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Chapter 3

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Dax Urbszat

Psych Chapter 3 Outline • Communication in the Nervous System o Nervous Tissue: The Basic Hardware o The Neural Impulse: Using Energy to Send Information o The Synapse: Where Neurons Meet o Neurotransmitters and Behaviours • Organization of the Nervous System o The Peripheral Nervous Systems o The Central Nervous System • Looking Inside the Brain: Research Methods o Electrical Recordings o Lesioning o Electrical Stimulation of the Brain o Transcranial Magnetic Stimulation o Brain-Imaging Procedures • The Brain and Behaviour o The Hindbrain o The Midbrain o The Forebrain o The Plasticity of the Brain • Right Brain/Left Brian: Cerebral Laterality o Bisecting the Brain: Split-Brain Research o Hemispheric Specialization in the Intact Brain www.notesolution.com • The Endocrine System • Heredity and Behaviour: Is it All In The Genes? o Basic Principles of Genetics o Investigating Hereditary Influence o The Interplay of Heredity and Environment • The Evolutionary Bases of Behaviour: o Darwin’s Insights o Subsequent Refinements to Evolutionary Theory o Behaviours as Adaptive Traits Communication in the Nervous System Nervous Tissue: The Basic Hardware • Cells in nervous system fall into two major categories: o Glia o Neurons • Neurons: The individual cells in the nervous system that receive, integrate, and transmit information. o Neurons permit communication within the nervous system. o Soma: Soma, or cell body, contains the cell nucleus and much of the chemical machinery common to most cells. Soma is Greek for body. o Dendrites: Part of the neuron that are specialized to receive information. Greek word for tree. Each branch is a dendrite. www.notesolution.com o Axon: Long, thin fibre that transmits signals away from the soma to the other neurons or to muscles or glands. o Myelin Sheath: Insulating material derived from glia cells. They encase some axons. o Terminal Buttons: Small knobs that secrete chemicals called neurotransmitters. o Synapse: Junction where information is transmitted from one neuron to another. Greek for junction. o Information is received at the dendrites, passed through the soma along the axon, and transmitted to the dendrites of other cells at meeting points called synapses. • Glia: Cells found throughout the nervous system that provide various types of support for neurons. Greek for glue. o Smaller than the neurons, but outnumber them 10 to 1. o Supply nourishment to neurons, help remove thee neurons’ waste products, provide insulation around many axons (Myelin sheath). The Neural Impulse: Using Energy to Send Information • The Neuron at Rest: A Tiny Battery www.notesolution.com o Inside and outside the neuron, there are fluids containing electrically ions. o Positively charged sodium and potassium flow at a slower rate than negatively charged chloride, thus there is a slightly larger rate of negative charge ions (meaning the cell is at rest) o The resting potential of a neuron is its stable, negative charge when the cell is inactive. • The Action Potential o When the voltage is constant, the cell is quiet and there are no messages being sent. o When the neuron is stimulated, the channels in its cell membrane open, allowing positively charged sodium ions to rush in. Thus, the neuron either becomes less negative, or even positive creating action potential. o Action Potential is a very brief shift in a neuron’s electrical charge that travels along an axon. o When charged with action potential, the neuron fires the action potential down the axon and the cell membrane closes off. o The absolute refractory period is the minimum length of time after an action potential during which another action potential cannot begin. • The All-or-None Law o The firing of action potential is a gun, you fire everything and there is no half-way firing. o A neuron fires or it doesn’t, all action potential is the same size. o However, neurons can convey information about the strength of a stimulus by varying the rate at which they fire the action potential (stronger = faster volley of neural impulses) www.notesolution.com The Synapse: Where Neurons • Sending Chemicals: Chemicals as Couriers o Two neurons don’t actually touch. Separated by the synaptic cleft. o Synaptic Cleft: A microscopic gap between the terminal button of one neuron and the cell membrane of another neuron. o The neuron that sends the signal is the presynaptic neuron, and the one that receives is called the postsynaptic neuron. o The arrival of an action potential at an axon’s terminal buttons triggers the release of neurotransmitters – chemicals that transmit information from one neuron to another o In the terminal buttons, the chemicals are stored in small sacs, called synaptic vesicles. o These neurotransmitters spill into the synaptic cleft, and may bind with special molecules in the postsynaptic cell membrane at various receptor sites. These sites are specifically “tuned” to recognize and respond to some neurotransmitters and not others. • Receiving Signals: Postsynaptic Potentials o When a neurotransmitter and a receptor molecule combine, it causes a postsynaptic potential (PSP) o Postsynaptic Potential: Voltage change at a receptor site on a postsynaptic cell membrane. o Postsynaptic potential doesn’t follow the all-or-none law. www.notesolution.com o Instead they are graded (vary in size, increase/decrease probability of a neural impulse in the receiving cell in proportion to the amount of voltage changes. o Two types of messages can be sent from cell to cell: Excitatory Inhibitory o An excitatory PSP is a positive voltage shift that increases the likelihood that the postsynaptic neuron will fire an action potential. An inhibitory PSP is a negative voltage shift that decreases the likelihood that the postsynaptic neuron will fire action potentials. o Reuptake: Process in which neurotransmitters are sponged up from the synaptic cleft by the clef by the presynaptic membrane allowing the synapses to recycle their materials. • Integrating Signals: Neural Networks o Neurons fire together/sequentially in the millions to perform certain functions. o The nervous system eliminates old synapses which are no longer being used and tends to create an abundance of new synapses. This is called synaptic pruning. o Donald Hebb called these neuron networks cell assemblies. o Hebb also created the Hebbian Learning Rule. “When an axon of cell A is near enough to excite a cell B and repeatedly or persistently take part in firing it, some growth process or metabolic change take place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased”. Thus one neuron stimulating another neuron repeatedly produces learning. Neurotransmitters and Behaviour • Agonist: Chemical that mimics the actions of a neurotransmitter. • Antagonist: Chemical that opposes the action of a neurotransmitter. Neurotransmitt Functions and Characteristics ers www.notesolution.com Acetylcholine Activates motor neurons controlling skeletal muscles (ACh) Contributes to the regulation of attention, arousal, and memory Some ACh receptors stimulated by Nicotine Only transmitter between motor neurons and voluntary muscles Dopamine (DA) Contributes to control of voluntary movement, pleasurable emotions Decreased levels associated with Parkinson’s Disease Overactivity at DA synapses associated with schizophrenia Cocaine and amphetamines elevate activity at DA synapses Norepinephrine Contributes to modulation of mood and arousal (NE) Cocaine and amphetamines elevate activity at NE synapses Serotonin Involved in regulation of sleep and wakefulness, eating, aggression Abnormal levels may contribute to depression and obsessive compulsive disorder Prozac and similar antidepressant drugs affect serotonin circuits. GABA Serves as widel
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