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Chapter 4

chapter4

12 Pages
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Department
Psychology
Course Code
PSYC62H3
Professor
Suzanne Erb

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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 isall or none
-Neurotransmission is primarily a chemical process and may begraded”
-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.
-Pre—and 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
-The cell membranes is a barrier between the extracellular fluid and the inside of the cell
that contains small pores or channels.
-K+ and Cl- diffuse easily through them, Na+ diffuses through with difficulty, and the
large proteins ion essentially do not diffuse through them at all. = selective permeability.
-In addition to concentration gradient and electrostatic forces, the concentration of the
different ions under resting conditions is determined by proteins embedded in neuronal
membranes that utilize energy-dependent processes to transport ions across the
membrane. E.g. Co-transporters and sodium-potassium pumps are some of the protein
channels.
-The concentration gradient would normally result in equal concentrations of the various
ions on both sides of the neuron membrane, because of the negatively charged protein
ions retained inside, the Cl- ions are repelled though the membrane, so the net effect is a
greater concentration of Cl- ions outside the neuron.
-Conversely, the K+ and Na+ ions are pulled inside because the negatively charged
protein ions, there is a greater concentration of K+ inside and a greater concentration of
Na+ outside because of the sodium-potassium pumps.
-The sodium-potassium pump is more effective in transporting Na+ than K+; for every
three Na+ ions pumped out, only two K+ ions are pumped in, which allows the inside of
the cell membrane to be negative relative to the outside at the resting potential.
-A shift of 10mV towards 0 is the threshold potential; it triggers a rapid sequence of
events lasting about 4millisec, which is referred to as an action potential.
-During this sequence, the electrical potential is reversed, going from -70mV to ~
+30mV, and then returns to the original potential, with an actual overshoot of the -70mV
level before the final resting potential re-achieved.
AP
-The first step requires that the membrane potential shift from its resting potential to its
threshold potential.
-This step involves the opening of ion channels by way of chemical interactions with
receptors embedded in the membranes of the neurons dendrites and soma (Na+ channels
open).
www.notesolution.com

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Description
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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