Download autonomic nervous system, 032117

Autonomic Nervous System
http://www.michiganneurology.com
Note
Much of the text material is from, “Principles of Anatomy and
Physiology” by Gerald J. Tortora and Bryan Derrickson (2009,
2011, and 2014). I don’t claim authorship. Other sources are
noted when they are used.
The lecture slides are mapped to the three editions of the
textbook based on the color-coded key below.
14th edition
13th edition
12th edition
Same figure or table reference in all three editions
2
Outline
•
•
•
•
•
•
Basic principles
More detail on motor control
Neurotransmitters and receptors
Physiological responses
Autonomic integration and control
Two medical conditions
3
Basic Principles
4
Autonomic Nervous System
•
The autonomic nervous system (ANS) responds to certain types of
visceral sensations and excites or inhibits effectors to control some
bodily functions.
•
Effectors include smooth muscle, cardiac muscle, and endocrine and
exocrine glands.
Visceral = pertaining to organs or tissue coverings of organs.
Page 523
Page 581
Page 546
5
Autonomic Nervous System
•
The ANS consists of sensory neurons, integrative centers in the brain
and spinal cord, and motor neurons.
•
It operates via lower- and higher-level reflex arcs, and almost always
without conscious awareness or conscious control.
Effector = a muscle, gland, or organ capable of responding to
a stimulus, especially action potentials.
Page 523
Page 581
Page 546
6
Divisions
•
The motor (output) components of the ANS are the sympathetic and
parasympathetic divisions.
•
Most organs receive input from both ANS divisions—this is known as
dual innervation.
•
The divisions often, but not always, work in opposition to one another.
Page 524
Page 582
Page 547
7
Divisions (continued)
http://www.yesselman.com
8
Divisions (continued)
•
Action potentials from one division stimulate the organ to increase its
activity (excitation).
•
Action potentials from the other division decrease the organ’s activity
(inhibition).
•
For example, sympathetic activation increases and parasympathetic
activation decreases heart rate.
•
In a few instances, the two divisions work together, such as the male
sexual response.
Page 524
Page 582
Page 547
9
Control
•
The ANS was originally named “autonomic” because it was thought
to function autonomously of brain function.
•
Nuclei in the hypothalamus and brainstem are now known to be involved in regulating its motor activity.
Autonomous = self-governing; independent; free of external
influence or control.
Page 524
Page 582
Page 547
10
Limited Conscious Control
•
Due to the lack of sensory awareness, very few autonomic responses
can be consciously altered.
•
Consider, however:
Practitioners of yoga and other meditative techniques can learn
from long and diligent practice how to regulate some autonomic
functions, such as heart rate.
- Biofeedback using electronic monitoring can provide sensory
feedback to enhance the ability to exert some conscious control
of ANS functions.
-
Page 524
Page 582
Page 547
11
http://counseling.ucr.edu
Biofeedback
12
Sensory Input
•
Most sensory input is from sensory neurons located in blood vessels,
visceral organs, and muscles.
•
The sensory neurons are called interoreceptors since they respond to
internal sensations.
•
They include mechanoreceptors to detect stretch in the walls of hollow
organs and blood vessels, and chemoreceptors to monitor blood CO2
level.
Page 524
Page 582
Page 547
13
Sensory Input (continued)
•
The sensory signals from interoreceptors are generally not consciously
perceived since they usually don’t reach the level of the cerebral cortex.
•
Intense activation of interoreceptors can, however, produce conscious
sensations.
•
For example, inadequate coronary blood flow can result in chest pain
known as angina pectoris.
•
Somatic (body) sensations can sometimes affect the ANS—for example,
intense pain can produce changes in autonomic activity such as in heart
rate.
Page 524
Page 582
Page 547
14
Other Sensory Inputs
•
The special senses acting through the limbic system can also affect
autonomic responses.
•
For example, the reaction to an unexpectedly loud noise can include
an increased heart rate in a physiological response known as sympathetic arousal.
•
We will discuss this fight or flight response later in the lecture.
Page 524
Page 582
Page 547
15
Motor Output
•
Autonomic motor neurons regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) the physiological actions of their
effectors.
•
ANS motor responses include changes in the diameter of the pupils,
changes in heart rate, and dilation and constriction of blood vessels.
