1. Autonomic Nervous System
TEACH Lesson Plan Manual for Herlihy’s The Human Body in Health and Illness
5th edition
Chapter 12
Autonomic Nervous System

2. Lesson 12.1 Autonomic Nervous System
Describe the function and pathway of autonomic (visceral) reflexes.
Do the following regarding the autonomic nervous system:
Describe the function of the autonomic nervous system.
Identify the two divisions of the autonomic nervous system.
State the anatomical and functional differences between the sympathetic and parasympathetic nervous systems.
Define autonomic terminology used in pharmacology.
Differentiate between autonomic tone and vasomotor tone.

3. Lesson 12.1 Autonomic Nervous System, cont’d
Discuss autonomic nervous system neurons, including:
Define cholinergic and adrenergic fibers.
Name the major neurotransmitters of the autonomic nervous system.
Name and locate the cholinergic and adrenergic receptors.
Explain the terms used to describe the effects of neurotransmitters and drugs on autonomic receptors.

4. Autonomic Nervous System
Allows the organs to respond to changing body needs
Carries out automatic and unconscious visceral responses
Regulates organ function (visceral reflexes)
Examples: Pupillary response and blood pressure reflex
Examples of visceral reflexes include regulation of heart rate, pupillary response to light, and secretions and motility of the digestive tract.
What would it be like if, during a race, you were breathless because your cells needed more oxygen and you had to make a conscious decision to increase their oxygen supply? (Because this type of conscious control of heart rate and respiration is impossible, the ANS takes care of it automatically, both speeding up and slowing down heart rate and respiration as bodily needs require.)

5. Visceral Reflex Pathway
Activation of receptor
Transmission of sensory information to central nervous system (CNS)
Processing of sensory information by CNS
Transmission of motor response to effector organ(s)
Visceral response
The regulation of blood pressure via the baroreceptor reflex illustrates the five stages of the visceral reflex pathway. A sudden decrease in blood pressure activates the baroreceptors (pressure receptors). Sensory nerves (CN IX and CN X) carry the nerve impulse to the medulla oblongata, a part of the brain stem (CNS).
The medulla oblongata determines that the blood pressure is low. It sends a motor signal to the relevant effector organs, the heart, and blood vessels. These organs respond in ways that elevate blood pressure to normal.

6. Division of the Autonomic Nervous System
Sympathetic
Fight-or-flight
Parasympathetic
Feed and breed
The ANS has two divisions, parasympathetic and sympathetic.
Most organs have dual innervation; they are innervated by parasympathetic and sympathetic nerves.
For example, sympathetic stimulation of the heart increases heart rate and parasympathetic stimulation of the heart decreases its rate.
Increased sympathetic activity causes constriction of the blood vessels, and decreased sympathetic activity causes the blood vessels to dilate.
Looking at Figure 12-1, explain why the parasympathetic division is called the craniosacral outflow and the sympathetic is called the thoracolumbar outflow. (These terms refer to the places where the fibers exit the CNS.)
Refer to Table 12-1 to see different organ responses (p. 219).

7. Sympathetic Reponses Fight-or-flight response
Heart rate and contractile strength increase
Blood vessels constrict
Blood pressure increases
Bronchial tubes dilate
Pupils dilate
Adrenal medulla secretes epinephrine and norepinephrine
Excess sweating (diaphoresis)
Flight-or-flight causes physical responses that allow the body to deal with an emergency.
How does your body feel when you are scared to death? (Students’ responses should include increased heart rate, increased rate of breathing, and other responses listed on the slide.)
Continuous stress leads to overworking the sympathetic nervous system and can cause stress-induced illnesses.

8. Parasympathetic Responses
Feed-and-breed response
Heart rate decreases
Blood pressure decreases
Digestive tract stimulates motility and secretion
Parasympathetic stimulation characterizes the body’s state when in a calm or nonthreatened mode—hence the alternate nickname, “rest and digest.”
This state is characterized by resting heart rate and respiratory activity and by other responses listed in Table 12-1 (p. 219).
However, in a situation that is perceived as hopeless, a massive parasympathetic discharge can cause a very slow and sometimes fatal heart rate. This is called “bradying down,” after the word bradycardia (a heart rate less than 60 beats/min).

