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Biomedical subjects

E Henneman

Publications and source records attributed to E Henneman.

At least 19 recordsLinked to original sources
PubMed1995

Ethical issues in hospital-based nursing practice.

A professional nursing ethic is a living, dynamic set of standards for nurses' professional moral behavior. For a professional ethic to be adequate, it must address the ethical issues perceived as relevant to the profession. The purpose of this descriptive study was to identify the ethical issues hospital-based nurses face in their practice. The authors sought to determine whether there were any differences in these ethical issues over time or according to specialty practice, position, age, educational level, or years in practice. Different groups of nurses (N = 794) were surveyed on five separate occasions over 9 years. Data were analyzed using descriptive and chi 2 statistics. The most frequent ethical issue faced was pain relief and management. Over time, the percentage of nurses who reported being faced with ethical issues related to morphine drips increased. Implications for future research on development of a normative nursing ethic are discussed.

Adult↗
PubMed1993

Subcutaneous administration of the amino-terminal fragment of human parathyroid hormone-(1-34): kinetics and biochemical response in estrogenized osteoporotic patients.

A standard dose (400 U or 25 micrograms) of human (h) PTH-(1-34) was administered sc in 11 estrogen-treated patients with postmenopausal osteoporosis. Increments in circulating hPTH-(1-34) were brisk, peaking at 30 min, with variable peak levels averaging 10 times normal. Clearance of the peptide from the circulation followed an expontential pattern, with a mean t1/2 of 75 min. Peptide administration was followed by an immediate decline in serum concentrations of PTH-(1-84), which remained suppressed at about 65% of the basal value for the duration of the study (4 h). Serum calcium did not increase until 120 min, thus occurring after the diminution in PTH-(1-84). Serum phosphorus declined promptly as urinary phosphate excretion increased. There were no clear changes in urinary calcium excretion, but urinary cAMP excretion increased within 120 min. In 9 of 11 patients, the serum concentration of 1,25-dihydroxyvitamin D increased, with mean levels increasing progressively after 90 min to approximately 30% above baseline (P < 0.05). In conclusion, sc administration of 25 micrograms hPTH-(1-34) produces significant short term changes in mineral homeostasis that appear to be mediated by the kidney, parathyroid gland, and skeleton, with the latter displaying the most delayed response.

Calcitriol↗
PubMed1993

A collaborative practice model for critical care.

Collaborative practice behavior is a concern for healthcare providers and administrators, because it is associated with positive outcomes for both patients and staff in the intensive care unit. Despite the documented benefits derived from collaborative practice, it remains the exception rather than the dominant pattern for nurse-physician interactions. National concern for quality care and rising healthcare costs mandates that collaborative practice behaviors between nurses and physicians replace competition as the means for resolving differences. The purpose of this article is to describe collaborative practice, propose a theoretical framework for collaborative practice and discuss the development, implementation and evaluation of a collaborative practice model.

Cooperative Behavior↗
PubMed1989

Influences of morphology and topography of motoneurons and muscle spindle afferents on amplitude of single fiber excitatory postsynaptic potentials in cat.

Excitatory postsynaptic potentials (e.p.s. p.s.) elicited by impulses in single muscle spindle afferent fibers from the medial gastrocnemius (m.g.) muscle were recorded intracellularly from homonymous and heteronymous motoneurons in order to study factors that influence the amplitudes of such responses. Impulses in large afferent fibers elicited larger single-fiber e.p.s.p.s. than those in smaller afferents. Mean e.p.s.p. amplitudes were related exponentially to afferent conduction velocities of both Ia and spindle group II fibers. The closer a motoneuron was to the spinal entry point of an afferent fiber, the larger was the mean e.p.s.p. amplitude evoked in it. Impulses in the same afferent fiber elicited larger e.p.s.p.s in small than large motoneurons when the two cells were located at the same craniocaudal levels. Other factors being equal, the single-fiber e.p.s.p.s evoked in homonymous and heteronymous motoneurons were approximately equal in amplitude. Relatively simple morphological and topographical explanations for the findings were advanced and their functional significance for orderly recruitment in partitioned and unpartitioned reflexes was described.

Action Potentials↗
PubMed1988

Reflex inhibition of urethral sphincters to permit voiding in paraplegia.

When the spinal motoneurons innervating the external sphincter of the urethra cannot be inhibited voluntarily due to lesions of the spinal cord, the normal capacity to relax this physiologic valve during micturition is lost. Even if contractions of the bladder occur, urinary outflow may be completely blocked at the sphincter, leading to distention of the bladder and the risk of urinary infection. A method is described for controllably relaxing the sphincter, which permits free outflow of urine in paraplegic cats. One pudendal nerve is sectioned, paralyzing half of the sphincter, but leaving the experimental animals entirely continent. The motoneurons supplying the other half of the sphincter are inhibited by means of spinal reflexes, eliminating active resistance to urethral flow. The simplicity of this approach suggests that it may prove equally effective in human paraplegia.

Animals↗
PubMed1985

Structural and topographical influences on functional connectivity in spinal monosynaptic reflex arcs in the cat.

