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3.7 Hair cell tuning

We have determined that the location of the peak of the travelling wave on the basilar membrane is determined by the frequency of the originating sound. The hair cells run the length of the basilar membrane. When a certain frequency sound stimulates a point on the membrane, it responds by moving, and the hair cells at that site are stimulated by the shearing force that this movement creates (Author(s): The Open University

3.6 Synaptic transmission from hair cells

In addition to being sensory receptors, hair cells are also presynaptic terminals. The membrane at the base of each hair cell contains several presynaptic active zones, where chemical neurotransmitter is released. When the hair cells are depolarised, chemical transmitter is released from the hair cells to the cells of the auditory nerve fibres. Excited by this chemical transmitter, the afferent nerve fibres contacting the hair cells fire a pattern of action potentials that encode features of
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3.5.2 Mechanical force directly opens and closes transduction channels

It is believed that tip links aid in causing ‘channels’ to open and close near the top of the hair cell (Figure 16). Tip links are filamentous connections between two stereocilia. Each tip link is a fine fibre obliquely joining the distal end of one stereocilium to the side of the longest adjacent process. It is thought that each l
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3.5.1 Hair cells transform mechanical energy into neural signals

The tectorial membrane runs parallel to the basilar membrane, so when the basilar membrane vibrates up and down in response to motion at the stapes, so does the tectorial membrane. However, as shown in Figure 14, the displacement of the membranes causes them to pivot about different hinging points and this creates a shearing force betw
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3.3 The role of the basilar membrane in sound reception

So far we know that sound-induced increases and decreases in air pressure move the tympanum inwards and outwards. The movement of the tympanum displaces the malleus which is fixed to its inner surface. The motion of the malleus and hence the incus results in the stapes functioning like a piston – alternately pushing into the oval window and then retracting from it. Since the oval window communicates with the scala vestibuli, the action of the stapes pushes and pulls cyclically on the fluid
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2.6.2 End-of-unit questions

Question 8

Express the following numbers using scientific (powers of ten) notation:

  • (a) 2.1 million

  • (b) 36 000

  • (c) 1/10

  • (d) 0.00005


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2.5.2 Quantum fields and unification

From its inception, quantum physics was concerned not just with particles such as electrons, but also with light and other forms of electromagnetic radiation. In 1900 Planck discovered the quantum in the transfer of energy from matter to radiation, and in 1905, Einstein's explanation of the photoelectric effect assumed that the transfer of energy from radiation to matter occurred in a similarly quantised fashion. It is therefore hardly surprising that the development of quantum mechanics was
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Faraday and Maxwell

Michael Faraday (1791–1867)

Figure 21
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2.2.2 Energy and conservation

Newtonian mechanics is concerned with explaining motion, yet it contains within it the much simpler idea that some things never change. Take the concept of mass, for example, which appears throughout Newtonian mechanics, including the law of gravitation. In Newtonian mechanics, mass is conserved. This means that the mass of the Universe is constant and the mass of any specified collection of particles is constant, no matter how much rearrangement occurs within the system. A chemist might take
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3.3 Drawing conclusions

Sections 2.1 and 2.2 have summarised some of the major aspects of the Pusztai affair, but it should be said that almost every detail has been the subject of prolonged and heated dispute. Our purpose is not to attempt to denigrate individuals or institutions. Rather, the hope is that the tale carries some general messages of value about how science is undertaken and communicated, which can sometimes become clearer when things go wrong.

Communicating preliminary scientific information via
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2.5 Using stars to probe the interstellar medium

The effects of interstellar material on starlight can be used to probe the properties of the interstellar medium itself. A few examples are:

  • The presence of particular interstellar atoms or molecules may be determined by identifying the observed spectral lines or bands.

  • The temperature of the gas may be determined from the relative strengths of different lines or bands produced by different energy state changes of the same atom or mol
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2.5.1 Summary of Section 2

Desert animals are classified in terms of their body size and physiology into three groups: evaders, evaporators and endurers. The logic for this classification is that the smaller the animal, the larger its surface area to volume ratio. Small animals therefore gain and lose heat faster than large animals, warming rapidly when exposed to intense solar radiation, and cooling rapidly at night. Small endothermic evaders, e.g. kangaroo rats, rest in cool microenvironments, e.g. shade or burrows,
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6.6.2 Hibernation-induction trigger

Researchers have devoted much effort to the search for a possible blood-borne chemical messenger that might communicate a signal within the brain and to other body tissues, causing entry to hibernation. Serum from hibernating animals such as the woodchuck (Marmota monax; Figure 8), when injected into active animals, can induce torpor. Partly purified serum extracts are also able to induce hibernation-like behavioural changes in a variety of mammalian species. Chemical analysis of the s
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6.5 The neurotransmitters histamine and serotonin: a role for chemical signalling between neurons of

As in all other regions of the brain, the integration of physiological change in the hypothalamus, conducted by the dialogue between many thousands of nerve cells, is the result of transmissions across chemical synapses. The functions of the hypothalamus are therefore dependent upon neurotransmission by a number of different chemical mediators and are critically dependent on the balance between their respective activities. Monoamine neurotransmitters (histamine and serotonin) operate in subgr
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6.4 Rapid-response genes and rhythmic neuronal activity

Reactive changes in the brain are usually marked by changes in neuronal electrical activity. If these changes are to be of long duration, adjustments in neuronal electrical behaviour may be made through changes in gene expression. Rapid-response genes (sometimes called ‘immediate-early’ genes) are activated within minutes of the onset of such sustained electrical activity. These genes are master controls, acting as a gateway to a series of linked events: alteration of electrical firing pa
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Acknowledgements

The content acknowledged below is Proprietary (see terms and conditions) and is used under licence.

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

Text

Figures


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5.4 Fatty acids as indicators of diet

Although polar fish and invertebrates are difficult to study alive for the reasons just described, some information about their diet and habits can be obtained from analysis of the lipid composition of their tissues. At high latitudes, the supply of most kinds of marine food changes with the seasons, just as it does on land, and many fish eat little or nothing for long periods, living off their reserves of triacylglycerols. Lipids are major fuels for polar fish and, although many fish have li
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4.4.1 Introduction

Since its development, the three-way catalyst has been exposed to the full spectrum of techniques available for the characterisation of catalytic materials. The data provided can be correlated with the results of activity tests and kinetic measurements, which provide information on the performance of the catalyst. This reveals that although the catalyst functions as a composite material, it can be divided into distinct groups of catalytic centres that provide several different types of site,
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8.2 Wilson's disease

The effects of a protein that is absent, or present but not doing its job, may not be evident for many years. This is called late onset, and is exemplified by Wilson's disease. Many molecules within the body require small amounts of minerals such as iron, magnesium or copper to function properly. There are mechanisms for absorbing these minerals from the diet. However, in excess, these same minerals can be toxic, as is the case with copper. So there are also mechanisms for getting rid
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7.8 Summary of Section 7

This section has sought to illustrate the formation of connections between neurons and their targets by exploring a few examples. The picture that emerges is one of cells at different stages of development subjected to a vast array of signals. These signals are the medium through which environmental factors exert their effects. To some of these signals, some cells respond; to other signals, other cells respond. What a cell, a neuroblast, a growth cone actually does is dependent on the combina
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