So, hello everyone. This is the first lecture of the course on muscle physiology, structure

and function. So, in this lecture we will talk about how muscle works, how muscle produce

force and what are the interactions between the muscle and the nervous system. We will

only talk briefly about the nervous system because we will see this in the next lecture.

In this lecture we will mainly concentrate on how muscles generate force and what are

the biochemical and structural changes that the muscle uses. So, in the human body we

have around 650 muscles and most muscles are bilateral, so you have in one side and also

in the other. So, I think from an evolutionary perspective it is an artwork on nature. If

we look at it from an engineering perspective we can of course see many limitations of the

human muscle. For example, that it's relatively slow, the Tino machines can perform much more

accurate movements, but if we study the law of biology we see that it is an extremely

optimized machine and in many ways it surpasses artificial intelligence methods that allows,

for example, the control of a dexterous artificial hand still cannot reach human-like precision

and mostly flexibility, which the nervous system is incredibly capable of. So, the muscle

and its structures allows the body to move in the environment. This is one example, for

example, during running we have a large number of muscles that are activated and allows the

human body to move. So, the muscles are attached to the bones through the tendon and the muscle

and the tendon and the skeleton forms the structures that allows us to interface with

the environment. As you can see already in these pictures there are several muscle groups

that you can clearly spot and each of these muscle groups are controlled by the nervous

system. So, the nervous system has a very challenging task because as you can see it

does not only mean to control a large number of muscles, but it has also to modulate the

force each muscle is applying at the skeletal level. So, it is from a computational perspective

it is very interesting to understand how the brain optimizes the control of muscle forces.

Before going there let's understand how the muscle actually produces force and what are

the limits of the muscles. So, in the human body we have muscles that are penated, you

can see this one here that have a penational angle and muscles with longitudinal muscle

fibers. So, to give you an example the bicep bicep brachy muscle it has longitudinal muscle

fibers, parallel muscle fibers, while other muscles such as the vascular medialis, for

example this muscle is a very clear example by the first dorsal interosseous muscles you

see that they have these patterns and other muscles for example the vascular medialis

they have this kind of pattern. So, it is interesting because the muscles that have

fascicles in parallel they have a greater range of motions and the shortening velocity

whereas on the other hand when you have muscle fibers that are transversal and are not longitudinal

so all penate muscles produce more force per volume.

You will see this why in the next slides. So, if we look at the anatomy of the muscle

we see as I mentioned before there is the tendons, then there is the first layer which

is called the deep fascia, then below the deep fascia we have the epimysium and then

the perimysium. So, these three layers are important to know because the epimysium, the

perimysium and the endomysium because as you will see they separate distinct muscle fibers

and distinct muscle compartments. So, you have the deep fascia and the epimysium that

is around all the muscle belly that we call the muscle belly and then we have within the

muscle belly we have the muscle bundles that are a pack of muscle fibers. So, you can call

muscle bundles but the classic term is muscle fascicles. Each muscle fascicle is composed

by muscle fibers. These are individual muscle fibers that you can observe in a microscope

if you put a sample of muscles and each muscle fiber is composed of a large number of myofibrils

that you can see here. So, inside the myofibril you have something called the sarcomere and

we will see this in the next slide but something it's very important to know that already

from this line that you can see here a striated shape and this is what gives the name also

striated muscle fibers because there are some proteins that we will see later that make