The Senses 17
range also encompasses much lower frequency sounds than would be expected. This
can be a particular advantage for pet cats because it allows them to hear the full range
of human speech, even the low-pitched human male voice. Cats also have very sensi-
tive hearing, allowing them to hear not just the vocalizations but also the movements
of small animals and insects.
Their ability to detect minor differences in pitch and intensity between sounds is,
however, inferior to our own and they are less able to detect sounds of very short
duration. Our increased ability in this respect might be due to our need to detect such
small changes in sound that occur in human language (Bradshaw, 2013).
The pinna (the external part of the ear) plays a very important role in both the
location of sounds and as a directional amplifier. Individual muscles allow each pinna
to be moved independently and these movements can be both rapid and precise ena-
bling the cat to accurately pinpoint the source of a sound.
Olfaction (Sense of Smell)
Olfaction is an extremely important sense for cats because it is used in communica-
tion, reproduction, feeding and hunting. It is therefore not surprising that cats have a
highly sensitive and discriminative sense of smell.
Olfactory receptor cells, which have a direct neural connection to the olfactory
bulb in the brain, are found in the olfactory epithelium – the lining of the nasal cav-
ities. In humans this covers an area of around 2–5 cm^2 and contains around 5 million
receptors. In cats the olfactory epithelium is supported by the scroll-like nasal
turbinate bones, the ethmoturbinals, and covers a total surface area of approxi-
mately 20–40 cm^2 , containing around 200 million receptors (Ley, 2016). These are
receptors of not just one type, but several hundred different types, enabling the cat
to distinguish between an incredibly enormous number of different odours (Bradshaw
et al., 2012).
The vomeronasal organ
The vomeronasal organ, also known as the Jacobson’s organ, is an additional olfac-
tory organ found in many mammals but not in humans or other higher primates.
It provides the animal with a sense that is probably something between taste and
smell and appears to be used primarily to detect and identify pheromones used in
intra-species communication (see Chapter 3). It consists of two blind-ended fluid-filled
sacs, situated within the hard palate, that contain around 30 different types of
chemical receptors. Scent is actively taken in through the mouth and towards the
vomeronasal organ via two small slits, known as the nasopalatine ducts, positioned
just behind the upper incisors.
When utilizing the vomeronasal organ, a cat will exhibit a slightly odd facial
expression or ‘grimace’ whereby the mouth is held slightly open with the upper lip
raised (Fig. 2.2). This is also known as the flehmen response, from the German verb
meaning to bare the upper teeth. Flehmen is a voluntary behaviour and it is possible
that the presence of other visual or olfactory signals, such as the scent of urine, might
trigger this reaction (Mills et al., 2013).