The Human Body : The Brain (1967)

foreign [Music] this young man's heart continues to beat even while he sleeps his blood pressure remains controlled he breathes evenly regularly the digestion of last night's dinner continues Arnie can hear too at all these internal body functions are automatically controlled by a portion of his sleeping brain rhythmic electrical waves have been detected that move to and from and through the human brain when a person sleeps they might look like this these tiny currents are electrochemical in origin and their pattern changes as this same person fights toward consciousness new things are happening information in the form of sound from an alarm clock is arriving from outside his body and this information must be ignored or acted upon as Arnie becomes a little more conscious and alert there is still a different pattern to the electrochemical signals in his brain as other portions of it begin to function as he remembers he was studying for a test last night before he went to bed and that this test is today but after we know there are electrochemical signals in the brain what do we really know about it a model gives a transparent inner membrane hugs the surface of the brain itself a tough outer membrane lines the skull and a fluid between them actually buoys the brain up and helps protect it from damaging bumps against the skull bones besides being well protected the brain in an actual brain more than a hundred billion nerve cells receive stimuli decide what to do about them and transmit controlling signals to all parts of the body if we cut through the center of a human brain we can locate general areas of control the forebrain or cerebrum generally controls voluntary activities involuntary activities are mainly controlled both by the midbrain and the hindbrain Arnie knows that it's in the mid and hindbrain that the beat of the heart and the intake of air are regulated and the body's blood pressure stabilized and the mid and hind brain can control quite elaborate motor responses too without our necessarily ever being aware of them Arnie can study for his exam with the front part of his brain while the back Parts control the many motor responses involved in chewing with our model once again we can see where trunk lines of nerves connect the body with the brain always in pairs many nerves carry stimuli between the various muscles and organs and the Brain for example this nerve carries stimuli from Arnie's mouth the presence of food there causes sensory impulses to move to the hindbrain which then automatically sends motor impulses back to the various muscles involved in chewing and also to the salivary glands as the food is pushed toward the back of the mouth it triggers new stimuli to move to the hindbrain the hindbrain then automatically sends out coordinating signals to the muscles involved in swallowing each step of this involuntary process sets off new stimuli which move to the hindbrain coordinating signals then return to the appropriate muscles to move the food along and to the proper glands to secrete the necessary digestive juices breathing and blood circulation are controlled in much the same way and many other involuntary body processes are controlled from the mid and hind portions of the brain the optic nerve is involved with vision these nerves control the muscles of the eyes these nerves control facial muscles and Report taste and these coordinate balance as well as hearing such involuntary processes are coordinated in the midbrain and hindbrain automatically continually keeping our bodies alive and usually without our being aware of them certain other involuntary body responses are coordinated in another important center this lies deep within the forebrain or cerebrum it is a massive extremely specialized tissue the hypothalamus with neurons sensitive to specific stimuli in the bloodstream for example some neurons of the hypothalamus respond automatically to the stimulus of a high level of blood sugar by turning the appetite off Arnie's full and it's time to head for school and that brings us to the brain's second function for the human brain clearly does more than just automatically keep each of us alive as a human being you know consciously that you're alive you respond to the stimuli in your environment from Cars to pretty girls and these responses occur in this part of your brain the forebrain further you are usually conscious of these responses Arnie responds to the school bus horn by turning his head and running toward it for he's conscious of the fact that if he doesn't run he may miss it the decision to run for the bus is a conscious voluntary act and occurs in the forebrain but the coordination of the many muscles involved in running is unconscious and the smooth blending of all the signals required is done in the mid and hind brain when the cerebellum of the hindbrain is damaged as in this experimental animal voluntary movement is still possible the cat moves toward the food but there is little coordination of its muscles the injured cerebellum is unable to do its job the human cerebellum is dwarfed by the forebrain the cerebrum the center of conscious Association of stimuli it's this part of our brains that makes it possible for us to learn so many different things what is the geography of this cerebrum first of all its outer layer is the Gray colored bodies of billions of nerve cells this is the cerebral cortex the gray matter of our brains this cortex is convoluted and wrinkled crowding a great number of these cell bodies into a limited space if this piece of cloth were the cerebral cortex convoluting it reduces the amount of space it occupies without reducing its surface area the bodies of these nerve cells form the topmost layers of both halves or hemispheres of the cerebrum below the cortex fibers lead away from the cell bodies and because these millions of nerve fibers are covered with a fatty insulator myelin they appear as a white Mass the white matter of our brains along this section many of these nerve fibers cross over from one hemisphere of the cerebrum to the other binding the two halves into a single unit within the white matter of the cerebrum is a smaller mass of gray matter the thalamus that perceives large external stimuli like a bump on the elbow the thalamus helps coordinate our voluntary muscular responses to such stimuli beneath the thalamus is the hypothalamus which besides controlling blood sugar and other things controls emotions emotions like fear perhaps fear of not knowing the answer to these questions well this one isn't too difficult what are the major functions of the cerebral cortex much has been learned about the cerebral cortex through research with human patients under control particular functions of the body for example the neurons that make up this band control the voluntary muscles of the body the neurons of this area control the responses of voluntary muscles in the lower leg nearby are neurons that control voluntary muscles of the upper leg then comes a group of neurons that controls the muscles in the Torso a much larger group that controls the many muscles of the hand and arm and finally an extremely large group that controls muscles in the neck and head including those involved in speech running in a band alongside the motor neurons is the somasthetic area the nerves in this area perceive stimuli from outside the body for example stimuli from the skin of the foot and leg are perceived here and from the Torso here a large group of somasthetic neurons receives signals from the hand and arm and another large group from the face including the lips and tongue sound is perceived here sight is perceived here so the cortex perceives stimuli from the environment in various centers and controls voluntary responses to the same stimuli from this band but the cortex does still more here's an example we might fill this bottle with any number of liquids bitter tasting unpleasant smelling medicine colorless odorless water or an attractively colored effervescent soda pop Arnie's cortex perceives these various stimuli Associates them with memories of the same or similar stimuli then directs a particular response to them different stimuli find different associations in the cortex and different responses are produced this Association of stimuli with previous experiences stored in the cortex is basically memory and the unique thing about the human cortex is that it goes a Step Beyond just Association of actual stimuli for example these printed words can be almost as effective a stimulus to the cortex as the actual object the words stand for so far as we one Theory compares the cortex to the storage portions of an electronic computer computers like the cortex control a variety of complex tasks on the basis of information that's stored within them in this case in the form of magnetic patterns on tape perhaps some similar kind of coding takes place in the RNA nucleotide chains of the cortex when a new stimulus actually changes the structure of the chains this then forms an entirely new kind of protein molecule which is actually a bit of information never before found in the body such proteins the theory goes are stored by the billions in the associative areas of the cortex a very different Theory suggests that within the cortex the individual neurons after repeated stimulation by external stimuli form electrochemical circuits among themselves billions of circuits may be set up each storing bits of information or associations but these are just theories and much research must still be done before anyone knows just how the human brain really works during the last few minutes a number of stimuli have flashed across the screen stimuli that have been perceived by your brain somehow your brain Associates these stimuli with one another and with memories already stored within your brain and in some way not yet understood it hopefully produces new associations new ideas new understandings about the human brain [Music]