how neurons send and receive signals topic 3 neural conduction and synaptic transmission 1
TRANSCRIPT
How Neurons Send and Receive Signals
TOPIC 3Neural Conduction and Synaptic Transmission
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INTRO
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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COMMUNICATION WITHIN A NEURON
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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
The Neuron
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There are three general types of neurons
Sensory neuron A neuron that detects changes in the external or
internal environment and sends information aboutthese changes to the central nervous system.
Motor neuron A neuron located within the central nervous system
that controls the contraction of a muscle or thesecretion 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
Cells of the Nervous System
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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.
Cells of the Nervous System
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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
Neuron Basic Structure
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Internal structureMembrane
A structure consisting principally of lipid molecules that defines the outer boundaries of a cell and also constitutes many of the cell organelles.
CytoplasmThe viscous, semi-liquid substance contained in the interior of a cell.
MitochondriaAn organelle that is responsible for extractingenergy from nutrients.
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INTERNAL STRUCTURE
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Internal structure Adenosine triphosphate (ATP)
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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Internal structure Deoxyribonucleic acid (DNA)
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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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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Measuring electrical potentials (Neural Impulses) of axonsAxons have two basic electrical potentials
Resting membrane potentialAction potential
Communication Within a Neuron
MEMBRANE POTENTIAL
Measuring membrane potentialTo 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 changeDepolarizationHyperpolarizationThreshold of excitation
ElectrodeA conductive medium that can be used to applyelectrical stimulation and record electrical potentials.
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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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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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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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When do membrane potential change?
DepolarizationReduction (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 excitationThe value of the membrane potential that must be reached to produce an action potential.
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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.
ACTION POTENTIAL
Is the technical term used to describe nerve impulseConsists of a brief polarisation that spreads along an axonDifferent 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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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 Potentialshttp://faculty.washington.edu/chudler/son.html.
SCL: Passive and Active Transport across the Neural Membranehttp://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html.
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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. © 2011 Pearson Education, Inc. All rights reserved.
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