The following is a list of muscles in the human body: (1) biceps and triceps of the
upper arms, (2) smooth muscle in the intestines, (3) pectorals of the chest, (4)
gluteals at the top of the legs, (5) cardiac muscle of the heart. Which of these muscles are consistently under the control of the autonomic nervous
system? (A) 1, 2, and 3; (B) 1, 3, and 4; (C) 2 and 5; (D) 5 only; (E) 2 and 3.
To answer this question, we need to recall what muscle groups are under the control
of the autonomic nervous system and why.
The autonomic nervous system is one subdivision of the motor division found within
the peripheral nervous system. The motor division is subdivided into two parts based on the type of motor function
to be carried out. The somatic nervous system is the subdivision that regulates voluntary and conscious
activities. The somatic nervous system requires the action of the skeletal muscles. The skeletal muscles help to carry out responses like lifting boxes, which involves
your biceps; running, which involves your gluteal muscles; or push-ups, which
involve the pectoral muscles.
The autonomic nervous system is the subdivision that controls all of the involuntary
and subconscious activities of the body. To carry out all of the involuntary responses, the autonomic nervous system requires
the action of the smooth muscles and glands. The autonomic nervous system is further subdivided into two components: the
sympathetic and the parasympathetic nervous systems.
The sympathetic nervous system is responsible for the body’s fight-or-flight response
and triggers several physiological changes that prepare the body to confront or flee
a perceived threat. For example, this could include increasing the heart and breathing rates to prepare
the body to respond to a dangerous situation.
In contrast, the parasympathetic nervous system is responsible for the body’s
rest-and-digest response, which occurs when the body is relaxed, resting, or
feeding. This system keeps your body working as it should during rest periods and controls
responses like decreasing the heart rate and stimulating the digestive enzymes.
So, looking at the list of muscle actions from the question, any muscles that are
involved in carrying out involuntary functions and therefore use the smooth muscles
would be regulated by the autonomic nervous system.
Now that we have this information, we can answer the question. The muscles that are consistently under the control of the autonomic nervous system
are number (2), the smooth muscles in the intestines, and number (5), the cardiac
muscles of the heart.