Exam 1 - Neurotransmitters and Receptors Flashcards
what are the criteria for neurotransmitters?
- must be present in presynaptic neuron
- must be released in response to presynaptic depolarization, and this release is dependent on Ca2+ influx into the presynaptic terminal
- specific receptors that recognize it must be present on the post-synaptic cell
describe ionotropic receptors
- ligand-gated
- directly linked to ion channel
- 2 fxnal domains: 1 extracellular to bind neurotransmitter + 1 transmembrane as channel
- 4 or 5 protein subunits
- produce PSPs w/i 1-2 ms of presynaptic AP (fast)
- neurotransmitter binds receptor and causes ion channel to open
describe metabotropic receptors
- GPCRs
- receptor and ion channel physically separate
- channel activated by intermediate G-proteins and second messengers
- receptor = monomeric protein w/ 2 domains: 1 extracellular to bind neurotransmitter + 1 intracellular to bind G-protein
- 7 transmembrane segments
- produce PSPs w/i ms to minutes after AP (slow)
- direct or indirect interaction with ion channel to open it
describe nicotinic acetylcholine receptor (nAChR) structure
-ionotropic receptor
-funnel-shaped integral membrane protein of 5 subunits
-large extracellular portion
-each subunit has:
-long, hydrophilic N-terminal domain
-3 hydrophobic segments in membrane (TM 1,2,3)
-stretch of hydrophilic domain
-fourth hydrophobic domain in membrane near C-
terminus (TM4)
-ACh binding site near disulfide bond in N-term domain
-TM2 segment in each subunit lines pore
describe how nAChR is opened
ACh binding causes TM2 segments to rotate about 90 degrees, allowing ions to pass through the pore
what does it mean to be cholinergic and which receptors are cholinergic?
bind ACh
- sympathetic and parasympathetic preganglionic neurons
- parasympathetic postganglionic neurons
what happens to vesicular membrane once neurotransmitters are released into cleft?
it is recycled as well
- moves up side of axon terminal, then endocytoses and becomes another synaptic vesicle
- coated by clathrin
- energy for recycling from dynamin
describe types of glutamate receptors
- metabotropic
- ionotropic
- AMPA
- NMDA
what is the difference b/w AMPA and NMDA glutamate receptors
AMPA
- permeable to Na+, K+
- needs only Glutamate
NMDA
- permeable to Na+, K+, Ca2+
- need Glutamate + partial membrane depolarization
- important in learning and memory
what blocks the NMDA channel in the resting or hyperpolarized state?
Mg2+ is attracted to the negative charges on the inside of the cell membrane, but is not permeable -> clogs pore
partial depolarization makes the cell a little less negative, so Mg2+ isn’t attracted anymore -> Na+, K+, Ca2+ can enter
describe structure of glutamate ionotropic receptors
- 5 subunits
- TM2 segment forms hairpin loop w/i membrane
- requires binding of two transmitter molecules to open
what happens to glutamate after it has bound receptors in the synaptic cleft and been released?
-taken up into glial cells -> converted into glutamine -> cycled back to nerve terminal for conversion to glutamate
(example of a non-neuronal cell critical for fxn of synapse)
describe GABA receptors
- 5 subunits, each w/ 4 transmembrane segments
- used by inhibitory neurons in brain
- two types:
- GABAa: ionotropic GABA gated Cl- channel
- GABAb: metabotropic K+ channel
describe glycine receptors
- 5 subunits, each w/ 4 transmembrane segments
- less prominent than GABA receptors
- used by inhibitory interneurons in spinal cord
- ionotropic glycine gated Cl- channel
examples of metabotropic receptors
- alpha and beta-adrenergic receptors: epi and norepi
- GABAb receptors
- metabotropic glutamate receptors
- serotonin receptors
- neuropeptide receptors
- odorant receptors
- certain taste receptors
