1. Stimulus: A change in the internal or external environment that triggers a response. Examples include:
* External: Light, sound, touch, temperature change
* Internal: Changes in blood sugar, pressure, or chemical levels
2. Receptor: A specialized cell or group of cells that detects the stimulus. Examples include:
* Photoreceptors in the eyes for light
* Mechanoreceptors in the skin for touch
* Chemoreceptors in the nose and tongue for smell and taste
3. Sensory Neuron: A nerve cell that carries the signal from the receptor to the central nervous system (CNS), which is the brain and spinal cord.
4. Integration Center: In the CNS, the signal is processed and a decision is made about how to respond. This often involves:
* Synapses: Junctions where the sensory neuron communicates with other neurons.
* Interneurons: Neurons within the CNS that help process the information.
5. Motor Neuron: A nerve cell that carries the signal from the CNS to the effector.
6. Effector: A muscle, gland, or other organ that carries out the response. Examples include:
* Muscles: Contract to move the body
* Glands: Secrete hormones or other substances
Example:
* Stimulus: Stepping on a sharp object.
* Receptor: Pain receptors in the foot.
* Sensory Neuron: Carries the pain signal to the spinal cord.
* Integration Center: The spinal cord processes the signal and triggers a reflex.
* Motor Neuron: Carries a signal from the spinal cord to the leg muscles.
* Effector: The leg muscles contract, causing the foot to withdraw from the sharp object.
Types of Reflex Arcs:
* Spinal Reflexes: These bypass the brain and are processed entirely within the spinal cord.
* Cranial Reflexes: These involve the brain in processing the signal.
Key Features of Reflex Arcs:
* Rapid: Reflexes are fast, often involuntary responses.
* Automatic: They don't require conscious thought.
* Protective: They help us avoid harm.
Understanding the reflex arc helps us understand how our bodies respond to stimuli and how our nervous system works.
