DIENCEPHALON
Georgia Bishop PhD
OBJECTIVES
Describe the Anatomical Organization and Vascular Supply of the Diencephalon
1. Define the borders of the diencephalon.
2. Define the structures that comprise the diencephalon: thalamus, hypothalamus,
epithalamus and subthalamus.
3. Describe the general functions of the hypothalamus
4. Describe the circuits that regulate release of melatonin from the pineal gland
5. Define the differences between Relay, Association, and Intralaminar thalamic nuclei
6. Name the different types of inputs to the thalamic nuclei
7. Identify the vascular supply to the thalamus and general symptoms related to
compromise of these blood vessels.
8. Associate specific relay and association nuclei in the thalamus with their afferent inputs
and efferent projections.
BORDERS OF THE DIENCEPHALON - VENTRAL
OPTIC
CHIASM
INFUNDIBULUM
(STALK OF
PITUITARY
GLAND)
CP
IP
MAMMILLARY BODIES
PONS
DIENCEPHALON - DORSAL VIEW
PULVINAR
PI
SC
IC
MG
CP
LG
Lateral Geniculate Nucleus (Visual Information)
Medial Geniculate Nucleus (Auditory Information)
Pulvinar – Association Nucleus
Pineal Gland (Part Of Epithalamus) Related To Circadian Rhythms
INTERNAL BORDERS OF THE DIENCEPHALON
Internal Capsule
Lateral
Ventricle
3rd Ventricle
SAGITTAL VIEW OF THE DIENCEPHALON
Forebrain (Telencephalon)
Corpus Callosum
Posterior
Commissure
Fornix
Anterior
Commissure
LV
MB
Midbrain
OPTIC
CHIASM
DIENCEPHALON HAS 4 PARTS ALL WITH TERM “THALAMUS” (Gr. INNER CHAMBER)
DORSAL THALAMUS (THALAMUS)
HYPOTHALAMUS
EPITHALAMUS = PINEAL GLAND + HABENULA
SUBTHALAMUS
Epithalamus
Thalamus
Hypothalamus
EPITHALAMUS
MADE UP OF PINEAL GLAND AND HABENULA
HABENULA
PINEAL GLAND
PINEAL GLAND
Pineal Gland
Superior
Colliculus
SAGITTAL SECTION
CORONAL SECTION
Midline, unpaired structure located rostral to superior colliculus that resembles a pinecone.
This is an endocrine gland that secretes melatonin in response to light cues.
Under control of the sympathetic nervous system.
Melatonin is derived from serotonin and is secreted at high rates during darkness.
In many species, melatonin has an anti-gonadotropic effects and suppresses reproduction.
Decreases in melatonin secretion lead to increase in gonadal function.
Important in seasonal breeders that respond to increases in light as days get longer.
Effects in humans related to reproduction are not well understood. Tumors of the pineal gland have been
associated with precocious puberty presumably due to removal or destruction of pinealcytes and loss of
melatonin’s anti-gonadotropic effects.
In humans, more related to circadian rhythm and sleep/wake cycles.
LIGHT ALTERS MELATONIN RELEASE
Receives light information via circuitous pathway involving relays in the:
Light sensitive ganglion cells in the retina start the circuit.
OPTIC TRACT
OCC.
LGN
_
SCN
SC –
ILCC
+
X
PREGANGLIONIC
SYMPATHETIC
NEURONS
SCG
+
X
PINEAL
GLAND
X
MELATONIN
RELEASE
POSTGANGLIONIC
SYMPATHETIC
NEURONS
1. Retina to Hypothalamus (suprachiasmatic nucleus; SCN)
2. SCN suppresses (via other hypothalamic nuclei) Intermediolateral cell column of spinal cord (preganglionic
sympathetic neurons). This removes excitatory drive on
3. Intermediolateral cell column to Superior cervical ganglion (post ganglionic sympathetic neurons).
4. Post ganglionic sympathetic neurons to pineal gland reducing secretion of melatonin.
In dark, SCN is not activated and inhibition is removed. Thus melatonin is secreted.
LGN – LATERAL GENICULATE NUCLEUS
OCC – OCCIPITAL CORTEX
SC-ILC – SPINAL CORD – INTERMEDIOLATERAL
CELL COLUMN
SCG – SUPERIOR CERVICAL GANGLION
SCN – SUPRACHIASMATIC NUCLEUS OF
HYPOTHALAMUS
SUBTHALAMUS
LOCATED:
Inferior To Thalamus
Lateral To Hypothalamus (So you don’t see it on
a mid-sagittal section)
Medial To Internal Capsule
TH
IC
HYPOTHALAMUS
Hypothalamus
FUNCTION OF THE HYPOTHALAMUS
Involved in autonomic, endocrine, emotional, and somatic functions that are
designed to maintain the internal environment within a physiological range. For
example it is involved in:
Vasodilation
Feeding behavior
Regulation of pituitary function
Temperature regulation
More complex interactions involved in drives and emotional behavior:
Rage
Sleep
Sexual behavior
LINKS BETWEEN HYPOTHALAMUS AND LIMBIC SYSTEM
CORPUS CALLOSUM
FORNIX
AC
FORNIX – Pathway linking the hippocampus (part of Limbic System) with Hypothalamus
Mammillary bodies project to thalamus which then projects to prefrontal cortex.
THALAMUS
1. Pipeline for information flow to cerebral cortex
2. Decides which information should reach cerebral cortex accurately for further processing.
Makes up 80% diencephalon
All general and special sensory pathways relay in thalamus
Circuits used by motor pathways arising in the cerebellum and basal ganglia involve thalamic
relays
Circuits used by limbic system involve thalamic relays
Each system uses specific portions of the thalamus thus it is functionally divided into several
nuclei
Exception to rule: Chemically defined affrents such as 5HT from raphe and noradrenergic fibers
from locus coeruleus reach cerebral cortex directly.
