Occlusion effects -the neural challenges

OCCLUSION EFFECTS—
THE NEURAL CHALLENGES

• There remain those cases in which occlusion is
reduced--almost to the point of elimination--with
reported problems of "feeling plugged" still
occurring.
• Such instances fall into the category termed here
as the "non-acoustic/neural occlusion effect".


The “non-acoustic/neural occlusion effect” is
defined as the sensation of stimuli in parts of the
body at or away from the ears while wearing
hearing instruments, whether amplification is
operational or not.


• Non-acoustic/neural occlusion is believed to be
caused by the pressure of acoustic coupling
shells against the nerves of the outer ear.
• Its effects in individual cases are important to
understand, as it may involve both cranial and
cervical nerves.


Signs of Neural Occlusion
Reports of headaches, nausea, numbness,
pressure, tension, pain, tearing in the eyes,
running noses, tingling sensations, soreness,
hoarseness, sore throat, changes in breathing,
blood pressure, heart rate, and feelings of being
"plugged up" while wearing vented hearing
instruments, may be suspect signs of neural
occlusion.


• The literature on the nerve endings found in and
around the outer ear reveals numerous
discrepancies in location of individual nerves.
• This fact demonstrates the broad variability in
final development of the structures of the human
body.


The descriptions of neural pathways are intended
as general guidelines only.
Individual variation should be regarded as a
constant possibility.
In addition, the nerves found in the outer ear do
not follow straight line courses like those
frequently found in anatomic diagrams. They
usually form spiraling patterns of individual
neurons whose course is often subject to
meandering.


• There are four cranial nerves involved in the
process of sensory innervations of the outer ear.
They are: Cranial nerves V, VII, IX, and X.
• The Cranial nerves originate in the Pons and
Medulla in the brainstem (see FIGURE 5).


Please note:
Both Cranial and Cervical nerves can generally be
regarded as major communication points between
the brain and body for intake of sensory (afferent)
information and execution of motor (efferent)
activities.


The Vth (trigeminal) Cranial Nerve
• The Vth (trigeminal) cranial nerve is divided into
three major branches: the ophthalmic, maxillary,
and mandibular.
• One division of the mandibular branch is the
auricular-temporal nerve, which provides sensory
innervations to the top and front walls of the
external auditory meatus, to the tragus, and to
the crest of the helix.

The ophthalmic branch proceeds across the top of
the temporal muscle and around the front of the
face just above the brow.
Patients who report headache and/or muscle
tension in this area following insertion of their
hearing instrument may be triggering a neural arc
and stimulating contraction of the muscles above
the brow and along the upper side of the face.
Those contractions would then be registered by
the Trigeminal (Vth cranial) as feelings of tension,
etc.


The mandibular division of Vth cranial nerve
provides the sensory input from the lower teeth
and jaw, motor control of the tensor tympani and
the muscles of mastication.
The external ear canal initiated neural activity
leading to stimulation of the muscles and nerves of
the mandible, may be reported as pain deep in the
ear, lower jaw pain, pain in the lower teeth, tension
in the cheeks or mouth, difficulty in chewing, or
pain at the temporal-mandibular joint.


Please note:
Since the tensor tympani is directly involved in the
acoustic reflex, it is possible that insertion of an
acoustic coupling could result in the acoustic
reflex “firing” thus, causing damping of the sound
transmission through the ossicles and resulting in
a reported feeling of occlusion.


The VIIth Cranial (facial) Nerve
• The VIIth cranial (facial) nerve, is predominantly
a motor neuron.
• It does have sensory loci on the back of the
auricle and in the concha.
• In some reports, the nerve has been found to
branch from its sensory array at the tympanic
membrane to and through the external ear canal
to join the peripheral nerves in the auricle.


The chorda tympani branch of Cranial VII controls
contraction of the stapedius muscle as well as
providing the sensation of taste in the anterior
2/3rds of the tongue.


The facial nerve is unique among the twelve cranial
nerves, in that it normally is inherently capable of
cross-communication with:
• cranial nerves V, VIII, and IX, X, and
• the upper cervical nerves #2 & #3.


