Post on 18-Jan-2016
Anatomy & Physiology
Chapter 6: The
Muscular System
Muscles are responsible for causing movement in the body.
Three types:SkeletalCardiacSmooth
What are their differentiating characteristics?
Some Prefixes that relate to muscles:-Myo & -mys refer to muscle directly-Sacro refers to “flesh”
Muscular System-General Information
Comparison of Muscle Types
Comparison of Muscle Types
Anatomy of Skeletal MuscleCells are surrounded
and bundled by connective tissueEndomysium—wraps
around A SINGLE muscle fiber
Perimysium—wraps around a FASCICLE (bundle) of muscle fibers
Epimysium—covers the entire skeletal muscle
Fascia—on the outside of the epimysium*chicken breast example
Epimysium blends into one of the following connective tissue attachmentsTendons—cord-like structures
Mostly made of collagen fibersConnect _________ to ______________.
Aponeuroses—sheet-like structuresAttach muscles indirectly to bones,
cartilages, or connective tissue coverings*Think of it as “roots” of a muscle.
Skeletal Muscle Attachments
• Name 4 characteristics of Smooth Muscle:
1. Appearance:2. Nuclei:3.Common Location:4.Action:
Smooth Muscle Characteristics
Cardiac Muscle CharacteristicsName 5
characteristics:1. Appearance:2. Location:3. Nuclei:4. Action:5. Other:
In this chapter we will be focusing mainly on skeletal muscle
What are the 4 main functions:1.2.3.4.
Functions of Skeletal Muscles
Microscopic Anatomy of Skeletal MuscleSarcolemma—
specialized plasma membrane of muscle cells
Myofibrils—long organelles inside muscle cellLight and dark band
alternate giving muscles a “striated/striped” appearance
Light “I” bandsContain thin filaments
Another name for “thin filaments”?
Dark “A” bandsContain thick filaments
Myofibrils-Closer Look
Sacromeres are found within myofibrils and are composed of actin and myosin filaments.
It is known as the part of the muscle fiber that creates contractions.
Structure:Thick filament: Myosin filament
Made of protein myosinHave projections called myosin “heads”Has enzymes that break ATP, known as ATPase
Thin filament: Actin filamentComposed of protein actin
Myosin and Actin overlap to create cross bridging
Sacromeres
CrossBridge Cycling Occurs when thick and
thin filaments connect during a muscle contraction.
The myosin heads help with the binding process.
When they’re aren’t in a cross bridge cycle there is a “bare-zone”This occurs when
muscle is relaxed
Microscopic Anatomy of Skeletal MuscleSarcoplasmic
reticulum—specialized smooth ERThe SR surrounds
each myofibril and stores calcium.
Calcium is used to aid in muscle contraction.
How would a deficiency in electrolytes inhibit the sacroplasmic’s optimum action?
Excitability (also called responsiveness or irritability)—ability to receive and respond to a stimulusWhat are some examples of a stimulus?
Contractility—ability to shorten a muscle when needed
Extensibility—ability of muscle cells to be stretched/elongated.
Elasticity—ability to recoil and resume resting length after stretching.Muscle returns to normal state after a stretch
phase
Terms Related To Contraction of Skeletal Muscle
A motor nerve which innervates muscle must be stimulated in order to create a contraction.
Motor nerves have a neuron/axon They come in contact with a muscle via axon terminalsHence, the term “neuromuscular junction”The nerve endings and muscle cells never directly touch
The gap is known as “synaptic cleft” which absorbs the necessary neurotransmitter
Commonly used neurotransmitter: acetylcholine/AchCauses somewhat of a sodium/potassium pump mechanism
which creates an unbalanced electrical currentThe imbalance leads to an “action potential”The action potential travels along the cell and creates a
MUSCLE CONTRACTION
Nerve Stimulus & Action Potential
Synaptic gap contains ACh which attaches to the ACh receptors
GENERAL OVERVIEW OF HOW A NERVE STIMULUS OCCURS
Action Potential causing a muscle contraction
Transmission of Nerve Impulse to MuscleNeurotransmitter—
chemical released by nerve upon arrival of nerve impulseThe neurotransmitter
for skeletal muscle is acetylcholine (ACh)
ACh attaches to receptors on the sarcolemma
Sarcolemma becomes permeable to sodium (Na+)
Transmission of Nerve Impulse to MuscleSodium rushes into
the cell generating an action potential
Once started, muscle contraction cannot be stopped
How does it stop?Allowing entry of
Potassium ions
Neuromuscular Junction
Activation by nerve causes myosin heads (cross bridges) to attach to binding sites on the thin filamentThin filament is???
