Sympathetic Division Adrenergic Neurons and the Adrenal Medulla

Sympathetic Summary

Previous mini lecture described three options for a preganglionic fiberThe axon of a neuron that originates in the central nervous system and synapses in an autonomic gang to synapseThe junction between two neurons where communication occurs. with postganglionic fiberThe axon of a neuron that originates in an autonomic ganglion and extends to a target organ or tissu. We realized that pre ganglionic fibers are all myelinated and all cholinergic as they are in the parasympathetic nervous systemThe organ system that controls body functions using electrical and chemical signals.. Preganglionic fibers all release acetylcholinealso know as ACh A neurotransmitter that stimulates muscle contraction. in order to excite the post ganglionic fiber. There are nicotinic receptorsCholinergic receptors found on postganglionic neurons and skeletal muscle; they respond to acetylcho on every post ganglionic fiber in both the sympathetic and parasympathetic nervous system. These nicotinic receptorsProteins located on the surface or inside cells that bind specific molecules (e.g., neurotransmitter allow the postganglionic fiber to be excited using acetylcholine and the colinergic preganglionic neuron. What’s different with the sympathetic nervous system is that postganglionic neuron can be either cholinergic or adrenergic. The cholinergic postganglionic neuronsThe functional cells of the nervous system that transmit signals. will release ACH to connect with muscarinic receptorsCholinergic receptors found on the effector organs of the parasympathetic nervous system; they media on their target organ. A adrenergic postganglionic fiber will release norepinephrineA neurotransmitter involved in attention, arousal, and the fight-or-flight response. to connect with adrenergic receptorsReceptors that bind norepinephrine and epinephrine; divided into α (alpha) and β (beta) types with on the target organ. There is yet another option for releasing norepinephrine to reach target organsOrgans affected by specific hormones.. The adrenal medullaInner part of adrenal glands producing catecholamines (epinephrine, norepinephrine). functions somewhat like a postganglionic neuron. The cellsThe basic structural and functional units of life. of the adrenal medulla have nicotinic receptors. These receptors are capable of being excited by acetylcholine.

Adrenergic Postganglionic fibers

Adrenergic postganglionic fibers can release nor epinephrineadrenaline): Fight-or-flight hormone from the adrenal medulla.. We have not yet discussed this type of release from the post ganglionic neuron. We have discussed how a cholinergic postganglionic neuron uses acetylcholine to connect to nicotinic receptors. More epinephrine can Only Connect to adrenergic receptors and affect their target organ. Depending on the type of adrenergic receptorA structure that detects stimuli. the effect could be excitatory or inhibitory. These were the receptors that were classified into alpha and beta categories. We discussed alpha and beta blockers.

3 Fates of NE

Nor epinephrine is released into the synapse between the adrenergic postganglionic neuron and its target organ. It stimulates the target organ. It excites the target organ. There are three fates of norepinephrine afterward. Like other neurotransmittersChemicals released by neurons to transmit signals across a synapse., the preganglionic neuron can reuptakeThe reabsorption of neurotransmitters by the presynaptic neuron for reuse. your epinephrine. It can load it back into vesicles for release at another time. Nor epinephrine can also just diffuse away from the synapse and most likely be broken down by an enzyme. But norepinephrine can also enter into the bloodstream where it will circulate for a few minutes. This means that sympathetic effects on target organs can last for minutes. In contrast, acetylcholine is available for only seconds to excite parasympathetic neurons. Your epinephrine can enter the bloodstream. Therefore, norepinephrine can also affect organs not innervated with sympathetic postganglionic neurons. Norepinephrine circulates for a couple of minutes. It connects to any alpha and beta receptors it can find. Eventually, the liverA large organ that produces bile, detoxifies blood, and stores nutrients. degrades it.

The Adrenal Medulla

We think about how norepinephrine can circulate in the systemic system for a few minutes. This leads us to the special case of the adrenal medulla. The adrenal medulla is made of cells called chromaffin cellsAdrenal medulla cells that secrete catecholamines.. These cells are connected to neurons. They can secrete norepinephrine and epinephrine in a much larger capacity than individual neurons. So the chromaffin cells in the adrenal medulla are like really really big and powerful post ganglionic neurons. Neurons originate in your hypothalamusA small but vital brain region controlling hormones, temperature, and autonomic functions.. They use the descending white columns to travel down the spinal cordThe central nervous system structure that relays signals between the brain and body.. Then, they leave the spinal cord by way of the ventralRelating to the front or belly side of the body. root, the spinal nerve, and the ventral ramus. Finally, they reach all the way to the adrenal medulla. These neurons reach from the hypothalamus to the adrenal medulla. They are like any other sympathetic preganglionic neuron. They are myelinated. They use the splanchnic nerve root to reach the adrenal medulla. Once they reach the adrenal medulla, the action potentials stimulate the chromaffin cells. This stimulation causes them to release a massive amount of norepinephrine and epinephrine. These hormones will then circulate in your blood for a few minutes before being degraded by the liver. This is what creates that sinking feeling in your stomach is the massive release of epinephrine and nor epinephrine.