Correct Option
The correct option is 1 and 3 only.
Explanation
Nervous coordination in animals relies on the transmission of electrical signals, known as nerve impulses or action potentials. While this mode of communication is extremely rapid, it operates under specific physiological limitations regarding tissue connectivity and the cellular mechanism of impulse generation.
Statement-wise Analysis
- Statement 1 is Correct: Electrical impulses travel along specific pathways defined by neurons. Unlike chemical signals (hormones), which are transported by the blood and can reach almost every cell in the body, electrical impulses are restricted. They can only reach those cells that are directly connected by nervous tissue.
- Statement 2 is Incorrect: A cell cannot transmit impulses continuously without interruption. After an impulse is generated and transmitted, the cell requires a brief recovery time to reset its ion gradients and restore its resting potential. This interval is scientifically known as the refractory period. During this time, a new impulse cannot be generated.
- Statement 3 is Correct: The generation and propagation of an electrical impulse are driven by the movement of ions across the cell membrane. Specifically, the rapid influx of sodium ions ($Na^+$) and the subsequent efflux of potassium ions ($K^+$) through ion channels cause the changes in membrane potential that constitute the impulse.
Key Takeaway
Key Takeaway: Electrical communication in the nervous system is fast but limited by physical connectivity and the need for a refractory (reset) period, whereas chemical communication (hormones) is slower but can reach non-innervated cells.