Receptors (MOAs)

Question 1

What type of receptor is responsible for skeletal muscle contraction at the neuromuscular junction?

Answer 1

Nicotinic receptor (ionotropic), activated by acetylcholine.

Question 2

What happens when acetylcholine binds to nicotinic receptors in skeletal muscle?

Answer 2

Depolarization occurs, activating dihydropyridine receptors which then open ryanodine receptors, releasing Ca²⁺.

Question 3

What is the function of ryanodine receptors in skeletal muscle contraction?

Answer 3

They release calcium from the sarcoplasmic reticulum into the cytoplasm.

Question 4

How does calcium lead to skeletal muscle contraction?

Answer 4

Calcium binds troponin C, shifts tropomyosin, exposes myosin-binding sites on actin, enabling contraction.

Question 5

What role does ATP play in skeletal muscle contraction?

Answer 5

ATP binds to myosin, enabling the myosin head to pull actin for contraction.

Question 6

Which neurotransmitter activates M3 muscarinic receptors?

Answer 6

Acetylcholine (ACh), released from parasympathetic postganglionic neurons.

Question 7

What is the signal transduction pathway of M3 muscarinic receptors?

Answer 7

Activates Gq → PLC → PIP2 → IP3 + DAG → intracellular Ca²⁺ release and PKC activation.

Question 8

What effect does IP3 have inside the cell?

Answer 8

It stimulates the release of Ca²⁺ from intracellular stores.

Question 9

What is the effect of DAG in M3 receptor activation?

Answer 9

Activates protein kinase C (PKC), which contributes to smooth muscle contraction.

Question 10

How does M3 receptor activation affect smooth muscle?

Answer 10

Leads to Ca²⁺-dependent activation of MLCK → contraction.

Question 11

Where are β1-adrenergic receptors primarily found?

Answer 11

In the heart (SAN, AVN, myocardium) and kidney juxtaglomerular cells.

Question 12

What intracellular pathway is activated by β1-adrenergic receptors?

Answer 12

Gs protein → adenylyl cyclase → cAMP → PKA activation.

Question 13

What are the physiological effects of β1 receptor activation?

Answer 13

Increased heart rate, contractility, and renin release.

Question 14

How does PKA increase heart contractility?

Answer 14

It phosphorylates Ca²⁺ channels, increasing calcium influx into cells.

Question 15

Where are β2-adrenergic receptors found?

Answer 15

Bronchial and vascular smooth muscle.

Question 16

What is the intracellular pathway of β2 receptor activation?

Answer 16

Gs protein → adenylyl cyclase → ↑ cAMP → PKA activation.

Question 17

What does PKA do in β2-adrenergic signaling?

Answer 17

Inhibits MLCK, preventing smooth muscle contraction → relaxation.

Question 18

What are the physiological effects of β2 receptor activation?

Answer 18

Bronchodilation, vasodilation, and smooth muscle relaxation.

Question 19

Where are α1-adrenergic receptors located?

Answer 19

Vascular smooth muscle.

Question 20

What signaling pathway do α1 receptors use?

Answer 20

Gq → PLC → IP3 + DAG → Ca²⁺ release and PKC activation.

Question 21

What is the effect of α1 receptor activation?

Answer 21

Vasoconstriction and increased blood pressure.

Question 22

Where are α2-adrenergic receptors located?

Answer 22

Presynaptic terminals.

Question 23

What is the function of α2-adrenergic receptors?

Answer 23

Inhibit adenylyl cyclase → ↓ cAMP → ↓ neurotransmitter release (negative feedback).

Question 24

Which G protein is associated with α2-adrenergic receptors?

Answer 24

Gi protein, which inhibits adenylyl cyclase.

Question 25

What is the primary neurotransmitter released by preganglionic sympathetic neurons?

Answer 25

Acetylcholine (ACh).

Question 26

What is the primary neurotransmitter released by postganglionic sympathetic neurons?

Answer 26

Noradrenaline (norepinephrine), except in sweat glands where it is ACh.

Question 27

What type of receptors are located on sympathetic ganglia?

Answer 27

Nicotinic receptors (NN subtype).

Question 28

What is the primary neurotransmitter in both pre- and postganglionic parasympathetic neurons?

Answer 28

Acetylcholine (ACh).

Question 29

What receptor type is found on parasympathetic ganglia?

Answer 29

Nicotinic receptors (NN subtype).

Question 30

What receptor type is found on parasympathetic target organs?

Answer 30

Muscarinic receptors (mainly M2 and M3).

Question 31

Where are M2 muscarinic receptors mainly found?

Answer 31

Heart tissue (especially the SA and AV nodes).

Question 32

What is the intracellular signaling mechanism of M2 receptors?

Answer 32

Gi protein → ↓ adenylyl cyclase → ↓ cAMP → ↓ PKA.

Question 33

What is the effect of M2 receptor activation in the heart?

Answer 33

Slows heart rate (negative chronotropy) and reduces conduction velocity.

Question 34

What neurotransmitter and receptor are involved in sympathetic innervation of sweat glands?

Answer 34

ACh acting on muscarinic (M3) receptors.

Question 35

What is the physiological response of sweat gland activation?

Answer 35

Stimulates sweating (thermoregulatory response).

Question 36

What is the neurotransmitter at the adrenal medulla?

Answer 36

ACh from preganglionic sympathetic neurons.

Question 37

What type of receptor is found on adrenal medulla chromaffin cells?

Answer 37

Nicotinic (NN subtype).

Question 38

What is secreted from the adrenal medulla into the bloodstream?

Answer 38

Adrenaline (80%) and noradrenaline (20%).

Question 39

Which division of the ANS predominates in resting conditions?

Answer 39

Parasympathetic nervous system.

Question 40

Which division of the ANS predominates in blood vessel tone?

Answer 40

Sympathetic nervous system.