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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.
MAMMILLARY BODIES
OPTICCHIASM
INFUNDIBULUM(STALK OFPITUITARY GLAND)
PONS
IPCP
BORDERS OF THE DIENCEPHALON - VENTRAL
SC
IC
PULVINAR
MG
LG
PI
CP
Lateral Geniculate Nucleus (Visual Information) Medial Geniculate Nucleus (Auditory Information) Pulvinar – Association Nucleus Pineal Gland (Part Of Epithalamus) Related To Circadian Rhythms
DIENCEPHALON - DORSAL VIEW
Internal CapsuleLateral Ventricle
3rd Ventricle
INTERNAL BORDERS OF THE DIENCEPHALON
Posterior Commissure
MB
Anterior Commissure
OPTICCHIASM
Corpus Callosum
Fornix
LV
Midbrain
Forebrain (Telencephalon)
SAGITTAL VIEW OF THE DIENCEPHALON
DORSAL THALAMUS (THALAMUS)
Thalamus
Hypothalamus
Epithalamus
HYPOTHALAMUS
EPITHALAMUS = PINEAL GLAND + HABENULA
SUBTHALAMUS
DIENCEPHALON HAS 4 PARTS ALL WITH TERM “THALAMUS” (Gr. INNER CHAMBER)
EPITHALAMUS
PINEAL GLANDHABENULA
MADE UP OF PINEAL GLAND AND HABENULA
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.
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.
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.
Melatonin is derived from serotonin and is secreted at high rates during darkness.
PINEAL GLAND
Receives light information via circuitous pathway involving relays in the:Light sensitive ganglion cells in the retina start the circuit.
OPTIC TRACT
SCN
OCC.LGN
SC – ILCC
PREGANGLIONICSYMPATHETIC NEURONS
SCG
POSTGANGLIONICSYMPATHETIC NEURONS
PINEALGLAND
MELATONINRELEASE
LGN – LATERAL GENICULATE NUCLEUSOCC – OCCIPITAL CORTEXSC-ILC – SPINAL CORD – INTERMEDIOLATERAL CELL COLUMNSCG – SUPERIOR CERVICAL GANGLIONSCN – SUPRACHIASMATIC NUCLEUS OF HYPOTHALAMUS
_ + +X X
LIGHT ALTERS MELATONIN RELEASE
X
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 on3. 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.
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
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
FUNCTION OF THE HYPOTHALAMUS
FORNIX
FORNIX – Pathway linking the hippocampus (part of Limbic System) with Hypothalamus
AC
CORPUS CALLOSUM
Mammillary bodies project to thalamus which then projects to prefrontal cortex.
LINKS BETWEEN HYPOTHALAMUS AND LIMBIC SYSTEM
Makes up 80% diencephalon
All general and special sensory pathways relay in thalamus
Circuits used by limbic system involve thalamic relays
Each system uses specific portions of the thalamus thus it is functionally divided into several nuclei
Circuits used by motor pathways arising in the cerebellum and basal ganglia involve thalamic relays
Exception to rule: Chemically defined affrents such as 5HT from raphe and noradrenergic fibers from locus coeruleus reach cerebral cortex directly.
THALAMUS
1. Pipeline for information flow to cerebral cortex
2. Decides which information should reach cerebral cortex accurately for further processing.
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.
GENERAL PROPERTIES OF INPUTS TO THE THALAMUS
THALAMIC RETICULAR NUCLEUS
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.
INTERNALMEDULLARYLAMINA
P A
M
L
Internal Medullary Lamina (Thin Sheet Myelinated Fibers) Subdivides Thalamus Into Medial and Lateral Groups of Nuclei. Also Contains “Intralaminar Nuclei”
IC
Internal Medullary Lamina Splits Anteriorly To Define An Anterior Region
SCHEMATIC DIAGRAM OF THALAMUS (GREEN)
2
IML
IML
Internal Medullary Lamina (IML) Divides Thalamus Into Medial And Lateral Nuclear Groups. Note: It Splits Into 2 Branches Anteriorly.
RET NRET N
VA
IML
P A
M
L
IML123
4
1
34
A
A
DM
VL
DM
VL
VPL VPM
LG
MG
PUL
A – Anterior NucleusDM – Dorsomedial NucleusEml – External Medullary LaminaIML Internal Medullary LaminaLG – Lateral Geniculate NucleusMG – Medial Geniculate NucleusPUL - PulvinarRet – Reticular Nuclei In EmlVA – Ventral Anterior NucleusVL – Ventral Lateral NucleusVPL–Ventral Posterior Lateral NucleusVPM – Ventral Posterior Medial Nucleus
THALAMIC NUCLEI – TRANSVERSE SECTIONS
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.
P A
M
L
IML
VA
A
A
DM
VL
DMVL
CMPF
VPL VPM
LD
LG
MG
PUL
RET NRET N
THALAMIC – CORTICAL CONNECTIONS
IML
DM
ICP
PUT
GP
IML
IML
EML &RET N
EML &RET N
DM
DM
VA
VPL
VPM
PUL
CM/PF
DL
MG
LG
IML
VL
VL A
A
A
LM
P
A VA
VL
PUL
SC
PI
P A
M
L
D
V
III
THALAMUS – HORIZONTAL SECTION
IML
IML
EML &RET N
EML &RET N
DM
DM
VA
VPL
VPM
PUL
IL
DL
MG
LG
IML
VL
VL A
A
A
DM
VLR
R
D
ML
V
MASSAINTERMEDIA
IML
THALAMUS – CORONAL SECTION - ANTERIOR
DM
VL
VPL
VPM
R
R
DL
SUB
IML
IML
EML &RET N
EML &RET N
DM
DM
VA
VPL
VPM
PUL
IL
DL
MG
LG
IML
VL
VL A
A
IL
SN
CC
D
ML
V
THALAMUS – CORONAL SECTION – MID-THLAMUS
PUL
LGMG
IML
IML
EML &RET N
EML &RET N
DM
DM
VA
VPL
VPM
PUL
IL
DL
MG
LG
IML
VL
VL A
ASNCC
R
THALAMUS – CORONAL SECTION –POSTERIOR THALAMUS
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.
Diencephalon
Diencephalon
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