19th August 2013
Organization of the nervous system
Raghav Rajan
Bio 334 – Neurobiology I
August 19 th 2013
Bio 334 - Neurobiology I - Organization of the nervous system 1

Mammalian brain is very similar in its organization across species
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 2
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7

Orienting within the brain – absolute axes and relative axes
ANTERIOR
(in front)
SUPERIOR
(above)
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Anterior/Posterior,
Superior/Inferior – absolute axis system
Rostral/Caudal,
Dorsal/Lateral – relative to the long axis of the brain or spinal cord
POSTERIOR
(behind)
INFERIOR http://www.rci.rutgers.edu/~uzwiak/AnatPhys/APFallLect19.html
3 19th August 2013

Medial – lateral axes
LATERAL
(away from the midline)
MEDIAL
(near the midline)
LATERAL
(away from the midline)
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Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7

Ipsilateral and contralateral – things on the same side or the opposite side
IPSILATERAL
(same side)
CONTRALATERAL
(opposite side)
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Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7

Absolute and relative axes are the same in rats
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Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7

Planes of brain sections
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Kandel, Schwartz and Jessell, Principles of Neural Science
Bio 334 - Neurobiology I - Organization of the nervous system 7

Planes of brain sections
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system 8 http://homepage.smc.edu/russell_richard/Psych2/Graphics/human_brain_directions.htm

Divisions of the nervous system
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system http://serendip.brynmawr.edu/exchange/brains/structures
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Central Nervous System (CNS) consists of brain and spinal cord
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Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
Bio 334 - Neurobiology I - Organization of the nervous system 10

Brain is covered by 3 membranes called the meninges
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Dura mater
Arachnoid mater
Pia mater
Along with CSF – they serve as protection
CSF flows between
Arachnoid and Pia mater http://www.mayoclinic.com/health/medical/IM03177
19th August 2013
●
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Fish – one membrane
Birds, reptiles, amphibians -
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Ventricular system of the brain makes CerebroSpinal
Fluid (CSF)
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
12

Parts of the brain – continuing from development of the tripartite brain
19th August 2013
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
Bio 334 - Neurobiology I - Organization of the nervous system 13

Forebrain divides further into telencephalon, optic vesicles and diencephalon
●
Optic vesicles give rise to retina and optic nerves – part of CNS
19th August 2013
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
Bio 334 - Neurobiology I - Organization of the nervous system 14

Telencephalon grows into cerebral hemispheres, olfactory bulbs
●
●
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Cerebral lobes grow
Olfactory bulbs sprout out
Cells of the wall divide and differentiate
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Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7

Gray matter and white matter
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Gray matter – Collection of neuronal cell bodies
White matter – Collection of axons
Brain – gray matter outside, white matter inside
Spinal cord - opposite
19th August 2013 http://www.studyblue.com/notes/note/n/peripheral-nerve/deck/1119699
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Organization of telencephalic and diencephalic structures
19th August 2013
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
Bio 334 - Neurobiology I - Organization of the nervous system 17

Cortex connects with other parts through 3 major white matter systems
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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
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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
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"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
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Right hemisphere shown a picture of snow
Left hemishere shown a chicken foot
19th August 2013 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.
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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.
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Olfactory cortex, hippocampus
–
– older cortices at most 3 layers
– divided into subfields
Neocortex
–
–
– newer cortex
6 layers arranged into columns
19th August 2013
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
Bio 334 - Neurobiology I - Organization of the nervous system 22

Cortex has layered organization of cell bodies and neuronal processes
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Neocortex has 6 layers
Layer 1 does not have cell bodes
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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
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Cells from the ventricular zone exit the cell cycle and migrate outwards
Pre-plate forms layer I
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Dan H Sanes, Thomas A Reh, William A Harris, Development of the nervous system 2005. Chapter 3
Bio 334 - Neurobiology I - Organization of the nervous system 24

Newly born neurons “pull” themselves up to their final place or migrate along radial glia scaffolds
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Early born neurons may “pull” themselves up by somal translocatio n
Later born neurons migrate along radial glia
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Radial glia are
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Two modes of neuronal migration
Somal translocation
Radial glia migration
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system
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
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LGE – ventral telencephalon
Migrate tangentially into cortex
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Nadarajah B and Parnavelas JG. Modes of neuronal migration in the developing cortex. Nature Revs Neuros. (2002)
Bio 334 - Neurobiology I - Organization of the nervous system 27

Mammalian cortex (layers II-VI) develops in an insideout fashion – first neurons form inner layers
Monkey
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system
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 gyri
19th August 2013
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
Bio 334 - Neurobiology I - Organization of the nervous system 29

More lobes in the cortex
19th August 2013
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
Bio 334 - Neurobiology I - Organization of the nervous system 30

Layering of neocortex is different in different portions of cortex
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Brodmann made a cytoarchitechtural map of cortex – n=1!
Constantin von
Economo and
Georg N Koskinos
Kandel, Schwartz and Jessell, Principles of Neural Science
Bio 334 - Neurobiology I - Organization of the nervous system 31 19th August 2013

Brodmann divided cortex into 47 areas based on cytoarchitechture
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Functionally, there can be even more areas within each
Brodmann area
19th August 2013
Mark F Bear, Barry W Connors, Michael A Paradiso. Neuroscience: Exploring the brain (2007) – Chapter 7
Bio 334 - Neurobiology I - Organization of the nervous system 32

Layering may separate out inputs and outputs from different regions
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Projections to different regions arise from different layers
Layer I – III – intracortical connections
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Layer IV – thalamocortical input connections
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Layer V, VI – output connections to subcortical structures
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Different types of connections may also come into different layers
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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
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Kandel, Schwartz and Jessell, Principles of Neural Science
Bio 334 - Neurobiology I - Organization of the nervous system 34

And different areas connect up in a simple hierarchy like this!
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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?
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Two important concepts
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The right hemisphere senses the left side and controls the left side of the body
19th August 2013 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
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system
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!
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About 10,000 neurons
19th August 2013 Bio 334 - Neurobiology I - Organization of the nervous system http://bluebrain.epfl.ch/page-52063.html
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