When dental work is to be done, the gums and nerves in the teeth are anethetized by injection of lidocaine. This drug blocks Na+ channels in the membrane of the sensory cells.
This drug is an effective local anesthetic because the
A. Sensory cell membrane do not repolarize after impulses are sent
B. Sensory cell membranes do not depolarize and create impulses
C. Neurotransmitters are in sensory pathway are not released
D. Neurotransmitters are destroyed before the post synaptic neuron is stimulated
The correct answer is B. Sensory cell membranes do not depolarize and create impulses.
Lidocaine works by blocking sodium channels in the membranes of sensory cells. These sodium channels are responsible for allowing the entry of sodium ions into the cell, which initiates the depolarization of the cell membrane and generates nerve impulses.
By blocking these sodium channels, lidocaine prevents the depolarization of sensory cells, thereby inhibiting their ability to create and transmit nerve impulses. This effectively numbs the area and prevents the sensation of pain during dental work.
To determine the correct answer, let's analyze the options:
A. Sensory cell membrane do not repolarize after impulses are sent - This option is incorrect as local anesthesia does not affect repolarization of sensory cell membranes.
B. Sensory cell membranes do not depolarize and create impulses - This option is incorrect as local anesthesia blocks the generation of action potentials by blocking sodium channels in sensory cells.
C. Neurotransmitters in the sensory pathway are not released - This option is incorrect as local anesthesia does not involve the inhibition of neurotransmitter release.
D. Neurotransmitters are destroyed before the postsynaptic neuron is stimulated - This option is incorrect as local anesthesia does not involve the destruction of neurotransmitters.
The correct answer is B. Sensory cell membranes do not depolarize and create impulses. When lidocaine is injected, it blocks the sodium channels in the sensory cell membranes, preventing the influx of sodium ions necessary for depolarization and the subsequent generation of action potentials. This inhibition of depolarization prevents the sensory cells from sending impulses, resulting in the anesthetic effect.