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Chapter 3

Chapter 3 Textbook Notes

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Carleton University
PSYC 1001
Elaine Waddington Lamont

Chapter 3 Textbook Notes ● Neuropsychology - The study of the brain ● Communication in the Nervous System ○ Cells in the Nervous System: ■ Neurons - Individual cells in the nervous system that receive, integrate and transmit information. ~ 100 billion in the brain. ● Soma - (Cell body) Contains the cell nucleus and much of the chemical machinery common to most cells ● Dendrites - (Branches) The parts of the neuron that are specialized to receive information ● Axon - A long, thin fibre that transmits signals away from the soma to other neurons or to other muscles or glands ● Myelin Sheath - Insulating material, derived from glial cells, that encases some axons. Speeds up transmission of signals that move along axons ● Terminal Buttons - (axon ends) Small knobs that secrete chemicals called neurotransmitters ● Synapse - a junction where information is transmitted from one neuron to another ● Summary: Information is received at the dendrites, is passed through the soma and along the axon, and is transmitted to the dendrites of the other cells at meeting points called synapses ■ Glia - Cells found throughout the nervous system that provide various types of support for neurons. Outnumber neurons 10:1. Supply nourishment to neurons, structural support, remove neuron waste products, and provide insulation around many axons. Maybe receive and send signals ○ The Neural Impulse - Complex electrochemical reaction ■ There are electrically charged ions in and outside neurons ■ The resting potential of a neuron is its stable, negative charge when the cell is inactive (~ -70 millivolts) ■ When voltage of of neuron remains constant, cell is quiet/no messages sent. When neuron stimulated, channels in cell membrane open briefly letting Na ions in. Changes neurons charge creating an action potential ■ Action Potential - Very brief shift in a neuron’s electrical charge that travels along an axon ■ After firing of action potential, channels in cell membrane letting Na in, close up ■ Absolute Refractory Period - minimum time after action potential during which another action potential can’t begin ■ Relative Refractory Period - Period in which the neuron can fire but its threshold for firing is elevated, so more intense stimulation is needed to initiate an action potential ■ All or None Law - Either the neuron fires or it doesn’t (can’t ½ fire), and its action potentials are all the same size ■ Strength of stimuli determines rate at which neurons fire action potentials. Stronger stimuli will cause a neuron to fire more rapidly. (dim light cause 5 action potential fires per second vs bright light firing 100-200) ○ The Synapse ■ Synaptic Cleft - microscopic gap between the terminal button of one neuron and the cell membrane of another neuron ● Signals have to cross this gap to permit neurons to communicate ■ Presynaptic Neuron - Neuron that sends the signal across the synapse ■ Postsynaptic Neuron - Neuron that receives the signal ■ The arrival of an action potential at an axon’s terminal button triggers the release of neurotransmitters ■ Neurotransmitters - Chemicals that transmit information from one neuron to another. Stored in synaptic vesicles in the terminal buttons ■ After their release, neurotransmitters diffuse across the synaptic cleft to the membrane of the receiving cell where they bind to various receptor sites. These sites recognize & respond to only certain neurotransmitters ○ Receiving Signals: Postsynaptic Potentials ■ Postsynaptic Potential (PSP) - change in voltage at a receptor site on a postsynaptic cell membrane. Caused by neurotransmitter bing with receptor site ● Don’t follow all or none law. They vary in size and increase or decrease the probability of a neural impulse in receiving cell in proportion to the amount of voltage change ● Excitatory PSP - a positive voltage shift that increases the likelihood that the postsynaptic neuron will fire action potentials ● Inhibitory PSP - a negative voltage shift that decreases the likelihood that the postsynaptic neuron will fire action potentials ● The direction of the voltage shift depends on which receptor sites are activated in the postsynaptic neuron ○ Integrating Signals: Neural Networks ■ A neuron may receive signals from thousands of neurons, but it may pass its messages along to thousands of neurons as well ■ Neuron must integrate signals arriving at the same time before it decides whether to fire a neural impulse or not ■ If enough excitatory PSPs occur in a neuron, the electrical current can add up, causing the cell’s voltage to reach the threshold at which an action potential will be fired ■ Many inhibitory PSPs can cancel out the excitatory PSPs. The state of the neuron is a weighted balance between excitatory and inhibitory PSPs ■ Our perceptions, thoughts, and actions depend on patterns of neural activity in elaborate neural networks. Links in these networks are fluid as new synaptic connections may be made while some old connections whither away ■ Synaptic Pruning - Nervous system gradually eliminates old or less active synapses ■ Cell Assemblies - Linked, complex networks of neurons that influence behavior ○ Neurotransmitters and Behavior ■ Neurotransmitters play a role in everything from muscle movements, moods, and mental health ■ 9 common neurotransmitters: Acetylcholine, Dopamine, Norepinephrine, Serotonin, GABA, Endorphins ■ Agonist - A chemical that mimics the