Monday, 15 October 2012

BRAIN MYTH-BUSTING: We have five senses

Since elementary school, we're all taught that we have 5 senses: smell, touch, taste, sight, and sound. Pop culture has a term: "the sixth sense". Fictional characters with a sixth sense can usually do some cool supernatural thing, like reading thoughts or seeing dead people (as in the appropriately titled movie, The Sixth Sense). But guess what? We all have sixth senses. And seventh senses. And eighth senses. Some neuroscientists estimate we have up to twenty senses. And none of them are supernatural.

Here are some of the more over-looked senses:

Proprioception:
This is the sense of body position. It's how you know you're sitting or standing, even without looking. It's why you can scratch your bum without looking at your hand or your bum.

Equilibrium:
This is your sense of balance. The vestibular apparatus, which senses balance, is located inside your ear.

Acceleration:
The vestibular apparatus also senses how your body is moving. Are you speeding up? Slowing down? Spinning in circles? The ability to know this is one of your senses. (Next time you feel dizzy, blame your vestibular apparatus.)

The inner ear. The brown loops are the semi-circular canals, and they are part of the vestibular apparatus. I talk a lot more about the vestibular apparatus in my post on carsickness. (picture from wikipedia)

Nociception:
This is the sense of pain. It is not the same as touch! Some of these senses seem like they could count as "touch", but they aren't the same. This is because different neurons do the sensing, and the sense is processed in different areas of the brain. A good example is pain which, in brain-terms, is completely different from touch.

Temperature:
The ability to sense hot or cold is also different from touch.

Hunger:
Yep, that counts as a sense.

Thirst:
Well, if hunger does, thirst must.

The need to go to the bathroom:
Also separate from touch.

How much carbon dioxide is in your blood:
Why do you think it hurts so much to hold your breath? You can sense when your body needs more oxygen. Usually this runs on auto-pilot. Your brain monitors carbon dioxide levels and controls the lungs so you breathe regularly without thinking about it. But if you hold your breath, you'll start to feel it pretty quickly.

Chronoception:
You can sense the passage of time. Your body cycles through a natural 24-hour rhythm, called the circadian rhythm. This is controlled by an area of the brain called the superchiasmatic nucleus. You can also sense time on shorter or longer scales, even if you aren't consciously aware of it.

There are even more senses that I haven't listed here. Can you think of some? Think of all the things your body goes through on a given day. Think of the steps you take to take care of your body, and why you feel like you should take those steps.


Animal senses:
 
There's even more senses out there! Animals have lots of cool senses that humans don't have. Here are some examples:

Magnetoception:
Birds can sense magnetic fields. It's how they migrate.

Pheromones:
Pheromones are chemicals that animals use to communicate with each other. It's like smell, but different. Some people think humans can sense pheromones. I disagree, and the science backs me up. Next week's post is devoted to debunking the humans-sense-pheromones myth.

Bats use echolocation to find tasty bugs
Echolocation:
Dolphins and bats can tell where things are based on reflected sound. They make a sound, which bounces off an object, and they sense the bounced sound and can tell, from that, where something is.

Electric fields:
Some fish, including sharks, can sense electric fields around them. Some fish even make electric fields, which they use to communicate with each other.


Plant senses:

Plants have senses too!
Mustard plants can sense gravity.

Gravity:
Plants can sense gravity. This is how they grow upright.

Light:
Some plants can sense and turn towards light. This is important, since plants need light to live.

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