KEY CONCEPT FIGURE 23.50 A circuit model of nerve-impulse propagation along myelinated axons. (a) An electrical model of a myelinated axon (b) Impulse propagation in the myelinated axon 1. An action potential is triggered at this node; we close the switch. 2. Once the switch is closed, the action potential emf drives a current down the axon and charges the capacitance of the membrane. The ion channels are located at the nodes. When they are triggered, the potential at the node changes rapidly to +40 mV. Thus this section of the axon acts like a battery with a switch. The myelin sheath acts like the dielectric of a capacitor C between the conducting fluids inside and outside the axon. Myelin sheath ww ww Conducting fluid ww 3. When the voltage on the capacitor exceeds a threshold, it triggers an action potential at this node-the next switch is closed. Ion channels The conducting fluid within the axon acts like a resistor R.

The nerve impulses always travel in one direction from dendrites to axon terminals. What prevents an action potential from travelling backward? a. Hyperpolarization of the neuron makes the membrane more positive and prevents another action potential. b. After repolarization, the refractory period occurs, where the sodium ions are found outside the cell. c. After repolarization, the reversal of ions prevents another action potential as there would not be enough sodium ions outside the cell to rush in. d. The refractory period prevents another action potential by lowering the threshold potential.

Any change in a neuron's membrane potential that moves the membrane potential to a value more negative than the resting potential (e.g. -120mv) is:  a. Hypopolarization  b. Depolarization  c. An action potential  d. HyperpolarizationNOTE: A IS INCORRECT

The made-up drug leakyhose degrades myelin resulting in myelin becoming more porous and therefore a poor insulator. 2.) Which of the following would NOT be an effect of leakyhose? A. Propagation of the action potential would likely slow B. The action potential may degrade because it can’t properly be regenerated C. The action potential would not propagate but would rather reverse directions D. Saltatory conduction may be disrupted E. All of the above effects are consistent with the administration of leakyhose

What is/are true statements about Action Potentials? Select all that apply. Group of answer choices: A. action potentials propagate down axons B. nformation is coded through the frequency of action potentials C. action potentials are slower in myelinated axons D. action potentials vary depending on the strength of the stimulus

A laboratory experiment is set up where you have two fully functional nerves properly aligned so that it potentially can transmit an action potential through a synapse to the second nerve. The buffer outside the cells contain Na+, H+ and Cl- as the only inorganic ions. When you stimulate the nerve, surprisingly the second nerve does not respond. What is the most likely explanation for the failure of the second nerve response? State why you chose your answer. a. The lack of K+ in the buffer prevents propagation of the action potential b. Neurotransmitter is not being released into the synaptic space. c. An action potential can only be initiated by opening a ligand-gated channel. d. Although neurotransmitter is released, it is unable to stimulate opening of the second nerve' ligand-gated channel. e. Repolarization of the axon does not occur in this buffer.

Assume a neuron's membrane potential is -60 mV, what's the net consequence on the membrane potential of a 5 picoamp (pA) sodium current that occurs simultaneously with a 5 pA chloride current? a. There's a 5 pA hyperpolarizing current b. There's a 10 pA depolarizing current c. There's a 10 pA hyperpolarizing current d. There's a 5 pA depolarizing current e. There's no change in the membrane potential

The Nervous System Label a diagram of a neuron (individual nerve cell), noting the function of each of the following areas: a. dendrites b. cell body с. ахоп d. synaptic terminal Describe the location and function of myelin. Explain how neurons produce and transmit information, noting: Na*, K*, resting potential, and action potential. Explain the role of the following in transmitting an action potential across the synapse: .synaptic terminal of presynaptic neuron b. synaptic cleft c. neurotransmitter d. postsynaptic neuron receptor The Endocrine System Define hormone, noting the three different types of hormones. Define negative feedback and provide a few examples. Explain the dangers of synthetic hormones. Animal Reproduction and Development Define asexual reproduction. a. Define fission and provide an example. b. Define budding and provide an example. c. Define fragmentation/regeneration and provide an еxample. d. Define parthenogenesis and provide an example. State the advantages…

Indicate the specific events that are occurring at 1,2,3 and 4. B. At which area of the graph are sodium ions rapidly entering the neuron. C. At which area of the graph are potassium ions rapidly leaving the neuron? D. At which area of the graph is the sodium ion concentration higher outside than inside the neuron? Explain how a membrane that is said to be "resting" can continually use energy to transport ions. Action Potential Membrane potential (mV) +20+ 0- 20- -40- -60- -80 0 1 m 6 Time (milliseconds)

Action potentials are conducted more rapidlya. in small-diameter axons than in large-diameter axons.b. in unmyelinated axons than in myelinated axons.c. along axons that have nodes of Ranvier.d. All of these are correct.