Which of the following physiologic principles would be considered a function of the somatic nervous system?

A) Myasthenia gravis (MG):
Weakness of the extremities and diplopia (double vision) are hallmark symptoms of myasthenia gravis, an autoimmune disorder that affects the neuromuscular junction. In MG, antibodies attack acetylcholine receptors, leading to muscle weakness that worsens with activity and improves with rest. The weakness typically affects voluntary muscles, including those responsible for eye movement, which leads to symptoms such as diplopia and ptosis (drooping eyelids).

B) Multiple sclerosis (MS):
Multiple sclerosis involves the demyelination of neurons in the central nervous system, leading to a variety of neurological symptoms. While MS can cause weakness and visual disturbances, the typical symptoms of MS include fatigue, muscle spasticity, ataxia, and sensory deficits. Diplopia can occur in MS but is usually accompanied by other neurological signs such as numbness, tingling, or loss of coordination.

C) Cerebral palsy (CP):
Cerebral palsy is a group of disorders affecting movement and posture due to non-progressive brain injury or abnormal brain development, often occurring in early childhood. While CP can cause muscle weakness and coordination issues, it does not typically present with diplopia. Instead, it often involves spasticity, motor impairment, and difficulty with fine motor tasks.

D) Parkinson disease (PD):
Parkinson disease is characterized by tremors, bradykinesia (slowness of movement), rigidity, and postural instability. While PD can lead to muscle weakness and visual issues like blurred vision, it is not typically associated with diplopia as a primary symptom. The hallmark motor symptoms are primarily related to tremor and difficulty initiating movements rather than generalized weakness and double vision.

A) The cell body of the first motor neuron that lies in the brain stem:
This option refers to the somatic nervous system, which controls voluntary muscle movements. In response to a stressful or fearful situation, like the one described, the sympathetic nervous system is activated, not the somatic motor pathways. This is more related to voluntary motor control rather than the autonomic response to stress.

B) Reflex circuitry produced by the ANS reflex:
The autonomic nervous system (ANS) is involved in regulating involuntary functions like heart rate, blood pressure, and digestion. However, the "racing heart" response described here is primarily triggered by the sympathetic division of the ANS due to a stressor, such as seeing the cat. The reflex itself is part of a larger autonomic reaction, but the direct cause of the increased heart rate is the secretion of neurotransmitters.

C) Parasympathetic effect on the vagus nerve:
The parasympathetic nervous system (PNS) generally works to counteract the "fight or flight" response, promoting a relaxed state and slowing the heart rate. The vagus nerve is the primary parasympathetic pathway involved in decreasing heart rate. However, during stress or a fear response, the parasympathetic system is overridden by the sympathetic system, which increases heart rate, making this option incorrect.

D) Secretion of the sympathetic neurotransmitters produced in the adrenal medulla:
When a person experiences a stressor, like the sudden appearance of a cat, the sympathetic nervous system is activated, triggering the release of neurotransmitters like norepinephrine from sympathetic nerve endings and epinephrine (adrenaline) from the adrenal medulla. These chemicals act on the heart, causing it to race in response to the perceived threat.