Transcript Muscles

Stefan Sivkov
MU - Plovdiv
Why do we study muscles?

Body movement

Skeletal movement

Movement of blood

Movement of food

Uterine contractions
Muscle disorders
 Food resource
 Weight control

– Use it or loose it
General characteristics

600 muscles - 40 % body weight

Organ structure
 muscle, connective, nerve, epithelial tissue

Functions
• movement
• heat production
• posture control
• support
Embryogenesis
Mesodermal origin

Somites – primary mesodermal segments
 sclerotomes – vertebral column
 myotomes – muscles of body and limbs

dorsal – back muscles

ventral – antero-lateral and limb
muscles

Branchial gills – facial and neck muscles
Topological organization of
muscles

Paired and symmetrical

Segmental – in the body

Shortest distance between origin and insertion

Perpendicular to the joint axes
Classification

According to the form

According to the fiber direction

According to the function

According the number of joints

According to the position
Structure of the muscle
Contractile (fleshy) part

Extrafusal muscle fibers
 Muscle
fibers
Muscle bundles
Muscle
Connective tissue
in the muscle
1. Endomysium. Thin layer
around the muscle fiber.
2. Perimysium. Thicker layer
around a bundle of muscle fibers
(fascicle).
3. Epimysium. The outer
connective tissue layer.
Muscle spindle

Proprioreception

Intrafusal muscle fibers

thin (30 mm) and short (mm)

central portion (nuclear bag)
- sensory endings

peripheral parts
-
motor endings of g-motoneurons

Intrafusal fibers – nuclear bag and nuclear chain.

Fusimotor fibers – motor nerve fibers.

Primary (Іа) and secondary (ІІ) sensory nerve
fibers.

Registers changes in the muscle length and speed.
Sensation is modulated from CNS by fusimotor
system:
- static gamma system for changes in length
- dynamic gamma system for changes in speed.
Muscle tendon
Attachment of muscle

form – according to the muscle form

thickness – up to 20% muscle thickness

structure
– collagen fibers
– peritendineum – between and around the fibers
– Golgi corpuscles – stretch receptors
– blood vessels – less than in the muscle
Type I muscle fibers

Lowest contractile velocity

Lowest cross section surface

Highest aerobic capacity

Lowest anaerobic capacity

Slow, long-term contraction.

Long distance runners,
swimmers
Type II muscle fibers
Type II-b fibers have

Highest contractile velocity

Highest cross section surface

Lowest aerobic capacity

Highest anaerobic capacity

Quick, short-term contraction.

Sprint, weight-lifting, fitness
Type II-a fibers are intermediate.
Auxiliary structures

Fasciae
proper – one muscle
group – synergic
muscles
septae – separate
neighbouring muscle
groups

Synovial vaginae
 Outer
sheath
 Inner
sheath
 Mesotenon

Synovial bursae
Beneath tendons and muscles, close to
their insertions

Sesamoid bones
In tendons close to their insertions
Histological
characteristics of
muscle fibers
1. Cross striation.
а. Dark and light bands.
1) А-bands. Dark – anisotropic
2) І-bands. Light - isotropic.
б.1) Z disc in І band.
2) Н zone in А band; М линия, dark in Н.
Muscle biomechanics
Internal biomechanics

Physiological transection – perpendicular to fibers

Anatomical transection – through the widest part of the muscle

Vector of muscle strength

Effectiveness of muscle strength - negatively proportional to the
angle between the vector and the bone
Muscle biomechanics
External biomechanics
Movements in joints.

Synergists and antagonists
Muscle strength.

Number and length of the fibers
External biomechanics
Attachments
punctum mobile - insertion
punctum fixum - origin
Levers of muscle contraction
 Fulcrum
 Point of load
 Point of strength


I class lever – of equilibrium
II class lever
 ІІА class – of strength
 ІІВ class – of speed
Theory of sliding myofilaments
Cycle of crossed bridges
ATP required.



Crossed bridges
Myosin
On both sides of the myofilaments
Bidirectional on one side of the myofilament
А-bandsdo not change
І-bands narrow