Human Physiology Chapter 11

The adrenal medulla is important to the sympathetic branch of the autonomic nervous system because

-It is a source of catecholamines -It is considered a modified sympathetic ganglion -It releases epinephrine and norepinephrine directly into the blood

Which statements apply to the parasympathetic division of the nervous system?

-It is dominant during "resting and digesting." -Its ganglia are nearby, on or within their target organs

Which functions are controlled through the autonomic nervous system?

-Blood pressure -Heart rate -Water balance -Temperature regulation

Which area(s) of the brain exert(s) control over the autonomic nervous system?

-Cerebrum -Hypothalamus -Pons -Medulla

B3 receptor

-Found in adipose tissue -Sensitivity: NE>E -Effect on second messenger: increases cAMP

B2 receptor

-Found in certain blood vessels and smoother muscles of some organs -Sensitivity: E>NE -Effect on second messenger: increases cAMP

a2 receptor

-Found in gastrointestinal tract and pancreas -Sensitivity: NE>E -Effect on second messenger: Decreased cAMP

B1 receptor

-Found in heart muscle, kidney -Sensitivity: NE=E -Effect on second messenger: Increases cAMP

a1 receptor

-Found in most sympathetic target tissues -Sensitivity: Respond greater to norepinephrine than epinephrine -Effect on second messenger: Activates phospholipase C

The motor end plate is

A folded area of muscle cell membrane with ACh receptors clustered at the top of each fold.

Which tissues contain both cholinergic and adrenergic receptors, and how does this relate to their autonomic control?

A list is provided in Fig. 11-5 in the chapter. For most target organs listed, acetylcholine and (nor)epinephrine have opposite effects on the target organ.

Released by all autonomic preganglionic neurons description

Acetylcholine

Sympathetic tissue receptor description

Adrenergic receptor

The drug Chantix, which treats nicotine addiction, is an __________ for the nicotine receptor.

Agonist

Describe the different types of adrenergic receptors in the autonomic nervous system. Which neurotransmitter binds to each type? For those that bind more than one neurotransmitter, how does the response to the neurotransmitters compare?

Alpha 1, alpha 2, beta 1, beta 2, and beta 3 receptors are described in Table 11-2. Most of these receptors are more sensitive to norepinephrine than to epinephrine, but they will all respond to either neurotransmitter. These neurotransmitters are nearly identical structurally, and the response of the target tissue to the binding of either is the same.

Which area is NOT normally considered to be an autonomic control center?

Amygdala (Pons, Medulla, and Hypothalamus are)

Anne Frank wrote a diary about the years she and a few others spent in hiding from the Nazis during World War II. These people lived in the upstairs rooms of a shop, accessible only by a hidden stairway; Anne called these quarters the Secret Annex. One day Nazis raided the shop below, but were unsuccessful in locating the hideaways or finding proof of their presence during this particular raid. Clearly hearing what was occurring downstairs, Anne and her cohorts cowered in silence, for they feared being transported to "death camps." Later, Anne wrote that most of the residents of the Secret Annex experienced diarrhea shortly after this close call. Explain this response by their digestive systems.

Assuming there is no pathogenic or dietary cause, diarrhea probably resulted from the fight-or-flight response of the sympathetic nervous system. Digestive tract secretion and motility are inhibited during a sympathetic response. When the threat had passed and the sympathetic nervous system released the digestive targets from inhibition, there may have been a rebound effect in which the parasympathetic division overstimulated the motility of the tract. Increased motility with decreased time for reabsorption of water can result in diarrhea. It is also thought that the sympathetic response actually stimulates the lower gastrointestinal tract though it inhibits the upper tract. This could also account for the effects.

Antagonistic control of efferent output is typical of the __________ division.

Autonomic

The presence of two peripheral efferent neurons in a pathway is typical of the __________ division.

Autonomic

Both alpha-bungarotoxin and curare bind to the same neurotransmitter receptor, but only curare binds reversibly. Which receptor is involved? List some locations for this receptor. Would either toxin be appropriate to use as a paralytic during surgery? Explain your answer. Are all such receptors necessarily affected by a given toxin in the same way?

Both of these toxins bind to the nicotinic acetylcholine receptor. This type of receptor is located on skeletal muscle and in autonomic ganglia. For a paralytic during surgery, curare would be appropriate but bungarotoxin would not, because the irreversibility of bungarotoxin binding results in permanent paralysis of skeletal muscles. Bungarotoxin binds to the receptors in skeletal muscle but not to those in autonomic ganglia, illustrating a structural difference in the receptors in these two sites.

