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CHORAL JOURNAL Volume 55 Number 3 61
Lights, music, excitement: that is what
Las Vegas has to offer. The bustle of the
Vegas Strip dazzles and amazes. In all the
drama of that city, however, little atten-
tion is given to the electricity that lights
it up. When one thinks of Las Vegas, they
may conjure many images, but probably
none will be of the power cords that
make that city run.
Similarly, when we wax eloquent or
transcend through singing, we rarely
give thought to the power cord mak-
ing all of our efforts possible. Over the
past fty years we have developed rich
voice training traditions, sophisticated
theories of voice production, and a
comprehensive understanding of laryn-
geal health. We have come a long way
in appreciating the unique nature of the
tissues of the vocal folds and protecting
their delicate but strong vibrating edge.
We have ample evidence that voice
training provides excellent protection
from injury and harm and have begun
to develop sophisticated motor theories
especially for voice production.
multi-disciplinary perspective of voice
science frequently takes for granted the
nerve that supplies the vocal folds with
power and gives them life.
The Vagus Nerve and its Home,
the Nervous System
The nervous system is the commu-
nication network of our body. It sends
commands for us to move, breathe,
digest, pump blood, secrete hormones
and chemicals, regenerate, feel, and
even think.
It is divided into the Cen-
tral Nervous System (CNS) and the
Peripheral Nervous System (PNS).
The CNS houses the brain and spinal
cord, and the PNS is comprised of the
nerves that go out to the muscles, soft
tissues, glands, and organs of the body.
The PNS helps maintain homeostasis,
encourage metabolism, control muscles,
release glandular secretions, and decode
environmental phenomena into per-
ceived reality (e.g. sight and hearing).
The basic unit in the nervous system
is called a nerve. Its main function is to
Nerves contain three
basic parts: a cell body called a soma,
dendrites that carry information from
other structures (other nerves, glands,
muscles, etc . . .) to the soma, and axons,
which carry information away from the
soma to the next structure.
The relay
of messages along these nerves can
be simple as a re ex.
However, nerve
communication is often much more
complicated, involving many nerves
to and from the brain in an elaborate
bucket brigade of signals.
Nerves communicate with each
other by way of electrical signals gener-
ated in the soma and traveling down
the axon to an end point.
At this end
point the electrical signal releases a
chemical into the space between the
axon and the next structure (usually
another nerve but sometimes a muscle
or gland).
Depending on the chemical,
the next structure is either activated or
shuts down. Subsequent sets of electri-
cal signals travel along dendrites into the
soma of the next nerve.
This form of
Miriam van Mersbergen is ___________
Professor of __________ and Director
of _____________ at Northern Illinois
Email address ………………
Viva La Vagus!
Miriam van Mersbergen
62 CHORAL JOURNAL Volume 55 Number 3
electrical communication continues until
the system completes is function.
Most peripheral nerves travel in bun-
dles, similar to electrical wires, and exit
the CNS from the spinal cord. How-
ever, twelve peripheral nerves, called
Cranial Nerves, exit the brainstem. They
regulate the muscles, glands, and sensory
organs of the head and neck and are
identi ed by Roman Numerals.
Nerve X, the largest of these nerves, is
called Vagus Nerve.
Beginning in the
brainstem, the nerve travels through
the jugular foramen (the large hole at
the bottom of the skull), into the neck,
and down through the thoracic cavity
to the abdomen.
Vagus, the Latin for
“wandering, appropriately re ects the
nerve’s meandering pathways.
Leaving the brain stem, the vagus
nerve branches off in different direc-
tions and extends as far down as the
Many of these branches are
named according to their function, such
as the auricular branch, which conveys
sensory information from the skin inside
the external ear canal and tympanic
membrane, and the laryngeal branch,
which innervates the larynx.
branches of the vagus travel far below
the larynx into the thorax and abdomen
and assist in the regulation of the organs,
glands, and soft tissue of these regions.
