Neurophysiology PNS Efferent AQA Answers

**[Neurophysiology -- PNS Efferent AQ Answers]:** **Question 1** - What are the divisions of the autonomic nervous system? - **Answer:** The divisions of the autonomic nervous system are the sympathetic nervous system, parasympathetic nervous system, and the enteric nervou...

**[Neurophysiology -- PNS Efferent AQ Answers]:** **Question 1** - What are the divisions of the autonomic nervous system? - **Answer:** The divisions of the autonomic nervous system are the sympathetic nervous system, parasympathetic nervous system, and the enteric nervous system **Question 2** - **2a:** What are the CNS control centers of the ANS? - **Answer:** The medulla oblongata, the pons, and the hypothalamus. - **2b:** 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? - **Answer:** The CNS. - **2c:** What division of the nervous system do short reflexes integrate with? - **Answer:** The PNS. **Question 3** - **3a:** What are aggregations of cell bodies referred to as in the CNS? - **Answer:** Aggregations of cell bodies in the CNS are referred to as nuclei. - **3b:** What are aggregations of cell bodies referred to as in the PNS? - **Answer:** Aggregations of cell bodies in the PNS are referred to as ganglia. - **3c:** Where are the autonomic motor nuclei specifically located within the gray matter of the spinal cord? - **Answer:** The autonomic motor nuclei are located in the antero-lateral horn. - **3d:** Where are the visceral sensory nuclei specifically located within the gray matter of the spinal cord? - **Answer:** The visceral sensory nuclei are located in the postero-lateral horn. **Question 4** - **4a:** The SNS is also referred to as the thoracolumbar division of the ANS. Why? - **Answer:** The cell bodies of the neurons originate from the thoracic and lumbar regions. - **4b:** The PNS is also referred to as the craniosacral division of the ANS. Why? - **Answer:** The cell bodies of the neurons originate from the cranial and sacral regions. **Question 5** - **5a:** Why are the cells in the adrenal medullae considered to be modified postganglionic sympathetic neurons? - **Answer:** 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. - **5b:** What are the cells in the adrenal medullae? - **Answer:** Chromaffin cells. - **5c:** What do these cells secrete? - **Answer:** Mostly epinephrine, but also norepinephrine. - **5d:** What are catecholamines? - **Answer:** The catecholamines are dopamine, norepinephrine, and epinephrine. - **5e:** What is PNMT, what does it do and where is it primarily located? - **Answer:** PNMT is an [enzyme](https://en.wikipedia.org/wiki/Enzyme) found primarily in the [adrenal medulla](https://en.wikipedia.org/wiki/Adrenal_medulla) that converts [norepinephrine](https://en.wikipedia.org/wiki/Norepinephrine) to [epinephrine](https://en.wikipedia.org/wiki/Epinephrine). **Question 6** - **6a:** What are the differences in lengths of the axons, both preganglionic and postganglionic, between the parasympathetic nervous system and the sympathetic nervous system? - **Answer:** 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. - **6b:** Why does this difference between the axon lengths exist? - **Answer:** 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. - **6c:** What neurotransmitter is secreted from preganglionic PNS fibers? - **Answer:** Acetylcholine. - **6d:** What neurotransmitter is secreted from the preganglionic SNS fibers? - **Answer:** Acetylcholine. - **6e:** What receptors do the cell bodies of the postganglionic neurons of both the PNS and SNS have? - **Answer:** Both postganglionic cell bodies have nicotinic receptors (nAChRs). - **6f:** Where are these cell bodies located? - **Answer:** In the PNS, these cell bodies are located in terminal ganglia and sacral ganglia. In the SNS, these cell bodies are located in sympathetic chain ganglia and collateral ganglia. - **6g:** What neurotransmitter is secreted from postganglionic PNS fibers? - **Answer:** Acetylcholine. - **6h:** What neurotransmitter is secreted from the postganglionic SNS fibers? - **Answer:** Norepinephrine. - **6i:** What type of receptors do the effector cells being innervated by the PNS have? - **Answer:** Muscarinic receptors. - **6j:** What type of receptors do the effector cells being innervated by the SNS have? - **Answer:** Adrenergic receptors. **Question 7** - **7a:** What is a neuroeffector junction? - **Answer:** A neuroeffector junction is the synapse between a neuron and an effector other than another neuron. - **7b:** How does it differ from a synapse? - **Answer:** The neuroeffector junction differs from a synapse in that the presynaptic neuron has swollen regions known as varicosities, instead of terminal knobs. - **7c:** What signals exocytosis of neurotransmitters from varicosity? - **Answer:** The influx of calcium. - **7d:** What does norepinephrine bind to once released from a varicosity? - **Answer:** Norepinephrine binds to adrenergic receptors. **Question 8** - **8a:** What are the target tissues and organs of the autonomic nervous