2. The active part of locomotor apparatus.
Myology.
• Plan:
• 1. Muscles as an organ.
• 2. Muscles development, anomalies.
• 3. The work of muscles. Elements of biomechanics.
• 4. Classification of the muscles.
3. 1. Muscles as an organ.
• Each skeletal muscle fiber is a single cylindrical muscle
cell. An individual skeletal muscle may be made up of
hundreds, or even thousands, of muscle fibers bundled
together and wrapped in a connective tissue covering.
Each muscle is surrounded by a connective tissue sheath
called the epimysium. Fascia, connective tissue outside the
epimysium, surrounds and separates the muscles. Portions
of the epimysium project inward to divide the muscle into
compartments. Each compartment contains a bundle of
muscle fibers. Each bundle of muscle fiber is called a
fasciculus and is surrounded by a layer of connective
tissue called the perimysium. Within the fasciculus, each
individual muscle cell, called a muscle fiber, is surrounded
4.
5. • Skeletal muscle cells (fibers), like other body cells,
are soft and fragile. The connective tissue covering
furnish support and protection for the delicate cells
and allow them to withstand the forces of
contraction. The coverings also provide pathways
for the passage of blood vessels and nerves.
6. • Commonly, the epimysium, perimysium, and endomysium extend
beyond the fleshy part of the muscle, the belly or gaster, to form a
thick ropelike tendon or a broad, flat sheet-like aponeurosis. The
tendon and aponeurosis form indirect attachments from muscles to
the periosteum of bones or to the connective tissue of other muscles.
Typically a muscle spans a joint and is attached to bones by tendons
at both ends. One of the bones remains relatively fixed or stable
while the other end moves as a result of muscle contraction.
7.
8. • Skeletal muscles have an abundant supply of blood vessels and
nerves. This is directly related to the primary function of skeletal
muscle, contraction. Before a skeletal muscle fiber can contract, it
has to receive an impulse from a nerve cell. Generally, an artery and
at least one vein accompany each nerve that penetrates the
epimysium of a skeletal muscle. Branches of the nerve and blood
vessels follow the connective tissue components of the muscle of a
nerve cell and with one or more minute blood vessels called
capillaries.
9. 2. Muscles development, anomalies.
• Myogenesis is the formation of muscle tissue during
embryonic development from stem cells in the mesoderm.
• Human embryonic stem cells are pluripotent, meaning
they differentiate into all cell types, including muscle cells.
• Muscle tissue is formed in the mesoderm layer of the
embryo in response to signals from fibroblast growth
factor, serum response factor, and calcium.
10. • In the presence of fibroblast growth factor, myoblasts fuse
into multi-nucleated mytotubes, which form the basis of
muscle tissue.
• Unused myoblasts dedifferentiate into myosatellite cells,
which remain in the muscle fiber until needed to
differentiate into new muscle cells when a muscle is
damaged or stressed.
• Myocytes are tubular muscle cells or fibers that develop
from myoblasts.
• Myocytes are specialized as cardiac, skeletal, or smooth
muscle cells.
11. • Myogenesis: The formation of muscle tissue during the
development of an embryo.
• Mesoderm: One of the three tissue layers in the embryo of
a metazoan animal. Through embryonic development, it
produces many internal organs of the adult, including the
muscles, spine, and circulatory system.
• Myoblasts: A type of embryonic stem cell that gives rise to
muscle cells.
12.
13. • Myogenesis is the formation of muscular tissue,
particularly during embryonic development. Muscle fibers
form from the fusion of myoblasts into multi-nucleated
fibers called myotubes. In early embryonic development,
these myoblasts proliferate if enough fibroblast growth
factor (FGF) is present. When the FGF runs out, the
myoblasts cease division and secrete fibronectin onto their
extracellular matrix. The second stage involves the
alignment of the myoblasts into the myotubes.
14. • The third stage is the actual cell fusion itself. In this stage,
calcium ions are critical for development. Myocyte
enhance factors (MEFs) promote myogenesis. Serum
response factor (SRF) plays a central role during
myogenesis, required for the expression of striated alpha-
actin genes. Expression of skeletal alpha-actin is also
regulated by the androgen receptor, which means steroids
can regulate myogenesis.
