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 Sherringtons 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 EPSP, sodium gates open. During 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 Leowi 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 frogs’s heart, and thereby increase 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 types 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. Neuropeptide 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 receptors. 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 onto inactive chemicals, which then diffuse away.
How do amphetamine and cocaine influence synapses ?
They block reuptake of released dopamine, serotonin, and norepinephrine.
Why is methylphenidate generally less disruptive to behavior than cocaine is despite the drugs’ similar mechanisms?
The effects of a methylphenidate pill develop and decline in the brain much more slowly than do those of cocaine.
How do cannabinoids affect neurons?
Cannabinoid released by the postsynaptic neuron attach to receptors on presynaptic neurons, where they inhibit further release of both glutamate and GABA.
Which part of the pituitary-anterior or posterior- is neural tissue, similar to the hypothalamus? Which part is glandular tissue and produces hormones that control the secretions by other endocrine organs?
The posterior pituitary is neural tissue, like the hypothalamus. The anterior pituitary is glandular tissue and produces hormones that control several other endocrine organs.
In what way is a neuropeptide intermediate between neurotransmitters and hormones?
Ordinary neurotransmitters are released in small amounts close to their receptors. Neuropeptides are released into a brain area in larger amounts or not at all. When released, they diffuse more widely. Hormones are released into the blood for diffuse delivery throughout the body.
