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Jab-Like and Jolt-Like Headache
Definition
Jab-Like and Jolt-Like Headache refers to a benign stab- bing headache.
Primary Exertional Headache
Jabs and Jolts Syndrome
Primary Stabbing Headache
Japanese Meridian Therapy
Acupuncture
Jaw Claudication
Definition
Pain during mastication due to ischemia of the masseter muscles in temporal arteritis.
Headache Due to Arteritis
Jaw-Muscle Silent Periods (Exteroceptive Suppression)
GIORGIOCRUCCU
Department of Neurological Sciences, La Sapienza University, Rome, Italy
Cruccu@uniroma1.it
Synonyms
Masseter inhibitory reflex; Masseter Silent Periods; Ex- teroceptive Suppression
Definition
The jaw-muscle silent periods are trigemino-trigeminal inhibitory reflexes elicited by electrical, mechanical, or radiant heat stimuli delivered to the oral region (in the territory of the maxillary and mandibular trigeminal divisions); on electromyographic recordings from con- tracted jaw-closers, this reflex inhibition appears as an early and a late phase of suppression, also called ES1 and ES2 exteroceptive suppressions or SP1 and SP2 silent periods.
Characteristics
Whereas in the reflex control of jaw movement in lower mammals, the jaw-opening and jaw-closing muscles act in equilibrium, in humans the jaw-openers (digastric and suprahyoid muscles) play a marginal role. The jaw- closers (masseter, temporalis and pterygoid muscles) serve both functions, for reflex jaw closing under normal circumstances (excitation) and for reflex jaw opening when they undergo inhibition. The jaw-closers are ex- cited by way of the Aα muscle spindle input andstrongly inhibited by way of Aβ capsulated mechanoreceptors and Aδ free nerve endings. The powerful inhibition exerted by cutaneous and intraoral mechanoreceptors probably compensates for the unusual organization of the jaw-closing motoneurons, which undergo inhibitory control neither by reciprocal nor by recurrent inhibition.
Electrical or mechanical stimuli delivered to the oral region evoke a reflex inhibition of the jaw-closing muscles, the masseter inhibitory reflex(Fig. 1). On EMG recordings from contracted jaw-closers, this re- flex inhibition appears as an early and a late phase of suppression, also called ES1 and ES2 extero- ceptive suppressions(Godaux and Desmedt 1975), or
SP1 and SP2 silent periods (Cruccu and Deuschl 2000). Probably because electrical stimuli yield a mixed – nociceptive and non-nociceptive – input, whether the first or the second or both components are
nociceptive reflexes remains controversial (Miles and Turker 1987). Innocuous mechanical stimuli will elicit both components, however, and indirect evidence supports the view that the afferents belong to the in- termediately myelinated Aβ group. Afferent impulses reach the pons via the sensory mandibular or maxil- lary root of the trigeminal nerve. The first inhibitory
1032 Jaw-Muscle Silent Periods (Exteroceptive Suppression)
Jaw-Muscle Silent Periods (Exteroceptive Suppression), Figure 1 Masseter inhibitory reflex and brainstem circuits. Left: first (1) and second (2) inhibitory periods. Recording from the right masseter muscle. Stimulation of the right mental nerve. Upper traces: 8 trials are superimposed. Lower trace:
rectified and averaged signal. The horizontal line indicates 80% of the background EMG level. Calibration 20 ms / 200μV. Right: schematic drawing of the reflex circuits. Afferents for the first inhibitory period connect with an inhibitory interneuron (1) located close to the ipsilateral trigeminal motor nucleus. The afferents for the second inhibitory period descend along the spinal trigeminal tract and connect with a multisynaptic chain of excitatory interneurons. The last interneuron is inhibitory (2) and projects bilaterally onto the jaw-closing motoneurons. Vm, trigeminal motor nucleus; Vp, trigeminal principal sensory nucleus; Sp V tract, spinal trigeminal tract; VI, abducens nucleus; VII, facial nucleus; XII, hypoglossal nucleus; Lat Ret, lateral reticular formation. (From Cruccu and Deuschl 2000).
period (10–13 ms latency) is probably mediated by one inhibitory interneuron, located close to the ipsi- lateral trigeminal motor nucleus. This interneuron projects onto jaw-closing motoneurons bilaterally. The whole circuit lies in the mid-pons. The afferents for the second inhibitory period (40–50 ms latency) de- scend in thespinal trigeminal complexand connect to a polysynaptic chain of excitatory interneurons, probably located in the medullary lateral reticular formation. The last interneuron of the chain is inhibitory and gives rise to ipsilateral and contralateral collater- als that ascend medially to the right and left spinal trigeminal complexes, to reach the trigeminal motoneu- rons (Cruccu et al. 2005; Ongerboer de Visser et al.
1990).
As shown by experiments with noxious, high-intensity laser stimuli directed to the perioral region, selective ac- tivation of Aδ afferents elicits a single, late (70 ms la- tency) silent period in jaw-closing muscles (Ellrich et al.
