the senses
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The Senses. Chapter 35.4. Sensory Receptors. Sensory receptors react to specific stimuli Stimuli include light, sound, motion, chemicals, pressure, and changes in temperature. Sensory Receptors. - PowerPoint PPT PresentationTRANSCRIPT
The SensesChapter 35.4
Sensory Receptors
• Sensory receptors react to specific stimuli
– Stimuli include light, sound, motion, chemicals, pressure, and changes in temperature
Sensory Receptors
• Each sensory receptor reacts to a specific stimulus by sending impulses to other neurons, and eventually to the central nervous system (CNS)
Most sensory receptors are found in sense organs
ex. eyes, inner ear, nose, mouth, and skin
Categories of Sensory Receptors
• There are five major categories of sensory receptors:
1. pain receptors
2. thermoreceptors
3. mechanoreceptors
4. chemoreceptors
5. photoreceptors
Categories of Sensory Receptors
• Pain receptors– Found all over the body EXCEPT in the brain
Respond to chemicals released by damaged cells
• Thermoreceptors– Located in the skin, body core, and hypothalamus
Detect variations in temperature
• Mechanoreceptors– Found in the skin, skeletal muscles, and inner ear
Sensitive to touch, pressure, stretching of muscles, sound, and motion
Categories of Sensory Receptors• Chemoreceptors
– Located in the nose and taste budsSensitive to chemicals in the external environment
• Photoreceptors– Located in the eyes
Sensitive to light
Vision
• Light enters through the cornea (a tough transparent layer of cells)cornea helps focus light
• Light passes through a chamber filled with a liquid called aqueous humor
• At the back of the chamber is the irisiris is the colored part of eye
Vision
• In the middle of the iris is the pupil (small opening) Regulates the amount of light that enters the
eye
• Behind the iris is the lens Changes shape to help adjust the eye’s
focus to see near or distant objects– controlled by muscles
Vision
• Behind the lens is a chamber filled with vitreous humor (a transparent, jelly-like fluid)
• Light is focused on retina– Photoreceptors found here– Converts light to nerve impulses which are
then carried to the CNS
The Retina
• Two types of photoreceptors found on the retina:– Rods
very sensitive to light but not to colors
– Cones
not as sensitive to light but responds to light of different colors, producing color vision
Retina• Cones are concentrated in
the foveafovea = site of sharpest
vision
• A blind spot is a spot on the retina where no photoreceptors existblind spot = where optic
nerve passes through back of eye
Choroid
Retina
Blood vessels
Optic nerve
Fovea
Vitreous humor
Sclera
Ligaments
Iris
Pupil
Cornea
Aqueous humor
Lens
Muscle
Section 35-4
Figure 35-14 The Eye
Question
• If a tree falls in the woods and no one is there to hear, does it make a sound?
Auditory canal
Tympanum Round window Eustachian tube
Bone
Cochlea
Cochlear nerve
Semicircular canals
Oval window
StirrupAnvilHammer
Section 35-4
Figure 35-15 The Ear
Hearing• Sound is vibrations in the air
– The ear distinguishes the pitch and loudness of the vibrations
• Vibrations enter the ear through the auditory canal– These vibrations hit the tympanum (eardrum)
Hearing
• The vibrations picked up by the tympanum are transferred to three boneshammer, anvil, stirrup
• These are the smallest bones in the body
• The stirrup transmits the vibrations to the oval window
• When the oval window vibrates, it creates pressure waves in the cochlea
Cochlea
• The cochlea is fluid-filled and lined with tiny hairs– The pressure waves
produced by the oval window push the hairs back and forth
– This hair movement produces a nerve impulse that is transmitted through the cochlear nerve to the CNS
Balance
• Semicircular canals, and two tiny sacs behind them, monitor the position of your body, especially your head, in relation to gravity
• Each canal and sac is filled with fluid and hair– As your head changes position, the fluid moves causing the
hair to bend– The CNS receives a nerve impulse to determine body motion
and position
Smell and Taste
• The senses of smell and taste are a result of chemoreceptors sending nerve impulses in response to chemicals in the environment
– Smell ability of chemoreceptors lining the nasal passageway to respond to chemicals
– Taste ability of taste buds to detect chemicals• Taste buds are broken into categories: salty, bitter, sweet,
and sour• The tongue’s sensitivity to each varies by region
Touch
• It is a unique sense in that the nerves are not found in one particular region of the bodyall regions of skin are sensitive to touch– It responds to temperature, pressure, and pain
• Different body parts have different concentrations of nervesmore touch receptors found on fingers, toes, and face
Cerebral cortex
Nasal cavity
Taste bud
Smell sensory area
Tastesensory area
Thalamus
Olfactory(smell) bulb
Olfactorynerve
Smell receptor
Taste pore
Taste receptor
Sensorynerve fibers
Section 35-4
The Senses of Smell and Taste