PSL 310 Biology Study Set: Efferent Exam 2 Terms & Definitions

What are the divisions of the autonomic nervous system?

The sympathetic nervous system, parasympathetic nervous system, and the enteric nervous system.

What are the CNS control centers of the ANS?

The medulla oblongata, the pons, and the hypothalamus.

While there are control centers in the CNS for ANS function, the ANS primarily works by way of reflexes. What division of the nervous system do long reflexes integrate with?

The CNS.

What division of the nervous system do short reflexes integrate with?

The PNS.

What are aggregations of cell bodies referred to as in the CNS?

Nuclei.

What are aggregations of cell bodies referred to as in the PNS?

Ganglia.

Where are the autonomic motor nuclei specifically located within the gray matter of the spinal cord?

The antero-lateral horn.

Where are the visceral sensory nuclei specifically located within the gray matter of the spinal cord?

The postero-lateral horn.

The SNS is also referred to as the thoracolumbar division of the ANS. Why?

The cell bodies of the neurons originate from the thoracic and lumbar regions.

The PNS is also referred to as the craniosacral division of the ANS. Why?

The cell bodies of the neurons originate from the cranial and sacral regions.

Why are the cells in the adrenal medullae considered to be modified postganglionic sympathetic neurons?

The adrenal medullae is under control of preganglionic sympathetic neurons. The cells in the adrenal medulla are modified postganglionic sympathetic neurons and secrete epinephrine into the blood stream instead of neurotransmitters into a synaptic cleft.

What are the cells in the adrenal medullae?

Chromaffin cells.

What do these cells secrete?

Mostly epinephrine, but also norepinephrine.

What are catecholamines?

Dopamine, norepinephrine, and epinephrine.

What is PNMT, what does it do and where is it primarily located?

PNMT is an enzyme found in the adrenal medulla that converts norepinephrine to epinephrine.

What are the differences in lengths of the axons, both preganglionic and postganglionic, between the parasympathetic nervous system and the sympathetic nervous system?

In the parasympathetic nervous system, the preganglionic axons are long and the postganglionic axons are short. In the sympathetic nervous system, the preganglionic axons are short, and the postganglionic axons are long.

Why does this difference between the axon lengths exist?

In the PNS, the ganglia are distant from the spinal cord and are often close to, and sometimes within, the organ where the target cell is located.

What neurotransmitter is secreted from preganglionic PNS fibers?

Acetylcholine.

What neurotransmitter is secreted from the preganglionic SNS fibers?

Acetylcholine.

What receptors do the cell bodies of the postganglionic neurons of both the PNS and SNS have?

Nicotinic receptors (nAChRs).

Where are the postganglionic neuron (PNS and SNS) cell bodies located?

PNS: In terminal ganglia and sacral ganglia. In the SNS, these cell bodies are located in sympathetic chain ganglia and collateral ganglia.

What neurotransmitter is secreted from postganglionic PNS fibers?

Acetylcholine.

What neurotransmitter is secreted from the postganglionic SNS fibers?

Norepinephrine.

What type of receptors do the effector cells being innervated by the PNS have?

Muscarinic receptors.

What type of receptors do the effector cells being innervated by the SNS have?

Adrenergic receptors.

What is a neuroeffector junction?

The synapse between a neuron and an effector other than another neuron.

How does the neuroeffector differ from a synapse?

The presynaptic neuron has swollen regions known as varicosities, instead of terminal knobs.

What signals exocytosis of neurotransmitters from varicosity?

The influx of calcium.

What does norepinephrine bind to once released from a varicosity?

Adrenergic receptors.

What are the target tissues and organs of the autonomic nervous system?

Cardiac muscle, smooth muscle, adipose, and glands.

The effectors of the ANS are said to have, in general, dual antagonistic innervation. What does this mean?

They are controlled by both the sympathetic nervous system and the parasympathetic nervous system.

What are the ANS exceptions?

Vascular smooth muscle (except in the heart and genitals), sweat glands, and adipose are all only innervated sympathetically.

What is the fight-or-flight division of the ANS?

The sympathetic nervous system.

Why is it referred to as this?

Because the body will prepare you to respond during fight-or-flight situations. For example, fleeing from a bear chasing you in the woods.

During a sympathetic response, what happens to your pupils?

The pupils dilate (mydriasis).

What happens to your salivary glands in a sympathetic response?

The salivary glands decrease secretion, producing less saliva.

What happens to the heart in a sympathetic response?

Heart rate increases.

What happens to the lungs in a sympathetic response?

The lungs bronchodilate.

What happens to the GI tract in a sympathetic response?

Digestion is inhibited.

