Intro to autonomic nervous system

Question 1

Does the autonomic nervous system have sensory function?

Answer 1

No.

Question 2

What are the similarities between innervation of somatic vs. innervation of visceral structures?

Answer 2

1. The same basic neuronal components (spinal cord gray matter, nerve fibers, ganglia) 2. Supplied by both afferent (sensory) and efferent (motor) neural pathways. 3. The sensory pathways serving both types of structures have afferent (sensory) fibers from sensory (pseudounipolar) cells in spinal (dorsal root) ganglia.

Question 3

What do visceral motor neurons innervate?

Answer 3

cardiac muscle, smooth muscle, & glands.

Question 4

What does the sympathetic division of the ANS do?

Answer 4

Fight, flight or fright.

Question 5

What does the parasympathetic division of the ANS do?

Answer 5

Rest and digest

Question 6

How many neurons in a basic autonomic pathway?

Answer 6

2 neurons

Question 7

In the basic autonomic pathway, where is the first neuron?

Answer 7

In the CNS (either brain or spinal cord)

Question 8

In the basic autonomic pathway, where is the second neuron?

Answer 8

Nn a specific type of ganglion called an autonomic ganglion (NOT dorsal root ganglia), derived also from neural crest cells that migrate to their specific locations.

Question 9

What the of neurons arise from the lateral horn of the spinal cord? From what part of the spine?

Answer 9

T1 - L2 lateral horn has sympathetic S2 - S4 lateral horn has parasympathetic

Question 10

What are the key details of neuron #1 in the ANS pathway?

Answer 10

• gives preganglionic fiber
• cell body in the CNS, axon passes out to the periphery
• synapses onto a neuron in an autonomic ganglion
• uses acetylcholine (ACh) as its neurotransmitter

Question 11

What are the key details of neuron #2 in the ANS pathway?

Answer 11

• gives postganglionic fiber
• cell body in an autonomic ganglion
• axon terminates on the target organ: cardiac muscle, smooth muscle, or gland
• uses ACh (parasympathetic) or NE (typically for sympathetic) as its neurotransmitter

Question 12

What is the primary feature that distinguishes the autonomic NS from the somatic system?

Answer 12

The presence of ganglia in the autonomic motor pathway.

Question 13

Where do preganglionic fibers leave the spinal cord?

Answer 13

Anterior (ventral) roots

Question 14

What is a brain stem nucleus?

Answer 14

a group of cell bodies (and their dendrites) in the CNS, analogous to a ganglion in the PNS.

Question 15

What does CN X supply?

Answer 15

Cranial nerve X (Vagus nerve) is the only cranial nerve that supplies thoracic and abdominal organs.

Question 16

Where are the cell bodies of post-ganglionic fibers?

Answer 16

autonomic ganglia in the peripheral nervous system.

Question 17

Describe paravertebral ganglia

Answer 17

sympathetic; located just adjacent to the vertebral column

Sometimes simply referred to as “sympathetic chain ganglia”

Question 18

Describe pre-vertebral ganglia

Answer 18

sympathetic; also called “preaortic”, located near the abdominal aorta

Question 19

Describe intramural ganglia

Answer 19

parasympathetic; located “in the wall” (= intramural) of the target organ; contribute to the enteric nervous system – “brain in the gut”

Question 20

True/False: Many organs are innervated by both sympathetic and parasympathetic systems

Answer 20

True!

They often act as a “push/pull” system, where one will increase and action while the other decreases the same action. (eg. heart rate)

Question 21

Which organs are innervated by only the sympathetic nervous system?

Answer 21

Sweat glands and most smooth muscle of blood vessels (some blood vessels also have parasympathetic)

Question 22

What do pre-ganglionic nerve fibers of both parasympathetic and sympathetic systems use as neurotransmitter?

Answer 22

acetylcholine (ACh)

Question 23

What do parasympathetic postganglionic fibers use for neurotransmitter?

Answer 23

acetylcholine (ACh)

Question 24

What do sympathetic postganglionic fibers use for neurotransmitter?

Answer 24

Mostly norepinephrine (NE).

Question 25

Do sympathetic and parasympathetic nerve fibers share ganglia?

Answer 25

No, they do not like to share.

They do not synapse in the same ganglion, with some exceptions that we don’t have to learn yet.

Question 26

Where do parasympathetic preganglionic fibers synapse?

Answer 26

Parasympathetic ganglia in the head, and in intramural ganglia of thoracic and abdominal viscera

Question 27

Where do sympathetic preganglionic fibers synapse?

Answer 27

Paravertebral or prevertebral ganglia.

Question 28

Which cranial nerves give rise to parasympathetics?

Answer 28

III, VII, IX, and X

Question 29

What is the longest parasympathetic nerve and what does it innervate?

