196,243 research outputs found
Medium-latency response to muscle stretch in human lower limb: estimation of conduction velocity of group II fibres and central delay
No full textIn standing subjects, ankle dorsiflexion evoked short-latency responses (SLRs) at
41 and 57 ms, on the average, in soleus (Sol) and flexor digitorum brevis (FDB),
respectively. Medium-latency responses (MLRs) occurred at 70 and 95 ms. The time
between the MLRs was 25 ms and between the SLRs was 16 ms. The difference between
these two values represents the extra-time to conduct the FDB volley for MLR from
distal to proximal muscle, in excess to that for SLR. The velocity of the
afferents mediating the FDB MLR (21.4 m/s on average) was estimated by dividing
the distance between the two muscles by the sum of the above extra-time and the
conduction time of Ia fibres along the same distance. The central delay of FDB
MLR (6.7 ms on average) was obtained by dividing the distance between FDB and
spinal cord by the sum of afferent and efferent MLR conduction times. The central
delay of FDB SLR (1.4 ms) was analogously obtained. These findings give an
estimation of the conduction velocity of the group II afferent fibres in humans
and support the hypothesis that the FDB MLR is relayed through a spinal
oligosynaptic pathway
Medium-latency stretch reflexes of foot and leg muscles analysed by cooling the lower limb in standing humans
No full text1. In standing subjects, an ankle-dorsiflexing perturbation of the supporting
surface evokes a short-latency response (SLR) and a medium-latency response (MLR)
to stretch in both soleus (Sol) and flexor digitorum brevis (FDB) muscles. The
SLR is the counterpart of the monosynaptic reflex, whilst the MLR might be either
mediated by Ia fibres, the delay being due to a long-loop central circuit, or by
fibres of slower conduction velocity. Since small afferents are slowed more than
large ones by low temperature, a greater latency increment for the MLR than the
SLR induced by cooling of the limb would point to a peripheral origin of the MLR.
2. In nine subjects, one limb was cooled by circulating water in a tube wrapped
around it for about 120 min. Perturbations were delivered to the same limb prior
to and during cooling, and after rewarming. EMG was recorded by surface
electrodes from the Sol and FDB muscles. 3. The mean increase in latency of MLRs
was significantly greater than that of SLRs in both muscles. On average, the Sol
SLR increased from 42.4 to 47.0 ms and the Sol MLR from 72.0 to 82.3 ms. The FDB
SLR increased from 58.1 to 66.5 ms and the FDB MLR from 94.9 to 110.5 ms. The
mean difference (MLR minus SLR) increased from 29.6 to 35.2 ms for Sol, and from
36.8 to 43.9 ms for FDB at the end of cooling. After 30 min of rewarming, the
responses of both muscles recovered towards control values. 4. The greater
latency increment of the MLRs than of the SLRs favours the hypothesis of a slower
conduction velocity of the responsible afferent fibres. The most likely candidate
fibres are the spindle group II afferents
Group II spindle fibres and afferent control of stance. Clues from diabetic neuropathy
No full textOBJECTIVE: Since patients with large-fibre neuropathy do not show abnormal body
sway during stance, the hypothesis was tested that postural control is not
impaired until myelinated fibres of medium size are affected.
METHODS: In 22 diabetic neuropathic patients and 13 normals, we recorded: (1)
body sway area (SA), (2) stretch responses of soleus (Sol) and flexor digitorum
brevis (FDB) to toe-up rotation of a platform, (3) Sol and FDB H reflex and FDB F
wave, (4) conduction velocity (CV) of tibial, deep peroneal and sural nerve. In
patients, detection thresholds for vibration, cooling (CDT), warming and
heat-pain (HPDT) were assessed.