Explain why fight or flight responses occur.

During dangerous conditions, you want your body to pump more blood to your heart, thereby increasing the amount of oxygen going to your lungs and tissues.

What is the difference between an agonist and an antagonist?

When something (a drug, for example) binds to a receptor and increases its function, that would be considered an agonist. If the drug binds to the receptor and inhibits its function, that would be considered an antagonist.

Which adrenergic receptor is responsible for vasoconstriction and bronchoconstriction?

The α1 adrenergic receptor.

What condition could an antagonist for a1 receptor (vaso/bronchoconstriction) treat?

Hypertension.

What is an example of an antagonist to an a1 (vaso/bronchoconstriction) receptor?

Prazosin (Minipress).

If someone took an α1 antagonist, what would happen?

The blood vessels of the individual would vasoconstrict less, leading to vasodilation, causing a decrease in blood pressure.

What are some examples of agonists to this receptor?

Phenylephrine and pseudoephedrine.

If someone took an α1 agonist, what would happen?

The blood vessels of the individual would vasoconstrict more, increasing blood pressure.

Some individuals are advised to not take over-the-counter Sudafed. Why?

The main ingredient in Sudafed is pseudoephedrine, which is an α1 agonist. Taking this medication would cause vasoconstriction, thereby increasing blood pressure. Individuals with high blood pressure should not take Sudafed for this reason.

Most blood vessels of the human body are innervated by just one division of the ANS - the sympathetic nervous system. What is the effect of the SNS on vascular tone?

Increased vascular tone (vasoconstriction).

How can a blood vessel vasodilate and vasoconstrict when it is only innervated and controlled by the SNS?

Vasoconstriction is regulated through the firing frequency of the preganglionic sympathetic neuron. More SNS stimulus leads to vasoconstriction, while less SNS stimulus leads to vasodilation.

Which adrenergic receptor decreases digestion? In other words, what adrenergic receptor decreases peristalsis of the GI tract, as well as insulin secretion from pancreas?

The α2 adrenergic receptor.

Which adrenergic receptor is responsible for increasing heart rate and contractility of the heart?

The β1 adrenergic receptor.

What condition could an antagonist for the B1 receptor treat?

Hypertension.

What is an example of an antagonist to the B1 receptor?

Metoprolol (Lopressor).

If someone took a β1 antagonist, what would happen?

The heart would contract less, thereby lowering heart rate. If the heart isn't contracting as much blood per minute, then less blood is packed into the vessels at once, decreasing blood pressure.

What are some examples of agonists to the B1 receptor?

Isoproterenol and the sympathomometics (ephedra, ma Huang, synephrine).

If someone took an β1 agonist, what would happen?

The heart would contract more frequently, thereby increasing heart rate. If the heart contracts more, more blood is pushed into the arteries, increasing blood pressure.

What is a cardiac slow cell funny channel?

A voltage-gated sodium channel.

How is the funny channel regulated?

It opens when a slow cell repolarizes. It is also internally regulated by cAMP.

Which adrenergic receptor is responsible for bronchodilation?

The β2 adrenergic receptor.

What condition could an agonist for the B2 receptor treat?

Asthma.

What is an example of an agonist to the B2 receptor?

Short-acting β agonists (SABAs), such as albuterol (Ventolin).

What is an EpiPen?

An EpiPen is an injection containing epinephrine, a chemical that constricts blood vessels and dilates bronchioles in the lungs.

What receptor does the active drug of the pen act on?

It acts on β2 adrenergic receptors.

Why do some people carry an EpiPen on their person at all times?

An EpiPen is carried by people prone to severe allergic, anaphylactic reactions in response to insect stings, bites, and certain foods.

How does an EpiPen affect the contractile state of the bronchiole smooth muscle cell?

Once epinephrine binds to the β2 adrenergic receptor, cAMP will inhibit myosin light chain kinase. This leads to bronchiole smooth muscle relaxation and opened airways in the lungs.

What is the rest-and-digest division of the ANS?

The parasympathetic nervous system (PNS).

Why is it referred to "rest and digest?"

The PNS is referred to as the rest and digest division of the ANS because your body is in the recovery or rest phase from a flight or fight response. The digestive system is active during this time.

During a parasympathetic response, what happens to your pupils?

The pupils constrict (miosis).

What happens to your salivary glands in a parasympathetic response?

The salivary glands increase secretion, producing more saliva.

What happens to the heart in a parasympathetic response?

Heart rate decreases.

What happens to the lungs in a parasympathetic response?

The lungs bronchoconstrict.

What happens to the GI tract in a parasympathetic response?

The GI tract stimulates peristalsis and secretion.