15. Characteristics of Myoblasts
• A myoblast is a type of embryonic progenitor cell that
differentiates to form muscle cells. Skeletal muscle fibers
are made when myoblasts fuse together, so muscle fibers
have multiple nuclei. The fusion of myoblasts is specific to
skeletal muscle (e.g., biceps brachii), not cardiac or smooth
muscle.
• Mesoderm: The embryonic layer from which muscle
tissues develop, including cardiac muscle, skeletal muscles
cells, tubule cell of the kidney, red blood cells, and smooth
muscle in gut.
16. • Myoblasts that do not form muscle fibers dedifferentiate
back into satellite (myosatellite) cells. These cells remain
adjacent to a muscle fiber, situated between the
sarcolemma and the endomysium (the connective tissue
that divides the muscle fascicles into individual fibers).
Satellite cells are able to differentiate and fuse to augment
existing muscle fibers and form new ones. In undamaged
muscle, the majority of satellite cells are quiescent; they
neither differentiate nor undergo cell division. In response
to mechanical strain, satellite cells become activated and
initially proliferate as skeletal myoblasts before
undergoing myogenic differentiation.
17. Anomalies.
• Flexor carpí radialis brevis v. Profundus. A very good
specimen of this muscle was found in the left fore-arm of a
tall muscular subject. The origin was from the anterior
surface of the radius from the level of the lower end of the
oblique line to about an inch and half above the lower end
of the bone. Its position was external to the flexor longus
pollicis and pronator quadratus. The fibres passed
downwards and slightly inwards and formed a small
round tendon which passed through the anterior annular
ligament in a separate canal on the outer side of that for
the tendon of flexor carpi radialis. Its insertion was by two
slips, the larger into the base of the 2nd metacarpal bone
outside the tendon of the flexor carpi radialis and partly
blended with the latter, while the smaller turned obliquely
18. • Levator Clavicule. Two specimens were observed. One
arose from the posterior tubercles of the transverse
processes of the 3rd and 4th cervical vertebræ, and was
inserted into the middle part of the upper border of the
clavicle, in the interval between the trapezius and sterno-
cleido-mastoid. The other arose from the transverse
process of the 6th cervical vertebra, while its insertion was
blended with the inner part of the clavicular insertion of
the trapezius on its posterior aspect.
19. • Supra Clavicularis Proprius v. Tensor Fuscice Colli. Of
this very rare muscle I have found one example. The inner
end was attached in front of the clavicular head of the
sterno-cleido-mastoid about an inch and three-quarters
outside the sterno-clavicular articula tion, while the outer
extremity, at a distance of about wo inches from the
acromial end of the clavicle, had a somewhat broader
attachment in front of the trapezius. The muscle between
its points of attach ment formed a slight curve with the
convexity upwards, and was enclosed and fixed in its
position in a sheath formed by the deep cervical fascia.
Short tendinous fibres attached it to the bone at either end;
the remainder of its length was fleshy, with a few bundles
20. • Chondro-epitrochlearis. example was ob served. The
attachments were similar to those of the chondro
epitrochlearis described by Prof. Macalister. Arising by
flesby fibres from the cartilage of the sixth rib on the right
side, in close connection with the lower border of the
pectoralis major, it followed the course of the lower border
of that muscle till it reached the inner side of the arm, and
then turned downwards on the inner aspect of the limb,
forming a narrow flattened tendon which blended with
the brachial aponeurosis immediately above and in front
of the epitrochlea..
21. • Sterno-cleido-mastoid.-Numerous minor variations were seen. In
several cases the sterno-mastoid and cleido-mastoid were
completely separate from origin to insertion, and in one the spinal
accessory nerve passed between the two parts. In another case,
besides the entire separa tion of the two parts of the muscle, the
cleido-mastoid was in its turn subdivided into two parallel planes of
muscular fibres (a superficial and a deep), with a thin layer of fat and
connective tissue between.
22. • Pterygoideus proprius. Of this muscle I have met with
three examples. In each instance it was attached by one
end to the crest on the great wing of the sphenoid, and by
the other to the posterior border of the external pterygoid
plate. Of the rarer form described by Prof. Macalister,
where the inferior extremity is attached to the tuber
maxillare.
• Transversus nuche . Two well-marked examples, with
similar attachments, were seen. Passing from the external
occipital protuberance and inner end of superior curved
line, for about half an inch, the fibres proceeded
horizontally outwards to blend with the tendinous
insertion of sterno-cleido-mastoid at the outer end of the
superior curved line and base of mastoid process.
