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Neuro: 10:00-11:00
Thursday, January 8, 2009
Dr. Lester
CNS=Central Nervous System
The Spinal Cord
PNS=Peripheral Nervous System
Scribe: Marjorie Hannon
Proof: Caitlin Cox
Page 1 of 4
I. Introduction [S1]: The Spinal Cord
II. Grey and White Matter [S2] Make sure you know what we are talking about when we talk about grey and white
matter, and know how these differ in the brain and spinal cord.
a. Grey and white matter in the brain: grey matter is any area where you have a large accumulation of cell bodies.
The white matter is the pathways; the white being where you have the myelin. [S3]
b. Grey matter [S4]
i. The cortex is grey matter. The cell bodies are doing all of your big cortical processing in the outer band, or
the outer grey matter.
ii. Nuclei and ganglia are also grey matter.
1. A nucleus is a big collection of cell bodies (so it is a large piece of grey matter) in the CNS (brain and
spinal cord)
2. A ganglion is also a big collection of cell bodies but is in the PNS (the nerves going out from the
spinal cord to the various parts of the body and coming back in).
a. There is one major exception to that: basal ganglia (basal ganglia are in the brain).
3. Other than our exception, when you here ganglion think PNS, and when you hear nucleus think CNS
c. White matter [S5]
i. Here is what is happening: you are putting together bunches of cell bodies and bunches of fibers and they
tend to synapse on another bunch of cell bodies that send out another bunch of fibers. So you have, for
example, maybe cortex here, a nucleus here, and then these going off to a more distal target. That is
going to be the basic architecture you will see in some of the pathways.
ii. Terminology for the pathways that we are going to talk about include:
1. Nerve- a big bundle of white matter pathways in the PNS.
2. Tract- a similar bundle of white matter pathways in the CNS.
3. Fasciculus or Funiculus- a group of fibers with common origin and destination. What is the
difference between that and a nerve or a tract? In terms of function, not a lot.
a. Fasciculus or funiculus tend to be pathways going from one part of the CNS to another,
where as the nerves tend to be the input and output from the nervous system (we talk about
motor nerves, sensory nerves, motor tract, sensory tract). When you are just talking about
the smaller pathways, inside the brain for example, you will see fasciculus or funiculus.
b. You do not have to worry about whether the pathway is a fasciculus or a funiculus because it
will be named for you already.
4. Lemniscus- another name for a tract and refers to a long ribbon-like, flat, fiber pathway. This term
just highlights the morphology of the pathway.
5. Peduncle- a massive group of fibers. Usually several different tracts put together. In some cases, it
even provides a little bit of structural support for the brain.
a. When we get to lab, you will see that the cerebral peduncles are these massive white matter
structures on the midbrain
d. When we name tracts, we are naming them with the origin first and the destination last. [S6]
i. If you ever see the name of a pathway that you are not familiar with, it is easy to figure out. For example:
1. Corticospinal tract- starts at the cortex and goes to the spinal cord
2. Mammilothalmic tract- starts at the mammilary bodies and goes to the thalamus
3. Spinocerebellar tract- starts at the spinal cord and goes to the cerebellum
4. Corticobulbar tract- starts at the cortex and goes to the brain stem
a. Bulbar refers to the brain stem (or the “bulb” as it used to be called)
III. The Spinal Cord [S7], General Organization
a. [S8] The spinal cord is very small and short (42-45 cm long). It is about 1 cm wide at its widest point. Your
spinal cord does not go all the way down your back.
b. The pattern of grey and white matter in the spinal cord is reversed as compared to the brain.
i. The white matter tracts are on the outside and grey matter is on the inside. (In the brain, the cortex is grey
matter on the outside. Then we have some nuclei on the inside that are grey matter and all the white
matter pathways are running in between there).
ii. Staining reverses this. When you are looking at transverse sections, remember that they have been
stained for myelin. This myelin, which is white matter, has now been stained to appear dark. This is
necessary because it is hard to distinguish grey matter from white matter with the naked eye in an
unstained gross section. Just remember that in the spinal cord, the inside is the cell bodies (grey matter).
c. [S9] Just remember that the staining makes it appear reversed. Don’t let this confuse you.
