The Autonomic Nervous System and Visceral Reflexes- Chapter 15

Autonomic nervous system (ANS)

motor nervous system that controls glands, cardiac muscle, and smooth muscle

Visceral nervous system

Another name for the autonomic nervous system

- Viscera of thoracic and abdominal cavities

- Some structures of the body wall

What are the primary target organs of the autonomic nervous system?

Cutaneous blood vessels, sweat glands, piloerector muscles

What are the structures of the body wall the autonomic nervous system innervates?

involuntarily

The autonomic nervous system carries out actions ______________________

True

True or False: Visceral effectors do not depend on ANS to function

To adjust their activity to body's changing needs

What do visceral effectors depend on the ANS for?

Visceral Reflexes

unconscious, automatic, stereotyped responses to stimulation

- Receptors: nerve endings that detect stretch, tissue damage, blood chemicals, body temp, and other internal stimuli

- Afferent neurons: lead to CNS

- Integrating center: interneurons in CNS

- Efferent neurons: carry motor signals away from CNS

- Effectors: carry out response

What is the visceral reflex arc?

They have a slower response

What makes the effectors of the visceral reflex arc different than the effectors of the somatic reflex arc?

Baroreflex: 1. High blood pressure detected by arterial stretch receptors

2. Afferent neuron (glossopharyngeal nerve) carries signal to CNS

3. Efferent signals on vagus nerve of ANS travel to the heart

4. Heart then slows, reducing blood pressure

What is an example of a visceral reflex?

Sympathetic division and parasympathetic division

What are the two divisions of the ANS?

Sympathetic division

prepares body for physical activity: exercise, trauma, arousal, competition, anger, or fear

- Increase heart rate, blood pressure, airflow, blood glucose levels

- Decrease blood flow to skin and digestive tract

What two things does the sympathetic division do that happen at the same time?

"fight-or-flight"

The sympathetic division creates a ______________________ reaction

Parasympathetic division

calms body function reducing energy expenditure and assists in bodily maintenance

Digestive waste

What does the parasympathetic division help eliminate?

resting and digesting

The parasympathetic vision controls the ___________________________ state

Autonomic tone

normal background rate of activity; represents the balance of the 2 systems; balance shifts with body's changing needs

Parasympathetic tone

maintains smooth muscle tone in intestines, holds resting heart rate down to about 70 to 80 BPM

Heart rate would go to about 100 BPM (resting)

What would happen if you severed the parasympathetic tone?

Sympathetic tone

keeps most blood vessels partially constricted and maintains blood pressure

Would faint, blood goes to easily to all parts of the body

What would happen if you lost the sympathetic tone?

Sympathetic division, parasympathetic division

______________________________ excites the heart but inhibits the digestive and urinary function, while __________________________ has the opposite effect

2 neurons to get to target organ

What must signals travel across in autonomic pathways?

synapse, autonomic ganglion

In an autonomic pathway, the signal must cross a __________________ where these 2 neurons meet in an __________________________

Preganglionic neuron

first neuron with cell body in brainstem or spinal cord, part of autonomic pathway

postganglionic neuron

The preganglionic neuron synapses with a _____________________ whose axon extends the rest of the way to the target cell

Varicosities

What does the postganglionic neuron have that allows it to synapse with multiple cells?

Comparison of somatic and autonomic pathways

What is this?

Thoracolumbar division (T1-L2); arises from thoracic and lumbar regions of the spinal cord

What is the sympathetic division also known as?

short, long

The sympathetic motor innervation has ________ preganglionic and _________ postganglionic fibers

Lateral horns and nearby regions of gray matter of spinal cord

Where do the preganglionic cell bodies begin in the sympathetic motor innervation?

By way of spinal nerves T1-L2

How do fibers exit the spinal cord in the sympathetic division?

Nearby sympathetic chain of ganglia (located on both sides of spinal cord)

Where do the spinal nerves of the sympathetic division that exit the spinal cord lead to?

Sympathetic chain of ganglia

series of longitudinal ganglion adjacent to both sides of vertebral column from cervical to coccygeal levels

Every level of the body

Where are sympathetic fibers distributed to?

Communicating rami

Each sympathetic chain ganglion is connected to a spinal nerves by 2 branches, called what?

Preganglionic fibers, white communicating ramus

_______________________________ are small myelinated fibers that travel from the spinal nerves to the ganglion by way of the ________________________________________

White communicating ramus

What is the only way to the sympathetic chain?

Postganglionic fibers, gray communicating ramus

___________________________ leave ganglion by way of ______________________________ (unmyelinated)

The spinal cord

Where does the gray ramus return to?

The rest of the way to the target organ

Where do postganglionic fibers extend to?

By spinal, sympathetic, and splanchnic nerves

After entering the sympathetic chain, how do nerve fibers leave the sympathetic chain?

- Some postganglionic fibers exit a ganglion by way of gray ramus

- Return to spinal nerve and travel rest of the way to the target organ

What is the spinal nerve route?

Most sweat glands, piloerector muscles, and blood vessels of skin and skeletal muscles

Where does the spinal nerve route lead to?

Sympathetic nerve route

some postganglionic fibers leave by way of sympathetic nerves that extend to heart, lungs, esophagus, and thoracic blood vessels

carotid plexus

The sympathetic nerves that leave via the sympathetic nerve route form __________________ around each carotid artery of the neck and issue nerve fibers to effectors in the head

Sweat, salivary, nasal glands; piloerector muscles; blood vessels; dilators of iris

What do the carotid plexuses do?

cardiac nerves

Some fibers of superior and middle cervical ganglia form ____________________ to the heart

Splanchnic nerve route

some fibers that arise from spinal nerves T5 to T12 pass through the sympathetic ganglia without synapsing

Continue on as the splanchnic nerves

What do the fibers in the splanchnic nerve route do?

