Autonomic Pharmacology (Ar) - Lec 01 Part 1 - Review of physiology

Summary

This video provides a concise review of the principles of physiology of the autonomic nervous system (ANS), essential for understanding pharmacology. The ANS regulates involuntary functions and consists of the sympathetic and parasympathetic systems. The video covers the roles of higher centers, nerves, chemical transmitters, and receptors in both systems. It explains how autonomic nerves transmit signals, the significance of ganglia, the fate of neurotransmitters like acetylcholine, and the impact of various receptors on internal organs. The importance of drug selectivity and the implications of enzyme deficiencies are also discussed to aid in comprehending autonomic malfunction treatments.

Takeaways

• 😀 The autonomic nervous system (ANS) regulates involuntary functions such as those of the intestines, lungs, and heart.
• 😀 The ANS is divided into the sympathetic and parasympathetic systems, each with higher centers, nerves, chemical transmitters, and receptors.
• 😀 Higher centers in the brain and spinal cord control autonomic functions, sending signals via nerves to internal organs.
• 😀 Autonomic nerves rely on ganglia, which act as relay stations; sympathetic ganglia are near the spinal cord, while parasympathetic ganglia are near organs.
• 😀 Most internal organs have dual nerve supply from both sympathetic and parasympathetic systems, but the ratio of nerve supply can vary.
• 😀 Nerve signals in the ANS are transmitted by chemical neurotransmitters; acetylcholine is released in both systems at ganglia, while norepinephrine is released at sympathetic nerve endings.
• 😀 Receptors for neurotransmitters include nicotinic acetylcholine receptors in ganglia and muscarinic or adrenergic receptors at nerve terminals on organs.
• 😀 Drugs can target different levels of the ANS: higher centers, ganglia, nerve endings, and receptors, with receptor-level targeting being the most selective.
• 😀 Acetylcholine is broken down by cholinesterase enzymes; true cholinesterase is specific to acetylcholine, while pseudocholinesterase (butyrylcholinesterase) breaks down multiple substances.
• 😀 Deficiencies in pseudocholinesterase can lead to severe reactions to drugs like succinylcholine, used as a muscle relaxant during surgeries, resulting in prolonged muscle paralysis.

Q & A

What is the primary focus of the video series on pharmacology?

The primary focus of the video series is a quick revision on the principles of physiology of the autonomic nervous system, which is necessary for understanding the mechanism of action of drugs in this chapter.

What are the two divisions of the autonomic nervous system?

The two divisions of the autonomic nervous system are the sympathetic and parasympathetic systems.

What are the four elements discussed in relation to each system in the autonomic nervous system?

The four elements discussed are higher centers, nerves, chemical transmitters, and receptors.

What role do higher centers play in the autonomic nervous system?

Higher centers control all autonomic or visceral functions of the body and can be targeted by drugs to control the autonomic nervous system.

How do autonomic nerves differ from motor nerves in terms of their travel distance?

Autonomic nerves do not travel the whole distance as one segment. They first rely on a station called a ganglion, which regulates the strength of signals before reaching internal organs.

What is the main difference between the ganglia of the parasympathetic and sympathetic systems?

Parasympathetic ganglia are situated near the organs, while sympathetic ganglia are found very far from the organs and close to the spinal cord.

What neurotransmitter is released in both parasympathetic and sympathetic ganglia?

Acetylcholine is the neurotransmitter released in both parasympathetic and sympathetic ganglia.

What type of receptors does acetylcholine act on in ganglia?

Acetylcholine acts on nicotinic acetylcholine receptors in ganglia.

What are the main adrenergic receptors in the sympathetic system?

The main adrenergic receptors in the sympathetic system are alpha-1, alpha-2, beta-1, beta-2, and beta-3 receptors.

Why are ganglion blockers no longer used in controlling the autonomic nervous system?

Ganglion blockers are no longer used because they are non-selective and affect both sympathetic and parasympathetic ganglia, leading to depression of all autonomic functions throughout the body.

How can we selectively control the autonomic nervous system at the level of receptors?

We can selectively control the autonomic nervous system at the level of receptors by using drugs that target specific receptor subtypes, such as beta-1 blockers or alpha-1 blockers.

What happens to acetylcholine after it performs its function on the receptor?

After performing its function on the receptor, acetylcholine must be broken down immediately by choline esterase enzymes to prevent continuous stimulation.

What are the two types of choline esterase enzymes, and what are their roles?

The two types of choline esterase enzymes are true choline esterase (acetylcholine esterase), which specifically breaks down acetylcholine, and pseudocholine esterase (butyrylcholinesterase), which is non-specific and breaks down various choline esters, including some drugs.

What potential problem can arise in patients with pseudocholine esterase deficiency during surgery?

Patients with pseudocholine esterase deficiency can experience prolonged muscle paralysis and respiratory inhibition if given succinylcholine, a muscle relaxant, because the enzyme responsible for breaking down the drug is deficient.