This document summarizes the anatomy and physiology of skeletal muscle contraction. It describes the gross and molecular structures of muscle fibers, including the sarcomere unit composed of actin and myosin filaments. The sliding filament model of contraction is explained, where crossbridges on the myosin head bind to actin and hydrolyze ATP for movement. Calcium released from the sarcoplasmic reticulum initiates the crossbridge cycling. Fast and slow muscle fiber types are compared. The energetics and mechanisms of isotonic and isometric contractions are also summarized.

1. DR.MUMTAZ ALI NAREJO
KHAIRPUR MEDICAL COLLEGE
SINDH PAKISTAN

2. Aims
 Funtional unit of muscle
 Gross anatomy of muscle
 Molecular anatomy of muscle fibre
 Molecular anatomy of actin and myosin filament
 General mechanism of muscle contraction
 Molecuar mechanism of muscle contration
 Fenn effect
 Relation of tension with length of sarcomere
 Relation of velocity with load
 Energetics of muscle contraction
 Isotonic vs isometric muscle contraction
 Fast vs slow fibre
 Motoneuron
 Tetanization

3. SKELETAL MUSCLE FIBRE
 40% = skeletal muscle
 10% = smooth & cardiac muscle
 10 to 80 micrometers
 Sarcolemma
 myofibrils
 1500 myosin +3000 actin filaments
 Thick =myosin=dark band=A=anisotropic
 Thin = actin=light band =I=isotropic
 Myosin projections =bridges
 Actin ends =z disk
 Sacromere = b/w two z disk
 H zone = b/w two dark bands
 Striated appearance
 sarcomere = 2micrometers

6.  Titin molecule = actin & myosin
 Largest protein molecule
 One end = z disk
 One end = myosin
 Sarcoplasm =intracellular
fluid b/w myofbril
K+ , Mg++ , protein,
Mitochondria=ATP
• Sarcoplasm reticulum :
Calcium storage

7. GENERAL MECHANISM OF
MUSCLE CONTRACTION
 action potential =>motor nerve to muscle fibers
 At each ending, nerve =>acetylcholine =>muscle fibre
membrane =>acetylcholine gated channels
 Muscle fibre membrane=>influx of Na+
=>depolarization=>action potential =>muscle fibre
membrane=>Sarcoplasmic reticulum=> Ca++
=>contractile process

8. MOLECULAR MECHANISM
OF MUSCLE CONTRACTION
 Siliding filament mechanism
 Crossbridges of myosin
 Action potential=>
 Sarcoplasmic reticulum=>
 Ca++=>contractile process
 ATP=>ADP

11. Myosin filament
 200 myosin=>myosin filament
 myosin filament=1.6 micrometer
 480,000
 6 chains
 2 heavy + 4 light
 Heavy =200000
 Light = 20000
 Tail+ 2 heads
 Tail =>body of filament
 Head + arm > crossbirdges
 Flexibal part => hinges
 Head =>ATPase activity

12. Actin filament
 Actin+tropomyosin+troponin
 Actin=double helical
 Each actin = 1micometer
 Each strand =>polymerized G-actin
 G-actin=42000
 Each G-actin attached one ATP
 Tropomysin=70,000 ,40 nanometer
 Relxed state ,top of active site =>
no contraction
 Troponin I =actin
 Troponin T =tropomyin
 Troponin c = Ca++
 1 myosin+2 actin filaments+Ca++
 Fenn effect=contraction direct relation
ATP cleavage

15.  V=0.1 sec

16. Energetic of muscle contraction
 W = L ×D
 percentage of energy input that is converted into work
instead of heat
 Maximum efficiency = moderate velocity
 walk-along mechanism
 pumping Ca++
 pumping Na+ & K+
 Muscle fibre = 4 mosm ATP (1-2 sec)
 Phosphocreatinine
 Glycogen => pyruvic acid + lactic acid + ATP
 Oxidative metabolism= 95% energy

17. Charcteristics of muscle
contraction

18. Fast vs slow muscle fibre
Type 1 ,slow fibre , red
muscle
Type 2 ,fast fibre .white
muscle
 Smaller
 Smller nerve fibre
 Extensive blood supply &
capillaries
 Inc mitochondria
 myoglobin
 Large
 Large nerve fibre
 Extensive sarcoplasmic
reticulum
 Large amount of glycotic
enzymes

20. refrences
 Gyton text book of physiology 13th edition
 Netter atlas of physiology

21. THANKYOU