Autonomic Nervous System Flashcards
ANS Generalities (5)
A. Regulates smooth muscle, cardiac muscle, and glands.
B. Operates without conscious control.
C. Regulates “Visceral Activities”.
D. Entirely Motor System (efferent) - however there are some afferent visceral fibers which travel with the nerves of the ANS back to the CNS.
- Sensory Information
1. Physiological information (not consciously monitored)
2. Pain = only conscious perception from viscera
(possibly “fullness” also)
E. Cells of autonomic nervous system develop from the neural crest.
Two Principal Divisions
A. Sympathetic - Thoracolumbar
B. Parasympathetic - Craniosacral
- most organs innervated by ANS have dual innervation by both divisions. These two divisions usually act in opposition to each other - what one tends to stimulate, the other tends to inhibit and vice versa.
Functions (2 big details)
a. The parasympathetic division is usually concerned with stimulation of activities which tend to restore and conserve the body’s energy - stimulates activities which will aid in the digestion and absorption of food. Tends to inhibit or reduce some other activities of the body which require energy.
b. The sympathetic division is usually concerned with activities which require energy. This is the system responsible for enormous feats of body during periods of intense stress - called the “fight or flight” response - stimulates activities which will aid one in fighting off or escaping from danger (e.g. increases blood supply to skeletal muscle, cardiac muscle, lungs, and brain - inhibits blood supply to digestive organs).
Control of ANS (3 details)
- The ANS is under CNS control and is not totally “autonomous” as the name implies.
- However, normally a conscious control is not necessary - control is normally accomplished via the hypothalamus.
- Our cerebral cortex does have indirect affects on the ANS however.
examples: - fear stimulates sympathetic division possibly through thoughts from cerebrum.
- thoughts of some food types may stimulate digestive system action.
- psychological or emotional stress may cause stimulation of the sympathetics.
Autonomic Ganglia - 3 General Groups
A. Sympathetic Trunk or Paravertebral Ganglia
1. These form a chain of ganglia located on either side of the vertebral column from the base of the skull to the coccyx. 2. Receive and transmit fibers only from the Sympathetic Division of ANS.
B. Prevertebral Ganglia
1. These ganglia lie anteriorly to the spinal column close to large abdominal arteries for which they are named (examples: Celiac and Superior Mesenteries). 2. These also receive and transmit fibers only from the Sympathetic Division.
C. Terminal or Intramural Ganglion
1. These ganglia are located very close to, or in the walls of, organs that they innervate. 2. These ganglia receive and transmit fibers from the Parasympathetic Division of the ANS only.
Structure of ANS (8 details)
A. Each visceral efferent consists of 2 sets of neurons which synapse with each other in ganglia outside of the CNS.
B. First of the 2 neurons has its nerve cell body within the CNS and sends an axon to the ANS ganglia. This is called the Preganglionic Neuron.
C. The second of these 2 neurons has its nerve cell body in the autonomic ganglia and is synapsed upon by the preganglionic neuron. The axons of these neurons course to the innervated organ = Postganglionic Neuron. Preganglionic neurons often synapse on multiple postganglionic neurons.
D. Thoracolumbar Preganglionic Neurons of the sympathetic division have their nerve cell bodies in the lateral gray horns of the thoracic and first two lumbar segments of the spinal cord.
E. Craniosacral Preganglionic Neurons of the parasympathetic division have their nerve cell bodies in nuclei within the brainstem or within the gray matter of sacral segments of the spinal cord. 90% of parasympathetic outflow is contained in the vagus nerve = cranial nerve X
F. Each preganglionic neuron of the sympathetic division synapses with multiple (20 or more) postganglionic neurons which in turn pass to several organs.
G. Preganglionic neurons of the parasympathetic division pass to only a few (1-4) postganglionic neurons which in turn pass to only a single organ.
H. Preganglionic fibers are usually myelinated and postganglionic fibers are usually unmyelinated. Therefore, fibers passing from CNS to sympathetic trunk leave spinal nerves and travel to the ganglia via white rami communicans. Some postganglionic sympathetic fibers pass directly to the organs they innervate, but most rejoin spinal nerves via a gray rami communicans (unmyelinated)
Sympathetic Division (3 big details w/ sub details)
A. Even though sympathetics arise from only the thorax and lumbar regions - the sympathetic chain extends from the base of the skull to the coccyx.
