BIOL 3322: Chapter 3
36 Cards in this Set
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What is a reflex?
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(an automatic muscular
response to stimuli).
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What experimental evidence did Sherrington have for synaptic delay? For temporal , summation?
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Sherrington measured reflex speeds using dogs. He pinched a dog’s foot and observed that the dog flexed the leg after a short delay. He then measured the total distance that the impulse traveled, from the skin receptor to the spinal cord then from the spinal cord back down the leg. He obs…
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What evidence did he have for spatial summation? For coordinated excitation and inhibition?
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Sherrington discovered that:
a.Reflexes are slower than conduction along an axon.
b.Several weak stimuli presented at slightly different times or locations produce a stronger reflex than a single
stimulus does.
-Excitation of one set of muscles leads to a relaxation of others
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What is an EPSP?, and what ionic flow is largely responsible for it?
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A graded depolarization is known as an excitatory postsynaptic potential (EPSP) and occurs when Na+ ions enter the postsynaptic neuron. EPSPs are not action potentials: The EPSP’s magnitude decreases as it moves along the membrane.
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What is an IPSP, and what ionic flows can produce it?
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Inhibitory postsynaptic potential (IPSP): A temporary hyperpolarization of a postsynaptic cell (this occurs when K+ leaves the cell or Cl- enters the cell after it is stimulated).
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What influence do EPSPs and IPSPs have on neurons with a spontaneous rate of firing?
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Spontaneous firing rate: The ability to produce action potentials without synaptic input (EPSPs and IPSPs increase or decrease the likelihood of firing action potentials).
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What did T. R. Elliott propose?
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T.R. Elliott (1905): suggested that the sympathetic nerves stimulate muscle by releasing adrenaline or a similar chemical. However, the evidence was not convincing and most scientists continued to belief that synapses communicated electrically.
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Describe Loewi's experiment with the two frogs' hearts.
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Otto Loewi (1960): fluid from a stimulated frog heart was transferred to another heart. The fluid caused the new
heart to react as if stimulated.
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What are the major events, in sequence, at a synapse?
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The Sequence of Chemical Events at a Synapse
1.Neurons synthesize chemicals called neurotransmitters.
2.Action potentials travel down the axon. At the axon or presynaptic terminal, the action potentials cause Ca2+ to enter the cell, which leads to the release of neurotransmitters fr…
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List the major neurotransmitters.
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Amino acids, Neuropeptides, Acetylcholine, Monoamines, Purines, and Gases
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How is nitric oxide unlike most other neurotransmitters?
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Vesicles: tiny nearly spherical packets that store high concentrations of neurotransmitters near the presynaptic terminal.
-Nitric oxide is an exception to this rule, as neurons do not store nitric oxide for future use.;
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List the three catecholamines in the order of their synthesis. What is their amino acid precursor?
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Dopamine (DA), Epinephrine (E), and Norepinephrine (NE)): closely related, containing catechol and an amine group, phenylalanine and tyrosine as precursors.
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How might one increase the amount of acetylcholine in the brain? Serotonin?
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Choline is the precursor for acetylcholine. Choline is obtained from certain foods.
The amino acid tryptophan is the precursor for serotonin. The amount of tryptophan in the diet controls the levels of
serotonin.
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Describe the process of exocytosis.
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When an action potential reaches the axon terminal, the depolarization causes voltage-dependent calcium gates to open. As calcium flows into the terminal, the neuron releases a neurotransmitter into the synaptic cleft within 1-2 milliseconds. This process of neurotransmitter release is ca…
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What generalization can be drawn regarding the release of neurotransmitter(s) at the terminals of a given neuron?
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Dale’s Principle: A neuron can release only one neurotransmitter.
Modified concept: a neuron releases the same combination of neurotransmitters at all branches of its axon.
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Contrast ionotropic and metabotropic synaptic mechanisms. List three ionotropic neurotransmitter receptors.
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Ionotropic effects: The neurotransmitter attaches to the receptor, causing the immediate opening of an ion gate (e.g., glutamate opens Na+ gates).
