Structure and Function of the Human Nervous System

The human nervous system regulates internal conditions and responds to environmental stimuli through homeostasis. Key components include:

• Receptors that detect changes in internal or external conditions
• Coordination centers like the brain and spinal cord that process information
• Effectors such as muscles and glands that produce responses

The nervous system consists of specialized cells called neurons adapted for transmitting electrical impulses:

• Sensory neurons carry signals from receptors to the central nervous system
• Motor neurons transmit signals from the CNS to effectors
• Relay neurons in the spinal cord connect sensory and motor neurons

Definition: The central nervous system (CNS) is the main coordination center that receives sensory information and coordinates responses.

Synapses connect neurons and allow signals to be passed through chemical neurotransmitters. The basic pathway is:

Stimulus → Receptor → Coordinator → Effector → Response

Highlight: Neurons have key adaptations like long axons insulated by myelin sheaths to rapidly transmit signals over long distances.

Reflex arcs provide rapid, automatic responses to reduce injury risk without conscious thought. The steps in a reflex arc are:

1. Receptors detect a stimulus
2. Sensory neurons send signals to relay neurons in the spinal cord
3. Motor neurons transmit signals to an effector
4. The effector (e.g. muscle) produces a response

Example: Quickly pulling your hand away from a hot surface is an example of a reflex action.