Now let’s turn to the median nerve. Now, there is
a number of places the median nerve
can be damaged. It could be damaged in the
arm, at the elbow, and at the carpal tunnel.
Remember, the median nerve doesn’t supply
anything in the arm, but it supplies considerable
amounts of muscles in the anterior compartment
of the forearm and in the hand. So damage
to the nerve, to the median nerve, again via
maybe traumatic injury to the median nerve,
principally at the elbow joint is a common
place. But again, you can have damage up in
the arm or down, as we’ll see in the
But damage at the elbow can lead to paralysis
of FDS, flexor digitorum superficialis, and
the lateral two tendons of flexor digitorum
profundus. So these muscles will be paralyzed.
You’ll also have paralysis of the thenar
muscles working on the thumb, and lumbricals
1 and 2, those laterally positioned lumbricals.
The effect, well again, if you appreciate
what these muscles do, then the effect of
damage to the median nerve is going to be
an inability to flex the proximal interphalangeal
joints of digits 1 to 3, and weakened flexion
of digits 4 and 5. You’re also going to have
an inability to flex the distal interphalangeal
joints of digits 2 and 3. So you can see
paralysis of the median nerve
leads to quite some substantial inabilities
of the contractile abilities of these muscles
leading to quite a significant functional
deficit. You’ll also be able to see that
there’s going to be flexion still be possible
at the distal joints of digits 4 and 5 due
to the flexor digitorum profundus having
the ulnar innervation. So because the tendons
that pass the digits 4 and 5, from flexor
digitorum profundus, are from the ulnar nerve,
then these are going to be spared. You’re also going
to have inability to flex the metacarpophalangeal
joints of digits 2 to 3. And due to loss of
the lumbricals, you won’t be able to extend
the interphalangeal joints of digits
1 and 2.
So this means that when a patient is asked
to form a fist, digits 2 and 3 essentially
remain extended. And this is what we can see
here. Due to a loss of the flexor digitorum
profundus and the flexor digitorum superficialis
and the various other muscles I’ve mentioned
like the lumbricals, because these are effectively
paralyzed that when someone is asked to form
a fist, then the function of the flexor digitorum
profundus that is supplied by the ulnar nerve
is still intact, these digits can flex, but
the remaining digits remain extended.
And this is known as hand of benediction.
And we can see that here on the picture.
We can see digits 4 and 5 have flexed, but digits
2 and 3 remain extended. And this is indicative
of median nerve damage. If the median nerve
was damaged in the carpal
tunnel, then you wouldn’t have that problem
because the median nerve would have already
given off the branches to the muscles in the
anterior compartment of the forearm.
So the muscular branches already have come off here.
So the function of these muscles will be preserved.
However, as the nerve passes through the carpal
tunnel, it can be due to carpal tunnel syndrome
that you could have this problem, or if you
try to lacerate if there’s a laceration
of your wrists, then perhaps the median nerve
could be damaged. And this could lead to paralysis
of the thenar muscles and lumbricals
1 and 2.
So these are supplied by the recurrent branch
of the median nerve that passes through the
carpal tunnel, and therefore, it’s likely
to be damaged. Because of that, you have an
inability to oppose the thumb, and you lose
the fine motor movement that is possible
via the lumbricals with digits 2 to 3. So
loss of fine motor movements of the lumbricals,
and we can see that here. We see the lumbricals
will be damaged, and we see the thenar eminence
here will be damaged due to damage to the
recurrent branch of the median nerve.
Sensory loss, well, you’ll have tingling or
reduced, loss of sensation over the lateral
three and a half fingers. We can see that here,
sensory loss over fingers 1, 2, 3, and
the lateral surface of finger 4 due to sensory
branches from the median nerve emerging distal
to the carpal tunnel. So these branches, these
sensory branches coming from the medial nerve
that supply these fingers are coming once
it has pass the carpal tunnel. So they will
be damaged, and you’ll have that
tingling, reduced sensation.
However, sensation of the central palm
will be preserved because the branch that
supplies the central palm, this palmar branch
here, actually comes off the median nerve
before it passes through the carpal tunnel.
So because of that, it’s not going to be
damaged. So if there is sensory loss of the
1, 2, 3 and a half fingers but with carpal
tunnel damage, the central palm sensation