According to Prof. Macalister, this muscle is always
symmetrical.
23. • Omo-hyoid. In one instance I found the anterior belly of
this muscle represented purely by tendon. In another case
the origin of the muscle was solely from the base of the
coracoid process. This peculiar form of the muscle has
been described by Gruber under the name of coraco-hyoid.
An additional origin from the clavicle was found in several
instances, but a purely clavicular origin I have not had an
opportunity of observing.
• Stylo-hyoid. Complete absence of this muscle was
observed in one instance. Two examples of doubling of the
muscle were met with, the duplicate arising in one
instance from the base of the styloid process.
• In one instance. Peroneus quartus. well-marked example
of this muscle was met with. The origin was blended with.
The lower fibres of attachment of the peroneus brevis; the
insertion was into an elevation on the outer surface of the
24. 3. The work of muscles. Elements of
biomechanics.
• Muscles allow us to consciously move our limbs, jump in
the air, and chew our food.
• But they are also responsible for many more processes
that we cannot actively control, such as keeping our hearts
pumping, moving food through our guts, and even making
us blush.
• Our muscles need signals from our brains and energy
from our food to contract and move.
• To build new muscles through exercise, we make use of
their remarkable ability to repair themselves when
damaged.
25. • Contraction gets muscles moving
• There are two types of muscle: striated and smooth. The
former have regular stripes, or striations, when observed
under a microscope. These striations are due to the
arrangement of muscle fibers, which form parallel lines.
• The muscles that move our body parts are called skeletal
muscles, and they are a type of striated muscle. We can
actively control these with our brain. Another type of
striated muscle are those that keep our hearts pumping,
which we are unable to actively control.
• Specific molecules within the muscle fibers allow
striated muscles to contract rapidly, allowing us to
move. The main players in this intricate process are
molecules called actin and myosin.
26. • Scientists continue to disagree on what allows actin and
myosin work together to make an entire muscle contract.
What is known, however, is that this process depends on
energy generated from the food that we eat.
• The contractions that smooth muscles produce tend to be
more gradual than those produced by striated muscle. An
example is the slow and controlled movement of food
through the digestive system.
• Smooth muscles do not have striations and we cannot
actively control what they do.
27. Calcium stimulates contraction
• The pathways that regulate contraction in striated and smooth
muscles are very different. But they do have one thing in common:
calcium is the key molecular messenger in the process.
• Striated muscles receive their triggers from the brain via motor
neurons. This results in calcium rushing into the muscle, allowing
actin and myosin to spring into action.
• Smooth muscle cells can be activated by neuronal signaling or
by hormones. Both mechanisms lead to a change in calcium
levels in the muscle cells. This leads to activation of myosin, and,
in turn, muscle contraction.
• Some smooth muscles are in a permanent state of contraction, and
the muscles that line our blood vessels are in this category. A
constant supply of calcium allows these muscles to regulate blood
flow. For example, when the muscles that line the blood vessels in
our face relax, we blush.
28. Muscle repair
• When we exercise, we damage our muscles. Afterward,
stem cells repair the damage and the muscles get stronger.
• New research led by George Washington University School
of Medicine and Health Sciences in Washington, D.C. –
published this week in the journal Science Signaling –
challenges a common assumption about this process.
• Cell generate reactive oxygen species (ROS) as a byproduct,
especially when energy consumption is high, such as
during exercise. ROS can be very toxic to cells and were,
until now, thought to hinder muscle repair.
29. • “It is still a common belief within
the fitness community that taking
antioxidant supplements after a
workout will help your muscles
recover better,” explains lead study
author Adam Horn.
• But the team’s research showed
that muscles tightly control ROS
levels after injury, and that ROS
are essential for repair.
• If you are among those who look to
antioxidants to speed up muscle
repair after your workout, it might
be worth letting your muscles do
their own thing.
30. • Elements of biomechanics.
•
• The skeletal muscles are organized multinucleated
myofibers, whose function is to generate length and
velocity dependent forces for movement or stability. Their
function depends on their intrinsic properties and
extrinsic arrangement.
• Components
• The skeletal muscles could be organized in three different
components based on their function and architecture
namely.
