Background

In anatomy, special senses are the senses that have organs specifically devoted to them such as vision, gustation, olfaction, audition, and equilibrioception. These senses have specialized organs that detect and process stimuli and send signals to the brain which lead to the perception of that stimulus. These specialized organs include the tongue, the nose, the eyes and the ears.

The tongue is a crucial organ in mechanical digestion and taste. Taste buds contain taste receptor cells which are the smallest functional unit in gustation. Taste buds can be found throughout the length of the upper digestive tract. On the surface of the tongue are protrusions called papillae. Circumvallate papillae are arranged in a v shape pattern on toward the base of the tongue, on the dorsal aspect, and contain more than 100 taste buds each. The fungiform papillae are found all over the dorsal aspect of the tongue and contain only about 5 taste buds each. The foliate papillae are found on the lateral aspects of the tongue and only contain taste buds during childhood. Finally, there are the filiform papillae which, like the fungiform papillae, are found all over the tongue, however, they do not contain taste buds.  Instead, their barbed shape provides the friction for moving food around during mastication.

The olfactory epithelium is easily discernable on most models. Unlike any of the following special senses, neurons from the olfactory bulb bypass the thalamus and synapse directly with the olfactory cortex.

The ear is a complex organ which houses special structures that allow us to hear, balance and orientate ourselves. Sound waves are collected by the auricle and funneled into the external acoustic meatus. The ear is divided into three sections, the outer, middle, and inner ear. The outer ear consists of the auricle which extends through the external auditory canal and terminates at the tympanic membrane. The main structures of the middle ear are the auditory ossicles, Eustachian tube, oval window and round window. The auditory ossicles inward from the tympanic membrane, are the malleus, incus, and stapes. The base of the stapes covers the oval window which allows sound waves to pass from the tympanic membrane, into the cochlea of the inner ear. The inner ear is the innermost region of the ear where the cochlea, vestibule, and semicircular canals are.   The cochlea, vestibule, and semicircular canals are responsible for hearing, static and dynamic equilibrium respectively. The vestibulocochlear nerve branches,  into the cochlear branch, which innervates the cochlea, and the vestibular branch which innervates the vestibule and semicircular canals.

The eye is the specialized organ of sight which has three principal layers, the fibrous tunic, the vascular tunic and the neural tunic. Furthermore, there are two main chambers, the anterior chamber, containing aqueous humor and the posterior chamber, that contains vitreous humor.  In the neural tunic of the retina, light propagates from the ganglionic cells through the bipolar cells to the rods and cons, which, somewhat paradoxically hyperpolarize opposite the direction of light.

The lacrimal apparatus frames the eye and coats the sclera and cornea in lacrimal fluid, a bacteriacide, which lubricates and protects them. The lacrimal apparatus is made of the lacrimal gland, lacrimal canaliculi, lacrimal sac and nasolacrimal duct. This network of structures allows tears produced by the lacrimal gland to cover the eye, drain through the lacrimal puncta into the lacrimal canaliculi, collect in the lacrimal sac, travel down the nasolacrimal duct and finally empty into the nose. This is why crying leads to a runny nose.

Vocabulary for Special Senses can be found on page(s) 169-171.