Innervaton.

Contents.

  • Sensory Innervaton.
  • Motor Innervaton.
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    • Sensory Innervaton.

    Each spindle has one primary sensory ending .. spiral or annular (ring) terminations of a Group Ia afferent nerve which encircle all 3 types of intrafusal fibre.

    Some spindles have no secondary sensory endings at all.. others have up to 5 (2 on one side 3 on the other side of the primary ending. Commonly find one primary (P) with one secondary ending adjacent (S1). Can have a further secondary ending(s) further out (S2 position) and there may be functional significance in S1 and S2 positions. Secondary endings are irregular spirals to chain fibres. S1 secondaries may have spray endings on Sb2 and Db1 fibres also.

    All 3 intrafusal fibres contribute to Group Ia input.

    Mainly chain fibres contribute to Group II input.

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    Motor Innervaton.

    2 types of fusimotor innervation from gamma motoneurones in the spinal cord... dynamic and static (originally named on the basis of their effects of Ia afferent discharge during muscle stretch).

    Dynamic gamma axons innervate Db1 fibres at one or both poles by means of indented plate endings. Together they constitute the 'dynamic intrafusal system'.

    The Sb2 is innervated by static gamma axons which generally form trail endings superficially on the fibres.

    Chain fibres have a complex motor innervation. They receive static gamma axons with a variety of terminal morphologies.

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