Name and describe the three motor tracts that comprise the ...

[NClaborn]

Name and describe the three motor tracts that comprise the lateral group of descending fibers and explain their relative functions in motor control.
 
  What will be an ideal response?

Question 2

Diagram the elements that comprise skeletal muscle. Indicate the location and function of (a) extrafusal muscle fibers, (b) alpha motor neurons, (c) the muscle spindle, (d) intrafusal muscle fibers, and (e) the gamma motor neuron.
 
  What will be an ideal response?

[smrerig]

Answer to Question 1

Answer: Motor neurons arising from the primary motor cortex project to the spinal cord motor neurons that control voluntary movement. The lateral group of fibers includes the corticospinal tract, which starts (mostly) in the primary motor cortex and decussates in the caudal medulla en route to the spinal cord. These fibers control the distal parts of the limbs (hands, fingers, and toes). The corticobulbar tract projects from the medulla to the motor nuclei of the 5, 7, 9-12 cranial nerves and is involved in control of the muscles of the neck, face, tongue, and a portion of the extraocular muscles. The rubrospinal tract projects from the midbrain red nucleus to the spinal cord; this tract controls movements of the forearms and hands that are independent of trunk movements.

Answer to Question 2

Answer: This diagram is based on that of Figure 8.2 (page 234). The extrafusal fibers should be labeled as being in parallel with the intrafusals and showing that their contraction performs the work of the muscle. The gamma motor neurons should be shown as innervating the intrafusal fibers; their firing contracts the intrafusal fiber and takes up the slack of that fiber. GTOs are in series with the extrafusal fiberstheir activation inhibits the alpha motor neuron, thus preventing overcontraction of the muscle on a joint.