Atomic Anesthesia

Atomic Anesthesia: Overview

  • Module: Atomic Anesthesia

  • Lesson: 1

Introduction to Atomic Anesthesia

  • Goal: To simplify complex science topics for aspiring CRNAs (Certified Registered Nurse Anesthetists) and current Nurse Anesthesia Residents.

    • Mission: To help students build a solid foundation of the sciences through innovative learning experiences.

    • Method: Creation of bite-sized, easy-to-understand content that promotes 'light-bulb' and 'ah-ha' moments.

    • Commitment: To guide future CRNAs through their graduate schooling effectively.

Overview of the Autonomic Nervous System (ANS)

  • Definition: A component of the peripheral nervous system regulating involuntary physiological processes.

    • Functions include:

    • Heart rate

    • Blood pressure

    • Respiration

    • Digestion

    • Sexual arousal.

  • Divisions of the ANS:

    • Sympathetic Nervous System (SNS)

    • Parasympathetic Nervous System (PNS)

    • Enteric Nervous System

Structure of the Nervous System

1. Central Nervous System (CNS) vs. Peripheral Nervous System (PNS)

  • CNS: Comprises the brain and spinal cord.

  • PNS: Includes cranial (I-XII) and spinal nerves (31 pairs).

    • Pathways:

    • Afferent Pathways (ascending; sensory to spinal column)

    • Efferent Pathways (descending; innervates effector organs).

2. The Autonomic vs. Somatic Nervous System

  • Somatic Nervous System: Regulates voluntary motor control of skeletal muscle.

  • Autonomic Nervous System: Regulates the body’s internal environment through involuntary control of organ systems.

Neuronal Structure of the Autonomic Nervous System

  • Neurons: Autonomic neurons typically utilize two neurons in a pathway:

    • Preganglionic Neuron: Connects to a ganglion.

    • Postganglionic Neuron: Extends from the ganglion to the target organ.

    • Exception: The adrenal medulla is only innervated by a preganglionic fiber.

  • Nicotinic Receptors: Found in ganglia of both SNS and PNS activated by acetylcholine (Ach).

Synapses in the Nervous System

1. Definition of Synapse

  • Synapse: A junction where a nerve cell transmits signals to another neuron or to target cells. There is a gap (synaptic cleft) where neurotransmitters are released.

2. Types of Synapses

  • Axodendritic: Connection between axon and dendrite of two neurons.

  • Axosomatic: Connection between axon and the soma (cell body) of two neurons.

  • Neuromuscular: Motor neuron to muscle fiber.

  • Neuroglandular: Neuron to gland cell, affecting glandular secretions.

Sympathetic Nervous System (SNS)

1. Overview

  • Nickname: "Fight or Flight" system.

  • Function: Prepares the body for action in response to stress or danger.

  • Effects:

    • Increases heart rate.

    • Dilates pupils.

    • Redirects blood flow to muscles.

    • Inhibits digestion and non-essential functions.

2. Fiber Lengths

  • Characteristics:

    • Short preganglionic fibers and long postganglionic fibers.

    • Receptors:

    • At ganglia: Nicotinic.

    • At organ: Alpha or Beta adrenergic receptors.

  • Exceptions:

    • The adrenal medulla contains only a preganglionic fiber modified into chromaffin cells.

    • Sweat glands have muscarinic receptors.

3. Effects on Specific Organs

  • Case Studies:

    • Eye: Pupil dilation (mydriasis) & far vision.

    • Stomach & Intestines: Decreased motility & slow digestion.

    • Glands: Reduced secretion from salivary & digestive glands.

    • Kidneys: Increased renin secretion.

    • Heart: Increased heart rate and contractility (increased CO).

    • Bladder: Decreased urination.

    • Lungs: Bronchodilation.

    • Gonads: Orgasm & ejaculation.

4. Ganglia of the Sympathetic Nervous System

  • Types:

    • Paravertebral Ganglia: Closer to spinal cord, involved in signal transmission for SNS.

    • Prevertebral Ganglia: Located in the abdomen (including celiac, superior mesenteric, and inferior mesenteric ganglia).

5. Receptors and Neurotransmitters

  • Primary neurotransmitter: Norepinephrine.

  • Types of adrenergic receptors:

    • Alpha-1

    • Alpha-2

    • Beta-1

    • Beta-2.

  • Function: Increases heart rate and contracts the cardiac muscle, altering blood vessel diameter.

Adrenal Glands

  • Location: Sits atop the kidneys.

  • Divisions: Composed of adrenal cortex and adrenal medulla.

  • Key Function: Releases epinephrine and norepinephrine (80/20 ratio) into the bloodstream, contributing to the immediate stress response.

Parasympathetic Nervous System (PNS)

1. Overview

  • Nickname: "Rest and Digest" system.

  • Function: Counteracts sympathetic effects, promoting relaxation and digestion.

  • Effects:

    • Slows heart rate.

    • Constricts pupils.

    • Aids in digestion through increased motility.

2. Fiber Lengths

  • Characteristics: Long preganglionic and short postganglionic fibers.

  • Receptors:

    • At ganglia: Nicotinic.

    • At organ: Muscarinic receptors.

    • Postganglionic fibers often found in the end organ itself, with the vagus nerve as the primary innervator for many organs (75% of innervation).

3. Parasympathetic Ganglia

  • Location: Closer to or within the organs they innervate, consisting of the following ganglia:

    • Ciliary Ganglion (CN III)

    • Pterygopalatine Ganglion (CN VII)

    • Submandibular Ganglion (CN VII)

    • Otic Ganglion (CN IX).

4. Effects on Specific Organs

  • Case Studies:

    • Eye: Pupil constriction (miosis) & near vision.

    • Stomach & Intestines: Increased motility and promotion of digestion & defecation.

    • Glands: Increased secretion from salivary & digestive glands.

    • Tear Ducts: Increased tear production (lacrimation).

    • Heart: Decreased heart rate and contractility (decreased CO).

    • Bladder: Increased urination.

    • Lungs: Bronchoconstriction and increased secretions.

    • Gonads: Arousal & erection.

5. Receptors and Neurotransmitters

  • Main neurotransmitter: Acetylcholine (ACh).

  • Types of cholinergic receptors:

    • Muscarinic (M1-M5): G-protein coupled receptors.

    • Nicotinic (Nm/N1, Nn/N2): Ligand-gated ion channels.

Pharmacological Implications

1. Key Drugs and Their Functions

  • Epinephrine, Norepinephrine & Dopamine: Activate adrenergic receptors in the SNS to enhance heart rate and contractility.

  • Beta Blockers: Inhibit adrenergic receptors causing dominance of the PANS, decreasing heart rate and contractility.

  • Acetylcholinesterase Inhibitors (such as Neostigmine): Block breakdown of ACh, increasing its presence and activity on cholinergic receptors of the PANS leading to decreased heart rate.

  • Antimuscarinics (such as Atropine and Glycopyrrolate): Block muscarinic receptors in the PANS, allowing increased heart rate and contractility through SANS activation.

  • Dual Innervation: The heart receives inputs from both SNS and PNS; their pharmacological modulation greatly affects cardiac function.

    • Homeostasis Maintenance: Both divisions work to maintain bodily homeostasis through oppositional balance.

Conclusion

  • The autonomic nervous system regulates involuntary bodily functions and consists of:

    • Sympathetic Division: Activates "fight or flight" responses with adrenergic receptors and neurotransmitters such as epinephrine and norepinephrine.

    • Parasympathetic Division: Facilitates "rest and digest" activities using cholinergic receptors and acetylcholine as a neurotransmitter.

Thank you! Let us know if you have questions or need clarifications.