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NEUROPHYSIOLOGICAL BASIS OF FUNCTIONAL
DE-AFFERENTATION OF THE NERVOUS SYSTEM
CAUSED BY WEAK OR ABSENT MUSCLE
CONTRACTIONS
NEVROFIZIOLOŠKE OSNOVE FUNKCIONALNE DE-AFERENTACIJE ŽIVČNEGA SISTEMA
KOT POSLEDICA ŠIBKIH ALI POPOLNOMA ODSOTNIH MIŠIČNIH KONTRAKCIJ
Nejc Sarabon1, Milan R. Dimitrijevič2, 3
1 Institute of Sport, Faculty of Sport, Gortanova 22, 1000 Ljubljana, Slovenia
2 Institute of Clinical Neurophysiology, Neurological Clinic, Clinical Center, Zaloška 7, 1525 Ljubljana, Slovenia
3 Department of Physical Medicine & Rehabilitation, Baylor College of Medicine, Houston, Texas, USA.
Arrived 2004-02-06, accepted 2004-05-10; ZDRAV VESTN 2004; 73: Suppl. II: 25–7
Izvleček – V članku razglabljamo o učinkih, ki nastanejo kot
posledica upadlih gibalnih sposobnosti pri progresivnih živč-
no-mišičnih boleznih in se domnevno odražajo v spremenje-
nem centralnem stanju možganske aktivnosti. Nakazujemo
možnost, da takšno zmanjšanje proprioceptivne aktivnosti
lahko vodi v delno funkcionalno de-aferentacijo. Kratkemu
pregledu nevrofizioloških dokazov o centralnih projekcijah
perifernega proprioceptivnega dotoka sledi oris funkcional-
ne vloge proprioceptivnih informacij, ki je prikazana skozi
analizo pasivnega in aktivnega gibanja ter gibanja povzročene-
ga z vibracijo mišičnih kit. Prispevek sklenemo s predlogom
za uporabo enostavnih vibracijskih protokolov v vsakdanjem
življenju ljudi z živčno-mišičnimi okvarami, kar lahko pri-
pomore k povečanju mentalne vzdržljivosti teh ljudi s sicer
neprizadetimi mentalnimi funkcijami.
Abstract – In this short article we discuss putative effect of
decreased ability for movement in the progressive neuromus-
cular disorders on the central state of brain activity. We pro-
pose possibility that such reduced activation of propriorecep-
tors can lead to partial ‘functional de-afferentation’.
Furthermore, we briefly reviewed neurophysiological eviden-
ces of peripheral inputs to the central projections. We dis-
cussed contribution of the proprioceptive input after passive,
active movements and movement induced by vibration of
muscles tendons.
Finally we are proposing to introduce simple vibratory proto-
cols in daily life of people with progressive neuromuscular
disorders in order to prevent central effects of reduced proprio-
ception to endurance of brain activity of people with intact
mental functions.
Introduction
Muscle contraction is origin of force during movement perfor-
mance and at the same time, it is source of afferent input from
stretched, contracting muscle, moving joint, skin. In the neuro-
logical conditions of chronic muscle weaknesses of muscle
dystrophies and spinal muscle atrophies, as it is the case in the
progressive neuromuscular disorders, the nervous system, due
to weak or absent volitional and automatic movements it is
deprived of multi-afferent input. In this short note our aim it is
to bring to the attention of the professionals involved in the
rehabilitation programs for the people with chronic muscular
disorders notion that during nervous system controlled and
stretched relaxed or shorten muscles. During reflex, automat-
ic and/or volitional movements there is rise of proprioceptive
input to the brain (1–3).
The purpose of this paper it is to discuss why in the life of
people suffering from neuromuscular disorders it is essential
to introduce simple practice of supported movements, mus-
cle contraction in the unloaded environment for the body
weight, i. e. supported standing, walking, and swimming.
Furthermore, we shall argue that eliciting tonic input from
muscles and cutaneous receptors by external vibration (handy
devices mounted on the wheel chairs, beds, working and rest-
ing places) it is possible to enhance sensory proprioceptive
and exteroceptive inputs to the nervous system and to facili-
tate the brain sensory processing mechanisms, the sensory-
motor integration mechanisms and augment appreciation of
self body awareness, cognition of weakened movements with-
out involving visual input and others available modalities of
sensory inputs.
Proprioceptors
Receptors placed within the skin, joint ligaments, joint cap-
sules and muscles can provide proprioceptive input. Muscle
Spindle Afferent Discharge from resting and contracting
muscles in humans become possible by direct recordings from
fascicles of peripheral nerves of large afferents (4). It was
found that when muscles were relaxed, there was a low and
approximately constant discharge in the spindle afferents as a
group, indicating that the fusimotor drive was very low or ab-
sent (5, 6). To passive movement, the muscle spindles respon-
ded with an increase of the discharge rate as the muscle was
stretched and vice versa. In contrast, the muscle spindles were
strongly activated during voluntary contraction.
