UNIT 4 Modules 5 8 Unit 4 Brains Bodies and Behavior Module 5 Neurons The Building Block of the Nervous System Neurons Are Specialized Cells Designed for Communication Did a neurological disorder cause a musician to compose Bolero and an Artist to paint it 66 years later After finishing the painting Adams began to experience behavioral problems including increased difficulty speaking Neuroimages of Adams s brain taken during this time show that regions in the front part of her brain which are normally associated with language processing had begun to deteriorate while regions of the brain responsible for the integration of information from the five senses were unusually well developed The deterioration of the frontal cortex is a symptom of frontotemporal dementia a disease associated with changes in artistic and musical tastes and skills as well as with an increase in repetitive behaviors As she worked on her painting her brain may have been undergoing the same changes that Ravel s had undergone 66 years earlier In fact it appears that Ravel who composed Bolero may have suffered from the same neurological disorder He was beginning to show behavioral symptoms that interfered with his ability to move and speak Scientists have concluded on the basis of an analysis of his written notes and letters that Ravel was also experiencing the effects of frontotemporal dementia Every behavior begins with biology Our behaviors as well as our thoughts and feelings are produced by the actions of our brains nerves muscles and glands Neurons are nerve cells involved with all information processing in your brain A neuron is a cell in the nervous system whose function it is to receive and transmit information Neurons consist of three major parts a cell body or soma which contains the nucleus of the cell and keeps the cell alive by nourishing it a branching treelike fiber known as the dendrite which collects information from other cells and sends the information to the soma and a long segmented fiber known as the axon which transmits information away from the cell body toward other neurons or to the muscles and glands UNIT 4 Modules 5 8 Some neurons have hundreds or even thousands of dendrites and these may be branched to allow the cell to receive information from thousands of other cells The axons are also specialized and some may be very long up to several feet in length To improve the speed of their communication and keep their electrical charges from shorting out with other neurons axons are often surrounded by a myelin sheath The myelin sheath is a layer of fatty tissue surrounding the axon of a neuron that acts as an insulator and allows faster transmission of the electrical signal Axons branch out toward their ends and at the tip of each branch is a terminal button The nervous system operates using an electrochemical process An electrical charge moves through the neuron and chemicals are used to transmit information between neurons Within the neuron when a signal is received by the dendrites it is transmitted to the soma in the form of an electrical signal and if the signal is strong enough it may then be passed to the axon and then to the terminal buttons If the signal reaches the terminal buttons they are signaled to emit chemicals known as neurotransmitters which communicate with other neurons across the spaces between the cells known as synapses Signals from other neurons are received at the dendrites and the cell body of a receiving neuron The space between a sending and receiving neuron is called a synapse When a neuron receives a signal it travels down the dendrite to the cell body where it is processed If the signal exceeds threshold it is pushed out of the cell body and down the axon toward the synapse between this neuron and the next one The signal travels to the end of the axon called the terminal button where the signal travels across the synapse to the next button Neurons Communicate Using Electrochemical Processes The electrical signal moves through the neuron as a result of changes in the electrical charge of the axon Normally the axon remains in the resting potential a state in which the interior of the neuron contains a greater number of negatively charged ions than does the area outside the cell When the segment of the axon that is closest to the cell body is stimulated by an electrical signal from the dendrites and if this electrical signal is strong enough that it passes a certain level or threshold the cell membrane in this first segment opens its gates allowing positively charged sodium ions that were previously kept out to enter This change in electrical charge that occurs in a neuron when a nerve impulse is transmitted is known as the action potential Once the action potential occurs the number of positive ions exceeds the number of negative ions in this segment and the segment temporarily becomes positively charged UNIT 4 Modules 5 8 The axon is segmented by a series of breaks between the sausage like segments of the myelin sheath Each of these gaps is a node of Ranvier The electrical charge moves down the axon from segment to segment in a set of small jumps moving from node to node When the action potential occurs in the first segment of the axon it quickly creates a similar change in the next segment which then stimulates the next segment and so forth as the positive electrical impulse continues all the way down to the end of the axon As each new segment becomes positive the membrane in the prior segment closes up again and the segment returns to its negative resting potential In this way the action potential is transmitted along the axon toward the terminal buttons The entire response along the length of the axon can happen up to 1 000 second An important part of the action potential is that it operates in an all or nothing manner The neuron either fires completely the action potential moves all the way down the axon or it does not fire at all Neurons can provide more energy to the neurons down the line by firing faster but not by firing more strongly The neuron is prevented from repeated firing by the presence of a refractory period a brief time after the firing of the axon in which the axon cannot fire again because the neuron has not yet returned to its resting potential The primary role of the myelin sheath is that it coats the axon and allows the messages transmitted from the axon to move quicker Neurotransmitters The Body s Chemical Messengers Not only do