46) While walking down the street, a cat jumps out of an alley into the pathway of an adult. They note that his /her heart is "racing." this response is primarily due to:

A) Norepinephrine (Levophed): Norepinephrine is a potent vasoconstrictor primarily used in acute hypotensive states to raise blood pressure. It is not indicated for the treatment of seasonal rhinitis, as its primary effect is not on the nasal passages or the symptoms associated with allergies, such as congestion.

B) Dopamine (Intropin): Dopamine is typically used in critical care settings for conditions such as shock and low blood pressure. While it affects dopaminergic and adrenergic receptors to improve renal perfusion and increase heart rate, it is not used to treat conditions like seasonal rhinitis, which involve nasal congestion.

C) Ephedrine (generic): Ephedrine is a sympathomimetic drug that stimulates alpha-adrenergic receptors, leading to vasoconstriction in the nasal passages and a reduction in swelling and congestion. This makes it a suitable choice for managing the symptoms of seasonal rhinitis, as it helps relieve nasal congestion by constricting blood vessels in the nasal mucosa.

D) Dobutamine (Dobutrex): Dobutamine is primarily used in the treatment of heart failure and shock because it increases heart rate and cardiac output. It does not have the properties needed to alleviate nasal congestion in rhinitis and is therefore not appropriate for this condition.

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.