o
These mammals emit sounds and wait to see how long until the waves
hit objects and return to the animal to determine their location:
echolocation.
o
Sonar and radar are based on echolocation.
Body positions and movement are detected by systems associated with hearing
systems:
using calcium carbonate crystals to detect vibrations also helps other
organs detect body positions in space and movement such as acceleration.
Statocyst is a structure that allows more invertebrates to align themselves with
gravity. Stathocysts contain ciliated hair cells with cilia attached to gelatinous
membranes with crystals of calcium carbonate.
o
The stones/statholiths increase the mass of the gelatinous
membranes so it will be able to bend the cilia when direction changes.
A similar structure is found in the inner ear of vertebrates: the labyrinth is
surrounded by bone and perilymph.
Structure of the labyrinth and semicircular canals: the receptors for gravity in
the membranous chambers of the labyrinth are the utricle and the saccule.
Within these structure are the hair cells with stereocilia and kinocillium (like in
the lateral line of fish): the hair like processes are embedded in the gelatinous
material, the otolith membrane containing calcium carbonate crystals.
o
The utrical is more sensitive to horizontal movement and the saccule
to vertical movement. In both cases the acceleration cause the
stereocilia to bend and produce action potentials in the associated
neuron.
The membranous labyrinth of the utricle and saccule are continued over to the
semicircular canals that are oriented in three different planes so that angular
acceleration from any direction can be detected.
At the ends of the canals are swollen chambers called ampulae and the cilia of
another group of hair cells protrude. The tips of the cilia are embedded with
gelatinous material called cupula that protrude into the endolymph fluid of each
semicircular canal.
When the head rotates the fluid in the semicircular canal pushes against the
cupula and causes the cilia to bend. Depending on the direction the cilia are bent
it causes a depolarization or hyperpolarization.
Vestibular apparatus is the saccule, utricle, and semicircular canals. Saccule and
utricle provide a sense of linear acceleration and the semicircular canal provides
a sense of angular acceleration.
o
The brain uses info from the vestibular apparatus to know about the
body’s position and to maintain equilibrium.
43.4 Chemoreceptors: taste, smell, and pH
Chemical receptors bind to chemicals or ligands in the extracellular fluid. The
response to the chemical signals is that they produce action potentials, which is
because of stimulation that associated neurons cause depolarization.
Taste (gustation) is a combination of physical and psychological factors. There
are five categories: sweet, sour, umami (glutamate and other amino acids), bitter,
and salty.
