hello anatomy colleagues this is Dr. Alsup and we're going to continue our discussion on skeletal
muscle basics with connective tissue and a lot of time we don't think we think of the muscle cells
we think of that kind of reddish muscle belly the connective tissue plays such a huge role in terms
of the skeletal system both on the microscopic as well as the macroscopic or gross level
all right so we have a few learning objectives that we're going to touch on we're going to talk
about we're going to start at the smallest scale or the most microscopic scale then we're going to
increase in size and visibility ending with tendons and fascia the all-important fascia
okay so connective tissue again as i mentioned we are starting at the most microscopic level
with the endomysium sometimes you'll hear endomysium but really endomysium is going to
be the correct way and you can see kind of endo- so you're thinking kind of more inside here and
this is going to surround each muscle fiber or each one of those individual muscle cells
so if we're looking at this kind of blown-up illustration here you can see you're looking at
one myofiber that's been kind of enlarged here you have all those myofibrils throughout
and then surrounding that fiber or that muscle cell is going to be a layer of connective tissue
that surrounds it okay so already at this really small scale we have connective tissue associated
with muscle and it plays a role because it brings in neurovasculature of great importance that
vasculature is going to supply nutrients to allow for a lot of that function to occur in this region
now moving a little bit larger scale or a little not quite it can be visible
is going to be the perimysium and it is continuous with that endomysium
and so you can see so we'll so this was the kind of close-up picture here we're going to
focus more on this picture here this is like the full muscle belly one that you would see
and what the perimysium does is it surrounds these regions referred to as fascicle and fascicle is
a new term for us basically this is going to be groups of muscle fibers or muscle cells that are
kind of grouped up together and surrounded by connective tissue specifically this perimysium
and you may have seen fascicles before if you're ever looking at some type of meat
that's been cooked and it's kind of pulled apart into these kind of bundles those are fascicles and
the shiny part that's surrounding those fascicles is the connective tissue which is the perimysium
again perimysium is going to be continuous with the endomysium as well as the larger
or more macroscopically visible epimysium and the epimysium is going to surround the
entirety the whole muscle belly all right so if you've ever looked at say a dissected muscle
generally there is some shiny kind of very sometimes it's a little translucent connective
tissue surrounding it that is the epimysium it's thicker than the connective tissue associated
with the smaller scale myofiber or even around those fascicles
and it will surround and bind all those fascicles or those bundles of muscle fibers
together into one muscle belly and then that's surrounded by connective tissue
now this is a key point i've been mentioning it throughout but make sure that you understand this
that all this connective tissue is continuous so that endomysium is continuous with the perimysium
which is continuous with the epimysium and the epimysium is continuous with tendons and you've
likely heard tendons before and this is unlike ligaments ligaments remember are bone to bone
connecting bone to bone tendons connect the muscle belly to bone okay so hugely important in terms of
movement and really it's just that continuation of the connective tissue past the muscle
all right you can kind of see that here here's the epimysium that's surrounding the muscle belly
and at one po at some point the muscle belly kind of stops but you still have a continuation
of connective tissue and that is the tendon how long the tendon is how wide the tendon is
the shape size of the tendon varies quite a bit between muscles but you're always going to have
some level of that connective tissue between the actual muscle and bone and what's key here
and really important is that that tendon will as mentioned attached to the bone but what it
does is it actually kind of is continuous with that perime- or the periosteum that's surrounding
the outside of the bone and it will actually kind of interweave and blend with the collagen
of the osseous extracellular matrix so if you think of a muscle contracting that's going to
kind of bring the tendon with it and since it's so intimately connected to the bone
that will allow the bone to move and to get some of those major skeletal movements we have
again as mentioned we can have all different shapes and sizes
of tendons sometimes they're really rope-like sometimes you can't even really see the tendon but
rest assured it's there it's like right up against the bone you can have these regions referred to as
aponeurosis and this kind of just means a flat sheet of tendon and one of the the most obvious
ones are associated with the palm of the hand and you can see this here on a dissection this
palmer aponeurosis so very different than say the more rope-like tendons that we tend to think of
a few characteristics generally tendons are highly organized in terms of the directionality of their
collagen fibers okay so that's they very often will appear very opaque sometimes depending on