Neuro: 10:00-11:00
Scribe: Marjorie Hannon
Thursday, January 8, 2009
Proof: Caitlin Cox
Dr. Lester
The Spinal Cord
Page 2 of 4
d. [S10] The spinal cord is segmented anatomically. As the neural tube is forming, there are these developmental
origins of segments that will turn into pairs of roots of nerves. The input and output occurs at each level of the
spinal cord, in a series longitudinally along the cord.
i. Dorsal rootlets (kind of on your back, think dorsal fin) are the input, so they are carrying sensory
information into the spinal cord.
ii. Ventral rootlets are the output which is the motor, so it is the motor neurons from the spinal cord going
outward to the muscle.
iii. The fibers that are coming and going (dorsal input and ventral output) combine and become one spinal
nerve in the PNS.
iv. The picture is a cross section of how each level looks longitudinally.
e. [S11] Each set of rootlets forms a spinal nerve that innervates a corresponding segment of the body, called a
dermatome. It is very specifically arranged. This is true for both the motor and sensory processes.
f. [S12] You can see the nerves coming off the spinal cord going to their various destinations. (Dr. Banos believes
this is a motor mapping. He says the sensory and motor mappings match up pretty well). You can divide the
body up into the dermatomes: a certain piece of skin or patch of skin corresponds to a specific spinal nerve.
i. This is important in spinal cord injuries when you are trying to get a level of where someone’s deficits are.
You can take a pin prick or soft touch and test each dermatome on either side and get the various levels of
your deficits.
ii. It can be multiple modalities; you can have your motor level and sensory level. You can even test muscles
at some of these but the arrangement of the muscles is where the motor dermatomes are going to differ
from the sensory, but don’t worry too much about this right now.
iii. Just realize that these dermatomes are mapped across your body to what they control.
iv. If you follow these nerves back (look at the arms and hands), they go really high up. They are connected
to the spinal cord in your neck. We will talk more about this later. The nerves in your legs come up and
connect near the middle to lower back.
g. [S13] There are 31 numbered segments in the spinal cord that are divided into categories.
i. 8 cervical (C1 – C8): These are high up and near your neck.
ii. 12 thoracic (T1 – T12)
iii. 5 lumbar (L1 -- L5)
iv. 5 sacral (S1 -- S5): These are the lowest that have clinical significance
v. 1 coccygeal: We don’t worry too much about this one. It is literally down in the coccyx.
vi. When you look at medical records for someone who has had spinal injury, you can get an idea of where in
the spine it is talking about based on the numbering. For example, a C1 injury is about the worst you could
have because it is so high up. If it says T12, you know it is referring to the thoracic segment.
h. [S14] The spine is housed within the vertebral column, and this is how it is arranged. This is a cross section
from above, so these vertebral bodies are solid pieces of bone with a little bit of cushion in between and then
you have this tiny hollowed out section among the spinal processes and your spinal cord is running in there.
Remember that even though the spinal cord is protected by bone, the bones are very small and that is one
reason the cord is so susceptible to injury.
i. [S15] Each cord segment has a corresponding vertebra of the same name. You have C1, C2, C3 segments of
the spinal cord, but you also have C1, C2, C3 vertebrae; therefore when you are talking it is important to specify
whether you are talking about the spinal cord or vertebrae.
i. Spinal nerves enter and exit underneath their corresponding vertebral segment. Remember, however, that
the spinal cord is only 42-45 cm long and your spine is longer than that (goes to your lower back).
j. [S16] So how do all of those nerves line up at the level of the vertebrae? They will extend down to the level that
they need to exit. Therefore, they line up nicely up top (C1-C3) but once you get into the lumbar, they are
traveling down and then exiting underneath their vertebrae.
i. This forms a fringe-like tail of nerves that we call the cauda equina. (Meaning “horses tail”)
ii. This means the cord segments and vertebral segments don’t line up perfectly.