RESULTS: Body SA was increased in patients with respect to normals. Toe-up
rotation elicited short- (SLR) and medium-latency (MLR) responses in Sol and FDB
in all normals. In patients, SLR was absent in FDB and reduced in Sol, and MLR
was delayed in both muscles; the FDB H reflex was absent. The CV of tibial nerve
group II afferent fibres, as estimated from the afferent time of FDB MLR, was
reduced in patients. All sensory detection thresholds were increased. Stepwise
multiple regression showed that increased SA was explained by increased latency
of MLR, decreased CV of group II fibres and augmented CDT and HPDT.
CONCLUSIONS: Unsteadiness in diabetic neuropathy is related to alterations in
medium-size myelinated afferent fibres, possibly originating from spindle
secondary terminations
Balance control under static and dynamic conditions in patients with peripheral neuropathy
No full textReflex contribution of spindle group Ia and II afferent input to leg muscle spasticity as revealed by tendon vibration in hemiparesis
No full textOBJECTIVE: Foot dorsiflexion evokes a short- (SLR) and a medium-latency EMG
response (MLR) in the soleus of standing subjects. SLR is mediated by spindle
group Ia, while group II fibres contribute to MLR through an oligosynaptic
circuit. We studied the effects of Achilles' tendon vibration on both responses
in spastic patients to disclose any abnormal excitability of these pathways.
METHODS: SLR and MLR were evoked in 11 hemiparetics and 11 normals. The
vibration-induced changes in both responses were correlated to the Ashworth score
of the affected leg.
RESULTS: There were no differences between normals and patients in the size of
control SLR or MLR. Vibration decreased SLR to 70% in normal subjects, but
increased it to 110% in patients, in both affected and unaffected leg. Vibration
did not affect MLR in normals, but increased it to 165% on the affected and 120%
on the unaffected side of patients. Ashworth score was solely correlated with the
degree of vibration-induced increase of MLR.
CONCLUSIONS: While the lack of inhibitory effect of vibration on SLR confirms a
reduced inhibitibility of the monosynaptic reflex, the increased MLR indicates a
disinhibition of group II pathway in patients, connected to the loss of
descending control on group II interneurones. Spastic hypertonia depends on
release of group II rather than group Ia reflex pathways.
SIGNIFICANCE: These findings give a neurophysiological support for the
pharmacological treatment of spastic hypertonia and suggest a method for the
assessment of its effects
Inhibitory effect of the Jendrassik maneuver on the stretch reflex
No full textThe Jendrassik maneuver (JM) is a method for enhancing sluggish tendon-tap jerks
at medical examination. It is the thesis of this paper that JM effects should not
be limited to the monosynaptic reflex pathway but extend to the entire response
elicited in the stretched muscle. This consists of a short-latency response (SLR)
corresponding to the mono- and oligosynaptic reflex and a medium-latency response
(MLR) relayed by group-II spindle afferent fibers and likely made of a segmental
burst and a transcortical loop. Soleus (Sol) SLR and MLR were evoked by toe-up
and tibialis anterior (TA) MLR by toe-down platform rotation in 15 standing
subjects and recorded by surface electromyogram (EMG). For each stimulus type, up
to 20 perturbations were elicited during i) quiet stance (Control) and while ii)
performing JM, iii) leaning forward (FW), iv) holding onto a stable frame
(Holding). For each subject, stimulus type and condition, rectified EMG traces
were averaged. Based on the comparison of the population grand averages,
selective effects of JM on the responses were identified. Appropriate time
windows were set for measuring the area of SLR and of the early and late burst of
MLR (MLR1 and MLR2). Significant changes in response size, but not latency, were
induced by all conditioning procedures. During toe-up, JM slightly increased Sol
SLR; FW increased both Sol background activity and SLR; MLR1 was not affected by
JM, but increased by FW; MLR2 was strongly diminished by JM and increased by FW.
During toe-down, JM did not affect TA MLR1, but strongly diminished MLR2. Under
Holding condition, Sol SLR to toe-up was unaffected, but both MLR1 and MLR2 to
toe-up and toe-down were diminished, in both Sol and TA. JM selectively decreases
the response component (MLR2) starting about 100 ms from onset of the stretch, in
both extensor and flexor muscles. Latency and quality of the JM effect on MLR2
indicate that JM operates by gating a long-loop, possibly transcortical pathway.
