Spinal Cord

The spinal cord is a part of the Vertebrate Central Nervous System that is enclosed in and protected by the Vertebral Column (it passes through the Spinal Canal ). It consists of Nerve Cells . The cord conveys the 31 Spinal Nerve pairs of the Peripheral Nervous System , as well as Central Nervous System pathways that innervate Skeletal Muscle s.

The vertebral column consists of , thoracic, and lumbar vertebrae, and the Sacrum and Coccyx .

INJURY

Spinal cord injuries are caused by damage to the spinal cord, such as falling on the neck or back, or having the spinal cord moved or disrupted in another way. The vertebral bones or Intervertebral Disk s can shatter, causing the spinal cord to be punctured by a sharp fragment of bone. Usually victims of spinal cord injuries will suffer loss of feeling in certain parts of their body. In good cases a victim might only suffer loss of hand or foot function. More severe injury may result in Paraplegia , Tetraplegia , or full body Paralysis below the site of injury to the spinal cord.

The two most common areas of the spinal cord most injured are the Cervical spine (C1-C7) and the Lumbar Spine (L1-L5). The lumbar region of the spine is connected to the ribs.

EMBRYOLOGY

In the human Fetus , the spinal cord extends all the way down to the Sacral Vertebrae . As a person matures, the rest of the body grows faster than the spinal cord, so that adulthood, the spinal cord reaches only to the level of the first or second lumbar vertebrae. Below this level, there is no spinal cord, only Spinal Nerve s that form the Cauda Equina .

ANATOMY

The spinal cord originates inside the Brain at the inferior end of the Medulla Oblongata , exiting the Skull via the Foramen Magnum . It is wrapped in three layers of membranes, called Meninges .

The spinal cord carries Sensory signals and Motor innervation to most of the Skeletal Muscle s in the body. Just about every Voluntary Muscle in the body below the head depends on the spinal cord for control. Similarly, most cutaneous sensation below the neck is transmitted via the spinal cord. Most of the Sympathetic Pathway s and the lower (i.e. non- Vagal ) Parasympathetic Pathway s also go through the spinal cord.

A cross-section through the spinal cord reveals that there is a Central Canal that carries Cerebrospinal Fluid (CSF) surrounded by Grey Matter on the inside, and this is surrounded by White Matter . (This is the opposite to the Brain 's Cerebral Cortex .) A section of the cord can be divided into neat symmeterical halves by the dorsal median sulcus and ventral median fissure.

The dorsal (towards the back) side of the spinal cord carries sensory information. The neurons that bring somatosensory information to the spinal cord reside in the Dorsal Root Ganglion . Sensation from the lower body travels up the ''gracile tract'', while sensation from the upper body and arms travels up the ''cuneate tract'', which lies lateral to the gracile tract. There is no cuneate tract in the lumbar part of the spinal cord as sensory information from the arms does not travel through this area.

Motor information (signals coming from the brain to move the muscles) travels down the ventral (toward the front) half of the spinal cord. Motor Neuron s are located in the anterior (this means close to the front, in humans it means the same as ventral) horn of the grey matter. There are two main columns of neurons in the anterior horn, the ''medial'' and ''lateral motor columns''.

The spinal cord proper ends at the level of L1. It terminates at a conical point known as the Conus Medullaris , from which the pia mater extends caudally as the ''filum terminale'' and attaches to the dorsal surface of the first cocygeal vertebra. After the termination of the cord, the spinal nerves continue as dangling nerves called the Cauda Equina (literally "horse's tail").

The actual cord is approxiamately Cylindrical in shape, but the diameter varies at different vetebral levels. There are two enlargements, cervical and lumbar. The ''cervical enlargement'' is due to the cord segments from C5 to T1 which innervates the upper limb via the Brachial Plexus . The '' Lumbar enlargement'' arise from segments L1 to S3 (only the region around L1/L2 is part of the spinal cord proper) and innervates the lower limbs via the Lumbar and Sacral plexi.

There is a higher proportion of white matter in the Cervical (neck) part of the spinal cord. This is because information to and from the whole body (such as the feet) must pass through here. In contrast, the lumbar and sacral areas do not carry information from anywhere above them, so have less white matter.

PATHOLOGY

EXTERNAL LINKS

Nerve Structures of the Spine

Information About

Spinal Cord