Wednesday, June 16, 2021
Tuesday, June 15, 2021
General Anesthetics: Properties
General anesthetics (inhalational and intravenous agents) have a rapid, smooth onset of action and clinically desirable rapid reversal of effect. Concentrations of inhalational agents in the body and the pharmacokinetics depend on the drugs’ partial pressure in the lungs and solubility in blood and brain tissue. Induction of anesthesia is more rapid for drugs with high partial pressure in the lungs and high solubility in blood (eg, nitrous oxide, desflurane, sevoflurane). Onset of anesthesia is slowed when pulmonary blood flow is reduced.
Local Anesthetics: Spinal Afferents and Local Anesthetic Mechanisms of Action
Local anesthetics cause temporary loss of pain sensation without loss of consciousness by blocking conduction along sensory nerve fibers. Some selectivity for pain afferents is achieved partly by using the agent close to target neurons. All currently used drugs block voltagedependent Na+ channels in excitable cells, which decreases the likelihood of an action potential. The target site of the drugs is on the cytoplasmic side of the neuron membrane, so drug molecules must pass through the membrane.
Tissue injury can lead to cellular changes involving release of chemicals (eg, histamine) that start or quicken neuronal impulses that are interpreted as pain. Many neuronal pathways transmit pain sensation. For example, pain from peripheral injury reaches the CNS via primary afferent neurons, whose cell bodies form the DRG.
Motor Neurons and Drugs
Skeletal muscle spasticity often results from neuronal, not muscle, deficits. The reflex arc involved in coordinated skeletal muscle action involves several neurons, including interneurons, in the spinal cord. These spinal polysynaptic reflex arcs are depressed by a number of drugs, including barbiturates. However, nonspecific depression of synapses is not desirable because normal muscle function can be disrupted.
Monday, June 14, 2021
Psychosis and Dopamine Pathways
Psychoses are psychogenic mental disorders involving a loss of contact with reality. The most common is schizophrenia, in which perception, thinking, communication, social functioning, and attention are altered. Caused by genetic and environmental factors, it affects approximately 10% of the population. Symptoms are called positive (eg, delusions, hallucinations) or negative (eg, flat affect, apathy); cognitive dysfunction may occur.