Furthermore, the new neuro-radiological methods, Positron
Emission Tomography and Functional Magnetic Resonance and
their usefulness in the assessment of functional activity of the
ZDRAV VESTN 2004; 73: II-25–7
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enhance proprioceptive input to the CNS in the people with
decreased movements activities and preserved peripheral and
sensory nervous system functions. In man with vibratory stimu-
lation of skeletal muscles it is possible to evoke a high-frequen-
cy sustained discharge in the Ia afferents and slowly
enlarging autogenetic reflex contraction (TVR). This TVR can
have sufficient strength to lift an arm or a leg against gravity (8,
9). It has been shown in recordings from whole muscle nerve
fascicles and securely fastened to the muscle tendon vibration
induced barrage of impulses from the intramuscular stretch
receptors increases in strength with increasing amplitude (up
to 2 mm) and increasing frequency (up to 200/sec) of the
mechanical oscillations (10).
Vibratory stimulus within the range of 100–200 sec and 1–2
mm applied to the tendon it is an appropriate stimulus when
our intention is to activate the primary endings in humans.
Vibrators oscillating at about 150/sec with an amplitude of
about 1.5 mm, fairly independent of the external load, are
easy made of compact cylindrical DC motors equipped with
an appropriate excenter on the axis. Such small vibrators are
easy to handle (11).
The following Figure 2 is illustrating simplicity of procedure for
vibratory induced proprioceptive input to the CNS, shown here
by microneurographic recording of induced spike activity dur-
ing vibratory tonic reflex response. In the other words vibration
is very simple and potent procedure when applied in the
people with progressive neuromuscular disorders to accomplish
externally controlled increase of proprioceptive input.
Vibratory stimulation of muscle tendons in addition to tonic
movement can induce also impairments of sense and illusion
of movements. Both of those effects is evidence for central
effects of vibratory induced (12–14).
Let us mention that regional blood flow studies, PET tomogra-
phy study, revealed that perception of passive flexion/exten-
sion movements and illusions of movements are associated
with different patterns of brain activation. Primary sensory
cortex and Supplementary Motor area do respond only to
passive movements. However, perception of passive move-
ment and of illusory movement induced by tendon vibration
activated areas in parietal and temporal lobes (7). Thus a very
Figure 1. The muscle spindle receptor and corresponding large
fibers simplified sketch. Certain axons of primary sensory
fibers are entering spinal cord gray matter to reach spinal
motor cells and others extended via white matter to the ros-
tral structures of the CNS. Numerous axons of the posterior
columns of the spinal cord are projecting to the nuclear struc-
tures of the medulla oblongata, thalamus and cortical senso-
ry and motor structures.
brain functions shown that primary and secondary somato-
sensory cortex are involved in central processing of proprio-
ceptive signals during passive and active movement (7).
Therefore whenever we are confronted with reduced move-
ments’ activities in people with otherwise intact primary, pe-
ripheral and central sensory mechanisms we should keep in
mind this in Figure 1 shown simplified illustration of segmen-
tal and brain projection of the large afferents from muscle
spindles. It is important to be aware that large myelinated Ia
afferents provide input to the spinal cord gray matter but in
the same time muscle spindles contribute to the propriocep-
tive brain functions too. Thus we should give some thoughts
how to enhance proprioceptive input to the brain in the
people suffering from progressive neuromuscular disorders.
We should remember that brain’s sensory-motor integration
mechanisms activity depends on sensory information from
the body and the central state of brain functional level. Thus,
higher nervous system functions awareness, attention and
different functions of consciousness have also contribution
from sensory peripheral input. Therefore, if de-afferentation
is due structural lesion of peripheral nerves, ascending senso-
ry pathways of the spinal cord, brain stem, sub-cortical one or
by functional one, due to restriction of movements by splint-
ing, prolonged bed rest, exposed prolonged conditions of re-
duced gravity or by muscles weaknesses due to neuromuscu-
lar disorders, we should recognize consequences of the
structural as well as functional de-afferentation of the brain.
When brain functions are altered then they can be repaired by
another modalities of sensory inputs (i. e. visual by acustic,
proprioceptive by exteroceptive). However, this compensa-
tory brain functions are decreasing range of brain’s capacity to
adapt, to anticipate, to set implementation by control and
executing desired movements and appropriate movements.
Externally induced proprioception and
tonic vibratory reflex
Skin, tendons and muscle receptors are also sensitive to vib-
ration and by eliciting vibratory tonic reflex it is possible to
Figure 2. Simplified sketch of applied vibrator to the forearm
of the upper limb. During the vibratory tonic reflex shown in
the figure at the right corner, microneurographic recording
reveals large spike activity in the median nerve fascicle of the
large myelinated sensory nerve fibers.
d07.p65 5.6.2004, 4:4126
II-27
simple protocol of passive and active movements, vibratory
induced proprioceptive input with different mental task can
provide variety of brain activations and enhancing higher ner-
vous system functions.
Therefore we should make en effort to prevent central
effects of the decreased proprioceptive, partial ‘functional
deafferentation’, on alterations in the subjects mood, aware-
ness, attention and other mental functions.
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SARABON N, DIMITRIJEVIČ MR. NEUROPHYSIOLOGICAL BASIS OF FUNCTIONAL DE-AFFERENTATION OF THE
NERVOUS SYSTEM CAUSED BY WEAK OR ABSENT MUSCLE CONTRACTIONS
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