The vagus nerve carries messages
from the CNS to the body (efferent/
motor) and relays messages to the CNS
from the body (afferent/sensory).
cell bodies of this nerve are housed in
four large areas in the brain stem, creat-
ing a hub where nerves from different
parts of the body communicate with
each other.
The proximity of nerve cell
bodies in this area allow various parts of
the body to communicate complicated
information with each other, allowing for
sophisticated processing of information.
The Vagus Nerve
and Voice Production
Three branches of the vagus nerve
are involved in voice production: the
pharyngeal branch, the recurrent laryn-
geal branch, and the superior laryngeal
When the pharyngeal branch
leaves the brainstem and deviates, it
travels to the mucous membranes and
muscles of the pharynx, carrying sensory
information from this area to the brain.
When you have a throat infection, for
example, the vagus nerve carries the
information that lets you know your
throat is sore. The pharyngeal branch
also innervates most of the muscles of
the pharynx and allows the palate to
lift, maximizing the resonating space in
our throat and creating those rounded
tones we desire.
The recurrent laryngeal branch
leaves the larger laryngeal branch and
terminates in the larynx. It is called re-
current because it travels past the larynx
into the thorax and loops up into the
larynx from below. On the right side,
the nerve travels around the subclavian
artery (right below the right clavicle),
circling back into the larynx. The left side
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CHORAL JOURNAL Volume 55 Number 3 63
travels further, winding around the aorta
before returning back to the larynx.
The implications of right and left differ-
ences will be discussed later. The recur-
rent laryngeal nerve innervates most of
the muscles in the larynx, particularly
the muscles responsible for opening
and closing the vocal folds, which is
necessary for voicing.
This nerve also
innervates some of the muscles of the
lower pharynx and esophagus to assist
in swallowing. It transmits sensory in-
formation from the mucous membrane
of the upper trachea right below the
vocal folds.
The superior laryngeal nerve also
exits the larger laryngeal branch, split-
ting off into two smaller branches.
intrinsic branch, which carries sensory
information about the mucous mem-
branes of the larynx, is active in provid-
ing information during a cough response.
The extrinsic branch innervates the
cricothyroid muscle, a laryngeal muscle
responsible for pitch control during
Vocal Dif culties from
Vagus Nerve Damage
Voice impairment arises when the
vagus nerve is damaged. The most dev-
astating impairment arises when damage
occurs to the recurrent or superior
laryngeal nerves.
Injury to the recur-
rent laryngeal nerve impairs the ability
of the vocal folds to open and close by
weakening or paralyzing the muscles
responsible for these actions. At best,
poor closure of the vocal folds leaves
a speaker or singer with a soft, breathy,
asthenic voice—unable to sustain sound
for more than 4 5 seconds at a time. It
can cause irregular vibration of the vocal
folds, leaving the voice not only weak
but hoarse, with pitch breaks, cracks,
and diplophonia (two pitches at once).
Individuals with recurrent laryngeal
nerve injuries frequently complain of
feeling out of breath during speaking and
singing. The cause of nerve injuries arises
from complete severing of the nerve,
partial tearing of the nerve, stretching
the nerve, compressing the nerve, or
disease residing in the nerve cell body.
Because the recurrent laryngeal nerve
travels into the thorax, any thoracic
surgery places an individual at risk for
As discussed earlier, the left
sided recurrent laryngeal nerve travels
around the aorta. So, injuries on the
left-side can be seen often in cardiac sur-
geries when the surgeon has to stretch
the nerve to retract it or to gain access
to the heart.
Sometimes the nerve is
severed during tumor removal. At times
viral infections reside in the cell bodies
of the recurrent laryngeal nerve, causing
damage to nerve functioning.
Recovery from recurrent laryngeal
nerve injury is directly related to the
degree and extent of the damage.
Damage from a mild stretch or com-
pression of the nerve may resolve
quickly, and normal voicing may return
within a few months. When damage is
considerable, however, recovery might
not be complete and normal functioning
my never return, rendering an impaired
Treatment for larger nerve in-
juries includes surgical procedures that
can assist in vocal fold closure, therapy
to facilitate optimal voicing and reduce
poor compensations for weakness, and
a combination of both. Such treatments
are available at regional and national
voice centers where an individual may
consult with a laryngologist (an ear, nose,
throat physician specializing in voice), a
speech language pathologist specializing
in voice, a registered nurse, and oc-
casionally a singing teacher who works
directly with the medical team.
