Question

question 70
0.25 pts
which is true of a reflex arc?
it does not involve the brain.
it always consists of an afferent neuron and an efferent neuron.
it always consists of an afferent neuron, an efferent neuron, and an interneuron.
it always consists of an afferent neuron, an efferent neuron, the brain, and the spinal cord.
question 71
0.25 pts
the autonomic nervous system includes only efferent neurons.
true
false
question 72
0.25 pts
which part of the brain releases the hormone melatonin?
hypothalamus
thalamus
pineal gland
cerebellum

Explanation:

Question 70

A reflex arc can be spinal (doesn't involve brain) or cranial (involves brain), so "It does not involve the brain" is false. A simple reflex arc (like knee - jerk) has an afferent (sensory) neuron, an interneuron, and an efferent (motor) neuron? No, wait, the simplest reflex arc (monosynaptic) has an afferent and an efferent neuron (they synapse directly). But many reflex arcs have interneurons. Wait, no, the option "It always consists of an afferent neuron and an efferent neuron" is incorrect because some have interneurons. Wait, no, the correct understanding: A reflex arc pathway: sensory receptor → afferent neuron → (interneuron in CNS) → efferent neuron → effector. But the monosynaptic reflex (e.g., knee - jerk) has no interneuron, just afferent and efferent neurons synapsing in the spinal cord. Wait, the options:

• Option 1: "It does not involve the brain" — some reflexes (cranial reflexes) involve the brain, so this is false.
• Option 2: "It always consists of an afferent neuron and an efferent neuron" — monosynaptic reflexes have these two, but polysynaptic have interneurons. But the other options are more wrong.
• Option 3: "It always consists of an afferent neuron, an efferent neuron, and an interneuron" — monosynaptic don't have interneurons, so "always" is wrong.
• Option 4: "It always consists of an afferent neuron, an efferent neuron, the brain, and the spinal cord" — many reflexes (spinal) don't involve the brain, so "always" is wrong. Wait, maybe I made a mistake. Wait, the correct answer is "It always consists of an afferent neuron and an efferent neuron"? No, no, the monosynaptic reflex has afferent and efferent, polysynaptic has afferent, interneuron, efferent. But the option "It always consists of an afferent neuron and an efferent neuron" — the key is "always". Wait, no, the other options: "It does not involve the brain" is false (some do, some don't). "It always consists of... brain and spinal cord" is false (spinal reflexes don't need brain). "It always consists of... and an interneuron" is false (monosynaptic don't). So the best option is "It always consists of an afferent neuron and an efferent neuron"? Wait, no, maybe the answer is "It always consists of an afferent neuron, an efferent neuron, and an interneuron" is wrong, "It does not involve the brain" is wrong, "It always consists of... brain and spinal cord" is wrong. So the correct option is "It always consists of an afferent neuron and an efferent neuron"? Wait, no, I think I messed up. Let's recall: A reflex arc is the neural pathway for a reflex. The basic components are sensory receptor, sensory (afferent) neuron, integration center (CNS, which can be spinal cord or brain, and can have interneurons), motor (efferent) neuron, and effector. In a monosynaptic reflex (like knee - jerk), the integration center is a synapse between afferent and efferent neurons (no interneuron). In polysynaptic, there are interneurons. So the statement "It always consists of an afferent neuron and an efferent neuron" is true because every reflex arc has at least these two (afferent to carry sensory info, efferent to carry motor info). The other options: "It does not involve the brain" — some reflexes (e.g., pupillary reflex) involve the brain, so false. "It always consists of... and an interneuron" — monosynaptic don't, so false. "It always consists of... brain and spinal cord" — spinal reflexes don't need brain, so false. So the correct option is "It always consists of an afferent neuron and an efferent neuron".

The autonomic nervous system (ANS) is part of the peripheral nervous system. The ANS has efferent (motor) neurons that control involuntary functions, but it also has afferent (sensory) neurons that send information about internal organs to the CNS. Wait, no, actually, the ANS is mainly considered to have efferent pathways (sympathetic and parasympathetic), but does it have afferent? Wait, the question is "The autonomic nervous system includes only efferent neurons." Is this true? Wait, the ANS has sensory (afferent) neurons that monitor the internal environment (e.g., chemoreceptors, baroreceptors) and send signals to the CNS, and then efferent neurons that carry out the responses. But sometimes, the ANS is described as consisting of efferent neurons (the motor part), but technically, the afferent neurons related to visceral sensations are part of the ANS? Wait, no, the standard definition: The autonomic nervous system is the part of the peripheral nervous system that controls involuntary functions, and it consists of efferent (motor) neurons (sympathetic and parasympathetic). The afferent neurons that carry visceral sensory information are part of the general visceral afferent fibers, which are part of the peripheral nervous system but sometimes considered part of the ANS? Wait, maybe the answer is "False" because the ANS has afferent (sensory) neurons too. Wait, no, maybe the question is considering that the ANS (the motor part) has only efferent, but the sensory part is separate. Wait, the statement "The autonomic nervous system includes only efferent neurons." If we consider the ANS as the motor (efferent) system for visceral organs, then it's true? Wait, no, I'm confused. Let's check: The autonomic nervous system has two divisions: sympathetic and parasympathetic, which are efferent (motor) pathways. But there are also visceral afferent neurons that carry information from visceral organs to the CNS, which are part of the ANS? Or are they part of the somatic sensory? No, visceral afferents are part of the autonomic (visceral) sensory system. So if the ANS includes both afferent and efferent, then the statement is false. But some sources say that the ANS (autonomic motor system) consists of efferent neurons. So the answer: If the question is about the autonomic motor system, then it's true. But I think the correct answer is "True"? Wait, no, let's recall: The autonomic nervous system is responsible for involuntary control of visceral functions. It has afferent (sensory) and efferent (motor) components. The afferent components carry information from visceral receptors to the CNS, and the efferent components (sympathetic and parasympathetic) carry commands from the CNS to visceral effectors. So if the ANS includes both, then the statement "includes only efferent" is false. So the answer is "False".

Melatonin is a hormone that regulates sleep - wake cycles. The pineal gland is the part of the brain (a small endocrine gland in the brain) that releases melatonin. The hypothalamus releases many hormones (like TRH, CRH) but not melatonin. The thalamus is a relay center for sensory information, not for melatonin release. The cerebellum is for motor coordination, not hormone release.

Answer:

B. It always consists of an afferent neuron and an efferent neuron (assuming the options are labeled A, B, C, D as: A. It does not involve the brain. B. It always consists of an afferent neuron and an efferent neuron. C. It always consists of an afferent neuron, an efferent neuron, and an interneuron. D. It always consists of an afferent neuron, an efferent neuron, the brain, and the spinal cord.)

Question 71