9. Autonomic Terminology and Pharmacology
Sympathomimetic
Increases heart rate, force of cardiac contraction, and blood pressure
Parasympathomimetic
Decreases heart rate, increases digestive activity
Vasomimetic
Vagolytic
Many drugs work by altering autonomic activity. Thus, many pharmacology terms refer to the autonomic nervous system.
If a drug causes effects similar to parasympathetic activity, it is also called vagomimetic. If a drug slows parasympathetic activity, it is called vagolytic.

10. Autonomic Tone and Vasomotor Tone
Sympathetics and parasympathetics continuously fire at a low level
Each system dominates in specific situations
Resting heart rate: Parasympathetics
Vasomotor (blood vessel) tone: Sympathetics
In the resting state, parasympathetic activity is generally stronger. Parasympathetic tone maintains the resting heart rate at around 72 beats/min.
When physical activity increases, the sympathetic system fires more intensely, resulting in increased heart rate.
Autonomic tone also keeps the blood vessels somewhat constricted, helping regulate blood pressure.
Life-threatening situations such as hemorrhagic shock can also activate the sympathetic nervous system; most of the symptoms of shock are due to sympathetic activity.

11. Numbers and Ganglia
Arrangement of both sympathetic and parasympathetic fibers
Preganglionic fiber
Ganglion
Postganglionic fiber
Preganglionic fiber (neuron 1) transmits information from the CNS to a ganglion, a collection of cell bodies.
Postganglionic fiber (neuron 2) transmits information to the effector organs, such as the heart, stomach, and bladder in the viscera.
In the sympathetic and parasympathetic divisions, the type and length of fiber, as well as the location of the ganglia, differ.

12. Neurons of the Sympathetic Nervous System
Location of ganglia
Close to and parallel to spinal cord
Paravertebral ganglia
Naming of fibers
Preganglionic: Cholinergic
Postganglionic: Adrenergic
The neurons of the sympathetic nervous system leave the spinal cord at the thoracic and lumbar levels (T1 to L2). The sympathetic nervous system is therefore called the thoracolumbar outflow.
Preganglionic fibers make numerous connections within the paravertebral ganglia, creating the more diffuse response that would be expected in a fight-or-flight situation.
The firing of a single sympathetic neuron is capable of providing a generalized, widespread sympathetic response; many organs respond to sympathetic firing.
The adrenal gland (adrenal medulla) acts as a modified sympathetic ganglion.
Postganglionic fibers are adrenergic and secrete norepinephrine as their neurotransmitter.
See Table 12-2 for more information (p. 223).

13. Parasympathetic Neurons
Location of ganglia
Near or in effector organ
Naming of fibers
Preganglionic: Cholinergic
Postganglionic: Cholinergic
The neurons of the parasympathetic nervous system leave the CNS at the level of the brain stem and sacrum. The parasympathetic nervous system is therefore called the craniosacral outflow.
Parasympathetic ganglia are located close to or within the target organs, so there is no need for them to have a chain of ganglia running along the spinal cord. Because the ganglia are close to the target organs, parasympathetic activity results in a localized response.
In the parasympathetic system, both preganglionic and postganglionic fibers are cholinergic and secrete acetylcholine as their neurotransmitter. (See Table 12-2 on p. 223.)

14. Running with Cranial Nerves
Oculomotor nerve (CN III)
Facial nerve (CN VII)
Glossopharyngeal nerve (CN IX)
Vagus nerve (CN X)
The oculomotor nerve innervates most of the extrinsic eye muscles (skeletal muscles) that move the eyeball.
The oculomotor nerve also carries parasympathetic fibers to two intrinsic eye muscles: the constrictor muscle of the eye, which causes pupillary constriction, and the ciliary muscle, which controls the shape of the lens of the eye.
The facial nerve carries parasympathetic fibers to the tear glands (eyes), salivary glands (mouth), and nasal glands (nose).
The glossopharyngeal nerve carries parasympathetic fibers to the salivary glands in the mouth.
The vagus nerve (the “wanderer” nerve) carries over 80% of the parasympathetic fibers.

