A sketch of the central nervous system and its origins
G. E. Schneider 2009Part 5: Differentiation of the brain vesicles
MIT 9.14 Class 1212
Forebrain of mammals with comparative studies relevant to its evolution
The forebrain (prosencephalon) Topics
• Major subdivisions and overview of ‘tweenbrain – Hypothalamus and epithalamus: related to “limbic”
system structures of the forebrain – Thalamus and subthalamus: related more 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
Also: Review of neuroanatomy covered thus far
DVR
LG
MG
Thickened Ventricular Layer
Rostral end of the thickening neural tube: a few more descriptive terms
DVR = Dorsal Ventricular Ridge
LG = Lateral Ganglionic Eminence
MG = Medial Ganglionic Eminence
Hindbrain
Midbrain
Forebrain
Preview: Evidence on endbrain evolution
• Recent data has come from studies of expression patterns of regulatory genes, like the hox genes, in various species.
• Prior to these studies, cross-species comparisons were made using only morphological data (cytoarchitecture, connections patterns).
Homeobox gene expression: Emx-1 Dlx-1
s = septum
h = hyperstriatum
dvr = dorsal ventricular ridge
dc = dorsal cortex
st = striatum
am = amygdala & claustrum
Dorsal
Medial Lateral
Ventral
Archetypal Embryonic Stage
Turtle
dc
sst
dvr
Chick
st
dvr
hMouse
sst
cx
am
Frog
s
st
dc
Evolution of telencephalon based on expression patterns of regulatory genes during development--Based on work of Anibal Smith Fernandez et al., figure from Allman (2000), p 113.
Figure by MIT OpenCourseWare.
We will return to these pictures of the endbrain at the end of this section.
• First: Major features of the forebrain structure
• and then a pause for a brief review of major concepts in brain anatomy.
Forebrain (prosencephalon) :
endbrain (telencephalon)
&
‘tweenbrain (diencephalon)
The forebrain (prosencephalon)
• Major subdivisions and overview– Diencephalon
• Hypothalamus (and epithalamus)• Thalamus (and subthalamus)
– Telencephalon • Pallium
– Limbic – Non-limbic (neocortex)
• Corpus striatum – Ventral (limbic) – Dorsal (non-limbic)
• Origins and course of 2 major pathways
Diencephalon 1: Hypothalamus & epithalamus
• Visceral inputs • Connections with endbrain and midbrain:
“Limbic system" connections • Functions include gating of pathways
ascending through thalamus.
Diencephalon 2: Thalamus & subthalamus
(= dorsal thalamus & ventral thalamus)
• Somatic inputs from the lemniscal pathways
• Connections from midbrain tectum and tegmentum (somatic parts of midbrain)
Somatic regions
Limbic regions
The forebrain (prosencephalon):
• Major subdivisions and overview – Diencephalon
• Hypothalamus (and epithalamus) • Thalamus (and subthalamus)
– Telencephalon • Pallium
– Limbic cortex – Non-limbic cortex (neocortex)
• Corpus striatum & pallidum – Ventral – Dorsal
• Origins and course of 2 major pathways
Telencephalon: major structures – Neocortex
• “Primary” sensory and motor cortical areas • Unimodal association cortex • Heteromodal association cortex
– Limbic cortex • Olfactory cortex • Paleocortical & closely related structures
– Corpus striatum • Dorsal striatum (sometimes called neostriatum)• Ventral striatum structures including Olfactory Tubercle • Globus pallidus & ventral pallidum: output structures of
the striatum
The forebrain (prosencephalon):
• Major subdivisions and overview – Diencephalon
• Hypothalamus (and epithalamus) • Thalamus (and subthalamus)
– Telencephalon • Neocortex • Corpus striatum • Limbic endbrain
• Origins and course of 2 major pathways
‘Tween-brain
and
Endbrain
Fibers of medial lemniscus to VP, & from Cb to VA, VL
Olfactory cortex
Let’s look at these sections one at a time:
‘Tweenbrain (diencephalon)
Fibers of medial lemniscus to VP, & from Cb to VA, VL
Fibers of “Lateral Forebrain Bundle”
Endbrain (telencephalon)
Olfactory cortex
Origins and course of 2 major pathways:
• Lateral forebrain bundle,to and from: – Corpus striatum – Neocortex, via:
• Neocortical white matter,
Outputs of neocortex viaInternal capsule-Cerebralpeduncle-Pyramidal tract
(See following slide)
• Medial forebrain bundle, to and from: – Olfactory cortex – Limbic cortex – Subcortical limbic
structures: amygdala, basal forebrain
– lateral hypothalamic area
– limbic midbrain areas
Forebrain: endbrain &
‘tweenbrain: the lateral forebrain
bundleCorticospinal tract Pyramidal tract
Cerebral peduncles (includes corticopontine)
Cortical white matter Æ Internal capsule
MFB
REVIEW
Somatic regions
“Limbic” regions
REVIEW:
‘Tween-brain and Endbrain limbic & MFB
Lateral forebrain bundle
Medial forebrain bundle
Lateral forebrain bundle
Medial forebrain bundle
The neocortex is involved in both major systems
A schematic summary
Hypothalamus
Some Major Endbrain Connections
Neocortex
Dorsal striatum
Brainstem Spinal cord
Limbic structures
This leaves out a great many details!
