1. This is a report of experiments carried out on the cat and on man, which demonstrate that cond... more 1. This is a report of experiments carried out on the cat and on man, which demonstrate that conditioning of a muscle by contraction and movement can lead to changes in amplitude of stretch reflexes elicited in that muscle. 2. In triceps surae of the cat, the reflex response to a brief stretch was recorded after conditioning with a whole-muscle contraction followed by a pause at a length either 5 mm longer or shorter than the length at which the reflex was elicited. Following conditioning at the long length the reflex response was less than half as large as that following conditioning at the short length. 3. The changes in reflex amplitude could be correlated with an altered stretch responsiveness of muscle spindles in the soleus muscle. When the muscle had been held long during conditioning, a subsequent brief stretch applied at an intermediate length elicited fewer impulses in primary endings of spindles than after conditioning at a short length. 4. The same kind of experiment was...
... From estimates of reflex size with and without fusimotor stim-ulation we conclude that the si... more ... From estimates of reflex size with and without fusimotor stim-ulation we conclude that the size of the tendon jerk is dominated by muscle ... A computer program, Igor, by WaveMetrics (Lake Oswego, Ore., USA), run on an Apple Macintosh SE/30 computer was used to analyse the ...
Nine participants performed two bouts of a step exercise, during which the quadriceps muscle of o... more Nine participants performed two bouts of a step exercise, during which the quadriceps muscle of one leg acted eccentrically. Before and after the exercise, isokinetic torque was measured over a range of knee angles to determine the optimum angle for torque. Immediately after the first bout of exercise, the quadriceps showed a significant (P 5 0.05) shift of 15.6+1.48 (mean+s x) of its optimum angle in the direction of longer lengths, suggesting the presence of damage. A drop in peak torque, together with delayed soreness and swelling, confirmed that damage to muscle fibres had occurred. After the second bout of exercise, 8 days later, the shift in optimum angle was 10.4+1.08, which was significantly less than after the first bout (P 5 0.05). Other indicators of damage were also reduced. In addition, the muscle exhibited a sustained shift in optimum angle (3.4+0.98), suggesting that some adaptation had taken place after the first bout of exercise. We conclude that muscles like the quadriceps can show evidence of damage after a specific programme of eccentric exercise, followed by an adaptation response. This is despite the fact that the quadriceps routinely undergoes eccentric contractions in everyday activities.
A continuing controversy surrounds the question of whether Golgi tendon organs are examples of re... more A continuing controversy surrounds the question of whether Golgi tendon organs are examples of receptors in which impulses may be generated at more than one site. This paper reports a systematic examination of a number of models incorporating single or multiple impulse generators and of the compatibility of their predictions with experimental observations. Two phenomena, in particular, that must be accounted for are nonlinear summation and cross-adaptation. When two motor units each with a direct effect on the tendon organ are stimulated together, the rate of discharge is greater than either individual rate but is less than their sum. In cross-adaptation a conditioning response elicited by one motor unit contraction produces adaptation of the discharge associated with stimulation of a second motor unit. A model with a central impulse generator can be modified to account for nonlinear summation by postulating a nonlinear transformation in the generator current-to-impulse rate convers...
This is a report of experiments on muscle spindles of the soleus muscle of the anaesthetized cat.... more This is a report of experiments on muscle spindles of the soleus muscle of the anaesthetized cat. Following a step shortening of the muscle, muscle spindles fall silent. At suitable muscle lengths their discharge may restart several seconds later to gradually recover a maintained rate of discharge. These experiments examine the question of where within the spindle the resumption of a resting discharge may originate. It was found that stimulation of some static fusimotor fibres immediately after the shortening led to early recovery of the resting discharge. Stimulation of dynamic and other static gamma motoneurones had much less effect. Since the dynamic gamma axons innervate almost exclusively the bag1 intrafusal fibre, contraction of this fibre appears to have little influence on the mechanisms responsible for restarting the resting discharge. Bag2 and chain fibres do seem to be involved. For primary endings, the bag2 fibre contraction was especially effective since static axons, which did not evoke 'driving' of the afferent response, and which are thought to predominantly innervate bag2 fibres, did restart the resting discharge. For secondary endings, stimulation of nearly all gamma axons led to an early restart of the resting discharge suggesting that here the nuclear chain fibres were responsible.
