The Nervous System

• The nervous system consists of two parts: the central nervous system (CNS) which includes the brain and the spinal cord, and other nerves running to and from the central nervous system
• Automatic control systems involved in homeostasis have a stimulus, a receptor, a Coordination Center, an effector, and a response
• Receptors detect a stimulus and send electrical impulses down neurons to the central nervous system
• The central nervous system acts as the Coordination Center and sends electrical impulses down other neurons to effectors
• Effectors, usually muscles or glands, bring about a response such as muscle contraction or hormone secretion
• The nervous system enables humans to react to their surroundings and coordinate their behavior
• The reflex arc is a key part of homeostasis and involves several stages
• When touching a hot object, the stimulus (heat) is detected by a receptor in the skin
• An electrical impulse is passed from the receptor along a sensory neuron to the central nervous system
• At the end of the sensory neuron, a chemical is released at a synapse and diffuses across to a relay neuron in the central nervous system
• The chemical triggers an electrical impulse in the relay neuron, which then passes across to another synapse
• Another chemical is released at the synapse, triggering an electrical impulse in a motor neuron
• The electrical impulse passes down the motor neuron to an effector, such as a muscle, which contracts to move the hand away from the heat
• The response of pulling the hand away from the heat is automatic and rapid, as reflexes do not involve decision-making by the conscious part of the brain
• Reflexes help to protect us from danger by allowing quick responses without conscious thought