Sunday, December 9, 2007

nervous systems- Brain development

Thrusday in AP Biology we discussed the brain which plays a major part in our nervous systems.

Our nervous system is in two parts the Central Nervous System and the Peripheral Nervous System.The CNS ( central nervous system) is made of the brain and spinal cord containing mostly interneurons, also known as associative nuerons and commonly called brain nerves. They recieve signals from the sensory nueron and send the signal to the muscles which are moved by the motor neurons. The PNS ( peripheral nervous system) is made of the sensory pathway which recieves information comming in from the senses and Motor pathways which send information to muscles. The motor pathways is divided into two group Somatic(voluntary) and Autonomic(involuntary). The somatic controlls things liek muscle movements we can control and the Autonomic controls things like our heart rate and digestive system. The autonomic nervous system can then be divided into the sypathetic and parasympathetic divisons. sympathetic controls our arousal and energey used in a "fight or fight" response which the parasympathetic calms and brings us to an easy resting and digesting state.

Cephalization is the clustering of nuerons in the brain at the front end of a bilaterally symetrical animal. The brain is at this location becuase it is where the majority of our senses are located. Organisms with radially or no symetry contain nerve nets such as the cnidarian which has no complex actions becuase it ahs not complex nervous system. orgnaisms wiht radilaly like echinoderms contain more organization but their base on nerve nets still limits complex movements. Organisms containing a brain and CNS have more complex muscle control. once a Brain is developed peripheral nerves can begin as well as an increase in internuerons. most complex brains are found in predator mollusks.

The evolution of vertebrate brains shows and increase in size and complexity of the forebrain and it shows the dominacne of the cerebrum which controls higher order thinking, which explains why humans have a larger forebrain and cerebrum than for example sharks or frogs.

The human brain consists of the forebrain, the midbrain and, the hindbrain.The hind brain are the oldest structures the provide autonomic and body functions. this includes the pons, medulla oblongata and cerebellum. the structures help in the cordination of movement such as blance the maintence of homeostatis and impulses to higher brian orders as well as many involuntary actios like breathing and heart rate. The midbrain is involved in the intergration sensory information, including visual and auditory reflexes. reticular formation controls our sleep and awakefulness which can be seen through an EEG by showing electrical activity, the more activity means the more change in electrical charge. The forebrain contains the most highly evolved structures in the human brain, it hold the cerebrum which is divided into two hemipheres left and right which control the opposite side fo the body, these hemispheres are connected between the corpus callosum. The left hempisphere coontrosl many functions involving school and thinknig, like language math and logic while the right hemisphere controls the socialness, artistic ability and creativeness, ect. the cerebrum is divided into lobes with different function the frontal which controls reasoning, temporal controllingg auditory, occiptal controllingg eyesight and parietalcontrollnig senses. The limbic system controls basic emotions. we also all ahve reflexes which are autonomic responses for survival. They are reations without going to the brain.

That concludes the nervous system and basic brain development.

tomorows sherpa will be.. seung ??

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