9.14 - brain structure and its origins spring 2005 e of ... · “limbic” forebrain system ....
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9.14 - Brain Structure and its OriginsSpring 2005 Massachusetts Institute of Technology Instructor: Professor Gerald Schneider
From end of last class:
Division of the midbrain into two functionallydistinct regions, “limbic” and “somatic”
1. Somatic: Connected to the somatic sensory and motor systems
2. Limbic: Connected to the autonomic nervous system and the closely associated “limbic” forebrain system
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These functionally distinct regions continue rostrally into the ‘tweenbrain.
Somatic regions
Limbic regions
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A sketch of the central nervous system and its origins
G. E. Schneider 2005 Part 5: Differentiation of the brain vesicles
MIT 9.14 Class 1111(session 12)(session 12)
Forebrain of mammals with comparative studies relevant to its evolution
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The forebrain (prosencephalon)
• General picture and subdivisions (color coded) – Hypothalamus (and epithalamus): related to “limbic”
system structures of the forebrain – Thalamus (and subthalamus): related to somatic
sensory and motor systems
• Origins and course of 2 major pathways: related to– somatic sensory & motor systems, and – limbic system
• Evidence concerning forebrain evolution
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Rostral end of the thickening neural tube
DVR
Forebrain
Midbrain
Hindbrain
DVR = Dorsal Ventricular Ridge
LG = Lateral Ganglionic Eminence
MG = Medial Ganglionic Eminence
Thickened Ventricular Layer
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Figure removed due to copyright reasons.Please see:Allman, and John Morgan. Evolving Brains. New York, NY: Scientific American Library.Distributed by W.H. Freeman and Co., 1999. ISBN: 0716750767.
Evolution of telencephalon based on expression patterns of regulatory genes during development. (Based on work of Anibal Smith Fernandez et al., figure from Allman textbook)
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(prosencephalon
(
Forebrain ) :
endbrain telencephalon)
&
‘tweenbrain(diencephalon)
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Diencephalon: Hypothalamus and epithalamus:
• Visceral inputs • Connections with endbrain and midbrain:
“Limbic system" connections • Gating of ascending pathways through
‘tweenbrain
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Diencephalon:Thalamus and subthalamus
(= dorsal thalamus & ventral thalamus)
• Somatic inputs from the lemniscal pathways
• Connections from midbrain tectum and tegmentum (somatic parts of midbrain)
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Somatic regions
Limbic regions
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The forebrain (prosencephalon):
• General picture and subdivisions – Hypothalamus (and epithalamus) – Thalamus (and subthalamus)
• Origins and course of 2 major pathways
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‘Tween-
Endbrain
Fibers of medial lemniscus to VP, & from Cb to VA, VL
Olfactory cortex
brain
and
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‘Tweenbrain (diencephalon)
medial Fibers of
lemniscus to VP, & from Cb to VA, VL
Fibers of “Lateral Forebrain Bundle”
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Endbrain (telencephalon)
Olfactory cortex
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Origins and course of 2 major pathways:
• Lateral forebrain bundle • Medial forebrain bundle– Corpus striatum outputs – Olfactory cortex
– Limbic cortex – Neocortical white matter – Subcortical limbic – Internal capsule-Cerebral structures: amygdala, basal
peduncle-Pyramidal tract forebrain – lateral hypothalamic area – limbic midbrain areas
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Forebrain:
‘tweenbrain:
Æ
Corticospinal tract Pyramidal tract
Cerebral peduncles (includes corticopontine)
Cortical white matter Internal capsule
endbrain &
the lateral forebrain
bundle
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MFB
Somatic regions
Limbic regions
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‘Tweenbrain and Endbrain limbic & MFB
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The neocortex is involved in both major systems
A schematic summary
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Some Major Endbrain Connections
Dorsal striatum
Neocortex
Limbic structures
Hypothalamus
BrainstemSpinal cord
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This leaves out a great many details!
• For example, the ventral striatum is lumped together with “limbic” structures.
• Ventral striatum is critical in habit formation, and is probably the most primitive part of the corpus striatum in evolution.
