Okay, let's tackle this question about where α-adrenergic receptors are located in the urinary bladder. The question is asking for the specific part of the urinary bladder where these receptors are found.

First, I need to recall the anatomy and physiology of the urinary bladder. The bladder has several layers: the mucosa, submucosa, muscularis propria (which is the detrusor muscle), and the adventitia or serosa. The detrusor muscle is responsible for contracting to expel urine.

α-Adrenergic receptors are part of the sympathetic nervous system. When activated, they cause smooth muscle contraction. In the bladder, the sympathetic stimulation via α-receptors would affect the internal urethral sphincter. The internal urethral sphincter is made of smooth muscle and is under involuntary control, helping to prevent urine leakage when the bladder is filling. The external urethral sphincter, on the other hand, is skeletal muscle and under voluntary control via the pudendal nerve.

So, the internal urethral sphincter is the part where α-adrenergic receptors are located because sympathetic activation (via α-receptors) causes it to contract, maintaining continence. The detrusor muscle, which is part of the bladder wall, has β3-adrenergic receptors that promote relaxation during storage.

Now, looking at the options, the correct answer should be the internal urethral sphincter. The distractors might be other parts like the detrusor muscle, external urethral sphincter, or even the bladder mucosa. The detrusor has β3 receptors, so α receptors there would be incorrect. The external sphincter is skeletal muscle, so it doesn't have α receptors. The mucosa doesn't have smooth muscle, so α receptors aren't there either.

Clinical pearl: Remember that α-blockers are used for overactive bladder because they relax the internal sphincter, aiding voiding. Also, the external sphincter is voluntary, so it's a different story.

**Core Concept**
α-Adrenergic receptors mediate smooth muscle contraction in the urinary bladder's internal urethral sphincter. This mechanism is critical for maintaining urinary continence by preventing involuntary leakage during bladder filling.

**Why the Correct Answer is Right**
The internal urethral sphincter, composed of smooth muscle, contains α1-adrenergic receptors. Sympathetic stimulation via these receptors causes sphincter contraction, opposing detrusor relaxation to preserve continence. This contrasts with the detrusor muscle, where β3-adrenergic receptors promote relaxation during storage.

**Why Each Wrong Option is Incorrect**
**Option A:** The detrusor muscle contains β3-adrenergic receptors, not α-receptors, which mediate contraction of the internal sphincter.
**Option B:** The external urethral sphincter is skeletal muscle, innervated by somatic motor neurons (pudendal nerve), and lacks α-adrenergic receptors.
**Option C:** The bladder mucosa lacks smooth muscle and adrenergic receptors.

**Clinical Pearl / High-Yield Fact**
α-Blockers (e.g., tamsulosin) selectively relax the internal urethral sphincter, improving urinary flow in benign prostatic hyper

✓ Correct Answer: B. Base of bladder