Reflex Arcs and the Human Brain

Study Notes

Reflex arcs bypass conscious thought allowing for rapid automatic responses to stimuli
The reflex arc is a direct neural connection between sensory neurons, which detect stimuli, and motor neurons, which control muscle movement
The connection occurs in the spinal cord, where nerves from the entire body converge
Reflex arcs ensure quicker reaction times
Reflex arcs exist in animals because the brain's processing speed is often inadequate for swift responses

The brain is the central coordinating system in the body for complex thought processes, movement, and sensation
The brain receives signals through nerve impulses from all areas of the body
It integrates information to form conscious decisions and responds to stimuli
The brain also sends signals via nerve impulses to muscles, causing voluntary movements like writing, talking, or moving objects
The brain and spinal cord form the central nervous system

Plants lack a nervous system and muscles but still exhibit responses to stimuli
Plants respond to stimuli through growth-related movements, such as bending towards light
The most noticeable example is the sensitive plant, Mimosa pudica, which folds its leaves rapidly as a response to touch
Plants exhibit tropism, which is directional growth in response to external stimuli
Phototropism is a growth response towards light, which helps the plant maximize sunlight absorption for photosynthesis
Geotropism is a growth response to gravity, where the roots grow downwards and shoots upwards in response to gravitational pull.
Hydrotropism is growth toward a water source and chemotropism is growth toward chemicals.

Animals, like plants, have hormones that regulate growth and other bodily functions
Hormones are chemical messengers produced by endocrine glands and released directly into the bloodstream
These hormones act on target organs or tissues, eliciting specific physiological responses
Adrenaline is a hormone that prepares the body for "fight or flight" response
Adrenaline increases heart rate, respiration, and blood flow to muscles, diverting blood from the digestive system and skin
The endocrine system is a critical part of control and coordination in animal bodies.
Hormone imbalances can have a significant effect on growth and development.

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