LEC 7: Autonomic Nervous System - 08.20.2014 Flashcards Preview

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Flashcards in LEC 7: Autonomic Nervous System - 08.20.2014 Deck (56):

What are the two basic fiber types in a spinal nerve

1. Afferent fibers

2. Efferent fibers


How many total Afferent and Efferent fibers are there

(2) Afferent Fibers

(2) Effernt Fibers

Total of (4) Fibers in a spinal nerve


What are General fibers

  • Fibers that can be found anywhere in the body "from the nose to the toes"
  • All fibers in spinal nerves are General fibers


NB: no "special" fibers in spinal nerves (cranial nerves only)



What are the four (4) fiber types

1. General Somatic Afferent (GSA)

2. General Somatic Efferent (GSE)

3. General Visceral Afferent (GVA)

4. General Visceral Efferent (GVE)


Label this drawing

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Dorsal Root Ganglion (DRG), which contains Afferent Sensory Fibers

1. Cell Body of General Somatic Afferent Fiber

  • takes sensation (sensory) from body walls

2. Cell Body of General Visceral Afferent Fiber

  • takes sensation (sensory) from inside organs


referred pain

  • pain perceived somewhere in body, other than at/from the source of irritation
  • e.g. heart pain felt/perceived in left arm
  • basis of referred pain is that somatic/visceral bodies lie in same root




The Autonomic Nervous System

The peripheral nervous system (PNS) is divided into two (2) branches:

1. Somatic System - dervies from somites, innervates skeletal muscle and skin

2. Autonomic System - innervates smooth muscle, cardiac muscle, glands

NB: As opposed to CNS (brain and spinal cord), the PNS is composed of all the nerves/ganglia that communicate with CNS.


What does the somatic branch of the peripheral nervous system innervate

skeletal muscle and skin; dervied from "somites"


What does the autonomic branch of the peripheral nervous system innervate

smooth muscle, cardiac muscle, glands


Which fibers make up the autonomic nervous system (ANS)

General Visceral Efferent (GVE) Fibers


How many neurons are relayed in the ANS

the ANS is a 2 (neuron) motor system


What does the ANS control

1. feeding

2. fighting

3. fleeing

4. sex

NB: it innervates the visceral structures


viscus, viscera

viscus (singular, Latin) "hollow organ"

viscera (plural, Latin) for "internal organs"


What does the ANS innervate

visceral structures made up of:

  • smooth muscle (e.g. eye, bladder, erectile tissue, gastrointestinal tract, arrector pili, blood vessels)
  • cardiac muscle (heart)
  • glands (e.g.sweat, salivary, lacrimal, adrenal, liver)


arrector pili

small muscles attached to hair follicles in mammals; contraction of these muscles causes the hairs to stand on end "goose bumps"


lacrimal glands

tear glands


Is the ANS motor or sensory

(by our definition) the ANS is purely motor (efferent); there is not a sensory part of the ANS by this definition

NB: true that there is an afferent (sensory) trigger, carried by General Visceral Afferent (GVA) fibers, but by our definition GVA is NOT part of the ANS


Afferent = sensory = dorsal root ganglion

Efferent = motor = ventral root


How many motorneurons are involved in the ANS

Two (2) motorneurons


A image thumb


splanchnon (Greek, singular) "hollow organ"


Describe the two (2) motorneuron relay in the ANS

  • (2) General Visceral Efferent (GVE) fibers
  • 1st neuron = preganglionic neuron (presynaptic)
    • nucleus (initial cell body) in brain stem
    • axon = myelinated
    • Neurotransmitter = acetylcholine
  • 2nd neuron = postganglionic neuron (postsynaptic)
    • ganglion (cell body) receives signal from 1st
    • axon = unmyelinated
    • effector (target) = smooth muscle, cardiac muscle, glands


nucleus and tract

  • nucleus = nerve cell bodies (somas) found WITHIN the CNS (brain and spinal cord)
  • tract = nerve cell processes (axons/fibers) found WITHIN the CNS (brain and spinal cord)


ganglion and nerve

  • ganglion = nerve cell bodies (somas) found OUTSIDE the CNS
  • nerve = nerve cell processes (axons/fibers) found OUTSIDE the CNS



How are anatomical subdivisions of ANS determined

By location (either brain or spinal cord of first (preganglionic) cell bodies


NB: cell bodies of preganglionic nerves (1st nerves) also called nuclei


What are the two (2) subdivisions of the ANS

1. sympathetic nervous system

  • thoracolumbar (inital cell bodies are in T/L portion of spinal cord)

2. parasympathetic nervous system

  • craniosacral (initial cell bodies are in S portion of spinal cord or in brain stem)


Where are the preganglionic cell bodies located in the sympathetic division of the ANS

thoracolumbar spine (T1-L2)


Describe the fibers of the sympathetic division of the ANS

  • Short preganglionic fibers
  • Long postganglionic fibers


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For the sympathetic division of the ANS, where are the cell bodies of the preganglionic nerves located 

In the intermediolateral nucleus (column), T1-L2


NB: remember that nucleus is the word for many cell bodies of neurons within the CNS

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In the sympathetic nervous system, where is the cell body of the second neuron located (in other words, where does the first synapse occur)

Can be either:

1. paravertebral ganglia: chain of ganglia, also known as sympathetic chain

  • most of the cell bodies of the sympathetic nervous system

2. prevertebral ganglia: series of ganglia that sit in front of the aorta

  • celiac, superior mesenteric, inferior mesenteric


Label this picture

Q image thumb

A. Ventral Root

B. Doral Root

C. Spinal Nerve

D. Dorsal Ramus

E. Ventral Ramus

F. Lateral Cutaneous Branch

G. Anterior Cutaneous Branch


Label this diagram (G-N)