1. A kangaroo hopping above a certain speed appears to consume less oxygen than a quadrupedal mam... more 1. A kangaroo hopping above a certain speed appears to consume less oxygen than a quadrupedal mammal, of similar weight, running at the same speed (Dawson & Taylor, 1973). This is thought to be achieved by storage of elastic energy in tendons and ligaments. 2. Energy can be stored in a tendon by stretching it, but only if the muscle fibres in series with it are stiff enough to resist most of the length change. We have measured length and tension changes in the contracting gastrocnemius muscle of the wallaby Thylogale during rapid, controlled stretches, and from this determined the amount of movement in muscle fibres and tendon (method of Morgan, 1977). 3. When the muscle was developing close to its maximum isometric tension, up to eight times as much movement occurred in the tendon as in the muscle fibres. This is made possible by the wallaby having a long and compliant tendon. 4. Measurement of work absorption by the muscle with a full length of free tendon and when the tendon had been shortened, showed that with the shortened tendon a larger proportion of movement occurred in the muscle fibres, producing a steep rise in work absorption by the muscle and a consequent increase in energy loss.
The Golgi organ (also called Golgi tendon organ, tendon organ, neurotendinous organ or neurotendi... more The Golgi organ (also called Golgi tendon organ, tendon organ, neurotendinous organ or neurotendinous spindle), is a proprioceptive sensory receptor organ that is located at the insertion of skeletal muscle fibers into the tendons of skeletal muscle. It provides the sensory component of the Golgi tendon reflex.
In the past, the peripheral sense organs responsible for generating human position sense were tho... more In the past, the peripheral sense organs responsible for generating human position sense were thought to be the slowly adapting receptors in joints. More recently, our views have changed and the principal position sensor is now believed to be the muscle spindle. Joint receptors have been relegated to the lesser role of acting as limit detectors when movements approach the anatomical limit of a joint. In a recent experiment concerned with position sense at the elbow joint, measured in a pointing task over a range of forearm angles, we have observed falls in position errors as the forearm was moved closer to the limit of extension. We considered the possibility that as the arm approached full extension, a population of joint receptors became engaged and that they were responsible for the changes in position errors. Muscle vibration selectively engages signals of muscle spindles. Vibration of elbow muscles undergoing stretch has been reported to lead to perception of elbow angles beyon...
1. Afferent responses were recorded from filaments of the trigeminal nerve in each of two platypu... more 1. Afferent responses were recorded from filaments of the trigeminal nerve in each of two platypuses (Ornithorhynchus anatinus) anaesthetized with a-chloralose. All receptive fields were located along the lateral border of the upper bill. Discrete receptive fields could be identified as belonging to two distinct classes of sensory receptor. 2. The most prominent response was an irregular resting discharge which could be increased or decreased by weak electric pulses. These receptors were insensitive to moderately strong mechanical stimulation, and it was concluded that they were electroreceptors. 3. Each electroreceptor had a single spot of maximum sensitivity on the bill surface. When the stimulating electrode over this spot was the cathode it excited the receptor for the duration of the stimulating pulse, using stimulus strengths as low as 20 mV. When it was the anode, it inhibited the discharge. Cathodal excitation was followed by rebound inhibition and anodal inhibition by rebound excitation. 4. Receptors responded to cathodal steps with an initial high-frequency burst of impulses, followed by a lower maintained rate of discharge. Rapidly changing pulses were similarly effective in exciting receptors, adding support to the claim that platypuses are able to detect moving-prey by the electrical activity associated with muscle contraction. 5. The centres of the receptive fields of two electroreceptors were marked by the insertion of fine entomological pins. Histological examination established the presence of a large mucus-secreting gland at the marked spot. The epidermal duct of the gland contained an elaborate myelinated innervation, with morphologically distinct axon terminals that we identify as the electroreceptors. 6. As well as electroreceptors, the skin of the bill contained three kinds of mechanoreceptors: slow-adapting receptors, rapidly adapting, vibration-sensitive receptors and receptors with an intermediate adaptation rate. The slowly adapting receptors were characterized by their low threshold to mechanical stimuli, irregular discharge and significant dynamic sensitivity. Vibration receptors showed maintained responses to sinusoidal vibration of the skin up to 600 Hz. 7. These experiments confirm an earlier report that the platypus bill is an electrodetector organ. The presence of electroreceptors of a unique structure and J. E. GREGORY AND OTHERS supplied by the trigeminal nerve indicates that electroreception has evolved independently in monotremes. This in turn emphasizes that monotremes are a highly evolved group which split off from the main mammalian stem a long time ago.
Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 1998
This is a summary of the current knowledge of sensory receptors in skin of the bill of the platyp... more This is a summary of the current knowledge of sensory receptors in skin of the bill of the platypus,Ornithorhynchus anatinus, and the snout of the echidna,Tachyglossus aculeatus. Brief mention is also made of the third living member of the monotremes, the long–nosed echidna,Zaglossus bruijnii. The monotremes are the only group of mammals known to have evolved electroreception. The structures in the skin responsible for the electric sense have been identified as sensory mucous glands with an expanded epidermal portion that is innervated by large–diameter nerve fibres. Afferent recordings have shown that in both platypuses and echidnas the receptors are excited by cathodal (negative) pulses and inhibited by anodal (positive) pulses. Estimates give a total of 40 000 mucous sensory glands in the upper and lower bill of the platypus, whereas there are only about 100 in the tip of the echidna snout. Recordings of electroreceptor–evoked activity from the brain of the platypus have shown th...
Innervation ratios were estimated for motor units supplying superficial lumbrical muscles of the ... more Innervation ratios were estimated for motor units supplying superficial lumbrical muscles of the cat after assigning units to one of three types, FF/FI, FR, and S, and estimating their axonal conduction velocity, based on published data. Similarly, unit tensions were converted to muscle fiber number using published values for specific tension and fiber cross-sectional area. A relation was established between axonal area of cross-section and number of fibers innervated which was matched reasonably well by a model of a branching motoneuron with preterminal diameter of 4.28 microm and a daughter-to-parent ratio of 1.48 at each level of branching. It is proposed that the main features of the model are likely to apply to all motoneurons.
Muscles subjected to eccentric exercise, in which the contracting muscle is forcibly lengthened, ... more Muscles subjected to eccentric exercise, in which the contracting muscle is forcibly lengthened, become sore the next day (delayed onset muscle soreness). In subjects who had their triceps surae of 1 leg exercised eccentrically by walking backwards on an inclined moving treadmill, mapping the muscle 48 hours later with a calibrated probe showed sensitive areas were localized but not restricted to the muscle-tendon junction. Injection of 5% sodium chloride into a sensitive site in the exercised leg did not produce more pain than injections into the unexercised leg, suggesting that nociceptor sensitization was not responsible. Applying controlled indentations to a sensitive area showed that the pain could be exacerbated by 20-Hz or 80-Hz vibration. In an unexercised muscle, vibration had the opposite effect; it reduced pain. Pain thresholds were measured before, during, and after a pressure block of the sciatic nerve. The block affected only large-diameter nerve fibers, as evidenced by disappearance of the H reflex and a weakened voluntary contraction, leaving painful heat and cold sensations unaltered. Pain thresholds increased significantly during the block. It is concluded that muscle mechanoreceptors, including muscle spindles, contribute to the soreness after eccentric exercise.
The properties of some receptors with afferent fibres in the cat's posterior knee joint nerve hav... more The properties of some receptors with afferent fibres in the cat's posterior knee joint nerve have been examined, especially those discharging tonically with the joint in intermediate positions between full flexion and extension. Some of these receptors behave like muscle spindles, and respond to manoeuvres which stretch popliteus muscle. Both in single unit and whole nerve recordings their discharge pauses during a popliteus twitch, and can be strikingly augmented by tetanic stimulation of a number of popliteus fusimotor fibres isolated from ventral root filaments. The action of succinylcholine on these receptors closely resembles its effect on popliteus spindle units with fibres sited normally in the popliteus nerve. Other units with properties suggesting origin from popliteus tendon organs were also observed; their fibres and those of the spindle units conducted at Group I velocity. It is concluded that some afferent fibres from popliteus spindles and possibly tendon organs commonly pursue an aberrant course in the posterior articular nerve of the knee joint.
Short news items are encouraged and can usually be included as late copy if space permits. Sugges... more Short news items are encouraged and can usually be included as late copy if space permits. Suggestions for articles Suggestions for future articles are welcome. Please contact either the Editorial Administrator or a member of the Editorial Group of Physiology News (see contents page for details).
