Skeletal muscle is under voluntary control, and are innervated by the somatic nervous system. Skeletal muscle is responsible for skeletal movement, such as swinging the arms or lifting the legs.

Cardiac and smooth muscle are under the control of the autonomic nervous system. Cardiac muscle contracts the heart autonomously, without additional neuronal input.

The only type of muscle tissue that can be controlled voluntarily is skeletal muscle tissue. Both skeletal and cardiac muscle tissue have the sarcomere as the functional unit, and only skeletal muscle has multinucleated cells. Smooth muscle does not have troponin, and therefore does not require calcium in order to contract.

Both cardiac and skeletal muscle is striated, however, cardiac muscle is mononucleated, whereas skeletal muscle in multinucleated. Smooth muscle is not striated. The student is observing muscle that is both striated and mononucleated, meaning it must be cardiac muscle.

Smooth muscle: mononucleated with no striations

Skeletal muscle: multinucleated with striations

Cardiac muscle: mononucleated with striations

Type I muscle cells, or red muscle cells, use aerobic respiration, whereas type II muscle cells, or white muscle cells, use anaerobic respiration. Aerobic respiration requires oxygen; therefore, myoglobin must be present to carry oxygen within type I muscle cells. Aerobic respiration occurs in mitochondria. This means that type I cells must have more mitochondria and myoglobin to facilitate aerobic respiration.

Calcium ions from the sarcoplasmic reticulum are essential for muscle contraction, and are found in equal amounts in both cell types.

The parasympathetic nervous system is more simply characterized as the “rest and digest” system, as it is activated during times of rest and helps in the digestion of food. Visceral smooth muscle tissue is mostly involved in digestion, and helps move food through the gastrointestinal tract.

In contrast, vascular smooth muscle is incorporated into the vascular tissues and plays a key role in vasoconstriction. Vasoconstriction helps increase blood pressure, increasing cardiac output during times of stress. Cardiac muscle is more active when the heart beats more rapidly, which would not occur while a person is at rest. Increased activity in vascular smooth muscle, cardiac muscle, and skeletal muscle occurs at times when the sympathetic nervous system ("fight or flight") is activated.

The extraocular muscles have small motor units to allow for very precise movements. These muscles are also non-fatigable because the muscles do not become weak after continual use throughout the day.

Large motor units would result in less precise control, affecting the ability of the eye to focus on a given target. Fatigable motor units would result in an inablility to keep the eye open and directed after sustained use.

To answer this question you must know that running for long periods of time, such as running a marathon, requires aerobic respiration and sustained muscle contraction over a longer period of time. Type I muscle cells are most suited for these exercises because they utilize aerobic respiration and are slow to fatigue. In contrast, type II muscle fibers can function on anaerobic respiration and fatigue very quickly.

Muscle cells do not undergo mitosis, and therefore cannot increase in number due to training. Instead, the size of the muscle fibers will grow. In a marathon runner, we would expect there to be very large type II muscle fibers in the muscles of the legs.

There are three classifications of muscle tissue: skeletal, cardiac, and smooth. A major distinction between these groups is that only skeletal muscle can be voluntarily controlled. Smooth muscle (such as that around blood vessels) and cardiac muscle (in the heart) are not consciously controlled. Each muscle type is unique to its specific function.

Recall that red muscle cells primarily use aerobic respiration and white muscle cells primarily use anaerobic respiration to produce ATP. Aerobic respiration, which involves the Krebs cycle and oxidative phosphorylation, occurs in the mitochondria. On the other hand, anaerobic respiration (glycolysis) occurs in the cytoplasm.

Type I muscle fibers, or red muscle, will use the mitochondria from ATP production and contain large amounts of myoglobin to help supply oxygen for these aerobic processes. In contrast, type II muscle fibers, or white muscle, will use glycolysis and lactic acid fermentation in the cytoplasm and contain very little myogloblin.

Cardiac muscle is organized into sarcomeres, giving it a striated appearance, and cardiac contraction is strongly dependent on calcium concentrations and release. While the heart is capable of beating without nervous innervation, autonomic regulation via the parasympathetic nervous system mediates the frequency of cardiac stimulation from the sinoatrial (SA) node.

Signals from the parasympathetic nervous system travel to the cardiac muscle via chemical synapses, by use of a neurotransmitter. Signals from one cardiac fiber to another are transmitted via electrical synapses, or gap junctions, the allow proliferation of the signal without a chemical intermediate.