Question

Arrange the following events in the proper sequence:

Answer 1

Answer:

Proper sequence of events:

5. Sensory receptor detects change in the environment.

2. Afferent neuron graded potential reaches threshold and fires an action potential.  

4. CNS reaches decision about response.  

1. Efferent neuron graded potential reaches threshold and fires an action potential.  

3. Target organ responds.  

Explanation:

Sensorial information is received by the peripheral nervous system and processed by the central nervous system. There are three types of neurons involved in this transmission: sensory or efferent neurons, interneurons, and motor or efferent neurons. First stimulus energy is received by sensory receptors specialized in responding to different stimuli.  Then it occurs the transduction or conversion of the stimulus energy (chemical, temperature, light, pressure, etc.) to action potential energy. The afferent neurons, located in dermis and epidermis, receive information from the sensory receptors, react to stimuli and transmit impulses to the central nervous system. This pathway is defined as the ascending pathway. Information is processed in the central nervous system by the interneurons which handle many sensory signals, evaluate them, compare them and use them for decision making. After that, an efferent neuron is stimulated to carry signals from the central nervous system to the effectors' cells of the target organ. The effector may be muscle or glandular tissue. This pathway is defined as the descending pathway. Finally, the target organ responds by contracting or hormone-releasing.