•
Unlike skeletal muscle tissue, tissues innervated by the ANS can function autonomously to some extent if their nerve supply is damaged.
ANS effectors = cardiac muscle, smooth muscle, and endocrine
and exocrine glands.
Innervation = to supply an organ or a body part with nerves.
Page 524
Page 582
Page 547
16
Motor Pathways
•
An autonomic motor pathway has two motor neurons positioned in
series.
•
The cell body of the first neuron is located in the CNS—its myelinated
axon extends to an autonomic ganglion positioned outside of the CNS.
•
The cell body of the second neuron is located in the autonomic ganglion—its unmyelinated axon extends to an effector.
•
An exception to this rule is the axon of the first motor neuron extends
directly to chromaffin cells in the adrenal medulla—there is no second
neuron.
Ganglion (plural, ganglia) = collection of cell bodies of neurons
outside of the CNS.
Page 524
Page 582
Page 547
17
Motor Pathways (continued)
Neuron 1
Neuron 2
Axon
Effector
Cell body and
dendrites
Synapse
(dendrites are not shown)
Schematic diagram = a drawing intended to explain
how something works.
18
Motor Pathways (continued)
Preganglionic
neuron
Postganglionic
neuron
Myelinated
axon
Unmyelinated
axon
Effector
Smooth muscle
Cardiac muscle
Endocrine and
exocrine glands
Central nervous
system
Peripheral
nervous system
(postganglionic
neuron)
19
Neurotransmitters
•
Somatic motor neurons release acetylcholine (ACh) at the neuromuscular junctions (synapses) with skeletal muscles.
•
Autonomic motor neurons release either ACh or norepinephrine (NE)
at their synapses.
•
More detail will be provided as we proceed with this lecture material.
Page 524
Page 582
Page 547
20
More Detail on Motor Control
21
Motor Pathways
•
As discussed, the cell body of an ANS preganglionic neuron is located
in the brain or spinal cord (central nervous system).
•
Its axon—a small-diameter, myleninated type B fiber—exits the CNS
as part of a cranial nerve or spinal nerve.
•
The axon extends to an autonomic ganglion in the PNS, where it synapses with a postganglionic neuron.
Page 526
Page 584
Page 549
Figure 15.1
22
Motor Pathways (continued)
•
The axon of the postganglionic neuron is a small-diameter, unmyleninated type C fiber.
•
The axon synapses with an effector, which could be smooth muscle,
cardiac muscle, or endocrine or exocrine gland.
Page 526
Page 584
Page 549
Figure 15.1
23
Parasympathetic Preganglionic Neurons
•
In the parasympathetic division, cell bodies of preganglionic neurons
are found in the nuclei of cranial nerves III, VII, IX, and X, and sacral
segments 2 through 4.
•
The parasympathetic division is therefore also known as the craniosacral division.
III—Oculomotor nerve
VII—Facial nerve
IX—Glossopharyngeal nerve
X—Vagus nerve
Page 529
Page 584
Page 549
Figure 15.3
24
Sympathetic Preganglionic Neurons
•
The cell bodies of the preganglionic neurons are located in the lateral
horns of the 12 thoracic segments and the first 2 to 3 lumbar segments
of the spinal cord.
•
The sympathetic division is therefore also known as the thoracolumbar
division.
Page 526
Page 584
Page 549
Figure 15.2
25
http://www.microscopy-uk.org.uk
Lateral Horn of Spinal Cord
WM = white matter; GM = gray matter.
26
Autonomic Ganglia
•
The autonomic ganglia differ in location and structure in the parasympathetic and sympathetic divisions.
•
Parasympathetic division—the ganglia are found close to, or in the
walls of, visceral organs.
•
Sympathetic division—the ganglia form an interconnected chain of
cell bodies and axons, known as the sympathetic ganglionic chain,
in close proximity to the spinal cord.
Page 529
Page 587
Page 549
Figure 15.2
Figure 15.3
27
Axon Lengths
•
Parasympathetic division—long preganglionic axons and short postganglionic axons.
•
Sympathetic division—almost always short preganglionic axons and
long postganglionic axons.
•
We will discuss the functional significance of these structural differences.
Page 529
Page 587
Page 549
Figure 15.2
Figure 15.3
28
Comparison of Axon Lengths
Parasympathetic division:
Long
Short
Effector
Sympathetic division:
Short
Long
Effector
Preganglionic neuron
Postganglionic neuron
29
Parasympathetic Postganglionic Neurons
•
One parasympathetic preganglionic neuron can synapse with up to
4 to 5 postganglionic neurons.
