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TheBlackCat · #4 (**permalink**) 17-February-2006, 04:17 AM

I can believe that, I almost lost my life to falling palm fronds more than a few times.

Do you know that pretty much every lifeform on Earth has basically the same genetic code? One of the few exceptions: mitochondria. Most mitochondrial genes are found in the nucleus, apparently being transferred there while they were still symbiotic cells. However, during the transfer a mutation changed the genetic code and the host nucleus could no longer read the modified code. This prevented further gene transfer and is why mitochondria only have a partial genome.

The photoreceptors in the vertebrate retina are actually in the back of the retina. Light has to pass through blood vessels, the axons carrying the information from all the receptors to the brain, 4 layers of neurons, then the cell bodies of the receptors before actually reaching the light-sensetive parts. The photoreceptors are actually active in the dark, they become inactivated by light. Invertebrate retinas are the opposite of this in both regards. The vertebrate retina is transparent, but it distorts the image significantly. The area of highest resolution, the fovea (the only area you can actually see clearly out of) has all the cell bodies pushed out to the side to reduce distortion.

The visual system in your brain cannot process areas of equal contrast. The retina does some simple image-processing that cancels out any area of uniform color and light intensity. The optic nerve only encodes for areas where light intensity or color changes (i.e. lines).

Every sense in your body, with the possible exception of taste, forms one or more maps in the human brain. A 2D map of the body for touch, a 2D map of the visual scene for vision, a map of frequency space for the ears, and a map of chemical features for smell. Most of these maps are preserved through multiple levels of processing.

Taste is the only sense where the actual receptors are not neurons. They are epithelial cells.

The normal double helix structure of DNA (B DNA) is not the only structure that DNA can take. A, B', and hairpin structures are also found in specific situations and Z DNA is possible but has not actually been proven to exist under physiological conditions.

The human brain is the largest consumer of energy in the human body. The human retina alone consumes about 5% of the body's oxygen intake. This is worse during sleep than when awake. It is so metabolically active it actually has its own cooling system to keep it from cooking itself alive.

Headphones are the leading cause of deafness among teenagers. If you go to a concert and your ears are ringing the next day, you are actually listening to your own sound receptors dieing.

Humans have an intensity sensetivity range of about 12 orders of magnitude. for vision The human eye is so sensetive that when properly dark-adapted humans can literally see a single photon of the right frequency as a flash of light if it hits a rod. Rods are so sensetive that if you sit in a perfectly dark room long enough you will actually see spontaneous flashes of light as single rhodopsin molecules (the actual photo-sensetive pigment) spontaneously activate with no light input. The rate of flashing actually acts as a rather effective thermometer due to its temperature-sensetive nature.

Humans have no rods (low-light cells) at the center of the visual scene. If you are in the dark, you actually see better if you don't look directly at something. If it is too dark the center of your visual scene is actually blind but the rest of your eye can see pretty well.

Your visual acuity goes down as your iris gets bigger because your cornea's spherical aberration increases. This is why you can see better at night if squint.

The human brain has about 10^12 neurons and 10^13 glial, or support cells. Each neuron, on average, makes about 1000 synapses with other neurons. That is about 1000000000000000 connections.

The human ear is not a passive sensory organ. The receptor hair cells that humans have sense sounds, but their frequency specificity is too low to be useful. However, these cells are outnumber about 4-1 by a set of active hair cells. These specifically change their shape in response to input from the central nervous sytem in order to improve the frequency tuning of the passive hair cells. Some people have disorders involving these hair cells that cause them to move even without sound input. These movement actually move the fluid in the cochlea, vibrating the eardrum and ultimately producing sounds that can be picked up by a microphone in the ear canal. Some people have it seo bad you can actually hear the sound just by putting your ear next to theirs.

50 years ago people though the cerebellum would be the first part of the brain to be figured out completely. It has only 5 types of cells and its structure is very uniform throughout the system. Great strides have been made in the understanding of the brain, but today we still do not exactly know what the cerebellum does, not to mention how it works.