system? - **Answer:** Cardiac muscle, smooth muscle, adipose, and glands. - **8b:** The effectors of the ANS are said to have, in general, dual antagonistic innervation. What does this mean? - **Answer:** They are controlled by both the sympathetic nervous system and the parasympathetic nervous system. - **8c:** What are the exceptions? - **Answer:** Vascular smooth muscle (except in the heart and genitals), sweat glands, and adipose are all only innervated sympathetically. **Question 9** - **9a:** What is the fight-or-flight division of the ANS? - **Answer:** The sympathetic nervous system. - **9b:** Why is it referred to as this? - **Answer:** This response is referred as fight-or-flight because the body will prepare you to respond during fight-or-flight situations. For example, fleeing from a bear chasing you in the woods. - **9c:** During a sympathetic response, what happens to your pupils? - **Answer:** The pupils dilate (mydriasis). - **9d:** What happens to your salivary glands? - **Answer:** The salivary glands decrease secretion, producing less saliva. - **9e:** What happens to the heart? - **Answer:** Heart rate increases. - **9f:** What happens to the lungs? - **Answer:** The lungs bronchodilate. - **9g:** What happens to the GI tract? - **Answer:** Digestion is inhibited. - **9h:** Can you explain why each of these responses you listed occur? - **Answer:** These responses occur to prepare your body for a fight-or-flight response. For example, 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. **Question 10** - What is the difference between an agonist and an antagonist? - **Answer:** 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. **Question 11** - **11a:** Which adrenergic receptor is responsible for vasoconstriction and bronchoconstriction? - **Answer:** The **α**~1~ adrenergic receptor. - **11b:** What condition could an antagonist for this receptor treat? - **Answer:** Hypertension. - **11c:** What is an example of an antagonist to this receptor? - **Answer:** Prazosin (Minipress). - **11d:** If someone took an **α**~1~ antagonist, what would happen? - **Answer:** The blood vessels of the individual would vasoconstrict less, leading to vasodilation, causing a decrease in blood pressure. - **11e:** What are some examples of agonists to this receptor? - **Answer:** Phenylephrine and pseudoephedrine. - **11f:** If someone took an **α**~1~ agonist, what would happen? - **Answer:** The blood vessels of the individual would vasoconstrict more, increasing blood pressure. - **11g:** Some individuals are advised to not take over-the-counter Sudafed. Why? - **Answer:** The main ingredient in Sudafed is pseudoephedrine, which is an **α**~1~ agonist. Taking this medication would cause vasoconstriction, thereby increasing blood pressure. Individuals with high blood pressure should not take Sudafed for this reason. **Question 12** - **12a:** 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? - **Answer:** Increased vascular tone, which is known as vasoconstriction. - **12b:** How can a blood vessel vasodilate and vasoconstrict when it is only innervated and controlled by the SNS? - **Answer:** 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. **Question 13** - Which adrenergic receptor decreases digestion? In other words, what adrenergic receptor decreases peristalsis of the GI tract, as well as insulin secretion from pancreas? - **Answer:** The **α**~2~ adrenergic receptor. **Question 14** - **14a:** Which adrenergic receptor is responsible for increasing heart rate and contractility of the heart? - **Answer:** The **β**~1~ adrenergic receptor. - **14b:** What condition could an antagonist for this receptor treat? - **Answer:** Hypertension. - **14c:** What is an example of an antagonist to this receptor? - **Answer:** Metoprolol (Lopressor). - **14d:** If someone took a **β**~1~ antagonist, what would happen? - **Answer:** 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. - **14e:** What are some examples of agonists to this receptor? - **Answer:** Isoproterenol and the sympathomometics (ephedra, ma Huang, synephrine). - **14f:** If someone took an **β**~1~ agonist, what would happen? - **Answer:** 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. **Question 15** - **15a:** What is a cardiac slow cell funny channel? - **Answer:** A voltage-gated sodium channel. - **15b:** How is the funny channel regulated? - **Answer:** It opens when a slow cell repolarizes. It is also internally regulated by cAMP. **Question 16** - **16a:** Which adrenergic receptor is responsible for bronchodilation? - **Answer:** The **β**~2~ adrenergic receptor. - **16b:** What condition could an agonist for this receptor treat? - **Answer:** Asthma. - **16c:** What is an example of an agonist to this receptor? - **Answer:** Short-acting **β agonists (SABAs)**, such as albuterol (Ventolin). **Question 17** - **17a:** What is an EpiPen? - **Answer:** An EpiPen is an injection containing epinephrine, a chemical that constricts blood vessels and dilates bronchioles in the lungs. - **17b:** What receptor does