1. How Neurons Send and Receive Signals
TOPIC 3
Neural Conduction and
Synaptic Transmission
How Neurons Send and Receive Signals
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Topics
Communication within a neuron
Video: Passive and Active Transport across the Neural Membrane
Postsynaptic Potentials
Generation of Action Potentials
Conduction of Action Potentials
Action Potentials are Nondecremental and Slow
Communication between neurons
Changing Views on Dendritic Function
Synaptic Contacts and Transmission
Neurotransmitters and Receptors
Pharmacology of Synaptic Transmission
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3. Communication within a neuron
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4. The Neuron
Afferent neurons relay messages from the sense organs and receptors—eyes, ears, nose, mouth, and skin—to the brain or spinal cord
Efferent neurons convey signals from the central nervous system to the glands and the muscles, enabling the body to move
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5. Cells of the Nervous System
There are three general types of neurons
Sensory neuron
A neuron that detects changes in the external or
internal environment and sends information about
these changes to the central nervous system.
Motor neuron
A neuron located within the central nervous system
that controls the contraction of a muscle or the
secretion of a gland.
Interneuron
A neuron located entirely within the central nervous system.
Interneurons carry information between neurons in the brain and between neurons in the spinal cord
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6. Cells of the Nervous System
Three classifications of neurons
Multipolar neurons
A neuron with one axon and many dendrites.
Bipolar neurons
A neuron with one axon and one dendrite attached to its soma.
Unipolar neurons
A neuron with one axon attached to its soma; the axon divides, with one branch receiving sensory information and the other sending the information into the central nervous system.
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7. Neuron Basic Structure Neurotransmitter
Chemical messengers that relay neural messages across the synapse
A chemical that is released into the synaptic cleft from a terminal button (axon) of a sending neuron, crosses a synapse, and binds to appropriate receptor sites on the dendrites or cell body of a receiving neuron, influencing the cell either to fire or not to fire;
Has an excitatory or inhibitory effect on another neuron.
Receptors
Protein molecules on the dendrite or cell body of a neuron that will interact only with specific neurotransmitters
Action of neurotransmitters
Excitatory
Influencing the neurons to fire
Inhibitory
Influencing neurons not to fire
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8. Internal structure Membrane Cytoplasm Mitochondria
A structure consisting principally of lipid molecules that defines the outer boundaries of a cell and also constitutes many of the cell organelles.
Cytoplasm
The viscous, semi-liquid substance contained in the interior of a cell.
Mitochondria
An organelle that is responsible for extracting
energy from nutrients.
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9. Internal Structure
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10. Internal structure Adenosine triphosphate (ATP) Nucleus Chromosome
A molecule of prime importance to cellular energy metabolism; its breakdown liberates energy.
Nucleus
A structure in the central region of a cell, containing the nucleolus and chromosomes.
Chromosome
A strand of DNA, with associated proteins, found in the nucleus; carries genetic information.
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11. Internal structure Deoxyribonucleic acid (DNA) Gene Microtubule
A long complex macromolecule consisting of two interconnected helical strands; along with associated proteins, strands of DNA constitute the chromosomes.
Gene
The functional unit of the chromosome, which directs synthesis of one or more proteins.
Microtubule
A long strand of bundles of protein filaments arranged around a hollow core; part of the cytoskeleton and involved in transporting substances from place to place within the cell.
Cytoskeleton
Formed of microtubules and other protein fibers,
linked to each other and forming a cohesive mass that gives a cell its shape.
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12. The Neural Impulse
Neural impulse – Brief electric surge that carries the neuron’s message
Ions – Charged particles that are moved across the cell membrane
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13. Communication Within a Neuron
Measuring electrical potentials (Neural Impulses) of axons
Axons have two basic electrical potentials
Resting membrane potential
Action potential
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Membrane potential
Measuring membrane potential
To learn how info sent from dendrites and soma of a neuron to its terminals, researchers study a neuron’s membrane potential
The membrane potential can change
Depolarization
Hyperpolarization
Threshold of excitation
Electrode
A conductive medium that can be used to apply
electrical stimulation and record electrical potentials.
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15. Measuring electrical potentials of axons (see figure in next slide)
Microelectrode
A very fine electrode, generally used to record activity
of individual neurons. Ie. Intracellular vs extracellular
Membrane potential
The electrical charge across a cell membrane; refers to the difference in electrical potential inside and outside the cell.
To measure a membrane potential
Oscilloscope
A laboratory instrument that is capable of displaying a graph of voltage as a function of time on the face of a cathode ray tube.
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17. Measuring electrical potentials of axons
Resting membrane potential
When intracellular and extracellular electrodes are outside of a neuron, the difference between the electrical potentials at their tips is zero
When the intracellular electrode penetrates the neuron, the potential jumps to approximately -70 mV in the giant squid axon. This is the resting potential of a neuron.
Positively and negatively charged ions are distributed unequally on the tow sides of the neural membrane.
Thus, when membrane is polarized, it carries a charge
The membrane potential of a neuron at rest, about 270 millivolts
The resting membrane potential of a neuron when it is not being altered by excitatory or inhibitory postsynaptic potentials.
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18. Measuring electrical potentials of axons
Factors contributing to uneven distribution
Homogenizing (ie Random motion & concentration of gradients)
Electrostatic pressure like repels like, opposites attract
Membrane is selectively permeable
Sodium-potassium pumps
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19. When do membrane potential change?
Depolarization
Reduction (toward zero) of the membrane potential
of a cell from its normal resting potential.
Hyperpolarization
An increase in the membrane potential of a cell,
relative to the normal resting potential.
Threshold of excitation
The value of the membrane potential that must be reached to produce an action potential.
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20. Measuring electrical potentials of axons
Action potential
The brief electrical impulse that provides the basis for conduction of information along an axon.
The sudden reversal of the resting potential, which initiates the firing of a neuron.
**Threshold of excitation
The value of the membrane potential that must be reached to produce an action potential.
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Action potential
Is the technical term used to describe nerve impulse
Consists of a brief polarisation that spreads along an axon
Different from receptor potential (synaptic potential) in several aspects
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Action potential
Do not vary in amplitude or intensity
‘All or nothing’ events – If the intensity of a stimulus fall below the neuron’s excitation threshold, nothing will happen.
Intensity of stimulus greater than threshold of excitation – does not matter whether it does so by small or large amount.
An action potential will be triggered!
Amplitude and frequency – same for any given cell.
THUS: to transmit info, - neuron vary the frequency of the action potentials – the number of AP that it transmit per second.
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23. Difference between a strong and weak stimulus
A weak stimulus may cause few neurons to fire and at a slow rate
A strong stimulus may cause thousands of neurons to fire at the same time and at hundreds of times per second
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Listening to Action Potentials
SCL: Passive and Active Transport across the Neural Membrane
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FIGURE 4.2 The passive and active factors that influence the distribution of Na+, K+, and Cl- ions across the neural membrane.
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BREAK 1
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