Frances J. R. Richmond

Absence of monosynaptic reflex in dorsal neck muscles of the cat

The monosynaptic reflex originating f rom receptors in muscle spindles is usually regarded as part of a fundamental servo mechanism controlling muscle length 6. The monosynaptic reflex does not exist in the oculomotor muscles 3,7-9, and we now provide experimental evidence that a monosynaptic reflex is not present in the dorsal muscles of the neck of the cat despite the fact that monosynaptic connections exist 11. These muscles, which serve to elevate and turn the head, have an exceptionally dense spindle content in man, rat and catl,a, 10. The initial observations were made in 5 cats anaesthetized with chloralose (60 mg/kg, i.v.) in which the central cut end of C2, C3 or C4 dorsal roots were stimulated. Monosynaptic reflexes recorded electrically from nerves to the muscles compiexus, biventer cervicis or splenius should have a latency of approximately 2 msec. Those reflexes recorded had a latency of 16-20 msec. In experiments on a further 11 chloralose-anaesthetized cats extracellular recordings were made with tungsten microelectrodes from motoneurones ofcomplexus, biventer cervicis and splenius. The C2 and C3 dorsal roots were cut and their central ends placed on stimulating electrodes for orthodromic stimulation (Fig. 1). Unit antidromic potentials were elicited by stimulation of the appropriate muscle nerve and were regarded as being from motoneurones if (a) they had a short constant latency (0.3-1.4 msec), and (b) if they were all-or-none. Ninety-six motoneurones were identified in this way. Only one could be orthodromically activated by single or paired stimuli at a latency of 2 msec or less even though the strength of the orthodromic stimulus was sufficient to excite all Gp I and I I fibres. In the lumbosacral cord, 1130 of motoneurones can be fired by orthodromic stimulation at the peak of post-tetanic potentiation 4. To see if a similar procedure could elicit monosynaptic reflexes in the upper cervical cord, 21 units were tested for orthodromic responsiveness following 15 sec of dorsal root stimulation at 300/sec. In no instance did this provoke a monosynaptic discharge. Ortbodromic stimulus was not particularly effective in exciting neck motoneurones and the firing which was observed in 26 of the 96 units tested occurred after a 7-25 msec latency.

Electromyographic studies of neck muscles in the intact cat. II. Reflexes evoked by muscle nerve stimulation.

SummaryShort-latency reflexes were studied in the neck muscles of four alert cats following electrical stimulation of nerves supplying biventer cervicis (BC), splenius (SP) or rectus capitis posterior (RCP). Reflexes were assessed by comparing levels of EMG activity of muscles before and after each stimulus, as the cats lapped milk, licked their paws or walked on a treadmill. When BC or SP nerves were stimulated at 1.5–4 times threshold (T) for their motor axons, no short-latency heteronymous reflexes could be identified in most neck muscles. However, stimulation of RCP nerves produced inhibitory effects as early as 3–4 ms in the ipsilateral BC, CM, and SP muscles and 6 ms in contralateral BC. At stimulus strengths above 4xT, a more complex pattern of inhibitory or excitatory effects was observed in CM, SP and the intervertebral muscle spinalis dorsi. The reflex effects were attenuated or abolished by partial or complete C1 dorsal rhizotomy (2 cats). Cervicocollic reflex data may need to be reevaluated to consider the possible effects of disinhibition rather than excitation in short-latency reflex pathways.

The distribution of Golgi tendon organs and muscle spindles in masseter and temporalis muscles of the cat.

Abstract Golgi tendon organs and muscle spindles were identified in serial sections of the temporalis and masseter muscles of kitten and cats. In the kitten, the position of each receptor was plotted in three-dimensional reconstitutions of the muscles. Seventy-four spindles and twenty tendon organs were identified in the temporalis, all in the region of the insertion into the mandible. Thirty-four spindles and six organs were located at the origin of the masseter muscle. The receptors were in deep portions of both muscles. All tendon organs were found to form complexes with one or more spindles.