1997; Romaniello et al. 2002). This nociceptive reflex (laser silent period, LSP) is supposedly mediated by the spinal trigeminal nucleus, pars caudalis.
Technical Requirements and Normal Values
The masseter inhibitory reflex is usually evoked by tran- scutaneous electrical stimulation of the mentalis terri- tory (to test the mandibular division) or of the infraorbital territory (to test the maxillary division), by placing the cathode on the skin overlying the mental or the infraor- bital foramen and the anode 2 cm laterally. A stimulus lasting 0.1 ms delivered at an intensity of about 3 × the sensory threshold allows best visualization of the first and second inhibitory periods without causing exces- sive discomfort. The patient clenches the teeth at maxi- mum strength, receives the stimulus and is then allowed
a few seconds’ rest. At least 8 trials, but preferably 16, are repeated and superimposed. Quantitative studies of the excitability of the brainstem inhibitory interneurons require measurement of the size of responses (e.g. area of suppression); the level of background EMG activity must be kept constant and the signal is full-wave rectified and averaged (Fig. 1).
The onset latency should correspond to the beginning of the EMG suppression. This is usually taken at the in- tersection between the inhibitory shift and a line corre- sponding to 80% of the mean background EMG activity.
The size of the response can be evaluated by measuring the area of suppression or the duration, taking the end- latency at the point when EMG returns to 80%. The onset latency is the most reliable measure for clinical applica- tions (Table 1 shows normal values). The latency of the first inhibitory period (though not the second) has a rel-
Jaw-Muscle Silent Periods (Exteroceptive Suppression), Table 1 Masseter Inhibitory Reflex in 100 normal subjects aged 15–80 years
Latency (ms) First inhibitory period (SP1 or ES1)
Second inhibitory period
(SP2 or ES2)
Median 12 45
Mean 11.8 45.1
SD 0.8 5.2
Range 10–13.6 38–60
20-year old subjects* 11.1 42
70-year old subjects* 12.3 48
*standard curve calculations for age-latency (from Cruccu and Deuschl 2000)
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Job Capacity Evaluation 1033
atively narrow range of variability, thus allowing com- parisons between subjects. The intraindividual latency difference between sides is small (range 0–1.2 ms, mean 0.3 ms±[SD]0.37msin100normalsubjects).Alatency difference between sides larger than 1.2 ms is abnormal.
The second inhibitory period is considered abnormal if it is absent unilaterally or the latency difference between sides exceeds 8 ms. The second inhibitory period may be absent bilaterally in elderly patients or in patients with malocclusion (Cruccu et al. 1997).
Clinical Applications
Brainstem inhibitory reflexes cannot be tested by clini- cal procedures alone. In some patients, clinical exami- nation discloses no signs of trigeminal impairment, yet testing the masseter inhibitory reflex reveals trigeminal or brainstem dysfunction. As inblink reflexstudies, the pattern of abnormality (afferent, mixed or efferent) provides information on the site of the lesion (Cruccu et al. 2005; Ongerboer de Visser et al. 1990). Nevertheless, except in rare conditions such as a purely motor trigem- inal neuropathy and hemimasticatory spasm, the “effer- ent” type of abnormality (abnormal responses confined to the muscle on one side, regardless of the side of stim- ulation) is extremely uncommon.
The two inhibitory periods of the masseter inhibitory reflex have distinct EMG features and clinical applica- tions. The first inhibitory period appears to be insensi- tive to peripheral conditioning and suprasegmental mod- ulation, its latency varies little and it is probably medi- ated by a small number of afferents. For these reasons it is the best available response for assessing function of the maxillary and mandibular afferents in focal and in generalized diseases. In patients with symptomatic
trigeminal neuralgiaor focal lesions within the pons, it has a diagnostic sensitivity similar to that of the R1 blink reflex (Cruccu and Deuschl 2000; Cruccu et al. 2005).
The second inhibitory period is far less sensitive than the first to lesions along the reflex arc. Being me- diated by a multisynaptic chain of interneurons of the lateral reticular formation however, it is mod- ulated by suprasegmental influences. Like the R2 blink reflex, the second inhibitory period shows a strongly enhanced recovery cycle in patients with ex- trapyramidal disorders and an increased habituation in hemiplegia (Cruccu and Deuschl 2000). The sec- ond inhibitory period (recorded from the temporalis muscle and called ES2) is a focus of research in sev- eral centers for patients with headache. Although the findings are still controversial, some data suggest that this response might help in differentiating tension-type headache from vasomotor headaches (Schoenen et al.
1987).
Unlike the electrically elicited masseter inhibitory reflex (Cruccu et al. 1997), the laser silent period, a purely no- ciceptive reflex, has been demonstrated to undergo mod- ulation by experimental pain and found to be absent in
patients with temporo-mandibular pain(Romaniello et al. 2002, 2003).
