Diencephalon
(“in-between brain”)
3rd Ventricle
CNS divisions
Directional terms – forebrain level
dorsal
superior
caudal
posterior
rostral
anterior
ventral
inferior
Diencephalon – regional organization
Thalamus (dorsalis) – topographic and nuclear
organization (Gr. thalamos, “inner chamber”)
Metathalamus – the geniculate bodies
Epithalamus – pineal gland and habenula
Subthalamus (thalamus ventralis)
Hypothalamus – divisions, nuclei and
connections
The Diencephalon
The Diencephalon
THALAMUS
EPITHALAMUS
SUBTHALAMUS
HYPOTHALAMUS
The
Diencephalon
Fornix
Adhesio Interthalamica
Posterior
commissure
Pineal Gland
Hypothal Sulcus
Anterior Commissure
Lamina Terminalis
Mammillary Body
Optic Chiasm
Infundibulum
Diencephalon
dorsal surface
Diencephalon – superior dorsal view
anterior
tubercle
3rd ventricle
Diencephalon – lateral dorsal view
Diencephalon
ventral surface
Metathalamus
Pulvinar
Lateral
Geniculate
Medial
Geniculate
Borders of thalamus
Lat. ventricle
Int.capsule
3rd Ventricle
Borders of thalamus
Posterior
commissure
Fornix
Hypothalamic sulcus
Lamina terminalis
Лимбичен таламус
Thalamus
Origin of CNS subdivisions
Secondary vesicles
Diencephalon is larger during brain
development than in postnatal brain
Neural tube folding (5th -8th wk)
Diencephalic development
The diencephalon consists of roof and alar
plates but lacks the basal and floor plates
Lateral
ventricle
Alar plate → thalamus, hypothalamus, neurohypophysis, and infundibulum
Roof plate → epiphysis, habenular nuclei and the posterior commissure
Alar vs. Basal in forebrain
alar
basal
Diencephalic development
Embryonic brain
Adult brain
Thalamocortical axons pass through the ventral
telencephalon (VT) and future basal ganglia
(GP/STR) before they reach the cortex
Estimated time of development of various brain regions
2 mo
6 mo
Modified from Bayer SA et al. Neurotoxicology 14:83–144, 1993
General organization of the thalamus
Reticular
nucleus
Internal
medullary
lamina
Nuclear groups
Interthalamic adhesion
Internal medullary lamina
External medullary lamina
External
medullary
lamina
Midline nuclei
Thalamic nuclei form nuclear groups
I.
Lateral Group
II.
Medial Group
III. Anterior Group
IV. Posterior Group
V.
Intralaminar Group
VI. Reticular nucleus
metathalamus
Thalamus – section at anterior level
LV
LV
3v
reticular
internal medullary
lamina
Thalamus – section at mid-level
LV
LV
3v
reticular
internal medullary
lamina
Thalamus – section at posterior level
LV
LV
3v
reticular
internal medullary
lamina
Thalamus is the critical relay for the flow of
sensory information to the neocortex
Cortex
Motor
pathway
Sensory
pathway
Thalamus is more than simply a relay!
It acts as a gatekeeper for information to the
cerebral cortex, preventing or enhancing the
passage of specific information depending on
the behavioral state
Thalamic nuclei – lateral group
Ventral nuclear group
I.
Lateral Group
II.
Medial Group
III.
Anterior Group
IV.
Posterior Group
V.
Intralaminar Group
VI.
Reticular nucleus
ventral posterolateral nucleus (VPL)
ventral posteromedial nucleus (VPM)
ventral posteroinferior nucleus (VPI)
ventral lateral nucleus (VL)
ventral anterior nucleus (VA)
Dorsal nuclear group
Lateral dorsal nucleus (LD)
Lateral posterior nucleus (LP)
Pulvinar-lateral posterior complex
Connections of the lateral thalamic nuclei
Ventral Nuclear Group
Cortex
Prefrontal
SMA
MI, PM
SI
SN pars reticulata
Basal Cerebellum
ganglia
SMA - supplementary motor area
MI (M1) – primary motor cortex
PM – premotor cortex
SI (S1) – primary somatosensory cortex
Trigeminal lemniscus
Medial lemniscus,
Spinothalamic tracts
Somatosensory map (somatotopic
organization) in VPL & VPM
VPL
+taste fibers
VPM
Connections of the lateral thalamic nuclei
Dorsal Nuclear Group
cingulate gyrus,
precuneus
Somatosensory
Association
Area
Visual
Association
area
Pulvinar
Hippocampal formation
Superior colliculus,
Pretectal area
Thalamic nuclei – medial group
Mid
Dorsomedial Nucleus (MD)
I.
