FoundationalConceptsNeuroscience

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Afferent nerve Efferent nerve

Figure 15.12. Inner-ear hair cell. Afferent fibers (Latin af = toward, ferre =
carry) carry signals from the body’s periphery to the brain; efferent fibers
(Latin e = out) carry signals from the brain to the periphery. Afferent signals
convey sensory information to the brain; efferent signals at least in part func-
tion to adjust the sensitivity of the inner ear to sound.

Hair cells are exquisitely sensitive structures. Incredibly tiny

movements of the hairs are sufficient to open the mechanically-gated

ion channels, leading to release of neurotransmitter at the synapse

with the auditory nerve. If the hair cells were any more sensitive, they

would be too sensitive—the thermal buffeting of the hairs resulting

from the random movements of molecules at body temperature

would open the channels and lead to signals even in the absence of