"Dual innervation" refers to an organ receiving

Both sympathetic and parasympathetic nerves

Describe the general rules for the identity of neurotransmitters secreted by pre- and postganglionic neurons in the autonomic division. Be sure to specify the types of receptors, where relevant, and describe the exceptions.

Both sympathetic and parasympathetic neurons secrete acetylcholine onto nicotinic receptors within the autonomic ganglion. Postganglionic sympathetic neurons secrete norepinephrine onto adrenergic receptors. Postganglionic parasympathetic neurons secrete acetylcholine onto muscarinic receptors. Exceptions include sympathetic postganglionic neurons that secrete acetylcholine, and nonadrenergic, noncholinergic neurons that secrete substance P, somatostatin, vasoactive intestinal peptide, adenosine, nitric oxide, or ATP.

In a laboratory experiment, adding curare, which binds to acetylcholine receptors, to the solution around a muscle decreases the size of the end plate potential. Adding prostigmine, an acetylcholinesterase blocker, increases the size of the end plate potential. Explain why.

By binding to acetylcholine receptors, curare prevents the binding of acetylcholine. Curare does not open the receptor channels. An end plate potential results from the opening of several ACh receptor channels. Thus, if the receptor is blocked, any end plate potential that is produced would be smaller. Prostigmine blocks the enzyme that stops ACh action by degrading the neurotransmitter. Interfering with this enzyme prolongs the action of ACh, thus more receptor channels open and the end plate potential is larger.

Parasympathetic tissue receptor description

Cholinergic muscarinic receptor

Target receptor for preganglionic neurons description

Cholinergic nicotinic receptor

Sweat glands contain

Cholinergic receptors

Describe the different types of cholinergic receptors in the nervous system. Which neurotransmitter binds to each type?

Cholinergic receptors are either nicotinic or muscarinic; they are distinguishable by the binding of either nicotine or muscarine to the same receptors. Both receptors bind to acetylcholine.

Each of these statements is true except one. Identify the exception. A) Monoamine oxidase is the main enzyme responsible for the degradation of catecholamines. B) β1 receptors respond equally well to both epinephrine and norepinephrine. C) β2 receptors are not innervated by sympathetic neurons, so are more sensitive to epinephrine, delivered via the blood. D) Activation of α receptors opens Na+ channels in the membrane.

D

Nicotine enhances the release of __________ in the brain

Dopamine

Explain what is meant by antagonistic control.

For fine-tuned control over the body's internal state, one autonomic branch may have an excitatory effect on a particular organ while the other branch is inhibitory.

To perform surgery with a minimum of pain for the patient and hassle for the surgeon, a patient may be administered a general anesthetic to prevent sensation and consciousness, as well as a paralytic to prevent reflexive muscle spasms. From what you have learned of motor control, suggest mechanisms by which a paralytic can prevent muscle contraction. With paralytics, what extra measure must be taken to keep the patient alive? Name such a paralytic agent.

From Ch. 9, students should remember that somatic motor control involves the motor areas of the cerebral cortex and the basal nuclei, as well as the cerebellum. A drug that affects activity selectively in those areas could act as a paralytic; however, it is difficult to imagine the nature of the selectivity that would be required, given the use of similar neurotransmitters and receptors throughout the brain. These motor control areas of the brain act upon the spinal motor neurons, which release acetylcholine onto skeletal muscle fibers. These fibers have a type of receptor not found on autonomic targets: the nicotinic acetylcholine receptor. The neuromuscular junction is the single point of control of a skeletal muscle by its motor neuron. A drug that interferes with synaptic transmission at this junction could be a paralytic. Because the respiratory muscles are also controlled by nicotinic neuromuscular junctions, artificial respiration must be provided by the surgical team until the paralytic is cleared from the system. Curare is a drug that works this waycurare binds to the nicotinic ACh receptor, preventing the muscles from being activated by ACh.

Increased parasympathetic stimulation

Increases gastric motility

Though you are an attentive parent, you lost track of your inquisitive toddler for a few minutes, just long enough for him to wander into the garage and open a package of insecticide that you use to control insects in your garden. You have no idea if any of the poison has been ingested, inhaled, or absorbed through his skin. You take the package away from your child and read under the "caution" section that it is an anticholinesterase. Given that this poison was made for insects, not humans, should you be worried? Explain your answer. What would happen to the child if he has indeed been affected? Explain which type of synapses could be affected. Propose an antidote (it's OK if you don't remember a specific compound, just describe what type of effect may reverse the effects of the insecticide).