Action points Grants The Society offers funding through the following grant schemes: Travel Grant... more Action points Grants The Society offers funding through the following grant schemes: Travel Grants, Non-Society Symposia Grants, Outreach Grants, International Teaching and Research Grants and the Vacation Studentship and Departmental Seminar Schemes. For full information, please visit: www.physoc.org/grants Membership applications Applications for membership of The Physiological Society are considered on a rolling basis, and a decision is normally made within 15 working days. For full information, please visit: www.physoc.org/membership Is your membership information correct? Please check and update your details at www.physoc.org, under 'My Physoc Profile'.
American Journal of Physiology-Legacy Content, 1976
The semitendinous muscle of the lizard Tilique contains both slow and twitch fibers; by subdivisi... more The semitendinous muscle of the lizard Tilique contains both slow and twitch fibers; by subdivision of its motor nerve, fibers of each type may be stimulated separately. When, during repetitive stimulation of nerve filaments, the muscle was lengthened or shortened, the tension changes included an initial short-range stiffness, followed by a later compliance. With increasing velocities of movement, the short-range stiffness increased toward a limiting value. For slow fibers this limiting value was reached with lower velocities of movement than for the twitch fibers. Provided that the same velocity of movement was used and the movements began from similar initial isometric tensions, the slow fibers resisted the movements with a greater stiffness than the twitch fibers. It is suggested that not all of the observed differences between the two fiber types can be interpreted simply in terms of differences in rates of formation and breakdown of cross-links.
Functional electrical stimulation (FES) is used to provide paralyzed human subjects with postural... more Functional electrical stimulation (FES) is used to provide paralyzed human subjects with postural support and a limited range of movements. Problems encountered with FES include jerky movements from tension oscillations during stimulation and rapid muscle fatigue. In this paper, we report experiments on anesthetized cats that test a new, computer-controlled method of stimulation of the muscle nerve supply, distributed across several inputs, which reduces these problems. After 5 min of continuous, distributed stimulation of the medial gastrocnemius muscle at 6 pulses per second (pps) across 6 channels, tension fell to 55.9 ± 3.9% (SE) of its original value. In comparison, after 5 min of synchronous stimulation of one muscle portion at 36 pps, tension fell to 11 ± 3.7%. At higher stimulation rates, 10 pps per channel (distributed) and 60 pps (synchronous), the differences in fatigue were even greater. Similar results were obtained when an intermittent, rather than a continuous, stimul...
1. This is a report of experiments carried out on the cat and on man, which demonstrate that cond... more 1. This is a report of experiments carried out on the cat and on man, which demonstrate that conditioning of a muscle by contraction and movement can lead to changes in amplitude of stretch reflexes elicited in that muscle. 2. In triceps surae of the cat, the reflex response to a brief stretch was recorded after conditioning with a whole-muscle contraction followed by a pause at a length either 5 mm longer or shorter than the length at which the reflex was elicited. Following conditioning at the long length the reflex response was less than half as large as that following conditioning at the short length. 3. The changes in reflex amplitude could be correlated with an altered stretch responsiveness of muscle spindles in the soleus muscle. When the muscle had been held long during conditioning, a subsequent brief stretch applied at an intermediate length elicited fewer impulses in primary endings of spindles than after conditioning at a short length. 4. The same kind of experiment was...
... From estimates of reflex size with and without fusimotor stim-ulation we conclude that the si... more ... From estimates of reflex size with and without fusimotor stim-ulation we conclude that the size of the tendon jerk is dominated by muscle ... A computer program, Igor, by WaveMetrics (Lake Oswego, Ore., USA), run on an Apple Macintosh SE/30 computer was used to analyse the ...
Nine participants performed two bouts of a step exercise, during which the quadriceps muscle of o... more Nine participants performed two bouts of a step exercise, during which the quadriceps muscle of one leg acted eccentrically. Before and after the exercise, isokinetic torque was measured over a range of knee angles to determine the optimum angle for torque. Immediately after the first bout of exercise, the quadriceps showed a significant (P 5 0.05) shift of 15.6+1.48 (mean+s x) of its optimum angle in the direction of longer lengths, suggesting the presence of damage. A drop in peak torque, together with delayed soreness and swelling, confirmed that damage to muscle fibres had occurred. After the second bout of exercise, 8 days later, the shift in optimum angle was 10.4+1.08, which was significantly less than after the first bout (P 5 0.05). Other indicators of damage were also reduced. In addition, the muscle exhibited a sustained shift in optimum angle (3.4+0.98), suggesting that some adaptation had taken place after the first bout of exercise. We conclude that muscles like the quadriceps can show evidence of damage after a specific programme of eccentric exercise, followed by an adaptation response. This is despite the fact that the quadriceps routinely undergoes eccentric contractions in everyday activities.
