Man the slave & master / by Mark Graubard.

  • Graubard, Mark, 1904-1992.
Date:
1939
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Man the slave & master / by Mark Graubard. Source: Wellcome Collection.

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    the muscle contracts. After a short time, it returns to its previous condition. Contraction is also evoked by drop ping acid on it, touching it with a hot needle, or sending electric current through it. On the other hand, the muscle will not respond if you shine a light or direct air waves upon it, merely look at it, or meditate over it. This means that there are certain forces in the environment which, if brought in contact with the muscle, cause it to contract. Other forces are ineffectual. Those agencies which provoke a response are called stimuli. A muscle is stimulated by tem perature, pressure, chemical substances, and electrical current. If the muscle is isolated together with its connecting nerve, or for that matter, if a nerve leading to any other muscle is removed from its original place and brought in contact with the isolated tissue and then gently touched with a glass rod, contraction will occur. Hot and cold substances and electricity will produce the same response. Thus, the nerve is stimulated and the muscle with which it is connected responds by contracting. From these observations we conclude that muscles have the ability to contract and nerves to convey stimuli to them. Muscular cells are oblong, spindle-shaped fibres. Nerve cells, called neurons , are long fibres containing bulbous bodies harbouring nuclei. At one end of the bulb are thin, branched projections called dendrites ; at the other end, a long thread called the axon , provided with small branched terminations. Dendrites and axons form connecting joints between neurons, not by actual fusion but through contact of cell materials. The axon of one cell connects with the dendrites of the next, the axon of the latter with the dendrites of a third, and so on. The junction between the dendrites of one cell and the branched endings of the axon of another is called a synapse . The catenary arrangement of nerve fibres joined by synapses accounts for the nerve's function as a conductor. Synapses are found either in the brain