Chapter 15: The Autonomic Nervous System

Question 1

Compare the somatic and autonomic nervous system on the following characteristics:

Sensory input 
Control of motor output 
Motor neuron pathway 
NTs and hormones 
Effectors 
Responses

Answer 1

Sensory input

• SNS: from somatic and special senses
• ANS: mainly from interocetpors; some from somatic and special senses

Control of motor output

• SNS: voluntary control from cortex
• SNS: involuntary control from hypothalamus, limbic system, brain stem, and spinal cord; limited control from cortex

Motor neuron pathway

• SNS: 1 neuron pathway: somatic motor neurons extending from CNS synapse with effector
• ANS: 2-neuron pathway: preganglionic neurons synapse with postganglionic neurons; postganglionic neurons synapse with effector

NTs and hormones

• SNS: release only ACh
• SNS: sympathetic & parasympathetic preganglionic (ACh); parasympathetic postganglionic neurons (NE); sympathetic postganglionic (ACh)

Effectors

• SNS: skeletal muscles
• ANS: smooth muscle, cardiac muscle, glands

Responses
SNS: contraction of skeletal muscles
ANS: contraction or relaxation of smooth muscle

Question 2

Define interoceptors

Answer 2

Sensory receptors located in blood vessels, visceral organs, muscles, and nervous system that monitors the internal environment

Associated with the autonomic sensory neurons

Question 3

Define autonomic motor neurons

Answer 3

Regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities in their effector tissues

Question 4

Describe the subdivision of the autonomic nervous system

Answer 4

Sympathetic - fight or flight as

Parasympathetic - rest and digest

Question 5

Define ganglion

Answer 5

A collection of neuronal cell bodies in the PNS

Question 6

What does dual innervation mean?

Answer 6

They receive impulses from both sympathetic and parasympathetic neurons

Question 7

Each division of the ASN has 2 motor neurons. Describe them

Answer 7

Preganglionic neuron - cell body is in the brain/spinal cord; its axon exits CNS as a cranial/spinal nerve; it is a myelinated type B fibre

Postganglionic neuron - lies entirely outside the CNS; cell body located in an autonomic ganglion, where it forms synapses with one or more preganglionic neurons; it is an unmyelinated type C fibre that terminates in several effector

Question 8

Define the thoracolumbar division

Answer 8

In the sympathetic division, preganglonic neurons have their cell bodies in the lateral horns of the gray matter in the 12 thoracic segments and the first 2 lumbar segments of spinal cord

Axon of the preganglionic neurons are known as thoracolumbar outflow

Question 9

Define the craniosacral division

Answer 9

In the parasympathetic division the cell bodies of preganglionic neurons are located in the nuclei of 4 cranial nerves in brain stem and in the lateral gray matter of the 2-4 sacral segments of spinal cord

Axons of the preganglionic neurons are known as craniosacral outflow

Question 10

Define sympathetic ganglia

Answer 10

The sites of synapses between sympathetic preganglionic and post ganglion neurons; two types:

Trunk ganglia - lies in a vertical row on either side the the vertebral column and extend from the base of the scull to coccyx; the postganglionic neurons innervate organs above the diaphragm

Prevertebral ganglia - lies anterior to the cerebral column and close to the large abdominal arteries; the postganglionic neurons innervate organs below the diaphragm

Question 11

Define parasympathetic ganglia

Answer 11

Preganglionic axons of the parasympathetic division synapse with postganglionic neurons in there terminal ganglia

Question 12

List the 4 ways axons of a sympathetic preganglionic neurons that pass to truck ganglia may connect with postganglionic neurons

Answer 12

1. synapse with postganglionic neurons in the ganglion it first reaches
2. Axon may ascent or descend to a higher or lower ganglion before synapses with postganglionic neurons
3. Axon may continue without synapsing through the truck ganglion to end a prevertebral ganglion and then synapse
4. Axon may extend to chormaffin cells of the adrenal medullae that are functionally similar to postganglionic neurons

Question 13

Describe autonomic plexuses

Answer 13

Tangled networks of axons of both sympathetic and parasympathetic nervous in the thorax, abdomen, and pelvis

Question 14

What are the major plexuses in the thorax?