Superior laryngeal nerve injuries
have similarly devastating effects on
voicing. Because the superior laryngeal
nerve is responsible for sensation in the
larynx, damage to this nerve can either
leave an individual with hyposensitivity,
placing him or her at risk for aspira-
tion because saliva and food can enter
the airway without proper detection.
Additionally, some superior laryngeal
nerve damage can leave a larynx with
hypersensitivity, which causes an indi-
vidual to have excessive coughing with
64 CHORAL JOURNAL Volume 55 Number 3
minor sensory changes.
In some cases
individuals can develop excessive cough-
ing reactions after smelling faint odors,
breathing in deeply, or changing neck
positions. The superior laryngeal nerve
also innervates the cricothyroid muscle,
which is responsible for pitch changes.
A hallmark symptom of damage to this
nerve is the inability to raise pitch above
mid-range, despite Herculean efforts.
The vocal folds also have dif culty
closing completely, because while the
cricothyroid muscle stretches the vocal
fold, it places the vocal folds on a differ-
ent plane. When one vocal fold remains
unstretched due to damage, this plane
difference creates a gap, allowing for air
leakage. Superior laryngeal nerve injury
also arises from severing, tearing, and
stretching the nerve. Because the supe-
rior laryngeal nerve travels through the
thyroid gland, thyroid surgeries place an
individual at risk for damage. Recovery
and treatment of the superior laryngeal
nerve, similar to recovery and treat-
ment of the recurrent laryngeal nerve,
is available at regional and national voice
centers. Although vocal fold closure can
be achieved surgically, pitch functioning,
which is necessary for singing, unfortu-
nately cannot be surgically repaired.
Injuries to the pharyngeal branch
of the vagus nerve are far less com-
Although such an injury does
not directly affect voice functioning,
it can impair an individual’s ability to
elevate the soft palate and move the
muscle of the pharynx to create the
necessary space for optimal resonance.
Damage can leave an individual sounding
hypernasal with a soft, muf ed quality.
Prosthetic devices can assist an individual
in maintaining a moderately elevated
velum, but at this point they cannot
assist in volitionally elevating the velum
or widening the pharynx during singing.
Master of our Well Being
Traveling down past the neck and
into the body, the vagus nerve performs
some of its most vital tasks. Its main
function is to regulate the Autonomic
Nervous System (ANS), a special part
of the nervous system that maintains
the homeostasis of body functions, such
as heart rate, respiration rate, blood
pressure, body temperature, and diges-
When homeostasis is disrupted
through exercise, illness, or stress, a
subsystem of the ANS, the Sympathetic
Nervous System, kicks in and prepares
the body to move, respond, or adapt to
the change.
This state of readiness is
also known as the Fight or Flight System.
When the stress is over, the Parasympa-
thetic Nervous System down-regulates
the body, bringing its functions back to
baseline. Working in opposition to the
Fight or Flight System, the Parasympa-
thetic Nervous System is known as the
Rest and Digest System.
We can thank the vagus nerve for
keeping the heart rate from elevating
too high for too long, maintaining blood
vessel constriction (which regulates
blood pressure) during activity, reacti-
vating the digestive system after being
shut down, and stabilizing the respiration
rate and making sure it coordinates with
the heart. When these branches are
disrupted, individuals can experience
arrhythmias (irregular heart beat), dizzi-
ness, shortness of breath, and a variety
of digestive disorders, such as irritable
bowel syndrome.