Second set of ganglia: collateral ganglia and synapse there with postganglionic fibers

What do the splanchnic nerves lead to?

abdominal aortic plexus

Collateral ganglia contribute to a network called ______________________________

Abdominal aorta

What does the abdominal aortic plexus wrap around?

Celiac, superior mesenteric, and inferior mesenteric

What are the 3 major collateral ganglia in the abdominal aortic plexus?

Postganglionic fibers

What accompanies the arteries and their branches to their target organs of the celiac, superior mesenteric, and inferior mesenteric?

Stomach, spleen, liver, pancreas, small intestine, and kidneys

What is the postganglionic target organ of the celiac ganglion (collateral ganglia)?

Small intestine, colon, and kidneys

What is the postganglionic target organ of the celiac and superior mesenteric ganglia (collateral ganglia)?

Rectum, urinary bladder, and reproductive organs

What is the postganglionic target organ of the inferior mesenteric ganglion (collateral ganglia)?

adrenal (suprarenal) glands

Paired _______________________________ on superior poles of kidneys

Adrenal cortex (outer layer) and adrenal medulla (inner core)

What are the 2 glands that make up the adrenal (suprarenal) glands?

Adrenal cortex (outer layer)

part of adrenal glands, secretes steroid hormones

Adrenal medulla (inner core)

part of adrenal glands, sympathetic ganglion consisting of modified postganglionic neurons without dendrites or axons

Preganglionic sympathetic neurons

What is the adrenal medulla stimulated by?

It secretes a mixture of hormones into the bloodstream

What happens when the adrenal medulla is stimulated?

Catecholamines

What is the hormone class the adrenal medulla secretes into the bloodstream?

Epinephrine (adrenaline) and norepinephrine (noradrenaline)

What hormones make up the class of catecholamines?

Craniosacral division

What is the parasympathetic division also known as?

Brain and sacral regions of spinal cord

Where does the parasympathetic division arise from?

Certain cranial and sacral nerves

What do the fibers of the parasympathetic division travel in?

- Midbrain, pons, medulla

- Sacral spinal cord segments S2 to S4

What are the origins of the long preganglionic neurons?

terminal ganglia

Preganglionic fibers of the parasympathetic division end in ______________________ in or near target organs

long, short

The parasympathetic division has _________ preganglionic fibers and ______________ postganglionic fibers

- Oculomotor nerve (III)

- Facial nerve (VII)

- Glossopharyngeal nerve (IX)

- Vagus nerve (X)

What are the 4 cranial nerves the parasympathetic nerves leave the brainsteam from?

Oculomotor nerve (III)

narrows pupil and focuses lens

Facial nerve (VII)

regulates tear, nasal, and salivary glands

Glossopharyngeal nerve (IX)

parotid salivary gland

Vagus nerve (X)

viscera as far as proximal half of colon, only cranial nerve that goes below diaphragm

Cardiac, pulmonary, and esophageal plexus

What are the plexuses the vagus nerve splits into?

Levels S2 to S4 of spinal cord

What do the remaining parasympathetic fibers arise from (not from the cranial nerves)?

Pelvic splanchnic nerves that lead to inferior hypogastric plexus

What do the parasympathetic fibers that arise from levels S2 to S4 of the spinal cord form?

Synapse at this plexus

What do some fibers of the parasympathetic system do at the hypogastric plexus?

Most pass through, travel through pelvic nerves to terminal ganglia

What do most fibers of the parasympathetic system do (if they don't synapse at the hypogastric plexus)?

Distal half of colon, rectum, urinary bladder, and reproductive organs

What do the parasympathetic fibers that arise from levels S2 to S4 of the spinal cord innervate?

Enteric Nervous System/Enteric Plexus

nervous system of the digestive tract

True

True or False: The enteric system does not arise from the brainstem or spinal cord (no CNS components)

Smooth muscle and glands

What does the Enteric Nervous System innervate?

in the walls of the digestive tract

The enteric nervous system is composed of 100 million neurons found ______________________________________________

Its own ganglia and reflex arcs

What does the enteric nervous system have?

Motility of esophagus, stomach, and intestines and secretion of digestive enzymes and acid

What does the enteric nervous system regulate?

Sympathetic and parasympathetic systems

Normal digestive function also requires regulation by what?

- Sympathetic and parasympathetic fibers secrete different neurotransmitters (norepinephrine and acetylcholine)

- Receptors on target cells vary

How can different autonomic neurons have different effects- constricting some vessels but dilating others?

- Target cells respond to same neurotransmitter differently depending on type of receptor they have for it

- There are 2 different classes of receptors for acetylcholine and 2 classes of receptors for norepinephrine

How can receptors on target cells vary?

All preganglionic neurons in both divisions and the postganglionic parasympathetic neurons

What is acetylcholine secreted by?

Cholinergic fibers

axons that secrete ACh

Cholinergic receptor

any receptor that binds ACh

Muscarinic receptors and nicotinic receptors

What are the 2 types of cholinergic receptors?

In all cardiac muscle, smooth muscle, and gland cells

Where are muscarinic receptors found?

Either due to subclasses of muscarinic receptors

Are muscarinic receptors excitatory or inhibitory?