LIFESCI 3K03 Lecture Notes - Lecture 6: Quadriceps Femoris Muscle, Motor Neuron, Intrafusal Muscle Fiber

• School: McMaster University
• Department: Life Sciences
• Course: LIFESCI 3K03
• Professor: Mike Vesia

Document Summary

Intrafusal muscle fibres are swollen in the middle, so they are more swollen when the muscles are short (contracted), and less swollen when the muscle is long. The circumference of the intrafusal muscle fibre is related to the length of the muscle. Within the spindles there are two types of intrafusal fibres the nuclear bag and the nuclear chain. Large, primary afferents, (#1a), originate from both bag and chain fibres. Smaller, secondary afferents (#2), originate only from chain fibres. The numbers 1a,1b, 2 refer to the size of the fibre. 1a is the largest and therefore the most rapidly conducting, 1b, from the golgi tendon is slower, and 2 is the slowest. Sensory neurons wrapped around the intrafusal fibres include type 1a afferents and type 2 afferents. Type 1a afferents = signal the length of the muscle (static, stationary position) as well as changes in the length during movement (dynamic, during movement) (nuclear bag)