A handbook for nurses / by J.K. Watson.

  • Watson, J. K. (James Kenneth)
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: A handbook for nurses / by J.K. Watson. Source: Wellcome Collection.

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    electrical impulses. For example, when we move the hand an impulse passes from some portion of the brain through the medulla into the spinal cord, and thence through the anterior roots of those nerves which go to the upper limb. But these impulses do not keep to the same side as that on which they started, but cross over in the medulla oblongata to the opposite side; so that when we move our right hand the impulse has had its origin in the left side of our brain. Not only do im- pulses of motion cross over, but also those of sensation. If we prick our right thumb, a sensory impulse is conveyed to our brain, not to the right but to the left side. It used to be believed that the impulses of sensation crossed on entering the spinal cord, but it is now held that they too cross in the medulla, a little higher than the motor impulses. When we come to speak of paralysis, we shall find that the disease is on the opposite side to that which is affected by the paralysis. The path of these impulses is shown in the diagram (fig. 14), the thick unbroken lines repre- senting the course of the motor impulses, and the thin inter- rupted lines the sensory im- pulses. It is obvious that if these motor and sensory paths be interrupted either in the brain, the cord, or in the nerves after they leave the cord, a cor- responding degree of paralysis will result in the case of the motor nerves, and of loss of sensation (anaesthesia) in the case of the sensory nerves, as the impulses cannot now be carried to and fro. We have so far referred to the spinal cord as being the medium for the transmission of nervous impulses Grossing of motor impulses in the medulla. Crossing of sensory impressions in the medulla, Fig. 14.—Diagram to show the course of impulses of mo- tion and sensation and their crossing in the medulla (« and 6). Thick black lines indicate motor and thin interrupted lines sensory impulses. Ar- rows mark the direction taken, motor impulses descending and sensory impulses ascending. CL. Cerebrum, left. C R. Cerebrum, right. s. Spinal cord. d. skin and muscles. Path of motor and sensory impulses shown diagram- mauoally.
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