11. Nervous Tissue and Nervous System

In unmyelinated axons, action potentials are propagated by_________ conduction.

Dr. Roberts is testing a new drug that blocks sodium channels in the axons of a neuron. Which of the following statements is correct?

Would you expect to find larger motor units in the postural muscles of the back or the muscles of the hand? Explain your answer.

Explain why cardiac muscle cells and some smooth muscle cells will continue to contract even when their nerve supply has been removed

Which of the following statements best describes saltatory conduction?

a. Every section of the axolemma must be depolarized and triggered to generate an action potential.

b. The internodes must generate action potentials.

c. The dendrites and cell bodies propagate EPSPs toward the trigger zone.

d. Only the nodes of Ranvier must generate action potentials.

Identify the following as properties of electrical synapses (ES), chemical synapses (CS), or both (B).           

a. ______The plasma membranes of presynaptic and postsynaptic neurons are joined by gap junctions.          

b. ______Transmission is unidirectional and delayed.          

c. ______A presynaptic neuron and a postsynaptic neuron are involved.          

d. ______The use of neurotransmitters packaged into synaptic vesicles is required.          

e. ______Transmission is nearly instantaneous and bidirectional.

The trigger for exocytosis of synaptic vesicles from the presynaptic neuron is:

a. arrival of an action potential at the axon terminal and influx of calcium ions.

b. summation of IPSPs at the presynaptic neuron.

c. binding of neurotransmitters to the axon hillock.

d. influx of Na+ into the postsynaptic neuron.

Which of the following is not a method by which the effects of neurotransmitters are terminated?

a. Reuptake into the presynaptic neuron

b. Diffusion away from the synaptic cleft and uptake by glial cells

c. Movement back to the cell body by retrograde axonal transport

d. Degradation by enzymes in the synaptic cleft

A ________ is characterized by multiple input neurons synapsing on one postsynaptic neuron.

a. diverging circuit

b. discharge zone

c. facilitation zone

d. converging circuit

Mark the following statements as true or false. If a statement if false, correct it to make a true statement.

a. An excitatory postsynaptic potential is caused by K+ or Cl− channels opening in the membrane of the postsynaptic neuron.

Mark the following statements as true or false. If a statement if false, correct it to make a true statement.

b. Postsynaptic potentials may summate by spatial summation in which multiple neurons fire onto a single postsynaptic neuron.

Mark the following statements as true or false. If a statement if false, correct it to make a true statement.

c. An inhibitory postsynaptic potential causes the membrane potential of the postsynaptic neuron to approach threshold.

Mark the following statements as true or false. If a statement if false, correct it to make a true statement.

d. Spatial summation can combine two EPSPs, two IPSPs, or an EPSP and an IPSP.

Explain how an action potential is propagated down an axon in continuous conduction. Why is saltatory conduction faster than continuous conduction?