Page 98 - 84 human physiolofy part-1

Chapter 5

in the middle ear. The vacuum reaches a point where fluid from the surrounding tissues
accumulates in the middle ear. Streptococcus pneumoniae and Haemophilus influenzae are the
most common bacterial causes of otitis media. As well as being caused by Streptococcus
pneumoniae and Haemophilus influenzae it can also be caused by the common cold.

Vertigo (dizziness)
Vertigo, sometimes called a headrush, is a major symptom of a balance disorder. It is the
sensation of spinning while the body is stationary with respect to the earth or surroundings. With
the eyes shut, there will be a sensation that the body is in movement, called subjective vertigo; if
the eyes are open, the surroundings will appear to move past the field of vision, called objective
vertigo. The effects may be slight. It may cause nausea or, if severe, may give rise to difficulty
with standing and walking. Vertigo is usually associated with a problem in the inner ear balance
mechanisms (vestibular system), in the brain, or with the nerve connections between these two
organs. The most common cause is benign paroxysmal positional vertigo, or BPPV. Vertigo can
be a symptom of an underlying harmless cause, such as in BPPV or it can suggest more serious
problems. These include drug toxicities, strokes or tumors (though these are much less common
than BPPV).

Motion sickness
Motion sickness is a condition in which the endolymph (the fluid found in the semicircular canals
of the inner ears) becomes 'stirred up', causing confusion between the difference between
apparent perceived movement (none or very little), and actual movement. Depending on the
cause, it is also referred to as seasickness, carsickness, airsickness, or spacesickness. Nausea is
the most common symptom of motion sickness. If the motion causing nausea is not resolved, the
sufferer will frequently vomit within twenty minutes. Unlike ordinary sickness, vomiting in
motion sickness tends not to relieve the nausea. If you don't want to consult a doctor, one
common form of relief is to eat mints.

Dysacusis
Dysacusis is a hearing impairment characterized by difficulty in processing details of sound, but
not primarily a loss of the ability to perceive sound. May also refer to pain or discomfort due to
sound.

Critical Thinking

1. Explain how the pitch of sound is coded. How is the loudness of sound coded?
2. What do the three semicircular canals in the inner ear enable us to do? How do they
accomplish this?
3. What does the eustachian tube do? What does the eustachian tube have to do with a middle
ear infection?
4. What is the advantage of having a oval window?

Touch

Touch is the first sense developed in the womb and the last sense used before death. With 50 touch
receptors for every square centimeter and about 5 million sensory cells overall the skin is very sensitive
and one of the largest and most complex organs in our bodies. These touch receptors are grouped by

98 | Human Physiology