AP Biology Physiology #6

Action potentials are normally carried in only one direction: from the axon hillock toward the axon terminals. If you experimentally depolarize the middle of the axon to threshold, using an electronic probe, then

• an action potential will be initiated and proceed only back toward the axon hillock.

• two action potentials will be initiated, one going toward the axon terminal and one going back toward the axon hillock.

• no action potential will be initiated

• an action potential will be initiated, but it will die out before it reaches the axon terminal.

Assume that excessive consumption of ethanol increases the influx of negative chloride ions into "commonsense" neurons whose action potentials are needed for you to act appropriately and not harm yourself or others. Thus, any resulting poor decisions associated with ethanol ingestion are likely due to

• more action potentials in your "commonsense" neurons

• more EPSPs in your "commonsense" neurons

• increased membrane hyperpolarization of "commonsense" neurons

• fewer IPSPs in your "commonsense" neurons

The accompanying diagram represents the steps that occur during the production of an action potential in a neuron. Refer to the figure and select the best description of the sequence of events that occur with a nerve impulse is transmitted along a neuron.

• An action potential is created when Na⁺ ions enter a neuron and trigger more Na⁺ ions to enter the neuron to repolarize the neuron.

• An action potential is created when vesicles in the neuron release neurotransmitters and resting potential restored when neurotransmitter is degraded.

• An action potential is created when voltage-gated channels open to allow Na⁺ into the cell, and resting potential is restored when K⁺ channels open

• An action potential is created when Na⁺K⁺ pumps are activated and resting potential is restored when all ion channels open.

When an action potential arrives at the presynaptic membrane, depolarization occurs, opening voltage-gated channels. This allows an influx of Ca²⁺ ions that are needed to trigger the release of neurotransmitter into the synapse. If a calcium channel blocker, such as cadmium, is injected into the presynaptic cell, which explanation best describes cadmium's effect on the transmission of the impulse?

• Blocking the voltage-gated channels causes the synaptic vesicles to release their neurotransmitters within the presynaptic cell thus reversing the direction of the impulse.

• Elevated levels of cadmium block the ligand-gated ion channels on the postsynaptic membrane that prevents neurotransmitters from binding.

• Elevated cadmium levels cause synaptic vesicles to fuse with the presynaptic membrane thus releasing their neurotransmitters into the synapse triggering an impulse

• Elevated cadmium levels prevent the influx of Ca²⁺ ions into the postsynaptic cell that prevents the release of neurotransmitters into the synapse.

The myelin sheath plays an important role in neuron structure and function. However, when the myelin sheath is missing or fully intact, there are consequences. There are many conditions that cause demyelination of neurons, some are autoimmune disorders, such as multiple sclerosis, and others are heredity. The symptoms of these conditions vary, but often include speech impairment and difficulty coordinating movement. Which of the following correctly connects the symptoms of demyelination with the process of nerve impulse transmission?

• Demyelination prevents the formation of an action potential in sensory neurons that transmit signals from the environment to the central nervous system.

• Demyelination slows nerve impulse transmission

• Demyelination targets the central nervous system

• Demyelination prevents the uptake of neurotransmitters reacted to propagate a message to the next neuron

What happens if a neuron is stimulated enough midway in an exon to trigger an action potential?

• The nerve impulse could not be transmitted because it must be initiated at the dendrite end of a neuron.

• Since neuron transmission is one-way, the nerve impulse would only be transmitted to the end of the exon and then through neurotransmitters to the next neuron.

• The nerve impulse would go both directions from the stimulus point, but only the axon end could transfer the message through neurotransmitters to another neuron

• The nerve impulse would go both directions and the dendrite end would be stimulated to send a second message through this neuron.

C. elegans is a model organism and was the first eukaryotic organism to have its genome sequence. The free-living nematode is often used in laboratories investigating reproduction, particularly egg laying. There are 16 muscles, 2 types of neurons, and multiple receptors involved in the process of laying eggs in C. elegans and there are mutations in all of these structures for the study of process. One particular mutation that prevents the laying of eggs by the worm is rescued by the neurotransmitter, serotonin. the rescue suggests that the mutation is most likely in which of the following?

• one of the muscles needed for egg-laying

• a postsynaptic . neuron involved in egg laying

• a pre-synaptic neuron involved in egg laying

• a receptor for serotonin on cells needed for egg laying

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The point of connection between two communication neurons is called the

• dendrite

• synapse

• cell body

• axon hillock

In a simple synapse, neurotransmitter chemicals are released by

• the dendritic membrane

• axon hillock

• the presynaptic membrane

• ducts on the smooth endoplasmic reticulum

For a neuron with an initial membrane potential of -70mV, an increase in the movement of potassium ions out of their neuron's cytoplasm would result in

• replacement of potassium ions with calcium ions

• hyperpolarization of the neuron

• neuron switching on its sodium-potassium pump to restore the initial conditions

• replacement of potassium ions with sodium ions

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