Topic 17 Nervous System Basics Part 2

Neuronal Communication

Information from one neuron flows to another neuron across a synapse

presynaptic ending

a synaptic knob that contains synaptic vesicles filled with neurotransmitters, mitochondria and other organelles

postsynaptic ending

contains receptor sites for neurotransmitters

chemical synapse structure

presynaptic neurons have synaptic vesicles with neurotransmitter and postsynaptic have receptors for these neurotransmitters

synaptic knob

expanded area of axon, contains synaptic vesicles of nuerotransmitters

neuronal communication channels

action potential travels down the synaptic knob, causes voltage gated calcium channel to open, causes exocytosis into neurotransmitters in synaptic cleft

2 types of NT receptors

inotropic and metabotropic

ionotropic

direct, no second messenger is involved, fast

metabotropic

indirect, extra steps - two modes

two modes of metabotropic receptor

direct coupling - slow

second messenger system - even slower

4 types of neurotransmitter

acetylcholine, amino acid and neurotransmitters, monoamines, and neuropeptides

2 classes of neurotransmitters

excitatory and inhibitory

excitatory neurotransmitters

cause depolarization of postsynaptic membranes, promotes action potential

inhibitory neurotransmitters

causes hyper polarization of postsynaptic membranes, suppress action potentials

Main inhibitory NTX’s are GABA and glycine

synaptic transmission - 3 examples

excitatory cholinergic synapse, inhibitory GABA-nergic synapse, excitatory adrenergic synapse

monoamines

epinephrine, catecholamines, norepinephrine, dopamine, and serotonin

amino acids

GABA

neuropeptides

substance p, endorphin

excitatory cholinergic synapse

exactly the neuromuscular junction

inhibitory GABA-ergic synapse

nerve signal triggers release of GABA which crosses synapse, GABA receptors trigger opening of Choline channels producing hyperpolarization

adrenergic synapse

respond to norepinephrine, epinephrine releases, bind to receptor, uses second messenger system, causes a sodium channel to open, causes cell to depolarization because it is an excitatory receptor

EPSP

excitatory postsynaptic potential

excitatory postsynaptic potential

NT causes opening of more ligand gated sodium channels on postsynaptic membrane

IPSP

inhibitory postsynaptic potential

inhibitory postsynaptic potential

NT causes postsynaptic membrane to become more permeable to Potassium or Chloride

Summation

weak stimulation of a postsynaptic neuron may generate an EPSP, but it fades quickly before reaching threshold

2 ways to add up EPSP to reach threshold

temporal and spatial summation

synaptic delay

delay of 0.2-0.5 milliseconds occur between arrival of action potential at synaptic knob, to the beginning of an AP in the postsynaptic cell

More synapses in a chain the slower the message

neuromodulators - chemical signals

have long term effects on entire group of neurons. Rather than brief, quick effects at an individual synapse

neuromodulators - modulate activity

adjusting the rate of neurotransmitters release by presynaptic neurons

adjusting the sensitivity of postsynaptic neurons to neurotransmitters, altering the rate of neurotransmitter reuptake or breakdown to prolong the effects

neuromodulators

adjusting the rate of NT release from the presynaptic neuron

pre-synaptic inhibition and pre-synaptic facilltation

presynaptic inhibition

one presynaptic neuron suppresses another

prevents voltage gated calcium channels from opening, it releases less or no neurotransmitter

presynaptic facilitation

one presynaptic neuron enhances another

Neurotransmitter Reuptake

neurotransmitter is recycled back into presynaptic neuron

opioid receptors

endogenous opioids, drug agonist at opioid receptor, drug antagonists

endogenous opioids

natural in the body

dynorphin, endorphins

drug agonist at opioid receptor

produces analgesic response

morphine, fentanyl, codeine, methadone

drug antagonists

blocks receptors but does not activate them

naxolene, naltrexone