Answer 14

Cardiac plexus - supplies heart

Pulmonary plexus - supplies bronchial tree

Question 15

Describe the following plexuses

Celiac plexus 
Superior mesenteric plexus 
Inferior mesenteric plexus 
Hypogastric plexus 
Renal plexus

Answer 15

Celiac - surrounds celiac trunk
Superior mesenteric - supplies small and large intestines
Inferior mesenteric - supplies the large intestine
Hypogastric - supplies the pelvic viscera
Renal - supplies the renal arteries within kidneys and ureters

Question 16

Describe Horner’s syndrome

Answer 16

The sympathetic innervation to one side of the face is lost due to an inherited mutation, and injury, or disease that effects sympathetic outflow throughout he sprier cervial ganglion

Question 17

Define white ramus

Answer 17

White rami are structures containing sympathetic preganglionic axons that connect the anterior ramus of the spinal nerve with the ganglia of the sympathetic trunk

White means they contain myelinated axons

Question 18

Define gray ramus

Answer 18

Structures containing sympathetic postganglionic axons that connect the ganglia of the sympathetic trunk to spinal nerves

Gray means they are unmyelinated

There is a gray ramus leading to each of the 31 pairs of spinal nerves

Question 19

Define cranial parasympathetic outflow

Answer 19

Consist of parasympathetic preganglionic axons that extend from the brain stem in 4 cranial nerves

Question 20

Define sacral parasympathetic outflow

Answer 20

Consist of parasympathetic preganglionic axons that extend from the brain stem in 2-4 sacral nerves

Question 21

Define pelvic splanchnic nerves

Answer 21

As the preganglionic axons course through the sacral spinal nerves, they branch off these nerves to form pelvic splanchnic nerves

These nerves synapse with postganglionic neurons located in terminal ganglia in walls of the innervated viscera

Question 22

Describe the myenteric and submucosal plexuses of the enteric system

Answer 22

Most of the nerve fibers that innervate the digestive organs arise from these two plexuses:

Myenteric - positioned between the outer longitudinal and circular muscle layers from the upper esophagus to the anus

Submucosal - occupies the gut wall between the circular muscle layer and the muscularisis mucosae and runs from the stomach to the anus

Question 23

Define cholinergic neurons. Which neurons in the ANS are cholinergic?

Answer 23

They release ACh

In the ANS, they include
1) all the sympathetic and parasympathetic preganglionic neurons

2) sympathetic postganglionic neurons that innervate most sweat glands
3) All parasympathetic postganglionic neurons

Question 24

What are the two types of cholinergic receptors?

Answer 24

Nicotinic receptors - present in plasma membrane of dendrites and cell bodies of both sympathetic and parasympathetic postganglionic neurons, membranes of chromatin cells, and motor end plat of NMJ

Muscarinic receptors - present in the plasma membrane s of all effectors innervated by parasympathetic postganglionic axons and most sweat glands

ACh actiaves both types of receptors and they are named as such since nicotine and muscarine mimics the action of ACh when bound

Question 25

In the ANS, adrenergic neurones release what neurotransmitters? Which neurons in the ANS are adrenergic?

Answer 25

Noradrenalin or norepinephrine (NE)

Most sympathetic postganglionic neurons are adrenergic

Question 26

Define adrenergic receptors and discuss the subtypes

Answer 26

Adrenergic receptors bind to both NE and epinephrine; 2 main types are:

Alpha and beta which are found on viserveral effectors innervated by moth sympathetic postganglionic axons

They are further subdivided based on the specific responses they elicit

• a1 and b1 receptors generally produce excitation
• a2 and b2 cause inhibition
• b3 are present only on cells of adipose tissue, where activation causes thermogenesis

Question 27

Differentiate between and agonist and antatongist

Answer 27

Agonist - substance that binds to and activates a receptor, in the process mimicking the effect of a natural NT or hormone

Antagonist - substance that binds to and blocks a receptor, thereby preventing a natural Nt or hormone from exerting its effect

Question 28

Define autonomic done

Answer 28

The balance between sympathetic and parasympathetic activity, which is regulated by the hypothalamus

Question 29

What happens durning the sympathetic fight or flight response?

Answer 29

• Pupils dilate
• Increased HR & BP
• Airways dilate, allowing father movement into lungs
• Blood vessels contract, decreasing blood for to GI
• Exercise related organs dilate, increasing blood flow
• Glycogenesis: increase in glucose
• Unessential processes are inhibited

Question 30

What happens during the parasympathetic rest and digest response?

Answer 30

SLUDD is activated 
Salivation 
Lacrimation
Urination 
Digestions 
Defectation 

And HR, airways, and pupil diameter decrease

Question 31

Describe the components of an autonomic reflex

Answer 31

Receptor - autonomic sensory receptors are mostly associated with interoceptors

Sensory neuron - conducts impulses from receptor to CNS

Integrating center - internerons within CNS relay signals from sensory to motor neurones, mainly located in hypothalamus and brainstem for ANS

Motor neurons - in autonomic reflex arc 2 motor neurones connect the CNS to the effect: preganglionic neuron conducts motor impulses from CNS to antonomic ganglion and the postganglionic neuron innervates effector

Effector -smooth muscle, cardiac muscle, and glands

Question 32

Which regions is the major control and integration center of the ANS?

Answer 32

Hypothalamus