Central Nervous System and Analgesics

Naloxone and Opioid Receptors

• Naloxone is an opioid antagonist, which means it blocks the effects of opioids at their receptors.
• Naloxone has a short duration of action, typically lasting 30 to 90 minutes.
• Naltrexone, also an opioid antagonist, has a much longer duration of action, lasting for 24 to 72 hours.
• Naloxone is a pure antagonist, meaning it only blocks opioid receptors and does not have any agonist activity.
• Naloxone is most appropriately used in situations where opioid overdose is suspected. It can reverse respiratory depression and other symptoms of opioid overdose.
• Naloxone's mechanism differs from that of opioids because it binds to the same receptors as opioids, but it does not activate them. Instead, it blocks the binding of opioids to these receptors.

Sedation Mechanism

• Sedation is primarily achieved through the reduction of neuronal activity in the central nervous system.
• The reticular activating system (RAS) in the brainstem is a key area affected by the sedation mechanism.
• Decreased noradrenaline release leads to decreased neuronal activity and promotes sedation.
• The release of GABA is mainly decreased during sedation.
• Sedation primarily affects neuronal function by reducing the firing rate of neurons and decreasing their excitability.

Phenytoin and Neuronal Function

• Phenytoin, an anticonvulsant medication, primarily works by blocking the repetitive firing of neurons.
• Phenytoin reduces the release of glutamate, an excitatory neurotransmitter, which helps to decrease neuronal excitation.
• Phenytoin can also suppress abnormal neuronal impulses, helping to reduce seizures.
• Phenytoin is classified as a sodium channel blocker.
• Phenytoin's role in neuronal firing is to stabilize neuronal membranes and limit excessive or repetitive firing.

Analeptics and the Nervous System

• Analeptics are stimulants of the central nervous system.
• Strychnine, an analeptic, acts on the spinal cord by blocking the inhibitory neurotransmitter glycine.
• Strychnine increases reflex excitability, leading to muscle spasms and convulsions.
• The use of strychnine is associated with increased tonic convulsions of all limbs.
• Strychnine primarily affects the skeletal muscles, causing muscle spasms and tetany.

Anaesthesia Techniques

• Peripheral nerve block anaesthesia involves injecting a local anaesthetic around a nerve or group of nerves, blocking their ability to transmit pain signals.
• Epidural anaesthesia is administered into the epidural space, located between the dura mater and the vertebral canal.
• Infiltration anaesthesia is the primary technique used in dentistry. It involves injecting local anesthetic directly into tissues near the site of surgery.
• Epidural anaesthesia's key characteristic is that it produces a segmental block, meaning only the nerves supplying specific areas of the body are affected.
• Peripheral nerve block anaesthesia can provide complete anaesthesia for specific regions of the body without the need for general anaesthesia.

Morphine and its Effects

• Morphine's primary action related to the emetic chemoreceptor trigger zone (CTZ) is to stimulate this area, leading to nausea and vomiting.
• Morphine commonly causes pupillary constriction (miosis).
• Morphine stimulates the cough reflex due to its effects on the spinal cord.
• Constipation is another potential side effect of morphine administration.
• The oculomotor center in the brainstem is responsible for controlling pupillary size and other eye movements. Morphine affects this center, causing pupillary constriction.