1

L03.  ROOTS of NEUROETHOLOGY IN CELLULAR NEUROBIOLOGY

1

© Carl D. Hopkins Aug. 28, 2011

Announcements

1) Course website: http://courses.cit.cornell.edu/bionb4240/index.htmGoogle Chrome?

2) Writing AssignmentsW1

3) Discussion sectionWednesday 9:05 AM, this room.

2

OutlineL03. Roots in Cellular Neurobiology1. Krogh's Principle2. Neuron doctrine3. Neuron as connector, integrator, rectifier, transducer,

logical device, memory storage, circuit.

3

“For a large number of problems [in biology] there will be some animal of choice, or a few, on which it can be most conveniently studied.”

—August Krogh, The Progress of Physiology, The American Journal of Physiology, 1929. 90(2) pp. 243-251

KROGH’S PRINCIPLE

4

August Krogh Denmark. Nobel Prize 1920. Discovery of capillary motor regulating mechanism

Squid The Discovery of the Giant Squid Axon1936: Young, J. Z. Proc. Roy. Soc. London B. 121:319 (Description of the giant axon of squid, Loligo)

Young thought the these curious structures were blood vessels, but he was able to show that upon stimulation with electrical currents they caused the mantle to contract so he realized they were

John Z. Young F.R.S. 1907-1997Zoologist, Oxford University

contract, so he realized they were nerve fibers.

2

Giant nerve fibers in squidBullock and Horridge (1965)

Must See Videos:http://www.science.smith.edu/departments/NeuroSci/courses/bio330/squid.html

A. L. Hodgkin and A. F. Huxley, RESTING AND ACTION POTENTIALS IN SINGLE NERVE FIBRES. Physiol. (London), 104(1945)176.

2 ms

• ability to record intracellular voltage• first voltage clamp (2 electrodes inside: I, V) • ability to perfuse (replace) intracellular ions,

d l t f tit ti d i ti f ti

After the Discovery of Squid Axon

• development of quantitative description of action potentials

• ability to record from both pre- and post-synaptic neurons at giant synapse

“…The squid axon did more for axonology than any other single advance in technique during the previous 40 years.”

Alan Hodgkin (1973) see quote by R. Keynes (2005)

Nerve nets in hydra and jellyfish (Cnidaria)

Nerve net in hydra Neurons in jellyfish

NEURON DOCTRINE

3

Santiago Ramon y Cajalused Golgi methodprovided evidence for Neuron doctrinefirst evidence of multitude of cell types, neural circuts

13

Kitten cerebellum

Basket endings convincing proof of separate cells.

- basket cell surrounds cell body but does not connect to purkinje cell.

Axons may cross, but not connect.

Each element autonomous (a cell).

Golgi Method

14

Calaj’s Neuron Doctrine• The nervous system is

composed of cells: glial cells and neurons.

• Neurons are morphological units.

• Neurons make intimate contacts (contiguous but not continuous)

16

continuous).• Cell bodies and dendrites

are conductors, just like axons.

• Dynamic polarization• When there are axon

collaterals, they act together.

• Axons arise in development by neurite outgrowth

Summarized in Nobel speech (1906) - shared with Golgi.

Electron Microscopy Clinches The Neuron Doctrine

First EM: Germany,1930’s.

Fixation of tissues (Palade and Porter, 1950’s)

Palay, Palade, DeRobertis:

17

Neurons with distinct membranes at synapses (extra-cellular space in synaptic cleft) (1954-9).

ANALYSIS LEVEL

molecularwhole animal

18

subcellular

cellular

circuits

4

layout

wiring

19

whole machine

components

inside components

software

The Neuron By AnalogyNeuron as a wire.

Neuron as a rectifier.

Neuron as transducer.

Neuron as a connector

20

Neuron as a connector.

Neuron as an summing circuit.

Neuron logic.

Neuron as a memory storage device.

Neuron in a circuit.

Neuron as a Wire Neuron Shape: long axon makes long distance, highly

specific contact possible.

Neuron electrical properties: signals travel within a neuron (insulation)

21

travel at high speed (propagation)use electric signals (=action potentials)

Branching: permit elaborate connectionsdivergenceconvergence

Neuron ShapeAxon serves as information

conduit.-- long distances-- efficiently packaged

Consider a scale model of motor neuron (soma = 100

22

microns; axon = 1 m)(ratio = 1:10,000)

Axons, longitudinal view Axons, cross section

Dye filled axons

Axon bundles make up nervesDorsal Roots (sensory)

sensory

white matter

gray matter

23

Ventral roots (motor)

spinal cord

ganglion (cell bodies)

Nerve Cells Communicate with Targets Using Electric Signals1) Resting neurons are electrically polarized.