Explain why each of the parasympathetic responses occur.

These responses occur to restore your body to homeostasis from a fight-or-flight response. For example, during resting conditions, you want your body to pump less blood to your muscles and more to your digestive organs.

Which muscarinic receptors are responsible for bronchoconstriction?

The M2 and M3 adrenergic receptors.

What condition could an antagonist for these receptors treat?

Asthma.

What is an example of an antagonist to the M2 receptor?

Short-acting muscarinic antagonists (SAMAs), such as ipratropium (Atrovent).

Which muscarinic receptor is responsible for decreasing heart rate?

The M2 receptor.

What is an example of an antagonist to the M2 receptor?

Atropine.

If someone took an M2 antagonist, what would happen?

Heart rate would increase.

How do erectile dysfunction medications work? Explain the entire mechanism with all cells, signaling molecules and enzymes involved.

Acetylcholine activation of the M3 receptors in endothelial cells leads to the activation of nitric oxide synthase, which will induce nitric oxide production. Nitric oxide will diffuse into the smooth muscle cells of blood vessels and activate guanylate cyclase. Guanylate cyclase converts GTP into cGMP, which stimulates the vascular smooth muscle cells to relax (causing vasodilation). Because of this, more blood has the capability to flow into the genitals, causing an erection.

What is the mechanism by which drugs like Viagra work?

Viagra inhibits cGMP PDE; thus, cGMP is not degraded and allows for more vascular smooth muscle relaxation.

For what individuals are drugs like Viagra potentially dangerous?

Hypotensive patients.

Where are baroreceptors located?

Baroreceptors are located in the carotid arteries in the neck and in the aortic arch.

How do they function?

They sense changes in blood pressure and stimulate a response in opposition to this change.

What carries the sensory information from these receptors to the medulla of the brainstem?

The glossopharyngeal nerve and the vagus nerve.

What are the efferent SNS and PNS responses to the heart and vasculature in response to an acute increase in blood pressure?

During an acute hypertensive episode, blood pressure needs to decrease. The SNS will decrease activity to the heart, slowing heart rate and decreasing contractility, as well as to the vasculature, causing vasodilation. The PNS will increase activity to the pacemaker of the heart to slow heart rate.

What are the efferent SNS and PNS responses to the heart and vasculature in response to an acute decrease in blood pressure?

During an acute hypotensive episode, blood pressure needs to increase. The SNS will increase activity to the heart, increasing heart rate and contractility, as well as to the vasculature, causing vasoconstriction. The PNS will decrease activity to the pacemaker of the heart, thereby increasing heart rate.

Where are chemoreceptors located?

Chemoreceptors are located in the carotid bodies, which are located in the carotid arteries that run through the neck to the brain. They are also located in the aortic bodies, which are found in the aortic arch.

How do chemoreceptors function?

They sense changes to the concentrations of carbon dioxide and oxygen in blood, as well as changes in the pH of blood.

What carries the sensory information from these receptors to the medulla of the brainstem?

The glossopharyngeal nerve and the vagus nerve.

What are the efferent SNS and PNS responses to the heart and vasculature in response to an acute increase in pH in the plasma?

During an acute increase in plasma pH (alkalosis), blood pressure needs to decrease. The SNS will decrease activity to the heart, slowing heart rate and decreasing contractility, as well as to the vasculature, causing vasodilation. The PNS will increase activity to the pacemaker of the heart to slow heart rate.

What are the efferent SNS and PNS responses to the heart and vasculature in response to an increase in carbon dioxide?

During an acute increase in carbon dioxide (hypercapnia), blood pressure needs to increase. The SNS will increase activity to the heart, increasing heart rate and contractility, as well as to the vasculature, causing vasoconstriction. The PNS will decrease activity to the pacemaker of the heart to increase heart rate.

The enteric nervous system (ENS) is composed of what two nerve plexuses?

The myenteric and submucosal plexuses.

Where are the myenteric and submucosal plexuses found in regard to the four layers of the GI tract?

The submucosal plexus is in the submucosa and the myenteric plexus is buried in the smooth muscle of the muscularis.

What are the alternate names of each plexus?

The submucosal plexus is also referred to as the Meissner's plexus, and the myenteric plexus is also referred to as the Auerbach's plexus.

What is the somatic nervous system (SNS)?

The somatic nervous system carries motor and sensory signals to and from the CNS.

What effectors does the SNS control?

Skeletal muscle.

Where are the somatic motor nuclei located in the gray matter of the spinal cord?

In the anterior horn.

Where are the somatic sensory nuclei located in the gray matter of the spinal cord?

In the posterior horn.