Chapter 16

What does the stimulation of beta receptors trigger?

Changes in the metabolic activity of the target cell. These changes occur indirectly, as each beta receptor is a G protein whose stimulation results in an increase in intracellular cAMP.

What percentage of axons in each spinal nerve are sympathetic postganglionic fibers?

8 percent

What happens when the medial and lateral pathways are stimulated during sympathetic activation?

A general elevation in muscle tone causes the person to look tense and they may begin to shiver

What does an increase in sympathetic activity generally stimulate?

It stimulates tissue metabolism and increases alertness

In general when is the sympathetic division activated?

Only during periods of exertion, stress, or emergency, and the parasympathetic division predominates under resting conditions

What percentage of secretory output does epinephrine (adrenaline) account for?

75-80%

What is the general functional pattern of collateral ganglia?

1. A reduction of blood flow and energy use by organs that are not important to short-term survival (such as the digestive tract) 2. The release of stored energy reserves

What is the overall pattern of responses to increased levels of parasympathetic activity?

1. Decreased metabolic rate 2. Decreased heart rate and blood pressure 3. Increased secretion by salivary glands and digestive glands 4. Increased motility and blood flow in the digestive tract 5. Stimulation of urination and defecation

What is the general pattern of responses to increased levels of sympathetic activity?

1. Heightened mental alertness 2. Increased metabolic rate 3. Reduced digestive and urinary functions 4. Activation of energy reserves 5. Increased respiratory rate and dilation of respiratory passageways 6. Increased heart rate and blood pressure 7. Activation of sweat glands

Why do the effects of NE or E released by the adrenal medullae last even longer?

1. The bloodstream does not contain MAO or COMT 2. Most tissues contain relatively low concentrations of those enzymes

Do the subdivisions of the ANS work together?

1. They may work independently with some structures innervated by only one division or the other 2. The two divisions may work together, each controlling one stage of a complex process

How many neurons does the ENS have?

100 million

How many ganglia does each sympathetic chain contain?

3 cervical, 10-12 thoracic, 4-5 lumbar, and 4-5 sacral

What happens when alpha-2 receptors are stimulated?

A lowering of cyclic-AMP levels in the cytoplasm. This reduction generally has an inhibitory effect on the cell. The presence of alpha-2 receptors in the parasympathetic division helps coordinate sympathetic and parasympathetic activities. When the sympathetic division is active, the NE released binds to parasympathetic neuromuscular and neuroglandular junctions and inhibits their activity

What is the adrenal medulla?

A modified sympathetic ganglion where preganglionic fibers synapse on neuroendocrine cells

What is a varicosity?

A swollen segment of each branch that is packed with neurotransmitter vesicles

What does the stimulation of alpha receptors do?

Activates enzymes on the inside of the cell membrane

Where do chains of varicosities pass?

Along or near the surfaces of the effector cells

What are the two classes of sympathetic receptors?

Alpha and Beta

What does generalized sympathetic activation and the release of E by the adrenal medulla affect?

Alpha and beta receptors throughout the body

What does localized sympathetic activity involving the release of NE at varicosities primarily affect?

Alpha receptors located near the active varicosities

What type of receptor does NE stimulate to a greater degree?

Alpha, but E stimulates both classes of receptors

What is the more common type of alpha receptor?

Alpha-1

What is the enteric nervous system?

An extensive network of neurons and nerve networks located in the walls of the digestive tract

What is cyclic-amp?

An important second messenger that can activate or inactivate key enzymes.

Where are collateral ganglia located?

Anterior to the vertebral bodies

Where are postganglionic fibers of the sympathetic division not long?

At the adrenal medullae

Why are preganglionic fibers in the sympathetic division relatively short?

Because the ganglia are located relatively near the spinal cord

Where are the preganglionic neurons of the sympathetic division located?

Between segments T1 and L2 of the spinal cord and ganglionic neurons that are located in the ganglia near the vertebral column

What does the enzyme catechol-O-methyltransferase do?

Breaks down the rest of the NE not broken down by MAO

How does the sympathetic division change the activities of tissues and organs?

By releasing NE at peripheral synapses and distributing E and NE throughout the body in the bloodstream

What do collateral ganglionic neurons do?

Contain ganglionic neurons that innervate tissues and organs in the abdominopelvic cavity

What happens after fibers pass through the intervertebral foramen?

