A&P Final Ch. 9

Define the term motor unit

A motor neuron and all the muscle fibers that it controls. The size of a motor unit indicates how precise a movement can be.

Explain how an electrical signal from the nervous system arrives at the neuromuscular junction.

A motor neuron is a nerve that propagates an electrical impulse from the nervous system to skeletal muscle fibers.

Describe the organization of muscle tissue from cell to whole muscle to groups of muscles.

Myofilaments > Myofibril > Muscle fiber > Muscle fascicle > Muscle

Describe, in order, the events that occur at the neuromuscular junction that elicit an action potential in the muscle fiber.

1. Release of ACh into the synaptic cleft 2. Activation of ACh receptors at the motor end plate 3. Termination of ACh activity by the enzyme acetylcholinesterase (AChE 4. Arrival of an action potential at the synaptic terminal of the motor neuron 5. Diffusion of ACh across the synaptic cleft 6. Production of muscle fiber action potential

Describe a skeletal muscle fiber including the transverse (T) tubules, sarcoplasmic reticulum and myofibrils.

Muscle fibers are composed of bundles of myofibrils which are as long as the entire muscle fiber. Each fiber contains thousands of myofibrils that have a banded appearance, giving the fibers a striated appearance. T tubules are narrow tubes tightly bound to the sarcoplasmic reticulum that are continuous with the sarcolemma and extend into the sarcoplasm to form passageways through the muscle fiber. Sarcoplasmic reticulum forms a tubular network around each individual myofibril.

Name the connective tissue layers that surround each cell, fascicle, muscle, and group of muscles and indicate the specific type of connective tissue that composes all of these layers.

The epimysium is a dense layer of collagen fibers that surrounds the entire muscle. The perimysium is collagen and elastic fibers that separate groups of muscle fibers, called muscle fascicles, from each other. The endomysium is a thin layer of areolar CT that surrounds each muscle fiber, which contains bundles of protein filaments called myofibrils.