First Clinical Experience with BION Implants for Therapeutic Electrical Stimulation

The objective of this study was to assess the usability and safety of BION injectable neuromuscular microstimulators for therapeutic electrical stimulation (TES) to treat two conditions involving disuse atrophy: poststroke shoulder subluxation in hemiplegic subjects and knee osteoarthritis. Clinicians were provided with PC‐based software to track implants and to design the exercise programs. Subjects self‐administered TES (3 sessions/day, 10–30 min/session) for 6 or 12 weeks. Outcome measures included subluxation for the shoulder study and knee function and pain for the osteoarthritis study. All subjects were comfortable with the BION equipment and therapy; eight of 10 experimental subjects elected to continue treatment after the study period. Shoulder subluxation was reduced by 55% ± 54%; knee function was enhanced by 65% ± 24%; and knee pain decreased by 78% ± 18%. The devices did not migrate and did not cause inflammation or pain. Thresholds were stable over time. We conclude that the use of BION implants to exercise atrophic muscles was well‐accepted and provided effective rehabilitation in these two clinical conditions.

Long-term biocompatibility of a miniature stimulator implanted in feline hind limb muscles

Chronic foreign-body responses and muscular changes were examined following the implantation of active miniature stimulators into the hind limb muscles of cats for periods of up to three months. The radio-frequency (RF)-powered stimulators were injected into muscles through a 12-gauge hypodermic needle. The tissue responses around the active stimulators were compared histologically to those provoked by passive devices, broken glass, silicone tubing, polyester suture material coated with polybutylate, and two of the internal components of the stimulator (ferrite, integrated circuit chip). Active and passive stimulators produced similar, benign foreign-body reactions that resulted in an essentially identical fibrous capsule over time. The responses were similar to those produced by the internal components and the suture material, and were more modest than those produced by the broken glass. The capsule did not appear to interfere with the functionality of active devices because thresholds measured during the post-implantation survival period did not change significantly over time. Unexpectedly, the severity of the reaction differed significantly amongst the various target muscles. Medial gastrocnemius exhibited the most severe response, whereas tibialis anterior had the least reaction.

Facial input to neck motoneurons: trigemino-cervical reflexes in the conscious and anaesthetised cat

Cutaneous facial inputs influencing head movement were examined in the conscious and anaesthetised cat. EMG recordings were made in neck muscles of conscious, unrestrained cats in which an unexpected light cutaneous stimulus was applied to the glabrous skin of the planum nasale (PN). These observations established that head aversion movements were associated with synchronised activation of both deep and superficial dorsal neck muscles. In anaesthetised cats in which activity in the motoneurons of the large dorsal neck muscles was examined, mechanical stimulation of the PN or electrical stimulation of the infraorbital nerve (ION) produced a short latency, reflex activation. The reflex could be elicited by excitation of low threshold, rapidly conducting fibres in the ION. Intracellular recording from neck motoneurons showed that there is a short latency, probably disynaptic, excitatory pathway from low threshold nerves in the ION to neck motoneurons, but discharge of neck motoneurons occurred several milliseconds later, presumably as a result of activity in a longer multisynaptic pathway.

Percutaneous fiber-optic sensor for chronic glucose monitoring in vivo

We are developing a family of fiber-optic sensors called Sencils (sensory cilia), which are disposable, minimally invasive, and can provide in vivo monitoring of various analytes for several weeks. The key element is a percutaneous optical fiber that permits reliable spectroscopic measurement of chemical reactions in a nano-engineered polymeric matrix attached to the implanted end of the fiber. This paper describes its first application to measure interstitial glucose based on changes in fluorescence resonance energy transfer (FRET) between fluorophores bound to betacyclodextrin and Concanavalin A (Con A) in a polyethylene glycol (PEG) matrix. In vitro experiments demonstrate a rapid and precise relationship between the ratio of the two fluorescent emissions and concentration of glucose in saline for the physiological range of concentrations (0-500mg/dl) over seven weeks. Chronic animal implantation studies have demonstrated good biocompatibility and durability for clinical applications.

