By Carrie Whitmore

Human Senses vs.

Shark Senses, Fish Senses,

and Dolphin Senses

Vision, Hearing, and Smell

HUMAN SENSES:VISION:Has a transparent lens that focuses light on the retina. The retina has over a hundred light receptors that give us the power to see. Our sharp color vision comes from a small area called the blind spot because it interprets raw images our eyes see.Controlled by one-third of the brain. Whenever the brain is overwhelmed with emotion/thinking, vision can be impaired.The human brain receives just about an unlimited amount of images in a lifetime. It makes decisions on where to place its attention. We can’t always trust our eyes.

The brain combines input of both eyes into one three-dimensional image.Two defects in human vision are blindness and color blindness.In strong light, the iris contracts, which reduces the size of the aperture which admits light into the eye. A protective obscure substance reduces the exposure of sensitive light cells.

HEARING:The outer ear is shaped like a cup to direct sound towards the tympanic membrane. This transmits vibrations to the inner ear and goes through many small bones in the middle ear called malleus, incus, and stapes.The inner ear (cochlea) is a spiral-shaped chamber that is internally covered by fiber nerves that react to vibrations and transmit impulses to the brain from the auditory nerve.Our brain combines the input of both ears to figure out the direction and distance of sound.The human ear can perceive frequencies from 16 (very deep bass) and 28,000 (a very high pitch) cycles per second

The inner part of the human ear has a vestibular system that is formed by three semicircular canals, which are just about at right angles to each other and are responsible for the sense of balance and spatial orientation. Finally, the inner ear also has chambers that are filled with a viscous fluid and small particles that contain calcium carbonate.Movement of the particles over small hair cells in inner ear send signals to the brain that are interpreted as motion and acceleration.

The nose is the organ that is responsible for smell.The cavity is lined with mucous membranes, which have receptors that are connected to the olfactory nerve.Smells consist of vapors of various substances.The smell receptors interact with the molecules of the smell vapors and transmit the sensations to the brain.The nose also has a structure called the vomeronasal organ. The function of this organ has not been determined yet, but it is thought to be sensitive to pheromones which influence the reproductive cycle.

SMELL:

Smell receptors of the nose are very sensitive to several types of sensations, such as camphor, musk, flower, mint, ether, acrid, or putrid.The sense of smell can be temporarily lost when a human has a cold/is ill.

SHARK SENSES:VISION:In the majority of shark species, their eyes are well developed, large, and have complex structures.Some species are able to sense light and dark through a very thin section of skin on the top of their heads which leads straight to the pineal gland of their brain.Many sharks who live in shallow waters can regulate the amount of light that enters their eyes by dilating or contracting their pupils in the same manner humans do.Focusing in sharks’ eyes is accomplished with the aid of the rectus muscles that pull the lenses closer to or further away from the retina just as a camera lens focuses

Focusing in sharks’ eyes is accomplished with the aid of the rectus muscles that pull the lenses closer to or further away from the retina just as a camera lens focuses.These muscles, along with the oblique muscles control the direction the eye goes in.Due to the poorly lit environment where some species live, they lack the ability to stop light from entering their eyes.Most species posses excellent vision in low light conditions. The structure in their eyes that is responsible for this is called the tapetum lucidum. Sharks share this ability with some nocturnal mammals/reptiles that require extreme sensitive vision to survive.

It is unclear on whether sharks can hear the same as humans or not. The ears of a shark is completely internal. They’ are embedded within the front of the skull. Sharks’ ears are responsible for balance and equilibrium. Their inner ear has many ducts and sacs which are known as endolymphatic ducts.Around the membranous labyrinth is more series of fluid filled canals (cartilaginous labyrinth) that are supplied through the perilymphatic ducts.This protects and supports the more fragile membranous labyrinth within. The sacculus is a large inner chamber into which the ducts lead.

HEARING:

Within this area is called the lagena that has been sound en discovered to receive waves in some fishes.Their swaying back and forth registers on nearby sensory cells that send signals to the brain resulting in sensations of imbalance that the shark then fixes and corrects.

The idea that sharks are able to smell a drop of blood from a mile away in the ocean is highly exaggerated.Sharks have a pair of nares (nostril like holes), which are located just under the edge of the snout.Each individual nare is divided by a nasal flap into two openings. Through these, water is channeled into the incurrent aperture and passed over the lamellae exits. Dissolved molecules transported along in the water bind to receptor cells that then sends a signal to the brain (chemosensory function).Sharks’ nares are completely separate from their mouth and throat and do not aid in respiration at all.

SMELL:

Once sharks pick up a scent trail, they swims up the through the trail while moving their heads side to side. As their snout is bobbed from side to side through the scent trail, the shark is able to figure out the direction from which the odor is coming from.Odor detection is not only used in hunting, but sharks also produce pheromones to signal their reproductive state to potential mates. Smell may also be used in navigation.

VISION:Goldfish have superior vision compared to humans.Humans can see red, green, and blue and can tell light from dark.Fish, however, can see those three colors plus ultraviolet light that gives them polarized vision. It gives them the ability to resolve predators/prey through surface of the water without trouble. This is why goldfish can recognize their owners and know their time of feeding.Fish eyes are different from human eyes. Their lenses are perfectly round which allows them to see underwater.

Fish who live in freshwater have no eye-lids that regulate the amount of light that enters their eyes.Many species of fish can see in color. This is why fishing hooks are made in every single color imaginable. That way fish don’t get used to one color and stay away from the hook.Fishes eyes are located with one on each side of its head. This allows fish to see on either side of the fish at the same time.However, the location of their eyes creates a blind spot that is located directly in front of the head.

FISH SENSES:

HEARING:

Fish have ears, but they are internal and don’t have openings.Sound travels three times faster through water than the air.Fish have a hearing range that is equal to AM radio. This is not bad, since humans can hardly hear underwater.Their difficult hearing system makes them vulnerable to profound internal and nerve damage when loud noises occur.

This is why people are not supposed to break pond ice with a hammer during winter.160 decibels will destroy human ears, but in the dense water much less is needed to destroy the auditory and nervous systems of fish.Ponders have reported in the past that loud low frequencies that are repeated, like snow plows stress their fish out.

SMELL:Fish are given the ability to smell through their nostrils called nares. They are located on the snout of the fish.Odors that are in the water allow the fish to locate prey and predators.However, most fish do not rely on their sense of smell to feed because what a fish can smell at a specific time greatly depends on the strength and direction of the water current.

Dolphins have extremely good vision. They have binocular vision, like a human does, but only to a certain degree.They can’t see colors really well. They have the vision of a severely color-blind person. However, they don’t need much color vision, when they spend 95% of their lives underwater.

VISION:

DOLPHIN SENSES

Some of the dolphins behaviors that are associated with their vision show high uses of both sides of their brain, which is associated with intelligence.

HEARING:Blindfolded dolphins have

been known to find small objects in their tanks using echolocation. With their echolocation, dolphins can hear sounds from tiny objects that are as far off as 120 yards away.Dolphins have two hearing organs. The melon is a big off-center lump on their foreheads that allows them to focus their echolocation sounds. Dolphins also have regular

ears .Dolphins hearing is one of the best in the mammalian world.

SMELL:The smell sense of a dolphin is not that complex.Dolphins may not have a sense of smell at all. They don’t have olfactory lobes in their brains and olfactory nerves are missing in all toothed whales. This indicates that dolphins may not have a sense of smell at all. It is still not known.

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Du Plessis, Amelia. "Sharks." Sharks - Senses. Sharks, 2011. Web. 3 Nov 2011. <http://www.sharks.org.za/senses.html>.

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