Question

How do muscle cells move in response to nerve impulses?

Answer 1

Hint: The movement involves motor neurons and neuromuscular junctions.
Skeletal muscles are stimulated by motor neurons to contract.

Complete Answer:
The synapse between a neuron and a muscle cell is called a neuromuscular junction. Here, nerve impulses are transferred from a motor neuron to a muscle fiber. A neurotransmitter called Acetylcholine is involved in this process.
The basic contractile unit of a muscle fiber is called a sarcomere. It is mainly made of two protein filaments - Actin and Myosin. Actin filaments are thin and Myosin filaments are thick in nature. Another protein called tropomyosin also runs close to this protein filament. In a muscle cell, two long strings of actin molecules are twisted to form the thin filament. The protein troponin is also distributed along regular intervals. The function of troponin is to cover or mask the binding sites on actin filaments.
When a nerve impulse or an action potential is generated acetylcholine is released into the neuromuscular junction. Calcium ions are released, which bind to a subunit on the actin filament. This causes the myosin heads to attach to binding sites on the actin filament and pull the actin heads towards the central part of the sarcomere. This action uses energy, which is produced by ATP hydrolysis. The myosin slides along the actin filament and the muscle is said to contract.

Additional Information:
Actin is a globular protein, and also forms a part of the cytoskeleton of cells. Myosin is both a fibrous protein and a globular enzyme. Acetylcholine is the chief neurotransmitter of the nervous system.

Note:
There are over 40 neurotransmitters found in the human nervous system. Each performs a wide array of functions. Some other common neurotransmitters are: Dopamine, Gamma-Amino Butyric Acid (GABA) and Norepinephrine.