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  • Winter 2008 - Issue Number 73
  • Winter 2008 - Issue Number 73

Below are the feature articles from Physiology News Issue 73, Winter 2008.

To read the full articles please download the issue.

  • Features

Olfactory marker protein: a gift to molecular biologists, an enigma to physiologists

Olfactory marker protein (OMP), a small cytoplasmic protein almost exclusively expressed in nasal chemosensory cells, has made major contributions to research progress in olfaction ever since its discovery over 35 years ago. However, the function of OMP and its mechanism of action has remained an enigma. Slowly, answers to these questions are beginning to emerge

  • Features

So what does cause the breakpoint of breath-holding?

The precise mechanism causing the breakpoint of breath-holding is unknown, but it is possible that breath-holding eventually stimulates diaphragm chemoreceptors that in turn cause the irresistible urge to breathe
  • Features

Movement automaticity shows less activation, but more connectivity: a model for brain efficiency

Functional MRI (fMRI) was used to investigate interactions in the brain when movements were sufficiently practiced as to become automatic. When a motor task achieved automaticity a group of brain regions became less active, but more strongly connected. Tao Wu and colleagues speculate that this increase in connectivity reflects more efficient brain function when a task is well learned

  • Features

Does muscle pain increase muscle stiffness?

Animal studies have shown that muscle pain can reflexly excite gamma motor neurones and thus increase muscle spindle stretch sensitivity and discharge rate. According to the popular, but clinically unproven, hypothesis this reflex loop may perpetuate into a sustained 'vicious cycle' - reciprocally aggravating muscle tone and pain. Yet a lack of clear experimental evidence – and recently obtained new data in humans that contradicts this notion – has cast doubt on whether this model can be used to explain physiological mechanisms and translate into the development of treatments

  • Features

How many sensors in the bladder?

Sensory neurons projecting from the urinary bladder (bladder afferents) play a key role in neural circuits underlying both urine storage and normal micturition. They are responsible for all sensations from the bladder such as fullness, the urge to micturate, discomfort and pain. Afferents from different regions of the bladder probably have characteristic receptive fields, response properties and conduction velocities. Indeed, recent experiments in vitro have identified several distinct functional classes of bladder afferents. How then can we relate the functions of various types of afferents in normal and pathological states of the urinary bladder?
  • Features

A little bit of ammonium may be good for your brain

Although specific ammonium-transporting proteins are well known in bacteria and plants, only recently has molecular and functional evidence begun to accumulate for ammonium transporters in animals. We describe how an ammonium transporter on the glial cells of bee retina plays an essential role in energy metabolism, and suggest an update of an old idea of a neuron-astrocyte flux of ammonium at synapses in mammalian brain

  • Features

Levitating arms: unravelling the mystery

A Christmas party trick with an intriguing history and physiology
  • Features

Motor neuron activation is conditional during muscle fatigue

The timing of the action potentials discharged by a motor neuron when it is recruited during a fatiguing contraction depends on the amount of synaptic input it requires to reach activation threshold. Action potentials are discharged continuously when the force at which the motor unit is activated is close to the target force of the contraction, but the discharge is much less regular when the target force is further below activation threshold of the motor unit
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