APHY 201 Chapter 9 Autonomic Nervous System

What are the control centers of the autonomic system?

Brain and spinal cord

What do autonomic neurons do?

They receive sensory input and control involuntary motor neurons that affect the heart, smooth muscle, and glands

What is the role of interneurons in the ANS?

They process sensory info and help direct the right response to keep balance in the body

How many neurons connect the CNS to skeletal muscle in the somatic system?

One neuron from spinal cord to skeletal muscle

How many neurons connect the CNS to an effector in the autonomic system?

Two neurons: preganglionic and postganglionic

Where do preganglionic neurons start and end?

Start in brain or spinal cord, synapse in autonomic ganglion

Where do postganglionic neurons start and end?

Start in ganglion, synapse on target organ

Where are autonomic ganglia located?

Head, neck, abdomen, and chains along each side of spinal cord

Where can preganglionic neurons originate from?

Midbrain, hindbrain, thoracic, lumbar, and sacral spinal cord

What happens to visceral organs if nerves are cut?

They don't waste away; they still work on their own

What do smooth muscles maintain without nerves?

A resting tone; they become more sensitive if nerves are cut (denervation hypersensitivity)

Which muscles can contract without nerves?

Cardiac muscle and some smooth muscle, though ANS can speed or slow them

Can autonomic neurons excite and inhibit?

Yes, they can either stimulate or slow down depending on the organ and receptor

What neurotransmitter do somatic motor neurons release?

Acetylcholine (ACh), always excitatory

What neurotransmitters do autonomic neurons release?

Mainly acetylcholine and norepinephrine; effects can be excitatory or inhibitory

What are the effector organs of the somatic system?

Skeletal muscles

What are the effector organs of the autonomic system?

Cardiac muscle, smooth muscle, and glands

Do somatic motor neurons use ganglia?

No, they go straight from spinal cord to muscle

Do autonomic motor neurons use ganglia?

Yes, postganglionic neurons are in paravertebral, prevertebral, or terminal ganglia

What kind of junction do somatic neurons use?

A specialized motor end plate

What kind of junction do autonomic neurons use?

No special end plate; receptors spread all over smooth muscle cells

What is the effect of a nerve impulse in the somatic system?

Always excitatory, muscle contracts

What is the effect of a nerve impulse in the autonomic system?

Either excitatory or inhibitory, depending on receptors

What kind of nerve fibers are in the somatic system?

Fast, thick, heavily myelinated fibers

What kind of nerve fibers are in the autonomic system?

Preganglionic are thin and lightly myelinated; postganglionic are very thin and unmyelinated

What happens to skeletal muscle if nerves are cut?

Paralysis and atrophy

What happens to smooth or cardiac muscle if nerves are cut?

Muscle tone and function continue; they become more sensitive to stimulation

Where do sympathetic preganglionic neurons come from?

Thoracic and lumbar spinal cord (thoracolumbar division)

Where do sympathetic preganglionic neurons synapse?

In paravertebral ganglia along the spinal cord (sympathetic chain)

What are white rami communicantes?

Myelinated preganglionic fibers that branch off spinal nerves and enter sympathetic chain

What are gray rami communicantes?

Unmyelinated postganglionic fibers that rejoin spinal nerves

How are sympathetic axons distributed?

They travel with spinal nerves to skin and muscles, innervating blood vessels and glands

What is sympathetic divergence?

One preganglionic neuron synapses with many postganglionic neurons at different levels

What is sympathetic convergence?

Many preganglionic neurons synapse on one postganglionic neuron

What does mass activation in the sympathetic system allow?

Unified "fight or flight" response and tonic activity

What are collateral ganglia?

Ganglia outside the sympathetic chain where splanchnic nerves synapse

What are examples of collateral ganglia?

Celiac, superior mesenteric, and inferior mesenteric ganglia

What do collateral ganglia innervate?

Digestive, urinary, and reproductive organs

What does the adrenal cortex secrete?

Steroid hormones

What does the adrenal medulla secrete?

Epinephrine and norepinephrine during mass activation

What is the adrenal medulla embryologically?

A modified sympathetic ganglion innervated by preganglionic neurons

Where do parasympathetic preganglionic neurons come from?

Brain (cranial) and sacral spinal cord (S2-S4)

What is the parasympathetic division also called?

Craniosacral division

Where do parasympathetic preganglionic neurons synapse?

In terminal ganglia located near or inside effector organs

What is unique about parasympathetic postganglionic neurons?

They are very short because terminal ganglia are near or inside effectors

Which cranial nerves carry parasympathetic fibers?

Oculomotor (III), Facial (VII), Glossopharyngeal (IX), Vagus (X)

What does the oculomotor nerve (III) control parasympathetically?

Ciliary ganglion → ciliary muscle in the eye

What does the facial nerve (VII) control parasympathetically?

Pterygopalatine ganglion → nasal mucosa, pharynx, palate, lacrimal glands; Submandibular ganglion → salivary glands

What does the glossopharyngeal nerve (IX) control parasympathetically?

