The Nervous System
Section 35-4: The Senses
The Senses
• Sensory Receptors: neurons that react to
specific stimuli such as light or sound by sending
impulses to other neurons and eventually to the
central nervous system.
• Sense organs:
• Eyes (Sense of Vision)
• Ears (Sense of Hearing and Equilibrium)
• Nose (Sense of Smell aka Olfactory)
• Mouth (Sense of Taste aka Gustatory)
• Skin (Sense of Touch)
Sensory Receptors
• 5 general categories:
• Pain Receptors
• Throughout body except the brain.
• Responds to tissue damage.
• Thermoreceptors
• Located in skin, body core, and hypothalamus.
• Responds to changes in temperatures
• Mechanoreceptors
• Found in skin, skeletal muscles, and inner ears.
• Responds to movement and pressure
• Chemoreceptors
• Found in nose and tongue
• Responds to chemical changes
• Photoreceptors
• Found in the eyes
• Responds to light
Vision: Parts of the Eye
• Pupil
• Small opening where light enters
• Size adjusted by the iris
• Lens
• Structure that adjusts the focus
• Retina
• Inner layer of the eye containing photoreceptors
• Rods
• Photoreceptors that are sensitive to light
• Detects black and white
• Cones
• Photoreceptors that detect color
• Concentrated in the fovea
• Fovea
• Area on the retina where vision is sharpest
Vision
• Light enters the eye through the pupil and focused at the
fovea of the retina
• Photoreceptors (rods and cones) receive the light
• Impulses are sent to the brain where they are interpreted as
visual images
Ear
• Has two functions
• Hearing
• Balance
Hearing
1. Sound vibrations enter the outer ear through the auditory
canal
2. Vibrations cause the eardrum to vibrate
3. Vibrations are picked up by the middle ear bones – hammer,
anvil, and stirrup
4. Vibrations transmitted to the cochlea found in the inner ear
5. Cochlea contains receptors, hair cells, that receive these
vibrations
6. Impulses are sent to the brain where the vibrations are
translated as sound
Balance (Equilibrium)
• Found in the inner ears above the cochlea
• Semicircular Canals
• Monitor the position of your body in relation to
gravity
• Contain hair cells
• Movement of hair cells when you move your body
sends impulses to the brain to determine motion
and position (cerebellum) and maintain balance
Smell and Taste
• Detects chemicals
• Chemoreceptors
• Chemoreceptors for
the tongue are called
Taste Buds
Touch and Related Senses
• Skin
• Contains receptors
that respond to
temperature, touch,
and pain
• Not all parts are
equally sensitive
• Greatest density
found in fingers,
toes, and face
Exit Slip
• 35-4 Section Assessment #1-5
• Page 909
• For #5, feel free to perform the demonstration in class 