Biology Chapter 48 Key Concepts and Mastering Bio Answers

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Describe the basic pathway of info flow through neurons that causes you to turn your head when someone calls your name
Sensors in your ear transmit info to your brain. There the activity of interneurons in processing centers enables you to recognize your name. In response, signals transmitted via motor neurons cause contractions of muscles that turn your neck
How might increased branching of an axon help coordinate responses to signals communicated by the nervous system?
Increased branching would allow control of a greater number of postsynaptic cells, enhancing coordination of responses to nervous system signals
Under what circumstances could ions flow through ion channels from regions of low ion concentration to regions of high ion concentraion?
Ions can flow against a chemical concentration gradient if there is an opposing electrical gradient of greater magnitude
Suppose a cell’s membrane potential shifts from-70 mV to -50 mV. What changes in the cell’s permeability to K+ or Na+ could cause such a shift?
A decrease in permeability of K+, an increase to permeability of Na+, or both
Ouabain, a plant substance used in some cultures to poison hunting arrows, disables the sodium-potassium pump. What change in the resting potential would you expect to see if you treated a neuron with ouabain?
The activity of the sodium-potassium pump is essential to maintain the resting potential. With the pump inactivated, the sodium and potassium gradients would gradually disappear, resulting in a greatly reduced resting potential
In multiple sclerosis, myelin sheaths harden and deteriorate. How would this affect nervous system function?
Loss of the insulation provided by myelin sheaths leads to a disruption of action potential propagation along axons
Suppose a mutation cause gated sodium channels to remain inactivated longer after an action potential. How would this affect the frequency at which action potentials could be generated?
The maximum frequency would decrease because the refractory period would be extended
How is it possible for a particular neurotransmitter to produce opposite effects in different tissues?
It can bind to different types of receptors, each triggering a specific response in postsynaptic cells
Organophosphate pesticides work by inhibiting acetylcholinesterase, the enzyme that breaks down the neurotranmitter acetylocholine. Explain how these toxins would affect APSPs produced by acetylcholine
These toxins would prolong the EPSPs that acetylcholine produces because the neurotransmitter would remain longer in the synaptic cleft
Which term describes the difference in electrical charge across a membrane?
Membrane potential-the difference in electrical charge across a membrane.
Resting neurons are most permeable to which of the following ions?
K+, Resting neurons are most permeable to K+ ions
True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane.
False-The potential energy of a membrane potential comes both from the difference in electrical charge and from the concentration gradient of ions across a membrane.
Which channel is mainly responsible for the resting potential of a neuron?
Potassium leak channel- K+ ions flow along their concentration gradient to maintain the resting potential of a neuron.
Which term describes an electrical signal generated by neurons?
Action potential-a rapid electrical signal generated by neurons.
Which channel maintains the concentration gradients of ions across a neuronal membrane?
The sodium potassium pump moving Na+ ions out and K+ ions in-channel maintains the ion concentration gradients across a neuronal membrane.
What behavior is observed if the voltage across a neuronal membrane is set to -20 mV?
The sodium channel opens, and Na+ ions flow in- Sodium ions flow into the cell when the membrane potential is between -20 mV and 30 mV.
Which structure is not part of a neuron? cell body, dendrite, myelin sheath, axon
myelin sheath- layer of Schwann cells wrapped around a neuron.
Which event triggers the creation of an action potential?
The membrane depolarizes above a certain threshold potential-Influx of Na+ ions into the neuron can lead to membrane depolarization above the threshold potential; this event triggers the creation of an action potential.
What term describes how a neuronal membrane’s potential is altered in the presence of inhibitory signals?
Hyperpolarization-Inhibitory signals hyperpolarize the membrane and make the membrane potential even more negative than normal.
Where in the neuron do action potentials begin?
Axon hillock-the region where voltage-gated channels begin in a neuron, near the cell body.
How is an action potential propagated down an axon after voltage-gated sodium channels open in a region of the neuron’s membrane?
Sodium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated sodium channels farther down the axon.-The entry of sodium ions into the neuron and their diffusion to adjacent areas of the membrane causes those portions of the membrane to become depolarized and results in the opening of voltage-gated sodium channels farther down the axon, which release potassium ions to the outside, returning the charge to its previous state.
What is the sequence of events that occurs once the membrane potential reaches threshold
-Membrane reaches threshold
-Many voltage-gated Na+ channels open
-Na+ rush into the cell, moving down their electrochemical gradient
-Membrane potential rises (depolorizes) rapidly
What causes the release of neurotransmitter molecules?
an action potential reaching the end of an axon- When an action potential reaches the end of an axon, vesicles fuse with the plasma membrane and release neurotransmitter into the synaptic cleft.
The space between an axon of one neuron and the dendrite of another neuron is called?
Synaptic cleft- space between two neurons that meet at a synapse.
Neurons store neurotransmitter molecules in vesicles located within ?
Synaptic terminals-Vesicles within synaptic terminals contain neurotransmitter that may be released into the synaptic cleft.
The “information receiving” section of a neuron is its _____.
dendrites
Which term describes the difference in electrical charge across a membrane?
membrane potential
Resting neurons are most permeable to which of the following ions?
K+
True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane.
false
Which channel is mainly responsible for the resting potential of a neuron?
potassium leak channel
Which term describes an electrical signal generated by neurons?
action potential
Which channel maintains the concentration gradients of ions across a neuronal membrane?
The sodium-potassium pump moving Na+ ions out and K+ ions in.
What behavior is observed if the voltage across a neuronal membrane is set to -20 mV?
The sodium channel opens, and Na+ ions flow in.
Choose the set that includes the most charged compounds that are more abundant inside neurons, in the cytosol, than outside the neurons, in the extracellular fluid.
potassium ions and proteins
In a neuron, during the depolarization phase that may trigger an action potential _____.
some voltage-gated sodium channels are open
Acetylcholine receptors on skeletal muscles are described as being “ionotropic” receptors because _____.
binding of acetylcholine to the receptor protein converts the protein to an open ion channel
Where are neurotransmitter receptors located?
the postsynaptic membrane
Which of the following is a direct result of depolarizing the presynaptic membrane of an axon terminal?
Voltage-gated calcium channels in the membrane open.
Identify the correct statement(s) about the resting membrane potential of a cell.
Concentration gradients of potassium (K+) and sodium (Na+) across the plasma membrane represent potential energy.
Potassium (K+) and sodium (Na+) gradients are maintained by active transport in a resting mammalian neuron.
Which of these causes the release of neurotransmitter molecules?
an action potential reaching the end of the axon
The space between an axon of one neuron and the dendrite of another neuron is called a(n) _____.
synaptic cleft
Neurons store neurotransmitter molecules in vesicles located within _____.
synaptic terminals
Which of the following characteristics determines when the refractory period ends?
how long it takes for the voltage-gated Na+ channels to reactivate at the end of an action potential

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