Question

Squid benefit from having axons of multiple sizes that innervate their muscle fibers in the mantle because

A) squid need larger diameter axons to innervate larger groups of fibers.
B) the larger diameter axons innervate fibers that are farther away because the signals are conducted more rapidly through them.
C) smaller fibers are not energetically efficient.
D) larger fibers generate larger action potentials, which allows for more neurotransmitter release.

Answer 1

Squid have axons of multiple sizes that innervate their muscle fibers in the mantle. This is because larger diameter axons are needed to innervate larger groups of fibers. Additionally, larger fibers generate larger action potentials, allowing for more neurotransmitter release.

Step-by-step explanation:

Squid benefit from having axons of multiple sizes that innervate their muscle fibers in the mantle because A) squid need larger diameter axons to innervate larger groups of fibers. B) the larger diameter axons innervate fibers that are farther away because the signals are conducted more rapidly through them. C) smaller fibers are not energetically efficient. D) larger fibers generate larger action potentials, which allows for more neurotransmitter release.

As you have learned, every skeletal muscle fiber must be innervated by the axon terminal of a motor neuron in order to contract. Each muscle fiber is innervated by only one motor neuron. The actual group of muscle fibers in a muscle innervated by a single motor neuron is called a motor unit. The size of a motor unit is variable depending on the nature of the muscle.

The axons will also branch to innervate multiple muscle fibers. Together, the motor neuron and all the muscle fibers that it controls make up a motor unit. Motor units vary in size. Some may contain up to 1000 muscle fibers, such as in the quadriceps, or they may only have 10 fibers, such as in an extraocular muscle. The number of muscle fibers that are part of a motor unit corresponds to the precision of control of that muscle. Also, muscles that have finer motor control have more motor units connecting to them, and this requires a larger topographical field in the primary motor cortex.

Answer 2

The correct answer is that larger diameter axons allow for rapid signal conduction to muscle fibers that are farther away, which is beneficial for squids' movement. Having multiple sizes of axons aids in both quick responses and fine muscle control.

Step-by-step explanation:

Squid benefit from having axons of multiple sizes that innervate their muscle fibers in the mantle for several reasons. However, the correct answer to why squids have axons of multiple sizes is that the larger diameter axons innervate fibers that are farther away because the signals are conducted more rapidly through them. Larger axons can conduct electrical signals faster than smaller ones, which is beneficial for coordinating rapid and efficient contractions of the muscles, especially in the mantle, which is crucial for the squid's propulsion.

On the other hand, the overall efficiency of muscle fiber innervation is not solely dependent on axon size. Each motor unit that a motor neuron and the muscle fibers it controls form can vary in size. Some motor units in muscles that require fine control have more motor units with smaller axons connecting to them, which are represented by a larger topographical field in the primary motor cortex. This shows that having multiple sizes of axons is also related to the precise control of muscle movements.