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Biomedical subjects

G Lennerstrand

Publications and source records attributed to G Lennerstrand.

At least 91 records · Page 5Linked to original sources
PubMed1978

Binocular interaction studied with visual evoked responses (VER) in humans with normal or impaired binocular vision.

In an attempt to evaluate binocular functions in an objective manner, visual evoked responses (VER) were recorded in sixteen subjects, six with normal binocular functions and ten with various degrees of squint and binocular impairment. The two eyes were stimulated monocularly or dioptically with a polaroid checker board pattern viewed through rotating polaroid discs. The rate of pattern reversal was 7 per sec for one eye and 10 per sec for the other, allowing stimulus locked responses to be recorded from each eye individually, even during dioptic viewing. In normal subjects the VER of each eye to binocular stimulation were reduced to half or less of the monocular value. The reduction was much smaller in humans with impaired binocular vision, at least for the dominant eye. In stereoblind subjects the response of the dominant eye was the same for monocular and binocular stimulation. The VER changes might reflect binocular interaction in visual cortex neurons, which probably are binocular in normal subjects but driven only from one eye in stereoblind subjects.

Adolescent↗
PubMed1978

Some observations on visual evoked responses (VER) to dichoptic stimulation.

The possibility that the interocular depression of VER seen with dioptic stimulation, might reflect alternate suppression or binocular rivalry, unnoticed by the test subjects, was investigated in VER experiments using dichoptic stimulation with patterns of dissimilar form. Red and blue grating and checker board patterns were produced on a colour TV screen. Appropriate filtering allowed the two eyes to be stimulated separately. Provided the patterns were dissimilar enough to produce binocular rivalry, no interocular depression was noticed in the VER. The interocular depression became larger as the patterns were made similar in size and reached a maximum for patterns identical in shape. Thus the interocular depression of the VERs reported for dioptic stimulation did not seeem to be related to binocular rivalry. The results also give electrophysiological support to the notion of spartial frequency and orientation selective channels in the human visual system.

Adult↗
PubMed1978

Mechanical properties of succinylcholine activated muscle fibers in the inferior oblique muscle of the cat.

To determine the mechanical properties of the multi-innervated fibres in inferior oblique muscle of the cat, these fibers were selectively activated by means of an intravenous injection of succinylcholine chloride (Sch). For small sinusoidal length changes (+/- 1 mm) of low frequency, tension in the Sch activated muscle exhibited a component that was sensitive to the direction of stretch but was independent of the velocity. At higher frequencies of length change (16 Hz) a form of negative friction was observed. Negative friction had not been previously noted in mammalian muscles, although a similar friction was observed both in the muscles of insects and amphibians. These properties were expressed in the form of a simple mechanical model.

Animals↗
PubMed1977

Morphology of motor units in cat extraocular nodule.

Muscle fibers from single motor units in cat inferior oblique were marked iontophoretically with procion red injected through an intracellular pipette. The fibers were isolated by dissection and characterized by electron microscopy. A fiber in a slow motor unit with non-conducted electrical responses showed slow fiber morphology of the amphibia-type. Fast, twitch motor units contained fibers with twitch fiber morphology. Thus, a good correlation between muscle fiber structure and function was obtained in these eye motor units, examined with both physiological and morphological techniques.

Animals↗
PubMed1977

Contractile and histochemical properties of the inferior oblique muscle in the rat and in the cat.

Mechanical and histochemical properties of inferior oblique muscles(IO) were compared in adult albino rat and pigmented cat. The twitch contraction times and the fusion frequencies were about the same in both species indicating similar contractile properties of the fast contracting fibers. Rat IO seemed to contain fewer slowly contracting fibers than cat IO; half-decay time of the twitch was shorter in rat than in cat muscles and fusion started at higher stimulus frequencies. Fatique resistance was lower in rat than in rat than in cat. Post-tetanic potentiation occurred in the cat but not in the rat IO. Almost all fibers of rat IO were rich in myofibrillar ATPase. In cat IO most fibers showed high myofibrillar ATPase activity, but some fibers in the global layer had moderate to small amounts of this enzyme. This correlates well with the physiological differencies between cat and rat IO.

Adenosine Triphosphatases↗
PubMed1977

Extraocular muscle fibers: ultrastructural identification of iontophoretically labeled fibers contracting in response to succinylcholine.

