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

Thank you for completing this module

If you have any questions, please contact me: Bishop.9@osu.edu

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