Special Senses
Chemical Senses: Smell & Taste
Both taste and smell use chemoreceptors. A chemoreceptor turns a chemical stimulus into a nerve signal. Both of these senses complement each other and respond to many of the same stimuli.
The sense of smell is the first sense babies use when they are born.
Olfactory (smell) receptors are in the roof of the nasal cavity. Chemicals must be dissolved in the mucus of the nose in order for them to be detected by the olfactory receptors.
Impulses are transmitted to the olfactory bulb and travels to the smell center on the temporal lobe.
The sense of smell is the first sense babies use when they are born.
Olfactory (smell) receptors are in the roof of the nasal cavity. Chemicals must be dissolved in the mucus of the nose in order for them to be detected by the olfactory receptors.
Impulses are transmitted to the olfactory bulb and travels to the smell center on the temporal lobe.
Vision
70% of all sensory receptors are in the eyes! Each eye has over 1 million nerve fibers. How do we protect such precious organs? The eye is protected by the orbital bone which creates the eye socket and is also cushioned by a layer of fat surrounding most of the eye.
Accessories of the Eyes
Accessories of the Eyes
- eyelids and eyelashes - glands on the edge of the lid (tarsal gland) and between the eyelashes (ciliary glands) produce an oily secretion that lubricates the eye
- conjunctiva - membrane lining the eyelids and connecting to the outer surface of the eye secrete mucus to lubricate the eye and keep it moist
- lacrimal apparatus (lacrimal gland & ducts) - produce lacrimal fluid & empties/drains fluid from eyes
- extrinsic eye muscles - 6 muscles attached to outer surface of the eye that produce movements
Pathway of Light Through the Eye
- Light must be focused to a point on the retina for optimal vision
- Light is refracted (bent) by the cornea, aqueous humor, lens, and vitreous humor
- The eye is set for distance vision (over 20 feet away) - the lens must change shape to focus on closer objects
- The image formed on the retina is: reversed, upside down and smaller than the original object.
The optic chiasma is where the optic nerves from each eye cross each other. Fibers from the medial side of each eye cross over to the opposite side of the brain. The fibers continue through the optic tracts (containing fibers from both eyes) allow for overlap of the visual fields, giving us depth perception. The signal ends up in the visual cortex of the brain in the occipital lobe. |
Sensory Layer
Rods are found towards the edges of the retina and allow vision in dim light and in peripheral vision.
Cones allow for detailed color vision and are densest in the center of the retina.
Rods are found towards the edges of the retina and allow vision in dim light and in peripheral vision.
Cones allow for detailed color vision and are densest in the center of the retina.
Hearing & Equilibrium
The ears are responsible for two senses: hearing and equilibrium. The receptors used for both are mechanoreceptors, which means they respond to mechanical touch or distortion.
The ear is divided into 3 areas: The external ear, middle ear and inner ear (bony labyrinth).
The ear is divided into 3 areas: The external ear, middle ear and inner ear (bony labyrinth).
- The pinna (outer ear) collects sound waves moving through the air and directs them to the eardrum.
- The tympanic membrane (eardrum) vibrates with sound.
- Sound vibrations move from the eardrum, get amplified as they move through through the auditory ossicles (bones in the middle ear) to the oval window of the cochlea.
- Sound vibrations cause the fluid and tiny hair cells inside the cochlea to move.
- Hair cell movement creates neural signals, which are picked up by the auditory nerve.
- The auditory nerve sends signals to the brain, where they are interpreted in the temporal lobe as sound and speech. Continuous stimulation can lead to sensory adaptation.
Noise-Induced Hearing Loss
Sounds that are too loud, especially too loud and long-lasting can damage sensitive structures in the inner ear causing Noise-Induced Hearing Loss (NIHL). Noise above 85 decibels can cause permanent hearing loss. Read what the National Institutes of Health has to say. |
Can earbuds really cause permanent hearing loss? YES!
How do earbuds damage the ear?If you're using earbuds and people around you can hear your music,
_ it's loud enough to be causing permanent hearing loss! |
Balance
Your sense of balance, or equilibrium actually requires coordination of input from your eyes, sense of touch and the vestibular system of the inner ear.
The vestibule and 3 semicircular canals (each in a different plane) are filled with fluid and hair-like structures that get distorted as the fluid moves in response to the position of your head. These signals are processed in the brain along with input from the eyes and sense of touch - if there is conflicting input, you may experience motion sickness. |