A&P II Chapter 16 - Autonomic Nervous System + Higher-Order Functions

Autonomic Nervous System (ANS)

visceral motor system

What does the ANS have involuntary control of?

visceral effectors (smooth muscle, glands, cardiac muscle, adipocytes)

What does the ANS coordinate?

cardiovascular, respiratory, digestive, urinary, + reproductive functions

Where are interative centers of the ANS located?

the hypothalamus

Autonomic Ganglia

clusters of cell bodies of the visceral motor neurons that innervate visceral effectors

Where are autonomic ganglia located?

outside of the CNS

What do CNS visceral motor neurons synapse with in the ANS?

visceral motor neurons in autonomic ganglia

What do CNS motor neurons synapse with in the SNS?

skeletal muscle cells

Preganglionic Neurons

cell bodies in brainstem + spinal cord

Preganglionic Fibers

axons of preganglionic neurons

What do preganglionic fibers do after projecting to autonomic ganglia?

synapse with postganglioic (ganglionic) neurons

Postganglionic Neurons

cell bodis in autonomic ganglia

Postganglionic Fibers

axons of postganglionic neurons

What do postganglionic fibers synapse with

peripheral target organs

What is the sympathetic division of the ANS said to deal with?

stress or emergency, “fight or flight”

What does the sympathetic division increase?

alertness, respiratory rate, metabolic rate + muscular abilities

What are the effects of the sympathetic division? (7)

• heightened mental alertness

• increased metabolic rate

• reduced digestive + urinary functions

• activation of energy reserves

• increased respiratory rate + dilation of respiratory passageways

• increased heart rate + blood pressure

• activation of sweat glands

What is the parasympathetic division said to do?

conserves energy + maintains resting metabolic rate, “rest + digest”

What are the effects of the parasympathetic division? ()

• decreased metabolic rate

• decreased heart rate + blood pressure

• increased secretion by salivary + digestive glands

• increased motility + blood flow in digestive tract

• stimulation of urination + defecation

Thoracolumbar Divison

cell bodies of preganglionic neurons are in lateral horns of thoracic + lumbar sections of spinal cord (between T1 + T2)

What are characteristics of preganglionic fibers for the thoracolumbar division?

they are short + synapse with many postganglionic eurons

What do preganglionic fibers release at synapse?

acetyl choline (ACh)

Where are postganglionic neuron cell bodies located?

ganglia near spinal cord

What are characteristics of postganglionic fibers of the thoracolumbar division?

they are long + synapse with target organs

What do postganglionic fibers release at peripheral synapses?

norepinephrine

What are sympathetic preganglionic fibers?

myelinated

Where do preganglionic fibers pass through?

spinal anterior roots + then through white rami communicante to reach sympathetic ganglia

Sympathetic Ganglia

clusters of cell bodies of postganglionic neurons

What does each sympathetic ganglia innervate?

a particular body organ/group

Where are sympathetic chain (paravertebral) ganglia located?

on either side of vertebral column

What synapses for sympathetic chain ganglia?

one preganglionic fiber synapses on many postganglionic neurons

What are postgnglionic fibers seen as?

unmyelinated + pass through gray rami communicantes

What do sympathetic chain ganglia postganglionic neurons innervate?

effectors in body wall, thoracic, cavity, head, neck, + limbs

How many cervical sympathetic chain ganglia are there?

3

How many thoracic sympathetic chain ganglia are there?

10-12

How many lumbar sympathetic chain ganglia are there?

4-5

How many sacral sympathetic chain ganglia are there?

4-5

What do the two coccygeal ganglia fuse to form?

ganglion impar

What can one preganglionc fiber synapse?

many postganglionic neurons

What is a white rami communicante for?

myelinated preganglionic fibers

What is gray rami communicante for?

unmyelinated postganglionic fibers

After entering gray rami communicantes, what can postganglionic fibers do?

return to spinal nerves to reach the body wall, head, neck, or limbs

After forming sympathetic nerves, what can postganglionic fibers do?

travel to visceral organs in the thoracic cavity, including the heart + lings

What does every spinal nerve receive?

a gray ramus from a sympathetic chain ganglion

What ganglia are located anterior to the vertebral column?

collateral (prevertebral) ganglia

What do collateral ganglia receive?

preganglionic fibers traveling through splanchnic nerves

What do collateral ganglia provide?

sympathetic innervation to abdominopelvic organs

What do collateral ganglia reduce?

blood flow + energy use in organs not immediately essential for survival

What does collateral gangla promote?

the release of stored energy

What are the three major collateral ganglia?

celiac, superior + inferior mesenteric

What are the major targets of the celiac collateral ganglia?

