1. 8/4/2015 The Muscular System  The Striated Muscle (those responsible for voluntary movements) l Anatomy - Two types of fibers u Extrafusal Fiber: these fibers do the work of the muscle. u Intrafusal Fiber or Muscle Spindle: controls muscle tone and provides important sensory information. l Contraction u Controlled by the nervous system u Muscles only shorten (i.e., only go one direction) u Organized in opposition pairs.

2. 8/4/2015 The Stretch Reflex  Neural Input into the Muscle l Extrafusal fibers are input by alpha motor neurons u These neurons are large and fast. l Intrafusal Fibers are input by gamma motor neurons u These neurons are relatively small and slow. u They are involved in the control of muscle tone. 

3. 8/4/2015 Proprioception: Sensing Muscle Condition and Limb Position  Sensory Endings in Muscles l Anulospiral : wraps around muscle spindle, senses dynamic changes in muscle length. l Flower spray : looks like little flowers, sense static changes in muscle length, helps determine position.

4. 8/4/2015  motor neuron sensory neuron interneuron Innervation of a Skeletal Muscle The arm is commanded to a particular position.

5. 8/4/2015  motor neuron sensory neuron interneuron A weight is applied to the arm.

6. 8/4/2015  motor neuron sensory neuron interneuron A weight is applied to the arm.

7. 8/4/2015  motor neuron sensory neuron interneuron This weight pushes down the arm which stretches the muscle.

8. 8/4/2015  motor neuron sensory neuron interneuron This stretch is detected by the sensory neurons in the arm and transferred to the interneron in the spinal chord.

9. 8/4/2015  motor neuron sensory neuron interneuron A command to further contract the muscle is sent out the alpha motor neuron.

10. 8/4/2015  motor neuron sensory neuron interneuron The arm is returned to its commanded position.

11. 8/4/2015 The Stretch Reflex and Muscle Tone The Intruafusal Muscle Fiber or Muscle Spindle Gamma Motor Neuron Rubber bands Posts Model of the Muscle Spindle and Stretch Detection ] [

12. 8/4/2015 Muscle Tone u Muscle tone is the general state of contraction of the muscles. u If you have low muscle tone the muscles are flaccid (relaxed). u If high muscle tone, the muscle is contracted. u Muscle tone changes over time, e.g. during a step l Muscle tone is low as we pick up our leg l Muscle tone is high on all leg muscles as we prepare to put it back down and it has to support our weight

13. 8/4/2015 The Spindle and Stretch The Muscle Spindle Gamma Motor Neuron Model of the Muscle Spindle and Stretch Detection ] [

14. 8/4/2015 The Spindle and Stretch The Muscle Spindle The ends of the spindle are pulled out Gamma Motor Neuron Model of the Muscle Spindle and Stretch Detection ] [

15. 8/4/2015 The Spindle and Stretch u What happens when the spindle is stretched? u Which motor neuron is effected?

16. 8/4/2015 Activation of the  Motor Neuron The Muscle Spindle Gamma Motor Neuron Model of the Muscle Spindle and Stretch Detection ] [

17. 8/4/2015 Activation of the  Motor Neuron The Muscle Spindle The middle is pulled in Gamma Motor Neuron Model of the Muscle Spindle and Stretch Detection ] [

18. 8/4/2015 The effects of  motor neuron activation u What happens to the rubber bands in the model? u Can the sensory endings tell the difference in the cause of the stretch? u What happens when the spindles are stretched? u How could this be used in muscle tone?