Organ Systems I: Ionotropic Transmission (Part 3)

[liveonearth]

1. autocrines = signal themselves, local feedback regulation
2. paracrines = diffuse signal to other local cell
3. neural or synaptic transmitters = cross synapse to bind with post synaptic receptors
4. endocrines = hormones traveling in the blood and binding with receptors on cells all over body
5. neuroendocrines = endocrines released from neurons into blood, eg: posterior pituitary and adrenal medulla do this.

Reveiw of synaptic transmission:
1. presynaptic action potential depolarizes membrane
2. voltage gated Ca++ channels open, Ca++ flows in
3. Ca++ triggers vesicles to release a "quantum" of transmitter into synaptic cleft. "Amplitude of AP determines amount of transmitter released." (from Brons notes, but I thought a nervous AP was an all or none event without variation in amplitude??? Notes say presynaptic inhibition reduces AP amplitude and reduces transmitter release.)

Ionotropic (directly) gated transmission = receptors are transmitter/ligand gated ion channels, binding with neurotransmitter changes its configuration to alter its permeability to ions

EPSP = excitatory postsynaptic potential = transient depolarization caused by transmitter gated increase in permeability of Na/K channels causing net effect of depolarization, bringing postsynaptic cell closer to threshhold, increasing excitability. IPSP is inhibitory by similar mechanism, different channel. An increase in permeability of Cl-/K+ channel results in net hyperpolarization. (GABA, gamma-aminobutyric acid & glycine)

Summation: the sum of the effects of the above channels and everything else that affects the synaptic potentials. Two kinds: spatial and temporal. Spatial involves excitement & inhibition from lots of different parts of the nerve cell, temporal involves repeated potentials from just one synapse that can summate to create overall excitation or inhibition.

Synchonization of PSP's among large populations of neurons produces EEG waves.

RECAP of channel types & locations:
-- Non-gated (ex: K+ leakers) all over nerve cell except in initial segment & nodes of ranvier
-- Voltage gated (ex: Na+/K+ channels, Ca++ channels) in initial segment, nodes of Ranvier (to propagate APs) and on axon terminal (for transmitter release).
-- Neurotransmitter/ligand gated (ex: Na+/K+ channels, Cl- channels) postsynaptic dendrite membranes (EPSPs) and postsynaptic cell body membrane (IPSPs)