Lateral Group
II.
Medial Group
III.
Anterior Group
IV.
Posterior Group
V.
Intralaminar Group
VI.
Reticular nucleus
pars magnocellularis (MDmc)
pars parvocellularis (MDpc)
pars paralaminaris (MDpl)
Midline Nuclear Group (poorly
developed in humans)
paratenial nucleus
reunience nucleus
submedial nucleus
rhomboid nucleus
Midline thalamic nuclei
Interthalamic adhesion
Midline nuclei
Thalamic nuclei – anterior & posterior groups
Mid
Anterior Nuclear Group
I.
Lateral Group
II.
Medial Group
III.
Anterior Group
IV.
Posterior Group
V.
Intralaminar Group
VI.
Reticular nucleus
anteroventral nucleus (AV)
anterodorsal nucleus (AD)
anteromedial nucleus (AM)
Posterior Nuclear Group
(medial to the Pulvinar,
merge with MGB)
suprageniculate nucleus
nucleus limitans
posterior nucleus
Connections of the thalamic nuclei
Medial & Anterior Nuclei
Mamillary
Prefrontal Frontal
bodies,
Cortex
Eye Field
Hippocampus
Cingulate
gyrus
Basal
forebrain
Medial
Frontal
Gyrus
SN pars reticulata, superior
colliculi, reticular formation
Thalamic nuclei – intralaminar group
Mid
Caudal Nuclear Group (most
important in humans)
centromedian nucleus
parafascicular nucleus
Rostral Nuclear Group
I.
Lateral Group
II.
Medial Group
III.
Anterior Group
IV.
Posterior Group
V.
Intralaminar Group
VI.
Reticular nucleus
paracentral
centrolateral
centromedial
Afferent
Efferent
Connections of the thalamic
intralaminar nuclei
Receive from many subcortical and
cortical areas
Project to
other thalamic nuclei
cortex
striatum (the projection is
topographically organized:
centromedian nucleus → putamen;
parafascicular nucleus → caudate)
Intralaminar & midline nuclei are non-specific
thalamic nuclei
Thalamic nuclei – reticular nucleus
I.
Lateral Group
II.
Medial Group
III.
Anterior Group
IV.
Posterior Group
V.
Intralaminar Group
VI.
Reticular nucleus
A continuation of the reticular formation
of the brain stem into the diencephalon
Unique among thalamic nuclei!!!
its axons do not leave the thalamus
Receives collaterals of corticothalamic
projections and thalamocortical
projections
Sends to other thalamic nuclei
GABAergic (inhibitory) → plays a role
in integrating and gating activities of
thalamic nuclei
Metathalamus
Tricorn
Shape
Pulvinar
Medial
Geniculate
Lateral
Geniculate
Metathalamic nuclei
Medial Geniculate Nucleus (MG)
ventral or
principal nucleus
dorsal nucleus
medial nucleus
Lateral Geniculate Nucleus (LG)
dorsal nucleus (LGd)
ventral nucleus (LGv)
Lateral Geniculate Nucleus (LGd) → Visual Pathway
Dorsal Nucleus (LGd)
Magnocellular Part
1, 2
Parvocellular Part
3, 4, 5, 6
dorsolateral
contralateral afferents
1, 4, 6
ipsilateral afferents
2, 3, 5
ventromedial
Ventral Nucleus (LGv)
part of thalamic
reticular nucleus
Visual Pathway
1. Optic nerve
2. Optic chiasm
3. Optic tract
4. Lateral
geniculate
body
5. Optic radiation
6. Visual cortex
Visual pathway via LGN
loops
Ocular dominance columns in primary visual cortex (V1)
C
I
I
C
I = from ipsilateral retina
C = from contralateral retina
Overview of thalamic connectivity
VL
VA
DM
V
P
L
V
P
M
MGB
LP
Pul
AN = Anterior nn.
