Review of Chapter 11. Chapter 12: Sensory Reception. Section 12.1 Sensory Receptors and Sensation. Your senses of sight, hearing, taste, smell, and touch keep you informed about the external environment so that you can respond to it.
Sensory Receptors and Sensation
Your senses of sight, hearing, taste, smell, and touch keep you informed about the external environment so that you can respond to it.
Ex. Optical Illusions
In people that can see, vision supplies 80 to 90 percent of the important sensory information reaching the brain.
The human eye is a fluid-filled ball measuring 2.5 cm in diameter that focusses incoming light energy on the photoreceptors of the retina. The eye has three layers that have different tissues and functions:
Because the lens is flexible it can account for seeing things at short and far distances. The ability of the lens to change shape in order to focus images clearly on the retina is called accommodation.
Astigmatism occurs naturally in many people if there is an uneven curvature of part of the cornea. This prevents the cornea from being able to bend light rays so that they meet at the correct focal point causing blurry vision.
Some people have an elongated eyeball so that the focussed light falls in front of the retina. This condition is called myopia or nearsightedness since they can see close objects but not far objects. This condition can be corrected by wearing concave lenses that diverge incoming light rays.
Some people have short eyeballs that cause the light rays to not focus before they reach the retina so they can see farther distances but not up close. This condition is called hyperopia or farsightedness. This can be corrected using convex lenses that converge light rays.
There are three types of cones that can detect red, blue, and green wavelengths of light. The combination of these cones being activated allows us to see the range of colours.
The rods contain a light-absorbing pigment called rhodopsin, which is composed of retinal (from Vitamin A) and the protein opsin. In the dark, rods emit an inhibitory neurotransmitter that inhibits nearby nerve cells. When the rod absorbs light, the rhodopsin splits into retinal and opsin which triggers a reaction that stops the release of the inhibitory neurotransmitter, thus allowing a neural impulse to the optic nerve.
Humans have forward-facing eyes, called binocular vision, which allows us to perceive depth and three-dimensional images.
Changes in the consistency of the vitreous fluid can cause retinal detachment where the retina is pulled away from the choroid vessels that supply it with nutrients and oxygen. This is caused by an inflammatory disorder, advanced diabetes, or trauma to the eye.
Macular degeneration occurs when the cones are destroyed due to thickened choroid vessels. This causes blurred vision or a blind spot in central vision. Age is the principal factor in developing this but other factors include cigarette smoking, obesity and exposure to sunlight. Exercise, not smoking, and a diet rich in green leafy vegetables and fish can help prevent this.
Mechanoreceptors and Chemoreceptors
The ear can be divided into three main divisions which each collect and direct auditory information to the hearing receptors:
The middle chamber of the cochlea contains the organ of Corti which is the organ of hearing.
The stapes strike the oval window, which vibrates the window and creates pressure waves in the fluid of the cochlea. The pressure waves make the basilar membrane move up and down, which causes the stereocilia of the hair cells to bend against the tectorial membrane. The hair cells sense this bending and relay the message to the nerves which carry an impulse to the brain.
Proprioceptors are another type of mechanoreceptors involved in coordination. They are found in muscles, tendons, and joints throughout the body and provide information about body position to the brain.