Chapter 13: Physiology of the Peripheral Nervous System

Question 1

Peripheral nervous system subdivisions

Answer 1

1) Somatic motor system

2) Autonomic nervous system

Question 2

Job of Autonomic nervous system

Answer 2

In most organs the parasympathetic nervous system provides the predominant tone. In blood vessels, the sympathetic. Regulate many involuntary processes.

1) Regulation of the heart
2) Regulation of secretory glands
3) Regulation of smooth muscles

Question 3

Somatic motor system

Answer 3

Controls voluntary movement of muscles

Question 4

Functions of parasympathetic nervous system relevant to pharmacology

Answer 4

• Slowing of heart rate
• Increased gastric secretion
• Emptying of the bladder
• Emptying of the bowel
• Focusing the eye for near vision
• Constricting the pupil
• Contracting bronchial smooth muscle

Question 5

Principal functions of the sympathetic nervous system

Answer 5

• Regulating the cardiovascular system
• Regulating body temperature
• Implementing of the “fight-or-flight” response

Question 6

By influencing the heart and blood vessels, the sympathetic nervous system can achieve three homeostatic objectives:

Answer 6

• Maintenance of blood flow to the brain
• Redistribution of blood flow during exercise
• Compensation for loss of blood, primarily by causing vasoconstriction

Question 7

The sympathetic nervous system helps regulate body temperature in three ways

Answer 7

1) By regulating blood flow to the skin, sympathetic nerves can increase or decrease heat loss.
2) Sympathetic nerves to sweat glands promote secretion of sweat, thereby helping the body cool
3) By inducing piloerection (erection of hair), sympathetic nerves can promote heat conservation.

Question 8

The fight-or-flight response consists of:

Answer 8

• Increasing heart rate and blood pressure
• Shunting blood away from the skin and viscera and into skeletal muscles
• Dilating the bronchi to improve oxygenation
• Dilating the pupils (perhaps to enhance visual acuity)
• Mobilizing stored energy, thereby providing glucose for the brain and fatty acids for muscles

Question 9

There are three basic patterns of autonomic innervation and regulation:

Answer 9

• In some organs (eg, the heart), sympathetic and parasympathetic nerves have opposing effects.
• In other organs (eg, male sex organs), the sympathetic and parasympathetic systems have complementary effects.
• And in still other organs (notably blood vessels), function is regulated by only one branch of the autonomic nervous system.

Question 10

Feedback Regulation

Answer 10

A process that allows a system to adjust itself by responding to incoming information.

Question 11

Elements of a feedback loop

Answer 11

1) a sensor
2) an effector
3) neurons

Question 12

The purpose of the sensor

Answer 12

To monitor the status of a physiologic process. Information picked up by the sensor is sent to the CNS where it is integrated with other relevant information. Signals are then sent from the CNS along nerves of the autonomic system to the effector.

Question 13

The purpose of the effector

Answer 13

In response to the signals from the CNS, the effector makes appropriate adjustments in the process. The entire procedure is called a reflex.

Question 14

Baroreceptor Reflex

Answer 14

The most important feedback loop of the autonomic nervous system that helps regulate blood pressure.

1) Baroreceptors located in the carotid sinus and aortic arch monitor changes in blood pressure and send this information to the brain.
2) In response, the brain sends impulses along nerves of the autonomic nervous system, instructing the heart and blood vessels to behave in a way that restores blood pressure to normal.

Question 15

Baroreceptors

Answer 15

Receptors that sense blood pressure

Question 16

Autonomic Tone

Answer 16

The steady, day-to-day influence exerted by the autonomic nervous system on a particular organ or organ system.

Question 17

Ganglion

Answer 17

Simply a mass of nerve cell bodies

Question 18

Preganglionic neurons

Answer 18

Neurons that go from the spinal cord to the parasympathetic ganglia
Neurons leading from the spinal cord to the sympathetic ganglia

Question 19

Postganglionic neurons

Answer 19

Neurons that go from the ganglia to effector organs

Question 20

The anatomy of the parasympathetic nervous system offers two general sites at which drugs can act:

Answer 20

1) The synapses between preganglionic neurons and postganglionic neurons
2) The junctions between postganglionic neurons and their effector organs.

Question 21

Medulla of the adrenal gland

Answer 21

Influences the body by releasing epinephrine into the bloodstream.

Question 22

The peripheral nervous system employs three neurotransmitters

Answer 22

Acetylcholine
Norepinephrine
Epinephrine

Question 23

Acetylcholine

Answer 23

Transmitter employed at most junctions of the peripheral nervous system. Released by:

1) all preganglionic neurons of the parasympathetic nervous system
2) all preganglionic neurons of the sympathetic nervous system
3) all postganglionic neurons of the parasympathetic nervous system
4) all motor neurons to skeletal muscles
5) most postganglionic neurons of the sympathetic nervous system that go to sweat glands

Question 24

Norepinephrine

Answer 24

Transmitter released by practically all postganglionic neurons of the sympathetic nervous system. The only exceptions are the postganglionic sympathetic neurons that go to sweat glands, which employ acetylcholine as their transmitter.

Question 25

Epinephrine

Answer 25

Major transmitter released by the adrenal medulla. (The adrenal medulla also releases some norepinephrine.)
The function is to prepare the body for fight or flight.
The only transmitter that acts at beta2 receptors
Therefore, times of fight or flight will be the only occasions on which beta2 receptors will undergo significant physiologic activation.