Please Note:
The neural cross-communication process is not
fully understood, but lends general support to the
idea that individual neural stimuli could influence
other neural pathway responses.


• Innervations of Cranial VII (facial) nerve could
cause muscle tension in the face which would be
sensed by neurons of the cranial Vth
(trigeminal).
• The Vth (trigeminal), with its' numerous
branches, may create changes in the sense of
taste, a runny nose, tearing or dryness in the
eyes, either dryness or excess saliva in the
mouth, and/or tension in the eyelids.


Please note:
Contraction of the stapedius could cause feelings
of occlusion as well as increased sensitivity to low
frequency sounds—they will have difficulty
modulating their own voice.


The IXth (glossopharyngeal) Nerve
• The Glossopharyngeal cranial nerve IX,
innervates sensation to the mucous membrane
of the tympanic cavity, as well as controlling
motor activity in opening and closing the
Eustachian tube.
• Branches of cranial IX have been found to extend
into the ear canal.


The IXth (glossopharyngeal) Nerve

• The primary sensory divisions of this nerve are
involved in the back of the tongue and mouth,
and the top of the throat.
• They could produce complaints of numbness,
soreness, and tension in these areas.


The Xth (Vagus) Nerve
• Most hearing instrument specialists are familiar
with the occasional cough response when
inserting an impression block.
• The cough reflex is generated through Arnold's
branch of the Vagus nerve, Cranial X.
• The Vagus provides sensory innervations to the
bottom and back walls of the external meatus.



Since one branch of Cranial X also provides
monitoring of blood pressure, reports of hearing
aid wearers with rapid heart rate and increased
blood pressure may have much more than an
emotional basis!



It travels through the body, innervating the
recurrent laryngeal nerves on each side of the
larynx, parts of the lungs, the pericardial sac
around the heart, and parts of the stomach and
intestines.


• Identification of this innervation following
insertion of the hearing instrument. May involve:
hoarseness in the voice, coughing, chest pain,
changes in breathing patterns, changes in heart
rate, and nausea.
• Note: reports of heart problems and vomiting
are found in the literature, but should be
considered an extremely rare instance.


Cervical Nerves #2 & #3
• Cervical nerves 2 and 3 join to form the great
auricular nerve, receiving sensory information
from the helix, anti-helix, lobule, and the mastoid
process.
• This is likely the location of stimulation for the
reported problems of tension in the neck and the
feeling of tightness in the neck experienced in
some hearing instrument users after insertion of
their aids.


Cervical Nerves #2 & #3
The reported problems of tension and the feeling
of tightness in the neck after hearing instrument
insertion, is a direct connection between the Xth
(Vagus) nerve and Cervical 2 and 3; thus,
increasing the potential for these complaints even
when the instruments involved do not place direct
pressure on the helix, anti-helix, or the mastoid.


Temporal Mandibular Joint (TMJ)
• Of special concern in cases involving non-
acoustic occlusion effects is the role of the
temporal-mandibular joint.
• Since the TMJ induces movement in the ear
canal, the presence of an acoustic coupler could
cause more pressure on the nerves in the area of
the TMJ than would normally be found.


When neuropathy due to trauma, disease
processes, chemical changes, heredity, or aging
causes alterations in the normal transfer of neuro-
electrical signals, the result could be multiple
stimuli from a single sensory event. This neuro-
electrical "short circuit" is presumed to be the
basic process involved in non-acoustic occlusion.


The presence of and pressure from an occluding
object in the ear canal could cause a cross-firing of
the nerve, stimulating another nerve. It is likely that
the most common cross-firing patterns occur
within single major neural pathways.


It becomes increasingly evident that suggestions
concerning the value and applicability of the
principles of reflexology and acupressure,
stemming from the concept of neural interaction as
the norm rather than an exception may reflect a
true understanding of the afferent/efferent
connections and the behavioral effects of these
nerve branches.


It is clear that the tactile reality of wearing an
instrument must be considered in the fitting
of hearing aids along with the acoustic needs
of the patient.

Occlusion effects -the neural challenges

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