Download 7_ Myology complete

THE MUSCULAR SYSTEM

The study of the muscles -Myology.

Various movements of the body are made possible
due to the contraction of the muscles.

40 to 50% of body weight is made up of muscles.
FUNCTION OF MUSCLES





1. Skeletal movement and locomotion.
2. Vasodilatation / vasoconstriction.
3. GI tract peristalsis for movement of food and
undigested residue.
4. Generation of body heat through muscle
contraction in movement.
5. Cardiac pump - circulation of blood.
CLASSIFICATION OF MUSCLES
muscle
Smooth
Cardiac
Skeletal
ARRANGEMENT OF SKELETAL MUSCLES
Skeletal muscles may be arranged in any one of the
forms mentioned below:
 Sheet: muscle arranged into a large flat sheet spread
over an area. E.g. muscles making the ventral
abdominal walls- external abdominal obliquous
 Sheet rolled into bundles: sheet of muscle rolled
around limbs-Semi-membranosus
 Bundles: muscle arranged into thick bundles either as
a cone or spindle form-mainly involved in movement of
bones for locomotion. E.g. biceps, triceps


Rings: muscles arranged into circular form around the
natural orifices like eyes, mouth, anus, vaginasphincter anii
Discrete cell or cluster: are muscles either occurring
as single strand or arranged into cluster or group.
FUNCTIONAL GROUPING OF SKELETAL MUSCLES
1.
2.
3.
4.
5.
Flexors: -muscles located on the side of the limb
towards which the limb bends. Bicep -elbow joint.
Extensors: -muscles located on the sides of the limb
towards which the bending is restricted or not
possible. e.g. triceps.
Adductors: -muscles that tend to pull a limb towards
the median plane. e.g. pectoral muscles.
Abductor: -muscles that tend to move the limb away
from the median plane. Eg. deltoideus
Sphincter: -muscle that surround the natural opening
in the body. e.g. anal sphincter
6. Cutaneous muscles:-muscle seen beneath the skin
and are responsible for the movement of the skin.
Ligaments: are the chords or bands that attach one end
of a bone to another and is made up of tough
connective tissues.
Tendon: chord that attach the muscle to the bones
MUSCLES ACTING ON HEAD
MUSCLES ACTING ON NECK AND BACK
ANOTHER BAD MATHEMATICS
SKELETAL MUSCLE STRUCTURE



Entire muscle bundle covered with fibrous connective
tissue-Epimysium (fascia)
The connective tissue sheath covers bundles of
muscle fibres (fasculi)-Perimysium
Connective tissue between individual muscle fibersendomysium.
•
•
•
•
•
•
Individual m. cell = fiber
Cell membrane covering a fiber = sarcolemma
T Tubules (transverse)-inward continuation of
sarcolemma. Impulses travels deep into the muscles
through these tubules.
Sarcoplasmic reticulum-network of membrane within
sarcolemma.
Sarcoplasm-equivalent to cytoplasm.Sorrounds
muscle cells. Within SR.
Components of muscle fibers: 200 - 2000
myofibrils - depending on the diameter of muscle;
each myofibril has striations or banding
•
Each myofibrils contains approximately 1500 thick
and 3000 thin myofilaments
Thick filaments-bundles of myosin molecules
 Two parts- The tail lies parallel to one another forming
the length.
 Head-projects outwards like arms with flexible
attachment to tail
Thin filaments
 Made up of three types of proteins-Actin, Tropomyosin,
troponin.
 Troponin is attached to tropomyosin at specific sitesTroponin-Tropomysin complex.
 Troponin-Tropomysin complex is winded on Actin
chain.
ARRANGEMENTS OF MYOFILAMENTS




A bands-Anisotropic, dark, high density, thick
filaments and overlapping thick and thin filaments
I bands- Isotropic, low density, light zones. Composed
of thin filaments only.
Z line- dense line. Bisects each I band. One end of
each thin filament is attached to Z line.
Sarcomere- the segment of myofribrils between
adjacent Z lines (the fundamental unit of contraction)
MUSCLE CONTRACTION
•
•
•
•
Arrival of a impulse to a NMJ releases
acetylcholine (neurotransmitter) there.
ACh is the neurotransmitter that increases m.
fiber permeability to Na+ ions, after which
depolarization begins.
Produces action potential on the sarcolemma.
Propagation of action potential over the entire
sarcolemma.





When action potential reaches specific receptors
(dihydropyridine) on the sarcolemma-becomes
permeable to Ca ions.
Ca ions diffuses from sarcoplasmic reticulum into
sarcoplasm (sorroundings of muscle fibers).
Ca ions binds to the troponin-molecular changesexposes the myosin binding sites on the actin.
Myosin head binds to actin.
ADP and P on myosin head is released upon binding.





Myosin head rotates from resting stage towards the
centre of sarcomere.
Sliding action pulls the thin filament past the thick
filament.
Whole muscle is shortened-contraction.
Another ATP is attached to the myosin head-myosin
head detaches.
Repeats the process of attachment, rotation,
detachment-shortening of whole muscle-contraction.



Contraction continues as long as excess Ca in the
sarcoplasm.
No action potential in the sarcolemma- Ca is pumped
back out of sarcoplasm with the help of energy from
ATP.
No exposure of binding site for myosin headDetached-Relaxation.
SMOOTH MUSCLES
•
•
•
Plasticity:
 Stress – relaxation property- stretching without
increasing the final tension or pressure exerted
within the content. Without pain
Smooth muscle does not lose its contractile ability
if the expansion is within physiologic limits.
Returns back to normal tension upon emptying.
•
•
Contraction can be initiated by stretch, hormones,
neural, chemical or mechanical stimuli.
Slow sustained contraction often rhythmic i.e.,
peristalsis, permitting stretching of smooth m.
w/out much change in tension unless stretching
is sudden --> contraction
CARDIAC MUSCLES
•
•
Cardiac muscle fibers join, form a network
Intercalated disks = apposed cell membranes
where gap junctions occur permitting electrical
transmission from one cardiac m. cell to the next
- very low electrical resistance here
Individual cardiac muscle cells do not require nerve
stimulation to contract
 Action potentials first occur spontaneously within
specialized myocardial pacemaker cells within the
heart, and these are propagated throughout the heart
by a specialized conduction system and from cell to
cell via the intercalated disks.
 Autonomic nerves innervate the pacemaker cellsmodify the rate of spontaneous action potentialsdetermines contraction rate of the entire heart.

Muscle contraction signaling

Muscle contraction mechanism