A continuing controversy surrounds the question of whether Golgi tendon organs are examples of re... more A continuing controversy surrounds the question of whether Golgi tendon organs are examples of receptors in which impulses may be generated at more than one site. This paper reports a systematic examination of a number of models incorporating single or multiple impulse generators and of the compatibility of their predictions with experimental observations. Two phenomena, in particular, that must be accounted for are nonlinear summation and cross-adaptation. When two motor units each with a direct effect on the tendon organ are stimulated together, the rate of discharge is greater than either individual rate but is less than their sum. In cross-adaptation a conditioning response elicited by one motor unit contraction produces adaptation of the discharge associated with stimulation of a second motor unit. A model with a central impulse generator can be modified to account for nonlinear summation by postulating a nonlinear transformation in the generator current-to-impulse rate convers...
This is a report of experiments on muscle spindles of the soleus muscle of the anaesthetized cat.... more This is a report of experiments on muscle spindles of the soleus muscle of the anaesthetized cat. Following a step shortening of the muscle, muscle spindles fall silent. At suitable muscle lengths their discharge may restart several seconds later to gradually recover a maintained rate of discharge. These experiments examine the question of where within the spindle the resumption of a resting discharge may originate. It was found that stimulation of some static fusimotor fibres immediately after the shortening led to early recovery of the resting discharge. Stimulation of dynamic and other static gamma motoneurones had much less effect. Since the dynamic gamma axons innervate almost exclusively the bag1 intrafusal fibre, contraction of this fibre appears to have little influence on the mechanisms responsible for restarting the resting discharge. Bag2 and chain fibres do seem to be involved. For primary endings, the bag2 fibre contraction was especially effective since static axons, which did not evoke 'driving' of the afferent response, and which are thought to predominantly innervate bag2 fibres, did restart the resting discharge. For secondary endings, stimulation of nearly all gamma axons led to an early restart of the resting discharge suggesting that here the nuclear chain fibres were responsible.
1. A kangaroo hopping above a certain speed appears to consume less oxygen than a quadrupedal mam... more 1. A kangaroo hopping above a certain speed appears to consume less oxygen than a quadrupedal mammal, of similar weight, running at the same speed (Dawson & Taylor, 1973). This is thought to be achieved by storage of elastic energy in tendons and ligaments. 2. Energy can be stored in a tendon by stretching it, but only if the muscle fibres in series with it are stiff enough to resist most of the length change. We have measured length and tension changes in the contracting gastrocnemius muscle of the wallaby Thylogale during rapid, controlled stretches, and from this determined the amount of movement in muscle fibres and tendon (method of Morgan, 1977). 3. When the muscle was developing close to its maximum isometric tension, up to eight times as much movement occurred in the tendon as in the muscle fibres. This is made possible by the wallaby having a long and compliant tendon. 4. Measurement of work absorption by the muscle with a full length of free tendon and when the tendon had been shortened, showed that with the shortened tendon a larger proportion of movement occurred in the muscle fibres, producing a steep rise in work absorption by the muscle and a consequent increase in energy loss.
The Golgi organ (also called Golgi tendon organ, tendon organ, neurotendinous organ or neurotendi... more The Golgi organ (also called Golgi tendon organ, tendon organ, neurotendinous organ or neurotendinous spindle), is a proprioceptive sensory receptor organ that is located at the insertion of skeletal muscle fibers into the tendons of skeletal muscle. It provides the sensory component of the Golgi tendon reflex.
In the past, the peripheral sense organs responsible for generating human position sense were tho... more In the past, the peripheral sense organs responsible for generating human position sense were thought to be the slowly adapting receptors in joints. More recently, our views have changed and the principal position sensor is now believed to be the muscle spindle. Joint receptors have been relegated to the lesser role of acting as limit detectors when movements approach the anatomical limit of a joint. In a recent experiment concerned with position sense at the elbow joint, measured in a pointing task over a range of forearm angles, we have observed falls in position errors as the forearm was moved closer to the limit of extension. We considered the possibility that as the arm approached full extension, a population of joint receptors became engaged and that they were responsible for the changes in position errors. Muscle vibration selectively engages signals of muscle spindles. Vibration of elbow muscles undergoing stretch has been reported to lead to perception of elbow angles beyon...
