That got me to thinking about what has changed since I was in school. Sit down. No seriously, sit down. This is going to shock you.
Are you ready for this?
PLUTO IS NO LONGER A PLANET.
Are you okay? Stay with me...
Remember that whole "Sight, Smell, Taste, Touch, Hearing" thing? That was Aristotle's idea. Houghton mifflin is obviously still using his notes for their first grade readers, even though he kicked the bucket in 322 BC.
My teacher would occasionally make us write papers such as "If you had an extra sense, what would it be? Describe your life." Or "Think of a new color that no one has ever seen before. Describe it to me." Or "Describe the color RED to a blind person." ...When you're in first grade, this seems pretty difficult. I can only imagine what her collection of responses must have looked like. But the following information REALLY makes me disappointed in my first grade self...
You actually have more than five senses.
Here are a few:
Sight or vision is the ability of the brain and eye to detect electromagnetic waves within the visible range. The inability to see is called blindness.
Hearing or audition is the sense of sound perception. Sound can also be detected as vibrations conducted through the body by tactition. Lower frequencies than that can be heard are detected this way. The inability to hear is called deafness.
Taste or gustation is one of the two main "chemical" senses. The inability to taste is called ageusia.
- The four well-known taste receptors detect sweet, salt, sour, and bitter, although the receptors for sweet and bitter have not been conclusively identified. A fifth receptor, for a sensation called umami, was first theorised in 1908 and its existence confirmed in 2000. The umami receptor detects the amino acid glutamate, a flavour commonly found in meat and in artificial flavourings such as monosodium glutamate.
- Note: that taste is not the same as flavour; flavour includes the smell of a food as well as its taste.
Touch, also called tactition or mechanoreception, is a perception resulting from activation of neural receptors, generally in the skin including hair follicles, but also in the tongue, throat, and mucosa. The loss or impairment of the ability to feel anything touched is called tactile anesthesia. Paresthesia is a sensation of tingling, pricking, or numbness of the skin that may result from nerve damage and may be permanent or temporary.
Balance, equilibrioception, or vestibular sense is the sense which allows an organism to sense body movement, direction, and acceleration, and to attain and maintain postural equilibrium and balance.
Thermoception is the sense of heat and the absence of heat (cold) by the skin and including internal skin passages, or rather, the heat flux (the rate of heat flow) in these areas.
Proprioception, the kinesthetic sense, provides the parietal cortex of the brain with information on the relative positions of the parts of the body. Neurologists test this sense by telling patients to close their eyes and touch the tip of a finger to their nose. Assuming proper proprioceptive function, at no time will the person lose awareness of where the hand actually is, even though it is not being detected by any of the other senses.
Nociception (physiological pain) signals near-damage or damage to tissue. The three types of pain receptors are cutaneous (skin), somatic (joints and bones) and visceral (body organs).
Other internal senses
An internal sense or interoception is "any sense that is normally stimulated from within the body". These involve numerous sensory receptors in internal organs, such as stretch receptors that are neurologically linked to the brain.
Pulmonary stretch receptors are found in the lungs and control the respiratory rate.
Cutaneous receptors in the skin not only respond to touch, pressure, and temperature, but also respond to vasodilation in the skin such as blushing.
Stretch receptors in the gastrointestinal tract sense gas distension that may result in colic pain.
Stimulation of sensory receptors in the esophagus result in sensations felt in the throat when swallowing, vomiting, or during acid reflux.
Sensory receptors in pharynx mucosa, similar to touch receptors in the skin, sense foreign objects such as food that may result in a gag reflex and corresponding gagging sensation.
Stimulation of sensory receptors in the urinary bladder and rectum may result in sensations of fullness.
Stimulation of stretch sensors that sense dilation of various blood vessels may result in pain, for example headache caused by vasodilation of brain arteries.
Certain animals, including bats and cetaceans, have the ability to determine orientation to other objects through interpretation of reflected sound (like sonar). Blind people report they are able to navigate by interpreting reflected sounds (esp. their own footsteps), a phenomenon which is known as human echolocation.
Among non-human species, dogs have a much keener sense of smell than humans, although the mechanism is similar. Insects have olfactory receptors on their antennae.
Cats have the ability to see in low light due to muscles surrounding their irises to contract and expand pupils as well as the tapetum lucidum, a reflective membrane that optimizes the image. Pitvipers, pythons and some boas have organs that allow them to detect infrared light, such that these snakes are able to sense the body heat of their prey. The common vampire bat may also have an infrared sensor on its nose. It has been found that birds and some other animals are tetrachromats and have the ability to see in the ultraviolet down to 300 nanometers. Bees and dragonflies are also able to see in the ultraviolet.
Ctenophora have a balance receptor (a statocyst) that works very differently from the mammalian's semi-circular canals.
Electroception (or electroreception) is the ability to detect electric fields. Several species of fish, sharks and rays have the capacity to sense changes in electric fields in their immediate vicinity.
- The only order of mammals that is known to demonstrate electroception is the monotreme order. Among these mammals, the platypus has the most acute sense of electroception.
Magnetoception (or magnetoreception) is the ability to detect fluctuations in magnetic fields and is most commonly observed in birds, though it has also been observed in insects such as bees. Although there is no dispute that this sense exists in many avians (it is essential to the navigational abilities of migratory birds), it is not a well-understood phenomenon. One study has found that cattle make use of magnetoception, as they tend to align themselves in a north-south direction. Magnetotactic bacteria build miniature magnets inside themselves and use them to determine their orientation relative to the Earth's magnetic field.
Pressure detection uses the organ of Weber, a system consisting of three appendages of vertebrae transferring changes in shape of the gas bladder to the middle ear. It can be used to regulate the buoyancy of the fish. Fish like the weather fish and other loaches are also known to respond to low pressure areas but they lack a swim bladder.
The lateral line in fish and aquatic forms of amphibians is a detection system of water currents, mostly consisting of vortices. The lateral line is also sensitive to low frequency vibrations. The mechanoreceptors are hair cells, the same mechanoreceptors for vestibular sense and hearing. It is used primarily for navigation, hunting, and schooling. The receptors of the electrical sense are modified hair cells of the lateral line system.
Polarized light direction/detection is used by bees to orient themselves, especially on cloudy days. Cuttlefish can also perceive the polarization of light. Most sighted humans can in fact learn to roughly detect large areas of polarization by an effect called Haidinger's brush, however this is considered an entoptic phenomenon rather than a separate sense.
Slit sensillae of spiders detect mechanical strain in the exoskeleton, providing information on force and vibrations.
Some plants have sensory organs, for example the Venus fly trap, that respond to vibration, light, water, scents, or other specific chemicals. Some plants sense the location of other plants and attack and eat part of them.
What else is new since you were in school? Leave me a comment! :)