•
Each postganglionic axon, however, only innervates only one effector.
•
This anatomical arrangement enables parasympathetic responses to
be localized to one or possibly a few organs.
Page 529
Page 587
Page 549
Figure 15.3
30
Sympathetic Postganglionic Neurons
•
A sympathetic preganglionic neuron can synapse with 20 or more postganglionic neurons.
•
The sympathetic ganglionic chain also enables action potentials to propagate up and down the chain.
•
A postganglionic axon can therefore innervate many different effectors in
different parts of the body.
•
Wide divergence helps explain why sympathetic activation simultaneously
affects much of the body.
Page 529
Page 587
Page 549
Figure 15.2
31
Neurotransmitters and Receptors
32
Cholinergic and Adrenergic Neurons
•
Autonomic neurons are classified as cholinergic or adrenergic based
on the neurotransmitter synthesized and released at their synapses.
•
Receptors, made-up of proteins, are found on the plasma membrane
of the postsynaptic neuron or effector cell.
Cholinergic = acetylcholine (ACh) is the neurotransmitter.
Adrenergic = norepinephrine (NE) is the neurotransmitter.
Page 535
Page 593
Page 558
Figure 15.7
33
Cholinergic and Adrenergic Neurons
(continued)
Parasympathetic division:
Cholinergeric
Cholinergeric
Effector
Sympathetic division:
Cholinergeric
Adrenergic (usually)
Effector
Preganglionic neuron
Postganglionic neuron
Cholinergic = acetylcholine
Adrenergic = norepinephrine
34
Cholinergic Neurons
•
Cholinergic neurons in the two divisions of the autonomic nervous system include:
All preganglionic neurons in the parasympathetic and sympathetic
divisions.
- All postganglionic neurons in the parasympathetic division.
- Postganglionic neurons in the sympathetic division that innervate
exocrine (sweat) glands in the skin.
-
Page 535
Page 593
Page 558
Figure 15.7
35
http://thebrain.mcgill.ca
Synapse
36
Cholinergic Neurons (continued)
•
ACh, stored in the synaptic vesicles of the end buttons of axons, is
released via exocytosis in response to action potentials.
•
ACh diffuses across the synaptic cleft and binds to the cholinergic
receptors on the postsynaptic membrane to produce graded potentials.
•
Cholinergic receptors are either called nicotinic or muscarinic based
on certain unique properties.
Page 535
Page 593
Page 558
Figure 15.7
37
Tobacco Plant
http://etc.usf.edu
38
Nicotinic Receptors
•
Nicotinic cholinergic receptors respond to nicotine, a chemical not
naturally found in the human body.
•
Small amounts of nicotine, when introduced at nicotinic synapses,
binds to the postsynaptic receptors, and mimics the action of ACh.
•
The activation of nicotinic receptors produces depolarizing graded
potentials.
Page 535
Page 593
Page 558
Figure 15.7
39
Nicotinic Receptors (continued)
•
Nicotinic receptors are found in the:
Preganglionic neurons of the parasympathetic and sympathetic
divisions.
- Chromaffin cells of the adrenal medulla innervated by the sympathetic division.
- Neuromuscular junctions in skeletal muscle (which are innervated
by somatic motor neurons).
-
Page 535
Page 593
Page 558
Figure 15.7
40
http://ciuperci.org
Amanita muscaria
Muscarine is found in some species of mushrooms, including Amanita
muscaria. Its ingestion can result in intense parasympathetic
responses, convulsions, and death.
41
Muscarinic Receptors
•
Muscarinic cholinergic receptors are named for a mushroom toxin
known as muscarine.
•
Muscarine mimics the action of ACh when binding to postsynaptic
receptors.
•
These receptors are found in smooth muscle, cardiac muscle, and
glands innervated by postganglionic axons of the parasympathetic
division.
•
Most sweat glands innervated by postganglionic axons of the sympathetic division have muscarinic receptors.
Page 535
Page 593
Page 558
Figure 15.7
42
Muscarinic Receptors (continued)
•
Stimulation of muscarinic receptors produces depolarizing or
hyperpolarizing graded potentials based on the effector cell type.
