1. From the simple nerve nets to the nervous system of humans, nervous systems have developed. 2. The endocrine system

) that receive signals and transmit them to the cell body.
8. The cell body contains the nucleus, which houses the genetic material necessary for proper functioning of the neuron.
9. From the cell body, a long fiber called the axon extends to transmit signals to other neurons or to target cells.
10. Axons can be covered by a protective layer called the myelin sheath, which helps to enhance the speed of signal transmission.
11. At the end of an axon, there are small branches called axon terminals that release chemicals called neurotransmitters to communicate with other neurons or target cells.
12. The nervous system can be divided into two major parts: the central nervous system (CNS) and the peripheral nervous system (PNS).
13. The central nervous system consists of the brain and spinal cord, which are responsible for processing and integrating information.
14. The peripheral nervous system includes all the nerves that extend from the CNS to the rest of the body.
15. The peripheral nervous system can be further divided into the somatic nervous system and the autonomic nervous system.
16. The somatic nervous system controls voluntary movements and transmits information from the senses to the CNS.
17. The autonomic nervous system controls involuntary actions, such as heartbeat and digestion, and can be further divided into the sympathetic and parasympathetic divisions.
18. The sympathetic division is responsible for the fight-or-flight response, preparing the body for action in times of stress or danger.
19. The parasympathetic division is responsible for the rest-and-digest response, promoting relaxation and proper organ function.
20. The endocrine system consists of various glands that secrete hormones into the bloodstream to regulate bodily functions and maintain homeostasis.