GENERAL HISTOLOGY

Detailed explanation-1: -The circuitry of the myotatic reflex. Increased firing of the annulospiral stretch receptor of the Ia muscle spindle afferents activates the muscle, here denoted as the extensor muscle. In the knee-jerk reflex this corresponds to the quadriceps muscle.

Detailed explanation-2: -Muscle spindles are proprioceptors that consist of intrafusal muscle fibers enclosed in a sheath (spindle). They run parallel to the extrafusal muscle fibers and act as receptors that provide information on muscle length and the rate of change in muscle length. The spindles are stretched when the muscle lengthens.

Detailed explanation-3: -Wiring of the inverse myotatic reflex. Sensors in the tendon, the Golgi tendon organ, are activated upon stretch of the tendon, which requires considerable force. These sensors synapse on interneurons in the spinal cord that inhibit further activity of the motor neurons innervating the muscle.

Detailed explanation-4: -As already mentioned, the sensory signal for the stretch reflex originates in muscle spindles, sensory receptors embedded within most muscles (see previous section and Chapter 9).

Detailed explanation-5: -Almost every muscle contains muscle spindles. These delicate sensory receptors inform the central nervous system (CNS) about changes in the length of individual muscles and the speed of stretching.