🔴 Mechanism of Action 🔴

🔺 Bisphophonates (BPNs) :-

Bisphophonates are the anlogues of pyrophosphate.

They inhinit bone resorption and have ability to prevent osteoporosis.

🔸a)BPNs have strong affinity for calcium phosphate and have selective action in calcified tissue.
Bisphosphonates localised in the acidic zone under the osteoclasts due to their high affinity for calcium ions are released from bone surface due to high acidity the bisphosphonates are also released and are internalized by endocytosis.
This results in 👇👇
---- Accelerated apoptosis of osteoclasts reducing their number.
----Distribution of cytoskeleton and ruffled border of osteoclasts.

🔸b) It has been shown that now that the second and third generation potent amino-BPNs like alendronate, zolendronate, have important metabolic effects in the mevalonate pathway for isoprenoid lipid synthesis.

They inhibit prenylation of certain GTP binding proteins involved in cytoskeletal organization, membrane ruffling and vesical movement.
The net result is inactivation of osteoclasts, impaired vesicles fusion and enhanced apoptosis.

🔴 Mechanism of action 🔴

🔺 Peripherally acting Skeletal muscle relaxants :-

Site of action of both competitive and non-competitive depolarizing blockers is the end plate of skeletal muscle fibres.

🔺Competitive block (Non-depolarizing block) :-

Competitive blockers having high affinity to block nicotinic (Nm) cholinergic receptors at the muscle end plate , but no intrinsic activity. Rsults 👇👇

Skeletal muscle relax......

🔺Depolarizing Block :-

Decamethonium and Sch having high affinity as well as submaximal intrinsic activity at Nm cholinergic receptors.

They acts by loger lasting depolarization of muscle end plate produces repetitive excitation of fibre.

They do not dissociate from receptors and not metabolised and depolarization is going on for long lasting..... Resulting inactivation of Sodium Channels. In this state Ach released but no action is there.... Flaccid paralysis observed in mammals.

🔸a)Phase l block :- Rapid and onset results persistent depolarization of muscle end plate .
Depolarization declines shortly and repolarization occurs gradually.

🔸b)Phase ll block :- slow in onset and results from desensitization of the receptor to Acetyl choline.

🔴 Mechanism of action 🔴

🔺 Directly acting skeletal muscle relaxants :-

🔸Examples.....

🔹1) Dantrolene :- Neuromuscular transmission or MAP are not affected.
Dantrolene acts on Ryanodine receptor present in sarcopladmic reticulum and prevents release of calcium and muscle get relaxed.

🔹2) Quinine :- It increase the refractory period and decrease the excitability of motor end plates. Thus, response to repetitive nerve stimulation are reduced.

🔴 Mechanism of Action 🔴

🔺 Centrally acting skeletal muscle relaxants :-

🔹These drugs reduce skeletal muscle tone and lessen muscle spasm by a selective action in the cerebrospinal axis, without altering consciousness.

🔹They selectively depress spinal and supraspinal polysynaptic reflexes involved in the regulation of muscle tone without significantly affecting monosynaptically mediated stretch reflex.