Otic ganglion → parotid salivary gland

What does the vagus nerve (X) control parasympathetically?

Terminal ganglia in heart, lungs, esophagus, stomach, pancreas, liver, intestines

What do sacral parasympathetic nerves control?

Lower intestine, rectum, bladder, and reproductive organs (S2-S4)

What is the sympathetic division's main function?

Activates "fight or flight" with norepinephrine and epinephrine

What changes occur during sympathetic activation?

Increased heart rate, higher blood sugar, blood flow diverted to muscles

Does the sympathetic system also act tonically?

Yes, it constantly regulates heart, vessels, and organs

What is the parasympathetic division's main function?

Rest and digest; opposite of sympathetic

What effects occur during parasympathetic activation?

Slows heart rate and increases digestion

Which neurotransmitter is used by all preganglionic neurons?

Acetylcholine (ACh)

Which neurotransmitter is released by most parasympathetic postganglionic neurons?

Acetylcholine (ACh)

Which sympathetic postganglionic neurons release ACh?

Those that go to sweat glands and skeletal muscle blood vessels

What are cholinergic synapses?

Synapses where ACh is the neurotransmitter

What neurotransmitter is released by most sympathetic postganglionic neurons?

Norepinephrine (NE)

What are adrenergic synapses?

Synapses where norepinephrine is the neurotransmitter

What do sympathomimetic drugs do?

Act like sympathetic stimulation

What are catecholamines?

Adrenergic neurotransmitters such as norepinephrine and epinephrine

What are varicosities in autonomic neurons?

Swelling along axons that release neurotransmitters over a wide area

What is a "synapse en passant"?

Neurotransmitter release from varicosities "in passing" along the axon

Do sympathetic and parasympathetic neurons innervate the same tissues?

Yes, often, but usually with opposite effects

What are the two types of adrenergic receptors?

Alpha (α1, α2) and Beta (β1, β2, β3)

What do beta receptors use as a second messenger?

cAMP

What do alpha receptors use as a second messenger?

Ca²⁺ system

Which receptors are more sensitive to norepinephrine?

Alpha receptors

Which receptors are more sensitive to blood epinephrine?

Beta receptors

Where are α2 receptors located and what do they do?

On presynaptic axons; inhibit norepinephrine release (negative feedback)

What can α2 receptor drugs do?

Lower blood pressure by reducing sympathetic activity

Where are β3 receptors located and what do they do?

In adipose tissue; promote fat breakdown and heat production

What does adrenergic stimulation of the heart do?

Increases heart rate and contraction (β1)

What does adrenergic stimulation of the lungs do?

Causes bronchodilation (β2)

What does adrenergic stimulation of blood vessels do?

Constriction (α1) or dilation (β2 depending on location and hormone influence)

What do adrenergic agonist drugs do?

Mimic neurotransmitter action (stimulate receptors)

What do adrenergic antagonist drugs do?

Block neurotransmitter action (block receptors)

What effect does ACh from preganglionic neurons have?

Always stimulatory

What effect does ACh from parasympathetic postganglionic neurons have?

Usually stimulatory, sometimes inhibitory depending on receptor

What are nicotinic receptors?

Receptors in autonomic ganglia; stimulated by ACh; ligand-gated ion channels; blocked by curare

What are muscarinic receptors?

Receptors in visceral organs; stimulated by ACh; can excite or inhibit; use G-proteins; blocked by atropine

What are organs with dual innervation?

Most organs receive both sympathetic and parasympathetic input

What are antagonistic dual effects?

Sympathetic raises heart rate, parasympathetic lowers it; sympathetic slows digestion, parasympathetic increases it; sympathetic dilates pupils, parasympathetic constricts them

What are complementary dual effects?

Both divisions produce similar effects, like salivary glands (sympathetic makes thicker saliva, parasympathetic makes watery saliva)

What are cooperative dual effects?

Both divisions produce different effects that work together, like parasympathetic causes erection and sympathetic causes ejaculation

What organs have only sympathetic innervation?

Adrenal medulla, arrector pili muscles, sweat glands, most blood vessels

Why is sympathetic-only innervation important?

Allows control of temperature through blood flow and sweating

What brain region controls many autonomic reflexes?

Medulla oblongata

What higher brain region is the main ANS control center?

Hypothalamus (controls temperature, hunger, thirst, pituitary)

What limbic system role affects ANS?

Emotional states can trigger ANS responses (blushing, fainting, sweating, racing heart)

What does the cerebellum control in ANS?

Motion sickness responses like nausea, sweating, cardiovascular changes

How do the frontal and temporal lobes affect ANS?

Through emotion and personality influence

What is autonomic dysreflexia?

A dangerous condition after spinal cord injury above T6 that can cause stroke, heart attack, or pulmonary edema

What is spinal shock?

Temporary loss of reflexes after spinal cord injury; reflexes later return exaggerated

How does aging affect the ANS?

Increases sympathetic tone, raising risk of hypertension and cardiovascular disease