1. Afferent responses were recorded from filaments of the trigeminal nerve in each of two platypu... more 1. Afferent responses were recorded from filaments of the trigeminal nerve in each of two platypuses (Ornithorhynchus anatinus) anaesthetized with a-chloralose. All receptive fields were located along the lateral border of the upper bill. Discrete receptive fields could be identified as belonging to two distinct classes of sensory receptor. 2. The most prominent response was an irregular resting discharge which could be increased or decreased by weak electric pulses. These receptors were insensitive to moderately strong mechanical stimulation, and it was concluded that they were electroreceptors. 3. Each electroreceptor had a single spot of maximum sensitivity on the bill surface. When the stimulating electrode over this spot was the cathode it excited the receptor for the duration of the stimulating pulse, using stimulus strengths as low as 20 mV. When it was the anode, it inhibited the discharge. Cathodal excitation was followed by rebound inhibition and anodal inhibition by rebound excitation. 4. Receptors responded to cathodal steps with an initial high-frequency burst of impulses, followed by a lower maintained rate of discharge. Rapidly changing pulses were similarly effective in exciting receptors, adding support to the claim that platypuses are able to detect moving-prey by the electrical activity associated with muscle contraction. 5. The centres of the receptive fields of two electroreceptors were marked by the insertion of fine entomological pins. Histological examination established the presence of a large mucus-secreting gland at the marked spot. The epidermal duct of the gland contained an elaborate myelinated innervation, with morphologically distinct axon terminals that we identify as the electroreceptors. 6. As well as electroreceptors, the skin of the bill contained three kinds of mechanoreceptors: slow-adapting receptors, rapidly adapting, vibration-sensitive receptors and receptors with an intermediate adaptation rate. The slowly adapting receptors were characterized by their low threshold to mechanical stimuli, irregular discharge and significant dynamic sensitivity. Vibration receptors showed maintained responses to sinusoidal vibration of the skin up to 600 Hz. 7. These experiments confirm an earlier report that the platypus bill is an electrodetector organ. The presence of electroreceptors of a unique structure and J. E. GREGORY AND OTHERS supplied by the trigeminal nerve indicates that electroreception has evolved independently in monotremes. This in turn emphasizes that monotremes are a highly evolved group which split off from the main mammalian stem a long time ago.
Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 1998
This is a summary of the current knowledge of sensory receptors in skin of the bill of the platyp... more This is a summary of the current knowledge of sensory receptors in skin of the bill of the platypus,Ornithorhynchus anatinus, and the snout of the echidna,Tachyglossus aculeatus. Brief mention is also made of the third living member of the monotremes, the long–nosed echidna,Zaglossus bruijnii. The monotremes are the only group of mammals known to have evolved electroreception. The structures in the skin responsible for the electric sense have been identified as sensory mucous glands with an expanded epidermal portion that is innervated by large–diameter nerve fibres. Afferent recordings have shown that in both platypuses and echidnas the receptors are excited by cathodal (negative) pulses and inhibited by anodal (positive) pulses. Estimates give a total of 40 000 mucous sensory glands in the upper and lower bill of the platypus, whereas there are only about 100 in the tip of the echidna snout. Recordings of electroreceptor–evoked activity from the brain of the platypus have shown th...
Innervation ratios were estimated for motor units supplying superficial lumbrical muscles of the ... more Innervation ratios were estimated for motor units supplying superficial lumbrical muscles of the cat after assigning units to one of three types, FF/FI, FR, and S, and estimating their axonal conduction velocity, based on published data. Similarly, unit tensions were converted to muscle fiber number using published values for specific tension and fiber cross-sectional area. A relation was established between axonal area of cross-section and number of fibers innervated which was matched reasonably well by a model of a branching motoneuron with preterminal diameter of 4.28 microm and a daughter-to-parent ratio of 1.48 at each level of branching. It is proposed that the main features of the model are likely to apply to all motoneurons.
