Ch.5, Synapses Flashcards
ACh effect on mammals and frogs
mammals: decreases heart rate, activates VOLUNTARY skeletal muscles in the somatic nervous system, can excite or inhibit organs in the autonomic nervous system; HOWEVER, its effect depends on the receptor site not just the neurotransmitter
frogs: same thing
NE
norepinephrine: raises heart rate in mammals
EP/ adrenaline
same thing, raises heart rate in frogs
Otto Lowei
discovered neurotransmitter ACh in frog hearts, first discovered in the ANS
Features of a Chemical Synapse (x)
ASYMMETRICAL LOOK, pre and post look very different
-Unidirectional info flow: MUST specify pre and post-synaptic
-Pre = efferent, sending
-Post= afferent, receiving
separated by synaptic cleft
-has slight delay on communication, not simultaneous or immediate
-Converts chemical signal (neurotransmitter) into electrical signal (change in membrane potential) (transduction)
Features of an electrical synapse
SYMMETRICAL LOOK
-info flow is bidirectional: NO NEED TO SPECIFY PRE AND POST
-Seperated by gap junctions: act as hydrophilic channels that allow metabolites to pass/mostly polar molecules (nucleotides, sugars, amino acids)
-instantaneous: in the heart and hypothalamus (for hormone release) where neurons must work completely in sync for function
includes glial cells/tripartite synapse
Microtubule of the chemical synapse
tracks that transport substances to the axon terminal
Synaptic vesicle of the chemical synapse
round granules that contain neurotransmitter
Storage granule
large compartment that holds synaptic vesicles
Postsynaptic receptor vs post-synaptic membrane vs presynaptic membrane
- presynaptic membrane: has molecules that transmit chemical messages
- postsynaptic membrane: contains receptor molecules that receive chemical messages
- Postsynpatic receptor: site to which a neurotransmitter molecule binds
Synaptic cleft
small space separating presynaptic terminal and post-synaptic dendritic spine
Advantages of chemical vs electrical synapses
Chemical: flexibility, learning memory, plasticity
Electrical: instantaneous allows for synchronization of large population of neurons
Importance of synapses
- learning, memory, plasticity
- sites of drug action: drugs work either by inhibiting or exciting a response
- neuronal communication
- sites of neurological disorders, like neurodevelopmental or neurodegenerative (ADHD, alzheimers, autism, depression, schizophrenia)
Why does alcohol work as a depressant?
it excites GABA in the brain, which is a depressant: therefore has a depressant effect
5 steps of anterograde synaptic neurotransmission in order
anterograde: forward moving, going from pre to post
S-P-R-R-I
1. Synthesis: neuortransmitter is made or sent to neuron.
2. Packaging and storage: neurotransmitter is stored into vesicles to await the arrival of an action potential.
3. Release through exocytosis once threshhold is reached
4. Receptor action: binds to site and activates
5. Inactivation: don’t want to constantly excite the cell
Process of exocytosis in neurotransmission
action potential arriving at the terminal allows vesicles to bind to the membrane, fuse to it, and release neurotransmitter
8 types of synapses
Axodendritic: axon synapsing onto dendrite
Axoaxonic: axon terminal ends on another axon
Axosomatic: axon terminal ends on a cell body b
Axosecretory: hormone release, directly into capillaries
Axoextracellular: axon to somewhere outside the cell
Axosynaptic: axon terminal ends on another terminal
Axomuscular: motor neurons sending to muscle cells
Dendrodentric: dendrite sending to another dendrite
Connexin, connexon/hemichannels: what they are and where they they are
Connexin: 1 of the proteins needed to make a hemichannel
Connexon/hemichannel: 6 connexins joined to make a hemichannel
Major structural identifying feature of electrical synapses
fused pre and post-synaptic membranes: cytoplasm of two neurons is directly in contact
How does the structure of inhibitory and excitatory synapses differ?
Excitatory: wider cleft, rounder vesicles, dense material on membranes (greater postsynaptic density)
Inhibitory: narrower cleft, flatter vesicles, sparse material on membranes (less postsynaptic density)
Post-synaptic density
an electron-dense structure located at the postsynaptic membrane of excitatory synapses, containing a high concentration of scaffolding and signaling proteins.
Why are inhibitory synapses located closer to the cell body?
“open the gates” idea, want it to be close so the cell doesn’t keep getting excited: otherwise this will likely lead to rundown of the cell/seizures
any synapse located closer to the initial segment =more effect on initial segment
four criteria of neurotransmitters
RAMS
-Synthesis: neurotransmitter must be made in neuron or sent to it
-Release: its release must cause a response in the target cell
-same receptor action must be obtained when done experimentally
Mechanism to inactive
EPSPs and IPSps
decay rapidly over time, both forms of graded potentials
Why do cytoplasms need to be fused in electrical synapses
Bc the exchange of ions is directly between cells, vs in chemical synapses they communicate using chemical proxies
