & its connection to the
interpedunclar nucleus and tegmentum of the midbrain by
means of well defined tracts
It forms the part of limbic system

43. hypothalamus
It extends from the region of optic chiasma to the mammillary
bodies
lies below the hypothalamic sulcus, on the lateral wall of third
ventricle.
There is hardly any activity in the body that is not influenced by
the hypothalamus.

45. Hypothalamus
The hypothalamus is a very small, but extremely
important part of the diencephalon that is involved in
the mediation of endocrine, autonomic and behavioral
functions.
The hypothalamus:
(1) controls the release of 8 major hormones by the
hypophysis, and is involved in
(2) temperature regulation,
(3)control of food and water intake,
(4) sexual behavior and reproduction,

46. (5) control of daily cycles in physiological state and
behavior,
(6) mediation of emotional responses.
The hypothalamus is on either side of the third ventricle,
with the hypothalamic sulcus delineating its dorsal border.
The ventral aspect of the hypothalamus is exposed on the
base of the brain. It extends from the rostral limit of the
optic chiasm to the caudal limit of the mammillary bodies.

48. hypothalamus
It extends from the rostral limit of the optic chiasm to the
caudal limit of the mammillary bodies.
Three rostral to caudal regions are distinguished in the
hypothalamus that correspond to three prominent features
on its ventral surface:
1) The supraoptic or anterior region at the level of the optic
chiasm,
2) the tuberal or middle region at the level of the tuber
cinereum (also known as the median eminence—the bulge
from which the infundibulum extends to the hypophysis),
and
3)the mammillary or posterior region at the level of the
mammillary bodies.

49. Parts of hypothalamus
Optic part supraoptic nucleus above optic chiasma and
paraventricular nucleus above supraoptic nucleus
Tuberal region (at the level of the tuber cinereum) is
commonly divided into medial and
lateral parts by a plane passing through the fornix
Mammillary Region
Posterior nucleus, and lateral nucleus
The mammillary part of the hypothalamus consists of
the posterior hypothalamic nucleus and the prominent
mammillary nuclei. The posterior nucleus is a large, ill-
defined group of cells that may play a role in
thermoregulation

51. Hypothalamus has important
regulatory functions
Temperature
Emotional regulation
Hunger and thirst
Sexual behaviour
Neurosecretion
Endocrine control

52. Functions
Hypothalamus is concerned with many visceral activities,
involving a coordinated and balancing of sympathetic
and parasympathetic nervous system:-
Temperature control, with a heat loss area in the
preoptic nucleus and heat conservation area in the
posterior hypothalamic area.
Neural control of the neurohypophysis, with secretion of
antidiuretic hormone[ADH] by the supraoptic nucleus. It
helps in regulation of water balance

53. Contii..
Hormonal control of the adenohypophysis in form of
secretions of ACTH, TSH…
Control of eating, in form of feeding centre in the lateral
hypothalamic area and satiety centre in the ventromedial
nucleus
Regulates certain body functions that vary at
Different times of the day (e.g., body temperature,
hormone secretion, hunger)
or those that vary over a period of many days (e.g.,
menstrual cycle).
The projection from the retina to the suprachiasmatic
nucleus is thought to supply the clock with day-night
information needed for synchronizing diurnal (daily)
rhythms (also known as circadian rhythms)

54. Hypothalamusgetsitsbloodsupplybothfromthe
anteriorcerebralartery/a.cerebrianteriorandthe
posteriorcerebralartery/a.cerebriposterior.

55. Lesions to hypothalamus
Damage to the anterior hypothalamus blocks the production
of ADH, resulting in diabetes insipidus,
which is characterized by:-
rapid water loss from the kidneys.
CRH is released by the paraventricular and
taken up by the portal system where it has its action on the
anterior lobe of the pituitary.
Obesity. Frolich’s syndrome, Laurence-Moon-Biedl syndrome
Disrupt the state of the sleep-waking cycle: Somnolence
[persistent sleep]

56. When body temperature increases, neurons in the
anterior part of the hypothalamus turn on mechanisms
for heat dissipation that include sweating and dilation of
blood vessels in the skin. When body temperature
decreases, neurons in the posterior part of the
hypothalamus are responsible for heat production
through shivering, vasoconstriction in the skin,and
blockage of perspiration.
Lesions in the anterior part can result in hyperthermia
(increase in body temperature) and lesions in the caudal
part can result in hypothermia when the environmental
temperature is low.

57. Diencephalic autonomic epilepsy
is characterised by :
Flushing, sweating, salivation,lacrimation, tachycardia,
retardation of respiratory rate, unconsciosness.
Sexual disturbance- impotence,precocity.
Acute ulcerations in the upper part of the gastrointestinal
tract

58. THALAMIC STROKE
A thalamic stroke or hemorrhage is a potentially life-
threatening type of intracerebral hemorrhage. Since quick
medical treatment is the best way to prevent permanent
damage to the brain, it is important to understand the
symptoms of thalamic strokes.
Dejerine–Roussy syndrome or thalamic pain syndrome is a
condition developed after a thalamic stroke, a stroke
causing damage to the thalamus.Ischemic
strokes and Hemorrhagic strokes can cause lesioning in the
thalamus.

59. The lesions, usually present in one hemisphere of the brain,
most often cause an initial lack of sensation and tingling in the
opposite side of the body. Weeks to months later, numbness
can develop into severe and chronic pain that is not
proportional to an environmental stimulus,
called dysaesthesia or allodynia.[1] As initial stroke symptoms,
numbness and tingling, dissipate, an imbalance in sensation
causes these later syndromes, characterizing Dejerine–Roussy
syndrome. Although some treatments exist, they are often
expensive, chemically based, invasive, and only treat patients
for some time before they need more treatment, called
"refractory treatment.

60. Identification
A thalamic stroke occurs when a blood vessel inside a structure
in the lower part of your brain known as the thalamus suddenly
ruptures. This causes bleeding that seeps into other parts of your
brain, damaging cells.
Causes
Possible causes of thalamic stroke include aneurysms, high blood
pressure, protein deposits within your brain or a sudden brain
injury.
Time Frame
The symptoms of a thalamic stroke are most common during
times of activity. Typically, symptoms come on all at once and
rather suddenly.

61. Types of Symptoms
Common symptoms of thalamic stroke include loss of
coordination or balance, numbness, tingling, facial
paralysis, double vision, drooping eyelids, headaches,
nausea, vomiting and difficulty speaking, swallowing,
reading and writing. Some patients become very sleepy or
completely lose consciousness.
Treatment
Sometimes, surgery is necessary to remove the ruptured
blood vessel that caused the hemorrhage. After a
thalamic stroke, it is common to need physical,
occupational or speech therapy.

62. References
Snell’s neuroanatomy
Human physiology by A.K.jain
Gray’s anatomy
Wikipedia
Bd.chaurasia textbook for anatomy