References
1. Cruccu G, Deuschl G (2000) The clinical use of brainstem re- flexes and hand-muscle reflexes. Clin Neurophysiol 111:371–387 2. Cruccu G, Frisardi G, Pauletti G et al. (1997) Excitability of the central masticatory pathways in patients with painful temporo- mandibular disorders. Pain 73:447–454
3. Cruccu G, Iannetti GD, Marx JJ et al. (2005) Brainstem reflex circuits revisited. Brain 128:386–394
4. Ellrich J, Hopf HC, Treede RD (1997) Nociceptive masseter in- hibitory reflexes evoked by laser radiant heat and electrical stim- uli. Brain Res 764:214–220
5. Godaux E, Desmedt JE (1975) Exteroceptive suppression and motor control of the masseter and temporalis muscles in normal man. Brain Res 85: 447–458
6. Miles TS, Turker KS (1987) Reflex responses of motor units in human masseter muscle to electrical stimulation of the lip. Exp Brain Res 65: 331–336
7. Ongerboer de Visser BW, Cruccu G, Manfredi M et al. (1990) Effects of brainstem lesions on the masseter inhibitory reflex.
Functional mechanisms of reflex pathways. Brain 113:781–792 8. Romaniello A, Arendt-Nielsen L, Cruccu G et al. (2002) Modula- tion of trigeminal laser evoked potentials and laser silent periods by homotopical experimental pain. Pain 98:217–228 9. Romaniello A, Cruccu G, Frisardi G et al. (2003) Assessment of
nociceptive trigeminal pathways by laser-evoked potentials and laser silent periods in patients with painful temporomandibular disorders. Pain 103:31–39
10. Schoenen J, Jamart B, Gerard P et al. (1987) Exteroceptive sup- pression of temporalis muscle activity in chronic headache. Neu- rology 37:1834–1836
Job Analysis
Definition
Job analysis includes description of work tasks; meth- ods, techniques or processes involved and the work devices used, results; worker (skills, knowledge, adap- tations needed). Job analysis may expose environmental and organizational factors needed to accomplish the work tasks. The Revised Handbook of Analyzing Jobs (RHAJ) explores the procedures and techniques used to analyze jobs and to record the analyses. Such analy- ses underlie, and are congruent with, the occupational definitions of the Dictionary of Occupational Titles (DOT. A job analysis according to R/HAJ) addresses the worker’s relationship to data, people, and things (i.e. Worker Functions), the methodologies and tech- niques employed (i.e. Work Fields), the machines, tools, equipment, and work aids used (MTEWA), the mate- rial, procedures, subject matter, or services (MPSMS), and what worker attributes contribute to successful job performance (Worker Characteristics).
Vocational Counselling
Job Capacity Evaluation
Disability, Functional Capacity Evaluations
1034 Job Demands
Job Demands
Definition
Job demands are the mental and physical requirements necessary to fulfill requirements associated with specific jobs.
Pain in the Workplace, Risk Factors for Chronicity, Workplace Factors
Job Requirements
Definition
Job requirements are the demands an occupation or job tasks place on a worker for expected quality and quan- tity standard. The Dictionary of Occupational Titles (DOT) defines more than 20 000 occupations in the Labor Market in standards of Worker Functions; Work Fields, MPSMS, and Worker Characteristics.
Vocational Counselling
Job Satisfaction
Definition
A measure of how happy or pleased someone is with dif- ferent aspects of the work environment or the occupation as a whole.
Pain in the Workplace, Risk factors for Chronicity, Job Demands
Job Site Evaluation
Situational Assessment
Joint Deformities
Definition
Joint deformities are changes from the typical size or shape of a particular joint.
Chronic Pain in Children, Physical Medicine and Re- habilitation
Joint Nociceptors
Articular Nociceptors
JRA
Juvenile Rheumatoid Arthritis
Junctional DREZ Coagulation
DREZ Procedures
Just-Noticeable-Difference
Definition
On a stimulus continuum a, what is the smallest incre- ment? (a) such that a+?(a) just noticeably exceeds a?
This minimum increment of stimulus intensity is usu- ally called the ’just-noticeable-difference’ (JND or ’dif- ference threshold’ or ’difference limen’).
Pain Evaluation, Psychophysical Methods
Juvenile Rheumatoid Arthritis
Synonyms JRA
Definition
Is a condition characterized by joint inflammation and stiffness for more than 6 weeks in children 16 years or younger. The inflammation causes redness, swelling, warmth, and soreness in the joints. Any joint can be affected and inflammation may limit the mobility of affected joints. JRA is a disease of the immune system.
In JRA, the immune system attacks the body’s own healthy cells, which causes inflammation in the lining and connective tissues of the joints.
Experimental Pain in Children
Juxtaglomerular Apparatus
Definition
The functional entity in the kidney that consists of jux- taglomerular cells (epithelioid cells in the media of the afferent arterioles) and the macula densa (tubular epithe- lium at the region of afferent arteriole and efferent arte- riole to the glomerulus), and is involved in the regulation of salt and water excretion and renal blood flow.
NSAIDs, Adverse Effects