Each ventral root gives rise to a myelinated white ramus, which carries myelinated preganglionic fibers into a nearby sympathetic chain ganglion.

What happens when there is increased activity in the cardiovascular and respiratory centers of the pons and medulla oblongata when sympathetic activation occurs?

Elevated blood pressure, heart rate, breathing rate, and depth of respiration

What do the neuroendocrine cells of the adrenal medullae secrete?

Epinephrine and norepinephrine

What does the sympathetic division prepare the body for?

Heightened levels of somatic activity

What is an example of motor commands triggered by visceral sensory information controlling the activities of target organs?

In cold weather the ANS stimulates the arrector pili muscles and gives you "goosebumps"

Where do preganglionic fibers from the thoracic and superior lumbar segments of the spinal cord synapse in the sympathetic division?

In ganglia of the spinal cord

Where do preganglionic fibers synapse in the parasympathetic division?

In ganglia very close to (or within) the target organs

Where do preganglionic fibers originate in the parasympathetic division?

In the brain stem and the sacral segments of the spinal

Where are the integrative centers for the autonomic activity located?

In the hypothalamus

How are the synaptic terminals in the sympathetic nervous system different from neuromuscular junctions of the somatic nervous system?

Instead of forming synaptic knows, telondendria form a branching network

How does the ANS maintain homeostasis in physiological systems?

It adjust internal water, electrolyte, nutrient, and dissolved gas concentrations in body fluids without conscious awareness

What does the autonomic nervous system do?

It makes routine homeostatic adjustments in physiological systems, including the cardiovascular, digestive, urinary, and reproductive systems

What happens when the sympathetic division is fully activated?

It produces the "fight or flight" response, which readies the body for a crisis that may require sudden, intense physical activity

What is white rami?

Myelinated preganglionic fibers

What do sympathetic ganglionic neurons release at their varicosities?

NE

Do the effects of ACh or NE on the postsynaptic membrane last longer?

NE last for a few seconds, significantly longer than the 20-msec duration of ACh.

Where is the inferior mesenteric ganglion located?

Near the base of the inferior mesenteric artery, which supplies the large intestine and other organs in the inferior portion of the abdominopelvic cavity.

Where is the superior mesenteric ganglion located?

Near the base of the superior mesenteric artery, which provides blood to the stomach, small intestine, and pancreas.

What does the sympathetic chain ganglia do?

Neurons in these ganglia control effectors in the body wall, inside the thoracic cavity, and in the head and limbs

What are adrenergic neurons?

Neurons that use NE as a neurotransmitter

Where are beta receptors located?

On the membranes of cells in many organs, including skeletal muscles, the lungs, the heart, and the liver.

What are sympathetic nerves?

Postganglionic fibers innervating structures in the thoracic cavity, such as the heart and lungs

Which fibers are short and long in the parasympathetic division?

Pre-ganglionic fibers are long Post-ganglionic fibers are short

In the sympathetic division of the ANS which fibers are short and long?

Preganglionic fibers are short Postganglionic fibers are long

What nerves end at the inferior mesenteric ganglion?

Preganglionic fibers from the lumbar segments from splanchnic nerves

What happens at the celiac ganglion or superior mesenteric ganglion?

Preganglionic fibers from the seven inferior thoracic segments end here

What makes the chain ganglia look like a string of pearls?

Preganglionic fibers running between interconnect them

What are splanchnic nerves?

Preganglionic fibers that innervate the collateral ganglia

What do postganglionic fibers of the inferior mesenteric ganglion innervate?

Provide sympathetic innervation to the terminal portions of the large intestine, kidney, urinary bladder, and the sex organs

What causes the release of ACh at synapses with ganglionic neurons?

The stimulation of sympathetic preganglionic neurons

What does the enzyme monoamine oxidase do?

Reuses and breaksdown 50 to 80 percent of the NE

What triggers visceral reflexes?

Somatic or visceral sensory information

What are neuroendocrine cells?

Specialized neurons that secrete hormones into the bloodstream

What causes increased alertness?

Stimulation of the reticular activating system, causing the individual to feel "on edge"

What is sympathetic activation controlled by?

Sympathetic centers in the hypothalamus

What are the two subdivisions of the ANS?

Sympathetic division and parasympathetic division

What do postganglionic fibers from the celiac ganglion innervate?

The stomach, liver, gallbladder, pancreas, and spleen

What does cholinergic mean?