Marked non-uniformity of fiber-type composition in the primate suboccipital muscle obliquus capitis inferior

Abstract Obliquus capitis inferior (OCI) is a monoarticular suboccipital muscle linking the transverse process of the atlas (C1) to the spinous process of the axis (C2). Histochemical analysis of fiber-type composition showed that the muscle has a marked gradient of fiber-type distribution in which type I fibers comprise 95–100% of fibers in the deepest region but less than 10% of fibers in the superficial layer. Step-like changes in fiber-type proportions occurred between groups of fascicles. In most instances the boundaries between these fascicles did not exhibit different perimysial features from those fascicles with similar fiber-type proportions. OCI contained large numbers of muscle spindles, which were concentrated in deep regions rich in type I fibers. The degree of nonuniformity in fiber-type distribution seen in OCI is unusually large when compared with patterns described in other primate muscles, and has implications for the way that the muscle is studied anatomically and physiologically.

Feline caudofemoralis muscle Muscle fibre properties, architecture, and motor innervation

Abstract Feline caudofemoralis (CF) is a promising preparation in which to study the properties of mammalian fast-twitch skeletal muscle, but little is known about its muscle fiber properties, architecture, and motor innervation. We used histochemical techniques to confirm that it contained predominantly type IIB fibers (95±2%, n=8, with six of eight muscles composed exclusively of type IIA and IIB fibers), but physiological experiments showed less fatiguability than for the type IIB component of medial gastrocnemius. This may be related to the surprisingly strong and regular recruitment of CF during repetitive tasks such as walking and trotting, which we demonstrated electromyographically. We measured muscle length over the anatomical range of motion for CF (∼0.6–1.2 L0) and estimated working length during walking and trotting (∼0.95–1.15 L0). The specific tension was similar to that of the exclusively slow-twitch soleus muscle (31.2±4.7 N/cm2 compared with 31.8±4.1 N/cm2; P>0.8). Single fiber dissections of CF revealed a series-fibered architecture with a mean of 2.3 fibers, each 2.5 cm long, required to span the fascicle length. We identified two neuromuscular compartments in CF by cutting one of the two nerve branches innervating CF and depleting the glycogen stores in the intact motor units. These compartments were in parallel and extended the length of the muscle; their electromyographic activity was similar during various natural behaviors. CF and gluteus maximus motoneurons were labeled concurrently with a combination of fluorescent, retrograde tracers including Fluororuby, Fluorogold and Fast Blue. The CF motor nucleus was located in L7-S1, overlapping and intermingling extensively with the nucleus of the adjacent gluteus maximus muscle. Distributions of CF motoneuron diameter revealed one large peak around 50–55 µm, with relatively few small-diameter (less than 35 µm) cells. Using estimates of the total number of fibers in three muscles and the estimated number of α-motoneurons for those same muscles, we calculated a mean innervation ratio of ∼270, which is at the low end of the innervation ratios for type IIB motor units from other feline muscles and more similar to type IIA motor units. In general, CF appears to be a useful preparation in which to study the properties of fast-twitch muscle, but these properties may vary somewhat from type IIB fibers from different muscles.

What Are the Proprioceptors of the Neck

Publisher Summary The receptors that play an important role in neck reflexes and other postural processes have never been identified. Certain attractive candidates are the large numbers of muscle spindles first described by Voss and Cooper and Daniel in dorsal neck muscles of man and the cat. Neck muscle spindles resemble those described in the hindlimb, with the exception that many neck muscle spindles have a reduced intrafusal fibre complement of only a single nuclear bag fibre and a few nuclear chain fibers. In most neck muscles, the majority of spindles do not occur as single receptors but are arranged in complexes of up to 10 spindles in tandem, paired and parallel linkages. Most muscle spindle endings from large dorsal neck muscles had physiological properties similar to primary or secondary endings of hindlimb muscle spindles. About 20% of neck spindle endings had a mixture of response properties so that they could not be defined as primary or secondary endings by physiological criteria. Afferents from neck muscles conducted at relatively low velocities ranging from a low of 13 m/sec to a high of 90 m/sec. These conducting velocities are consistent with anatomical observations that neck muscle afferent fibers from neck muscles seldom exceed a diameter of 16 μm.