Module 14.2 The Sympathetic Nervous System Flashcards
What are the sympathetic chain ganglia?
The sympathetic chain ganglia, where most postganglionic cell bodies are found, run down both sides parallel with the vertebral column. They have a “chainlike” appearance, hence the name. The section of the chain that extends above the thoracic spinal cord terminates in the superior cervical ganglion, and the section that extends below the lumbar spinal cord terminates in the inferior sacral ganglion.
Where do preganglionic neurons originate and how do they connect to the sympathetic chain ganglion?
Preganglionic neurons originate in the lateral horns of the thoracic and lumbar spinal cord. They exit with the axons of lower motor neurons via the anterior root. The preganglionic axons quickly separate from the spinal nerve anterior ramus to form a small nerve called white (myelinated) rami communicantes, which leads to the postganglionic cell bodies in the sympathetic chain ganglion.
What happens to preganglionic axons that pass through chain ganglia without forming synapses?
Some preganglionic axons pass through chain ganglia without forming synapses. These may form synapses with collateral ganglia located near the target organ. Preganglionic axons that synapse with collateral ganglia near organs of the abdominopelvic cavity are components of splanchnic nerves.
What are the possible synapse locations between pre- and postganglionic neurons?
There are three possible synapse locations between pre- and postganglionic neurons. Preganglionic axons can synapse with postganglionic cell bodies in the sympathetic chain ganglion at the level of the spinal cord where they exited. They can also ascend or descend to synapse with postganglionic cell bodies in sympathetic chain ganglia found at a different spinal cord level than where they exited. Lastly, preganglionic axons can pass through chain ganglia and travel to collateral ganglia where they synapse.
How do postganglionic axons exit the ganglia?
Postganglionic axons exit the ganglia as small gray (unmyelinated) rami comunicantes. They reunite to travel with spinal nerves until they reach their target cells.
What are the neurotransmitters used in the sympathetic nervous system?
The neurotransmitters used in the sympathetic nervous system are Acetylcholine (ACh), Epinephrine (Adrenalin), and Norepinephrine (Noradrenalin).
What are the two major types of adrenergic receptors in the sympathetic nervous system?
The two major types of adrenergic receptors in the sympathetic nervous system are Alpha and Beta receptors.
What are the subtypes of Alpha receptors and where are they located?
The subtypes of Alpha receptors are Alpha-1 and Alpha-2. Alpha-1 receptors are located in the plasma membranes of smooth muscle cells of many different organs, including blood vessels in skin, GI tract, and kidneys, arrector pili muscles in dermis, and certain organs of genitourinary tract. Alpha-2 receptors are located in the plasma membranes of preganglionic sympathetic neurons instead of peripheral target cells.
What are the subtypes of Beta receptors and where are they located?
The subtypes of Beta receptors are Beta-1, Beta-2, and Beta-3. Beta-1 receptors are located in the plasma membranes of cardiac muscle cells, certain kidney cells, and adipose cells. Beta-2 receptors are located in the plasma membranes of smooth muscle cells lining airways of respiratory tract (bronchioles), and in the wall of urinary bladder, skeletal muscle fibers, and cells found in liver, pancreas, and salivary glands. Beta-3 receptors are primarily located in adipose cells and smooth muscle cells in walls of the digestive tract.
What are the two types of Cholinergic receptors and where are they located?
The two types of Cholinergic receptors are Muscarinic and Nicotinic receptors. Muscarinic receptors are located on sweat glands in skin. Nicotinic receptors are located in the membranes of all postganglionic neurons within sympathetic ganglia and adrenal medullae.
How do Alpha-2 receptors differ from other adrenergic receptor subtypes?
Alpha-2 receptors differ from other adrenergic receptor subtypes in that when norepinephrine binds to alpha-2 receptors, the axon terminal is hyperpolarized, which slows or cancels the action potential. This is a component of a negative feedback loop where preganglionic neuron activity is reduced or shut down to prevent excessive sympathetic output.
What are the effects of the Sympathetic Nervous System on cardiac muscle cells?
The effects of the Sympathetic Nervous System on cardiac muscle cells are that when norepinephrine binds to beta-1 receptors, ion channels open on cardiac muscle cells, raising both the rate and force of contraction. This increases the amount of blood delivered to tissues and blood pressure, maintaining homeostasis during increased physical activity.
What are the effects of norepinephrine on smooth muscle cells?
Norepinephrine has several effects on smooth muscle cells. It causes constriction of blood vessels serving the digestive, urinary, and integumentary system by binding to alpha-1 receptors, which decreases blood flow to these organs. It also causes dilation of bronchioles by binding to beta-2 receptors, which increases the amount of air that can be inhaled with each breath. Additionally, it causes dilation of blood vessels serving skeletal and cardiac muscle by binding to beta-2 receptors, which increases blood flow and allows for an increase in physical activity. It also causes contraction of urinary and digestive sphincters by binding to beta-2 and beta-3 receptors respectively, making emptying the bladder and bowel more difficult during increased physical activity.
What are the effects of norepinephrine on cellular metabolism?
During sympathetic activation, nearly all cells, especially skeletal muscle, require higher amounts of ATP. To meet this higher demand, norepinephrine has three effects: it triggers the breakdown of lipids and releases free fatty acids into the bloodstream when it binds to Beta-3 receptors on adipocytes; it triggers the release of glucose from glycogen and the synthesis of glucose from other resources when it binds to Beta-2 receptors on liver cells; and it triggers the release of the hormone glucagon, which increases blood glucose levels, when it binds to Beta-2 receptors on cells of the pancreas
What are the effects of the Sympathetic Nervous System on sweat glands?
The sympathetic nervous system attempts to maintain body temperature during periods of increased physical activity. Postganglionic sympathetic neurons release ACh onto sweat gland cells in the skin. ACh binds to muscarinic receptors that increase sweat gland secretion. This is a component of a negative feedback loop that corrects elevated body temperature.
