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O2

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on October 9, 2006 at 8:52:13 pm
 

O2. Organisms selectively detect and respond to changes in the internal and external environments.

Student Outcome: O2.1

Describe the importance of sensory receptors that detect changes in the external environment.

 

Everything we know about the world comes to us through our senses. Traditionally, we were thought to have just five of them—sight, hearing, touch, smell, and taste.

 

Scientists now recognize that we have several additional kinds of sensations, such as pain, pressure, temperature, joint position, muscle sense, and movement, but these are generally included under "touch." (The brain areas involved are called the "somatosensory" areas.)

 

Although we pay little attention to them, each of these senses is precious and almost irreplaceable—as we discover, to our sorrow, if we lose one. People usually fear blindness above all other disabilities. Yet deafness can be an even more severe handicap, especially in early life, when children learn language.

What we perceive through our senses is quite different from the physical characteristics of the stimuli around us. We cannot see light in the ultraviolet range, though bees can, and we cannot detect light in the infrared range, though rattlesnakes can. Our nervous system reacts only to a selected range of wavelengths, vibrations, or other properties. It is limited by our genes, as well as our previous experience and our current state of attention.

 

What draws our attention, in many cases, is change. Our senses are finely attuned to change. Stationary or unchanging objects become part of the scenery and are mostly unseen. Customary sounds become background noise, mostly unheard. The feel of a sweater against our skin is soon ignored. Our touch receptors, "so alert at first, so hungry for novelty, after a while say the electrical equivalent of 'Oh, that again,' and begin to doze, so we can get on with life," writes Diane Ackerman in A Natural History of the Senses.

 

If something in the environment changes, we need to take notice because it might mean danger—or opportunity. Suppose an insect lands on your leg. Instantly the touch receptors on the affected leg fire a message that travels through your spinal column and up to your brain. There it crosses into the opposite hemisphere (the right hemisphere of the brain controls the left side of the body, and vice versa) to alert brain cells at a particular spot on a sensory map of the body.

 

Source: http://www.hhmi.org/senses/a120.html


 

Student Outcome: O2.2

Compare nervous and hormonal communication.

 

Hormones generally act slowly and are produced in small amounts, often in bursts, influenced by factors in both the environment and within the body. Each hormone has different effects on different tissues, organs, and behaviors and, in general, affects metabolic processes, including the build-up and breakdown of carbohydrates, lipids, and proteins.

 

Hormones can affect only those cells with receptors that recognize the hormone and alter cell function. Neural communication sends rapid, digitized messages over fixed anatomical connections while hormonal communication sends slow, graded messages throughout the body that are read by cells with relevant receptors. Neural communication is more readily under voluntary control than hormonal communication. Both neurons and endocrine glands produce their transmitters or hormones and store them for later release.

 

Neurons are stimulated to produce an action potential that causes the release of transmitters into the synapse; endocrine glands are stimulated to secrete hormones into the bloodstream.

 

Source: http://www.sciencenetlinks.com/lessons_printable.cfm?DocID=65


 

Student Outcome: O2.3

Know the relationship between detection and a reflex response for one external stimulus.


 

Student Outcome: O2.4

Explain how the stimulus response model works in the coordination and control of body temperature.

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