• If you are citizen of an European Union member nation, you may not use this service unless you are at least 16 years old.

  • You already know Dokkio is an AI-powered assistant to organize & manage your digital files & messages. Very soon, Dokkio will support Outlook as well as One Drive. Check it out today!



Page history last edited by gerryc 14 years, 10 months ago

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


This is short overview of how information travels from nerves to brain to muscle.

YouTube plugin error


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


If you have time, check out this video on how nerves and the brain works and this one on how hormones work

YouTube plugin error YouTube plugin error


Here is a video showing how insulin works and the difference between Type I and Type II diabetes.

YouTube plugin error


Go here to see how hormones work - particularly the anti-diuretic hormone ADH uses control water levels in the body.


Student Outcome: O2.3

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


Sneezing, coughing, and blinking are simple reflexes. But they aren't as simple as they seem.


It's true that reflexes have a simple definition. They're involuntary actions or movements that occur in response to a stimulus. And you may not think that much goes on when you yawn, for example. But you might be surprised.


Each reflex action can involve countless complex communications and intricate coordination among nerve cells called neurons. These neurons are found in the central nervous system, which includes your brain and spinal cord, and the peripheral nervous system, which includes all the nerves that reach your body's extremities. Not all neurons are alike, however.


  • Sensory (or afferent) neurons carry messages to the brain and spinal cord.
  • Motor (or efferent) neurons carry messages away from the brain and spinal cord. They tell muscles to contract or relax and spur glands into action.
  • Interneurons send messages between nerve cells within the brain, spinal cord, and the periphery. These busy characters make up over 99 percent of the more than 10 billion neurons in our nervous system.


But why is the brain involved in reflex actions at all? As part of the nervous system, the brain has specialized functions, only some of which control thought or voluntary movement. The brain stem, for example, manages involuntary reflexes such as breathing and keeping our balance. We don't consciously decide to do these things. But a part of our brain is still involved.


Reflexes serve as primitive responses that protect our bodies from danger and help us adjust to our surroundings. We cough, for example, when an irritant enters our windpipe and we need to expel it through our mouth. We sneeze when we need to clear our nasal air passages of irritants and allergens. We blink when danger threatens the sensitive tissues of the eye and when we need to moisten and clean the cornea. (This reflex occurs 900 times an hour!) We yawn when nerves in the brain stem find there's too much carbon dioxide in the blood. A yawn makes the muscles in our mouth and throat contract and forces our mouth wide open, allowing us to expel carbon dioxide and take in a large amount of oxygen-rich air.


Source: http://www.tpt.org/newtons/13/rlxes.html


Pretty dry video on the reflex arc.

YouTube plugin error



Student Outcome: O2.4

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


Let us assume that you have stepped outside where it is much colder than inside. There is an initial change in your internal body temperature. The normal body temperature is called the set point and your body temperature drops below the set point. The immediate increases of heat loss from your warm skin upsets the cynamic balance between heat gain and heat loss. Your internal body temperature falls.


The first homeostatic response is that blood vessels to the skin narrow, reducing the amount of warm blood flowing through the skin and therefore reducing heat loss.


Given that there is no way to stay warm, e.g., putting on a jacket, it is necessary for the body to produce more heat to stay warm. Involutary, shivering, or voluntary, exercise, muscle activith may be used to generate heat.


The chemical reactions of muscle activy generates heat which raises the body temperature. The internal body temperature rises towards the set point.


As long as the internal temperature remains below the set point, there will be a tendency to remain active and generate more heat. If excess exercise is done, the temperature will rise above the set point and sweating may occur. As the temperature increases above the set point the desire for exercise will decrease.


Source: http://fog.ccsf.cc.ca.us/~mmalacho/physio/oll/Lesson1/hstasis.html


Good explanatory page with simple animation here.


Here is another good explantion - hope it is still there!


A fairly turgid video from the BBC - hence the accents.  It even has a site for you to go to and some work to do!


Comments (0)

You don't have permission to comment on this page.