The Special Senses
Five special senses:
These senses have specialized organs containing specialized receptor cells, which carry their
impulses by way of specialized somatic and visceral afferents.
Touch is the other sense –
somatic sense –
does not have a specialized sense organ.
Uses general receptors composed of modified dendrites of sensory neurons.
Includes pressure, vibration, pain, heat, and the combined info is carried in general
somatic afferents and general visceral afferents.
Vision and the Eye
Organ responsible for sight is the eye – it consists of three layers
Outer fibrous layer includes the sclera and cornea
Posterior potion is known as the sclera (the white of the eye)
Anterior portion is known as the cornea – is transparent and is where light enters
Aqueous humor fills the spaces between the cornea and lens
Includes the choroid, ciliary muscle and iris
Choroid (posterior) is darkly-colored and prevents light from dispersing through
Highly vascular and supplies blood to the other layers of the eye
Ciliary body (anterior) changes the shape of the lens, which allows it to focus
Iris (anterior to the ciliary body) contains the colored portion of the eye.
Controls the amount of light let into the pupil which is the hole in the center of
Iris uses muscle fibers to contract or dilate based on the amount of light in the
Sensory layer – includes the retina
Retina contains 2 types of photoreceptors which are cells that are sensitive to light.
The more numerous cells are rods – which are stimulated in dim light.
Rods are more sensitive to light but do not generate sharp or color images.
Cones operate in bright light which help to generate sharp color images.
Lens is located posterior to the iris and pupil
Interior of the eye, which is posterior to the lens, is the vitreous body
Vitreous body is filled with vitreous fluid which helps to hold the retina firmly to the choroid.
Vision Pathway (How we see)