Question 26

There are two basic categories of receptors associated with the peripheral nervous system:

Answer 26

1. Cholinergic receptors

2. Adrenergic receptors

Question 27

Cholinergic receptors

Answer 27

Receptors that mediate responses to acetylcholine. These receptors mediate responses at all junctions where acetylcholine is the transmitter.

Question 28

Adrenergic receptors

Answer 28

Receptors that mediate responses to epinephrine (adrenaline) and norepinephrine. These receptors mediate responses at all junctions where norepinephrine or epinephrine is the transmitter.

Question 29

Subtypes of cholinergic receptors

Answer 29

nicotinicN
nicotinicM
muscarinic

Question 30

Subtypes of adrenergic receptors

Answer 30

alpha1
alpha2
beta1
beta2
In addition to the four major subtypes of adrenergic receptors, there is the dopamine receptor.

Question 31

Activation of nicotinicN (neuronal) receptors

Answer 31

Promotes ganglionic transmission at all ganglia of the sympathetic and parasympathetic nervous systems. In addition, activation of nicotinicN receptors promotes release of epinephrine from the adrenal medulla.

Question 32

Activation of nicotinicM (muscle) receptors

Answer 32

Causes contraction of skeletal muscle.

Question 33

Activation of muscarinic receptors

Answer 33

Located on target organs of the parasympathetic nervous system, elicits an appropriate response from the organ involved.

1) Increased glandular secretions (from pulmonary, gastric, intestinal, and sweat glands)
2) Contraction of smooth muscle in the bronchi and GI tract
3) Slowing of heart rate
4) Contraction of the sphincter muscle of the iris, resulting in miosis (reduction in pupillary diameter)
5) Contraction of the ciliary muscle of the eye, causing the lens to focus for near vision
6) Dilation of blood vessels
7) Voiding of the urinary bladder (by causing contraction of the detrusor muscle [which forms the bladder wall] and relaxation of the trigone and sphincter muscles [which block the bladder neck when contracted]).

Question 34

Muscarinic cholinergic receptors on blood vessels

Answer 34

These receptors are not associated with the nervous system in any way. That is, no autonomic nerves terminate at vascular muscarinic receptors.

Question 35

Alpha1 Receptors

Answer 35

Located in the eyes, blood vessels, male sex organs, prostatic capsule, and bladder (trigone and sphincter).

Question 36

Ocular alpha1 receptors

Answer 36

Present on the radial muscle of the iris. Activation of these receptors leads to mydriasis. The fibers of the radial muscle are arranged like the spokes of a wheel. Contraction of the radial muscle causes the pupil to enlarge.

Question 37

Alpha1 receptors in blood

Answer 37

Present on veins and on arterioles in many capillary beds. Activation produces vasoconstriction.

Question 38

Alpha1 receptors in the sexual apparatus of males

Answer 38

Activation causes ejaculation

Question 39

Alpha1 receptors in the smooth muscle of the bladder and prostatic capsule

Answer 39

Activation causes contraction.

Question 40

Alpha2 receptors

Answer 40

Located on nerve terminals and NOT on the organs innervated by the autonomic nervous system.
These receptors are referred to as presynaptic or prejunctional.
The function is to regulate transmitter release.
Norepinephrine can bind to alpha2 receptors located on the same neuron from which the norepinephrine was released.
The consequence of this norepinephrine-receptor interaction is suppression of further norepinephrine release.
Hence, presynaptic alpha2 receptors can help reduce transmitter release when too much transmitter has accumulated in the synaptic gap.

Question 41

Beta1 Receptors

Answer 41

Beta1 receptors are located in the heart and the kidney.

Question 42

Cardiac beta1 receptors

Answer 42

Activation of these receptors increases heart rate, force of contraction, and velocity of impulse conduction through the atrioventricular node.

Question 43

Beta1 receptors in the kidney

Answer 43

Activation causes release of renin into the blood. Since renin promotes synthesis of angiotensin, a powerful vasoconstrictor, activation of renal beta1 receptors is a means by which the nervous system helps elevate blood pressure.

Question 44

Beta2 Receptors

Answer 44

• Activation in the lung leads to bronchial dilation.
• Activation in the uterus causes relaxation uterine smooth muscle.
• Activation in arterioles of the heart, lungs, and skeletal muscles causes vasodilation.
• Activation in the liver and skeletal muscle promotes glycogenolysis thereby increasing blood levels of glucose.
• Activation in skeletal muscle enhances contraction.

Question 45

Dopamine Receptors

Answer 45

In the periphery, the only dopamine receptors of clinical significance are located in the vasculature of the kidney. 111Activation of these receptors dilates renal blood vessels, enhancing renal perfusion.

Question 46

Receptor specificity of adrenergic transmitters

Answer 46

1) epinephrine can activate all alpha and beta receptors, but not dopamine receptors;
2) norepinephrine can activate alpha1, alpha2, and beta1 receptors, but not beta2 or dopamine receptors
3) dopamine can activate alpha1, beta1, and dopamine receptors. (Note that dopamine itself is the only transmitter capable of activating dopamine receptors.)

Question 47

Subdivisions of the autonomic nervous system

Answer 47

1) Parasympathetic nervous system

2) Sympathetic nervous system