New Mysteries Unfolding
Because of its communication be-
tween the viscera and the brain, the
vagus nerve plays an important role
in body/brain interactions. Recently,
neuroscientists have found a link be-
tween the presence of good gut bac-
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CHORAL JOURNAL Volume 55 Number 3 65
teria (probiotics) and elevated mood
and improved cognition. In a series of
animal and human studies, researchers
have found that organisms with bad
gut bacteria show signs of depression
and poor attention, but that this state
can be reversed by introducing healthy
Apparently, good bacteria
produce approximately 95 percent of
the body’s serotonin, a neurotransmitter
responsible for improved mood.
rst researchers were puzzled by the
suggested link between gut bacteria and
mood. But a growing understanding of
the vagus nerve’s role in communicating
gastrointestinal information to the brain
has made the brain-gut connection an
exciting new area of research.
The vagus nerve appears to also
assist in regulation of in ammatory re-
sponses from the body. Vagal communi-
cation between in ammatory responses
and the brain can also allow the brain to
regulate this in ammation and promote
adaptations to acute injury and chronic
irritation. Taylor and colleagues
that vagal tone, a measure of the vagus’s
ability to regulate the PNS, is associated
with depression and in ammation in
individuals who smoke tobacco, con-
rming a relationship between vagus
nerve functioning and regulation of
in ammation.
The vagal body/brain connection
does not stop there. The vagus nerve
can promote healing following strokes.
Anti-in ammatory agents produced by
the spleen are transmitted to the brain
via the vagus nerve and have been
found to reduce extraneous swelling in
the brain after stroke. Lee at al.
that simply producing these agents into
the brain after stroke was not affec-
tive; it was the vagal pathway from the
spleen to the brain that was necessary
University of Cambridge
66 CHORAL JOURNAL Volume 55 Number 3
to achieve this anti-in ammatory effect.
Other researchers
have found that the
production of anti-in ammatory agents
from the spleen have been important
in regulating in ammation observed
in arthritis, pancreatitis, and additional
in ammatory diseases. Vagal connec-
tions with the visceral organs have also
promoted regulation in the endocrine
system. Dockery
recently published an
article outlining the role of vagal nerve
pathways in diabetes, obesity, and nutri-
ent transfer in the stomach.
Because of its function in communi-
cating visceral activity with the brain, the
vagus nerve has been used to assist in
controlling the communication between
body and brain when the brain malfunc-
tions. Vagal nerve stimulators, like pace
makers, send regular, clear messages to
the brain, allowing the brain to respond
in more adaptive ways. The stimulator
is a small coil that is wrapped around
the nerve and is controlled by a small
magnet placed directly under the skin
on the chest.
Vagal nerve stimulators
have been used to control drug resistant
epilepsy, relieve intractable depression,
which is unresponsive to any forms of
medical and behavioral therapy,
may even regulate behavioral symptoms
of autism.
Recent applications to vagal
nerve stimulators assist in controlling
anxiety, improving cognitive function in
patients with Alzheimer’s, and managing
The vagus nerve’s in uence in brain/
body interaction has led psychologists
and neuroscientists to develop theories
of how the vagus nerve is responsible
for emotional development in children.
The polyvagal theory
is one such theo-
ry that suggests that the vagus supports
social interaction between individuals by
preparing an organism to interact with
Hal Leonard
CHORAL JOURNAL Volume 55 Number 3 67
others. The theory suggests that the va-
gal role in the parasympathetic nervous
system assists in reducing stress reac-
tions that might occur with increased
physical proximity or communication
that occurs in unknown situations.
The vagal down-regulation of stress
responses can explain why individuals
appear to have reduced heart rate and
blood pressure when interacting with
other individuals and animals, lending
support to the notion that petting our
furry or feathered companion is good
for our cardiovascular health.
The vagus nerve is a truly amazing
nerve, the superhighway of life respon-
sible for keeping us alive and thriving in
an ever-changing environment. Recent
research points to the vagus nerve as
an indispensable link in communication
between the brain and body. However,
vagal functioning truly shines in its ability
to allow us to voice and speak, to com-
municate our wants, needs, and desires.
What further evidence do we need
than the transcendence of singing to
place voicing as a vital part of the human
condition. Viva la Vagus!
Ingo R. Titze, Principals of Voice Production, 2nd ed.
(Iowa City: National Center for Voice and
Speech, 2000), 23 54.