how thin an aponeurosis it might be become a little more translucent but for the most
part tendons are fairly opaque these similar to what we had with cartilage are more poor they're
poorly vascularized so anytime you have poor vascularization there tends to be a slowness
to healing so if you have damage to a tendon it's a little bit slower to heal than say other regions
and also even though obviously that connective tissue surrounded certain components
of the muscle that endo-, peri-, and epimysium that surrounded portions of the muscle once you
that muscle belly ends and tendons do not have muscle cells associated with them so it's really
just as highly organized collagen fiber is going to connect to bones
now this tendons are also generally going to have some connection to fascia and fascia is a
more generalized term it just means this grossly visible connective tissue that serves to kind of
particularly when we're talking about the musculoskeletal system we'll often
compartmentalize groups of muscles and often those groups of muscles are in
obviously a similar location because they're kind of packaged together but oftentimes they
have a similar nerve that innervates them they generally have similar actions and we often call
these muscle compartments this is going to be unlike where we have the kind of dense regular
connective tissue associated with tendons fascia tends to be dense irregular connective tissue
and you can kind of see here if we're looking at the schematic of skin and you'll talk about skin
in a lot more detail you have the skin right here you'll often have a layer of superficial fascia
which is composed predominantly of fat and then you start getting into varying levels of fascia
and that's generally often referred to as deep or investing fascia
sometimes that epimysium is just sometimes considered an investing fascia as well sometimes
you'll hear that that term used interchangeably but you can see here in this cross section you
have these groupings of different muscles and we'll talk about these specific muscles
in more detail later but you can see that these muscles are separated from other groups of muscles
by a layer of fascia you can even see how that's going to have a connection
that fascia has a connection with those say the epimysium that's surrounding the muscle bellies
of those individual muscles so fast is huge if you ever do a dissection course you will
certainly become very familiar with fascia it is throughout the entirety of the body
not just associated with the musculoskeletal system but certainly also associated with msk
all right excellent so i hope that you've kind of gotten across the fact that
um while uh connective tissue is not certainly muscle cells it is so very intimately related to
even at that small scale of the cell layer to the larger scale of the entirety of the muscle belly
all the way to its connection of the bones and all those layers of connective tissue
are going to be connected and that's important because with any type of contraction even at
that small scale you're still going to have that really close connection to the connective tissue
which you need in terms of overall movement
all right excellent question time muscle tendons are closely associated with which structure
of the skeletal system all right so look at these answer choices if you you don't get it right off
the bat you can pause and go look back at your notes and when you're ready let's discuss how e
the periosteum is the correct answer so first off where is the periosteum so periosteum is going to
be that connective tissue layer that kind of surrounds the external surface of the bone
so if you think about a tendon that is from that muscle belly extending from the muscle
belly to the bone it makes sense for it to be really closely connected with that periosteum
in fact it kind of interweaves past it to become part of that um part of the matrix of the bone
generally a muscle tendon is not going to extend all the way to the medullary cavity
epiphyseal plate no that's a that's a joint remember so we're not generally going to have
tendons all the way you know to kind of going through say like the synovial cavity in that
type of region there um or even at the epiphyseal plate certainly tendons can play a role in terms
of protecting joints but generally you're not going to have a connection straight to that region
endosteum also a bit too internal similar to the medullary cavity and the articular cartilage
saying it's not going to connect to that cartilage on the ends of bones and to kind of go back to the
epiphyseal plate and joints when i was mentioning tendons certainly will play a huge role in terms
of protection of the joints sometimes it can kind of serve as an added protection to portions
of the joint say like an anterior portion of the joint once when we're talking about the knee but
generally you're not going to have that tight connection to say directly to the cartilage of
a joint it's more playing a protective portion to the outside of the joint and obviously it's
going to play a huge role in terms of allowing movement to occur with the contraction of muscle
okay excellent so we have one more video in terms of the skeletal muscle basics where which are the
different types of contraction and then talking a little bit about prime movers and that type of
stuff so thank you so much for your time and attention here if you have any questions
please reach out reach out and i'll be happy to always happy to talk anatomy