Act 20: Vertebrates Nervous and Endocrine System

• nervous system originated in a fundamental property of life: irritability.
• relatively rapid communication system, called the neural mechanisms.
• relatively less rapid mechanism or long-term adjustments in animals, called the hormonal mechanism (endocrine system).
• nervous systems of animals are of three types: nerve nets, ganglionic,

  and centralized nervous systems.
• Nerve nets, found in cnidarians, are diffused nerves along the body.
• Ganglionic nervous system consists of a series of ganglia (masses of nerve cell bodies) running the length of the body and connected by dorsal nerve cords
• The centralized nervous system of vertebrates consists of a central nervous system (CNS) (brain and spinal cord), and the peripheral nervous system (PNS) (cranial nerves and spinal nerves).
• The peripheral nervous system can be divided into afferent division (sensory) and efferent division (motor).
• neuron or the nerve cell is the basic functional unit of the nervous system.
• Receptors function to convert external and internal environmental stimuli into nerve signals, which are carried by afferent neurons into the central nervous system.
• Nerve signals also move to efferent neurons, which carry them via the peripheral nervous system to effectors.
• Dendrites carry impulses toward the cell body
• axons carry the impulses away from the cell body.
• Many neurons work in groups called reflex arc, a fundamental unit of neural operation, or the simplest functional unit of the nervous system capable of detecting a specific stimulus and causing a response to that stimulus.
• Hormones are chemical compounds released into the blood in

  small amounts and transported by the circulatory system through the body to a distant target cells or organs, where they initiate physiological responses. The