Cat extraocular muscle fibers (from the superior rectus or inferior oblique) were penetrated in vivo with Procion red-filled glass microelectrodes. When stable penetrations were obtained, succinylcholine (Sch), 8 to 20 microng, was injected into the femoral vein. In some fibers, a depolarization-repolarization response was obtained with the same time course (2 min.) as the total muscle contraction. The depolarizing fibers were labeled iontophoretically. The ultrastructural characteristics of five depolarizing fibers and three control (nondepolarizing) fibers were then studied. The fibers that did not depolarize to Sch had the characteristics of singly innervated cells, whereas those sensitive to Sch had morphological characteristics of multi-innervated fibers.

Animals↗
PubMed1976

Motor unit responses in the lateral rectus muscle of the cat: intracellular current injection of abducens nucleus neurons.

Single motor units of the cat's lateral rectus muscle were activated with short intracellular current pulses delivered through an intracellular micropipette penetrating a single motoneuron, and the mechanical responses in the muscle were recorded. Lateral rectus unit responses fell within the same range as those obtained earlier with extracellular stimulation of inferior oblique units, confirming that in the latter case single and not multiple motor units had been studied. It was also found that both fast and slow contracting muscle units were connected to fast conducting, large size motoneurons. The organization of motor unit recruitment in eye movements would thus seem different from the recruitment pattern in limb muscles. Intracellular stimulation of abducens nucleus "interneurons" did not initiate contractions at the ipsilateral lateral rectus muscle. These "interneuron", therefore did not appear to have excitatory inputs to the abducens motoneurons, but may be involved in relaying information to the other extraocular muscle nuclei or to other brain centers.

Abducens Nerve↗
PubMed1975

Absence of polyneuronal innervation in cat extraocular muscles.

1. Polyneuronal innervation is known to occur in several types of vertebrate muscle, including mammalian muscle spindle (Gray, 1957). Previous work had led to the suggestion that the multiply innervated cat extraocular muscles were similarly polyneuronally innervated. 2. The presence of polyneuronal innervation in fibres that show propagated conduction was explored in the two muscles innervated by the abducens nerve: the lateral rectus (which contains multiply innervated fibres) and the retractor bulbus (which does not). 3. Under conditions of twitch and tetanic stimulation, the sum of individual tensions from the two nerve branches was compared with the tension elicited from the whole nerve. An analysis of variance indicated that the lateral rectus and the retractor bulbus did not differ significantly in terms of tension excess. The twitch condition yielded a small but statistically significant (P smaller than 0-01) amount of tension excess, whereas the tetanic condition did not. 4. Twitches elicited by stimulation of one branch of the abducens nerve showed slight potentiation when preceded by a tetanic stimulation to the other nerve branch. This effect could be ready differentiated from the post-tetanic potentiation elicited by applying both twitch and tetanic stimuli to the whole nerve. 5. Muscle fatigue produced by intensive stimulation of one nerve branch did not decrease the amplitude of the tetanic contraction elicited by stimulation of the other branch. In fact, instead of crossed fatigue, a small but significant (P smaller than 0-05) potentiation was observed. 6. Analysis of the results of the three tests led to the conclusion that polyneuronal innervation could not be demonstrated in cat extraocular muslce fibers that showed propagated conduction. Thus, the end-to-end muscle fibre junctions (Floyd, 1970) apparently do not transmit conducted impulses.

Abducens Nerve↗
PubMed1974

Mechanical studies on the retractor bulbi muscle and its motor units in the cat.

1. For a description of some of the mechanical properties of the retractor bulbi muscle in the cat, the isometric tension development was studied in one of the four slips of the muscle and in single retractor bulbi motor units.2. The motor units and the muscle were activated by stimulating their motoneurones of origin in the abducens nucleus.3. All twenty-eight motor units studied were of the same fast, twitch type, which fatigued quickly. Similarities between the motor units and the muscle with regard to isometric tension development strongly suggest that the retractor bulbi is composed exclusively of this type of motor unit.4. On an average the motor unit had a twitch rise time of 9.2 msec and a half-decay time of 11.4 msec. The twitch tension was 36.7 mg. At stimulation with 175 pulses/sec or above the tetanus fused. The maximal tetanic tension developed was 440 mg and the maximal rate of tension rise was 24.5 g/sec. To prolonged tetanic stimulation most of the units fatigued completely within 10-15 sec.5. In a slip of the muslce similar values were obtained for contraction time, half-decay time, fusion frequency and fatigability. Tetanic tension reached 11.7 g and the maximal speed of tetanic contraction was 255 g/sec.6. As in other extrinsic eye muscles a linear relation was found between length and tension in the activated retractor bulbi. An increase in activation induced a parallel shift in the curves to higher tension values but the slopes of the curves remained unchanged. The average slope value was 1.7 g/mm.

Animals↗