Which type of receptors for the neurotransmitter acetylcholine are found in the sarcolemma at a neuromuscular junction?

• A. GABA receptors
• B. Nicotinic receptors
• C. Adrenergic receptors
• D. Muscarinic receptors

Answer: (B)

Verified step by step guidance

1. Understand the context: The neuromuscular junction is the site where a motor neuron communicates with a muscle fiber to initiate contraction. Acetylcholine is the neurotransmitter released by the motor neuron to signal the muscle fiber.
2. Learn about acetylcholine receptors: Acetylcholine binds to specific receptors on the sarcolemma (the membrane of the muscle fiber). These receptors are classified into two main types: nicotinic and muscarinic receptors.
3. Identify the receptor type at the neuromuscular junction: Nicotinic receptors are ionotropic receptors that directly mediate the opening of ion channels, allowing ions like Na⁺ and K⁺ to flow across the membrane. This leads to depolarization and muscle contraction.
4. Differentiate from other receptor types: Muscarinic receptors are metabotropic and are typically found in other tissues, such as the heart or glands, where they mediate slower, more prolonged responses. Adrenergic receptors respond to adrenaline/noradrenaline, not acetylcholine. GABA receptors are involved in inhibitory neurotransmission and are unrelated to acetylcholine.
5. Conclude: The correct receptor type for acetylcholine at the neuromuscular junction is nicotinic receptors, as they are specifically designed to mediate rapid muscle contraction in response to neural signals.