AUTONOMIC NERVOUS SYSTEM

 

I.                    Introduction: This is a Motor System:  INVOLUNTARY Motor Neurons to SMOOTH MUSCLE (in the walls of hollow organs),

CARDIAC MUSCLE & GLANDS

 

            II.        Organization: Somatic (voluntary) versus Autonomic (involuntary)

 

-          The Somatic (voluntary) Motor System

 

 

-     The Autonomic Nervous System (ANS; involuntary, motor) uses 2 neurons to reach SMOOTH MUSCLE (in the walls of hollow organs), CARDIAC MUSCLE & GLANDS. (It does have ganglia)

 

            A.        1st = preganglionic neuron:

 

            B.                 2nd = postganglionic neuron: cell body in a ganglion (an aggregation of cell bodies) in the PNS.

 

 

 

            III.       Structure

            A.                 SYMPATHETIC = Thoracolumbar: 1st neuron cell body in lateral horn of spinal cord (lateral horns are found from T1‑L2).


            1.                  The first (preganglionic) neuron leaves the lateral horn, travels through the ventral root, enters the spinal nerve and leaves it via the white ramus communicans.  It can then synapse with a second (postganglionic) neuron in either a paravertebral ganglion (23, aligned in what are referred to as the sympathetic trunk ganglia = sympathetic chain) or in a peripheral (= prevertebral = collateral) ganglion (4, anterior to the spinal cord).

 

 

 

 

 

            B.        PARASYMPATHETIC = Craniosacral

            1.         Cranial:

            a.         1st neuron (preganglionic) cell bodies in brain stem (CNS).  Their axons course through cranial nerves III, VII, IX & X.

 

 

 

 


            b.        

 

 

 

            2.         Sacral:

            a.         1st neuron (preganglionic) cell bodies in Lateral Gray Matter. Their axons go to Terminal Ganglia and synapse with 2nd neurons. 

 

 

 

 

 

 


            IV.   Functions

            A.                 Most organs receive both sympathetic and parasympathetic innervation.  The effects may be antagonistic (in opposition to each                 other) or cooperative (working together):      

      1.                  Antagonistic Effects:

 

 

 

Parasympathetic

Sympathetic

1.  Pupil

 

Circular M. (constricts)

Radial M. (dilates)

2.  Glands

 

 

 

 

a.  Lacrimal

Stimulates

 

 

b.  Sweat

 

Stimulates

 

c.  Salivary

 

Inhibited

 

d.  Gastric

Stimulates

 

3.  Heart Rate

 

Decreases

Increases

4.  Digestive System

 

Increases Activity

Decreases Activity

 

           

            2.                  Cooperative Effects:

 

 

Parasympathetic

Sympathetic

1.  Penis

Causes Erection

Causes Ejaculation

 

 

 

B.  Some organs receive one or the other, either sym. or para. nerves:

1.      Adrenal Gland: the sym. stimulates the release of epinephrine and norepinephrine (enhances sym. effects).

2.      

 

 

3.      

 

 

4.       Most blood vessels receive sym only. It causes constriction in visceral vessels and dilation in skeletal muscle vessels.  A few vessels receive parasympathetic.  It causes dilation (e.g., blood vessels in penis).


 

 

All of the following are true regarding the sympathetic nervous system EXCEPT:

a.                   uses paravertebral ganglia.

b.                  causes the pupils to dilate.

c.                   originates from the brain stem.

d.                  causes skeletal muscle blood vessels to dilate.

e.                   increases the heart rate.