Exam 1 Study Guide: Autonomic Nervous System & Endocrine System (KIN 224)

Autonomic Nervous System (ANS)

Somatic vs Autonomic Motor Organization

The somatic and autonomic nervous systems control different types of effectors and use distinct pathways for signal transmission.

• Somatic Nervous System: Voluntary control of skeletal muscle via a single lower motor neuron. The neuron synapses at a neuromuscular junction.

• Autonomic Nervous System: Involuntary control of visceral effectors (smooth muscle, cardiac muscle, glands) via a two-neuron chain: preganglionic and ganglionic (postganglionic) neurons, synapsing at an autonomic ganglion.

• Effector Responses: Somatic responses are rapid and precise; autonomic responses are slower and regulate homeostasis.

Example: Moving your arm (somatic) vs increasing heart rate during stress (autonomic).

Parasympathetic vs Sympathetic Divisions

The ANS is divided into two main branches, each with distinct anatomical and functional characteristics.

• Parasympathetic Division: "Rest-and-digest" activities; craniosacral origin; ganglia located near or within target organs; long preganglionic and short postganglionic axons; local, discrete activation.

• Sympathetic Division: "Fight-or-flight" activities; thoracolumbar origin; ganglia located near the spinal cord; short preganglionic and long postganglionic axons; widespread activation via divergence and adrenal medulla.

Example: Parasympathetic slows heart rate; sympathetic increases heart rate and dilates bronchi.

Sympathetic Pathways and Targets

Sympathetic signals reach effectors through several distinct pathways.

• Spinal Nerve Pathway: Targets body wall and limbs.

• Postganglionic Sympathetic Nerve Pathway: Targets heart and lungs.

• Splanchnic Nerve Pathway: Targets abdominal and pelvic organs.

• Adrenal Medulla Pathway: Direct stimulation of adrenal medulla releases epinephrine and norepinephrine into the bloodstream.

Example: Sympathetic stimulation causes adrenal medulla to release hormones for rapid systemic effects.

Sympathetic Trunk Anatomy

The sympathetic trunk is a chain of ganglia adjacent to the vertebral column, crucial for distributing sympathetic signals.

• Sympathetic Trunk Ganglia: Sites of synapse for sympathetic neurons.

• White Ramus Communicans: Carries preganglionic fibers into the trunk (myelinated).

• Gray Ramus Communicans: Carries postganglionic fibers out to spinal nerves (unmyelinated).

• Intercostal Nerve: Supplies thoracic wall.

• Greater Thoracic Splanchnic Nerve: Supplies abdominal viscera.

• Descending Thoracic Aorta: Major blood vessel in the thorax.

Example: Labeling sympathetic trunk structures on anatomical diagrams is a common exam task.

ANS Neurotransmitters and Receptors

Autonomic neurons use specific neurotransmitters and receptors to communicate with effectors.

• Acetylcholine (ACh): Released by all preganglionic neurons and parasympathetic postganglionic neurons.

• Norepinephrine (NE): Released by most sympathetic postganglionic neurons.

• Cholinergic Neurons: Release ACh; act on nicotinic (ganglia) and muscarinic (effector) receptors.

• Adrenergic Neurons: Release NE; act on adrenergic receptors (alpha and beta types).

Example: Muscarinic receptors mediate parasympathetic effects; adrenergic receptors mediate sympathetic effects.

Autonomic Regulation and Reflexes

The ANS maintains homeostasis through continuous regulation and reflexes.

• Autonomic Tone: Baseline level of activity in autonomic pathways.

• Dual Innervation: Most organs receive both sympathetic and parasympathetic input.

• Sympathetic-Only Targets: Some structures (e.g., blood vessels) are controlled only by sympathetic input.

• Adrenal Medulla Input: Provides rapid, systemic sympathetic effects.

• Autonomic Reflexes: Examples include micturition reflex (urination) and baroreceptor reflex (blood pressure regulation).

