Autonomic Nervous System Overview and Functionality

Somatic Reflexes: Involves skeletal muscle and is distinct from the autonomic functions being discussed.
The focus will be on the autonomic nervous system (ANS), which operates involuntarily.

Nervous System Components: - Autonomic Nervous System (ANS): functions automatically, without conscious control. - Contains two neurons: preganglionic and postganglionic. - Activates visceral effectors (organs).
Visceral Definition: Relates to internal organs (guts).

Receptor Feedback Loop: - Sensory receptors send information to the Central Nervous System (CNS). - The CNS sends output through the motor branch of the Peripheral Nervous System (PNS). - Output signal leads to an effect that aims to restore homeostasis.

Somatic vs. Autonomic: - Image shows differences based on neuron specifics and connections. - Somatic Nervous System: - Motor neuron body within the CNS, shorter pathway to effectors. - Autonomic Nervous System: - Divided into sympathetic and parasympathetic divisions. - Preganglionic and postganglionic arrangements differ: - Sympathetic Division: Longer preganglionic axon. - Parasympathetic Division: Longer preganglionic neuron, extends close to the effector.

Adrenal Glands: Functions in conjunction with sympathetic nervous system. - Comprised of outer cortex and inner medulla. - Some preganglionic fibers synapse directly in the adrenal medulla, triggering hormone release. - Hormones secreted respond quickly to stress - adrenaline (epinephrine) and norepinephrine.

Preganglionic Neurons: - Release Acetylcholine (ACh) in both divisions (somatic and parasympathetic).
- Activates nicotinic receptors on postganglionic neurons.
Postganglionic Neurons: - Parasympathetic: Releases ACh, acting on muscarinic receptors. - Sympathetic: Primarily releases norepinephrine (NE) to act on adrenergic receptors.

Cholinergic Receptors: Respond to ACh. - Nicotinic Receptors: Always excitatory. - Muscarinic Receptors: Can be excitatory or inhibitory (depends on specific subtype).
Adrenergic Receptors: Respond to NE and epinephrine. - Subtypes include alpha and beta receptors.

Agonist: Binds and stimulates a receptor.
Antagonist: Binds and inhibits a receptor, making it less likely to activate. - Some drugs enhance neurotransmitter action by inhibiting breakdown (e.g., MAOIs).
Examples of Drug Effects: - Atropine: Blocks muscarinic receptors, inhibiting parasympathetic effects. - Beta Blockers: Prevent heart stimulation, reducing heart rate and blood pressure.

Parasympathetic Actions (Rest-and-Digest): - Includes processes like salivation, lacrimation, urination, digestion, and defecation. - Sometimes referred to as Feed and Breed mechanisms.
Sympathetic Actions (Fight or Flight): - Mobilizes energy resources; increases heart rate and blood flow to muscles for immediate energy.
Hypothalamus: Controls autonomic functions, processing inputs related to emotions and stress response.

Certain structures innervated exclusively by one division: - Sympathetic Only: Sweat glands, adrenal medulla, blood vessels. - Parasympathetic Only: Certain functions in the genitalia, vasodilation, digestive processes.

Responses to temperature changes include: - Increased Temperature: Dilation of blood vessels, promoting heat loss. - Decreased Temperature: Constriction of blood vessels to maintain core temperature.

Understanding the differences between the sympathetic and parasympathetic divisions is critical for grasping how the autonomic nervous system regulates bodily functions.
Familiarity with neurotransmitters, receptors, and actions can aid in predicting drug effects and bodily responses under various conditions.