ANS review for quiz 4/ lecture 3/11/09

The sympathetic and parasympathetic motor pathways consist of two motor neurons in series, one following the other. The first autonomic motor neuron has its cell body in the CNS while its myelinated axon extends from the CNS to an autonomic ganglion which is a collection of neuronal cell bodies outside the CNS. It is here that the autonomic ganglion contains the cell body of the 2nd autonomic motor neuron. It has an unmyelinated axon that extends directly from the ganglion to the effector(smooth muscle, cardiac muscle, or a gland).

Rami Communicans are the term used for a nerve which connects two other nerves. They are also bundles of nerve fibers connecting a sympathetic ganglion to a spinal nerve; categorized as gray rami(unmyelinated postganglionic fibers) or white rami (myelinated preganglionic fibers).

There are two groups of sympathetic ganglia. Group 1 are called: sympathetic trunk ganglia which are located near the spinal cord. Most sympathetic preganglionic axons are short. Post ganglionic axons from sympathetic trunk ganglia mostly innervate organs above the diaphragm. Group 2 are called: prevertebral ganglia. They are located anterior to the vertebrate column. Postganglionic axons innervate organs below the diaphragm. There are 3 types. These include: Celiac ganglion, superior mesenteric ganglion, inferior mesenteric ganglion.

I also learned about cholinergic neurons and receptors. Cholinergic neurons release ACH. ACH is stored in synaptic vesicles and released by exocytosis. It then diffuses across the synaptic cleft and binds with specific cholinergic receptors. There are two types called: nicotinic and muscarinic receptors. Activation of nicotinic receptors by ACH causes depolarization, thus causing excitation. Muscarinic receptors sometimes cause depolarization(excitation) or hyperpolarization (inhibition) depending on the cell.

Adrenergic neurons and receptors release norepinephrine also known as noradrenalin This is also stored in synaptic vesicles and released by exocytosis. NE diffuses across the cleft and binds to specific adrenergic receptors. There are two types of adrenergic receptors. They are Alpha and Beta.

Prior to lecture, I knew a lot about ACH from A&P I. I did not know a lot about Norepinephrine. I decided to look it up after class to learn more than what the book states. Norepinephrine is both a hormone and a neurotransmitter. As a hormone, it is secreted by the adrenal gland. It works alongside epinephrine to given the body sudden energy in times of stress, known as the "Fight or flight" response. It is a stress hormone that affects the part of the brain where attention and responding actions are controlled.

Thyroid Gland

While reviewing the Endocrine System, I was eager to learn as much as I could about the thyroid gland. This is due to the fact that a few months ago I was diagnosed with hypothyroidism.  During a routine check up, I mentioned how tired I was feeling . I was coming home from work and school with the desire to do more activities but the energy was not there to let me. I also was not sleeping well for about 2 weeks.  I do work 10 hour days and go to school and just related my symptoms to stress.  I also noticed that I had a harder time losing weight. At first I blamed it on moving to a colder climate and not being as active as I was when I lived in Florida.  My Doctor decided to check my thyroid just in case. He ran a TSH level.  The level came back high which meant that I had hypothyroidism.  He started me on a medication called Synthroid. I am taking 25 mg daily.  I have been feeling a little better but I am not good at taking medicine and I quite often forget to take my medicine when I am suppose to.

To understand why my thyroid gland could be the cause to some of my above symptoms, I needed to understand what thyroid hormones stimulate.  I learned that thyroid hormones stimulate protein synthesis and increase the use of glucose and fatty acids for ATP production.  They also increase the breakdown of triglycerides and enhance cholesterol excretion, thus reducing blood cholesterol level.

I also learned that if you are hyperthyroidism, that your thyroid is said to be hyperactive. Hyperthyroidism is a condition in which there is overproduction of the thyroid hormone thyroxine, causing the levels of thyroid hormones in the blood to be too high.  Hyperthyroidism can significantly accelerate your body's metabolism, causing sudden weight loss, rapid or irregular heartbeat, sweating, and nervousness, or irritability.

During lecture, Hasi-Moto Disease was mentioned.  I have never heard of this disease prior to lecture but it is related to hypothyroidism.  Our instruction told us the symptoms of it was increase weight in the face.  She also said, the disease made a persons face appear very round.  Since I have hypothyroidism, I wanted to know more about this. I actually went home and looked it up online after class.  It is also known as chronic lymphocytic thyroiditis. I learned that it is an auto immune disease that attacks your thyroid gland.  The resulting inflammation often leads to an underactive thyroid gland (hypothyroidism).

Sympathetic and Parasympathetic responses

Sympathetic Responses are also known as the "fight-or-flight" response. This response is important in emergencies that casue stress that require us to either fight or run away.
During activation of the sympathetic division, the release of hormones by the adrenal medullae create a set of responses. These responses include:
-Dilation of the pupils
- Increase in heart rate, force of heart contraction and blood pressure
- The airways dilate, allowing faster movement of air into and out of the lungs
-Blood vessels that supply kidneys and gastrointestinal tract constrict
-Blood vessels that supply organs involved in exercise or fighting off danger
-skeletal muscle, cardiac muscle, liver, and adipose tissue dilate, allowing greater blood flow through these tissues.
-The liver increases breakdown of glycogen to glucose and adipose tissue. This increases the breakdown of triglycerides to fatty acids and glycerol which raises blood levels of these molecules for greater ATP production.
-Release of glucose by the liver increases blood glucose level for greater ATP production
-Processes that are not essential for meeting the stressful situation are inhibited.


In regards to this last effect. I learned that some functions turn off or even stop during the fight or flight response. An example that I learned is that your digestive secretions may actually slow down. I guess if your about to get robbed and you want to turn around and run away as fast as you can, your body may be trying more to keep up with your faster breathing and faster body movements to get you away from the dangerous scene. I never really thought about this before but after reading and learning about it, it makes sense. It's pretty interesting how our body works and responds to our experiences and to our internal and external environment.

I also learned that the parasympathetic division is also referred to as the rest-and-digest division. This is important is non emergency situations. It enhances the rest and digest activities. This means that the parasympathetic responses support body functions that conserve and restore body energy during times of rest and recovery. There are five parasympathetic responses that are stimulated by this division. These include: salivation, lacrimation, urination, digestion, and defecation. These five responses increase when activated. There are also three more responses that have a decrease effect. During this division, there is a decrease in heart rate, diameter of airways known as bronchoconstriction, and a decrease in diameter of the pupils known as constriction.

A good way for me to remember when these responses come in to play is to put it into my real life experiences. When I thought about what would happen if I came home and ran into a robber, or if I was startled by one, this would be the type of situation where my sympathetic nervous system would be called into action. This system would use energy, increase my blood pressure, increase my heart rate and slow down my digestion. It would also help my run as fast as I can out of there!

Now imagine if my day was much different than this. If it was a beautiful sunny day and things were pleasant at work and I got home early and decided to sit down and relax on the couch, my parasympathetic nervous system would kick in. With my body now relaxing, it would also be time for my blood pressure to decrease, my heart rate to slow down and my digestion can start.

These responses remind me just how much our insides are effected by whats going on, on the outside or in our daily lives. It got me thinking how things like stress effect us internally and trigger responses. I think being aware of how much control we actually have over our health can help us improve the quality of our daily living.