Example: Baroreceptor reflex adjusts heart rate in response to blood pressure changes.

Parasympathetic Outflow, Autonomic Plexuses, and Enteric Nervous System (ENS)

Parasympathetic signals originate from specific cranial and sacral regions and interact with autonomic plexuses and the ENS.

• Cranial Parasympathetic Outflow: Originates from cranial nerves III, VII, IX, and X.

• Pelvic Splanchnic Nerves: Provide parasympathetic input to pelvic organs.

• Autonomic Plexuses: Networks of nerves serving organs (e.g., cardiac, pulmonary, celiac plexuses).

• Enteric Nervous System: Controls gastrointestinal function independently of CNS input.

Example: The vagus nerve (cranial nerve X) supplies most parasympathetic innervation to thoracic and abdominal organs.

Endocrine System

Hormone Solubility, Transport, Receptors, and Signaling

Hormones are classified by their solubility, which determines their transport, receptor location, and signaling mechanisms.

• Lipid-Soluble Hormones: Includes steroids and thyroid hormone; transported bound to carrier proteins; receptors are intracellular; often alter gene transcription; effects are longer-lasting.

• Water-Soluble Hormones: Includes most biogenic amines and protein hormones; transported dissolved in plasma; receptors are on cell membranes; use second messenger systems (e.g., cAMP); effects are rapid and short-lived.

Example: Cortisol (lipid-soluble) vs insulin (water-soluble).

Hypothalamus-Pituitary Organization

The hypothalamus and pituitary gland coordinate endocrine control through distinct anatomical and functional relationships.

• Anterior Pituitary (Adenohypophysis): Glandular tissue; controlled by hypothalamic releasing/inhibiting hormones via portal blood; synthesizes and releases hormones (e.g., GH, ACTH, TSH).

• Posterior Pituitary (Neurohypophysis): Neural tissue; contains hypothalamic axons; stores and releases hypothalamic hormones (ADH, oxytocin).

Example: Anterior pituitary releases growth hormone; posterior pituitary releases ADH.

Endocrine Homeostasis

Endocrine glands regulate physiological variables through hormone release and feedback mechanisms.

• Thyroid Hormone: Regulates metabolism; controlled by TSH and negative feedback.

• Cortisol: Regulates stress response; controlled by ACTH and negative feedback.

• Insulin and Glucagon: Regulate blood glucose; insulin lowers, glucagon raises.

• GH/IGF: Growth hormone stimulates IGF release for growth.

• Calcitonin and PTH: Regulate blood calcium; calcitonin lowers, PTH raises.

Example: After eating, insulin is released to lower blood glucose.

Endocrine Cells, Gland Regions, and Hormone Sources

Specific endocrine cells and gland regions produce distinct hormones.

• Thyroid Gland: Follicular cells produce thyroid hormone; parafollicular cells produce calcitonin.

• Parathyroid Gland: Chief cells produce parathyroid hormone (PTH).

• Pancreas: Beta cells produce insulin; alpha cells produce glucagon.

• Adrenal Cortex: Produces corticosteroids (e.g., cortisol, aldosterone).

• Adrenal Medulla: Produces epinephrine and norepinephrine.

• Pineal Gland: Produces melatonin.

Example: Matching gland regions with hormone products is a common exam task.

Endocrine Signaling and Target Cells

Hormones reach target cells via the bloodstream, and only cells with appropriate receptors respond.

• Receptor Specificity: Determines which cells respond to a hormone.

• Endocrine vs Nervous Signaling: Endocrine is slower, longer-lasting, and widespread; nervous is rapid and localized.

Example: Only cells with insulin receptors respond to insulin.

Endocrine Reflex Stimuli

Hormone release is triggered by different types of stimuli.

• Humoral Stimuli: Changes in blood levels of ions or nutrients (e.g., calcium, glucose).

