Concept: The nervous system is a complex network of nerves and cells that transmit signals between different parts of the body. It is responsible for coordinating actions and sensory information. Step 1: Main components of the Nervous System
The nervous system is broadly divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
Central Nervous System (CNS): Consists of the brain and the spinal cord. It is the primary control center.
Peripheral Nervous System (PNS): Consists of nerves and ganglia outside the brain and spinal cord. These nerves connect the CNS to the limbs and organs.
Neurons (Nerve Cells): These are the basic functional units of the nervous system. A neuron typically consists of a cell body (soma), dendrites (branch-like structures that receive signals), and an axon (a long projection that transmits signals). Step 2: Analyzing the options
(1) Brain: The brain is the main control center of the nervous system, part of the CNS. So, it {is} part of the nervous system.
(2) Spinal cord (assuming "Spiral cord" is a typo for Spinal cord): The spinal cord is a long, tubular bundle of nervous tissue that extends from the brainstem to the lumbar region of the vertebral column. It is a major component of the CNS, transmitting nerve signals between the brain and the rest of the body. So, it {is} part of the nervous system.
(3) Tendon: A tendon is a tough, fibrous connective tissue that connects muscle to bone. Tendons are part of the musculoskeletal system, transmitting the mechanical force of muscle contraction to the bones, causing movement. They are not part of the nervous system.
(4) Dendrite: Dendrites are branched protoplasmic extensions of a nerve cell (neuron) that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project. They are integral parts of neurons and thus part of the nervous system. Step 3: Identifying the structure that is not part of the nervous system
Based on the analysis, a Tendon is part of the musculoskeletal system, not the nervous system.