Synapses that use ACh as a transmitter

What distributes the motor commands of visceral reflexes?

The ANS

What is the center of the adrenal gland?

The adrenal medulla

What are postganglionic fibers?

The axons of ganglionic neurons. They begin at the autonomic ganglia and extend to the peripheral target organs

What are preganglionic fibers?

The axons of preganglionic neurons

What is the third division of the ANS?

The enteric nervous system

What do the effects of sympathetic stimulation primarily result from?

The interactions of NE and E with adrenergic membrane receptors

What happens through the accelerated breakdown of glycogen in muscle and liver cells and the release of lipids by adipose tissues during sympathetic activation?

The mobilization of energy reserves

What does the effects of stimulating alpha and beta receptors depend on?

The production of second messengers, intracellular intermediaries with varied functions

In the head and neck, what do postganglionic sympathetic fibers leaving the superior cervical sympathetic ganglia supply?

The regions and structures innervated by cranial nerves III, VII, IX, and X

What is the function of alpha-1?

The release of intracellular calcium ions from reserves in the endoplasmic reticulum. This action generally has an excitatory effect on the target cell. For example, the stimulation of receptors on the surfaces of smooth muscle cells is responsible for the constriction of peripheral blood vessels and the closure of sphincters along the digestive tract.

What do postganglionic fibers of the superior mesenteric ganglion innervate?

The small intestine and the proximal 2/3 of the large intestine

What type of neurons are ANS integrative center neurons comparable to?

The upper motor neurons in the SNS

Where are membrane receptors located?

There are no specialized postsynaptic membranes but membrane receptors are scattered across the surfaces of the target cells

What are modified sympathetic ganglion?

They are ganglionic neurons located in the adrenal medulla, and have very short axons. When stimulated, they release their neurotransmitters into the bloodstream. The release of neurotransmitters into a capillary, not a synapse, allows them to function as hormones that affect target cells throughout the body.

How are the activities of the ENS initiated and coordinated?

They are influenced by the sympathetic and parasympathetic divisions, but many complex visceral reflexes are initiated and coordinated locally, without instructions from the CNS

Where are the cell bodies of the preganglionic neurons located?

They are situated in the lateral gray horns and their axons enter the ventral roots of these segments

What are the celiac ganglion?

They commonly consist of a pair of interconnected masses of gray matter situated at the base of that artery. The celiac ganglion may also form a single mass or many small interwoven masses.

What is the path of postganglionic fibers that control visceral effectors in the body wall, head, neck, or limbs?

They enter the gray ramus and return to the spinal nerve for subsequent distribution. These fibers innervate effectors such as the sweat glands of the skin and the smooth muscles in superficial blood vessels.

What do preganglionic fibers do?

They leave the CNS and synapse on ganglionic neurons

Where are splanchnic nerves located?

They lie in the dorsal wall of the abdominal cavity

Where is the sympathetic chain ganglia located? (lateral ganglia)

They lie on both sides of the vertebral column

How many collateral ganglia do the splanchnic nerves innervate?

Three

How are splanchnic nerves organized in adults?

Typically single rather than paired, even though they originate as paired ganglia. (They fuse together)

What is gray rami?

Unmyelinated postganglionic fibers

How long does NE released by varicosities affect its targets?

Until it is reabsorbed or inactivated by enzymes

How do abdominopelvic viscera receive sympathetic innervation?

Via sympathetic preganglionic fibers that pass through the sympathetic chain without synapsing. They synapse in the collateral ganglia.

What type of activity does the parasympathetic division stimulate?

Visceral activity, for example it is responsible for the state of "rest and repose" that follows a big dinner. General activation conserves energy and promotes sedentary activities, such as digestion.

What do ganglionic fibers innervate?

Visceral effectors such as cardiac muscle, smooth muscle, glands, and adipose tissue

What are ganglionic neurons?

Visceral motor neurons in peripheral ganglia (autonomic ganglia) which contain hundreds to thousands of ganglionic neurons

What are preganglionic neurons?

Visceral motor neurons in the brain stem and spinal cord

When will a preganglionic fiber synapse in one or more sympathetic chain ganglia?

When it carries motor commands that target structures in the body wall or thoracic cavity, or in the head, neck, or limbs

What is extensive divergence?

When one preganglionic fiber synpases on two dozen or more ganglionic neurons

What is sympathetic activation?

When the entire division responds during a crisis