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PSYC62H3 (313)
Chapter 4


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Suzanne Erb

Chapter 4 Conduction and Neurotransmission -Drugs that affect these psychological variables do so because they alter these biochemical and electrochemical processes. -Neurons are also mixed in with numerous other non-neuronal cellular elements called glial cell (ie, astrocytes, which ensheath synaptic connections between neurons and are required for synapse formation and maintenance, and oligodendrocytes, which wrap layers of myelin membranes around axons to insulate them from impulse conduction, which serve important metabolic and supportive functions. -Human nervous system contains ~ 85 billion neurons -The CNS utilizes from 20% (adult) to 60% infants of the resting energy consumption in humans -Two basic processes are involved in the communication network: conduction, which refers to changes within a neuron that allow the information to be transmitted from one part of the neuron to another part; and neurotransmission, which refers to changes that take place within one neuron because of the release of biologically active chemicals from adjacent neurons. -Conduction is primarily an electrochemical process that is all or none -Neurotransmission is primarily a chemical process and may be graded -Psychotropic drugs are simply chemicals that alter the normal processes of conduction, neurotransmission, or both. The Neurons -Each neuron has numerous excitatory (E) and inhibitory (I) inputs or synapses, which regulate the frequency of action potentials produced by them. -The main body of the neuron is called its some, part of which serve integrative function in the communication of information. -Normally, there are many dendrites extending from the soma, which serves as receivers of information from other neurons, and one axon, which serves as the pathway over which signals pass from the soma to other neurons. -The enlarged region where the axon emerges from the soma is called the axon hillock. -A short distance from their origin, many axons has a coating called the myelin sheath, which are analogues to the insulation on wire. -Gaps in the myelin sheath, where the axon comes into direct contact with the extra cellular fluid, are called the nodes of Ranvier. -The presence of these gaps allows for an increase in the rate of conduction down the axon. -Near its end, the axon branches, and at the tip of each branch is an enlargement called a terminal button = axon terminal. www.notesolution.com-Chemicals found within the axon terminal can be released into an exceedingly small gap between the neurons, called a synaptic cleft, allowing the neuron to affect the excitability of adjacent neurons. -The region it self is called a synapse, and it consists of presynaptic membrane of the axon terminal, the cleft, and the postsynaptic membrane of the ``target`` neurons. -Preand post-synaptic membranes are ``glued`` together by way of interlocking adhesion molecules that allow the tow membranes to work together as a functional unit that resists separation by physical methods Conduction -In the intra- and extracellular fluids are different concentrations of negatively and positively charged ions. -The four primary ions important for conduction are sodium Ca+, potassium K+, chloride Cl-, and large negatively charged protein molecules. -A fifth ion, a calcium ion with tow positive charges Ca++, it plays a vital role in a wide variety of actions within the nervous system. -There are two primary forces that influence the concentration of these ions across neuronal membranes. - A concentration gradient force refers to the fact that when there are different concentrations of molecules on the two sides of the membrane, they travel from high- concentration region to the low-concentration region. -Electrostatic pressure refers to the force exerted by the attraction of oppositely charged ions or by the repulsion of similarly charged ions. -Neurons can be in one of two states, one state is called the resting potential, although the term resting is not really appropriate because the cell is actually expending ~ one quarter of its totally energy maintain this state. -In this state, there is much higher concentration of negatively charged ions on the inside of the cell membrane than on the outside of the membrane. - A potassium ion being pulled out of the cell because of concentration gradient pressure and pulled in because of electrostatic pressure; a Chloride ion is being pulled into the cell because of concentration gradient and pushed out because of electrostatic pressure; the sodium ion being pulled into the cell by both electrostatic and gradient pressure. -The large negatively charged protein ions are clustered close to the inside membrane, and the positively charged sodium ions are clustered close to the outside membrane. -The close proximity of these two ions on the two sides of the cell membrane and their attraction for each other produces a considerable amount of pressure (voltage potential) at the membrane. -In the resting potential state, the cell is referred to as being polarized. -In the other state, in which there is rapid exchange of ions across the neuron membrane, the cell is referred to as being depolarized, a process resulting in what will be called an action potential. -At rest, the neuron has an electrical potential of ~70mV www.notesolution.com
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