A greatly expanded version of spike-triggered averaging (Mendell & Henneman, 1971), performed off-line on tape-recorded signals, was utilized to determine the presence or absence of functional connexions between stretch-afferent fibres and homonymous motoneurones. As many as 264 possible connexions between eleven Ia or spindle group II fibres and twenty-four motoneurones were studied in each single, acute experiment. Morphological and topographical factors influencing functional connectivity were analysed with the aid of wiring diagrams and connectivity matrices. In all experiments the greater the conduction velocity (i.e. diameter) of a Ia or group II fibre, the higher was the probability of its having functional connexions with homonymous motoneurones. The greater the longitudinal distance between the spinal entry points of Ia fibres and the location of a motoneurone, the less was the same probability. The influence of axonal conduction velocity of motoneurones on functional connectivity was apparent in some experiments, but not in others. In pooled data large motoneurones received functional connexions from a higher percentage of group II fibres than did small cells. The projection percentage reached 100 only when both Ia fibres and motoneurones were large, suggesting that motoneurone size influences the probability of functional connexions from group Ia as well as group II fibres. On a cell-to-cell level, connectivity apparently does not follow strict, deterministic rules. The results raise the question of how probabilistic connexions between afferent fibres and motoneurones give rise to deterministic outputs from the whole pool.

Action Potentials↗
PubMed1985

The size-principle: a deterministic output emerges from a set of probabilistic connections.

Orderly, size-related recruitment of motoneurones (MNs) illustrates how hundreds of cells operate as a functional entity to produce a highly deterministic output. The coherent action of the pool depends largely on the distribution of input to its members through the connections of afferent fibres. Three types of spike-triggered averaging have been utilized to study these connections. Impulses in individual Ia afferents elicit excitatory postsynaptic potentials ('single-fibre' EPSPs) in about 80% of homonymous MNs. After spinal transection 100% may respond, suggesting that Ia fibres project anatomically to all homonymous MNs. Functionally absent Ia connections are due to transmission failure. The sum of all the EPSPs elicited in a large population of MNs was recorded electrotonically from ventral roots. The mean amplitudes of these 'postsynaptic population potentials' (PSPPs) were correlated with the conduction velocities (CVs) of the Ia or spindle group II fibres. The greater the distance between the spinal entry point of a Ia fibre and the ventral root, the smaller was the PSPP. Tape recording of multiple afferents and the responses of up to 24 MNs permitted study of as many as 264 possible connections in a single, acute experiment. Construction of wiring diagrams and connectivity matrices from the data showed that functional connectivity is influenced by afferent fibre size, the effect of branching on fibre size, MN size and probably transmission failure, but that on a cell-to-cell level, connectivity does not follow strict, deterministic rules. The results raise the question of how probabilistic connections between afferent fibres and MNs give rise to deterministic outputs from the whole pool.

Animals↗
PubMed1984

Wiring diagrams of functional connectivity in monosynaptic reflex arcs of the spinal cord.

The direct functional connections between Ia and group II spindle afferent fibers from the cat medial gastrocnemius muscle and their homonymous motoneurons were examined in 10 acute experiments. Trains of stretch-evoked impulses from as many as 20 undivided sensory fibers were recorded simultaneously from 5 dorsal root filaments, as well as the corresponding excitatory postsynaptic potentials (EPSPs) they elicited in 10-20 motoneurons. Spike-triggered averaging [13] of these tape-recorded signals revealed the functional connections (or non-connections) between each Ia or group II afferent fiber and each motoneuron. Wiring diagrams constructed from these data indicate that the probability of a functional connection between an afferent fiber and a motoneuron decreases with the size of either and with the distance between the entry point of the afferent fiber and the motoneuron.

Afferent Pathways↗
PubMed1984

Simultaneously active and inactive synapses of single Ia fibres on cat spinal motoneurones.

A technique is described for recording large numbers of individual or single-fibre excitatory post-synaptic potentials (e.p.s.p.s) from single motoneurones by means of spike-triggered averaging. The cable properties of the motoneurones were calculated from the decay time course of a voltage transient in the motoneurone following a current pulse applied to the soma. From this response a theoretical shape index curve was calculated. Most individual or single-fibre e.p.s.p.s elicited by impulses in different Ia fibres had simple decay time courses and shape indices that fitted the theoretical shape index curve of the motoneurone from which they were recorded very well. This suggested that the active terminals of these afferent fibres were located within limited post-synaptic areas. In a few cases the original amplitude, latency and shape of individual e.p.s.p.s changed dramatically when they were re-averaged 40 min later after the membrane potential had decreased, but was still at an acceptable level. E.p.s.p.s with simple decay time courses changed to e.p.s.p.s with composite decay time courses, presumably due to activation of previously silent synapses. The results suggest that impulses conducted in a single afferent fibre from a muscle spindle do not necessarily activate all of the synapses which the fibre forms on a motoneurone, but may repeatedly fail to activate some endings during prolonged periods of spike-triggered averaging, while consistently activating others. Evidence regarding the site of transmission failure and the possible mechanism of its relief is discussed.

Action Potentials↗
PubMed1984

Recruitment order of motoneurons in stretch reflexes is highly correlated with their axonal conduction velocity.

