Download MBBS Physiology Presentations 68 Structure Skeletal Muscle Lecture Notes

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