HOW THE BRAIN WORKS

Whould you like to know the Cerebrum Is the Control Center of the Brain

 Although vertebrate brains differ in the relative importance of different components. the human brain is a good model of how Vertebrate brains function. About 85% of the weight of the human brain is made up of the cerebrum, the tan convoluted area in . The cerebrum is a large rounded area of the brain divided by a groove into right and left halves called cerebral hemispheres. The sectioned brain in
is cut along the center groove, with the left hemisphere removed, showing the right hemisphere. The cerebrum functions in language, conscious thought, memory, personality development. vision, and a host of other activities we call "thinking and feeling."  shows general areas of the brain color-coded for easy identification (yellow for the frontal lobe, orange for the parietal lobe, light green for the occidental
lobe, and light purple for temporal lobe) and the functions they control. The cerebrum, which looks like a wrinkled mushroom. is positioned over and surrounding the rest of the brain. like a hand holding a fist. Much of the neural activity of the cerebrum occurs within a thin. gray outer layer only a few millimeters thick called the cerebral cortex (cortex is Latin for "bark of a tree"). This layer is gay because it is densely packed with neuron cell bodies. The human cerebral cortex contains the cell bodies of more than II) billion nerve cells, roughly 10% of all the neurons in the brain. The wrinkles in the surface of the cerebral cortex increase its surface area (and number of cell bodies) threefold. Underneath the cortex is a solid white region of eliminated nerve fibers that shuttle information between the cortex and the rest of the brain.

FUNDAMENTAL PROPERTIES OF LIFE

What are the fundamental properties of life?

As we discussed in chapter 1, all known organisms share certain general properties. To a large degree, these proper-ties define what we mean by life. The following fundamental properties are shared by all organisms on earth.

Cellular organization. All organisms consist of one or more cells—complex, organized assemblages of molecules enclosed within membranes.

Sensitivity. All organisms respond to stimuli—though not always to the same stimuli in the same ways.  

Growth.  All living things assimilate energy and use it to maintain order and grow, a process called metabolism. Plants, algae, and some bacteria use sunlight to create covalent carbon-carbon bonds from CO2 and H2O through photosynthesis. This transfer of the energy in covalent bonds is essential to all life on earth. 

Development. Both unicellular and multicellular organisms undergo systematic, gene-directed changes as they grow and mature.
  
Reproduction. All living things reproduce, passing on individuals from one generation to the next.  

Regulation. All organisms have regulatory mechanisms that coordinate internal processes. 

Homeostasis. All living things maintain relatively constant internal conditions, different from their environment.

HOW BIOLOGISTS DO THEIR WORK?

   What do biologists do their work?

The Consent

 Late in November, on a single night Not even near to freezing, the ginkgo trees That stand along the walk drop all their leaves In one consent, and neither to rain nor to wind But as though to time alone: the golden and green Leaves litter the lawn today, that yesterday Had spread aloft their fluttering fins of light. What signal from the stair? What senses took it in? What in those wooden motives so decided To strike their leaves, to down their leaves, Rebellion or surrender? And if this Can happen thus, what race shall be exempt? What use to learn the lessons taught by time, If a star at any time may tell us: Now.

                                                                                                                                     Howard Nemerov

What is bothering the poet Howard Nemerov is that life is influenced by forces he cannot control or even identify. It is the job of biologists to solve puzzles such as the one he poses, to identify and try to understand those things that influence life.

 Nemerov asks why ginkgo trees (figure 1.A) drop all their leaves at once. To find an answer to questions such as this, biologists and other scientists pose possible answers and then try to determine which answers are false. Tests of alternative possibilities are called experiments. To learn why the ginkgo trees drop all their leaves simultaneously, a scientist would first formulate several possible answers, called hypotheses:

called experiments. To learn why the ginkgo trees drop all their leaves simultaneously, a scientist would first formulate several possible answers, called hypotheses:

Hypothesis 1:

 Ginkgo trees possess an internal clock that times the release of leaves to match the season. On the day Nemerov describes, this dock sends a "drop" signal (perhaps a chemical) to all the leaves at the same time. 

 Hypothesis 2:

 The individual leaves of ginkgo trees are each able to sense day length, and when the days get short enough in the fall, each leaf responds independently by falling.

  Hypothesis 3:

 A strong wind arose the night before Nemerov made his observation, blowing all the leaves off the ginkgo trees. 

Next, the scientist attempts to eliminate one or more of the hypotheses by conducting an experiment. In this case, one might cover some of the leaves so that they cannot use light to sense day length. If hypothesis 2 is true, then the covered leaves should not fall when the others do, because they are not receiving the same information. Suppose, however, that despite the covering of some of the leaves, all the leaves still fall together. This result would eliminate hypothesis 2 as a possibility. Either of the other hypotheses, and many others, remain possible.

This simple experiment with ginkgoes points out the essence of scientific progress: Science does not prove that certain explanations are true; rather, it proves that others are not. Hypotheses that are inconsistent with experimental results are rejected, while hypotheses that are not proven false by an experiment are provisionally accepted. However, hypotheses may be rejected in the future when more information becomes available, if they are inconsistent with the new information. Just as you can find the correct path through a maze by trying and eliminating false paths, scientists work to find the correct explanations of natural phenomena by eliminating false possibilities.