lecture 8 pt. 1 Flashcards
how were NT discovered
otto loewi- discovered Ach by placing 2 hearts in seperate containers allowing the flow of fluid and stimulating 1
neurotransmitter
chemical released by a neuron on a target with excitatory or inhibitory effect
hormones
acn be same chemicals as NT but travel longer distances and are slower acting
- outside CNS
synapse
junction where messenger molecules are released from one neuron to excite or inhibit the next
- most are chemical in mammals
structure of synapse
presynaptic membrane- axon terminal
postsynaptic membrane - dendritic spine
synaptic cleft- space in between
synaptic vesicle
presynaptic membrane bound spheres containing 1 or more NTs
storage granule
presynaptic membranous compartments that hold several vesicles containing NT
postsynaptic receptor
site to which NT molecule binds
electrical synapse
gap junction- fused pre and post synaptic membrane allows ion to pass directly qnd exchange substances
- very fast
- not very flexible, cannot amplify/ dimish signals, cannot change with experience
4 steps of neurotransmission
- synthesis
- release
- receptor action
- inactivation
2 ways NT can be synthesized
- axon terminal- building blocks from food pumped into cellfrom transporters
- cell body- packaged at golgi bodies and transported on microtubules
how are NT released
action potential opens up voltage gated Ca channels
- Ca then binds to camodulin forming a complex
- complex triggers release of vesicles to binding to presynaptic membrane and release into synapse
quantum
the amount of NT in one vesicle- depends on:
- amount of Ca entering axon terminal
- number of vesicles docked and primed
transmitter activated receptors
protein with binding site for specific NT
- may depolarize and cause EPSP or
- hyperpolarize and cause IPSP or
- initiate other reacitons to excite or inhibit other funcitons of receiving neurons
4 ways of deactivation
- diffusion
- degradation - enzymes break down
- reuptake - back into presynaptic axon terminal
- astrocyte uptake
excitatory vs inhibitory messages
excitatory:
- round vesicles, located on dendrites, dense material, wide cleft and large active zone
inhibitory synapse:
flat vesicles, located on cell body, sparse material, narrow cleft and small active zone
4 criterea for NTs
- must be present in neuron
- must be released and produce response in cell
- must activate in same way when experimentally placed
- must be a mechanism for removal after work is done
4 classes of NT
- small molecule
- peptide
- lipid
- gaseous
characteristics of small molecules
quick acting and quick replaced
synthesized from dietary nutrients and packed into vesicles for use in axon terminals
- variety of functions
ex. Ach, histamine, DA, NE, EP, 5-HT, Glu, GABA
peptide transmitters
chain of amino acids synthesized in the nucleus
- slow acting and slow to replace
- act as hormones that respond to stress, regulate eating, drinking, pleasure and pain, learning
lipid transmitters
not soluble in water, not stored in vesicles so made on demand
- diffuse across cell membrane
ex. endocannabinoids inhibit release of glutamate and GABA so dampen neuronal excitation and inhibition
gases
not stored in vesicles, synthesized on demand, cross membrane
ex. NO, CO
- slow cellular metabolishm, control intestinal wall muscles and dilate blood vessels
2 classes of receptors
- ionitropic- binding site for NT and pore that flows ions
- metabotropic- binding site for NT but no pore
- linked to G protein that affects other receptors and produces changes in metabolic activity
second messenger
chemical that carries a message to initiate a biochemical process
- activated by a NT
- alters ion flow in membrane channel, forms new ion channels
