Introduction+to+the+Autonomic+Nervous+System

=**Introduction to the Autonomic Nervous System**=


 * 1. Define somatic efferent, somatic affrent, visceral efferent, viseral afferent, effector.**

__Somatic Efferent__ Sensory neurons for pain, touch, temperature from skin

__Somatic Afferent__ Motor neurons to skeletal muscle

__Viseral Efferent__ Motor neurons to smooth muscle, cardiac muscle, and exocrine glands (lacrimal, mucous, salivary, sweat)

__Visceral Afferent__ Sensory neurons from organs (viscera) -- stretch, distension, pain

__Effector__ Somatic effectors are skeletal muscle and overlying skin. Visceral effectors are smooth muscle, cardiac muscle, and exocrine glands.


 * 2. Compare the sympathetic and parasympathetic divisions of the autonomic nervous system. How are these two similar?  How are they different?**

Visceral efferent components of the autonomic nervous system are divided into sympathetic, parasympathetic, and enteric systems. All these divisions are involved in the control of involuntary muscles somewhere in the body.

The sympathetic division is involved in the fight or flight response while the parasympathetic is involved in rest and digest.


 * Feature**||**Sympathetic**||**Parasympathetic**||
 * Location of preganglionic neurons||Spinal cord, lateral horn T1-L2||Brainstem and spinal cord, cranial nerves III, VII, IX, and X, lateral horn S2-S4||
 * Location of postganglionic neurons||Paravertebral ganglia adjacent to the vertebral column and prevertebral ganglia in front of the vertebral column||Named ganglia cranial nerves III, VII, and IX and terminal ganglia in the wall of the organ||
 * Neurotransmitter||Presympathetic: Ach, Postsympathetic: NE||Presympathetic: Ach, Postsympathetic: Ach||
 * Terminal Distribution||Blood vessels, sweat and salivary glands, arector pilli smooth muscle, skin in general||Not to blood vessels, mucous, lacrimal, GI, and salivary glands, not skin in general||


 * 3. Be able to diagram a "typical" visceral efferent path for both the sympathetic and parasympathetic division of the ANS.**

__T1-L2__ Preganglionic sympathetic visceral efferent originates in the laternal horn of the spinal cord and travels out through the ventral horn to the spinal nerve and exits via white ramus into a paravertebral ganglion. There it synapses with the postganglionic efferent and exits through the gray ramus and goes back into the spinal nerve where it can move out the ventral ramus or the dorsal ramus to get to effectors.

Ventral root can contain somatic and visceral efferents. Dorsal root can contain somatic afferents. Ventral and Dorsal ramus can contain somatic and viseral efferents and somatic afferents.

__Higher Than T1, Lower than L2__ Preganglionic sympathetic visceral efferents from T1-L2 originate at the lateral hornandtravel via ventral horn to the spinal nerve, exiting at the white rami and entering the paravertebral ganglion. To reach levels higher than T1 and lower than L2, the preganglionic efferent doesn't synapse at the paravertebral ganglion but continue either up or down through interganglionic segments that connect the paravertebral ganglions at every level in a chain. Once at the appropriate level, the preganglionic efferent synapses to the postganglionic efferent in the paravetebral ganglion and exit via gray ramus to reach the ventral and dorsal rami and onward to effectors.

Gray rami exist only in T1-L2, but white rami exist at every vertebral level.

__Abdominal Viscera T5-L2__ Abdominal viscera are supplied with sympathetic efferents via prevertebral ganglia that are associated with the main branches of the abdominal aorta and are not connected in a chain like paravertebral ganglion.

To reach the abdominal viscera, preganglionic efferents begin at the lateral horn and travel through the ventral root and spinal nerve, exiting via white ramus into the paravetebral ganglion. The preganglionic efferent does not synapse but continues on through a splanchnic nerve to enter a prevertebral ganglion. It synapses there to a postganglionic efferent which follows blood vessels toward the appropriate organ effector.

Like paravertebral efferents, prevertebral efferents can use interganglionic segments to ascend or descend to the appropriate level before exiting through a splanchnic nerve and prevertebral ganglion.

Prevertebral ganglion lie along the abdomenal aorta and are named by the major branches of the abdominal aorta that it is adjacent to.

__Adrenal Medula T8-T12__ In this special case, the "pre"-ganglionic efferent starts at the lateral horn, travels the ventral root and spinal nerve, exit the white ramus and continues without synapsing through the paraveterbal ganglion, splanchnic nerve, and prevertebral ganglion. It exits and follows blood vessels directly to the medual of the adrenal gland where it stimulates neurosecretory cells to release NE. There is no synapse to a post-ganglionic efferent. Parasympathetic nerves do //not// innervate the adrenal medula.


 * 5. List the four possible terminations for the preganglionic sympathetic fiber.**

(1) Paravertebral ganglion between T1-L2. (2) Paravertebral ganglion at a vertebral column higher than T1 or lower than L2. (3) Prevertebral ganglion between T5-L2. (4) Directly on the adrenal medula without synapsing to a postganglionic sympathetic fiber.


 * 6. What is a pelvic splanchnic nerve? Describe the course and termination for a pelvic splanchnic.**

Pelvic splanchnicnerves are found in the S2-S4 region and contain parasympathetic efferents (specifically) which travel to autonomic plexuses in the lower abdomen and pelvis.

Parasympathetic efferents come from cranial nerves III, VII, IX, and X, and also S2-S4.

At S2-S4, the parasympathetic efferent originates in the lateral horn, travels through the ventral root and the spinal nerve, exiting through the ventral ramus and traveling via pelvic splanchnic nerve toward terminal ganglion located on the surface of the effector organ (urinary bladder, vagina, vas deferens, rectum, etc.)