Ingo R. Titze and Katherine Verdolini Abbott,
VOCOLOGY: The Science and Practice of Voice
Habilitation (Salt Lake City: National Center
for Voice and Speech, 2012), 216240.
Douglas B. Webster, Neuroscience of Com-
munication, 2nd ed. (San Diego: Singular
Publishing, 1998), 4.
Ibid, 5.
Leonard L. LaPointe, Atlas of Neuroanatomy for
Communication Science and Disorders (New
York: Theime, 2011), 31.
Ibid, 35.
Ibid, 37.
Ibid, 28.
Webster, Neuroscience of Communication, 6.
Ibid, 7.
Ibid, 8.
Linda Wilson-Pauwels, Elizabeth J. Akesson, and
Patricia A. Stewart, Cranial Nerves: Anatomy
and Clinical Comments (Toronto: B. C. Decker,
Inc., 1988), vii.
Ibid, 136.
Frank H. Netter, The Ciba Collection of Medical
Illustrations, vol. 1: The Nervous System (New
Jersey: CIBA, 1991), 126.
Wilson-Pauwels, Akesson, and Stewart, Cranial
Ibid, vii.
Ibid, 127.
Ibid, 126.
Ibid, 128.
Raymond H. Colton, Janita K. Casper, and Rebecca
Leonard, Understanding Voice Problems: A
Physiological Perspective for Diagnosis and
Treatment, 4th ed. (Philadelphia: Lippincott
Williams, & Wilkins, 2011), 403.
Ibid, 405.
Ibid, 402.
Ibid, 129.
Ibid, 130.
Ibid, 131.
Ibid, 132.
Ibid, 129.
Ibid, 405.
Ibid, 130.
Nemer Al-Khtoum, Nabil Shawakfeh, Eyad
Al-Safadi, Osama Al-Momani, and Khalid
Hamasha, “Acquired Unilateral Vocal Fold
Paralysis: Retrospective Analysis of a Single
Institutional Experience, North American
Journal of Medical Science, 5 no.12 (2013):
Wilson-Pauwels, Akesson, and Stewart, Cranial
Nerves, 132.
Rogelio Mosqueda-Garcia, “Central Autonomic
Regulation. In David Robertson, Phillip A.
Low, and Ronald J. Polinsky, ed., Primer on
the Autonomic Nervous System (San Diego:
Academic Press, 1996), 3.
Robert W. Hamill, “Peripheral Autonomic Ner-
vous System. In David Robertson, Phillip
A. Low, and Ronald J. Polinsky, ed., Primer on
the Autonomic Nervous System (San Diego:
Academic Press, 1996), 13.
Wilson-Pauwels, Akesson, and Stewart, Cranial
Nerves, 132.
Paul Forsythe, Wolfgang A. Kunze, and John
Bienenstock, “On Communication between
Gut Microbes and the Brain, Immunology 28
no.6 (2012): 557.
Duncan A. Groves and Verity J. Brown, “Vagal
Nerve Stimulation: A Review of its
Applications and Potential Mechanisms that
Mediate its Clinical Effects, Neuroscience and
Biobehavioral Reviews 29 (2005): 493.
Paul Forsythe, et al., “Mood and Gut Feelings,
Brain, Behavior, and Immunity 24 (2010): 11.
Laine Taylor, et al., “Depression and Smoking:
Mediating Role of Vagal Tone and
In ammation, Annals of Behavioral Medicine
42 (2011): 339.
Soon-Tae Lee, et al., “Cholinergic Anti-
Inflammatory Pathway in Intracerebral
Hemorrhage, Brain Research 1309
(2010): 168.
D. Martelli, M.J. McKinley and R.M. McAllen, “The
Cholinergic Anti-In ammatory Pathway: A
Critical Review, Autonomic Neuroscience:
Basic and Clinical (forthcoming), 3. http://dx.doi.
Graham J. Dockray, “Enteroendocrine Cell
Signalling Via the Vagus Nerve, Current
Opinion in Pharmacology 13 (2013): 955.
Groves and Brown, Neuroscience and Biobehavioral
Reviews 29: 493.
