Chapter 3 Synapses Flashcards
What is a reflex?(3.1)
Automatic muscular response to stimuli
What experimental evidence did Sherrington have for synaptic delay? For temporal summation? (3.1)
Pinched a dogs foot…pinched foot flexed after a short delay.
Temporal summation rpt’d stimuli within a brief time have a cumulative effect.
Rpt’d light pinches of a dogs foot=> a response.
What evidence did he have for spatial summation? For coordinated excitation and inhibition? (3.1)
Summation over space- synaptic input form separate locations combine their effects on a neuron eg pinched two points at once on a dog.
Sensory input that arrives at the brain individually produces weak effects but if each neuron receives many incoming axons ensures the response is activated.
Describe John Eccles’s experimental support for Sherrington’s inferences. (3.1)
Eccles measured the post synaptic neuron during synaptic activation. After he had briefly stimulated an axon, Eccles recorded a slight depolarization of the membrane of the postsynaptic cell. Note: this is a partial depolarization also known as a graded potential. A graded potential is know as an excitatory postsynaptic potential. When Eccles stimulated an axon twice, he recorded two EPSPs. If the delay between EPSPs was short enough, the second EPSP added to what was left of the first one, producing temporal summation. A quick sequence of EPSPs combines to exceed the threshold and produce an action potential.
EPSPs (3.1)
Excitatory postsynaptic potential
Which is a graded potential or partial depolarization. Note: graded potentials can either be excitatory or inhibatory.
Spatial Summation (31)
Summation over space.
Synaptic inputs for separate locations combine their effects on a neuron.
What is an EPSP, and what ionic flow is largely responsible for it? (3.1)
Excitatory post synaptic potential aka graded depolarization.
This results from a flow of Na2+ ions into the neuron.
IPSPs (3.1)
Inhibitory postsynaptic potential which is temporary hyperpolarization.
What is an IPSP, and what ionic flows can produce it? (3.1)
Inhibitory postsynaptic potential-temporary hyperpolarization.
Open gate- K leaves cell or Cl enters the cell carrying neg charge.
Re: the relationship among EPSP, IPSP, and action potential. Why may some synapses have a greater influence than other? (3.1)
Different wiring–some need one synapse to excite it, others need 2 and others cause inhibition.
Re: the relationship among EPSP, IPSP and action potential. What influence do EPSPs and IPSPs have on neurons with a spontaneous rate of firing? (3.1)
Spontaneous rate of firing: periodic production of action potentials even without synaptic input.
EPSPs increase the frequency of action potentials
IPSPs decrease the frequency of action potentials
Re; The neuron as a decision maker.
What factors influence a cells “decision” whether or not to produce an action potential? (3.1)
The summation of EPSPs and IPSPs as a decision because it determines whether or not the postsynaptic cell fires and action potential.
What did T. R. Elliott propose? (3.2)
In 1905 he suggested that the sympathetic nerves stimulate muscles by releasing adrenaline or similar chemicals
Describe Loewi’s experiment with the two frogs’ hearts (3.2)
He repeatedly stimulated a frogs vagus nerve, thereby decreasing the heart rate. He then collected fluid from that heart transferred it to a second frogs heart, found that the second heart also decreased its rate of beating. Also did the same with the accelerator nerve => transfer of chemicals and not electricity.
What are the major events, in sequence, at a synapse? (3.2)
- Neuron synthesizes chemicals that serve as neuotransmitters.
- Action potentials travel down the axon at presynaptic terminals. An action potentila enables Ca2+ to enter the cell. Ca2+ releases neurotransmitters from terminals into the synaptic cleft
- Released molecules diffuse aacross the cleft attach to the receptors and alter activity of post synaptic neuron
- Neurotransmitters separate from their receptors
- Neurotransmitters either recycled back into presynaptic neuron or diffuse away
- Some post synaptic cells send reverse messages to control further release of neurotransmitters.
List major neurotransmitters (3.2)
Amino acids containing an amine group (NH2) Monoamines Acetylcholine Neuropeptides Purines Gases (nitric oxide)
How is nitric oxide unlike most other neurotransmitters? (3.2)
(NB this is not laughing gas)
Many neurons release nitric oxide when they are stimulated
Dilates nearby blood vessels=> increased blood flow to brain
When brain area becomes highly active => increased blood flow
How is the synthesis of peptide neurotransmitters different from that of most other neurotransmitters? (3.2)
Synthesis of peptides is from food aa’s
List the three catecholamines in the order of their synthesis. What is their amino acid precursor (3.2)
- dopamine (precursor is phenylalanine)
- Norepinephrine
- Epinephrine
Precursor is phenylalanine (from diet)
=> tyrosine
=> Dopa
=> Dopamine
=> norepinephrine
=> epinephrine
How might one increase the amount of acetylcholine in the brain? Serotonin? (3.2)
Increased choline in the diet (eg milk, eggs, peanuts) => increased acetylcholine
To increase serotonin- tryptophan such as soy and american corn (but decreases consumption of phenylalanine because it competes with binding sites.
How quickly can peptide neurotransmitters be transported to the terminal? Why is this not a problem for smaller neurotransmitter? (3.2)
1-2 miliseconds after calcium enters the presynaptic terminal it causes exocytosis (release of neurotransmitters in bursts form the presynaptic neurons into the synaptic cleft that separates one neuron form another.
Describe the process of exocytosis. (3.2)
Release of neurotransmitters in bursts form presynaptic neuron into the synaptic cleft.
What generalization ca be drawn regarding the release of neurotransmitters at the terminals of given neuron? (3.2)
The brain as a whole uses many neurotransmitters, no single neuron releases them all. Most neurons release a combination of two or more transmitters.
Eg: Motor neurons in the spinal cord have one branch to the muscles, where they release acetycholine and another branch to other spinal cord neurons, where they release both acetylcholine and glutamate.
A neuron releases a combination of transmitters to make the message more complex.
Contrast ionotropic and metabotropic synaptic mechanisms. List three ionotropic neurotransmitters receptors. (3.2)
3.2
Ionotropic receptors form an ion channel pore. Brief on off action
Metabotropic receptors are indirectly linked with ion channels on the plasma membrane of the cell through signal transduction mechanisms often G proteins. Slower but longer lasting effect
Both receptor types are activated by specific neurotransmitters.
Three ionotropic neurotransmitters: Nicotinic acetylcholine (excitatory) Glutamate Glycine -- inhibitory GABA (gamma-amino-butyric acid) inhibitory
