Study Notes on Stimuli and Responses in Humans and Plants
Vital Systems and Responses
Survival depends on the ability to detect and respond to stimuli.
Human Nervous System:
Central Nervous System (CNS): Comprised of the brain and spinal cord.
Peripheral Nervous System (PNS): Nerves connecting the CNS to sensory organs and muscles.
Functions: Interprets sensory impulses and coordinates movement. A reaction time faster than seconds in sprinting is considered a false start.
Human Actions
Voluntary: Controlled, conscious actions like reading or walking.
Involuntary: Automatic actions without conscious control.
Reflex Actions: Instantaneous responses (e.g., hand withdrawal) involving the spinal cord.
Automatic Actions: Vital functions (e.g., heartbeat, breathing) controlled by the medulla oblongata.
Sensory Organs
Eyes: The cornea and lens focus light onto the retina, which contains rod cells (sensitive to light intensity) and cone cells (sensitive to colors).
Ears: The cochlea converts sound vibrations into nerve impulses for the brain to interpret.
Skin: Contains specialized receptors for pain, pressure, touch, heat, and cold.
Tongue: Detects five primary tastes: sweet, salty, sour, bitter, and umami.
Plant Responses
Phototropism: Growth toward light sources.
Geotropism: Roots grow toward gravity (positive) while shoots grow against it (negative).
Hydrotropism: Roots grow toward water.
Nastic Movement: Rapid response independent of the stimulus direction, such as a Mimosa plant folding its leaves.
Sensory Limitations
Visual: Includes optical illusions and the blind spot where no photoreceptors exist.
Auditory: The human hearing range is approximately to , which can decrease with age.