Insects have acetycholine receptors that are similar enough to ours so that yes, you should be worried. Anticholinesterases block the degradation of acetylcholine, thereby prolonging its effects in both muscarinic and nicotinic synapses. If the dose is high enough, spastic paralysis could result, in which muscles contract uncontrollably. If this happens with the respiratory muscles, the victim may die of suffocation. Autonomic effects would also be expected, including sweating and nausea. A chemical such as atropine, which blocks muscarinic receptors, will alleviate some of the symptoms. Oximes (not mentioned in text) block nicotinic receptors and can be administered to counteract nicotinic effects of the poison.

An alien retrieved alive from a crashed UFO has had a thorough medical examination. A hormone with a distinct but similar structure to epinephrine has been isolated, and named ufo-epi: If the results of ufo-epi treatment of humans included pupil dilation, localized sweating, high blood pressure, and high blood glucose, which conclusion would be indicated?

It acts on alpha adrenergic receptors.

Phenelzine is a common MAO inhibitor that has been used to treat depression. It is not, however, prescribed as often as other antidepressants due to its effects on the autonomic nervous system. Describe several side effects that may result from taking phenelzine and explain why they might occur.

MAO inhibitors prevent the enzymatic breakdown of catecholamines such as norepinephrine. As a result, a higher concentration of norepinephrine remains in the synapse and therefore is able to elicit a longer / stronger response on its target tissues. Consequently, norepinephrine can prolong its activity through sympathetic pathways to increase heart rate and blood pressure, decrease gastric motility causing constipation as well as prevent penile ejaculation leading to sexual dysfunction.

What steps are necessary to terminate neurotransmitter action? What would happen if these steps failed?

Neurotransmitter molecules are either enzymatically degraded or are taken back into the presynaptic terminal (reuptake). Calcium ions are removed from the axon terminal. Failure of these steps prolongs the action of the neurotransmitter. Consequences vary according to the identity of the effector organ. In a skeletal muscle, for example, this can lead to spastic paralysis.

At the molecular level, what are the effects of nicotine on the nervous system? How are these effects exerted? How are these effects similar to or different from those of curare? How do these effects explain some of the physiological consequences of smoking?

Nicotine binds to a type of acetylcholine receptor known as the nicotinic receptor; nicotine does not bind to the other type of acetylcholine receptor, the muscarinic receptor. Like acetylcholine, nicotine activates the receptor and produces a postsynaptic response. Nicotinic receptors are located on skeletal muscles and on the postganglionic neurons of both the sympathetic and parasympathetic nervous divisions. Curare also binds to the nicotinic acetylcholine receptor, but it does not activate the receptor; therefore the effect of curare is paralysis of skeletal muscles. Overall, nicotine is a CNS stimulant, suggesting greater stimulation of the sympathetic division than of the parasympathetic division.

Primary sympathetic neurotransmitter description

Norepinephrine

Which of the following has its cell body in the ganglion?

Postganglionic neuron

The two divisions of the efferent side of the peripheral nervous system are

Somatic motor neurons and autonomic neurons.

The division of the autonomic nervous system that prepares the body for intense levels of activity and stress is the

Sympathetic division

Describe the major anatomical differences between the sympathetic and parasympathetic branches.

Sympathetic pathways exit the spinal cord in the thoracic and lumbar regions whereas parasympathetic pathways exit through the cranial and sacral regions. Also, sympathetic ganglia are located near the spinal cord; and therefore, sympathetic pathways typically have short preganglionic fibers and long postganglionic fibers. In contrast, parasympathetic ganglia are located on or near their target tissue; and therefore, parasympathetic pathways have long preganglionic fibers and short postganglionic fibers.

The two types of cholinergic receptors are __________ and __________.

nicotinic, muscarinic

Compare and contrast the voltage-gated sodium and potassium channels introduced in Ch. 8, with the acetylcholine receptor/channel. What may be confusing to the beginning physiology student trying to understand the ion specificity of the acetylcholine receptor? What type of change in the cell is produced by ion movement through each type of channel?