- resting potential

2) A i i l i d b

24

2) Action potentials: transient events caused by opening of ion channels in membrane. Propagates down axon.

3) Slow potentials: originate in sensory receptors, and at synapses. Local, do not propagate.

5

Nerve cell at rest has a voltage across its membrane = resting potential

25

Action PotentialsThe Action Potential

(spike): – Transient

(1 millisecond duration)–“de-polarization”

26

p–peak voltage = +55 mV

inside(mainly due to influx of Na+ ions)

–All or None (threshold)–propagates along axon

27

Some Ion Channels in Nerve Membranes are Voltage-Dependent• Ion selective AND Voltage dependent (opening controlled by voltage)

28

outsidecell

cell at rest (-70 mV) cell partly depolarized (-30 mV)

cell depolarized(+55 mV)

The Sodium Channel

29

Potassium Channels

30

Structure worked out in 1998 (Doyle et al. –Roderick MaKinnon lab)

6

How the action potential propagates

31

Propagation Velocity

32

• Measuring velocity with two electrodes• velocity = distance / time• myelinated nerve: 10 to 100 m/sec

t

Neuron as Rectifiers

33

SYNAPSESExcitatoryInflux of cations (+ charge)

cause membrane depolarization

34

Neuron as a TransducerHow do signals get started in

neurons?sensory receptor neuron

35

Crayfish Stretch Receptor Neural code for stretch intensity is the frequency of nerve impulses

36

7

Adaptation

SA

RA

37

Membrane channelsMSC mechanosensitiveNa – sodiumK – potassiumCl - chloride

Bo Rydqvist, Jia-Hui Lin, Peter Sand, Christer Swerup (2007) Mechanotransduction and the crayfish stretch receptor. Physiol. & Behavior. 92: 21-8.

Pharmachological blockers can sort out the various ion channels responsible for the receptor potential, adaptation, and spikes.

38Bo Rydqvist, Jia-Hui Lin, Peter Sand, Christer Swerup (2007) Mechanotransduction and the crayfish stretch receptor. Physiol. & Behavior. 92: 21-8.

39Wine, J. (1984). J. Experimental Biology. 112:283-319.

SummationSynapses: synaptic potentials sum on the

post-synaptic cell, providing for:-- spatial summation:-- temporal summation: -- subtraction:

40

Fine Tuning the Neuron as Integrator (summing network)

Excitatory synapse generates a depolarizing potential.

Membrane voltage decreases exponentially with distance

41

with distance.

Rise time increases with distance.

Consider a synapse on a dendrite.

Neuron as ConnectorSome neurons serve to

relay signals from one cell to another.’

Signal is relayed from input to the output

42

8

Neuron LogicAND logic

Output spike only if 1 + 2 are active at same time.

OR logicOutput spike if either 1 or 2

ti2

43

are active

NOT logicOutput spike if 1 OR 2, but NOT 3

1

2

3

Neuron MemorySynapses retain a

memory of recent events.

Depression: recent activity leads to decrease in response

44

decrease in response.

Facilitation: recent activity leads to increase.

Pre-synaptic inhibition.

Pre-synaptic facilitation.

Changing the Strength of a Synapse

• Fatigue– depletion of synaptic transmitter

• Habituation– decrease in amount of transmitter released, but not due to fatigue

• Sensitization

45

– increase in amount of transmitter released

Changing the Strength of Synapses

• Pre-synaptic excitation– a synapse on a synapse

(primes synapse to be stronger).

46

• Hebbian Learning– NMDA receptor for

glutamate: synapse is made stronger if activated when cell already depolarized

Neural Circuitsand Behavior

cell body

4. motorneuron

3. synapseTracing circuitry of neural connections leads to understanding of how behavior is influenced by neuronal action.

47

stimulus

1. sensory transduction

2. sensory dendrite

neuron

muscle

Neural Circuits and Behavior

48

Perception correlates with characteristics of neural circuit.

9

Neuronal Activity is both Necessary and Sufficient

A) Correlation between behavior and activity of a particular neuron (LGI)

B) Sufficient: artificial

49

stimulation of the neuron causes both a spike, and the behavior.

C) Necessary: if the neuron spike is blocked, the natural behavior is blocked, even though stimulus is OK.

