The Architecture of Nervous Systems
General principles from an evolutionary perspective.
Development of the vertebrate nervous system
Identity and organization of functional systems
Some basic structural features of the nervous system.
The Architecture of Nervous Systems
General principles from an evolutionary perspective.
Development of the vertebrate nervous system
Identity and organization of functional systems
Some basic structural features of the nervous system.
Non-mammalian neurobiology.
Cnidaria: hydra (also jellyfish, corals, and anemones)
Nerve net: diffusely distributed network of neurons
Two layers of body wall
Hydra
spongesHydra
Sensory cells are bipolar
Effector cells are muscles or glands
Motorneurons signal to effector cells and to each other as well.
Some general features of the nervous system are present in primitive animals.
Fundamental features of nervous systems:
Polarity of signaling:
information flows from dendrites and soma to axon
(exception: amacrine processes)
Divergence of signaling:
information travels widely
Convergence of signaling:
any one neuron receives input from multiple sources.
Cephalization:
neurons and sensory receptors become concentrated rostrally
Centralization:
neurons concentrate in body areas with specialized function
Flatworms: planaria
Flatworms are bilaterally symmetric and have three tissue layers (endoderm, mesoderm and endoderm)
The nervous system has collections of neurons called ganglia. Axons run through nerve cords.
Interneurons:
local interneurons
projection interneurons
Increase possibilities for information processing. Also can act as switches, pacemakers.
Flatworms: planaria
Annelids and arthropods (and molluscs):
are segmented: body segments are repeated along the rostrocaudal axis
have a ventral nerve cord
bilateral ganglia or fused ganglia are present in each segment and are connected by longitudinal bundles of axons
Examples:
Molluscs:
The Nobel Prize in Physiology or Medicine for 2000
Arvid Carlsson, Paul Greengard and Eric Kandelfor their discoveries concerning "signal transduction in the nervous system"
-are individually identifiable, have the same morphology in each individual
-can be repeatedly located in the same position
-are often very large in size
Invertebrate neurons: the Retzius cells of the leech as an example
In a ganglion in a test tube
Amphioxus: a primitive chordate
The amphioxus has a dorsal nerve cord and a notochord.
Amphioxus: a primitive chordate
The amphioxus has a dorsal nerve cord and a notochord.
Vertebrates: the nervous system forms from the neural plate.
Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon
Spinalcord
Descriptors for relationships:rostral (toward nose)caudal (toward tail)dorsal (toward back)ventral (toward belly)
superior (above)inferior (below)anterior (in front)posterior (behind)
Note: in the spinal cord dorsal/ventral and anterior/posterior are used interchangeably.
Vocabulary
Central nervous system: spinal cord and brain, including retina.areas containing nerve cell bodies = gray matterareas containing axons = white matterareas in which axons and dendrites synapse = neuropilcollections of nerve cell bodies= nuclei (nucleus)axon fiber tracts: fasciculi (fasciculus), peduncle,
commissure, lemnisci (lemniscus), tracts
Peripheral nervous system: sensory and autonomic ganglia, peripheral nerves.
collections of nerve cell bodies = gangliacollections of axons = nerves
Vocabulary
Afferents: axons (nerve fibers) projecting into CNS , inputs to brain, ascending fibers
(example: sensory fibers from periphery)
Efferents: fibers projecting out of CNS, outputs from brain; descending fibers
(example: motor fibers projecting to muscles.)
Interneurons: Intrinsic neurons with axonal connections that remain within the local circuit
Vocabulary
The spinal cord.
Cervical and lumbar enlargements: arise dueto masses of motoneurons for upper and lower limbs.
Central canal
Dorsal roots: carry sensory information from dorsal root ganglion into the dorsal horn.
Ventral roots: carry motor information out of the ventral horn.
The spinal cord.
Dorsal roots: carry sensory information from dorsal root ganglion into the dorsal horn.
Ventral roots: carry motor information out of the ventral horn.
The spinal cord.
Afferent
Efferent
Local circuits within the cortex also have afferents (inputs) and efferents (outputs).
Afferent Efferent
The Organization of the Nervous System
The basic wiring diagram of the nervous system.
(everything is connected to everything)
Behavior is determined by the motor system, which is influence by sensory input, intrinsic behavioral state and cognition.
Reflexes result from sensory input, some inputs are voluntary.
History of neuroanatomical techniques:
1873: Golgi impregnation
1885: Selective stains for degenerating myelinated fibers (Marchi and Algeri)
Mid 1950s: selective silver staining for all fibers (Nauta)
1970s: antibody staining, fluorescent markers, radiolabelled amino acids, retrograde tracers, in situ hybridization of nucleic acids
The Nobel Prize in Physiology or Medicine 1906
Camillo Golgi Santiago Ramón y Cajal
Pavia University Pavia, Italy
Madrid University Madrid, Spain
"in recognition of their work on the structure of the nervous system"
Golgi staining: potassium chromate and silver nitrate (1873)
Golgi's drawing of the hippocampus impregnated by his stain (from Golgi's
Opera Omnia).
Nobel e-museum
Camillo Golgi Nobel Lecture December 11, 1906
The Neuron Doctrine- theory and facts. “..Far from being able to accept the idea of the individuality and independence of each nerve element, I have never had reason, up to now, to give up the concept which I have always stressed, that nerve cells, instead of working individually, act together, so that we must think that several groups of elements exercise a cumulative effect on the peripheral organs through whole bundles of fibers.”
The nervous system as a diffuse reticular syncytium?
