The spinal cord is the pathway for sensory impulses to the brain and motor impulses from the brain. Anatomically, it is an ovoid column of nerve tissue that extends from the medulla oblongata to the second lumbar vertebra. It is completely encased by the spinal column. The centre of the cord, in the shape of the letter 'H', is grey matter that consists of cell bodies and the dendrites of neurons; the anterior horns of the grey matter contain somatic motor neurons whilst the posterior horns contain cell bodies of interneurons. The grey matter is surrounded by white matter that consists of myelinated axons that transmit information to and from the brain, between levels of grey matter or out to the body.