Behavioural Neuroscience week 2

Oligodendrocytes (CNS) & Schwann cells (PNS)

form myelin sheaths, inc speed/efficiency of axon conduction

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microglia

protect brain from invading organisms and injury, engulf and break down dead tissue, role in inflammatory response

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astrocytes

provide neurons with physical support, nutrients and clear waste, role in passage/blockade of chemicals from blood to CNS

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electrical transmision

within neurons, from cell body down axon to nerve terminals

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chemical transmission

between neurons, from nerve terminals across synapse to receptors on adjacent target cell

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synaptic junctions

direct electrical signalling between neurons

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electrical transmission1

inactive neuron, inside more neg charged (-70mv)=resting potential. Inactive neuron=polarised, intracellular and extracellular fluids contain + and - charged particles called ions-unequally distributed across membrane which creates resting potential

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electrical transmission 2

Ions: organic (A-) & chloride (Cl-) anions AND sodium (Na+) & potassium (K+) cations

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sodium potassium pump 1

if membrane pot becomes less neg the SPP breaks down-happens when neuron is stimulated. Na ions enter cell,cause cell to be more pos than outside=depolarised.

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sodium potassium pump 2

each neuron has threshold of excitation-point by which the depolarisation can trigger an elctrical signal. Signal travels down axon to its terminal-known as the action potential

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The synapse

contains extracellular fluid through which NT can diffuse. Synaptic contacts between neurons are normally on surface of cell body (axo-somatic), dendrites (axo-dendritic) or on terminals of another cell (axo-axonic)

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chemical transmission 1

when act pot arrives at axon terminal, Ca2+ in nerve membrane open, then enter cell causing synaptic vesicles to travel and fuse to synaptic membrane. S-vesicles break open and release NT into synaptic cleft

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chemical transmission 2

NT molecules from presynaptic cell diffuse across extracellular fluid in synapse and attach to specialied protein molecules called receptors on postsynaptic membrane-binding causes postsyn cells to open NTdep ion channels allowing passage of ions

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chemical transmission 3

cause electrical characteristics of that cell to change-postsyn potentials (PSPs). -can be excitatory or inhib (EPSP/IPSP)-4 types of NTdep ion channels (Na+,K+,Cl-,Ca2+).

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EPSPs

produce small influx of Na+ ions or Ca2+, causing partial depolarisation

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IPSPs

produce either small influx of Cl- ions or efflux of K+ ions, causing partial hyperpolarisation. These ions enter and leave cell via pores in membrane called ion channels/ionophores

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Neural integration

synapses are EPSP or IPSP. axon hillock acts as the integrator, adding up all signals from active synapses. if sufficiently depolarised (threshold of excitation usually -65mv) cell creates its own act pot

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1Receptors-protein molecules in nerve membrane that selectively bind to NT

when NT binds to the receptor this transduce the chemical signal into an electrical response (PSP) in the cell receiving the signal. Any substance recognised by the receptor is a LIGAND for that receptor

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2Receptors -two categories

1) ion-channel linked (ionotropic) receptors -fast response eg-acetylcholine 2)G-protein linked (metabotropic) receptors-slow response, last longer eg-noradrenaline

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Inactivation of NT 1

To inactivate NT molecules that have already been released in synapse, 2 mechanisms involved: enzymatic degradation AND/OR active reuptake into presynaptic nerve terminal

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Inactivation of NT 2

To prevent further release of NT, inhibitory auto receptors on presyn terminal buttons are activated: decrease synthesis or release of NT

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Glial function and synaptic neurotransmission

astrocytes: release chemical transmitters, contain receptors , conduct signals, play role in reuptake. Gap junctions:space between adj neurons bridged by connexins. electrical synapses: allow electrical signals to pass from one neuron to another

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Behavioural Neuroscience week 2

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