Autonomic Nervous System Overview

Autonomic Nervous System: Neurotransmitters & Receptors

• Acetylcholine is a parasympathomimetic neurotransmitter, meaning it mimics the effects of the parasympathetic nervous system.
• Atropine is a parasympatholytic drug, blocking the actions of acetylcholine at muscarinic receptors.
• Aminazaine is not a parasympathomimetic.

Sympathetic Nervous System

• Adrenaline and noradrenaline are sympathomimetic neurotransmitters, stimulating the sympathetic nervous system.
• Sympathetic stimulation leads to pupil dilation, increased heart rate, and blood pressure, as well as bronchodilation.
• Insulin secretion is inhibited by sympathetic stimulation.

Neuronal Axon Types

• Preganglionic neurons of the autonomic nervous system have myelinated axons classified as type A fibers.
• Postganglionic neurons have unmyelinated axons classified as type C fibers.

Ion Channels & Synapse Transmission

• Chemically-dependent ion channels are responsible for the transmission of nerve impulses across synapses. These include sodium, calcium, potassium, and chloride channels.
• Sympathetic ganglia use nicotinic receptors for neurotransmission, with acetylcholine as the primary neurotransmitter.
• Acetylcholine binds to muscarinic receptors in parasympathetic effector organs.

Hormonal Regulation of Metabolism

• Insulin, glucagon, and thyroxine are involved in the regulation of carbohydrate metabolism, while intermedin plays a role in skin pigmentation.
• Hypothalamic thermoregulation centers control body temperature via heat production and dissipation mechanisms.
• Cortisol, thyroid hormones, and growth hormone are involved in fat metabolism, while parathyroid glands play a role in calcium and phosphate balance.
• Parathyroid hormone increases blood calcium levels by stimulating osteoclasts and decreasing calcium excretion by the kidneys.
• Vitamin D3 also increases calcium absorption in the intestines.

Effects of Hormonal Imbalances

• Basedow's disease (hyperthyroidism) is characterized by increased heart rate, thermogenesis, appetite, and oxygen consumption. The patient may show weight loss despite increased appetite.

Neurotransmitter Effects

• Norepinephrine and epinephrine can constrict the pupil by stimulating the radial muscles of the iris.
• Acetylcholine acts on the circular muscles of the iris, causing pupil constriction (miosis).
• Atropine, by blocking muscarinic receptors, would dilate the pupil.

Insulin & Glucose Metabolism

• Insulin is secreted in response to increased blood glucose levels, promoting glucose uptake and utilization by cells.
• Insulin secretion can be stimulated by various factors including beta-adrenergic stimulation and leptin.
• Gluconeogenesis, the production of glucose from non-carbohydrate sources, occurs in the liver and is stimulated by glucagon and cortisol.
• Glycogenesis, the synthesis of glycogen, is activated when cellular ATP levels are high, typically after carbohydrate intake.
• Glycogenolysis, the breakdown of glycogen, is stimulated by glucagon and epinephrine.

Impacts of Hormonal Disorders

• Diabetes mellitus type 1 is characterized by insulin deficiency, leading to hyperglycemia, osmotic diuresis, increased lipolysis, and ketone body formation.
• Cortisol increases protein breakdown, while insulin promotes protein synthesis.

Effects of Sympathetic & Parasympathetic Stimulation

• Sympathetic stimulation increases heart rate and force of contraction (positive inotropic and chronotropic effects) while parasympathetic stimulation has the opposite effect (decreases heart rate).
• Sympathetic stimulation also increases oxygen consumption by the body.
• Parasympathetic stimulation promotes energy storage and conservation.

Effects of Other Hormones

• Somatomedin C, also known as IGF-1, has insulin-like effects and is stimulated by growth hormone (GH).
• Oxytocin, released from the posterior pituitary, stimulates uterine contractions during labor and milk ejection during breastfeeding.
• ADH (vasopressin), also from the posterior pituitary, increases water reabsorption in the kidneys, leading to concentrated urine and decreased diuresis.

Summary of Important Hormones & Their Effects

• Insulin: lowers blood glucose, promotes glucose uptake and utilization, stimulates protein synthesis, inhibits lipolysis
• Glucagon: raises blood glucose, stimulates glycogenolysis, promotes gluconeogenesis
• Cortisol: increases blood glucose, stimulates gluconeogenesis, inhibits glucose uptake by cells, increases protein breakdown, influences immune function
• Growth hormone (GH): stimulates protein synthesis, promotes growth, increases lipolysis, decreases glucose uptake
• Thyroid hormones (T3 & T4): regulate metabolism, increase oxygen consumption, increase heart rate, promote growth and development
• Parathyroid hormone (PTH): increases blood calcium levels, stimulates osteoclast activity, decreases calcium excretion by the kidneys
• Vitamin D3: increases calcium absorption in the intestines, regulates bone metabolism
• Aldosterone: regulates electrolyte balance, increases sodium reabsorption in the kidneys
• ADH (vasopressin): increases water reabsorption in the kidneys, regulates blood pressure
• Oxytocin: stimulates uterine contractions and milk ejection

These study notes highlight key concepts related to the autonomic nervous system, neurotransmitters, receptors, and hormonal regulation of physiological processes. You should now have a good foundation for deeper study in this area!

This quiz explores the key components of the autonomic nervous system, focusing on neurotransmitters like acetylcholine and their receptors. It also examines the sympathetic and parasympathetic systems, as well as the types of neuronal axons involved. Test your knowledge on these fundamental concepts of neurobiology!