Metabotropic effects: The neurotransmitter attaches to a receptor and initiates a cascade of metabolic reactions. This process is slowe…
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Discuss the role of second messengers in producing the metabotropic effects of neurotransmitters. What kinds of changes can they exert?
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When the neurotrans attaches to the receptor, it alters the configuration of the rest of the receptor protein, enabling a portion of the protein inside the neuron to react with other mol. Activation of the receptor by the neurotrans leads to activation of G-proteins, which are attached to…
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What is a G-protein? What is the "first messenger"? What is one common second messenger?
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G-protein (a protein coupled to GTP (guanosine triphosphate) - an energy-storing molecule).
"1st messenger"= the neurotransmitter
Second messengers (e.g., cyclic AMP): chemicals that carry a message to different areas within a postsynaptic cell.
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What is a neuromodulator? How may some neuromodulators differ from most neurotransmitters? Through what type of receptor (ionotropic or metabotropic) are neuromodulator's effects produced?
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Neuropeptides (or neuromodulators): Neurotransmitters that do not by themselves strongly excite or inhibit a neuron; instead, they alter (modulate) the effects of a neurotransmitter. They are released from the neuron, often from the cell body or dendrites, following repeated stimulation. …
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What is a major difference between the function of neurotransmitters and hormones? Through what kind of receptor (ionotropic or metabotropic) do many hormones act?
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Unlike neurotransmitters, which are released directly to another neuron, hormones convey messages to any
organ that can receive them.
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How are ACh, 5-HT, and the catecholamines inactivated? Why is inactivation important?
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Neurotransmitters need to be inactivated because they may continue to excite or inhibit the receptor.
2.Acetylcholine is broken down by the enzyme acetylcholinesterase (AChE); the two components are reabsorbed and recycled. 3.Serotonin and the catecholamines (i.e., dopamine and norepin…
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What is an agonist? An antagonist? d. How can one drug be an agonist at a given receptor, while another drug, with similar affinity for that receptor, is an antagonist?
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Drugs can affect synapses by either blocking the effects (an antagonist) or mimicking (increasing) the effects (an
agonist) of a neurotransmitter.
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List six ways in which drugs may affect synaptic function.
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Drugs can influence synaptic activity in many ways, including altering synthesis of the neurotransmitter, disrupting
the vesicles, increasing release, decreasing reuptake, blocking its breakdown into inactive chemicals, or directly
simulating or blocking postsynaptic receptors.
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What sorts of behaviors have been linked with alternative forms of genes for the D2 and D4 dopamine receptors? How strong is the association?
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Stimulant drugs directly stimulate dopamine receptor types D2, D3, and D4.
Stimulant drugs increase excitement, alertness, motor activity and elevate mood.
•Examples: amphetamines,PET scan Normal brain cocaine, methylphenidate (Ritalin), MDMA (Ecstasy), nicotine
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Specialized junctions between neurons are called:
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synapses
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Which of the following would most likely result in an IPSP?
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chloride ions entering the cell
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Which of the following is NOT a factor in determining whether or not two EPSPs combine to reach threshold?
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threshold of the presynaptic cell
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When an action potential reaches the end of an axon, the depolarization causes what ionic movement in the presynaptic cell?
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calcium into the cell
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Ionotropic effects:
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may depolarize or hyperpolarize the
postsynaptic membrane.
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A hormone is a chemical that is:
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conveyed by the blood to other organs, whose
activity it influences.
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A drug that produces excitement, alertness, elevated mood, and decreased fatigue is referred to as a:
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stimulant
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At the synapse, amphetamine:
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increases the release of dopamine from the
presynaptic terminal.
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9.A drug that relaxes a person and makes them less sensitive to pain is most likely a(n):
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opiate
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What effect do opiate drugs have on dopamine?
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They indirectly increase the release of
dopamine by blocking transmitters that
normally block dopamine.
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Drugs that grossly distort perception are known as:
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hallucinogens
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Which drugs most closely resemble the neurotransmitter serotonin?
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hallucinogens
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BIOL 3322: Chapter 2