204 Chapter 7
- Hyperpolarization is caused by all of these neurotransmitters
except
a. glutamic acid in the CNS.
b. ACh in the heart.
c. glycine in the spinal cord.
d. GABA in the brain. - Which of these may be produced by the action of nitric
oxide?
a. Dilation of blood vessels
b. Erection of the penis
c. Relaxation of smooth muscles in the digestive tract
d. Long-term potentiation (LTP) among neighboring
synapses in the brain
e. All of these
Test Your Understanding
- Compare the characteristics of action potentials with those
of synaptic potentials. - In a step-by-step manner, explain how the voltage-regulated
channels produce an action potential. - Explain how action potentials are conducted by an
unmyelinated axon. - Explain how a myelinated axon conducts action potentials,
and why this conduction is faster than in an unmyelinated
axon. - Describe the structure of nicotinic ACh receptors, and how
ACh interacts with these receptors to cause the production of
an EPSP. - Describe the nature of muscarinic ACh receptors and the
function of G-proteins in the action of these receptors. How
does stimulation of these receptors cause the production of a
hyperpolarization or a depolarization? - Once an EPSP is produced in a dendrite, how does it
stimulate the production of an action potential at the axon
hillock? What might prevent an EPSP from stimulating
action potentials? How can an EPSP’s ability to stimulate
action potentials be enhanced? - Explain how inhibition can be produced by (a) muscarinic
ACh receptors in the heart; and (b) GABA receptors in
neurons of the CNS. - List the endogenous opioids in the brain and describe some
of their proposed functions. - Explain what is meant by long-term potentiation and discuss
the significance of this process. What may account for LTP
and what role might nitric oxide play?
Test Your Analytical Ability
- Grafting peripheral nerves onto the two parts of a cut spinal
cord in rats was found to restore some function in the hind
limbs. Apparently, when the white matter of the peripheral
nerve was joined to the gray matter of the spinal cord, some
regeneration of central neurons occurred across the two
spinal cord sections. What component of the peripheral
nerve probably contributed to the regeneration? Discuss the
factors that promote and inhibit central neuron regeneration.- Discuss the different states of a voltage-gated ion channel
and distinguish between these states. How has molecular
biology/biochemistry aided our understanding of the
physiology of the voltage-gated channels? - Suppose you are provided with an isolated nerve-muscle
preparation in order to study synaptic transmission. In one
of your experiments, you give this preparation a drug that
blocks voltage-regulated Ca^1 channels; in another, you
give tetanus toxin to the preparation. How will synaptic
transmission be affected in each experiment? - What functions do G-proteins serve in synaptic
transmission? Speculate on the advantages of having
G-proteins mediate the effects of a neurotransmitter. - Studies indicate that alcoholism may be associated with a
particular allele (form of a gene) for the D 2 dopamine receptor.
Suggest some scientific investigations that might further
explore these possible genetic and physiological relationships. - Explain the nature of the endocannabinoids. Speculate about
how, by acting as retrograde neurotransmitters, they might
function to suppress pain in the CNS.
Test Your Quantitative Ability
Use the figure below (from figure 7.14 ) to answer questions
35–37:–70–50+300 1 234
Time (milliseconds)0Membrane potential (millivolts)Resting membrane potential- What is the membrane potential at 0.5 msec. after the action
potential began? - What is the membrane potential at 1.5 msec. after the action
potential began? - How much time was required for the membrane potential to
go from the resting membrane potential to zero mV?