LD = Lateral dorsal n.
VA
LP = Lateral posterior n.
Pul = Pulvinar
DM AN
DM = Dorsomedial n.
Mid = Midline nn.
L VA = Ventral anterior n.
DM
G VL = Ventral lateral n.
B VPL = Ventral posterolateral n.
VPM = Ventral posteromedial n.
LGB = Lateral geniculate body
MGB = Medial geniculate body
IL = Intralaminar nn.
CM = Centromedian n.
VL VPL
LP
Pul
LD
Pul
LGB
Summary of the connections of the
thalamic nuclei
Specific nuclei (sensory or motor)
Association nuclei (sensory or motor
Non-specific nuclei
Overview of major functions
thalamic nuclei
nonspecific
limbic
autonomic
A
motor
VA
IL
VL
somatosensory
taste
visual
LP
DM
R
VP
Pul
LG
internal regulator
MG
higher visual
auditory
Thalamic radiations = fibers which reciprocally
connect the thalamus & cortex via the internal capsule
Epithalamus & subthalamus
Subthalamus Basal Ganglia
Subthalamic
Zona
nucleus
incerta
Fields of Forel
Subthalamus
Subthalamus
Red Nucleus
Subthalamus
• Location: diencephalicmesencephalic border
• Abuts the posterior limb
of the internal capsule
• Shaped like a lens
Substantia
Nigra
Internal Capsule
(posterior limb)
Connections of subthalamus
Afferent
Efferent
Fields of Forel (fiber bundles containing
efferents to the thalamus)
H
H1
H2
H = “Haube” (German, cap)
prerubral field
thalamic fasciculus
lenticular fasciculus
The connections of subthalamic nucleus are
connections of the basal ganglia
A lesion in the
contralateral subthalamic
nucleus leads to
hemiballismus → violent
flinging involuntary
movements of one side of
the body.
Kandel, Schwartz, Jessell;
Principles of Neural
Science, 4th ed.
Zona incerta (zone “in between”)
Rostral continuation of the
mesencephalic reticular formation that
extends laterally into the reticular nucleus
of the thalamus
Involved in control of movement – its
stimulation has been shown to suppress
limb tremor (has GABA ergic neurons)
Has reciprocal connections with
neocortex, thalamus, brain stem, basal
ganglia, cerebellum, hypothalamus, basal
forebrain, and spinal cord
Epithalamus Limbic System
Habenular
nuclei
medial
lateral
Habenular
commissure
Pineal gland
Epithalamus
Habenular
commissure
(roof of pineal
recess)
Pineal gland
(secretes
melatonin)
Posterior
commissure (eye
movements and
light reflex)
Epithalamus
3rd Ventricle
Epiphysis (pineal gland)
Pinealocytes – secrete melatonin
night↑/day↓
other hormones
thyrotropin-releasing hormone (TRH)
leuteinizing hormone–releasing hormone (LHRH)
somatostatin–release inhibitory factor
Interstitial cells – glial-like
Blood vessels
(SRIF)
The pineal gland calcifies after the age of 16 years. This fact is
used in the detection of midline shifts in skull x-rays → in
case of a space-occupying lesion displacing the pineal.