the active drug of the pen act on? - **Answer:** It acts on **β**~2~ adrenergic receptors. - **17c:** Why do some people carry an EpiPen on their person at all times? - **Answer:** An EpiPen is carried by people prone to severe allergic, anaphylactic reactions in response to insect stings, bites, and certain foods. - **17d:** How does it affect the contractile state of the bronchiole smooth muscle cell? - **Answer:** Once epinephrine binds to the **β**~2~ adrenergic receptor, cAMP will inhibit myosin light chain kinase. This leads to bronchiole smooth muscle relaxation and opened airways in the lungs. **Question 18** - **18a:** What is the rest-and-digest division of the ANS? - **Answer:** The parasympathetic nervous system (PNS). - **18b:** Why is it referred to as this? - **Answer:** 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. - **18c:** During a parasympathetic response, what happens to your pupils? - **Answer:** The pupils constrict (miosis). - **18d:** What happens to your salivary glands? - **Answer:** The salivary glands increase secretion, producing more saliva. - **18e:** What happens to the heart? - **Answer:** Heart rate decreases. - **18f:** What happens to the lungs? - **Answer:** The lungs bronchoconstrict. - **18g:** What happens to the GI tract? - **Answer:** The GI tract stimulates peristalsis and secretion. - **18h:** Can you explain why each of these responses you listed occur? - **Answer:** 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. **Question 19** - **19a:** Which muscarinic receptors are responsible for bronchoconstriction? - **Answer:** The **M**~2~ and M~3~ adrenergic receptors. - **19b:** What condition could an antagonist for these receptors treat? - **Answer:** Asthma. - **19c:** What is an example of an antagonist to the **M**~2~ receptor? - **Answer:** Short-acting **muscarinic antagonists (SAMAs)**, such as ipratropium (Atrovent). **Question 20** - **20a:** Which muscarinic receptor is responsible for decreasing heart rate? - **Answer:** The **M**~2~ receptor. - **20b:** What is an example of an antagonist to the **M**~2~ receptor? - **Answer:** Atropine. - **20c:** If someone took an **M**~2~ antagonist, what would happen? - **Answer:** Heart rate would increase. **Question 21** - **21a:** How do erectile dysfunction medications work? Explain the entire mechanism with all cells, signaling molecules and enzymes involved. - **Answer:** Acetylcholine activation of the M~3~ 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. - **21b:** What is the mechanism by which drugs like Viagra work? - **Answer:** Viagra inhibits cGMP PDE; thus, cGMP is not degraded and allows for more vascular smooth muscle relaxation. - **21c:** For what individuals are drugs like Viagra potentially dangerous? - **Answer:** Hypotensive patients. **Question 22** - **22a:** Where are baroreceptors located? - **Answer:** Baroreceptors are located in the carotid arteries in the neck and in the aortic arch. - **22b:** How do they function? - **Answer:** They sense changes in blood pressure and stimulate a response in opposition to this change. - **22c:** What carries the sensory information from these receptors to the medulla of the brainstem? - **Answer:** The glossopharyngeal nerve and the vagus nerve. - **22d:** What are the efferent SNS and PNS responses to the heart and vasculature in response to an acute increase in blood pressure? - **Answer:** 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. - **22e:** What are the efferent SNS and PNS responses to the heart and vasculature in response to an acute decrease in blood pressure? - **Answer:** 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. **Question 23** - **23a:** Where are chemoreceptors located? - **Answer:** 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. - **23b:** How do they function? - **Answer:** They sense changes to the concentrations of carbon dioxide and oxygen in blood, as well as changes in the pH of blood. - **23c:** What carries the sensory information from these receptors to the medulla of the brainstem? - **Answer:** The glossopharyngeal nerve and the vagus nerve. - **23d:** What are the efferent SNS and PNS responses to the heart and vasculature in response to an acute increase in pH in the plasma? - **Answer:** 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. - **23e:** What are the efferent SNS and PNS responses to the heart and vasculature in response to an increase in carbon dioxide? - **Answer:** 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. **Question 24** - **24a:** The enteric nervous system (ENS) is composed of what two nerve plexuses? - **Answer:** The myenteric and submucosal plexuses. - **24b:** Where are they found in regard to the four layers of the GI tract? - **Answer:** The submucosal plexus is in the submucosa and the myenteric plexus is buried in the smooth muscle of the muscularis. - **24c:** What are the alternate names of each plexus? - **Answer:** 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. **Question 25** - **25a:** What is the somatic