Nerve and Muscle
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Written with undergraduate students in mind, the new edition of this classic textbook provides a compact introduction to the physiology of nerve and muscle. It gives a straightforward account of the fundamentals accompanied by some of the experimental evidence upon which this understanding is based. It first explores the nature of nerve impulses, clarifying their mechanisms in terms of ion flow through molecular channels in cell membranes. There then follows an account of the synaptic transmission processes by which one excitable cell influences activity in another. Finally, the emphasis turns to the consequences of excitable activity in the activation of contraction in skeletal, cardiac and smooth muscle, highlighting the relationships between cellular structure and function. This fourth edition includes new material on the molecular nature of ion channels, the activation of skeletal muscle and the function of cardiac and smooth muscle, reflecting exciting new developments in these rapidly growing fields.
resistance and capacitance in parallel. The output of the bridge was displayed on a cathode-ray oscilloscope, and Rv and Cv were adjusted to give a balance, and therefore zero output, with the axon at rest. When the axon was stimulated at one end, the bridge went briefly out of balance (Figure 4.2) with a time course very similar to that of the action potential. The change was shown to be due entirely to a reduction in the resistance of the membrane from a resting value of about 1000 Ω cm2 to an
certain excitable tissues have a Ca2+dependent spike mechanism. As may be seen in Figure 4.3, replacement of part of the external Na+ by glucose reduced both the rate of rise of the action potential and its height. The rate of rise was directly proportional to [Na]o, while in accordance with Equations (3.2) and (3.3) the slope of the line relating spike height to log10[Na]o was close to 58 mV until the point was reached where conduction failed. Subsequent experiments have shown that a similar
lower density of potassium channels in the tubular membrane than in the surface membrane that may minimize this. 10.3 Excitation–contraction coupling in skeletal muscle Such action-potential generation is the likely trigger for contractile activation in skeletal muscle. Excitation–contraction coupling refers to the sequence of events that intervene between action-potential activation and initiation of tension generation by the actin and myosin filaments. The immediate trigger for
characteristically prolonged plateau. But it is important to note that for a given fibre the shape and size of the action potential remain exactly the same as long as external conditions such as the temperature and the composition of the bathing solution are kept constant. As will be explained later, this is an essential consequence of the all-or-nothing behaviour of the propagated impulse. 2.3 Extracellular recording of the nervous impulse Figure 2.4 Intracellular records of resting and
stimulating wire and an electrode in the sea water outside. Depolarization is shown upwards. Sinusoidal wave at 1 kHz (1 kc/s) at bottom gives indication of timescale. (From Hodgkin et al., 1952.) a wide range of voltages. Hence an increase in stimulus strength above that which just excites the fibre with the lowest threshold results in excitation of more and more fibres, with a corresponding increase in the size of the muscle twitch. When the point is reached where the twitch ceases to increase