•
The binding of ACh to the muscarinic receptors in the digestive
tract inhibits (relaxes) its smooth muscle sphincters.
•
ACh excites the muscarinic receptors in the smooth muscle fibers
of the iris of the eye, causing the smooth muscles to contract and
decrease pupil size.
Page 537
Page 593
Page 558
Figure 15.7
43
Adrenergic Neurons
•
Adrenergic neurons release norepinephrine (sometimes called
noradrenalin).
•
Most postganglionic neurons in the sympathetic division are
adrenergic, except those that innervate sweat glands in the skin.
Page 536
Page 594
Page 559
Figure 15.7
44
Adrenergic Neurons (continued)
•
Norepinephrine is stored in synaptic vesicles and is released via
exocytosis in response to action potentials from sympathetic postganglionic neurons.
•
Norepinephrine diffuses across the synaptic cleft and binds to the
adrenergic receptors in the postsynaptic membrane of the effector
cell.
•
A depolarizing or hyperpolarizing graded potential results, depending on the cell type.
Page 536
Page 594
Page 559
Figure 15.7
45
Norepinephrine and Epinephrine
•
Adrenergic receptors in the postsynaptic membrane bind norepinephrine and epinephrine (a closely-related molecule of the catecholamine
family).
•
Most postganglionic neurons of the sympathetic division release
norepinephrine.
•
Epinephrine and small amounts of norepinephrine are also released
from the chromaffin cells of the adrenal medulla into general blood
circulation (in this sense they are hormones and not neurotransmitters).
http://mybrainnotes.com
Page 536
Page 594
Page 559
46
Neurotransmitter Inactivation
•
The action of norepinephrine is terminated when it is inactivated by an
enzyme (COMT or MAO) and is then reabsorbed by the end buttons of
the neurons.
•
Norepinephrine persists in the synaptic cleft for a longer period of time
than ACh since COMT and MAO are relatively slow-acting compared to
acetylcholine esterase (AChE).
•
Therefore, the effects triggered by norepinephrine are generally longerlasting than those triggered by ACh.
COMT = catechol-O-methyl transferase
MAO = monoamine oxidase
Page 536
Page 594
Page 559
47
Alpha and Beta Receptors
•
Adrenergic receptors are classified as either alpha () or beta ()
types.
•
As discussed, the receptors are found on the postsynaptic membranes of effectors innervated by most postganglionic axons in the
sympathetic division.
•
Sweat glands are a major exception.
Page 536
Page 594
Page 559
48
Alpha and Beta Receptors (continued)
•
Cells of most sympathetic effectors have either  or  receptors,
although some cells can have both types.
•
Norepinephrine stimulates  receptors more strongly than it stimulates  receptors.
•
Epinephrine, in comparison, is a strong stimulator of both  and 
receptors.
Page 536
Page 594
Page 559
49
Receptor Subtypes
•
Alpha and beta receptors have subtypes—they are 1, 2, 1, 2,
and 3.
•
The classification is based on the responses they trigger, and the
selective binding of drugs that can activate or block the receptors.
•
The 1 and 1 receptors generally produce excitation while 2 and
2 receptors produce inhibition of effector cells.
•
The 3 receptors are limited to brown adipose cells where activation produces thermogenesis.
Thermogenesis = the production of heat, especially within
an animal body.
Page 536
Page 594
Page 559
50
Receptor Agonists
•
Certain drugs and natural substances selectively activate or block
cholinergic and adrenergic receptors.
•
An agonist is a substance that binds to and activates receptors in
the postsynaptic membrane to mimic the effect of the neurotransmitter or hormone.
•
Phenylephrine, a common ingredient in cold and sinus medications,
is an agonist of 1 receptors.
•
The drug constricts blood vessels in the nasal mucosa to reduce the
production of mucus and relieve nasal congestion.
Page 536
Page 594
Page 560
51
Receptor Antagonists
•
An antagonist is a substance that binds to and blocks receptors to
prevent a neurotransmitter or hormone from exerting its effect.
•
Atropine blocks mucarinic (ACh) receptors—it dilates the pupils,
reduces glandular secretions, and relaxes smooth muscle of the
digestive tract.
•
Atropine is used to dilate the pupils during eye exams by optometrists and ophthalmologists.
•
It is also used as an antidote for certain chemical warfare agents
(such as nerve gas) that trigger massive amounts of ACh release.