(i.e. a mass of cytoplasm with many nuclei but no internal cell boundries)
The Neuron Doctrine: (Santiago Ramon y Cajal)
Neurons are cells. Each is an individual entity anatomically, embyologically, and functionally.
Also: Neurons have a functional polarity.
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Neurons have a functional polarity.
Incoming information arrives
Information is assimilated
Information is sent to next neuron
synapses
The irresistible conception of the reticular suggestion of which I have spoken to you (which changes every 5 or 6 years) has led several physiologists and zoologists to object to the doctrine of propagation of nerve currents by contact or at a distance. All their allegations are based on the findings of incomplete methods... In spite of the pains I have taken to perceive the supposed intercellular anastomoses in preparations made with diverse coloration processes I have never succeeded in finding any definite ones, that is to say, showing themselves as clearly and sharply as the free endings. If the said intercellular unions are not the result of an illusion, they represent accidental dispositions, perhaps deformities whose value would be almost nil in the face of the nearly infinite quantity of the perfectly observed facts of free ending.
Santiago Ramon y Cajal
Nobel lecture, Dec 12, 1906
The structure and connexions of neurons.
Synapses visualized by electron microscopy.
(20m nm cleft with synaptic vesicles on one side and postsynaptic density on the other)
REVISIONS of the NEURON DOCTRINE 1. The presence of electrical synapses – gap junctions (Furshpan and Potter, 1959) 2. Axo-axonic synapses 3. Dendro-dendritic synapses (e.g. amacrine cells of the retina; granule cells of the olfactory bulb (Shepherd)
4. Transynaptic regulation of transmitters, enzymes; transynaptic transport of amino acids, viruses 5. Metabolic subunits within the neuron (e.g. spines as microcompartments) 6. Backpropogation of action potentials from the soma to the dendrites
Laslo Zaborsky, Ph.D. MD. Rutgers U.
Multipolar
Unipolar
J. Comp. Neurol. 462(2): 168-179
Example of morphology of an invertebrate neuron:
the parasol cell of the crayfish brain.
(Mike Mellon, UVA Dept of Biology)
Olfactory,photic, tactile
Examples of morphology of vertebrate neurons.
Motor neurons and interneurons typically unipolar
Neuronal somata in rind or ganglia
Dendritic processes arise directly from axons in most cases
Synapses in neuropil
Few types glia
Lack myelin
Large cells in many instances
Individually identifiable in many instances
Neural circuits have relatively few neurons
Motor neurons and interneuons typically multipolar
Neuronal somata typically grouped in nuclei, cortical lamina or throughout ganglia
Dendritic processes arise from soma
Several distinct types of glia
Have myelin and thus saltatory conduction
Few cells that are very large
Few individually identified neurons
Neural circuits have many components
Similarities and differences between the nervous systems of invertebrates and vertebrates
Inverebrate nervous systems Vertebrate nervous systems
Nature 417, 359 - 363 (16 May 2002)
Robots in invertebrate neuroscience
BARBARA WEBB • Can we now build artificial animals? A combination of robot technology and
neuroethological knowledge is enabling the development of realistic physical models of biological systems. And such systems are not only of interest to engineers. By exploring identified neural control circuits in the appropriate functional and environmental context, new insights are also provided to biologists.
Robot modeling of a cricket’s escape response.
Nature 417, 359 - 363 (16 May 2002)
Robots in invertebrate neuroscience
BARBARA WEBB
…invertebrate systems have been a particularly successful area for the approach. Invertebrate behaviours tend to be more stereotyped and thus easier to analyse comprehensively. The number of neural connections between sensing and action is orders of magnitude less than for vertebrates, making the possibility of complete pathway mapping plausible. We should have comparable processing power available in modern computers to that in insect brains, so failure to replicate their behavioural capabilities will indicate areas in which we lack knowledge of how the systems work.
Understanding the physiological factors underlying the sign of the synaptic potential
Or
Understanding the physiological factors underlying the sign of the synaptic potential
Or
A day at the beach.
Lobster Dactyl Opener MuscleLobster Dactyl Opener Muscle
2.7º 0.5 mV
0.5 mV250 msExcitatory Junction
Potential (EJP)
Inhibitory JunctionPotential (IJP)
twitch contractions, relaxations & muscle
tone
500 ms30 mV50 mg
Intracellular recording
Muscle tension
Lobster Dactyl Opener MuscleLobster Dactyl Opener Muscle
insight overview318 NATURE | VOL 417 | 16 MAY 2002 | www.nature.com
Non-mammalian models for studyingneural development and functionEve Marder
Early neuroscientists scoured the animal kingdom for the ideal preparation with which to study specific problems of interest. Today, non-mammalian nervous systems continue to provide ideal platforms for the study of fundamental problems in neuroscience. Indeed, the peculiarities of body plan and nervous systems that have evolved to carry out precise tasks in unique ecological niches enable investigators not only to pose specific scientific questions, but also to uncover principles that are general to all nervous systems.
Nature 417, 364 - 365 (16 May 2002)
All Creatures Great and Small: National Institutes of Health
NINDS, NICHD, NIDA, NIDCD, NIGMS, NIMH : statements detailing the non-mammalian systems they fund and why.
Antibody staining for GABAA and GABAB receptors in the retina.
Neuroanatomical techniques
1873: Golgi impregnation
1885: Selective stains for degenerating myelinated fibers (Marchi and Algeri)
Mid 1950s: selective silver staining for all fibers
1970s: antibody staining, fluorescent markers, radiolabelled amino acids, retrograde tracers, in situ hybridization of nucleic acids
