synapses and neurotransmitters Flashcards
what is the criteria for neurotransmitters?
- be present in presynaptic terminals
- be released in response to stimulation
- act on the postsynaptic neuron
- blocking the neurotransmitter should prevent synaptic transmission
what are the main classes of neurotransmitters?
- amino acids
- amines
- peptides (made up of many amino acids)
evidence for neurons
- golgi stain
- physiological evidence from study of reflexes
- final evidence from electron microscopy
why are synapses important?
they enable flexible processing and allow for specialization and integration
what are electrical synapses?
gap junctions that allow current to pass directly between neurons
they directly connect the cytoplasm of two neurons
both depolarization and hyperpolarization are transmitted
how to tell if neurons are connected by gap junctions?
physical technique - dyes can be inserted into neurons using electrodes
dyes diffuse from one neuron to the other demonstrating presence of gap junctions
electrical technique - hyperpolarizing and depolarizing stimuli are passed from one neuron to the other
what are electrical synapses good for?
- fast communication
- synchronizing neurons
what are the steps in chemical synaptic transmission?
- package neurotransmitters in vesicles and put them in pre-synaptic terminal
- action potential arrives - voltage-gated ca2+ channels open
- Ca2+ influx - vesicles fuse to membrane, neurotransmitters released
- neurotransmitters diffuse across the synaptic cleft, activate receptors on postsynaptic cell
- neurotransmitters removed from cleft
what are the two types of synaptic vesicles?
synaptic vesicles - clear, recycled by endocytosis, small molecule transmitters
dense-core secretory granules - dense, ‘one and done’, peptide neurotransmitters
how do vesicles fuse with the membrane?
v-SNAREs on the vesicle have partner t-SNAREs on the membrane
calcium binds to synaptotagmin on v-SNAREs, causing a conformational change that makes the SNAREs ‘zipper’ together
what are SNAREs commonly used for?
they are targets for toxins which cause paralyses but small amounts can be used to get rid of wrinkled (botox)
what are the two types of neurotransmitter receptors?
ligand-gated ion channels (ionotropic receptors)
G-protein coupled receptors (metabotropic receptors)
what are ionotropic receptors?
ligand-gated ion channels
binding of neurotransmitter triggers a conformational change on ion channel allowing ions to pass through
what are metabotropic receptors?
G-protein-coupled receptors (not ion channels)
binding of neurotransmitter triggers conformational change of G-protein which has more complex effects
how are neurotransmitters removed from synaptic cleft?
- they diffuse away
- actively taken up by transporters for recycling (into presynaptic neuron/glia)
- destroyed in synaptic cleft by enzymes