return to biology 105 syllabus
Biology of Exercise
Quiz 3, part 4 Answers
4. Essay. Describe the muscle stretch reflex and compare
and contrast it to the reflexes involved in catching a fly ball in a baseball
game. You may use diagrams. Do not exceed 1 page. (14
points)
The stretch reflex is a very simple reflex. The amount of stretch in a muscle is detected by sensory receptors in the muscle and relayed towards the spinal cord via an afferent nerve. This info is passed to an efferent nerve via a synapse in the spinal cord and the signal is the passed towards contractile fibers in the muscle. In general, stretching of the muscle will lead to increased signals for the muscle to contract. There is very little opportunity for processing, because only a single synapse is involved.
In contrast, catching a fly ball is a very complex process. The
process is arranged in the same way as the simple stretch reflex.
Sensory information is brought into the central nervous system, processed,
and then an efferent signal is sent out to the muscles. A diverse
array of sensory info is collected during the process of catching a fly,
including visual, auditory, touch, and internal homeostatic information.
The processing is very sophisticated, including the participation of many
nerve cells in many different regions of the brain, including the cerebral
cortex where information is integrated and decisions are made. The
efferent output is also complicated, as the output to the muscles to make
coordinated movement in the appropriate direction needs to be complex.
In summary, both reflexes operate using a common path - stimulus, afferent path, processing in CNS, efferent path, and response. The difference is that catching a fly is much more complex.