Nervous System IX

Question 1

What is a nucleus ?

Answer 1

Nerve cell body inside CNS (brain and spinal cord)

Question 2

What is a ganglion ?

Answer 2

Nerve cell body outside the CNS

Question 3

What are the cranial-parasympathetic nerves?

Answer 3

From the brain: preganglionic cells bodies in brain stem nuclei associated with CN III, VII, IX, X(Vagus)

Vagus is the only cranial parasympathetic nerve functioning in the cervical, thoracic and lumbar regions, serving parasympathetics to visceral structures in the neck, thorax and abdomen

Question 4

What are the sacral parasympathetic nerves?

Answer 4

Sacral or pelvic region: preganglionic cell bodies in spinal cord segments S2, 3, 4- Functioning in the pelvic region (called pelvic splachnic nerves)

Question 5

There are No parasympathetic innervation to the…

Answer 5

Body walls and limbs (thus, parasympathetic fibers can only be found on nerves leaving the CNS (CN III, VII, IX, X and S2- 4), and then distributed to organs in the body cavities

Question 6

Explain the thoraco-lumbar sympathetic innervation

Answer 6

1. Preganglionic cell bodies are located in lateral horn of spinal cord segments T1-L2
2. All preganglionic axons enter the sympathetic chain through white rami communicantes
3. From the above outflow into the sympathetic chain, sympathetic are supplied to the entire body, (body wall/limbs as well as organs in body cavities). Thus, there must be routes from the sympathetic chain that lead to organs as well as the body wall

Question 7

What are visceral afferents?

Answer 7

sensory fibers that accompany both sympathetic and parasympathetic fibers (these visceral afferents are “hitch hiking” with sympathetic and parasympathetics and aren’t technically part of the SNS or PSNS

Question 8

What are autonomic ganglia ?

Answer 8

Collections of nerve cell bodies outside the CNS are called ganglia- autonomic ganglia contain postganglionic sympathetic or parasympathetic nerve cell bodies

Question 9

What are sympathetic ganglia ?

Answer 9

1. Sympathetic chain ganglia (paravertebral ganglia)- chain ganglia are found at all levels of the spinal cord/ spinal nerves
2. Pre-aortic (prevertebral) sympathetic ganglia are only located in the abdomen, and are associated with major branches of the abdominal aorta

Question 10

What are parasympathetic ganglia?

Answer 10

Discrete parasympathetic ganglia are only found in the head; FOR THE REST OF THE BODY, postganglionic parasympathetic cell bodies are found scattered near of in the walls of target organs

Question 11

Contrast sympathetic and parasympathetic axon and cell bodies

Answer 11

Sympathetic- short preganglionic axon with long postganglionic axons

Parasympathetic- long preganglionic axon with short postganglionic axons

Question 12

Where can sympathetic chain & ganglionic be found in the spinal cord?

Answer 12

T1-L2

Question 13

What does somatic refer to ?

Answer 13

Refers to body wall, parietal; denotes voluntary function, e.g. somatic plexus (brachial plexus, lumbar plexus etc.)

Question 14

What does visceral refer?

Answer 14

Refers to inside, e.g. the gut, heart etc. (visceral structures ); synonymous with SPLACHNIC, as in splachnic mesoderm or splanchnopleure

Question 15

What d9es somatic afferent and efferent mean?

Answer 15

Somatic afferent- sensory fibers from the body wall (conscious sensation)

Somatic efferent- motor fibers to the body wall (under voluntary control)

Question 16

What are visceral afferent and efferent?

Answer 16

Visceral afferent- sensory fibers from the viscera (unconscious sensation)

Visceral efferent- motor fibers to the viscera (under involuntary control-autonomic)

Question 17

Describe characteristics of the ANS

Answer 17

Involuntary

Efferent (motor) system; (plus Sensory hitchhikers)

Visceral-innervates 3 target areas:
Smooth muscles

Cardiac muscke(heart)

Glands (e.g. Sweat, mucous, tears)

Question 18

What are the major components of the ANS?

Answer 18

a) sympathetic nervous system (SNS=thoracolumbar)
b) parasympathetic nervous system=(PSNS= craniosacral)

Minor third component that is gut related:
C) enteric

Two neuron system from CNS to target structures:

a) preganglionic neuron (cell body in CNS)
b) postganglionic neuron( cell body in autonomic ganglion)

Question 19

What are spinal cord segments?

