The<unk>  is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. It encloses the central canal of the<unk> , which contains cerebrospinal fluid. The brain and<unk>  together make up the central nervous system (CNS). In humans, the<unk>  begins at the occipital bone, passing through the foramen magnum and entering the<unk>  canal at the beginning of the cervical vertebrae. The<unk>  extends down to between the first and second lumbar vertebrae, where it ends. The enclosing bony vertebral column protects the relatively shorter<unk> . It is around long in adult men and around long in adult women. The diameter of the<unk>  ranges from in the cervical and lumbar regions to in the thoracic area. The<unk>  functions primarily in the transmission of nerve signals from the motor cortex to the body, and from the afferent fibers of the sensory neurons to the sensory cortex. It is also a center for coordinating many reflexes and contains reflex arcs that can independently control reflexes. It is also the location of groups of<unk>  interneurons that make up the neural circuits known as central pattern generators. These circuits are responsible for controlling motor instructions for rhythmic movements such as walking.
Spinal cord
Brainstem
Retina
Forebrain
Hindbrain
Brain
Central nervous system
Sensory cortex