Myosin heads then bind to the next site of the thin filament and pull them toward the center of the sarcomere
The attachment/detachment of myosin heads causes crossbridgingResult?
the muscle is shortened (contracted)
The Sliding Filament Theory of Muscle Contraction
Crossbridge cycling
Muscle fiber contraction is “all or none”Within a skeletal muscle, not all fibers may be
stimulated during the same intervalDifferent combinations of muscle fiber
contractions may give different responses
Graded responses—different degrees of skeletal muscle shortening
Contraction of Skeletal Muscle
Contraction of Skeletal Muscle
Graded responses can be produced by changingThe frequency of
muscle stimulationThe number of
muscle cells being stimulated at one time
Muscle fiber contraction is “all or none”Once a muscle is stimulated all of it is
stimulated but not necessarily the WHOLE muscle
Within a skeletal muscle, not all fibers may be stimulated during the same interval
Different combinations of muscle fiber contractions may give differing responses
Graded responses—different degrees of skeletal muscle shortening
Contraction of Skeletal Muscle-General
Tetanus (summing of contractions)One contraction is immediately followed by anotherThe muscle does not completely
return to a resting stateThe effects are added
Leads to a stronger and smoother muscle contraction and
Fused (complete) tetanusNo evidence of relaxation before the following
contractionsResults in a sustained muscle contraction
Graded Responses-Tetanus
Muscle force depends upon the number of fibers stimulated
More fibers contracting results in greater muscle tensionDepends on action being performed
Muscles can continue to contract unless they run out of energy
Muscle Response to Stimuli
Initially, muscles use stored ATP for energy
ATP bonds are broken to release energy
Only 4–6 seconds worth of ATP is stored by muscles
After this initial time, other pathways must be
utilized to produce ATP
Muscles ONLY use ATP as their energy source
Energy for Muscle Contraction
Direct phosphorylation of ADP by creatine phosphate (CP)Muscle cells store CP
CP is a high-energy moleculeAfter ATP is depleted, ADP is
leftCP transfers energy to ADP by
adding a phosphate group, to regenerate ATP
Supplies are exhausted in less than 15 seconds
What exercises/activities would use this energy pathway???
Energy for Muscle Contraction
Aerobic respirationGlucose is broken down to carbon dioxide and
water, releasing energy (ATP)This is a slower reaction that requires
continuous oxygenCANNOT occur w/o oxygen
A series of metabolic pathways occur in the mitochondria
This pathway yields the MOST ATPAppx: 36 ATP/1 glucose molecule
Energy for Muscle Contraction
What exercises/activities would use this energy pathway???
Energy for Muscle ContractionAnaerobic glycolysis and lactic acid formation
Reaction that breaks down glucose without oxygenOccurs in cytosol
Glucose is broken down to pyruvic acid to produce some ATP
Pyruvic acid is converted to lactic acidThis reaction is not as efficient, but is fast
Huge amounts of glucose are neededLactic acid produces muscle fatigueOnly produces about 5% as much ATP as aerobic
respiration
What exercises/activities would use this energy pathway???
When a muscle is fatigued, it is unable to contract even with a stimulus
Common cause for muscle fatigue is oxygen debtOxygen must be “repaid” to tissue to remove
oxygen deficitOxygen is required to get rid of accumulated
lactic acidIncreasing acidity (from lactic acid) and lack
of ATP causes the muscle to contract lessIn extreme cases a person can collapse (i.e.
marathon runners)
Muscle Fatigue and Oxygen Deficit
Isotonic contractionsMyofilaments are able to slide past each other
during contractionsThe muscle shortens and movement occurs
Isometric contractionsTension in the muscles increasesThe muscle is unable to shorten or produce
movementThe static resistance causes myofibrils to spin
but NOT slide across each other
Types of Muscle Contractions
Some fibers are contracted even in a relaxed muscle
Different fibers contract at different times to provide muscle toneMuscle is firm and ready for activity
The process of stimulating various fibers is under involuntary control
Muscle Tone
Exercise increases muscle size, strength, and enduranceAerobic (endurance) exercise results in
stronger, more flexible muscles with greater resistance to fatigueHow is this resistance created at the cellular
level?Makes body metabolism more efficient
Resistance (isometric) exercise (weight lifting) increases muscle size and strengthMuscle fibers don’t increase rather the number
of myofibrils/myofilaments within the muscle fiber
Effect of Exercise on Muscles