Motor units of soleus and medial gastrocnemius (MG) muscles were studied in pairs during stretch reflexes in the decerebrate cat to determine the relation between their recruitment orders and axonal conduction velocities. In 97% of soleus pairs, the motor unit with the lower axonal conduction velocity was recruited first. Since the soleus is a homogeneous muscle in the cat, differences in motor-unit type are, therefore, not a sine qua non for orderly recruitment nor is recruitment random within homogeneous populations of motor units, as recently proposed (28). In the medial gastrocnemius, a heterogeneous muscle, the same high correlation (97%) between recruitment sequence and conduction velocity was observed. Thus, the factors that determine recruitment order in heterogeneous muscles are as closely correlated with axonal diameter as they are in homogeneous muscles. Comparison of axonal conduction velocities in our sample of MG units with those in three samples of type-identified MG units studied by other investigators also suggests that motor-unit type is not the critical factor controlling the sequence of activation in heterogeneous muscles. It is concluded that the combined effects of all presynaptic and postsynaptic factors that determine susceptibility to discharge in motoneurons during stretch reflexes are strictly correlated with their axonal conduction velocities, as predicted by the size principle.

Animals↗
PubMed1983

Does orderly recruitment of motoneurons depend on the existence of different types of motor units?

It has recently been proposed that the recruitment of motoneurons is correlated with their type rather than their size. To test this hypothesis the axonal conduction velocities (CVs) of 92 pairs of soleus motoneurons (all of the same histochemical type) were compared with their recruitment order. By means of spike-triggered averaging it has been shown that in 89 out of 92 pairs of soleus units the motoneuron with the lower CV was recruited first. The results indicate that orderly recruitment occurs in the absence of different types of motoneurons and is correlated with cell size within a cell type.

Action Potentials↗
PubMed1983

Effects of impulse frequency, PTP, and temperature on responses elicited in large populations of motoneurons by impulses in single Ia-fibers.

Excitatory postsynaptic potentials (EPSPs) were evoked in large populations of motoneurons by impulses in single Ia- and group II fibers and recorded from L7 and S1 ventral roots by means of a sucrose-gap technique and spike-triggered averaging, as previously described (33, 34). Factors known to influence conduction at branch points in peripheral nerves or transmission in the Ia projection to motoneurons were studied to determine their effects on these postsynaptic population potentials (PSPPs). When impulse frequency was plotted against the amplitude of these PSPPs, a sequence of low-frequency depression, higher frequency facilitation, and still higher frequency depression was regularly observed. Similar plots of PSPP amplitude versus impulse frequency in a small sample of group II spindle fibers did not reveal any low-frequency depression. Higher frequency facilitation and depression followed the same pattern as that produced by Ia-fibers. Early potentiation of the PSPPs was produced by applying 20 stimulating pulses at 500/s to branches of the medial gastrocnemius nerves containing single Ia-fibers. Single, posttetanic PSPPs were recorded at fixed intervals following each tetanus and averaged. A brief, initial depression followed by a rapidly declining potentiation of PSPPs was regularly observed. When the core temperature was reduced from 41 to 35 degrees C, there was an approximately linear increase in the amplitude of PSPPs. At each temperature a combination of cooling and posttetanic potentiation (PTP) elicited larger PSPPs than cooling alone. The effects of impulse frequency, PTP, and temperature on PSPPs may all be interpreted in terms of their known effects on action potentials or on conduction at branch points in peripheral nerves. Similar effects on transmission or transmission failure in the terminal arborizations of Ia-fibers would account for the influence of these factors on PSPPs. Alternatively, these same three factors might cause similar effects on PSPPs through influences they might exert on the transmitter release mechanism.

Animals↗
PubMed1982

Flexor reflex control of the external sphincter of the urethra in paraplegia.

In paraplegics and quadriplegics a profound paralysis of skeletal muscles occurs below the level of the spinal lesion. Unexplained in this state is the development of an overactive external urethral sphincter, which interferes with emptying of the bladder and may lead to infection of the urinary tract. Studies of cats show that the discharge of motoneurons causing this contraction has all the characteristics of a flexor reflex.

Animals↗
PubMed1979

Different species of alpha motoneurons in same pool: further evidence from effects of inhibition on their firing rates.

1. Single units of the plantaris pool were isolated in ventral root filaments of decerebrate cats and their critical firing levels (CFLs) were determined. Motoneurons of similar size were compared in firing rate (FR) during repetitive stimulation of the plantaris nerve to establish control values and also during added stimulation of various inhibitory nerves (sural, hamstrings, or peroneal). 2. Criteria, based on maximal firing rate, were developed whereby certain pairs of units of similar size could be reliably classified into different types. 3. A second, independent set of criteria was formulated by which the same pair of units could be classified according to their responses to added inhibitory inputs. 4. The ability to distinguish motoneurons consistently by more than one set of criteria reinforces the evidence that different physiological types of units exist within a single motoneuron pool. 5. The findings indicate that different types of cells either receive different densities of input from certain inhibitory sources or that they react differentially to the same amounts of these inputs.

Action Potentials↗