Spinal Cord

Similar to the brain, the neural tissue of the spinal cord consists of grey and white matter. The grey matter comprises the center of the cord and is surrounded by the white matter. The grey matter contains the motor neurons that innervate the extremities while the white matter neural fibers receive motor and sensory input from the trunk and extremities. Projections within the grey matter are called horns, these are arranged in pairs and named according to the direction in which they project, they are either dorsal horns (posterior) or ventral horns (anterior). The anterior or ventral horns contain the cell bodies of the motor neurons that pass through the spinal cord; injuries to these structures cause paralysis. The dorsal or posterior horns contain sensory fibers and cells; damage to these nerves results in loss of sensation. Damage of the white matter disrupts both sensory and motor function below the level of injury. There are two prominent enlargements in the cord, one, the cervical enlargement is located between the third cervical and the second thoracic vertebrae. Spinal nerves arising from this enlargement form the brachial plexus from which the peripheral nerves of the upper extremity are formed. These nerves control sensory and motor functions of the arms. A lower similar enlargement lying between the ninth and twelfth thoracic segment of the spine gives rise to spinal nerves that form the sacral and lumbar plexus from which peripheral nerves form to innervate the lower extremities

The cord is divided into left and right portions by two grooves that run the length of the cord; these are the anterior median fissure and posterior median sulcus. The terminal portion of the spinal cord ends at L1 and is called the conus medullaris. Fibrous nerve strands extend from the conus medullaris to the coccyx, these nerves are referred to collectively as the cauda equina. Like the brain, the spinal cord is covered by three meninges (dura mater, arachnoid membrane and pia mater) and is cushioned by cerebrospinal fluid