Question

the nervous system is important for the survival of animals. it allows quick responses to danger. sometimes the reaction to danger is faster than the understanding of what exactly the danger is; loud noise can make a person jump even if there is no danger. this fast response is the result of neurons in reflex arcs. the picture below shows the major parts of a reflex arc.
describe what is happening in the nervous system from the time the receptor receives information to the time movement occurs. be sure to include the following points in your answer.

1. the source of the nerve impulses in a reflex arc
2. the pathway of the nerve impulses in a reflex arc
3. the end result of the stimulation of a reflex arc

Explanation:

1. Source of nerve impulse: The stimulus (e.g., heat from a candle touching skin) activates sensory receptors in the body, which generate the initial nerve impulse.
2. Pathway of nerve impulses: The impulse travels from the sensory receptor along a sensory neuron to the spinal cord (central nervous system). In the spinal cord, it synapses with an interneuron (or directly with a motor neuron in some reflexes), then travels along a motor neuron to the target muscle/gland.
3. End result of stimulation: The motor neuron triggers the effector (muscle or gland) to produce an immediate, involuntary response (e.g., pulling the hand away from the hot candle) to protect the body, while a signal is also sent to the brain to register the sensation after the reflex action.

Answer:

1. The source of the nerve impulse is a stimulus (e.g., heat from the candle) detected by sensory receptors in the body.
2. The pathway is: Sensory receptor → Sensory neuron → Spinal cord (interneuron synapse) → Motor neuron → Effector (muscle/gland).
3. The end result is an immediate, involuntary protective response (e.g., withdrawing the hand) to avoid harm, with the brain processing the sensation after the reflex occurs.