nervous system (SNS)? - **Answer:** The somatic nervous system carries motor and sensory signals to and from the CNS. - **25b:** What effectors does it control? - **Answer:** Skeletal muscle. **Question 26** - **26a:** Where are the somatic motor nuclei located in the gray matter of the spinal cord? - **Answer:** In the anterior horn. - **26b:** Where are the somatic sensory nuclei located in the gray matter of the spinal cord? - **Answer:** In the posterior horn. **Question 27** - **27a:** How does the somatic nervous system motor neuron pathway differ from the ANS pathway? - **Answer:** In the somatic nervous system, there is just one neuron that goes to the effector. In ANS pathways, there are two neurons in series, the preganglionic and postganglionic neurons. - **27b:** What is secreted from the motor neuron and where? - **Answer:** Acetylcholine is secreted in the neuromuscular junction. **Question 28** - **28a:** What is a withdrawal reflex? - **Answer:** A withdrawal reflex is an involuntary process that causes a part of the body to automatically pull away from something that is causing pain. - **28b:** Can you provide a specific example and explain how it works in detail? - **Answer:** One example is when you touch something hot. In this process, the pain receptors in the affected area send a message to the spinal cord. When the message reaches the spinal cord, an interneuron sends a message along to the nerves that control flexor muscles near the affected area. These motor neurons then tell the appropriate muscles to flex, which results in pulling the body part away from whatever is causing the pain. - **28c:** What muscle is contracted and what muscle is relaxed? - **Answer:** The biceps contract and the triceps relax. **Question 29** - **29a:** What is a Golgi tendon reflex? - **Answer:** In a Golgi tendon reflex, skeletal muscle contraction causes the agonist muscle to simultaneously lengthen and relax. - **29b:** Can you provide a specific example and explain how it works in detail? - **Answer:** When you pick up a dumbbell that is too heavy, you will immediately drop it due to the Golgi tendon reflex. Increased tension stimulates sensory receptors and the sensory neuron is excited. In the spinal cord, the sensory neurons activate inhibitory neurons and the motor neuron is inhibited. The effector muscle relaxes and relieves excess tension. This protects the muscle fibers and tendons from potential damage. - **29c:** What muscle is contracted and what muscle is relaxed? - **Answer:** The triceps contract and the biceps relax. **Question 30** - **30a:** What is a patellar reflex (i.e., stretch reflex)? - **Answer:** The patellar reflex is the kicking movement of the lower leg in [response](https://www.britannica.com/topic/reflex-physiology) to a sharp tap on the patellar tendon. - **30b:** Can you provide a specific example and explain how it works in detail? - **Answer:** The tendon below your kneecap connects to the quadriceps muscle on the top of your thigh. The hammer's tap on the tendon slightly stretches the muscle. Sensory nerves in the muscle are stimulated by the stretching and send an impulse to an interneuron in the spinal cord. Motor nerves in the spinal cord then conduct the impulse right back to the quadriceps, triggering a muscle contraction that makes you kick. In addition, they also activate an inhibitory neuron that will prevent the hamstring muscles from contracting. - **30c:** What muscle is contracted and what muscle is relaxed? - **Answer:** The quadriceps contract and the hamstrings relax. **Question 31** - **31a:** What is a crossed-extensor reflex? - **Answer:** The crossed extensor reflex is a withdrawal reflex. - **31b:** Can you provide a specific example and explain how it works in detail? - **Answer:** When a person steps on a nail, the leg that is stepping on the nail pulls away, while the other leg takes the weight of the whole body. You activate the nociceptors that will send sensory information to the spinal cord. This will activate an inhibitory neuron that will prevent the quadriceps from contracting. The sensory neuron will also activate the hamstring muscles and contraction will occur. - **31c:** What muscle is contracted and what muscle is relaxed, in each leg? - **Answer:** In the leg stepping on the tac, the hamstrings will contract, and the quadriceps will relax. In the leg stabilizing the body, quadriceps will contract and the hamstrings will relax. **Question 32** - **32a:** Classify these four reflexes as contralateral or ipsilateral? - **Answer:** The crossed-extensor reflex is contralateral, while the withdrawal, golgi-tendon and the patellar reflexes are ipsilateral. - **32b:** What about the signal that is sent to the brain after the reflex has already occurred in the patellar and Golgi tendon reflexes? - **Answer:** This signal is sent by what is known as the axon collateral. This axon collateral synapses with the interneuron that also synapses with the motor neuron, and is responsible for notifying the brain of the incidence happening peripherally.