action of a neurotransmitter ■ Antagonist - A chemical that opposes the action of a neurotransmitter ■ Dopamine - Used by neurons that control voluntary movements, pleasurable emotions (reward) ● Overactivity at dopamine synapses associated with schizophrenia ● Decreased levels associated with parkinson's disease ■ Serotonin - Involved in regulating sleep, wakefulness, eating, aggression ● Abnormal levels may contribute to depression and obsessive- compulsive disorder ● Organization of the Nervous System ○ Peripheral Nervous System - Made up of all those nerves that lie outside the brain and spinal cord ■ Nerves - Bundles of neuron fibers (axons) that are routed together in the peripheral nervous system ■ PNS is the portion of the nervous system the extends outside the central nervous system ■ Peripheral Nervous System can be divided into Somatic Nervous System, and Autonomic Nervous System ● Somatic Nervous System (Voluntary) - made up of nerves that connect to voluntary skeletal muscles and to sensory receptors ○ Carry information from skin and muscles to CNS, and then carry commands from CNS to muscles ○ Afferent Nerve Fibres - axons that carry information inward to the CNS from the periphery of the body ○ Efferent Nerve Fibres - axons that carry information outward from the CNS to the periphery of the body ● Autonomic Nervous System (Involuntary) - made up of nerves that connect to the heart, blood vessels, smooth muscles, and glands ○ Mediates much of the physiological arousal that occurs when people experience emotions ○ Fight or Flight Response - Organisms respond to threats by preparing physiologically for attacking or fleeing ○ Autonomic Nervous System can be divided into the sympathetic and parasympathetic divisions: ■ Sympathetic Division - Branch of autonomic nervous system that mobilizes the body’s resources for emergencies ■ Parasympathetic Division - Branch of the autonomic nervous system that generally conserves bodily resources ● Slows heart rate, reduce blood pressure, and promote digestion ○ Central Nervous System - Consists of the brain and spinal cord ■ Cerebrospinal Fluid - Nourishes brain and provides a protective cushion for it ■ Spinal Cord ● Houses axons that carry brain commands to peripheral nerves and that relay sensations from the periphery of the body to the brain ● Damage to spinal cord can result in paralysis ■ The Brain ● Research Methods for Studying Brain ○ Electrical Recordings ■ Electroencephalograph (EEG) - A device that monitors the activity of the brain over time by means of recording electrodes attached to the surface of the scalp ● Electrodes are attached at various places on the skull, the resulting EEG recordings are translated into line tracings called brain waves and these brain waves give an overview of electrical activity in the brain ○ Lesioning - Destroying a piece of the brain ■ H.M. was a patient with anterograde amnesia. Had portions of brain removed including temporal lobe, hippocampus and amygdala because he had epilepsy. Had memory of events that occurred before surgery but, could not form new memories ■ Lesioning - Destroying a piece of the brain of an animal to see precisely what happens (ex. behavior) ● Typically done by inserting an electrode into a brain structure and passing a high frequency electric current through it to burn the tissue and disable the structure ○ Electrical Stimulation of the Brain - Involves sending a weak electric current into a brain structure to stimulate/activate it ■ Determine function of each part of the brain ○ Transcranial Magnetic Stimulation - A new technique that permits scientists to temporarily enhance or depress activity in a specific area of the brain ■ Hold magnetic coil above patients head that creates magnetic field. Researcher can vary time and duration of magnetic pulses, increasing or decreasing excitability of neurons. Used to temporarily deactivate discrete areas of the brain to learn more about their functions ● “Virtual Lesions” in human subjects ■ Limitation is it cannot be used to study areas deep in the brain (penetrates only 2 cm) ○ Brain Imaging Procedures ■ CT Scan - Computer enhanced X-ray of brain structure. Multiple angles shot. Least expensive and widely used. ■ PET Scan - Radioactively tagged chemicals are introduced into the brain. They serve as markers of blood flow or metabolic activity in the brain. Provide a colour coded map indicating which areas of the brain become active. Can pinpoint the areas of the brain that handle different activities ● Used to study activity of specific neurotransmitters ■ MRI - Uses magnetic fields, radio waves, and computerized enhancement to map out brain structure. Get better images of brain structure than CT scan , producing 3D image of brain in high resolution ■ fMRI - New variation of MRI that monitors blood flow and oxygen consumption in the brain to identify areas of high activity ● The Brain and Behavior ○ 3 Major Regions of the Brain ■ Hindbrain - Includes the cerebellum and two structure in the lower part of the brainstem: the medulla and the pons ● Medulla - Attaches to the spinal cord. In charge of largely unconscious but vital functions, including circulating blood, breathing, maintaining muscle tone, and regulating reflexes such as sneezing, coughing, and salivating ● Pons - Means “bridge”, includes a bridge of fibres that connects the brainstem with the cerebellum. Contains several clusters of cell bodies involved with sleep and arousal ● Cerebellum - Large deeply folded structure located adjacent to
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