GENERAL PROPERTIES OF INPUTS TO THE THALAMUS
Specific inputs - convey information that a given thalamic nucleus may pass on accurately to
cerebral cortex. (e.g., Medial leminiscus and spinothalamic tract to VPL; optic tract to LGN)
Regulatory inputs – contribute to decisions about the form in which information leaves thalamic
nuclei. Includes feedback from cerebral cortex, thalamic reticular nucleus.
Vast majority of input is regulatory. For example, in lateral geniculate nucleus, fewer than 10% of
synapses on projection neurons come from optic tract fibers; half or more come from visual
cortex.
THALAMIC RETICULAR NUCLEUS
The Only Thalamic Nucleus That Does Not Send Projections To The Cortex
Receives Inputs From Collaterals of Other Afferents to Thalamus as Well as the Cortex
Sends GABAergic Projections Back To The Thalamus.
THALAMIC RETICULAR
NUCLEUS
SCHEMATIC DIAGRAM OF THALAMUS (GREEN)
INTERNAL
MEDULLARY
LAMINA
IC
M
P
A
L
Internal Medullary Lamina (Thin Sheet Myelinated Fibers) Subdivides Thalamus Into Medial and
Lateral Groups of Nuclei. Also Contains “Intralaminar Nuclei”
Internal Medullary Lamina Splits Anteriorly To Define An Anterior Region
THALAMIC NUCLEI – TRANSVERSE SECTIONS
Internal Medullary Lamina (IML) Divides Thalamus Into Medial And Lateral Nuclear Groups. Note: It Splits Into 2 Branches
Anteriorly.
4
3
2
IML
IML
3
4
IML
2 1
DM
1
A
PUL
VL
A
DM
VL
M
P
VPL
A
MG
VPM
VA
L
IML
LG
RET N
A – Anterior Nucleus
DM – Dorsomedial Nucleus
Eml – External Medullary Lamina
IML Internal Medullary Lamina
LG – Lateral Geniculate Nucleus
MG – Medial Geniculate Nucleus
PUL - Pulvinar
Ret – Reticular Nuclei In Eml
VA – Ventral Anterior Nucleus
VL – Ventral Lateral Nucleus
VPL–Ventral Posterior Lateral Nucleus
VPM – Ventral Posterior Medial Nucleus
RET N
THALAMIC – CORTICAL CONNECTIONS
M
P
IML
LD
A
PUL
L
DM
A
VL
A
DM
CM
PF
MG
VPL
VL
VPM
VA
LG
RET N
RET N
Medial Group: Anterior Nucleus (A), Dorsomedial Nucleus (DM).
Recirpocal Connections With Prefrontal Cortex And Limbic System.
Lateral Group: Ventral Anterior (VA), Ventral Lateral (VL)
Relay Motor Information From Cerebellum And Basal Ganglia to Precentral Gyrus in Frontal Lobe.
Ventral Posterior Lateral (VPL), Ventral Posterior Medial (VPM)
Primarily Related To Relaying General And Special Sensory Information To Postcentral Gyrus in the Parietal Lobe.
Posterior Group – Lateral Geniculate (LG), Medial Geniculate (MG)
Relay Special Sensory Information Of Vision to the Occipital Lobe And Audition To the Temporal Lobe, respectively.
Pulvinar (Pul)
Projects To Association Areas In Temporal, Occipital And Parietal Lobes.
THALAMUS – HORIZONTAL SECTION
A
M
L
P
PUT
A
IML
DL
PUL
VPM
PUL
A
DM
DM
CM/
PF
PI
VL
SC
VA
VPL
LG
EML &
RET N
IML
III
A
VL
D
EML &
RET N
ICP
VL
DM
IML
MG
VA
IML
M
P
A
L
V
THALAMUS – CORONAL SECTION - ANTERIOR
D
L
M
A
R
V
VL
DM
R
IML
MASSA
INTERMEDIA
IML
IML
DL
PUL
A
VL
A
DM
DM
IL
VPM
MG
VL
VA
VPL
LG
IML
EML &
RET N
EML &
RET N
THALAMUS – CORONAL SECTION – MID-THLAMUS
D
L
M
V
DL
R
R
VL
DM
IL
VPM
VPL
IML
IML
DL
PUL
A
VL
A
DM
SUB
DM
IL
VPM
MG
SN
VL
VA
VPL
LG
IML
EML &
RET N
EML &
RET N
CC
THALAMUS – CORONAL SECTION –POSTERIOR THALAMUS
R
PUL
LG
IML
IML
DL
PUL
A
VL
A
DM
DM
IL
VPM
MG
VL
VA
VPL
LG
IML
EML &
RET N
MG
EML &
RET N
CC
SN
RELAY AND ASSOCIATION NUCLEI IN THE THALAMUS
SUMMARY OF INPUT AND OUTPUT OF THE THALAMUS
BLOOD SUPPLY TO THE DIENCEPHALON
Primarily derived from perforating branches of the posterior cerebral artery and the posterior
communicating artery.
Thank you for completing this module
 If you have any questions, please contact me:
 Bishop.9@osu.edu
Survey
We would appreciate your feedback on this module. Click on the
button below to complete a brief survey. Your responses and
comments will be shared with the module’s author, the LSI
EdTech team, and LSI curriculum leaders. We will use your
feedback to improve future versions of the module.
The survey is both optional and anonymous and should take
less than 5 minutes to complete.
Survey