Page 536
Page 594
Page 560
52
Physiological Responses
53
Autonomic Tone
•
Most body organs are innervated by the parasympathetic and sympathetic divisions.
•
The two divisions usually, but not always, work in opposition to one
another.
•
The balance of activity between the two divisions, called autonomic
tone, is regulated by the hypothalamus.
Page 536
Page 596
Page 560
54
Autonomic Tone (continued)
•
The two divisions can affect the same body organs differently because:
The postganglionic neurons release different neurotransmitters.
- Effector organs can have cholinergic and adrenergic receptors.
-
Page 537
Page 596
Page 560
55
Sympathetic Responses
•
The sympathetic division dominates during physical activities and
emotional stress.
•
Sympathetic activation favors body functions that support physical
activities, including fight or flight, as will be discussed in upcoming
slides.
•
It also reduces body functions involved in the storage of potential
energy from food—sympathetic activation slows down the digestive
process.
Page 537
Page 596
Page 560
56
Sympathetic Responses (continued)
•
Strong emotions such as fear, embarrassment, and rage can stimulate the sympathetic division.
•
Sympathetic activation and the release of norepinephrine and epinephrine from the adrenal medulla set in motion a complex series
of physiological responses.
•
The changes collectively are known as the fight or flight response,
which can be triggered by an intense stressor.
Stressor = a condition or agent that causes physiological
or psychological stress to an organism.
Page 537
Page 596
Page 560
57
Fight or Flight
http://www.uh.edu
http://darwin-online.org.uk
58
Fight or Flight Response
•
The fight or flight response produces a wide range of physiological
changes, including:
Dilation of the pupils.
- Dilation of the bronchioles (small air passageways) to improve
airflow.
- Increased heart rate, force of cardiac contraction, and blood
pressure to increase cardiac output.
-
Page 538
Page 596
Page 560
59
Fight or Flight Response (continued)
•
The physiological changes also include
Dilation of blood vessels to the skeletal muscles, cardiac muscle,
and liver to increase blood flow.
- Constriction of blood vessels to the kidneys and digestive tract to
reduce blood flow.
- Slowing-down of non-essential processes, including the smooth
muscle activity in the digestive tract.
-
Page 538
Page 596
Page 560
60
Fight or Flight Response (continued)
•
Additional physiological changes include:
Breakdown of glycogen to glucose in the liver (glycogenolysis).
- Release of the glucose from the liver to serve as an immediate
source of energy for anaerobic respiration in other body tissues.
- Breakdown of trigylcerides to glycerol and fatty acids (lipolysis)
to serve as a chemical energy source for aerobic respiration.
-
Page 538
Page 596
Page 560
61
Sympathetic Scope and Persistence
•
The effects of sympathetic activation, such as in the fight or flight
response, are more widespread and longer lasting than the effects
of parasympathetic activation.
•
The postganglionic axons of the sympathetic division diverge more
extensively, and therefore many different tissues are activated
simultaneously.
•
Epinephrine and norepinephrine are also secreted by the adrenal
medulla into general blood circulation, which serve to intensify and
prolong sympathetic responses.
•
COMT and MAO are slower to break-down norepinephrine and
epinephrine than the action of AChE on acetylcholine, to enable
sympathetic responses to persist longer.
Page 537
Page 596
Page 560
62
Sympathetic Inactivation
•
Norepinephrine and epinephrine are eventually inactivated by enzymes in the liver.
•
The metabolites are recycled for the re-synthesis of catecholamines.
Catecholamine = an amine derived from the amino acid tyrosine
that act as a neurotransmitter or hormone; includes
norepinephrine, epinephrine, and dopamine.
Page 538
Page 596
Page 560
63
Parasympathetic Responses
•
The parasympathetic division enhances the so-called rest and digest
activities.
•
The activities support body functions to conserve and restore energy
during periods of rest and recovery.
Page 538
Page 596
Page 561
64
Parasympathetic Activation (continued)
•
The ungainly acronym, SLUDD can used to recall the five major
parasympathetic responses.
•
These responses are: 1) salivation, 2) lacrimation, 3) urination, 4)
digestion, and 5) defecation.
•
Other parasympathetic responses include decreased heart rate,
decreased diameter of the airways, and constriction of the pupils.
