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University of Ottawa
Kenneth Campbell

Chapter 2 The Biology of the Mind21 Why are Psychologists Concerned with Human BehaviorEverything we do every idea every mood is a biological happening Without the body we would be nothing at all People often think of psychology and biology as two different streams but it is very important to think of them as the same thing as psychology is a biological scienceThe biology of the mind has come very far in the last few centuries In the early 1800s phrenology the study of bumps on the skull was proposed Although this idea proved incorrect it led the way for Localization of Function the idea that different areas of the brain are associated with different functionsNeural CommunicationAll brains follow the same basic principles This allows researchers to study on relatively simple organisms such as squids or sea slugs to find out how our own brain operates Though the human brain is much more complex than the brains of these simple organisms they all follow the same principles22 Neurons What are neurons and how do they transmit informationThe basic building block of the mind is the Neuron or the nerve cell Neurons allow for communication between the brain and muscles as well as thoughts and moods but how do they work How do they communicate There are various types of neurons but they all have the same basic structureSoma The cell body of a neuron This provides everything and anything that a neuron needs to function properly It provides the cell with nutrients and expels wasteDendrites The neurons bushy branching extensions that serve two main purposes 1 To increase the surface area of the neuron 2 To receive information from other neuronsAxon A taillike extension that passes messages between neurons by carrying the action potentialTerminal Buttons or Axon Terminals Nodes at the end of the axon that release neurotransmittersMyelin Sheath A fatty tissue that acts as insulation for the axon The myelin sheath helps amplify the action potential of a neuron The myelin sheath gets laid down until about age 25 Neural efficiency judgement and selfcontrol grow in that time If the myelin sheath somehow gets destroyed multiple sclerosis is the result Communication to the muscles slow down with eventual loss of muscle controlSynapse Location where the neurons meet to communicateSynaptic Cleft The gap between two neurons at the synapseEven though all neurons follow this basic structure there are three different types of neurons each with their own specialized jobSensory Neurons These neurons gather information from the outside world and relay the information to the sensory areas of the brainMotor Neurons These neurons carry out information to the muscles allowing for movementInterneurons These neurons which are only found in the central nervous system have the most complex job out of all of the different types of neurons They analyze organize and integrate information and there are billions of themNeurons transmit messages when stimulated by signals from our senses or when triggered by chemical signals from neighbouring neurons In response a neuron fires an impulse called the Action Potentiala brief electrical charge that travels down a neuron but what exactly is thisIn a neuron there are dissolved ions inside the soma and outside These are primarily Na Cl and K ions Although they are both found inside and out they are in different concentrations depending on what is happening with the neuron Depending on what is happening with the neuron these chemicals may have to pass through the Cell Membrane The cell membrane is porous and selectively permeable Meaning that water and chemicals can diffuse in and out but they cannot go as they please There are rules and regulations that they must followThis is the concentrations of chemicals when a neuron is at restInsideOutsideMore KMore NaMore Negative than outsideMore Positive than InsideThis imbalance leads to an electrical charge of 70mV causing the membrane to become polarizedEven when a neuron is at rest it is still receiving messages These messages will change the concentration of ions and change the overall charge of the membrane There are two different types of messages that neurons receive that will change the concentration of ionsInhibitory These messages tell the neurons not to fire This message will increase the amount of negative ions causing the membrane to hyperpolarize to 76mV The more negative a membrane the less likely it is to fireExcitatory These messages tell the neuron to fire Na ions will diffuse into the cell increasing the number of positive ions inside the cell This causes the membrane to depolarize to 63mV The more positive the charge the more likely it is to fireWhen will a neuron fire A neuron will fire when it reaches its threshold of excitement which is about 50 mV Large numbers of Na ions will rush into the cell and depolarizes the membrane This change in charge causes another axon channel to open and then another like a domino effect This is the action potential After a neuron fires it will go into a Refractory Period where it is not possible for a neuron to fire During this period SodiumPotassium Pumps actively pump Na out and K in to repolarize the membrane to 70mV 23 How Neurons Communicate How do nerve cells communicate with other nerve cellsNeurons interweave so intricately that it was once believed that the axon of one nerve cell fused with the dendrites of another to form an uninterrupted fabric of communication However this was proven incorrect as it was noticed that neural messages taking an unexpectedly long time to travel a neural pathway inferring that there was a brief interruption in the transmission This extremely tiny meeting point between neurons is called the Synapse If there is a gap between neurons how do they convey information to each other That is the work of Neurotransmitters chemical messengers that cross the synaptic gaps between neurons When an action potential reaches the terminal buttons of an axon found on a Pre Synaptic Neuron it causes the Synaptic Vesicles bags that contain neurotransmitters of a neuron to burst open releasing neurotransmitters into the synapse The neurotransmitters attach themselves to receptors that are found on the dendrites of a Post Synaptic Neuron and deliver their messageThe Fate of a Neurotransmitter After a neurotransmitter has delivered its message it detaches itself from the receptor and suffers one of two fatesReuptake The neurotransmitter goes back to the neuron that released it This is a form of recyclingDegradation Specialized enzymes will deactivate the neurotransmitterIf a neurotransmitter is not degraded or taken back it will deliver its message indefinitely and overstimulate or overinhibit the nervous system24 How Neurotransmitters Influence us How do neurotransmitters influence behavior and how do drugs and other chemicals affect neurotransmissionNeurotransmitters have a profound impact on behavior and feelings Specific neurotransmitters may affect specific behaviors and emotions
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