12.5 synapses

presynaptic neuron

sends the signal

postsynaptic neuron

receives the signal

synaptic cleft

spaces between the neurons

cell-adhesion molecules (CAMs) 

hold synapse together 

synaptic vesicles

stores neurotransmitters

postsynaptic density

area with receptors

ligand gated ion channels 

open when neurotransmitter binds

acetylcholine (ACh)

common transmitter at muscles

amino acid neurotransmitters

include glutamate, GABA

monoamines (biogenic amines) 

dopamine, norepinephrine, serotonin 

catecholamines

dopamine, epinephrine, norepinephrine

purines

ATP, adenosine

gases 

NO and CO; diffuse directly 

neuropeptides

large molecules like endorphins

neuromodulators

chemicals that adjust neuron activity long-term

cholinergic synapse 

uses ACh; usually excitatory 

GABA-ergic synapse

uses GABA; inhibitory

adrenergic synapse

uses norepinephrine; uses second messengers

second-messenger system 

uses molecules inside the cell to amplify signal 

cAMP

common second messenger

enzyme amplification

one molecule triggers many responses

acetylcholinesterase (AChE) 

enzyme that breaks down ACh 

reuptake

neuron resorbs neurotransmitter

monamine oxidase (MAO)

breaks down monamines in the axon terminal