The voltage-gated sodium channel opens in response to threshold voltage and allows sodium to enter the cell, thereby depolarizing the membrane potential. The potassium channel is also opened by threshold voltage and allows potassium to exit the cell, repolarizing or hyperpolarizing the membrane potential. The acetylcholine receptor is a neurotransmitter receptor as well as an ion channel. Because the channel is opened by binding of a chemical, it is a chemically gated channel. This channel is permeable to both sodium and potassium; when the channel opens, sodium diffuses into the cell and potassium diffuses out. The inward positive charge is sufficient to depolarize the skeletal muscle to threshold. Students are often confused by the fact that more than one type of ion moves through the acetylcholine receptor channel, and that the muscle cell is able to depolarize to threshold despite the exit of potassium.

Epinephrine and norepinephrine that are released from the adrenal glands affect target tissue for a longer period of time than the same substances released from neurons at their peripheral receptors. Why?

There are no enzymes to break down epinephrine and norepinephrine in the blood and very little in peripheral tissues.

Inside the ganglia are interneurons, which modulate messages

True for both sympathetic and parasympathetic

Contains cholinergic neurons.

True for both the sympathetic division and the parasympathetic divisions

On average, one preganglionic neuron synapses with eight or nine postganglionic neurons, each innervating a different target.

True for both the sympathetic division and the parasympathetic divisions

The neural pathway from the spinal cord to the target tissue has two neurons, the preganglionic neuron and the postganglionic neuron.

True for sympathetic and parasympathetic

Most preganglionic neurons originate in the thoracic and lumbar regions of the spinal cord

True only for sympathetic division

Dominates during resting-and-digesting activities.

True only for the parasympathetic division

The cell bodies of preganglionic neurons are found either in the brain stem or in the sacral region of the spinal cord

True only for the parasympathetic division

The neurotransmitter acetylcholine is released by neurons at the neuroeffector synapse

True only for the parasympathetic division

Important during stress or emergencies (fight-or-flight).

True only for the sympathetic division

Releases norepinephrine at the neuroeffector synapse

True only for the sympathetic division

The adrenal medulla is closely allied with this system.

True only for the sympathetic division

The ganglia are found in a chain that runs close to the spinal cord or along the descending aorta.

True only for the sympathetic division

67) Explain the use of the terms fight and flight in describing sympathetic motor responses. How does sympathetic activity explain your increased "jumpiness" when you are home alone at night, watching a horror movie on TV?

When presented with a real or imaginary threat, the sympathetic motor system produces changes that prepare the body to oppose the threat ("fight") or run away from the threat ("flight" is the past tense of "flee"). Responses include an increase in heart and respiratory rate, and increased blood flow to cardiac and skeletal muscle. Reading or watching scenes that are threatening to others, even if you could not possibly be at risk, can produce the same sympathetic response in you as if you were actually present in the scene. If the phone rings or there is a knock at the door, you are likely to react to that very quickly, because you are primed for action.

Most postganglionic sympathetic neurons secrete __________ onto their target cells.

norepinephrine

The signal molecule __________ elicits the stronger response from alpha receptors.

norepinephrine

Cholinergic receptors respond to the neurotransmitter __________.

acetylcholine

The two varieties of adrenergic receptors are __________ and __________.

alpha, beta

Cholinergic nicotinic receptors are found in the __________ of the ANS.

autonomic ganglia

Autonomic neurotransmitters are synthesized in the __________.

axon

The signal molecule __________ elicits the stronger response from beta2 receptors.

epinephrine

An alien retrieved alive from a crashed UFO has had a thorough medical examination. A hormone with a distinct but similar structure to epinephrine has been isolated, and named ufo-epi: If humans administered a physiological dose of ufo-epi responded to the chemical, which of the following would indicate ufo-epi is an epinephrine agonist?

increase in fatty acids in the blood

salivation

parasympathetic agonist

blocks secretion of pancreatic enzymes

parasympathetic antagonist

blocks urination

parasympathetic antagonist

Cholinergic muscarinic receptors are found at the __________ in the ANS.

parasympathetic neuroeffector junctions

decreased activity in digestive tract

sympathetic agonist

fat breakdown

sympathetic agonist

pupil dilation

sympathetic agonist

blocks secretion of adrenal catecholamines

sympathetic antagonist

blocks sweating

sympathetic antagonist

The __________ is the major source of parasympathetic output.

vagus nerve

__________ are swellings that contain vesicles filled with neurotransmitter.

varicosities