1. Higher up, spinal segments and vertebrae aren’t very far apart. When you are talking about the
lower spine, the spinal segments and vertebral segments can be vastly different.
k. [S17] This is what the cauda equina looks like. The red line indicates the end of the spinal cord. You can see
that the last nerves there have to dive down to exit under their appropriate vertebrae.
l. [S18] The cord is not of uniform thickness throughout is length. Why is that?
i. [S19] Different parts of the cord that innervate different parts of the body vary in complexity.
1. For example, nerves that control hands and fingers come off the cord need more machinery and are
more complex, so the cord will be a little bit thicker there.
Neuro: 10:00-11:00
Scribe: Marjorie Hannon
Thursday, January 8, 2009
Proof: Caitlin Cox
Dr. Lester
The Spinal Cord
Page 3 of 4
ii. The number of white matter pathways in the cord also affects the thickness.
1. Near the top, around the cervical cord, you have all the descending motor pathways and all of the
sensory pathways that have built from bottom up. This is different near the bottom- by the time you
get to the lower end of the cord, most of the motor pathways have already exited and there is very
little sensory being added on early.
iii. Therefore, the cord is bigger at the top and gets smaller toward the bottom and there will be thicker areas
for sites that innervate something with great complexity.
m. [S20] In general, this is not a wonderful drawing, but notice that it tapers down toward the end and that it has
two enlargements. The cervical enlargement- this is cord level not vertebral level- (C5-T1) and lumbar
enlargement (L2-S3).
i. What is the cervical enlargement for? Hands, arms, fingers (fine motor movement).
ii. What is the lumbar enlargement for? Feet, legs (walking)
IV. The Spinal Cord in Cross Section [S21]
a. Cord Sections [S22]:
i. Segments of the cord have similar organization (white matter outside, grey matter inside) but each area
(cervical, lumbar, etc) varies in appearance. As we give you these images, be able to tell where you are in
the cord.
b. Cord Section – Cervical [S23]
i. Cervical cord is wide, flat, and almost oval in appearance. White matter is sort of packed in everywhere.
You will never see more white matter in another area other than cervical. Why? You have so many
pathways (since it is so high up in the cord) the motor pathways haven’t gone off and you have all the
sensory coming up.
c. Cord Section -- Cervical Enlargement [S24]
i. What is the difference between these two (cervical enlargement vs. cervical cord)
1. Look at the grey matter. You can see that the cervical enlargement has what looks like duck feet.
Remember that the grey matter has the motor neurons and if you have pathways that have to
innervate a highly complex area, you will have a lot of grey matter in that part of the cord.
ii. The thing to remember about a motor neuron going to a muscle is that it is not the size of the muscle that
determines how much nerve power you should send to control it, it is the complexity. For example, a big
muscle in your body may only have a few major nerve pathways, but in your hand you have many little
muscles and therefore need a ton of individual fibers. So, don’t think there should be an enlargement in the
cord for a big muscle; it is the complexity of the muscle that dictates that.
d. Cord Section – Thoracic [S25]
i. This is a little bit rounder in appearance; there is less white matter, and less prominent ventral horns than
cervical enlargement. This should make sense because you don’t have as much fine motor skills in this
area. Arms and hands were coming off of the cervical enlargement, but the thoracic is the shoulders and
upper torso. There are fewer muscles to control in this area.
e. Cord Section – Lumbar [S26]
i. Less white matter than thoracic, even rounder, larger ventral horns- especially in lumbar enlargement.