Martelli, et al., Autonomic Neuroscience: Basic and
Clinical: 3.
Stephen W. Porges, “The Polyvagal Theory:
Phylogenetic Contributions to Social
Behavior, Physiology & Behavior 79 (2003):
Groves and Brown, Neuroscience and Biobehavioral
Reviews 29: 496.
Stephen W. Porges, “The Polyvagal Theory:
Phylogenetic Substrates of a Social
Nervous System, International Journal of
Psychophysiology 42 (2001): 125.
Porges, Physiology & Behavior 79: 510.
ResearchGate has not been able to resolve any citations for this publication.
Full-text available
Vocal cord paralysis continues to be an important issue in laryngology and is considered as a sign of underlying disease; the etiologies of this problem are varied and changing. The study was to carry out a retrospective analysis of patients with unilateral vocal fold paralysis diagnosed. The medical records of 53 patients diagnosed and treated for unilateral vocal fold paralysis were studied retrospectively. Data regarding age, sex, duration of symptoms, etiology, and side of paralysis were recorded. Out of the 53 cases, 36 were females and 17 males with a ratio of 2.1:1. The age of the patients ranged from 17-75 years. In 18.9% the cause was idiopathic. Surgical trauma (iatrogenic) problems was the most encountered etiology (66%), others included malignancy (non laryngeal) (7.5%), central (3.8%), external neck trauma (1.9%) and radiation therapy 1.9%. Thyroid surgery was the most commonly reported neck surgery in 50.9%. Thyroidectomy continues to be the single most common surgical procedure responsible for unilateral vocal cord paralysis. For this reason, routine pre and postoperative laryngoscopy should be considered in all patients undergoing surgeries with a potential risk for recurrent nerve paralysis to reduce the postoperative morbidity.
Full-text available
Interest in the microbiota-gut-brain axis is increasing apace and what was, not so long ago, a hypothetical relationship is emerging as a potentially critical factor in the regulation of intestinal and mental health. Studies are now addressing the neural circuitry and mechanisms underlying the influence of gut bacteria on the central nervous system and behavior. Gut bacteria influence development of the central nervous systems (CNS) and stress responses. In adult animals, the overall composition of the microbiota or exposure to specific bacterial strains can modulate neural function, peripherally and centrally. Gut bacteria can provide protection from the central effects of infection and inflammation as well as modulate normal behavioral responses. Behavioral effects described to date are largely related to stress and anxiety and an altered hypothalamus-pituitary-adrenal axis response is a common observation in many model systems. The vagus nerve has also emerged as an important means of communicating signals from gut microbes to the CNS. Studies of microbiota-gut-brain communication are providing us with a deeper understanding of the relationship between the gut bacteria and their hosts while also suggesting the potential for microbial-based therapeutic strategies that may aid in the treatment of mood disorders.
Understanding Voice Problems: A Physiological Perspective for Diagnosis and Treatment emphasizes the physiological perspective of voice disorders-and the behavioral and emotional factors that can influence these changes. Readers will find a strong foundation in normal phonatory physiology and acoustics as well as pathophysiology arising from voice misuse, abuse, or neurological involvement. Coverage includes in-depth explorations of patient interviewing, history-taking, examination, and testing and discussions of pediatric and geriatric voice considerations. The book contains numerous illustrations, including full-color plates of vocal fold pathologies. A companion website features nearly 30 video clips that demonstrate healthy, normally functioning larynges at work, plus larynges with various pathological problems.
This chapter focuses on the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS) as the first two aspects of the peripheral autonomic nervous system (ANS). The SNS is organized at a spinal and peripheral level such that cell bodies within the thoracolumbar segments of the spinal cord provide preganglionic efferent innervation to sympathetic neurons. Prevertebral ganglia are midline structures located anterior to the aorta and vertebral column, and are represented by the celiac ganglia, aortic-renal ganglia, and the superior and inferior mesenteric ganglia. The spinal cells of origin for the presynaptic input to sympathetic peripheral ganglia are located from the first thoracic to the second lumbar level of the cord, although minor variations exist. The postganglionic fibers in the SNS travel quite lengthy paths to arrive at target organs. For instance, fibers from the SCG traverse the extracranial and intracranial vasculature to reach such targets as the lacrimal glands, parotid glands, pineal gland, and pupils. Interactions between the adrenal cortex and adrenal medulla constitute a critical link between the autonomic and endocrine systems.