Answer 19

Repeating similar units

Question 20

What are 5he divisions of spinal cord segments?

Answer 20

8 cervical segments

12 thoracic segments

5 lumbar segments

5 sacral segments

Sympathetic chain within lumbar and thoracic segments

1 coccygeal segments

Question 21

Where are preganglionic sympathetic cell bodies located?

Answer 21

All preganglionic sympathetic cell bodies are located in the lateral horn of spinal segments T1-L2: therefore, lateral horns fir sympathetic outflow are only located from T1-L2

Question 22

Where do preganglionic sympathetic nerves enter the sympathetic chain?

Answer 22

Via WRCs: therefore WRCs are only found in association with spinal nerves & chain ganglia from T1-L2

Question 23

Where are WRCs located? What are GRCs?

Answer 23

Above T1 spinal cord and below L2 spinal cord segment, there are no lateral horns (no preganglionic sympathetic outflow above T1 or below L2). Thus there are no WRCs above T1 of below L2, since there are no preganglionic sympathetic outflow to enter the chain above T1 or below L2

GRCs are the “on-ramps” used by postganglionic sympathetics destined only for the body wall and limbs- GRCs ONLY lead to spinal nerves, the nerves of the body wall and limbs. GRCs are found at ALL levels of the full extent of the sympathetic chain (cervical to sacral)

Question 24

Summarize symoathetic fibers as routes from the chain

Answer 24

ALL preganglionic symoathetics enter the chain via WRCs from th3 chain, there are routes (everywhere) to:

1. The body wall and limbs
2. Thoracic organs(heart, airways, thoracic esophagus )
3. Abdominal organs
4. Pelvic organs
5. Structures in the head

Question 25

Summarize the routes of body wall and limbs at T1-L2 levels

Answer 25

Sympathetics to spinal nerves T1-L2:

a) preganglionic s with cell bodies in lateral horn if spinal segments T1-L2 enter the sympathetic chain via WRCs—>
b) synapse in ganglia at the same spinal level
c) postganglionics exit the chain via gray rami—> spinal nerves T1-L2—> dorsal and ventral rami of these spinal nerves—>
d) innervate sweat glands, arrectir pili muscles and vascular smooth muscle in the body wall at T1-L2 levels

Question 26

Summarize the routes of body wall and limbs above T1-L2 levels

Answer 26

Sympathetics to spinal nerves above T1:

a) preganglionics with cell bodies in lateral horn of upper thoracic segments enter the chain via WRCs—>
b) ascend in chain to synapse in cervical chain ganglia —>
c) postganglionics exit chain via gray rami communicans—> spinal/nerves C1-C8
d) dorsal and ventral rami of these spinal nerves—> supply neck/upper limbs above T1 level

Question 27

Summarize the routes of sympathetics to body wall and limbs

Answer 27

Sympathetics to spinal nerves below L2:

a) preganglionics with cell bod8es in lateral horn of upper lumbar spinal segments enter the sympathetic chain via WRCs—>
b) descend in chain —> synapse in lower lumbar and sacral chain ganglia—>

C) postganglionics exit chain via gray rami—> spinal nerves L3-S5–> dorsal and ventral rami of these spinal nerves—> innervates body wall & lower limbs below L2 level

Question 28

What are the only 2 types of sympathetic targets in the body wall and limbs ?

Answer 28

1. Sweat glands

2. Smooth muscle (arrector pili muscles, blood vessels in the skin, in connective tissues and in skeletal muscles)

Question 29

What is the function of dorsal root?

Answer 29

Dorsal root is sensory only (and so far we have only seen somatic sensory nerves coming from the body wall and limbs via the dorsal and ventral rami of spinal nerves

Question 30

What is the function of the ventral root?

Answer 30

Motor only, both somatic motor and preganglionic sympathetics (visceral motor)

Question 31

How does the spinal nerve branch with dorsal and ventral rami?

Answer 31

Spinal nerve and it’s branches (dorsal and ventral ramps) are mixed nerves:

Somatic motor, somatic(and visceral) sensory and postganglionic sympathetics(visceral motor)