synaptic transmission (1.6) Flashcards
Sherrington
early 1900s; pre- and post-synaptic neurons are separated by a gap (slower around reflex so there must be a gap; had no proof)
Loewi
1920s; synaptic transmission involves chemicals known as neurotransmitters (or neuromodulators); vagus nerve slows down heart (fluid from it)
directed vs nondirected synapse
directed synapse: site of release and contact are in close proximity; small NTs
nondirected synapse: site of release and contact are separated by distance; large NTs
major small-molecule NTs (4)
amino acids, monoamines, acetylcholine, unconventional neurotransmitters
large-molecule NT
neuropeptides
important amino acids (3)
Glutamate: most dominant NT in CNS; excitatory NT; target is thalamus (and hippocampus)
GABA: inhibitory NT; sleep (locus coeruleus —> wake-up)
Glycine: controls movement; target is spinal cord
monoamines (4)
dopamine: CNS; attention, reward, motivation; from tegmentum, targets basal ganglia and prefrontal
epinephrine: PNS; adrenaline (fight or flight); sympathetic nervous system
norepinephrine: CNS —> locus coeruleus (wake-up center), alertness; PNS —> with epinephrine, fight or flight
serotonin: CNS; source is Raphe nuclei; target is amygdala; controls mood
acetylcholine difference
broken down in synaptic cleft before being sucked back in
acetylcholine receptors (2)
nicotinic (n): iontropic
muscarinic (m): metabotropic
unconventional neurotransmitters
dendrites talk back to axons (i.e. more NO leads to more NT); target is hippocampus (learning and memory)
unconventional neurotransmitters soluble gases vs endocannaboids
soluble gases: exist only briefly; easily pass through cell membrane; involved in retrograde transmission (post- to pre-synaptic neuron); regulate activity of presynaptic cells
endocannabinoids: similar to THC (marijuana); exist only briefly; inhibit release of NT (affect presynaptic neurons)
neuropeptides
large molecules; released at nondirect synapses; metabotropic (alter gene expression, not foot in door); CNS target is hypothalamus (appetite); PNS target is kidneys (how much urine is produced)
large vs small NTs (synthesis, packaging, transport, storage, synapse)
small: synthesis in cytoplasm of terminal button; packaging in Golgi complex; no transport; storage near pre-synaptic membrane; direct synapse
large: synthesis in cytoplasm of cell body; packaging in Golgi complex; transport by microtubules to the button (40 cm/day); storage far from pre-synaptic membrane; nondirect synapse
coexistence
many neurons have two neurotransmitters (one small and one large; not two of one kind)
exocytisis process
neurotransmitter release; arrival of AP, influx of Ca+2, vesicles fuse to membrane and release NT
small NT vs large NT exocytosis
small: 1 AP releases 1 vesicle
large: temporal sum of APs releases vesicle (needs more calcium)
receptors, ligand, receptor subtypes
receptors: specific proteins for a given NT (lock for the NT key)
ligand: a molecule that binds to another (NT —> ligand of receptor)
receptor subtypes: enable one NT to transmit different kinds of messages to different parts of the brain
iontropic vs metabotropic receptors
ionotropic receptors: fast, results are PSPs (EPSP: Na+, IPSP: K+, Cl-), let ions flow, opened by chemical
metabotropic receptors: associated with signal and G proteins; slow, results are longer-lasting and more varied, signal proteins, says it’s going to release the G protein on the inside (2 messengers); alter gene expression
autoreceptors
metabotropic receptors on pre-synaptic (rather than post-synaptic) membrane; function is to maintain appropriate level of NT release (detect NTs that wandered off); auto regulation
small vs large neurotransmitters (synapse, receptor, function)
small: direct synapse; iontropic or metabotropic that act directly on ion channels; transmit rapid, brief PSPs
large: nondirect synapse; metabotropic that activate 2nd messengers; transmit slow, diffuse, long-lasting signals
reuptake vs enzymatic degradation
reuptake: scoop up and recycle NTs (more common)
enzymatic degradation: NT is broken down by enzymes (i.e. large NTs)
gap junctions (electrical synapses)
connect cytoplasm of two adjacent cells; exist between neurons, glia, and neurons and glia (can be formed by astrocytes and satellite cells); signals transmitted more rapidly than by chemical synapses
tripartite synapse
(hypothesis) astrocytes wrap around synapses and connect both pre- and post-synaptic cells (coordination?)
agonists vs antagonists
agonists: increase or facilitate activity
antagonists: decrease or inhibit activity (increase degradation)
