Intro to the Spinal Cord

Macroanatomy

First off, let’s get the terminology straight.  The spinal cordThe central nervous system structure that relays signals between the brain and body. is the thing composed of nervous tissue that is enclosed in the vertebral column.  The vertebral column is a series of vertebrae that enclose the spinal cord.  The spinal column is a hybrid between spinal cord and vertebral column and is not a good term to use.  Ever. 

Your vertebral column begins at the foramen magnumLarge hole at base of skull for spinal cord to pass through., which is the large hole in the skull. It extends to the second lumbar vertebra. This vertebra is actually a little bit higher than you may think it’s going to be. The tapered end of the spinal cord is called the conus medullaris.  A small string of connective tissue connects the conus medullaris to the sacrumTriangular bone formed by fusion of five vertebrae; connects spine to pelvis.. This string is called the filum terminale. As you grow in utero the length of your body does not grow in proportion to the spinal cord. The spinal cord lags behind the lengthening body. The spinal cord can’t keep up. As a result, the nerves start to grow out of the cauda equinaA bundle of nerve roots extending from the lower spinal cord, resembling a horse’s tail.. They do this to meet the growthAn increase in size and number of cells. demand.  These nerves leaving from the conus medullaris create a horse-tail appearance, leading to their name. 

I’ve included this vertebra here to remind you. The spinal cord is the structure that is in the vertebral foramenCentral hole in each vertebra where the spinal cord passes through.. The vertebral foramen is the big hole in the center of the vertebrae.  Remember that the vertebrae all stack together and the spinal cord is threaded through these holes.

Spinal Enlargements

There are two places along the spinal cord where it is enlarged.  This occurs in the cervical and in the lumbar regions.  These enlargements reflect the amount of peripheral tissue. The nerves serve this tissue in that area of the spinal cord.  Nerves in the enlargements serve the limbs. 

If we were to take transverse sections of the spinal cord at different levels, we would observe varying proportions of gray matterThe inner portion of the spinal cord composed mostly of neuron cell bodies and synapses.. The proportions differ at each level. These proportions vary at different levels. The increased amounts of gray matter in these enlargements is also a reflection of control of the limbs.

White and Gray Matter

The spinal cord has a white chocolate candy shell and a dark chocolate center.  This is opposite of the brain that has an outer cortex of gray matter.   We are going to spend a lot A LOT of time with this diagram over here on the right.  I have blown up a vertebra to show you how the spinal cord is threaded through the vertebral foramen. I also want you to look at those nerves coming off either side of the spinal cord.  These nerves are threaded through the space between the vertebra.  Now, if your discs are nice and plump, the discs will prevent the vertebra from pinching these nerves between them.  However, if you, like me, have the spineProminent ridge on the posterior scapula dividing it into supraspinous and infraspinous fossae. of a 94 year old woman, you have no space. As a result, these nerves are crushed.

Landmarks

This is the picture that you should print out many times. This way, you don’t have to keep redrawing it!  This is a transverse section A cut or slice of the body or an organ for study. of the spinal cord.  These nerves coming off are not part of the spinal cord. They are technically part of the peripheral nervous systemPNS All nervous tissue outside the CNS; includes nerves and ganglia. because they are not in the spinal cord or brain.  But, we will cover these nerves with the spinal cord. 

When we first look at a picture of a transverse section of the spinal cord, we want to tell front from back. We aim to distinguish dorsalRelating to the back side of the body. from ventralRelating to the front or belly side of the body.. We are switching to using dorsal, meaning back, for posterior.  We are also switching to using ventral, meaning belly, instead of anteriorThe front of the body or toward the front when standing in the anatomical position..  In the middle of the spinal cord is the central canalA hollow canal in an osteon containing blood vessels and nerves..  This canal runs through the entire spinal cord and circulates cerebrospinal fluid(CSF) – A fluid that cushions and nourishes the brain and spinal cord. (not blood).  On the anterior or ventral side, there is this huge fissureA deep groove in the brain’s surface. that dips into the spinal cord like a valley.  On the opposite, dorsal side, there is no fissure, but there is a sulcus, which is like a fold.  When you receive a transverse section of the spinal cord, you should always just start with labeling ventral and dorsal.