Muscles subjected to eccentric exercise, in which the contracting muscle is forcibly lengthened, ... more Muscles subjected to eccentric exercise, in which the contracting muscle is forcibly lengthened, become sore the next day (delayed onset muscle soreness). In subjects who had their triceps surae of 1 leg exercised eccentrically by walking backwards on an inclined moving treadmill, mapping the muscle 48 hours later with a calibrated probe showed sensitive areas were localized but not restricted to the muscle-tendon junction. Injection of 5% sodium chloride into a sensitive site in the exercised leg did not produce more pain than injections into the unexercised leg, suggesting that nociceptor sensitization was not responsible. Applying controlled indentations to a sensitive area showed that the pain could be exacerbated by 20-Hz or 80-Hz vibration. In an unexercised muscle, vibration had the opposite effect; it reduced pain. Pain thresholds were measured before, during, and after a pressure block of the sciatic nerve. The block affected only large-diameter nerve fibers, as evidenced by disappearance of the H reflex and a weakened voluntary contraction, leaving painful heat and cold sensations unaltered. Pain thresholds increased significantly during the block. It is concluded that muscle mechanoreceptors, including muscle spindles, contribute to the soreness after eccentric exercise.
The properties of some receptors with afferent fibres in the cat's posterior knee joint nerve hav... more The properties of some receptors with afferent fibres in the cat's posterior knee joint nerve have been examined, especially those discharging tonically with the joint in intermediate positions between full flexion and extension. Some of these receptors behave like muscle spindles, and respond to manoeuvres which stretch popliteus muscle. Both in single unit and whole nerve recordings their discharge pauses during a popliteus twitch, and can be strikingly augmented by tetanic stimulation of a number of popliteus fusimotor fibres isolated from ventral root filaments. The action of succinylcholine on these receptors closely resembles its effect on popliteus spindle units with fibres sited normally in the popliteus nerve. Other units with properties suggesting origin from popliteus tendon organs were also observed; their fibres and those of the spindle units conducted at Group I velocity. It is concluded that some afferent fibres from popliteus spindles and possibly tendon organs commonly pursue an aberrant course in the posterior articular nerve of the knee joint.
Short news items are encouraged and can usually be included as late copy if space permits. Sugges... more Short news items are encouraged and can usually be included as late copy if space permits. Suggestions for articles Suggestions for future articles are welcome. Please contact either the Editorial Administrator or a member of the Editorial Group of Physiology News (see contents page for details).
Action points Grants The Society offers funding through the following grant schemes: Travel Grant... more Action points Grants The Society offers funding through the following grant schemes: Travel Grants, Non-Society Symposia Grants, Outreach Grants, International Teaching and Research Grants and the Vacation Studentship and Departmental Seminar Schemes. For full information, please visit: www.physoc.org/grants Membership applications Applications for membership of The Physiological Society are considered on a rolling basis, and a decision is normally made within 15 working days. For full information, please visit: www.physoc.org/membership Is your membership information correct? Please check and update your details at www.physoc.org, under 'My Physoc Profile'.
American Journal of Physiology-Legacy Content, 1976
The semitendinous muscle of the lizard Tilique contains both slow and twitch fibers; by subdivisi... more The semitendinous muscle of the lizard Tilique contains both slow and twitch fibers; by subdivision of its motor nerve, fibers of each type may be stimulated separately. When, during repetitive stimulation of nerve filaments, the muscle was lengthened or shortened, the tension changes included an initial short-range stiffness, followed by a later compliance. With increasing velocities of movement, the short-range stiffness increased toward a limiting value. For slow fibers this limiting value was reached with lower velocities of movement than for the twitch fibers. Provided that the same velocity of movement was used and the movements began from similar initial isometric tensions, the slow fibers resisted the movements with a greater stiffness than the twitch fibers. It is suggested that not all of the observed differences between the two fiber types can be interpreted simply in terms of differences in rates of formation and breakdown of cross-links.
Functional electrical stimulation (FES) is used to provide paralyzed human subjects with postural... more Functional electrical stimulation (FES) is used to provide paralyzed human subjects with postural support and a limited range of movements. Problems encountered with FES include jerky movements from tension oscillations during stimulation and rapid muscle fatigue. In this paper, we report experiments on anesthetized cats that test a new, computer-controlled method of stimulation of the muscle nerve supply, distributed across several inputs, which reduces these problems. After 5 min of continuous, distributed stimulation of the medial gastrocnemius muscle at 6 pulses per second (pps) across 6 channels, tension fell to 55.9 ± 3.9% (SE) of its original value. In comparison, after 5 min of synchronous stimulation of one muscle portion at 36 pps, tension fell to 11 ± 3.7%. At higher stimulation rates, 10 pps per channel (distributed) and 60 pps (synchronous), the differences in fatigue were even greater. Similar results were obtained when an intermittent, rather than a continuous, stimul...
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