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CHS 9 - MUSCLE & MUSCLE TISSUE
Functions of Muscles:
Movement - pulling on something to change its position
Maintaining Posture - tension to prevent movement, keeping vertebral column upright
Stabilizing Joints - attaching to bone & keeping them close together
Heat Generation - release of energy during metabolism
Functional Characteristics of Muscles:
Extensibility - ability to be stretched or extended
Excitability/Irritability - ability to receive and respond to stimuli
Contractility - ability to shorten forcibly when adequately stimulated
Elasticity - ability to resume its resting length after being stretched
Types of Muscle Tissue:
Cardiac Muscles -
Cells have branching chains of uni or binucleate striations, intercalated
discs
Involuntary with intrinsic system regulation, hormones, and autonomic
nervous system controls
Found in the heart
Skeletal Muscles - (most of Ch. 9 is about)
Single, very long, multinucleated cells with striations
Voluntary via axonal endings of the somatic nervous system
Attached to bones and skin
Powerful
Smooth Muscles -
Single, fusiform, uninucleate, no striations
Involuntary with autonomic nerves, hormones, and local chemicals
Found on the wall of hollow organs (stomach, bladder, airways) and tracts
Fibers are small and spindle shaped
Types of Muscle Contractions:
Isometric - tension continues to increase but the muscle neither shortens nor
lengthens
Isotonic - the muscle changes in length and tension remains constant through most
of the contractile period
Concentric - the muscle shortens and does work
Eccentric - the muscle contracts as it lengthens
Types of Muscle Chemicals:
Lactic Acid - product of anaerobic glycolysis, increases during repetitive muscle
contractions, and causes muscle fatigue
Myoglobin - oxygen storage molecules in muscle
Creatine Phosphate - high-energy compound in muscle
Acetylcholine - neurotransmitter at the neuromuscular junction
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Acetylcholinesterase - enzyme released into neuromuscular junction to break down
acetylcholine
Calmodulin - cytoplasmic, calcium-binding protein
Ca++ - an ion released by terminal cisternae into the sarcoplasm to bind with troponin to
remove the blocking action of tropomyosin, resulting in cross bridges
Triad - structure in a skeletal muscle fiber made up of TWO terminal cisterna and a
transverse tubule
Elastic Filaments - allows the muscle fiber to recoil when the contraction ends
Types of Proteins and Their Actions:
Myosin - changes shape during the contraction cycle
In sliding filament model, myofilaments slide over one another resulting in the
overlapping of myosin with actin
Tropomyosin - covers the binding site
Actin - slides toward the M line during a contraction
Troponin - binds Ca++ & starts the contraction cycle
Types of Skeletal Muscle Fibers:
Oxidative fibers—use aerobic pathways
Glycolytic fibers—use anaerobic glycolysis
Slow Oxidative Fibers - most resistant to fatigue
Fast Glycolytic Fibers - have few mitochondria
Fast Oxidative Fibers - contract quickly & rely on aerobic respiration for ATP
Connective Tissue Sheaths of Skeletal Muscles:
Perimysium - surrounds each muscle bundle (fascicle)
Epimysium - surrounds entire muscle (dense layer of collagen fibers)
Endomysium - surrounds each muscle fiber
Deep fascia - binds muscles into functional groups
Cellular Components of Skeletal Muscle Fibers:
Myofibril - rod-like contractile elements within a muscle fiber 80% of cell volume, they
have striations: aligned repeating series of dark A bands and light I bands
Sarcomere - smallest functional unit of muscle fiber, region of myofibril between Z discs,
composed of thick and thin myofilaments
Sarcoplasmic Reticulum - series of membranous channels (modified ER) that
surround each myofibril
Sarcoplasm - cytoplasm of a skeletal muscle fiber
Sarcolemma - plasma membrane of a skeletal muscle fiber
Skeletal Muscle Fiber Areas:
H Band - area in the center of the A band containing only thick filaments
A Band - area of the sarcomere with overlapping thick and thin filaments
I Band - area of the sarcomere containing only thin filaments
Z disc - sheets of proteins that anchor thin filaments & connect myofibrils
H zone - lighter mid-region, no overlapping filaments
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M line - line of protein myomesin that holds adjacent thick filaments together
Muscle Actions:
Wave Summation - when a muscle is stimulated repeatedly for several seconds with a
constant stimulus, the amount of tensions gradually increases to maximum.
