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19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 1
Organization of the nervous system
Raghav RajanBio 334 – Neurobiology I
August 19th 2013
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 2
Mammalian brain is very similar in its organization across species
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 3
Orienting within the brain – absolute axes and relative axes
ANTERIOR(in front)
POSTERIOR
(behind)
INFERIOR(below)
SUPERIOR(above)
● Anterior/Posterior, Superior/Inferior – absolute axis system
● Rostral/Caudal, Dorsal/Lateral – relative to the long axis of the brain or spinal cord
http://www.rci.rutgers.edu/~uzwiak/AnatPhys/APFallLect19.html
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Medial – lateral axes
MEDIAL(near the
midline)
LATERAL
(away from the
midline)
LATERAL
(away from the
midline)
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
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Ipsilateral and contralateral – things on the same side or the opposite side
IPSILATERAL (same
side)
CONTRALATERAL (opposite
side)
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
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Absolute and relative axes are the same in rats
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 7
Planes of brain sections
Kandel, Schwartz and Jessell, Principles of Neural Science
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Planes of brain sections
http://homepage.smc.edu/russell_richard/Psych2/Graphics/human_brain_directions.htm
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Divisions of the nervous system
http://serendip.brynmawr.edu/exchange/brains/structures
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 10
Central Nervous System (CNS) consists of brain and spinal cord
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
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Brain is covered by 3 membranes called the meninges
● Dura mater● Arachnoid mater● Pia mater● Along with CSF – they serve as
protection● CSF flows between Arachnoid
and Pia mater
● Fish – one membrane● Birds, reptiles, amphibians -
two
http://www.mayoclinic.com/health/medical/IM03177
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Ventricular system of the brain makes CerebroSpinal Fluid (CSF)
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
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Parts of the brain – continuing from development of the tripartite brain
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 14
Forebrain divides further into telencephalon, optic vesicles and diencephalon
● Optic vesicles give rise to retina and optic nerves – part of CNS
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 15
Telencephalon grows into cerebral hemispheres, olfactory bulbs
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
● Cerebral lobes grow● Olfactory bulbs sprout out● Cells of the wall divide and differentiate● White matter systems develop
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Gray matter and white matter
● Gray matter – Collection of neuronal cell bodies● White matter – Collection of axons● Brain – gray matter outside, white matter inside● Spinal cord - opposite
http://www.studyblue.com/notes/note/n/peripheral-nerve/deck/1119699
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Organization of telencephalic and diencephalic structures
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 18
Cortex connects with other parts through 3 major white matter systems
● Cortical white matter – axons to and from cortex● Corpus callosum – connects the two hemispheres● Internal capsule – connects cortex to thalamus,
brain stem
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Lateralization of brain function – studied extensively in split brain patients by Roger
Sperry● Corpus callosum severed to treat
epilepsy● Mostly normal people● Clever experiments revealed brain
lateralization of function● Sperry won the Nobel in 1981 for
his work on split-brain patients● "The great pleasure and feeling in
my right brain is more than my left brain can find the words to tell you." Roger Sperry
http://en.wikipedia.org/wiki/Roger_Wolcott_Sperry
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Experiment on split-brain patient
● Right hemisphere shown a picture of snow
● Left hemishere shown a chicken foot
http://thebrain.mcgill.ca/flash/capsules/experience_bleu06.html
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Forebrain is the seat of voluntary action, perceptions, conscious awareness, cognition,
etc.● Telencephalon
– Cortex – neocortex, hippocampus, olfactory cortex– Basal telencephalon – basal ganglia, amygdala, etc.
● Diencephalon
– Thalamus– Hypothalamus
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Cerebral cortex – a layered structure important for sensations, voluntary movements, cognition,
etc. ● Olfactory cortex,
hippocampus
– older cortices– at most 3 layers– divided into subfields
● Neocortex
– newer cortex– 6 layers– arranged into columns
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
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Cortex has layered organization of cell bodies and neuronal processes
● Neocortex has 6 layers
● Layer 1 does not have cell bodes
● Golgi – cell bodies and processes
● Nissl – cell bodies and proximal dendrites
● Weigert stain – myelinated fibers
Kandel, Schwartz and Jessell, Principles of Neural Science
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This layering develops through neurogenesis from the ventricular zone
● Cells from the ventricular zone exit the cell cycle and migrate outwards
● Pre-plate forms layer I
Dan H Sanes, Thomas A Reh, William A Harris, Development of the nervous system 2005. Chapter 3
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Newly born neurons “pull” themselves up to their final place or migrate along radial glia
scaffolds● Early born
neurons may “pull” themselves up by somal translocation
● Later born neurons migrate along radial glia scaffolds
● Radial glia are progenitors!
Nadarajah B and Parnavelas JG. Modes of neuronal migration in the developing cortex. Nature Revs Neuros. (2002)
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Two modes of neuronal migration
Somal translocation
Radial glia migration
Nadarajah B and Parnavelas JG. Modes of neuronal migration in the developing cortex. Nature Revs Neuros. (2002)
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Interneurons are formed from a different source – the lateral ganglionic emminence
● LGE – ventral telencephalon
● Migrate tangentially into cortex
Nadarajah B and Parnavelas JG. Modes of neuronal migration in the developing cortex. Nature Revs Neuros. (2002)
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Mammalian cortex (layers II-VI) develops in an inside-out fashion – first neurons form inner
layersMonkey
Dan H Sanes, Thomas A Reh, William A Harris, Development of the nervous system 2005. Chapter 3
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Special features of human CNS
● More cortex – sulci and gyriMark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
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More lobes in the cortex
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 31
Layering of neocortex is different in different portions of cortex
● Brodmann made a cytoarchitechtural map of cortex – n=1!
● Constantin von Economo and Georg N Koskinos
Kandel, Schwartz and Jessell, Principles of Neural Science
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Brodmann divided cortex into 47 areas based on cytoarchitechture
● Functionally, there can be even more areas within each Brodmann area
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 33
Layering may separate out inputs and outputs from different regions
● Projections to different regions arise from different layers
● Layer I – III – intracortical connections
● Layer IV – thalamocortical input connections
● Layer V, VI – output connections to subcortical structures
Kandel, Schwartz and Jessell, Principles of Neural Science
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Different types of connections may also come into different layers
● Feedforward and feedback connections may originate and terminate in different layers
● Such connections may be used to determine the position of a particular area in the hierarchy of cortical areas
Kandel, Schwartz and Jessell, Principles of Neural Science
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And different areas connect up in a simple hierarchy like this!
● Visual system● Connections from 1991
paper (20 years ago)
Felleman DJ, Van Essen DC. Distributed hierarchical processing in the primate cerebral cortex. Cerebral Cortex (1991)
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So what can we take from all of this about the organization of neocortex?
● Two important concepts
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The right hemisphere senses the left side and controls the left side of the body
http://scienceblogs.com/thoughtfulanimal/2010/06/30/ask-a-scienceblogger-sensation/http://www.stanford.edu/group/hopes/cgi-bin/wordpress/2010/06/the-hopes-brain-tutorial-text-version/
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Columnar organization of cortex – cells in one column do similar things
Vernon B Mountcastle. The columnar organization of neocortex. Brain (1997)
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Columnar organization of cortex – cells in one column do similar things
Vernon B Mountcastle. The columnar organization of neocortex. Brain (1997)
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Blue brain project – simulate one rat cortical column – building block for brain with 100,000
columns!● About 10,000 neurons
http://bluebrain.epfl.ch/page-52063.html
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