Summary
Highlights
The nervous system has three basic functions: sensory (receiving stimuli internally and externally), integrative (processing information, making decisions, and storing memories), and motor (sending responses like muscle contraction or glandular secretion).
When touching a hot object, the nervous system first senses the heat, then integrates this information in the brain, which then elaborates a motor response to quickly withdraw the hand.
Anatomically, the nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS, located centrally, is composed of the encephalon (brain) and spinal cord. It is responsible for complex tasks like integrating sensory information, generating thoughts and emotions, and forming memories. Most motor commands originate here.
The PNS connects the CNS to sensory receptors, muscles, and glands in the periphery of the body. It consists of cranial nerves (emerging from the brain) and spinal nerves (emerging from the spinal cord), which conduct nerve impulses to and from the CNS. Afferent neurons carry information to the CNS, while efferent neurons carry information away from it. Interneurons within the CNS connect sensory and motor neurons.
The PNS further subdivides into the somatic nervous system (SNS), which controls voluntary reactions by sending information to skeletal muscles, and the autonomic nervous system (ANS), which controls involuntary functions like smooth muscle, cardiac muscle, and glands.
The ANS is divided into the sympathetic and parasympathetic nervous systems, which generally have opposing actions. The sympathetic system is active during stress (e.g., increasing heart rate, dilating bronchi for 'fight or flight' responses). The parasympathetic system is active during calm situations (e.g., controlling digestive functions, decreasing heart rate).
In summary, the nervous system's main functions are sensory, integrative, and motor. Anatomically, it's divided into the CNS (encephalon and spinal cord for complex functions) and PNS (cranial and spinal nerves transmitting impulses). The PNS includes the somatic system (voluntary actions) and the autonomic system (involuntary actions), with the autonomic system further split into sympathetic (stress responses) and parasympathetic (calm states).