Autonomic Nervous System, Part II

All Autonomic impulses are afferent, meaning that they travel from the CNS to the PNS. The ANS can be broken down into two major divisions, the Parasympathetic and the Sympathetic divisions. The Parasympathetic division is responsible for all of the feed-and-breed or rest-and-digest functions of the body and is the restorer of homeostasis. The preganglionic axon is long and the post ganglionic axon is short. The Sympathetic division can be seen as the parasympathetic divisions opposite. The Sympathetic division carries out the fight-or-flight responses in our body. In this division, the preganglionic axon is shot and the post ganglionic axon is long. In both divisions, the target cells are smooth muscle, cardiac muscle and glands. Another commonality is that all preganglionic neurons release Ach and all receptors on the post ganglionic neurons are thus nicotinic.

There are two different categories of receptors for the ANS. Cholinergeric, which includes both Nicotinic and Muscarinic receptors and Adrenergic receptors. Nicotinic receptors always cause excitation or activation and perform as both the receptor and channel. They also only bind Ach. Muscarinic receptors can either cause excitation of inhibition and use either a PKA pathway or a PKC pathway to allow chemicals to enter the neuron. Both pathways utilize G-Proteins. Adrenergic receptors also utilize these pathways and are broken down into a1, a2, b1, b2, b3 receptors. The 1's refer to impulses that cause constriction or contraction and the 2's refer to impulses that cause dilation. B3 is the odd man out and its impulse causes heat production. Muscarinic and Adrenergic receptors are found on the cells of terminal targets.

I understood from lecture that the Adrenal gland, a gland that sits on top of the kidneys, is part of the sympathetic nervous system. This gland produces both epinephrine and norepinepherine by diffusing the hormones into the blood stream. This direct link into the blood stream allows for a fast regulation of the hormone throughout the body. That was as much as I was able to retain from lecture, so I researched a little more on the Internet. I learned that adrenal medulla is the central core of the Adrenal gland. The neurons within it (called Chromaffin cells) produce the hormones that are released into the blood stream instead of producing an impulse as all of the other neurons that we have learned about do. These hormones aid in the fight-or-flight response by increasing blood pressure, metabolic rate and or glucose concentration. The neurons in the Adrenal Medulla also produce dopamine, which low-levels of this hormone has been linked to Parkinson's diseases.