This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
Reflex Centres are aroused to activity by nervous impulses conveyed to them through afferent nerves: they then excite efferent nerves and produce a movement or a secretion. Such nerve-centres do all the routine of the administrative control of the organs of the body, without troubling the psychic centres. They frequently act without the intervention of consciousness at all, and often in spite of the Will. When sugar is placed in the mouth it excites its sensory nerves; these stimulate a centre from which nerves go to the salivary glands, and these nerves, aroused by the centre, make the gland-cells secrete and pour saliva into the mouth; no effort of the Will can stop this reflex action, so called because a nervous impulse sent to a centre by one set of nerve-fibres is turned back or reflected. from it along another set. When a morsel of food enters the pharynx it excites the sensory nerves of the mucous membrane; these arouse a reflex centre of swallowing, which sends out nervous impulses to the swallowing muscles, and the food is sent on into the gullet whether we wish it or not. Sneezing when something irritates the mucous membrane of the nose, and coughing where some foreign mass enters the larynx, are other instances of reflex actions.
Can a man commit suicide by holding his breath? Are the automatic centres entirely free from control ? Illustrate.
How are reflex centres excited? What is the consequence of their stimulation ? What sort of work in the body is executed by reflex nerve-centres? Are we always conscious of their action ? Can the Will always control them ? What happens when sugar is placed on the tongue? Why is it called a "reflex action"?