• Reward and punishment mechanisms exist with a special role of ascending projections, e.g., from taste and pain systems.
• Next picture: the schematic summary is augmented
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Some Major Endbrain Connections
Neocortex
Brainstem Spinal cord
striatumDorsal striatum Limbic structures
Hypothalamus
Ventral
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Neuroanatomy review• Subdivisions of CNS; definitions of cell types
– Shapes of the neural tube at various levels • Sensory channels of conduction; dermatomes• Diaschisis: lesion-produced deafferentation results in
functional depression of neurons • Evolution of neocortex and major ascending and
descending pathways to and from it • Spinal cord structure; differences between levels • Propriospinal system • Autonomic N.S.: its components • Hindbrain organization; distortions of the basic plan• Cranial nerves: the 5th (trigeminal nerve)
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Neuroanatomy review• Midbrain: tectum and the tegmentum; species
differences; outputs for three major types of movement • Diencephalon: two major and two other
functional/structural subdivisions • Telencephalon: the endbrain (cerebral hemispheres and
basal forebrain); origins of two major pathways for descending axons (Both contain some ascending axons also)
• Other major pathways in mammals:– Spinothalamic tract – Dorsal columns, connecting to the medial lemniscus pathway
to the ventrobasal nuc. of thalamus (VP) – Corticospinal & corticopontine pathways (the former to all
levels of CNS, the latter connecting to the cerebellum)
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Notes on Evolution of ForebrainBriefly: 3 topics
• Neuromeres of the forebrain • Origins of neocortex • Non-cortical structures in amphibians, reptiles
and birds that are related to neocortex
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Neuromeric models of embryonic mammalian brain
2) Puelles & Rubenstein,’93
3) Revision of the model
1) Embryonic brain with curved longitudinal axis
Gene expression data indicate existence of neuromeres also in the non-amniotes lamprey and zebrafish.
Diencephalon
Mesencephalon
Rhombencephalon
Eye StalkD
DD
D
R CV
DP
OB
MP
Str. P5
P6
P4
P3
P2P1
Mes.
1st
R1R2
R3R4
R5R6
R7
PaStr.
VP
LP
DPMP
P5
P4P3
P6
Telencephalon
OB
Figures by MIT OCW.
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Figure removed due to copyright reasons.Please see:Allman, and John Morgan. Evolving Brains. New York, NY: Scientific American Library.Distributed by W.H. Freeman and Co., 1999. ISBN: 0716750767.
Evolution of telencephalon based on expression patterns of regulatory genes during development. (Based on work of Anibal Smith Fernandez et al., figure from Allman textbook)
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A) Radial glia cells (black lines) in embryonic mammals and birds
Embryology and the Claustroamygdalar DVR Hypothesis
B) Transcription factor expression: Tbr-1 Tbr-1 and Emx-1 Dix-2
Figures by MIT OCW.
DPMP
LP
G
DVR
Str.
Str.
CA
Neo
Mouse Chick
Mammal Bird
Regulatory Gene Expression in Mice and Chicks
Radial Glia in Embryonic Mice and Chicks
Tbr-1 Tbr-1 and Emx-1 Dlx-2
VP
DP
MP
LPMG
LGVP
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Migration of cells from the dorsal ventricular ridge and from ventricular layer to neocortex
A) Karten’s migrations B) migrationshypothetical Actual
LG, MG: Lateral, Medial Ganglionic Eminence Str.=Striatum; OC=Olfactory Cortex; N=Neocortex
eDVR
LG
MG
Str.
OC
N
eDVR
LG
MG
Str.
OC
N
Figure by MIT OCW.
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Selected References
Slide 26: Striedter, Georg F. Principles of Brain Evolution. Sunderland, MA: Sinauer Associates, 2005, p. 82. ISBN: 0878938206. Slide 28: Striedter, Georg F. Principles of Brain Evolution. Sunderland, MA: Sinauer Associates, 2005, p. 278. ISBN: 0878938206. Slide 29: Striedter, Georg F. Principles of Brain Evolution. Sunderland, MA: Sinauer Associates, 2005, p. 280. ISBN: 0878938206.