Systems Biology
The sympathetic nervous system is the "fight or flight" division of the autonomic nervous system, responsible for preparing the body to respond to stress. The sympathetic nerves originate from the thoracolumbar region of the spinal cord and its ganglia are arranged in parallel chains. Preganglionic neurons are relatively short, releasing acetylcholine, while postganglionic neurons are much longer and generally release norepinephrine. One exception is the postganglionic neurons in sweat glands, which release acetylcholine. Another exception involves the adrenal medulla, where preganglionic neurons synapse directly with chromaffin cells, which secrete norepinephrine and epinephrine into the bloodstream.
Sympathetic stimulation prepares the body for immediate survival by decreasing digestion, routing blood and energy to skeletal muscles, and causing piloerection. Other effects include increased electrical conductance in the skin, dilated pupils, increased airflow through the lungs, and elevated heart rate. These responses enable the body to effectively react to stressful situations, prioritizing short-term needs for survival over long-term maintenance.
Lesson Outline
<ul> <li> Introduction <ul> <li>The balance between sympathetic and parasympathetic stimulation supports homeostasis</li> <li>The sympathetic nervous system is the "fight or flight" division of the NS</li> </ul> </li> <li> Sympathetic Nervous System Anatomy <ul> <li>Nerves originating from thoracic and lumbar regions</li> <li>Two-neuron relay system with preganglionic neurons and postganglionic neurons</li> <li>Sympathetic ganglia arranged in chains alongside spinal column</li> </ul> </li> <li> Neurotransmitters in the Sympathetic System <ul> <li>Acetylcholine released by all preganglionic neurons (cholinergic)</li> <li>Norepinephrine released by almost all postganglionic neurons (exceptions: sweat glands and adrenal medulla) </li> </ul> </li> <li> Adrenal Medulla and Chromaffin Cells <ul> <li>Preganglionic neurons synapse with chromaffin cells</li> <li>Chromaffin cells secrete norepinephrine and epinephrine into the bloodstream</li> </ul> </li> <li> Effects of Sympathetic Stimulation <ul> <li>Decreased digestion</li> <li>Increased blood flow to skeletal muscles</li> <li>Piloerection (hair standing on end)</li> <li>Increased electrical conductance in the skin</li> <li>Dilated pupils</li> <li>Increased airflow through lungs (bronchodilation)</li> <li>Elevated heart rate</li> </ul> </li> </ul>
Don't stop here!
Get access to 71 more Systems Biology lessons & 8 more full MCAT courses with one subscription!
FAQs
The sympathetic nervous system (SNS) is a crucial component of the autonomic nervous system responsible for initiating the fight or flight response. When the body perceives a threat, the SNS activates physiological changes to prepare the body for a quick reaction. This includes increasing heart rate, dilating pupils, mobilizing energy resources, and increases blood flow to skeletal muscles (and redirects blood flow away from non-essential organs such as the digestive system), all of which enable the individual to either confront the danger or flee from it.
The thoracolumbar division is a term used to describe the location from which the sympathetic preganglionic neurons originate. These neurons are found in the spinal cord's intermediolateral cell column, specifically in the thoracic and upper lumbar segments (T1 to L2). This anatomical distribution of the preganglionic neurons provides the name "thoracolumbar division" to the sympathetic nervous system.
Preganglionic neurons have cell bodies located within the spinal cord and form synapses with postganglionic neurons in sympathetic ganglia. These neurons are characterized by shorter axons and release the neurotransmitter acetylcholine. Postganglionic neurons, on the other hand, have cell bodies in the sympathetic ganglia with longer axons that extend to the target tissues. Postganglionic neurons primarily release norepinephrine to activate the physiological changes associated with the fight or flight response.
Preganglionic neurons release acetylcholine because it is the neurotransmitter responsible for transmitting excitatory signals across synapses to activate postganglionic neurons. Once activated, postganglionic neurons release norepinephrine, which acts as the primary neurotransmitter of the sympathetic nervous system. Norepinephrine binds to adrenergic receptors on target cells, leading to widespread physiological changes required for the fight or flight response.
The adrenal medulla is a specialized part of the adrenal gland that serves as an extension of the Sympathetic Nervous System. In response to sympathetic activation, the adrenal medulla releases catecholamines, namely epinephrine and norepinephrine, directly into the bloodstream. This release amplifies the fight or flight response by increasing blood circulation, respiration rate, and glucose release while simultaneously preparing the body for rapid action during a perceived threat.
