The arrangement of the motor fibres to the cervical oesophagus in the common laboratory animals has been described by Hwang, Grossman & Ivy (1948). These workers have shown, by nerve stimulation and X-ray photography, that the motor fibres serving the cervical oesophagus emerge from the vagus either above or below the nodose ganglion, depending on the species, and enter the oesophagus from either a branch of the pharyngeal nerve or the superior laryngeal nerve. The dysphagia which follows section of these fibres in the dog and the degree of functional recovery which may occur has been described (Hwang, 1953).During an analysis of the myelinated fibres of the superior laryngeal nerve of the rat (Andrew, 1956b) activity in the motor fibres to the cervical oesophagus was detected electrically, and a preliminary report of the discharges of nerve action potentials which take place during swallowing has been given (Andrew, 1956 a). In the present paper an attempt is made to relate discharges of nerve impulses to and from the cervical oesophagus to other events in the act of swallowing. METHODSThe experiments were performed on thirty rats. Anaesthesia was induced with trichloro-ethylene vapour and maintained by intra-peritoneal injection of 25% (w/v), urethane solution 5 ml./kg body weight.Electrodes. The muscle action potentials were picked up with bipolar copper wire electrodes inserted into the muscle. The wires were enamel-insulated, except at the cut ends, and the tips were separated by a fraction of a millimetre. The wires (diameter 007 mm) were wound as a helical spring between the muscle and the input terminals of the amplifier. This arrangement permitted contraction of the muscle fibres to occur without a shift of electrode position and consequent change of action potential size. The electrodes were isolated from the control grids of the input valves by 0001 ,uF polystyrene dielectric condensers. Nerve action potentials were picked up with silver wire electrodes.Recording. The electrodes were connected to conventional capacity-coupled amplifiers and thence to double-gun recording cathode-ray oscillograph, monitor tubes and loudspeaker. The action potentials were recorded on moving bromide paper.
Summary. Nerve impulses in the medial articular nerve to the knee joint of the cat have been studied. The responses of sensory nerve endings located in the knee to position and movement of the tibia are described. The endings are slowly adapting and seem to be arranged sothat each has an arc of maximum sensitivity covering a few degrees of angular movement but these ranges are different for individual endings. The significance of this is discussed. The medial femoro‐tibial and the patellar ligaments were found to be equipped with endings which signalled tension. The responses of these endings to steady tensions were measured. An increased intracapsular pressure was produced by injecting fluid into the synovial cavity. Simultaneous recordings of pressure and impulse traffic show that a raised pressure was a potent stimulus to slowly adapting endings in the capsule. The articular surfaces and the synovial membrane were found insensitive to moderate mechanical and thermal stimulation.
The nerve conduction velocities and motor unit contraction properties of forty‐one hind limb motor units (soleus, 37; extensor digitorum longus, 4) and twenty‐nine motor units from the mid‐tail lateral segmental muscles of the rat were measured. The motor units of the soleus were found to form an homogeneous group as judged by contraction time with just one particularly slowly contracting unit. In the soleus muscle a negative correlation between conduction velocity of the nerve fibre and contraction time of the motor unit was found but no significant correlation between conduction velocity of the nerve fibre and the tetanic tension of the motor unit. The motor units of the tail muscleswere found to form two distinct groups, one of fast units and the other of slow units. In the tail muscles, the slowly conducting motor nerves innervated the slowly contracting units and the fast conducting nerves the fast contracting units. A relationship between the tetanic tension of the tail muscle motor units and nerve conduction velocity was demonstrated.
There is general agreement that nerve impulses from aortic baroceptor endings travel into the central nervous system either in the main vagus trunk or in a separate slender nerve, the aortic or depressor nerve, lying close to the vagus. An account, with references, of the earlier work which has contributed to this agreement is set forth in a paper by Katz & Saphir (1933). The variable distribution of the fibres between the two alternative pathways was noted in the rabbit by Bayliss (1893) who remarked on the difference in size of the depressor nerve from one rabbit to another. He found that when the depressor nerve was small, the more pronounced fall of blood pressure was produced by stimulation of the central end of the vagus.The possibility that a third route exists for cardiac depressor fibres through the recurrent laryngeal nerve, the communicating branch and the superior laryngeal nerve was considered by Howell & Huber in 1891 but they were unable to produce any supporting evidence from electrical stimulation experiments.The experiments to be described in this paper were initiated by the chance observation of nerve impulses synchronous with the heart beat in a filament of the superior laryngeal nerve of the rat. METHODSThe experiments were performed on eighteen rats and two rabbits. The animals were anaesthetized with urethane, given intraperitoneally as a 25 % (w/v) solution, 5 ml./kg body weight.The dieeetion of the superior laryngeal nerve. A mid-line incision was made on the ventral surface of the neck. The subcutaneous tissue was divided between the salivary glands. The. sternohyoid muscle was cut transversely at its attachment to the hyoid bone and reflected back and cut short as close to the sternum as possible. The connective tissue in the region of the common carotid artery at the level of the,thyroid cartilage was dissected with the aid of a lowpower binocular microscope to reveal the superior laryngeal nerve at its point of departure from the nodose ganglion. The nerve was detached from the ganglion and dissected free in the direction of the larynx. The nerve divides usually into four filaments as it approaches the larynx, and care
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