Nicotinic ligand-gated channels interact with the acetylcholine released by neurons at the neuromuscular junction. By binding to the neurotransmitter, these channels change shape and allow ions to enter into the muscle cell membrane, thus depolarizing it and driving an ultimate contraction.

Voltage-gated sodium and calcium channels play an important role in propagating the membrane depolarization, but do not interact with the neurotransmitter at the neuromuscular junction. Muscarinic receptors are also stimulated by acetylcholine, but are most commonly found in the parasympathetic nervous system, and do not play a significant role in muscle contraction.

Glycine and GABA are the main inhibitory neurotransmitters. Thus, they would be used by inhibitory neurons that work to downregulate the excitatory neurons at the neuromuscular junction. Inhibiting the release of these inhibitory signals would result in an involuntary, excitatory response, such as lockjaw.

It is important to note that neurons involved directly in the neuromuscular junction are ALWAYS excitatory. They can be turned off, via the inhibitory neurons discussed in the question above; however, if a neuron is directly part of the neuromuscular junction, it is excitatory.

Acetylcholinesterase is an enzyme that is responsible for breaking down excess acetylcholine in the neuromuscular junction. Acetylcholinesterase inhibitors will thus reduce the activity the enzyme that breaks down acetylcholine (ACh), effectively increasing acetylcholine concentrations in the neuromuscular junction. The result of this change will be an exaggeration of the effect of ACh on the postsynaptic muscle at the neuromuscular junction.

Importantly, inhibitors of this enzyme will not increase the amount of ACh produced by the neuron. Instead, it just prolongs the time of synaptic residence for already released ACh.

A neuron at the neuromuscular junction uses the neurotransmitter acetylcholine to signal the contraction of the muscle via action potential generation, which signals the release of calcium from the muscle sarcoplasmic reticulum.

Skeletal muscle is the only muscle type that is multinucleated. Both cardiac and smooth muscle cells have only one nucleus.

Smooth muscle is under involuntary control, innervated by the autonomic nervous system, and contains mononucleated cells. Skeletal muscle is striated, multinucleated, and under voluntary control. Cardiac muscle is striated, mononucleated, and under involuntary control.

Cardiac muscle also uses intercalated discs, specialized cellular junctions, to facilitate electrical conduction between cardiomyocytes. This helps coordinate the contraction of the heart.

Cardiac muscle is physiologically and morphologically distinct from skeletal and smooth muscle. Instead of using myosin light chain kinase (like smooth muscle), cardiac muscle uses the same sarcomere pattern of skeletal muscle. This explains the presence of striations in both types of tissue.

Cardiac muscle is unique, however, in that it has gap junctions that allow the exchange of ions between individual cells. This allows the myocardium, or muscular portion of heart tissue, to beat in a coordinated fashion, as cells are depolarizing alongside one another. Additionally, intercalated discs are present at the ends of sarcomeres, but are not present in skeletal muscle.

These two characteristics allow us to conclude that muscle cell type 2 is cardiac muscle, and will be found in the myocardium.

The presence of gap junctions within the intercalated discs of contractile cardiac myocytes allows for the rapid passage of ions from one cell to another. Once pacemaker cells in the sinoatrial node of the heart spontaneously generate action potentials, this wave of depolarization spreads into neighboring contractile myocytes via gap junctions. These gap junction connections are crucial to the heart operating in a unified and coordinated fashion, and are responsible for the characteristic wavelike contraction of the heart from the apex to the base. 

The pericardial membrane is the tissue that surrounds the heart. The easiest way to determine the answer in this problem is to understand that "cardial" indicates pertinence heart and that "peri" is a prefix meaning "around."

Cardiac contraction begins in the sinoatrial node. The impulse travels through both atria then followed by arriving at the atrioventricular node, which slows the impulse to allow for complete atrial contraction and ventricular filling. Then the impulse travels through the bundle of His, which branches into the right and left bundle branches and through the Purkinje fibers in the walls of both ventricles generating a strong contraction.

Cardiac output (CO) is defined as:

Rearrange to solve for heart rate.