Fróðskaparrit - 01.01.1968, Side 107

Motion Sickness
115
Hervey (1952) was due to 'habituation to wave motion, and
it lasted as long as that particular trip.
Discussion.
Motion sickness was so named by Irwin in 1881, for he
knew fihat the sickness was the same whatever che initial cause
for acceleration. It is now known that fihe receptors for motion
siokness are in the vestibular apparatus, ohiefly in fihe utricle,
where fihe otolith, which resembles a little pebble, rests upon
the hairlike receptors. Tlhe vestibular apparatus normally serves
ordinary postural reflexes, but fihere is a complex pathway
ior motion sickness involving fihe cerebellum and the brain
stem. There are also pachways to fihe cerebral hemispheres
transmitting the sensation of nausea. The efferent fibres cause
relaxation of the stomadh, contraction of fihe duodenum, and
sharp contraction of fihe abdominal muscles further accom-
panied by closing of fihe glottis and opening of the mouth
which leads to vomiting. This reflex vomiting is the essential
process of motion sickness, but nausea usually precedes vomit-
ing, and this is an integral part of motion siokness. Rarely
explosive vomiting may precede nausea, but at some stage
or other nausea is always present. Other symptoms, i. e. dizzi-
ness, headache, and sleepiness can be caused by anxiety (Glacer
and Whittow 1954). Equally perspiration and diarrhoea, which
often accompany vomiting, are not typical signs, but probably
the result of generalised central nervous exitation. Smells and
anxiety seem to make motion sickness worse.
There is experimental evidence that the reflex pathways are
facilitated by usage (Eccles 1953), and it is possible that people
may acquire the habit of being sick, so fihat when chey travel
and use a certain type of transport, they will suffer from
nausea and vomiting.
It is also known chat reflexes can be conditioned, thus a
per9on who has often been sick from the motion of a ship
may become sick again at the sight or smell of a ship.