Spindle Structure

• Structure of Muscle Spindle:

  • 2 to 4 millimetres long
  • ends of muscle spindles attach to outer sheaths of striated/extrafusal muscles fibres (muscle spindles are attached to muscle fibres), so when muscle belly lengthens, spindle lengthens etc
  • an average muscle spindle has 4 to 6 intrafusal fibres
• Structure of Muscle Spindle:

  • types of fibres within a spindle varies from spindle to spindle
  • all human skeletal muscle contain muscle spindles, but number and structure of spindles vary muscle to muscle in relation to muscle function - e.g. in muscle groups with fine and controlled dexterous functions, theres usually a higher number of muscle spindles and that are larger with more intrafusal fibres as the muscle group will need more afferent information on the movement, e.g. ocular muscles have a higher density of muscle spindles to control eye movements
• Muscle Spindle:

  • red line represents the capsule of the muscle spindle
  • outside the red lines (pink blocks) represent the extrafusal fibres of the muscle belly
  • inside the red lines is the inside of the muscle spindle