L2: Neuronal Transmission

cell bodies in CNS

nuclei

axons in CNS

tracts

cell bodies in PNS

ganglia

axons in PNS

nerves

2 types of cells in NS

neurons and glial cells

neurons

responsible for reception, conduction and transmission of electrical signals, mostly multipolar

glial cells

coat neurons in myelin for fast transmission of electrical impulses - oligodendrocytes, schwann cells…

orthodromic conduction

APs traveling from cell body to terminal buttons

antidromic conduction

APs traveling from terminal buttons to cell body

summation

neuron constantly integrates incoming information from EPSPs and IPSPs

Spatial summation

multiple EPSPs happening simultaneously

temporal summation

single neuron firing rapidly in succession

Action potential steps

Sodium channels open, sodium enters

Potassium channels open, potassium leaves

Ion transporters pump back to original locations

Sodium is

outside cell, wants to enter

Potassium is

inside cell, wants to leave

Depolarisation

EPSP, sodium entering

makes neuron more positive, increases likelihood of firing

Hyperpolarisation

IPSP, neuron more negative, decreases likelihood of firing, too much K+ leaving

3 qualities of graded potentials

instantaneous, graded, decremental

threshold of excitation

-65mv

absolute refractory period

1-2ms: no other action potential can be elicited

relative refractory period

can fire again if stimulus stronger than previous

Neuropeptides

large molecules, synthesized on ribosomes and packaged by Golgi complex of cell body, bind to metabotropic receptors, stored in terminal buttons

small neurotransmitters

synthesized in cytoplasm, packaged by golgi complex of terminal buttons, stored in vesicles, bind to ionotropic receptors

Exocytosis

neuron releasing neurotransmitters into synapse to communicate with next cell, way of cell expelling waste

2 types of neurotransmitters

neuropeptides and small neurotransmitters

ionotropic (ligand gated) receptors

binds directly to receptor to induce post synaptic potential

metabotropic receptors

requires g protein to break away and activate second messenger

Autoreceptors

type of metabotropic receptor, on presynaptic neuron, monitors and regulates own neurotransmitter release

connexins

protein channels which bridge gap junctions of synapse

electrical synapses provide

faster transmission than chemical synapses, don’t require neurotransmitters for signal

reuptake

transporters taking neurotransmitters back into the presynaptic buttons through transporters

enzymatic degradation

breaking NTs apart

2 types of neurotransmitter

excitatory and inhibitory

excitatory NT

binds and depolarises membrane, increases likelihood of AP

inhibitory NT

polarises membrane, decreases likelihood of AP

Axon hillock

integrates incoming signals to determine whether they meet the threshold of excitation