B. In cervical region, one sees 3 main sympathetic ganglia:
1) Superior Cervical Ganglion
This provides postganglionics to all structures of the head
2) Middle Cervical Ganglion
3) Inferior Cervical Ganglion (sometimes called Stellate Ganglion)
C. When a white ramus communicans enters the sympathetic trunk, several things may happen:
1. synapse immediately on postganglionic in ganglion.
2. pass up or down chain of ganglia in several levels.
3. pass through the trunk without synapsing and travel to prevertebral ganglia.
These are called Splanchnic Nerves (Thoracic Splanchnic Nerves = Greater , Lesser , and Least)
a. Greater Splanchnic Nerve
1. Arises from levels T-5 to T-9
2. Passes to celiac ganglion and celiac plexus
- postganglionics to stomach, spleen, liver, kidney, and small intestine.
3. also innervates the adrenal medulla
b. Lesser Splanchnic Nerve
1. Arises from T-10 to T-12
2. Passes to celiac plexus and plexuses around aorta and renal arteries including the superior mesenteric ganglion - postganglionics to small intestine and colon.
c. Lowest or Least Splanchnic Nerve
1. Arises from T-12
2. Passes to plexus around renal artery - postganglionics to the kidney
d. Lumbar Splanchnics
1. Include fibers in branches of sympathetic chain in the lumbar region
2. Pass to the plexus around aorta (Aortic Plexus)
e. Inferior Mesenteric Ganglion
1. Receives preganglionics from plexus around the aorta.
2. Postganglionics to distal colon, rectum, bladder, and genitals
Parasympathetic Division (4 big details w/ sub details)
A. Parasympathetic preganglionic fibers from the cranial region accompany the cranial nerves III, VII, IX, and X.
B. The most important single nerve of the parasympathetic division is the Vagus (X). This nerve provides 90% of the craniosacral outflow. The Vagus = preganglionic axons. The vagus innervates all thoracic viscera and abdominal viscera including the G.I. tract as far as the transverse colon. Right and left vagus nerves of neck become anterior and posterior vagal trunks and esophageal plexus around esophagus and then become intermixed with the sympathetic fibers in the plexuses of the abdomen
C. The parasympathetic outflow from the sacral region form the pelvic splanchnic nerves and innervate the colon, ureters, urinary bladder and reproductive organs. (note: these are different than sympathetic splanchnic nerves)
D. The cranial portion of the parasympathetics N.S. (with the exception of the vagus) have their postganglionic nerve cell bodies located in 8 ganglia (4 pair):
- ciliary ganglion - behind eye in posterior orbit
a. Preganglionics - CN III, Occulomotor Nerve
b. Postganglionics - to smooth muscle of ciliary muscle and sphincter pupillae muscles in the eye - pterygopalatine ganglion - in pterygopalatine fossa
a. Preganglionics - CN VII, Facial Nerve
b. Postganglionics - vasodilatory and secretory fibers to nose, palate, and lacrimal gland. - submandibular ganglion - suspended from the lingual nerve on the medial side of the mandible
a. Preganglionics - CN VII, Facial Nerve
b. Postganglionics - secretory fibers to submandibular and sublingual glands and to small glands in the oral cavity. - otic ganglion - located just medial to the mandibular division of the trigeminal nerve as it leaves the foramen ovale
a. Preganglionics - CN IX, Glossopharyngeal Nerve
b. Postganglionics - secretory fibers to the parotid gland
Transmitters (6 details) Neurotransmitters Sympathetic vs. Parasympathetic
- All preganglionic neurons in the ANS use acetylcholine as their neurotransmitter.
- All postganglionic neurons of the parasympathetic division also use acetylcholine as their neurotransmitter.
- Most postganglionic neurons of the sympathetic division use norepinephrine as their neurotransmitter.
- Neurons producing acetylcholine are called Cholinergic while those producing norepinephrine are called adrenergic.
- Acetylcholine is broken down very rapidly by acetylcholinesterase (AChE) and its effects are very short lived.
- Norepinephrine, on the other hand, is broken down more slowly by catechol-o-methyltransferase (COMT) and by monoamine oxidase (MAO) - as a result norepinephrine can enter the blood stream - thus sympathetic effects can be more widespread and longer lasting than parasympathetic effects.
Horner’s Syndrome
(illustrates sympathetic function in the head)
- Interruption of innervation from sympathetic trunk on one side.
- Exhibits on affected side only:
a. ptosis - drooping of upper eyelid
b. constricted pupil
c. flushing of skin color (capillary vasodilation)
d. lack of sweating - Sometimes appears with lung cancer or tumors in the upper thorax or neck.