This new information suggests that lesions of cortical areas or descending
pathways can exert enhancing effects on muscle tone by removing an inhibitory
action on the late component of the stretch reflex
The role of instrumental assessment of balance in clinical decision making
No full textThis review addresses the issue whether instrumental evaluations of balance may
be helpful in orienting the clinical decision regarding balance rehabilitation.
The aptitude of instrumental assessment of balance in supporting decision making
in patients with balance disorders connected with ageing and with neurological
diseases is considered. Among instrumental evaluations, recording of body sway
during quiet stance and dynamic conditions are described, together with
manoeuvres for recording postural reactions to predictable or unpredictable
postural perturbations. The posturography patterns encountered in elderly
subjects and patients affected by Parkinson's disease, spasticity, peripheral
neuropathy, cerebellar diseases, vestibular deficit and neck disorders are
presented and discussed. Findings from instrumental assessments of balance are
helpful in understanding the pathophysiology of balance disorders, in screening
for balance disorders, and in evaluating the natural progression of the disease
or the response to therapy, be it physical or pharmacological. Conversely, as far
as the prediction of the risk of falling in one individual patient is concerned,
the various posturography tests do not produce consistent results
Influences of transcutaneous electrical stimulation of cutaneous and mixed nerves on subcortical and cortical somatosensory evoked potentials
No full textAim of this study was to assess whether transcutaneous electrical nerve
stimulation (TENS) 'gates' somatosensory evoked potentials (EPs) peripherally or
centrally, and which afferent fibres and sensory nuclei mediate this effect. The
following waves were recorded after stimulation of the median nerve at the wrist
or of the digital nerves of the index finger: N9, the cervical N11 and N13, the
parietal P9, P11, P14, N18, N20, P22, P27, P40. When both median or digital nerve
EPs were conditioned by TENS delivered to the median nerve, reduction in
amplitude of N9, P14, N18 and later generated cortical waves was observed. To
measure the central contribution to this decrease, unconditioned 'reference' EPs
were evoked by stimulating with a current strength yielding an N9 potential of an
amplitude equal to that obtained during TENS. In this case, the amplitude of P14,
N18 and later cortical waves was significantly greater than during TENS. When
both median or digital nerve EPs were conditioned by TENS delivered to the
digital nerves, waves were only slightly affected. No effects were seen on the
EPs elicited from the median or index finger digital nerves when TENS was
administered to the contralateral median or digital nerves or to the ipsilateral
middle finger. It is concluded that TENS gates the somatosensory volley, both at
a peripheral level through a 'busy line-effect' on large afferent fibres, and
centrally at the level of the cuneatus nucleus
Balance in Parkinson's disease under static and dynamic conditions
No full textWe tested balance performance in 15 on phase Parkinson's disease (PD) patients (8
nonfallers, PD-NF; 7 fallers, PD-F) during quiet stance (stabilometry) and on a
platform continuously moving in the anteroposterior direction (dynamic test).
Neither stabilometry (eyes open or closed) nor the dynamic test (eyes open)
separated PD-F from PD-NF. With the dynamic test, eyes closed, PD-F with respect
to PD-NF showed larger head oscillations, smaller cross-correlation between head
and malleolus motion (more so in patients with low Unified Parkinson's Disease
Rating Scale, or UPDRS), and larger delays of head with respect to platform
motion. Further, across all PD patients, head displacement increased with the
equivalent levodopa dose, indicating a trend for medication to worsen balancing
capacity while improving UPDRS. The dynamic test is a sensitive tool for
detecting instability in PD-F since absence of visual flow selectively impairs
both association between body segment movements and anticipatory adjustments
Group II spindle afferent fibers in humans: their possible role in the reflex control of stance
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