Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st Year, 2nd Year, 3rd Year and Final year Physiology 68 Structure Skeletal Muscle PPT-Powerpoint Presentations and lecture notes
Structure and Function of
Skeletal Muscle
Skeletal Muscle
n Human body contains over 400 skeletal
muscles
n 40-50% of total body weight
n Functions of skeletal muscle
n Force production for locomotion and
breathing
n Force production for postural support
n Heat production during cold stress
Structure of Skeletal Muscle:
Connective Tissue Covering
n Epimysium
n Surrounds entire muscle
n Perimysium
n Surrounds bundles of muscle fibers
n Fascicles
n Endomysium
n Surrounds individual muscle fibers
Structure of Skeletal Muscle:
Microstructure
n Sarcolemma
n Muscle cel membrane
n Myofibrils
n Threadlike strands within muscle fibers
n Actin (thin filament)
n Troponin
n Tropomyosin
n Myosin (thick filament)
Structure of Skeletal Muscle:
The Sarcomere
n Further divisions of myofibrils
n Z-line
n A-band
n I-band
n Within the sarcoplasm
n Sarcoplasmic reticulum
n Storage sites for calcium
n Transverse tubules
n Terminal cisternae
The Neuromuscular Junction
n Site where motor neuron meets the muscle
fiber
n Separated by gap cal ed the neuromuscular cleft
n Motor end plate
n Pocket formed around motor neuron by
sarcolemma
n Acetylcholine is released from the motor
neuron
n Causes an end-plate potential (EPP)
n Depolarization of muscle fiber
Illustration of the
Neuromuscular Junction
Motor Unit
n Single motorneuron & muscle fibers it
innervates
n Eye muscles ? 1:1 muscle/nerve ratio
n Hamstrings ? 300:1 muscle/nerve ratio
Muscular Contraction
n The sliding filament model
n Muscle shortening occurs due to the
movement of the actin filament over the
myosin filament
n Formation of cross-bridges between actin
and myosin filaments
n Reduction in the distance between Z-lines
of the sarcomere
The Sliding Filament Model of
Muscle Contraction
Cross-Bridge Formation in
Muscle Contraction
Sliding Filament Theory
n Rest ? uncharged ATP cross-bridge complex
n Excitation-coupling ? charged ATP cross-
bridge complex, "turned on"
n Contraction ? actomyosin ? ATP > ADP & Pi +
energy
n Recharging ? reload cross-bridge with ATP
n Relaxation ? cross-bridges "turned off"
Muscle Function
n Al or none law ? fiber contracts
completely or not at al
n Muscle strength gradation
n Multiple motor unit summation ? more
motor units per unit of time
n Wave summation ? vary frequency of
contraction of individual motor units
Energy for Muscle Contraction
n ATP is required for muscle contraction
n Myosin ATPase breaks down ATP as fiber
contracts
n Sources of ATP
n Phosphocreatine (PC)
n Glycolysis
n Oxidative phosphorylation
Sources of ATP for Muscle
Contraction
Properties of Muscle Fibers
n Biochemical properties
n Oxidative capacity
n Type of ATPase
n Contractile properties
n Maximal force production
n Speed of contraction
n Muscle fiber efficiency
Individual Fiber Types
Fast fibers
Slow fibers
n Type IIb fibers
n Type I fibers
n Fast-twitch fibers
n Slow-twitch fibers
n Fast-glycolytic fibers
n Slow-oxidative fibers
n Type IIa fibers
n Intermediate fibers
n Fast-oxidative
glycolytic fibers
Comparison of Maximal
Shortening Velocities Between
Fiber Types
Histochemical Staining of Fiber
Type
Fiber Types and Performance
n Power athletes
n Sprinters
n Possess high percentage of fast fibers
n Endurance athletes
n Distance runners
n Have high percentage of slow fibers
n Others
n Weight lifters and nonathletes
n Have about 50% slow and 50% fast fibers
Alteration of Fiber Type by
Training
n Endurance and resistance training
n Cannot change fast fibers to slow fibers
n Can result in shift from Type IIb to IIa
fibers
n Toward more oxidative properties
Training-Induced Changes in
Muscle Fiber Type
Hypertrophy and Hyperplasia
n Increase in size
n Increase in number
Age-Related Changes in
Skeletal Muscle
n Aging is associated with a loss of muscle
mass
n Rate increases after 50 years of age
n Regular exercise training can improve
strength and endurance
n Cannot completely eliminate the age-
related loss in muscle mass
Types of Muscle Contraction
n Isometric
n Muscle exerts force without changing length
n Pul ing against immovable object
n Postural muscles
n Isotonic (dynamic)
n Concentric
n Muscle shortens during force production
n Eccentric
n Muscle produces force but length increases
Isotonic and Isometric
Contractions
Illustration of a Simple Twitch
Force Regulation in Muscle
n Types and number of motor units recruited
n More motor units = greater force
n Fast motor units = greater force
n Initial muscle length
n "Ideal" length for force generation
n Nature of the motor units neural stimulation
n Frequency of stimulation
n Simple twitch, summation, and tetanus
Relationship Between Stimulus
Frequency and Force
Generation
Length-Tension Relationship in
Skeletal Muscle
Simple Twitch, Summation,
and Tetanus
Force-Velocity Relationship
n At any absolute force the speed of
movement is greater in muscle with
higher percent of fast-twitch fibers
n The maximum velocity of shortening is
greatest at the lowest force
n True for both slow and fast-twitch fibers
Force-Velocity Relationship
Force-Power Relationship
n At any given velocity of movement the
power generated is greater in a muscle
with a higher percent of fast-twitch
fibers
n The peak power increases with velocity
up to movement speed of 200-300
degrees?second-1
n Force decreases with increasing movement
speed beyond this velocity
Force-Power Relationship
Receptors in Muscle
n Muscle spindle
n Detect dynamic and static changes in muscle
length
n Stretch reflex
n Stretch on muscle causes reflex contraction
n Golgi tendon organ (GTO)
n Monitor tension developed in muscle
n Prevents damage during excessive force
generation
n Stimulation results in reflex relaxation of muscle
Muscle Spindle
Golgi Tendon Organ
This post was last modified on 08 April 2022