Answer 29

The vagus nerve, and it innervates the thoracic

organs and some of the gut.

Question 30

Aside from the part that is innervated by the vagus nerve, the rest of the digestive tract is supplied by _______ nerves called ______________, that come from segments __________.

Answer 30

The rest of the digestive tract is supplied by parasympathetic nerves called pelvic splanchnic nerves, that from sacral cord segments S2, 3, and 4.

Question 31

The term thoracolumbar referes to which pathway of the ANS?

Answer 31

Sympathetic.

All of the sympathetic pre-ganglionic fibers originate from the lateral horn of T1-L2

Question 32

What are the two types of ganglia in the sympathetic nervous system?

Answer 32

Paravertebral and prevertebral

Question 33

What are the 3 types of targets of the sympathetic fibers?

Answer 33

Thoracic organs

Abdominal organs

Periphery (somatic regions - skin, muscle, etc.)

Question 34

What types of organs do paravertebral fibers target?

Answer 34

Thoracic organs and peripheral organs (mainly blood vessels and sweat glands)

Question 35

What type of organs do prevertebral fibers target?

Answer 35

Abdomino-pelvic organs

Question 36

What are the rami communicantes? (singular: ramus communicans)

Answer 36

Branches from the sympathtic chain ganglia that connect it to a spinal nerve.

Question 37

What are some key differences between white rami communicantes and grey rami communicantes?

Answer 37

White have preganglion fibers whereas grey have postganglion fibers.

White are found only in T1-L2, whereas grey connect to all pripheral nerves.

Also, white are (more) myelinated and grey are (less) myelinated.

Question 38

Describe how thoracic organs – e.g., heart and bronchial passages - are innervated.

Answer 38

• supplied by visceral branches (e.g., sympathetic cardiac nerves)
• postganglionic fibers
• are medial branches of chain ganglia/sympathetic trunk
• preganglionic fibers of this segment arise from T1-T4.
• synapse in a paravertebral ganglion.

Question 39

Describe how abdominopelvic organs are innervated.

Answer 39

• supplied by splanchnic nerves (arising from T5-L2)
• contain preganglionic fibers from T5-L2
• are medial branches of chain ganglia/sympathetic trunk
• pass through the paravertebral ganglia without synapse, then synapse in a prevertebral ganglion

Question 40

Do all nerves carry postganglionic sympathetic fibers?

Answer 40

Yes, they sure do.

Question 41

Both sympathetic and parasympathetic pathways innervate organs within the body cavity, but what does the sympathetic pathway innervate that the parasympathetic does not?

Answer 41

The sympathetic pathway also supplies smooth muscle and glands in the periphery:

smooth muscle in blood vessels of the skin and skeletal muscles

arrector pili smooth muscles (make your hair stand on end)

sweat glands

Question 42

Summarize the sympathetic innervation of the periphery.

Answer 42

• Cell bodies in the lateral horn of (T1-L2) supply preganglionic fibers for all parts of the body, from head to toe.
• The postganglionic neurons are located in paravertebral (chain) ganglia in the cervical, thoracic, lumbar, and sacral regions

Question 43

Are visceral afferents part of the ANS?

Answer 43

No, but they travel with both the sympathetic and parasympathetic nerve pathways.

Question 44

Do visceral afferent fibers synapse in the paravertebral ganglia?

Answer 44

NO. They pass through without synapsing!

Question 45

Where are the cell bodies of visceral afferent fibers that travel with the sympathetic pathway?

Answer 45

In the spinal (dorsal root) ganglia associated with T1 - L2 spinal nerves.

Question 46

Where are the cell bodies of the afferent fibers that travel with the parasympathetic pathways?

Answer 46

In the spinal ganglia associated with S2 - S4 spinal nerves and in the sensory ganglia of the vagus nerve.

Question 47

Why is visceral pain is interpreted by the nervous system as coming from a somatic region? What is this called?

Answer 47

Visceral afferent ends in a segmental level of the spinal cord that also receives somatic afferents. This is called “referred pain.”

Question 48

What is a big, clinically relevant example of referred pain?

Answer 48

Heart attacks!

Pain from a heart attack, carried by visceral afferents to spinal cord segments T1-T4, is felt in somatic regions (the chest wall and arm) where afferents also project to the T1-T4 segments.

Question 49

Describe the output cell of the somatic reflex.

Answer 49

It’s a motor neuron that ends on skeletal muscle.

Question 50

Describe the efferent cells of the visceral reflex.

Answer 50

Two types: preganglionic and postganglionic.

The postganglionic cell can target a smooth muscle cell (never skeletal).

Question 51

Where are the cells in both somatic and visceral reflexes?

Answer 51

There is a spinal ganglion cell in the PNS, and an interneuron in the CNS.