Exam 5: Axonal Pathfinding

What mechanism of axonal growth do the growth cones of early-arising pioneer neurons in the grasshopper leg use to find their destination? What two factors in their environment guide the path they take?

Refer to the figure. These data are from an experiment using growth cones cultured on substrates with different levels of adhesivity, ranked from least adhesive (laminin-nitrocellulose) to most adhesive (L1). Based on the theoretical prediction in graph A, what was the researchers' hypothesis about adhesivity and growth cone growth rate? Based on the observed data in graph B, how does growth rate actually correlate to adhesivity? What does this suggest about the role of adhesion in axonal growth?

Motor neuron axons are

Ramón y Cajal's visualization of growth cones showed that neurons

What is one possible reason that the developing nervous system sends axons across the body's midline rather than keeping them all on one side of the body or the other?

Guidance cues can attract growth cones by encouraging _______ in the growing cell.

Which of the following is a receptor for Slit?

The process by which growth cones move toward a specific chemical is called

If the band of semaphorins between the outer leg and inner leg of a developing grasshopper is removed experimentally before early sensory pioneer neurons send their axons to their targets, what will happen to the migration of the sensory neurons?

How do growth cones interact with attractive and repulsive cues in their environment?

Growth cones move fastest when growing via

What is the difference between anterograde and retrograde axonal transport, and in what way is each responsible for how a growth cone responds to its environment?

Whether an external cue is attractive or repulsive to a growth cone depends on

Refer to the figure. In a wild-type Drosophila, some axons (stained brown) cross over the midline and some project longitudinally on either side of it, forming a ladder-like pattern of axons. In the image on the right, all axons are bundled at the midline. What mutation could have caused the abnormal axonal projection pattern in the right-hand image?

If you wanted to determine whether motor neurons are already fated to innervate a particular target muscle before their axons exit the ventral root of the spinal cord, or if they just follow a path that leads them to the closest muscle in need of innervation, the best experimental design would be to