In today's lecture, we will be discussing
the spinal cord and the spinal nerves.
So first let's discuss the
functions of the spinal cord.
What does the spinal cord do?
The first function of the spinal
cord is to process reflexes.
Another function of the spinal cord is to intergrate
excitatory postsynaptic potentials or EPSPs
and inhibitory postsynaptic
potentials or IPSPs.
Recall that EPSPs are depolarizing potentials
and IPSPs are hyperpolarizing potentials.
And the summation of
these postsynaptic signals
determine whether a nerve's
impulse is generated or not.
The third and final function of the spinal cord
is to conduct sensory impulses to the brain
and motor impulses away from
the brain to the effectors.
So now let's discuss the external
anatomy of the spinal cord.
The spinal cord is going to begin as an extension
of the medulla oblongata of the brain.
This happens at the level of the
foramen magnum of the skull
and the spinal cord is going to terminate
at the level of the L2 vertebrae.
The spinal cord is
protected by three main ways.
The first way are the vertebrae themselves.
These bones provide a hard layer of
protection around the spinal cord.
A second layer of protection of the
spinal cord is going to be the meninges.
This connective tissue layer is going to provide a
lot of protection directly unto the spinal cord.
The third way that we protect the spinal
cord is by suspending it in cerebrospinal fluid.
This helps to prevent shock by allowing for shock
absorption when there are sudden movements.
So now let's take a closer look
at that connective tissue layer
that surrounds the spinal cord
also known as the meninges.
The meninges is composed of three layers.
If we start from the most deep
layer to the most superficial layer,
you get the mnemonic P-A-D or PAD.
P stands for pia mater.
The pia mater is a transparent connective tissue layer
that adheres to the surface of the spinal cord.
This layer is going to contain
blood vessels and this allows
for the supplying of oxygen
and nutrients to the spinal cord.
There are extensions from the pia
mater known as denticulate ligaments
that are going to fuse with the arachnoid
mater and the inner layer of the dura mater
and suspends the spinal cord so
that it is protected from displacement
and therefore from shock.
The middle layer of the
meninges is the arachnoid mater.
This is a thin, avascular covering
with a spiderweb arrangement
of collagen and elastic
fibers thus the word arachnoid.
The arachnoid mater is continuous with
the arachnoid mater of the brain.
And there is a space between this layer and the
pia mater known as the subarachnoid space.
In this space, you will find
the cerebral spinal fluid.
The third layer is going
to be the dura mater.
The dura mater is the outermost layer of the
meninges and it is the thickest and strongest layer.
It is composed of dense,
irregular connective tissue.
The dura mater is continuous with the
dura mater of the brain and forms a sac
that hangs from the foramen magnum of
the skull to the second sacral vertebrae.
It is also continuous with the outer coverings
of the spinal nerves known as the epineurium.
Don't worry, we will discuss
that later in the lecture.
The space between this layer and
the arachnoid layer below it
is known as the subdural space and in
this space, you have interstitial fluid.
So now let's discuss the
anatomy of the spinal cord.
Let's start with this external anatomy.
So extending from the spinal
cord, we have two roots and rootlets.
These are the posterior roots
and the anterior roots.
The posterior root also has a swelling
called the posterior root ganglion.
Now let's move in and look at the
internal anatomy of the spinal cord.
On the anterior portion of the spinal cord, we have
a fissure known as the anterior median fissure.
On the posterior end, we have
the posterior median sulcus.
In the center, we have the central canal.
Here is where we will find
some of the cerebrospinal fluid
In the white matter of the
spinal cord in the anterior portion,
we have the anterior white column.
On the lateral portion, we
have the lateral white column
and on the posterior portion, we
have the posterior white column.
In the grey matter, we have on the
anterior portion, the anterior grey horn.
On the lateral portion,
the lateral grey horn.
In the center, the cross bar is
referred to as the grey commissure
and it gives the grey mater
it's butterfly or H shape.
And then in the posterior portion,
we have the posterior grey horn.