Twitch - type of contraction represented by a single stimulus/relaxation sequence
Complete Tetanus - a muscle that is stimulated so frequently that the relaxation phase is
completely eliminated
Incomplete Tetanus - a muscle producing peak tensions with visible relaxation during
rapid cycles of contraction and relaxation.
Activities for Muscle Actions:
Endurance-type activities - best suited for slow oxidative fibers
Short-term intense movements - best for fast glycolytic fibers
400M or 800M sprint - best for fast oxidative fibers
Imbalances:
Strain - excessive stretching & possible tearing caused by overuse or abuse
Cramp - sustained spasm or tetanic contraction
Myalgia - pain resulting from any muscle disorder
Fibromyositis - inflammation of muscle, connective tissue coverings, tendons, and
capsules of nearby joints
Muscle Twitch Periods:
Latent Period - time b/n the stimulus/electrical event & the mechanical event of
contraction
Contraction Period - time during which the muscle is shortening
Refractory Period - very brief time after one stimulus during which the muscle is
unresponsive to a second stimulus
Relaxation Period - time during which the muscle is returning to its original length
Recovery Period - the body's need for oxygen is increased
Action Potential Information:
Resting Potential - initial polarized state
Action Potential - propagation of an electrical current along the sarcolemma
End Plate Potential - electrical event occurring only at neuromuscular junctions
Refractory Period - time when a fiber cannot be stimulated until repolarization is done
Repolarization - restoration of membrane potential to resting potential
Generation & Propagation of an Action Potential:
*Resting Sarcolemma Electrical Conditions are positive outside, negative inside
*Production of an end plate potential and depolarization of adjacent areas is the
depolarization & generation of action potential
*Increased positive charge inside sarcolemma changes permeability of adjacent areas,
opening voltage-regulated Na+ channels which is the propagation of the action potential
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*A change in sarcolemma after the wave of depolarization; Na+ channels close and K_
channels open allowing K+_ to create a positive charge outside the membrane is
repolarization
Force of Muscle Contractions Affected By:
Number of fibers
Relative size of the fibers—hypertrophy of cells increases strength
Frequency of stimulation— frequency allows time for more effective transfer of tension
to noncontractile components
Length-tension relationship—muscles contract most strongly when muscle fibers are 80–
120% of their normal resting length
load latent period, contraction, and duration of contraction
Developmental Aspects:
All muscle tissues develop from embryonic myoblasts
Myoblast-like skeletal muscle satellite cells have limited regenerative ability
Injured heart muscle is mostly replaced by connective tissue
Smooth muscle regenerates throughout life
Female skeletal muscle makes up 36% of body mass
Male skeletal muscle makes up 42% of body mass, primarily due to testosterone
Body strength per unit muscle mass is the same in both sexes
Terms to Know:
Synaptic Cleft - Space between the neuron and the muscle
Myosin molecules - cross bridges
Synaptic Knob - contains vesicles filled with acetylcholine
Motor End plate - contains receptors for acetylcholine
Axon Terminals forms neuromuscular junctions with a single muscle fiber
Motor Unit - a motor neuron & all the fibers it supplies
Cross Bridges - a link between the thick and thin filaments formed by the globular head
of thick filaments.
ATP - provides 95% of energy needed for contraction during moderate exercise
Myasthenia Gravis - autoimmune disease of acetylcholine receptors
Peristalsis - alternating contraction and relaxation of opposing layers of smooth muscle
Excitation-Contraction Coupling - events that form the link between electrical activity in
the sarcolemma and the initiation of a contraction
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