•
Parasympathetic activation is also involved in sexual arousal.
Lacrimation = secretion of tears.
Page 539
Page 597
Page 561
65
Autonomic Integration and Control
66
Autonomic Reflexes
•
Autonomic reflexes have a major role in regulating body functions
including:
Blood pressure, by regulating heart rate, force of ventricular
contraction of the heart, and diameter of blood vessels.
- Digestion, by regulating smooth muscle tone and motility of the
digestive tract.
- Defecation and urination, by regulating the opening and closing
of smooth muscle sphincters.
-
Motility = motion or movement.
Page 540
Page 599
Page 562
67
Components of an Autonomic Reflex Arc
•
Receptor—distal end of a sensory neuron (often an interoreceptor)
•
Sensory neuron—cell body and axon.
•
Integrative center in the spinal cord or brainstem—interneurons
•
Motor neurons
•
Effector—smooth muscle, cardiac muscle, or endocrine or exocrine
gland
Page 540
Page 599
Page 562
68
Autonomic Reflex Arcs
Sympathetic
division
Parasympathetic
division
http://www.medical-look.com
69
Hypothalamic Control
•
The hypothalamus is the key integrative and control center for the
autonomic nervous system.
•
It receives sensory input from visceral functions, smell (olfaction),
and taste (gustation).
•
It also receives input for body temperature, osmolarity, and concentration of various substances in the blood including glucose.
•
The hypothalamus also receives input from the limbic system for
emotional states.
Osmolarity = a measure of the concentration of a solution.
Page 541
Page 601
Page 563
70
Hypothalamic Control (continued)
•
Nuclei in the anterior and medial areas of the hypothalamus control
the parasympathetic division.
•
Nuclei in the posterior and lateral areas control the sympathetic
division.
•
Output from these autonomic centers is to the brainstem and spinal
cord.
Page 541
Page 601
Page 563
71
Two Medical Conditions
72
Raynaud’s Phenomenon
•
In Raynaud’s phenomenon, the fingers and toes become ischemic in
response to the thermal sensations of cold or to emotional stress.
•
The symptoms result from excessive sympathetic stimulation of the
smooth muscle in the arterioles of the digits, constricting the blood
vessels and reducing blood flow.
•
People with Raynaud’s phenomenon often have low blood pressure.
Ischemia = a decrease in the blood supply and therefore oxygen to
a body organ or tissue due to constriction or obstruction of the
blood vessels.
Arteriole = small branch of an artery that connects with a capillary.
Digits = fingers and toes.
Page 541
Page 601
Page 565
73
Raynaud’s Phenomenon (continued)
http://www.nlm.nih.gov
74
Raynaud’s Phenomenon (continued)
•
Some people who have Raynaud's phenomenon have an increased
number of -adrenergic receptors.
•
The phenomenon is most common in young woman, and is observed
most often in cold climates.
•
Treatment includes use of calcium channel blockers and alpha receptor blockers to relax the smooth muscles in the arteriole walls and improve blood flow.
•
Smoking, alcohol, and some illicit drugs can exacerbate the symptoms.
Page 541
Page 601
Page 565
75
Autonomic Dysreflexia
•
Autonomic dysreflexia is an exaggerated response of the sympathetic division in persons who have spinal cord injuries at or above T6
(the sixth thoracic segment).
•
The condition is due to interruption of ANS control by the hypothalamus.
Page 541
Page 601
Page 565
76
Autonomic Dysreflexia (continued)
•
Sensory nerve impulses, such as from a full urinary bladder, stimulate the sympathetic nerves inferior to the injured level of the spinal
cord.
•
Other triggering events (or stimuli) include:
Stimulation of pain receptors below the spinal cord injury
- Bowel distension
- Smooth muscle contractions from sexual stimulation
- Labor and delivery
-
Page 541
Page 601
Page 565
77
Autonomic Dysreflexia (continued)
•
Autonomic dysreflexia triggers a complex chain of events and
feedback mechanisms in the parasympathetic and sympathetic
divisions.
• The condition is characterized by:
Pounding headache
- Anxiety
- Flushed, warm skin with profuse sweating above the level of
injury
- Pale, cold, and dry skin below the injury level
-
•
Because the condition can be life-threatening, it requires immediate medical intervention, including identifying and removing the
stimulus.
Page 541
Page 601
Page 565
78