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.