• Hormonal Stimuli: Hormones stimulate release of other hormones (e.g., TSH stimulates thyroid hormone).

• Neural Stimuli: Nerve impulses trigger hormone release (e.g., sympathetic stimulation of adrenal medulla).

Example: Low blood calcium triggers PTH release (humoral stimulus).

Hormone Receptor Regulation and Interactions

Cells can adjust their sensitivity to hormones and hormones can interact in various ways.

• Up-Regulation: Increase in receptor number increases sensitivity.

• Down-Regulation: Decrease in receptor number decreases sensitivity.

• Synergistic Effects: Two hormones amplify each other's effects.

• Permissive Effects: One hormone enables another to act.

• Antagonistic Effects: One hormone opposes the action of another.

Example: Insulin and glucagon have antagonistic effects on blood glucose.

High-Yield Comparison Tables

Somatic vs Autonomic Motor Pathways

Feature	Somatic	Autonomic
Control	Voluntary	Involuntary
Effector	Skeletal muscle	Visceral organs
Pathway	One neuron	Two neurons
Synapse	Neuromuscular junction	Autonomic ganglion

Parasympathetic vs Sympathetic Division

Feature	Parasympathetic	Sympathetic
Origin	Craniosacral	Thoracolumbar
Activity	Rest-and-digest	Fight-or-flight
Axon Lengths	Long pre, short post	Short pre, long post
Activation	Local	Widespread

Lipid-Soluble vs Water-Soluble Hormones

Feature	Lipid-Soluble	Water-Soluble
Examples	Steroids, thyroid hormone	Biogenic amines, proteins
Transport	Carrier-bound	Dissolved in plasma
Receptor Location	Intracellular	Membrane
Signaling	Gene transcription	Second messenger

Anterior vs Posterior Pituitary

Feature	Anterior	Posterior
Tissue Type	Glandular	Neural
Control	Hypothalamic hormones via portal blood	Hypothalamic axons
Hormone Origin	Synthesized in pituitary	Synthesized in hypothalamus
Hormone Storage	Minimal	Stores ADH, oxytocin

Insulin vs Glucagon

Feature	Insulin	Glucagon
Effect	Lowers blood glucose	Raises blood glucose
Mechanism	Promotes uptake/storage	Stimulates breakdown/release

Sample Equations

Second Messenger Pathway (cAMP)

Water-soluble hormones often use second messenger systems:

$\text{Hormone} + \text{Receptor} \rightarrow \text{G-protein activation} \rightarrow \text{Adenylate cyclase} \rightarrow \text{cAMP production} \rightarrow \text{Protein kinase activation}$

Negative Feedback Example (Endocrine Axis)

Endocrine axes often use negative feedback:

$\text{Hypothalamus} \xrightarrow{TRH} \text{Anterior Pituitary} \xrightarrow{TSH} \text{Thyroid} \xrightarrow{T_3, T_4} \text{Target Cells}$

High levels of $T_3$ and $T_4$ inhibit TRH and TSH release.

Study Strategies

• Actively recall, sort, match, trace, label, and predict concepts.

• Build and practice comparison tables for paired concepts.

• Trace major pathways and axes aloud or on paper.

• Practice labeling anatomical diagrams, especially sympathetic trunk structures.

• Use the question pattern: What changed? What responds? What pathway or hormone is involved? What happens next? Does feedback occur?

Final Self-Check

• Chapter 15: Can you compare somatic and autonomic motor pathways, trace sympathetic routes, identify ANS neurotransmitters/receptors, explain autonomic tone, distinguish autonomic from somatic reflexes, and label sympathetic trunk structures?

• Chapter 17: Can you classify hormone solubility/signaling, distinguish humoral, hormonal, and neural stimuli, compare anterior and posterior pituitary, match endocrine cells with hormones, and trace thyroid, cortisol, insulin, glucagon, GH/IGF, calcitonin, and PTH regulation?