stomach, liver, gallbladder, pancreas, spleen

What are the targets of the superior mesenteric collateral ganglia?

small intestine + proximal 2/3 of large intestine

What are the major targets of the inferior mesenteric collateral ganglia?

kidneys, urinary bladder, distal large intestine, + sex organs

Adrenal Medulla

modified sympathetic ganglion located in the center of each adrenal gland

What does the adrenal medulla release into the bloodstream when stimulated?

epinephrine (adrenaline) + norepinephrine (noradrenaline)

What do adrenaline + noradenaline act as when released by the adrenal medulla?

hormones

What do adrenaline + noradrenaline affect throughout the body?

target cells, including cells not directly innervated by sympathetic postganglionic fibers

What is the difference between hormones released by the adrenal medulla than by direct sympathetic nerve stimulation?

they circulate through the blood + generally produce effects that last longer

What can the sympathetic divison do during a crisis?

produce a widespread response

Major effects of sympathetic activation

• Increased alertness

• Feelings of energy and euphoria

• Increased blood pressure

• Increased heart rate

• Increased breathing rate and depth

• Increased muscle tone

• Mobilization of energy reserves

What do all sympathetic preganglionic neurons release?

ACh at their synapses in autonomic ganglia

Cholinergic Synapses

synapses that use ACh

What is the effect of ACh at the ganglionic synapses identified as?

excitatory

What do most sympathetic postganglionic neurons release?

NE at target organ

Adrenergic Synapses

synapses that use NE

What are three ways NE is removed from the synaptic cleft?

• reuptake into varicosities for reuse

• breakdown by monoamine oxidase (MAO)

• breakdown by catechol-O-methyltransferase (COMT)

What do postganglionic sympathetic axons branch into?

telodendria containing numerous swollen regions (aka varicosities)

What do varicosities store + release?

neurotransmitter, allowing them to react target tissues along the axon

What is an example of a sympathetic postganglionic neuron that releases ACh?

fibers that stimulate sweat glands

What are some cholinergic fibers involved with in skeletal muscles + thebrain?

dilation of blood vessels

What do some sympathetic fibers release to produce vasodilation + increased blood flow?

nitric oxide (NO)

Adrenergic Receptors

membrane G-protein-coupled receptors that bind NE + epinephrine

What are the two major classes of adrenergic receptors?

alpha + beta

What are the more common alpha receptors?

alpha-1

Where are alpha-1 receptors primarily found?

smooth muscle cells

What does stimulation of alpha-1 produce?

an excitatory effect

What are alpha-1 receptor associated with?

release of intracellular calciu ions

What are alpha-2 receptors found on?

pre and postsynaptic sympathetic + parasympathetic neurons

What does stimulation of alpha-2 receptors do?

lowers intracellular cAMP

What does alpha-2 generally produce?

an inhibitory effect

What do alpha-2 receptors help coordinate

ANS activity

Where are beta receptors found?

in tissues including skeletal muscles, lungs, heart, + liver

What does stimulation of beta receptors do?

increases intracellular cAMP + changes metabolic activity

What is the major effect of a beta-1 receptor?

increased metabolic activity in muscles + heart

What is the major effect of beta-2 receptors?

relaxation of respiratory tract smooth muscle + dilation of respiratory passageways

What is the major effect of beta-3 receptors?

lipolysis (breakdown of triglycerides in adipocytes)

What is the parasympathetic division also known as?

craniosacral division

Where are parasympathetic preganglionic neuron cell bodies located?

in the brainstem + he lateral horns of the sacral spinal cord

What are parasympathetic preganglionic + postganglionic fibers considered?

pre are long, post are short

What do parasympathetic preganglionic + postganglionic fibers produce?

ACh

What does it take for parasympathetic preganglionic fibers to synapse?

relatively few postganglionic neurons

Where are parasympathetic postganglionic cell bodies located?

in ganglia within or adjacent to target organs

What does the arrangement of the parasympathetic division produce in comparison to sympathetic?

more localized + specific effects?

What cranial nerves do cranial parasympathetic pathways travel in?

III (oculomotor), VII (facial), IX (glossopharyngeal) + X (vagus)

What nerve provides ~75% of all parasympathetic output?

vagus (x)

Where do the sacral parasympathetic pathways arise from to form the pelvic nerves?

S2 - S4

What structures do cranial parasympathetic fibers innervate?

kidneys, urinary bladder, terminal portion of large intestine, + sex organs

What parasympathetic ganglia are located near the target organ + usually paired?

terminal ganglia

What parasympathetic ganglia are embedded within tissues of the target organ + contain interconnected masses + clusters of ganglion cells?

intramural ganglia