QUESTIONS

1. What do the following structures have in common:  Krause's end bulb, Merkel's disk, Pacinian corpuscles, free nerve endings, hair follicle receptors, Ruffini endings.
    
2. True/False:
   
   A motor nerve contains >50%  afferent fibers.
    
3. The receptor for both tonic & phasic stretch reflexes is an encapsulated organ located within muscle faciculi. It is called _______________.
    
4. What are extrafusal & intrafusal muscle fibers?
    
5. What in the hell is a gamma motor neuron & what is gamma bias?
    
6. What in the hell is a golgi tendon organ?
    
7. In testing postural reflexes, what is the difference between the extensor postural thrust reflex & the extensor thrust reflex?

              MISC QUESTION:

              What are:  Block vertebrae, Hemivertibrae, & butterfly vertebrae?




 

ANSWERS

1. All these guys are Mechanoreceptors (they do the sense of touch).
   
   
   
   
    
2. It's true. So-called motor nerves have nociceptor & mechanoreceptor fibers galore.
   
   
   
   
    
3. It is called a muscle spindle. There are 2 types of afferent fibers coming from it. The Group 1A fibers (one per spindle, they are large & myelinated) & Group 2 fibers (about which we know next to nothing.) The Group 1A fibers connect to  intrafusal muscle fibers & will tell the spinal cord when the spindle is contracting (ie keeping the spinal cord informed regarding the stretch status of the muscle.)
   
   
   
   
    
4. There are muscle fibers that attach to the muscle spindle.  The extrafusal fibers attach at the ends of the spindle & the intrafusal fibers attach within the spindle.  There are 2 types of intrafusal fibers:  nuclear bag fibers & nuclear chain fibers.  These fibers are responsible for changing the configuration of the spindle.
   
   
   
   
    
5. The efferents that attach to the ends of an intrafusal fiber are gamma motor neurons.  They cause the fiber to contract & the spindle to stimulate its group 1A fiber.  This action serves to increase muscle tone & muscle sensitivity to stretch & this phenomenon is called gamma bias.
   
   When an alpha motor neuron begins movement, the gamma motor neuron is stimulated to contract its intrafusal fibers. This coordinates the spindles level of stimulation to the level of muscle contraction so that the spindle's input can still be meaningful no matter what the muscle is doing. This phenomenon is called alpha gamma coactivation.
   
   
   
   
    
6. A golgi tendon organ is a tension receptor located near the muscle/tendon junction. It can respond to both stretch & contraction (as opposed to the spindle that  can respond to only stretch.)  The afferent fibers coming off the GTO are called 1B fibers.
   
   
   
   
    
7. Imagine you are lowering your patient vertically toward the exam table. When his/her little feet touch the table, the legs become rigid so as to support his/her weight. This is the extensor postural thrust reflex & it is normal.  The extensor thrust reflex is not normal. Picture your patient standing on all 4's on the table.  You pick up a foot & press your hand against the bottom sort of like he/she is standing on your hand.  If you get a little kick, that is the extensor thrust reflex. Normal animals do not do this.
   
   
   
   
    

             MISC ANSWER:

               Block vertebrae are basically two vertebrae stuck together.

               Hemivertebrae are vertebrae where 1/2 the vertebra has failed to
               ossify causing spinal curvature (the direction of the curvature
               depends on which 1/2 didn't ossify)

               Butterfly vertebrae are vertebrae with a cleft down the middle so
               they look like butterflies.