• The Series Elastic Component (SEC)
• The Parallel Elastic Component (PEC)
• The Contractile Component.
31. • The series and parallel elastic component are defined in
relation to their arrangement with the contractile
components, the later arranged in line with the contractile
components. The parallel elastic component is suggested to
consist of the membranes surrounding the contractile
components which includes the sarcolemma, sarcoplasmic
retinaculum , the perimysium and the epimysium , while
the series elastic components reside in the tendons and
aponeuroses.
32. Functions
• Elasticity is one of the properties of a muscle, necessary
for optimal function. These non-contractile components
contribute to the passive force generated by the muscles. It
is thought that the PEC distributes forces during passive
stretching and maintains the alignment of muscle fibers
while the SEC serves to store up elastic energy to be
released during muscle contraction and play a role in
stability during isometric contraction.
33. Clinical Implication
• The ability to stretch muscles (Muscle Compliance) could
be explained from the neurological (when considering the
neurophysiological basics of muscle tone) and
biomechanical models of the skeletal muscle.
Intramuscular connective tissue framework (non-
contractile components) serves to distribute forces during
muscle stretching . It has been shown that an increase in
the collagen to muscle fibre tissue exist as well as
reconfiguration of collagen arrangements in immobilized
muscles suggesting the roles of the biomechanical model
in clinical management of muscle stiffness and
contractures should be put into consideration in the
clinical management of such conditions.
34. • During plyometric
exercises, the SEC is
known to store up
potential energy that is
released during the
concentric muscle
contraction serving as a
spring suggesting the role
these components play in
shock absorption
especially during walking.
The perception of Delay
Onset Muscle Soreness
(DOMS) after eccentric
contraction is caused by
microtrauma to the PEC
and the SEC.
35. 4. Classifications of the muscles.
• The three main types of muscle include:
• Skeletal muscle – the specialised tissue that is attached to bones and
allows movement. Together, skeletal muscles and bones are called
the musculoskeletal system (also known as the locomotor system).
Generally speaking, skeletal muscle is grouped into opposing pairs
such as the biceps and triceps on the front and back of the upper
arm. Skeletal muscles are under our conscious control, which is why
they are also known as voluntary muscles. Another term is striated
muscles, since the tissue looks striped when viewed under a
microscope.
• Smooth muscle – located in various internal structures including
the digestive tract, uterus and blood vessels such as arteries. Smooth
muscle is arranged in layered sheets that contract in waves along the
length of the structure. Another common term is involuntary muscle,
since the motion of smooth muscle happens without our conscious
36.
37. Make-up of muscle
• Skeletal, smooth and cardiac muscle have very different
functions, but they share the same basic composition. A
muscle is made up of thousands of elastic fibres bundled
tightly together. Each bundle is wrapped in a thin
transparent membrane called a perimysium.
• An individual muscle fibre is made up of blocks of proteins
called myofibrils, which contain a specialised protein
(myoglobin) and molecules to provide the oxygen and
energy required for muscle contraction. Each myofibril
contains filaments that fold together when given the signal
to contract. This shortens the length of the muscle fibre
which, in turn, shortens the entire muscle if enough fibres
38. The neuromuscular system
• The brain, nerves and skeletal muscles work together to cause
movement. This is collectively known as the neuromuscular system.
A typical muscle is serviced by anywhere between 50 and 200 (or
more) branches of specialised nerve cells called motor neurones.
These plug directly into the skeletal muscle. The tip of each branch is
called a presynaptic terminal. The point of contact between the
presynaptic terminal and the muscle is called the neuromuscular
junction.
• To move a particular body part:
• The brain sends a message to the motor neurones.
• This triggers the release of the chemical acetylcholine from the
presynaptic terminals.
• The muscle responds to acetylcholine by contracting.
39. Shapes of skeletal muscle
• Generally speaking, skeletal muscles come in four main
shapes, including:
• Spindle – wide through the middle and tapering at both
ends, such as the biceps on the front of the upper arm.
• Flat – like a sheet, such as the diaphragm that separates
the chest from the abdominal cavity.
• Triangular – wider at the bottom, tapered at the top, such
as the deltoid muscles of the shoulder.
• Circular – a ring-shape like a doughnut, such as the
muscles that surround the mouth, the pupils and the anus.
These are also known as sphincters.
