Question

Which one of the following is the correct functional sequence of nerve fibers. * (a) Stimulus→ Impulse→ Muscular movements
(b) Impulse→ Stimulus→ Muscular movements
(c) Stimulus→ Muscular movements→ Impulse
(d) Muscular movements→ Impulse→ Stimulus​

Answer 1

Answer:

Local 

anesthetics

 (LAs) are drugs that block the sensation of pain in the region where they are administered. LAs act by reversibly blocking the sodium channels of nerve fibers, thereby inhibiting the conduction of nerve impulses. Nerve fibers that carry pain sensation have the smallest diameter and are the first to be blocked by LAs. Loss of motor function and sensation of touch and pressure follow, depending on the duration of action and dose of the LA used. LAs can be infiltrated into skin/subcutaneous tissues to achieve local anesthesia or into the epidural/

subarachnoid space

 to achieve regional anesthesia (e.g., 

spinal anesthesia

, 

epidural anesthesia

). Some LAs (

lidocaine

, prilocaine, tetracaine) are effective on topical application and are used before minor invasive procedures (

venipuncture

, 

bladder catheterization

, endoscopy/

laryngoscopy

). LAs are divided into two groups based on their chemical structure. The amide group (

lidocaine

, prilocaine, 

mepivacaine

, etc.) is safer and, hence, more commonly used in clinical practice. The 

ester group

 (procaine, tetracaine) has a higher risk of causing 

allergic reactions

 or systemic toxicity and is, therefore, reserved for patients with known 

allergies

 to drugs of the amide group. Overdose or inadvertent injection of an LA into a blood vessel can cause systemic toxicity, which mainly affects the 

CNS

 (

tinnitus

, 

seizures

, etc.) and the CVS (

bradycardia

, 

arrhythmias

, etc.