15. Fibers and Neurotransmitters
Two neurotransmitters
Acetylcholine (ACh)
Norepinephrine
Two types of fibers
Cholinergic
Adrenergic
Postganglionic fibers and associated neurotransmitters determine organ responses.
For example, sympathetic discharge releases norepinephrine, which increases heart rate.
Parasympathetic discharge releases acetylcholine, which decreases heart rate.

16. Neurotransmitters: Termination of Activity
ACh is secreted by cholinergic fibers and diffuses to its receptor
Afterward, it is degraded by acetylcholinesterase (AChE)
Norephinephrine (NE) secreted by adrenergic fibers
Do the effects of ACh or NE last longer? Why? (The effects of NE are more prolonged because of the manner in which NE is terminated.)
Most of the NE is reabsorbed by the adrenergic nerve terminals themselves. The termination of NE is called reuptake.
Excess NE can be degraded by an enzyme located within the adrenergic nerve terminal and is called monoamine oxidase.
Some of the NE is merely “washed away” from the synapse and is degraded by another enzyme found in surrounding tissue. The name of this enzyme is catechol-O-methyltransferase.

17. Two Types of Autonomic Nervous System Receptors
Cholinergic
Muscarinic
Nicotinic (NN)
Adrenergic
Alpha1
Beta1 and beta2
Neurotransmitters bind to specific receptors located on the effector organs, such as the heart, stomach, and pupil of the eye.
Norepinephrine binds to adrenergic receptors called alpha and beta receptors.
Acetylcholine binds to cholinergic receptors called muscarinic and nicotinic receptors.
Because of dual innervations, most effector organs have receptors for both norepinephrine and acetylcholine. This allows the ANS to speed up or slow down the effector organ.

18. Cholinergic Receptors
Muscarinic
Located on effector organ of parasympathetics
Nicotinic
NN (ganglia)
NM (not autonomic)
In this discussion, the muscarinic receptors are the important ones because they are located on the target organs of the parasympathetic nervous system.
Parasympathetic discharge activates muscarinic receptors.
The vagus nerve travels with the parasympathetic system. Parasympathetic discharge may be called vagal discharge; it activates the muscarinic receptors and slows heart rate.
NN receptors are located at the ganglia and will not be discussed further. NM receptors are not part of the ANS and are located in the neuromuscular junction. They are shown in part C of the slide and were described in Chapter 9.

19. Adrenergic Receptors Alpha1 and alpha2 Beta1 and beta2
All adrenergic receptors located on effector organs of sympathetic nervous system
When the sympathetic system fires, it releases norepinephrine, which activates adrenergic receptors. These are called alpha and beta receptors and are located on the effector or target organs.
For example, when the sympathetic system fires, its norepinephrine activates the beta1 receptors, increasing heart rate and contractile force. This results in a faster heart rate and a stronger contraction of the heart muscle.
Refer students to Table 12-4 on p. 225 for adrenergic receptors and responses.

20. Autonomic Pharmacology
Agonist directly activates receptors
Alpha1-adrenergic agonist
Muscarinic agonist
Antagonist prevents receptor activation
Beta2-adrenergic blocker
Muscarinic blocker (anticholinergic)
An agonist can be either naturally occurring or pharmacological. For example, epinephrine actives beta1 and beta2 adrenergic receptors, increasing heart rate and force of contraction and dilating the breathing passages. A pharmacological agent, such as ephedrine, mimics the action of epinephrine.
The most important antagonists (blockers) are pharmacological agents. For example, propranolol blocks both beta1- and beta2-adrenergic receptors, slowing heart rate and force of contraction.
The section of the text entitled “Doing Autonomic Pharmacology” (p. 226) includes six clinical vignettes illustrating autonomic pharmacology or the use of agonists and antagonists.

21. Questions?