Compare and contrast the structure and function of the saccule and utricle with that of the ...

Answer to q. 1

In mammals, the utricle, saccule, and semicircular canals function in approximately the same way in
that the deformation of hair cells in the proper direction ultimately results in an action potential being
sent to the brain. Depending on which hair cells are deformed (and in which direction), these signals
are used by the brain to determine the position of the head (utricle and saccule) and the rotation of the
head (semicircular canals). In the utricle and saccule the hair cells are covered by a gelatinous cupula
in which otoliths are embedded; gravity causes the otoliths to move within the cupula, and this
movement results in the generation of a nerve impulse. In the three semicircular canals, there are no
otoliths; instead, the canals are filled with endolymph. Rotation of the head causes movement of the
endolymph, and this movement deforms the hair cells resulting in the generation of an action potential.

Answer to q. 2

Sensory receptors convert (transduce) the energy of a stimulus into a change in membrane potential. In
particular, the energy of the stimulus causes the opening or closing of membrane channels that alters
the resting potential. This changed membrane potential is the receptor potential. The magnitude of the
change in membrane potential depends on the energy of the stimulus, and thus the receptor potential is
a graded response.