The Muscular System:
Skeletal Muscle Tissue
and Muscle Organization
Three types of muscle tissue
Skeletal muscle
Cardiac muscle
Smooth muscle
Introduction
Muscle tissues share four basic properties:
Excitability
Contractility
Extensibility: the ability to continue to contract over a range of resting lengths.
Elasticity
Functions of Skeletal Muscle
Produce skeletal movement
Maintain posture and body position
Support soft tissues
Regulate entering and exiting of material
Maintain body temperature
Anatomy of Skeletal Muscles
Muscle Fiber Organization
Muscle Organization
Tendons & Aponeurosis
Neuromuscular junction
Muscle cells
Sarcolemma – Openings to T-tubules
Sarcoplasmic reticulum – Terminal cisternae
Triads
Myofibril - Sarcomeres
Thick filaments
Myosin, titin
Thin filaments
Actin, tropomysin, troponin
Sarcomere Structure
Myofilaments
The Sliding Filament Theory
The H band and I band get smaller.
The zone of overlap gets larger.
The Z lines move closer together.
The width of the A band remains constant throughout the contraction.
Strength of contraction & Sarcomere length
The Sliding Filament Theory
The Start of a Contraction
Electrical events at the sarcolemmal surface:
Trigger the release of calcium ions from the terminal cisternae
The calcium ions diffuse into the zone of overlap and bind to troponin
Troponin changes shape, alters the position of the tropomyosin strand, and exposes the active sites on the actin molecules
The End of a Contraction
Electrical stimulation ends
calcium ions are pumped back into the sarcoplasmic reticulum
Troponin–tropomyosin complex cover the active sites,
Contraction will ends
The Neural Control of Muscle Fiber Contraction
Muscle Contraction: A Summary
Motor Units and Muscle Control
Muscle Contraction
Motor unit summation
Recruitment
Muscle tone
Resting tension
Muscle spindles
Muscle Hypertrophy and Atrophy
Exercise causes an increase in:
Number of mitochondria
Concentration of glycolytic enzymes
Glycogen reserves
Myofibrils:
Each myofibril contains a larger number of thick and thin filaments
The net effect is an enlargement, or hypertrophy, of the stimulated muscle.
Disuse of a muscle results in the opposite, called atrophy.
Types of Skeletal Muscle Fibers
Fast fibers
White fibers: large glycogen reserves
Slow fibers
Red fibers: myoglobin
Intermediate fibers
Similar to fast but with more mitochondria & capillaries
The Organization of Skeletal Muscle Fibers
Muscle Terminology
Origin remains stationary
Insertion moves:
Commonly the origin is proximal to the insertion.
If the muscle extends from a broad aponeurosis to a narrow tendon:
aponeurosis = origin
tendon = insertion
If there are several tendons at one end and only one at the other:
multiple = origins
single = insertion
Muscle Actions
Flexion of forearm vs flexion at the elbow
Prime movers – agonists
Synergists
Fixator
Antagonist
Names of Skeletal Muscles
Specific body regions:
Brachialis
Shape of the muscle:
Trapezius
Orientation of muscle fibers:
Rectus, transverse, oblique