When an action potential reaches the axon terminal, what happens next?

Correct Answer: c

Rationale: The correct answer is C because when an action potential reaches the axon terminal, endosomes containing neurotransmitters fuse with the cell membrane and release neurotransmitter into the synaptic cleft. This process is known as exocytosis. This neurotransmitter then binds to receptors on the postsynaptic neuron, initiating a new action potential. Choice A is incorrect because the muscle fiber contraction is initiated by the binding of the neurotransmitter to receptors on the muscle cell, not directly by the action potential reaching the axon terminal. Choice B is incorrect because acetylcholinesterase breaks down acetylcholine in the synaptic cleft after it has already been released and has completed its role in transmitting the signal. Choice D is incorrect because sodium channels opening at the motor end plate is part of the process of muscle cell depolarization and contraction, not directly related to the release of neurotransmitter at the axon terminal.

Correct Answer: C

Rationale: Rationale: 1. Lactogenic hormone stimulates mammary glands to produce milk, essential for lactation. 2. Oxytocin is a different hormone that causes milk ejection, not production. 3. Gonadotropins like FSH and LH affect gonads, not lactation. 4. Choice C directly relates to lactation, making it the correct answer.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Insulin is a hormone that regulates blood glucose levels by promoting glucose uptake into cells. 2. Beta cells of the islets of Langerhans in the pancreas are responsible for secreting insulin. 3. Insulin lowers blood glucose levels by enhancing glucose uptake and storage. 4. Therefore, choice A is correct as it accurately identifies the source of insulin secretion. Summary: - Choice B is incorrect as the liver does not secrete insulin. - Choice C is incorrect as insulin lowers blood glucose levels. - Choice D is incorrect as insulin is released in response to high, not low, blood glucose levels.

Correct Answer: C

Rationale: Correct Answer: C - Diabetes insipidus Rationale: 1. Diabetes insipidus is characterized by excess urine production due to inadequate ADH secretion. 2. Low blood volume occurs as a result of increased urine output, leading to dehydration. 3. Cushing syndrome involves excess cortisol production, not excess urine production. 4. Tetany is caused by low calcium levels, not excess urine production. 5. Oversecretion of ACTH leads to excess cortisol production, not excess urine production.

Correct Answer: D

Rationale: Step 1: ACTH, TSH, and gonadotropins are hormones that stimulate the secretion of other hormones. Step 2: These hormones target specific endocrine glands, such as the adrenal cortex. Step 3: Since these hormones stimulate the secretion of other hormones and target specific glands, they are classified as tropic hormones. Step 4: Thus, the correct answer is D: tropic hormones. Summary: A is incorrect as they are not hypothalamic-releasing hormones. B is incorrect as they are not secreted by the neurohypophysis. C is incorrect as they are not specifically aimed at the adrenal cortex.