Complex Behavior, Complex CircuitsStomatogastric Ganglion of

Lobster.A restricted neural network (30

cells).Controls muscles of gastric mill

and the pylorus (movements involved in griding of food

50

involved in griding of food and of digestion).

The PYLORIC muscles and patterns of contraction.

The End

51

ReferencesBullock, T. H. (1948). Properties of a single synapse in the stellate ganglion of squid. J. Neurophysiol. 11, 343-364.Bullock, T. H. (1959). The neuron doctrine in electrophysiology. . Science 129, 997-1002.Bullock, T. H., Bennett, M. V. L., Johnston, D., Josephson, R., Marder, E. and Fields, R. D. (2005). The Neuron Doctrine, Redux. Science 310, 791-793.Bullock, T. H. and Horridge, G. A. (1965). Structure and function in the nervous systems of invertebrates. San Francisco: W. H. Freeman & Co.Debanne, D. (2004). Information processing in the axon. Nat Rev Neurosci 5, 304-316.Doyle, D. A., Morais Cabral, J., Pfuetzner, R. A., Kuo, A., Gulbis, J. M., Cohen, S. L., Chait, B. T. and MacKinnon, R. (1998). The structure of the potassium channel: molecular basis of K+ conduction and selectivity. Science 280, 69-77.Hodgkin, A. L. (1973). Address of the President Sir Alan Hodgkin at the Anniversary Meeting, 30 November 1972. Proc. R. Soc. Lond. B 183, 1-19.Hodgkin, A. L. (1992). Chance and Design: Reminisces of Science in Peace and War. Cambridge: Cambridge University Press.Hodgkin, A. L. and Huxley, A. F. (1945). Resting and action potentials in single nerve fibres. J Physiol 104, 176-95.Hodgkin, A. L. and Huxley, A. F. (1952a). The components of membrane conductance in the giant axon of Loligo. J Physiol 116, 473-96.Hodgkin, A. L. and Huxley, A. F. (1952b). Currents carried by sodium and potassium ions through the membrane of the giant axon of Loligo. J Physiol 116, 449-72.Hodgkin, A. L. and Huxley, A. F. (1952c). The dual effect of membrane potential on sodium conductance in the giant axon of Loligo. J Physiol 116, 497-506.Hodgkin, A. L. and Huxley, A. F. (1952d). Movement of sodium and potassium ions during nervous activity. Cold Spring Harb Symp Quant Biol 17,

52

43-52.Hodgkin, A. L. and Huxley, A. F. (1952e). A quantitative description of membrane current and its application to conduction and excitation in nerve. J. Physiol. (London) 117, 500-544.Hodgkin, A. L., Huxley, A. F. and Katz, B. (1952). Measurement of current-voltage relations in the membrane of the giant axon of Loligo. J Physiol116, 424-48.Keynes, R. (2005). J. Z. and the discovery of squid giant nerve fibers. Journal of Experimental Biology 208, 179-180.Krogh, A. (1929). The progress of physiology. American Journal of Physiology American Journal of Physiology 90, 243-251.MacKinnon, R., Cohen, S. L., Kuo, A., Lee, A. and Chait, B. T. (1998). Structural conservation in prokaryotic and eukaryotic potassium channels. Science 280, 106-9.Palade, G. and Palay, S. L. (1954). Electron microscope observations of interneuronal and neuromuscular synapses. Anatomical Record 118, 335-336.Palay, S. L. and Palade, G. E. (1955). The fine structure of neurons. J Biophys Biochem Cytol 1, 69-88.Ramon y Cajal, S. (1906). The structure and connexions of neurons. Amsterdam: Elsevier Publishing Company 1967.Ramón y Cajal, S. (1909-1911). Histologie du système nerveux de l'homme et des vertébrés. Paris: A. Maloine.Ramón y Cajal, S. (1995). Histology of the Nervous System. New York: Oxford University Press.Rydqvist, B., Lin, J. H., Sand, P. and Swerup, C. (2007). Mechanotransduction and the crayfish stretch receptor. Physiol Behav 92, 21-8.Wine, J. (1984). The structural basis of an innate behavioural pattern. Journal of Experimental Biology 112, 283-319.Young, J. Z. (1936). The structure of nerve fibers in cephalapods and crustacea. Proceedings of the Royal Society of London (B) Biological Sciences121, 319-337.Young, J. Z. (1938). The functioning of the giant nerve fibres of the squid. Journal of Experimental Biology 15, 170-185.