Q image thumb

G. Spinal cord

H. Sympathetic trunk

I. Grey ramus

J. White ramus

K. Pia mater

L. Arachnoid mater

M. Dura mater

N. Vertebral body


Label this diagram (A-F)

Q image thumb

A. Ventral Root

B. Dorsal Root, Dorsal Root Ganglion

C. Paravertebral Ganglion (Cell bodies of 2nd motorneuron in Sympathetic Nervous System)

D. Spinal Nerves

E. Transverse Process

F. Intervertebral Foramen


Label this diagram

Q image thumb

A. Intermediolateral nucleus (column) 

  • Where cell body (nucleus) of preganglionic nerve sits (ANS, sympathetic)

B. Sympathetic Chain Ganglion 

  • Where synapse of preganglionic nerve and postganglionic nerve occurs (ANS, sympathetic)

C. Gray Ramus Communicans

  • no myelin sheath

D. White Ramus Communicans

  • myelin sheath



Splanchnic nerve

presynaptic fibers will travel via splanchnic nerve to the prevertebral ganglia

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Do preganglionic fibers have to synapse at the level or origin

No, synapses may occur at different levels

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What happens when preganglionic nerves do not synapse in the sympathetic chain ganglia (paravertebral ganglia)

  • Most presympathetic ganglia synapse in sympathetic chain ganglia (paravertebral ganglia)
  • Some miss the sympathetic change and travel, via the SPLANCHNIC NERVE to prevertebral ganglia


Label this diagram and give the root values of the nerves

Q image thumb

A. Sympathetic Chain

B. Greater Splanchnic Nerve (T5-T9)

C. Lesser Splanchnic Nerve (T10-T11)

D. Least Splanchnic Nerve (T12)

E. Lumbar Splanchnic Nerve (L1, L2)


Root Values

 vertebral level at which a nerve is born


Splanchnic nerves

On the whole, carrying preganglionic sympathetic nerves to second cell bodies that are living in these non-chain ganglia (transporting to prevertebral ganglia)


Where are grey and white communicans found


  • no grey/white communicans in cervical, lumbar (3-5), sacral, or coccygeal
  • can only have a presynaptic fiber if you're in the area of T1-L2


Cranial Nerves vs. Spinal Nerves notation

Cranial Nerves are Roman Numerals: III, VII, IX, X

Spinal Nerves are Arabic Numerals: S2-4


Parasympathetic Nervous System and its relationship to the nervous system as a whole

Nervous system is:

1. Central Nervous System (brain, spinal cord)

2. Peripheral Nervous System (outer nerves communicating with CNS)

  • Somatic
  • Autonomic
    • Sympathetic
    • Parasympathetic


Describe the fibers of the parasympathetic division of the ANS

  • Long preganglionic fibers
  • Short postganglionic fibers


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Where are the cell bodies of the presynaptic nerves (1st nerves) located in the parasympathetic nervous system

Two (2) possible places:

  • Nuclei of cranial nerves (nuclei = lots of cell bodies of nerves WITHIN the CNS)
  • Intermediolateral nucleus (Column) in S2-S4

A image thumb

Where is the synapse of 1st and 2nd motorneuron located in parasympathetic nervous system

Ganglia for synapse of parasympathetic nervous system are located in, on, or near effector

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What are the targets of the second nerve in the parasympathetic nervous system

Trick: same as sympathetic nervous system; targets of all of Autonomic Nervous System are:

  • smooth muscle
  • cardiac muscle
  • glands


From where do the nerves of the parasympathetic nervous system arise (where are the presynaptic cell bodies)

  • Brain Stem
    • Nerves III, VII, IX, X
    • Nerve X = vagus "wanderer"
  • Low portions of the Sacral part of the spinal cord
    • S2-S4
    • special name "pelvic splanchnics"



Dividing line in gut between vagal nerve (Cranial Nerve X) and pelvic splanchnic innervation is at...

Left Colic Fixture of Large Intestine

A image thumb

Cranial Nerve X

Vagus Nerve

  • vagus = Latin "wandering"
  • this is the "Big Mama" of nerves

Cranial Nerve X does everything through thorax, foregut, most of midgut, and up to LEFT COLIC FIXTURE of large intestine


Evolution of Autonomic Nervous System for Somatic Nervous System

ANS is probably the more ancient system (evolution)


Autonomic Nerve System is nerve fibers that innervate...

  • smooth muscle
  • cardiac muscle
  • glands

NB: It is not automatic, subliminal, or unconcious


How many neurons make up nerves in the ANS

Two (2) neurons, not only one


Sympathetic vs. Parasympathetic:

Region where preganglionic cell bodies found


  • thoraco-lumbar (T1-L2)


  • cranio-sacral (S2-S4)


Sympathetic vs. Parasympathetic:

Preganglionic fibers


  • short preganglionic fibers


  • long preganglionic fibers


Sympathetic vs. Parasympathetic:



  • synapse in prevertebral ganglia or paravertebral ganglia (sympathetic chain)
  • sometimes synapse in other ganglia that sit in gut (celiac, superior & inferior mesenteric)


  • synapse in ganglia located in, on, or near the effector structure


Sympathetic vs. Parasympathetic:



  • long postganglionic fibers


  • short postganglionic fibers


Sympathetic vs. Parasympathetic:

Postganglionic fibers


  • Thoracic splanchnics
    • Greater (T5-T9)
    • Lesser (T10, T11)
    • Least (T12)
  • Lumbar splanchnics (L1, L2)


  • Pelvic splanchnics (S2, S3, S4)