Chapter 2: Synapses Flashcards
What evidence led Sherrington to conclude that transmission at a synapse is not the same as transmission along an axon?
Sherrington found that the velocity of conduction through a reflex arc was slower than the velocity of an action potential along an axon. Therefore, some delay must occur at the junction between one neuron and the next.
What is the difference between temporal summation and spatial summation?
Temporal summation is the combined effect of quickly repeated stimulation at a single synapse. Spatial summation is the combined effect of several nearly simultaneous stimulations at several synapses onto one neuron.
What was Sherrington’s evidence for inhibition in the nervous system?
Sherrington found that a reflex that stimulates a flexor muscle prevents contraction of the extensor muscles of the same limb. He therefore inferred that an interneuron that excited motor neurons connected to the flexor muscle also inhibited the input to the extensor muscle.
What ion gates in the membrane open during an EPSP? What gates open during an IPSP?
During an EPSP, sodium gates open. During an IPSP, potassium or chloride gates open.
Can an inhibitory message flow along an axon?
No. Only action potentials propagate along an axon. Inhibitory messages—IPSPs—decay over time and distance
What was Loewi’s evidence that neurotransmission depends on the release of chemicals?
When Loewi stimulated a nerve that increased or decreased a frog’s heart rate, he could withdraw fluid from the area around the heart, transfer it to another frog’s heart, and thereby increase or decrease its rate also
Blood flow increases to the most active brain areas. How does the blood “know” which areas are most active?
In a highly active brain area, many stimulated neurons release nitric oxide, which dilates the blood vessels in the area and thereby makes it easier for blood to flow to the area.
Name the three catecholamine neurotransmitters.
Epinephrine, norepinephrine, and dopamine. Do not confuse the term catecholamine with acetylcholine.
When the action potential reaches the presynaptic terminal, which ion must enter the presynaptic terminal to evoke release of the neurotransmitter?
Calcium
How do ionotropic and metabotropic synapses differ in speed and duration of effects?
Ionotropic synapses act more quickly and more briefly
What are second messengers, and which type of synapse relies on them?
Second messengers are chemicals that alter metabolism or gene expression within a postsynaptic neuron. At metabotropic synapses, the neurotransmitter attaches to a receptor and thereby releases a second messenger
How do neuropeptides compare to other transmitters?
Neuropeptides are released only after prolonged stimulation, but when they are released, they are released in large amounts by all parts of the neuron, not just the axon terminal. Neuropeptides diffuse widely, producing long-lasting effects on many neurons.
How do LSD, nicotine, and opiate drugs influence behavior?
LSD binds to one type of serotonin receptor. Nicotine binds to one type of acetylcholine receptor. Opiates bind to endorphin receptors.
What happens to acetylcholine molecules after they stimulate a postsynaptic receptor?
The enzyme acetylcholinesterase breaks acetylcholine molecules into two smaller molecules, acetate and choline, which are then reabsorbed by the presynaptic terminal.
What happens to serotonin and catecholamine molecules after they stimulate a postsynaptic receptor?
Most serotonin and catecholamine molecules are reabsorbed by the presynaptic terminal. Some of their molecules are broken down into inactive chemicals, which then diffuse away.
