Chapter 6: Control and Coordination
Control and Coordination in Animals
Animals respond to their environment using two main systems: the nervous system and the endocrine system. The nervous system uses neurons to transmit electrical impulses. These impulses help detect stimuli and trigger appropriate responses—like reflex actions that occur instantly through reflex arcs in the spinal cord without involving conscious thought. The brain is the control center and is divided into the forebrain (thinking, sensory processing), midbrain (involuntary actions), and hindbrain (balance, posture, vital functions). Muscles carry out actions when triggered by nerve impulses, changing shape using special proteins. The spinal cord and brain are protected by the vertebral column and skull, with cushioning provided by fluid-filled membranes.
Coordination in Plants
Plants do not have a nervous system, but they still respond to stimuli. These responses are either rapid and independent of growth (like the folding of Mimosa leaves) or slow and growth-based (like bending towards light or roots growing downwards). These movements, called tropisms, include phototropism, geotropism, hydrotropism, and chemotropism. Information is communicated chemically using plant hormones such as auxins (promote growth), gibberellins (stimulate stem growth), cytokinins (promote cell division), and abscisic acid (inhibits growth and causes leaf fall).
Hormones in Animals
Animals use hormones as chemical messengers for regulation and long-term coordination. Glands like the pituitary, thyroid, adrenal, pancreas, testes, and ovaries release specific hormones into the blood. For example, insulin (from the pancreas) regulates blood sugar, thyroxine (from the thyroid) manages metabolism, and adrenaline (from adrenal glands) prepares the body for emergency actions. Growth hormone controls body development, while testosterone and estrogen govern sexual maturity. Hormone secretion is tightly controlled through feedback mechanisms to maintain balance in the body.