Pineal gland
(calcified)
Pineal gland
neuroglia
acervulus
(brain sand)
pinealocytes
Pineal gland
saggital section
Posterior
Commissure
cross-section
Habenula
(Latin diminutive of habena, “a small strap or rein”)
Receive the stria medullaris thalami – from septal (medial
olfactory) area in frontal lobe
Project habenulo-interpeduncular tract (fasciculus retroflexus
of Meynert) to the interpeduncular nucleus of the midbrain
The two habenular nuclei are connected by the habenular
commissure
Involved in limbic system – emotions and behavior
Connections of habenular nuclei
Septal nuclei
Blood supply to thalamus
medial territory
lateral territory
Blood supply to thalamus
Basilar root of the posterior cerebral a. →
paramedian branches (medial territory)
Posterior cerebral artery → geniculothalamic
branch (posterolateral territory)
Posterior communicating artery →
tuberothalamic branch (anterolateral territory)
Internal carotid artery → anterior choroidal
branch (lateral territory)
Intracerebral hemorrhage
Dejerine-Roussy syndrome
Posteior cerebral artery supplies VPL, VPM,
MG, LG, pulvinar
PCA infarct → Dejerine-Roussy syndrome
Pure hemisensory loss + no hemiparesis
Venous drainage of thalamus → vv. profundae cerebri
Hypothalamus
4 cm3 of neural tissue, 0.3% of the total brain
3rd Ventricle
Hypothalamus – ventral view
Hypothalamus – ventral view (landmarks)
Optic
Chiasm
Infundibulum
Mammillary
Bodies
Borders of hypothalamus
Hypothal Sulcus
Midbrain
Interpeduncular
fossa
Lamina Terminalis
Optic Chiasm
The hypothalamus serves this integrative function by
regulation of 5 basic physiological needs
It controls blood pressure and electrolyte composition by a
set of regulatory mechanisms that range from control of drinking
and salt appetite to the maintenance of blood osmolality and
vasomotor tone
It regulates body temperature by means of activities ranging
from control of metabolic thermogenesis to behaviors such as
seeking a warmer or cooler environment
It controls energy metabolism by regulating feeding, digestion,
and metabolic rate
It regulates reproduction through hormonal control of mating,
pregnancy, and lactation
It controls emergency responses to stress, including physical
and immunological responses to stress by regulating blood flow
to muscle and other tissues and the secretion of adrenal stress
hormones
Fornix divides the hypothalamus into
medial and lateral regions/zones
Medial – a cluster of nuclei organized into:
preoptic nuclear group
suprachiasmatic (supraoptic; anterior) group
tuberal (intermediate) nuclear group
mamillary (posterior) nuclear group
Lateral
medial forebrain bundle (axons)
lateral hypothalamic area (neurons)
Regions of the medial hypothalamus
Medial hypothalamus – preoptic region
Just caudal to the lamina terminalis
Nuclei
preoptic nuclei (continuous with one of
the circumventricular organs - organum
vasculosum laminae terminalis, OVLT;
receive hormonal inputs)
medial – GnRH → anterior pituitary
(reproduction & sexual arousal)
lateral – sleep and wakefulness (damage
→ insomnia)
preoptic periventricular nucleus →
part of the parvocellular neurosecretory
system
Medial hypothalamus – suprachiasmatic (supraoptic;
anterior) region
cross-section
3V
Lateral
hypothalamus
Supraoptic nucleus → ADH secretion into
neurophypophysis → retention of water in
kidneys (diabetes insipidus; polydipsia,
polyuria); (part of magnocellular system)
Paraventricular nucleus → oxytocin
secretion → contraction of uterine smooth
musculature during labour and promotion of
milk ejection (part of magnocellular system)
Anterior nucleus – thirst center → tumors
lead to refusal of patients to drink despite
severe dehydration
Suprachiasmatic nucleus (poorly
developed in humans) - circadian rhythm
regulator (sleep-wake/day-night cycles) →
receives bilaterally from retina; projects to
tuberal hypothalamic nculei (VIP-ergic
fibers); influences pineal gland via
sympathetic fibers (C8-T1 level of spinal
cord) → melatonin secretion
The paraventricular nucleus contains 3
distinct cell populations
Anterior pituitary
Medial hypothalamus – tuberal (intermediate) region
Ventromedial nucleus - satiety
center (lesions lead to ↑ appetite &
obesity); receives from amygdala via
stria terminalis
Dorsomedial nucleus – TRH
release; neuroendocrine control of
catecholamines (projects to spinal
cord autonomic neurons)
Arcuate nucleus
Fornix
3V
control of anterior pituitary via tuberoinfundibular tract and the hypophyseal
portal system (parvocellular system):
ACTH, dopamine, β-LPH, βEndorphin
major target of leptin actions
regulating food intake by acting on
food promoting (orexinergic) and food
inhibiting (anorexinergic) arcuate
neurons
Magnocellular vs parvocellular
neurosecretory systems
tuberoinfundibular
tract
Hypothalamus → posterior pituitary
(neurohypophysis)
Hypothalamus → portal blood system →
anterior pituitary (adenohypophysis)
Information flow between brain and
endocrine system
parvocellular paraventricular n.
