19th august 2013bio 334 - neurobiology i - organization of the nervous system1 organization of the...

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


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


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


Medial – lateral axes

MEDIAL(near the

midline)

LATERAL

(away from the

midline)

LATERAL

(away from the

midline)



Ipsilateral and contralateral – things on the same side or the opposite side

IPSILATERAL (same

side)

CONTRALATERAL (opposite

side)



Absolute and relative axes are the same in rats



Planes of brain sections

Kandel, Schwartz and Jessell, Principles of Neural Science


Planes of brain sections

http://homepage.smc.edu/russell_richard/Psych2/Graphics/human_brain_directions.htm


Divisions of the nervous system

http://serendip.brynmawr.edu/exchange/brains/structures


Central Nervous System (CNS) consists of brain and spinal cord



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


Ventricular system of the brain makes CerebroSpinal Fluid (CSF)



Parts of the brain – continuing from development of the tripartite brain



Forebrain divides further into telencephalon, optic vesicles and diencephalon

● Optic vesicles give rise to retina and optic nerves – part of CNS



Telencephalon grows into cerebral hemispheres, olfactory bulbs


● Cerebral lobes grow● Olfactory bulbs sprout out● Cells of the wall divide and differentiate● White matter systems develop


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


Organization of telencephalic and diencephalic structures



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


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


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


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


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



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



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


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)


Two modes of neuronal migration

Somal translocation

Radial glia migration



Interneurons are formed from a different source – the lateral ganglionic emminence

● LGE – ventral telencephalon

● Migrate tangentially into cortex



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


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


More lobes in the cortex



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



Brodmann divided cortex into 47 areas based on cytoarchitechture

● Functionally, there can be even more areas within each Brodmann area



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



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



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)


So what can we take from all of this about the organization of neocortex?

● Two important concepts


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/

http://scienceblogs.com/thoughtfulanimal/2010/06/30/ask-a-scienceblogger-sensation/


Columnar organization of cortex – cells in one column do similar things

Vernon B Mountcastle. The columnar organization of neocortex. Brain (1997)


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

19th august 2013bio 334 - neurobiology i - organization of the nervous system1 organization of the...

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