• E.g., in the diagram, 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
Some Major Endbrain Connections
Dorsal striatum Ventral Limbic structures Thal striatum
Hypothalamus
Brainstem
Neocortex
Spinal cord
“Striatum” (dorsal & ventral) includes the output structures—the pallidum (dorsal, ventral)
Check your knowledge: 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 causes a
functional depression of neurons • Evolution of neocortex with major ascending and
descending pathways to it 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)
Neuroanatomy review continued
• Midbrain: tectum and tegmentum; species differences; outputs for three major types of movement
• Diencephalon: two major and two additional subdivisions (functional/structural)
• Telencephalon: the endbrain (cerebral hemispheres and basal forebrain); origins of two major pathways for descending axons (Both contain some ascending axons also.)
• Some major axonal pathways in mammals: – Spinoreticular, trigeminoreticular tracts (mostly ipsilateral)– Spinothalamic tract; longest axons to ventrobasal nuc. of
thalamus (VB = VPM and VPL) – Dorsal columns, connecting to the medial lemniscus pathway,
which projects to the ventrobasal nuc. of thalamus – Corticospinal & corticopontine pathways (the former to all
levels of CNS, the latter connecting to the cerebellum via pons)
Notes on Evolution of Forebrain Briefly: 3 topics
• Neuromeres of the forebrain – Segmentation rostral to rhombomeres and
mesomere
• Origins of neocortex – Structural studies give evidence that non-cortical
structures in amphibians, reptiles and birds are related to neocortex of mammals
– Gene expression studies have clarified the phylogenetic relationships
nalian braimmayonic m embrs ofodelmmeric euroN2 8 p.,)5020(r etdeir StFrom
Figures by MIT OpenCourseWare.
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
Structural studies give evidence that non-cortical structures in amphibians, reptiles and birds are related to neocortex of mammals
• Each sensory system connects to thalamic cell groups, which project mainly to the neocortex of mammals
• In birds, also in reptiles and amphibians, thalamus contains unimodal cell groups that project to structures that appear to bestriatum (studies by Karten and others using, originally, Nautamethods for silver-staining of degenerating axons).
• A novel proposal was put forth by Harvey Karten when he was with Nauta at MIT: Embryonic cells migrate from a striatal location to neocortex. Thus, many neocortical cells in mammals are directly homologous to striatal cells in birds (more specifically, cells of the ectostriatum). – This has recently been tested, with surprising results.
Homeobox gene expression: Emx-1 Dlx-1
Evolution of telencephalon based on expression patterns of regulatory genes during development. Based on work of Anibal Smith Fernandez et al., figure from Allman (2000), p 113.
Dorsal
Medial Lateral
Ventral
Archetypal Embryonic Stage
Turtle
dc
sst
dvr
Chick
st
dvr
hMouse
sst
cx
am
Frog
s
st
dc
Figure by MIT OpenCourseWare.
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 Dlx-2
From Striedter (2005), p.278
Figures by MIT OpenCourseWare.
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
Migration of cells to neocortex includes cells from striatal area
arch reser ed in latfountions graimActual B) grations iml acitehtpohy Karten’s )A
eDVR = embryonic Dorsal Ventricular Ridge
eDVR
LG
MG
Str.
OC
N
eDVR
LG
MG
Str.
OC
N
LG, MG: Lateral, Medial Ganglionic Eminence From Striedter (2005), p. 280 Str.=Striatum; OC=Olfactory Cortex; N=Neocortex
Figures by MIT OpenCourseWare.
Next:
A major aspect of nervous system differentiation at the cellular level: The growth, plasticity and regeneration of axons.
MIT OpenCourseWare http://ocw.mit.edu
9.14 Brain Structure and Its Origins Spring 2009
For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.