periventricular, ventromedial,
dorsomedial nuclei
periventricular & arcuate
nuclei
periventricular n. – GIH
arcuate n. – GRH
arcuate n. – PIH
pituitary TSH = PRH
Dopamine
Medial hypothalamus – mammilary (posterior) region
Mamillary nuclei
3V
MTT
Tuberomammilary n.
medial (large) – receives from
hippocampus via fornix and sends to
anterior thalamus via mamillothalamic
tract (MMT) → involved in memory
lateral (small) - descending projection
to the midbrain and pons, the
mammillotegmental tract (reticular
formation)
tuberomammillary nucleus
(histaminergic) – widespread
projections to cortex → maintains
arousal (antihistamine drugs cause
drowsiness)
Posterior nucleus - the main source
of descending hypothalamic fibers
to the brain stem: dorsal
longitudinal fasciculus
The fornix
Hippocampus → mammillary medial nucleus
HypothalamusMammillothalamic tract (of Vicq d'Azyr)
ANTERIOR
NUCLEUS
Mamillothalamic tract
MAMMILLARY
BODY
Mammillary medial nucleus → anterior thalamic nuclei
Dorsal longitudinal fasciculus – integration of
hypothalamic & autonomic function
Posterior
nucleus
Lateral region of hypothalamus
Lies lateral to the fornix and mamillothalamic tract
The medial forebrain bundle connects the
hypothalamus with the septal area, cortex, amygdala
rostrally and brain stem reticular formation caudally
Lateral hypothalamic area
contains orexin (hypocretin)-ergic neurons → stimulate food
intake; inhibit anorexigenic neurons in ventromedial nucleus
and exite orexigenic neurons in arcuate nucleus
controls activities of monoaminergic and cholinergic systems
affecting sleep → destruction is associated with the sleep
disorder of narcolepsy
Medial & lateral hypothalamic nuclear groups
Fornix
Hypothalamus Limbic System
Interthalamic
adhesion
MTT
Tuber cinereum
Infundibulum
Optic nerve
Fornix
Afferents to the hypothalamus
(amygdala)
(amygdala)
Afferents to hypothalamus
To reticular
formation
Posterior
nucleus
Medial
forebrain
bundle
Preoptic
area
Efferents from hypothalamus
Endocrine pathways – posterior pituitary
Endocrine pathways – anterior pituitary
Functions of hypothalamic nuclei
Nucleus
Key functions
Preoptic nuclei:
Medial
Parvocellular hormone control
Lateral
Sleep-wakefulness
Paraventricular
Magnocellular hormones (oxytocin, vasopressin);
parvocellular; direct autonomic control
Anterior
Thirst
Supraoptic
Magnocellular hormones (oxytocin, vasopressin)
Suprachiasmatic
Circadian rhythm
Ventromedial
Appetitive/consummatory behaviors
Dorsomedial
Feeding, drinking, and body weight regulation
Arcuate
Parvocellular hormones; visceral functions
Mammillary
Memory
Tuberomammillary
Sleep-wakefulness (histamine)
Lateral hypothalamic
Various, including arousal, food intake; contain orexin
Summary of hypothalamus functions
The 3rd Ventricle
Narrow vertical cleft between the two halves of the
diencephalon
Lat. ventricle Fornix 3rd Ventricle
Borders
thalamus
pl. choroideus
hypothalamus
lamina terminalis
Lateral ventricle communicates with the 3rd
ventricle via the foramen of Monro
Four Parts:
• Lateral
Ventricle (2)
• Third
Ventricle
The
rd
3
ventricle has 4 recesses
Foramen of
Monro
Pineal recess
Optic
Infundibular
Pineal
Suprapineal
Recesses of the 3rd ventricle
Suprapineal
Pineal
Optic
Infundibular