behavior analysis in a natural environment in the laboratory cells, synapses & circuits

behavior analysis in a natural environment in the laboratory

cells, synapses & circuits basic properties of nerve cells synaptic transmission neuronal architecture & behavior

relating nerve cells to behavior

summary

#04: CELLS, SYNAPSES & CIRCUITS




summary





summary


behavior circuits of interacting neurons, 3 types:

SENSORY INPUT

CENTRAL PROCESSING

MOTOR OUTPUT

BEHAVIOR

NEURONAL ARCHITECTURE OF BEHAVIOR

behavior circuits of interacting neurons, 3 types:

sensory neurons... signal input specialized receptor cells convert features of environment neural signals

interneurons... central processing

motor neurons... motor output (behavior) drive muscle activity @ neuromuscular junction generate excitatory junctional potentials (EJPs)


electrical recordings:

electrode type

position ~ cells extracellular V, intracellular mV, advantages & disadvantages

p.24, fig.1.10


extracellular electrode

motor neurons

“unit” activity (>1)

~ current flow in extracellular space

p.24, fig.1.10


intracellular electrode

single motor neuron

p.24, fig.1.10



records propagation of action potentials along axons

p.24, fig.1.10


intracellular electrode

muscle fiber

EJPs signals... motor neuron others

p.24, fig.1.10



electromyogram (EMG)

whole muscle activity

p.24, fig.1.10


behavior circuits... simple ones (in mammals)

e.g., human knee jerk reflex...

tap knee below patella

stretches receptors in quads (muscle spindles)

activates sensory neurons (Ia)

synapse motor neurons ()

contraction of quads

p.25, fig.1.11


behavior circuits... simple ones (in mammals)

e.g., human knee jerk reflex...

simple ?

sensory-motor ?

monosynaptic ?

no, other neurons involvedp.25, fig.1.11


circuit complexity

e.g., primate visual cortex

boxes = assemblies of

103 s of neurons

106 s of synapses

2 main pathways V1 PG... object location V1 TE... visual form

p.25, fig.1.11


circuit complexity

e.g., primate visual cortex

Q: how to study cellular properties of neurons among such complexity ?

A: chose:

accessible behavior

in model organism providing special advantages

p.25, fig.1.11


advantages & disadvantages

interesting... it is ALL interesting (not only ~ humans)

maintenance, availability & access to sufficient #s

model system... biology & tools available behavior anatomy / physiology cell biology pharmacology genetics / genomics / proteomics



e.g., C. elegans (nematode)

+ cheap, maintenance, sample sizes, simple behavior, simple anatomy, small simple & well- characterized nervous system, development & cell biology, genetic & pharmacological tools good

– boring behavior, few properties of neuronal assemblies or structures, small neurons (electrophysiology difficult but accessible)



e.g., H. sapiens (humans)

+ interesting behavior, need to knowing how we function (medical), sequenced genome, ~ easy research funding arguments

– prohibitively complex in every respect, moral issues for invasive & experimental study, expensive, inconvenient & uncooperative subjects





summary


investigating how neurons behavior

e.g., crayfish response to tail tactile stimulus

record lateral giant interneuron (LGI) correlation (A): always stimulus behavior ?...

p.27, fig.1.12

RELATING NERVE CELLS TO BEHAVIOR



record lateral giant interneuron (LGI) correlation (A): always stimulus behavior ?... sufficient (B): trigger LGI alone response ?...

p.27, fig.1.12




record lateral giant interneuron (LGI) correlation (A): always stimulus behavior ?... sufficient (B): trigger LGI alone response ?... necessary (C): shut off LGI no response ?...

p.27, fig.1.12




record lateral giant interneuron (LGI) correlation (A): always stimulus behavior ?... sufficient (B): trigger LGI alone response ?... necessary (C): shut off LGI no response ?...

should always attempt to ask these 3 questions, but

we rarely find this type of simplicity in nature


investigating how synapses behavior

e.g., Drosophila escape response (mutants, pharmacological agents)

inject current across brain





measure speed of transmission in down-stream motor neurons

chemical synapses: slow





measure speed of transmission in down-stream motor neurons

chemical synapses: slow electrical synapses: fast (middle leg) escape behavior


investigating how restricted neural networks behavior

e.g., lobster ingestion

food esophagus 3 chamber stomach:

cardiac sac gastric mill pylorus




food esophagus 3 chamber stomach:

cardiac sac pylorus (A) gastric mill (C) } rhythmic

p.28, fig.1.13




stomatogastric ganglia (STG) rhythm

all 30 neurons known circuits mapped (B,D) functions in isolated preparations (A,C)

p.28, fig.1.13


p.30, fig.1.14

neural control behavior in complex organism

e.g., selective attention in monkeys (stimulus choice)

unit recordings in cortex cellular response to peripheral light (A)


p.30, fig.1.14



unit recordings in cortex cellular response to peripheral light (A) response > if animal pays attention (B)


p.30, fig.1.14



unit recordings in cortex cellular response to peripheral light (A) response > if animal pays attention (B) response >> if animal ~ behavior (C)




visual system response due to ~ stimulus other neural systems ~ attention (& ~ activity ?)

gain some understanding of mechanism, even at this simple level of analysis





summary


behavior... examples discussed: field studies ethology

ethograms FAP, SS, IRM, releasers, interlocking releasers

laboratory studies associative learning classical / Pavlovian conditioning, US, CS, UR, CR operant/instrumental conditioning

SUMMARY: INTRODUCTION & TERMS

nervous system neurons

channels, resting potentials, action potentials synapses

chemical, electrical, EPSPs, IPSPs plasticity, synaptic depression & potentiation, presynaptic inhibition & facilitation

circuits sensory neurons, interneurons, motor neurons recording neural activity


relating nerve cells to behavior neurons behavior

crayfish tail flip response synapses behavior

Drosophila escape response restricted circuits behavior

lobster digestion whole organism behavior

monkey selective attention


nervous system development and plasticity… neurogenesis, apoptosis and necrosis growth cell adhesion and axon pathfinding formation, maintenance and plasticity of synapses organogenesis

general brain and nervous system anatomy… humans other vertebrates invertebrates

SUMMARY: WE HAVE NOT DISCUSSED…

brains are not merely composed of neurons… glia… oligodendrocytes* and astrocytes (CNS) Schwann cells (PNS)*

form myelin sheath (vertebrates)

neuron cell structure… general categories… microfilaments, neurofilaments and microtubules axon transport structure and functional details at synapses ion channel anatomy


details about signals transmission… action potentials frequency coding signal propagation myelin function “types” of signalling

silent, beating, bursting effects of sustained neural stimulation changing neuron properties


measuring currents and channels… electrophysiology… criteria for ion channel activities

conductance, selectivity, gating, pharmacology activation, inactivation whole cell voltage clamp patch (voltage) clamp ion channel molecular biology and manipulation maintenance of ion concentration gradients


intercellular communication… gap junctions and neurosecretion neurotransmitter release transmitters and hormones receptors and transduction mechanisms neuromoduation


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behavior analysis in a natural environment in the laboratory cells, synapses & circuits