335-11_lec3 - BIO 335 lecture 3 Axon types in vertebrate...

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BIO 335 lecture 3 • Axon types in vertebrate nerves • This week’s lab: classifying axons by. .. - conduction velocity - stimulus properties • The conductances and currents that produce the action potential
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- Single nerve bundle - Thousands of axons - No giant axons: largest diameters <20 μ m Frog Sciatic Nerve R1 R2 S2 S1
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Stimulus intensity max Compound Action Potential Graded potential : Amplitude changes with stimulus intensity
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Stimulus intensity max Clicker question Because increasing stimulus strength… A. Increases the number of axons firing action potentials. B. Increases the amplitudes of individual action potentials. C. Increases the conduction velocity of axons firing action potentials. Q. Why is the CAP graded ?
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* * * * E fferent – conduct AP’s from CNS A fferent – conduct AP’s into CNS Peripheral Nerve Dorsal root ganglion Ventral root Dorsal root
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A fferent - conduct AP’s into CNS mechanoreceptors in skin – touch, pressure - fast and slow-adapting other skin receptors: pain, temperature stretch receptors in tendons and muscle spindles E fferent - conduct AP’s from CNS motor neurons – to force-producing muscle – to muscle spindles (modulate stretch-sensitivity) autonomic neurons Functional classification of axons
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Neurons with different functions have characteristic conduction velocities – multiphasic CAP
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A α A β A δ
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Fiber Type Axon Diameter (μm) Conduction velocity (m/s) Afferent - sensory Efferent - motor A α 18 42 muscle & tendon proprioceptors skeletal muscle A β 14 25 touch, pressure, vibration A δ 11 17
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335-11_lec3 - BIO 335 lecture 3 Axon types in vertebrate...

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