Senses
Acoustic senses
Hearing
Sharks have only an inner ear, consistting of three
chambers and an ear stone called an otolith. It
detects sound, acceleration, and gravity.
Sharks use sound to locate food, and it is often the
first sense they rely on to detect prey as under water,
sound travels faster and farther than on land.
Sharks are attracted to low-frequency
pulsed sounds, similar to those wounded or ill
prey would emit. Most attractive sounds are in
the frequency of 25 to 100 Hz. Some sharks are
attracted to sound sources from distances as
great as 250 m (820 ft.).
Lateral line
The lateral line system is a series of fluid-filled
canals just below the skin of the head and along the
sides of the body. The canal is open to the surrounding
water through tiny pores. The lateral line canals
contain a number of sensory cells called neuromasts. Tiny
hairlike structures on the neuromasts project out into
the canal. Water movement created by turbulence,
currents, or vibrations displaces these hairlike
projections and stimulates the neuromasts. This
stimulation triggers a nerve impulse to the brain.
Like the ear, the lateral line senses low-frequency
vibrations. It functions mainly in distance perception
and detecting low-frequency vibrations and directional
water flow.
Eyesight
Sharks have a basic vertebrate eye, but it is laterally
compressed. The lens is large and spherical. Although the threshold
of a shark's visual acuity has not been demonstrated, it is apparent
that they are well-suited for seeing in dim light. Their eyes are
particularly sensitive to moving objects.
Sharks have a large proportion of rods, which are
highly sensitive to changes in light intensity, making
sharks sensitive to contrasts of light and shadow.
The eye has a layer of reflecting plates called the
tapetum lucidum behind the retina. These plates act as
mirrors to reflect light back through the retina a second
time. The tapetum lucidum of a shark is twice as
effective as that of a cat.
Unlike those of other fishes, a shark's pupil can dilate
and contract. Cone cells are present, indicating that sharks may have
some sort of color vision. In clear water, a shark's vision is effective at a distance
up to about 15 m (50 ft.)
Taste
Sharks and batoids have taste buds inside their mouths. These
taste buds have not been studied extensively. Taste may be
responsible for a shark's final acceptance or rejection of prey
items.
Smell
Sharks have an acute sense of smell. Their ability to detect
minute quantities of substances such as blood in water is
well-known. They can detect a concentration as low as
one part per billion of some chemicals, such as certain amino
acids. A shark's sense of smell functions up to hundreds of
meters away from the source.
Paired external nostrils with an incurrent and an excurrent
opening lead to ventral olfactory organs (organs which function
in smelling). Olfactory organs are blind sacs which are not
connected with the mouth.
Ampullae of Lorenzini
External pores cover the surface of a shark's head. Each
pore leads to a jelly-filled canal that leads to a membranous sac
called an ampulla. In the wall of the ampulla are sensory cells
innervated by several nerve fibers.
The ampullae of Lorenzini form a complex and extensive
sensory system around a shark's head. The ampullae detect weak
electrical fields at short ranges, and all living animals produce
electric fields.
Ampullae of Lorenzini are effective only within inches, as
they sense bioelectrical fields in the final stages of prey
capture. Mainly considered electroreceptors, it is possible that the
ampullae of Lorenzini may also detect temperature, salinity,
changes in water pressure, mechanical stimuli, and magnetic
fields.
Sensory pits
Sensory pits are distributed in large numbers on the back,
flank, and lower jaw.
A sensory pit is formed by the overlapping of two enlarged
placoid scales guarding a slight depression in the skin. At the
bottom of the pit is a sensory papilla: a small cluster of
sensory cells that resembles a taste bud.
The precise function of sensory pits has not been
determined. They are most likely sense organs that are stimulated
by physical factors such as water current.
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