From a critical review of the evidence on the cholinergic anti-inflammatory pathway and its mode of action, the following conclusions were reached. 1) Both local and systemic inflammation may be suppressed by electrical stimulation of the peripheral cut end of either vagus. 2) The spleen mediates most of the systemic inflammatory response (measured by TNF α production) to systemic endotoxin, and is also the site where that response is suppressed by vagal stimulation. 3) The anti-inflammatory effect of vagal stimulation depends on the presence of noradrenaline-containing nerve terminals in the spleen. 4) There is no disynaptic connection from the vagus to the spleen via the splenic sympathetic nerve: vagal stimulation does not drive action potentials in the splenic nerve. 5) Acetylcholine-synthesizing T lymphocytes provide an essential non-neural link in the antiinflammatory pathway from vagus to spleen. 6) Alpha-7 subunit-containing nicotinic receptors are essential for the vagal antiinflammatory action: their critical location is uncertain, but is suggested here to be on splenic sympathetic nerve terminals. 7) The vagal antiinflammatory pathway can be activated electrically or pharmacologically, but it is not the efferent arm of the inflammatory reflex response to endotoxaemia.
Nutrient delivery to the gut activates neuroendocrine mechanisms that control digestion and energy intake and utilisation. These include the release from enteroendocrine cells of mediators including 5HT, CCK, GLP-1, PYY and ghrelin that act on vagal afferent neurons regulating food intake and autonomic reflexes controlling motility, secretion, inflammatory responses and mucosal defence. The mediators may act locally on vagal afferent fibres running close to their cell of origin, or distally after delivery in the circulation. Recent work indicates that the signalling mechanisms are strongly influenced by nutrient status. Thus, both food withdrawal and diet-induced obesity alter the sensitivity of vagal afferent neurons to stimulation as well as their patterns of expression of receptors and neuropeptide transmitters. Normally, leptin potentiates vagal afferent stimulation by CCK but this is lost in obesity. Recent studies suggest changes in the gut microbiota in obesity lead to increased LPS which suppresses leptin effects on vagal afferent neurons. There are obvious limitations to direct studies of vagal afferent signalling in man but recent work indicates fMRI brain imaging of CNS responses to CCK and ghrelin is feasible, informative and provides opportunities for future progress in human studies of gut-brain signalling.
Summary The reputed benefits of moderate caffeine consumption include improvements in physical endurance, cognitive function, particularly alertness and vigilance, mood and perception of fatigue. In contrast, there are concerns that excessive intakes increase the risks of dehydration, anxiety, headache and sleep disturbances. This paper is a review of double-blind, placebo-controlled trials published over the past 15 years to establish what range of caffeine consumption would maximise benefits and minimise risks for cognitive function, mood, physical performance and hydration. Of the 41 human studies meeting the inclusion criteria, the majority reported benefits associated with low to moderate caffeine intakes (37.5 to 450 mg per day). The available studies on hydration found that caffeine intakes up to 400 mg per day did not produce dehydration, even in subjects undergoing exercise testing. It was concluded that the range of caffeine intake that appeared to maximise benefit and minimise risk is 38 to 400 mg per day, equating to 1 to 8 cups of tea per day, or 0.3 to 4 cups of brewed coffee per day. The limitations of the current evidence base are discussed.
Fluid is essential for life and health. Nurses have an important role in helping patients maintain optimal levels of hydration, particularly in hospital or residential settings where access to fluid is less likely to be under the patient's control. This article describes the benefits of healthy hydration, outlines guidelines on fluid requirements for different patient groups and discusses which beverages should be promoted. Myths about caffeine consumption and hydration will also be addressed using new clinical evidence.