1. The cross sections are of regular lumbar and of lumbar enlargement (notice this one is not stained).
These two sections are hard to tell apart unless they are side by side to compare.
ii. The other tip that you are in lumbar and not thoracic: you begin to see the first fibers of the cauda equina.
iii. *HINT*: We do not have a lot of images in the image bank, so really learn these images.
f. Cord Section – Sacral [S27]
i. Know that this picture is not necessarily to scale with the other pictures.
ii. There is not much white matter, mostly grey. It looks as if there is just a ton of grey matter, but really there
is just so little white matter that it makes the grey look much more prominent. There are very few sensory
pathways to add on and not much motor left to be dealt with, so you end up with a small round segment
and a lot of cauda equina in the periphery.
g. Picture [S28]: This puts them all together to give you an idea of relative size.
h. Cross Sectional Organization [S29] There are a few landmarks here to identify
i. Posterior median sulcus (called a sulcus because it is not as prominent as a fissure)
ii. Anterior median fissure (much more prominent and or deeper than a sulcus)
iii. The posterior median sulcus and the anterior median fissure divide the spinal cord into halves, roughly.
iv. In the cervical cord, you also have a posterior intermediate sulcus. It divides two separate white matter
pathways.
v. Anterior white commisure- you have a little bit of white matter here, this is a pathway that connects the
sides of the spinal cord. Remember myelin stains darkly, so the pathway is the dark part in the picture.
1. Whenever you see the word commissure, it means a connection between things on two sides.
Neuro: 10:00-11:00
Scribe: Marjorie Hannon
Thursday, January 8, 2009
Proof: Caitlin Cox
Dr. Lester
The Spinal Cord
Page 4 of 4
vi. Tract of Lissauer- the primary input point or the spot where the sensory information enters the segments of
the cord. (Input tends to be on the posterior side and the sensory information is coming in.)
i. Grey Matter
i. [S30] The grey matter in the cord is laminar, it is not a continuous thing of cell bodies, but it is actually
subdivided into little areas that have different functions. There is a system called Laminae of Rexed that
breaks down what nuclei are in each segment. For our purposes, know that the lamina of Rexed exists,
but we do not need to know specifics about it.
ii. [S31] We should know that the grey matter is divided into the posterior (dorsal) horn, the intermediate grey,
and the anterior (ventral) horn.
iii. Grey Matter: Posterior Horn [S32]
1. Mostly interneurons.
a. The substantia gelatinosa is involved in the pain and temperature pathway.
b. The body of the posterior horn is involved in sensory processing.
iv. Grey Matter: Intermediate Grey [S33] significant structures:
1. Clarke’s Column- around T1-L3, is a column of cell bodies (basically making a ganglion within the
spinal cord) that is a crucial part of balance and proprioception system.
2. Intermediolateral cell Column- around T1-L3, is sympathetic neurons so it is involved in the
autonomic system.
v. Grey Matter: Anterior Horn [S34]
1. This is lower motor neurons- Basically, this is the cell bodies of the neurons that actually go out to
that muscle and innervate it. So you don’t have a neuron that starts in the brain and goes straight to
the muscles, it makes a stop right here. This is just motor, so it’s an easy one.
j. White Matter: The “Big Four Pathways” [S35,36] There are four major spinal pathways. These also correspond
to the things that are tested clinically in a neurologic exam. There are aspects of a neurologic exam that test
each one of these pathways.
i. Corticospinal tract (red on the slide). Notice that we have a couple of sections of it.
1. Voluntary motor control.
2. This is an extremely important and basic pathway.
ii. Dorsal Columns/medial lemniscus (blue on the slide)- huge white matter pathways. Remember that there
is a little division, so there is actually two parts to the dorsal column that we are going to talk about.
1. Discriminative touch (fine touch)
2. Conscious proprioception (proprioception is knowing where your body and limbs are in space): that
system that is bringing feedback to the brain from the muscles in the limbs
iii. Spinothalamic tract (green on slide).
1. Pain and temperature
iv. Spinocerebellar tracts (purple on slide). Notice that there are a dorsal and a ventral, so we kind of have
two tracts.
1. Unconscious proprioception.
2. You probably know that your cerebellum is for balance and part of balance is knowing where your
arms and legs are. The cerebellum has an independent or unconscious way of knowing that. Be
aware of the distinction of conscious and unconscious proprioception.