Muscle Structure- connective tissue component 1. Endomysium-
delicate connective tissue membrane that covers specialized
skeletal muscle fibers. 2. Perimysium- tough connective tissue
binding together fascicles 3. Epimysium-coarse sheath covering the
muscle as a whole 4. These 3 fibrous components may become a tendon
or an aponeurosis.
Slide 4
Size Shape and fiber arrangement 1. Skeletal muscles vary
considerably in size, shape, and fiber arrangement 2. Size- range
from extremely small (muscles to bones in ear) to extremely
large-(quadriceps) 3. Shape- variety of shapes, such as broad,
narrow, long, tapering, short, blunt, triangular, quadrilateral,
irregular, flat sheets, or bulky masses. 4. Arrangement- variety of
arrangements, such a s parallel to long axis, converge to a narrow
attachment, oblique, pennate, bipennate, or curved; the direction
of fibers is significant due to its relationship to function
Slide 5
Attachment of Muscles 1. Origin- point of attachment that does
not move when the muscle contracts. 2. Insertion- point of
attachment that moves when the muscle contracts
Slide 6
Muscle Action Muscle movement is a coordinated action of
several muscles; some muscles in the group contract while others
relax PRIME MOVER (agonist)- a muscle or group of muscles that
directly performs a specific movement ANTAGONIST- muscles that,
when contracting, directly oppose prime movers; relax while prime
mover (agonist) is contracting to produce movement; provide
precision and control during contraction of prime movers.
Slide 7
Muscle actions continued SYNERGISTS-muscles that contract at
the same time as the prime movers; they facilitate prime mover
actions to produce a more efficient movement FIXATOR MUSCLES- joint
stabilizers
Slide 8
LEVER- any rigid bar free to turn about a fixed point called a
fulcrum In the body the bones act as a lever, joints serve as a
fulcrum and the muscles applies a pulling force on a bone lever at
the point of attachment to the bone.
Slide 9
Levers (p284)
Slide 10
Tips on Naming Skeletal Muscles Direction of Muscle Fibers
rectus oblique Relative Size of Muscle Fibers maximus minimus
longus Location of the Muscle temporalis frontalis
Slide 11
Tips on Naming Muscle Number of Origins biceps triceps
quadriceps Location of Origin and Insertion sterno cleido
mastoid
Physiology of the Muscular System General Function of the
Muscular system MOVEMENT HEAT PRODUCTION POSTURE Function of
muscular tissue Excitability ( or irritability)- they can respond
to regulatory mechanisms like nerve signals. Contractility- Ability
to contract, pull on bones and produce movement Extensibility-
Ability to extend or stretch to return to resting length.
Slide 14
Muscle Cell overview Muscle cell are called fibers because they
are threadlike in shape. Sarcolemma is the plasma membrane of the
muscle cell. Sarcoplasmic Reticulum- Network of tubules and sacs
found within mm fibers Membrane of the SR continually pumps calcium
ions from the Sarcoplasm and stores the ions within its sacs.
Muscle fibers contain many mitochondria and several nuclei.
Myofibrils are numerous fine fibers packed close together in the
sarcoplasm
Slide 15
Slide 16
Sarcomere Segment of myofibril between two successive Z lines
Each myofibril consists of many sarcomeres Contractile unit of the
muscle fiber
Slide 17
Slide 18
T tubules Transverse tubules extend across the sarcoplasm at
right angles to the long axis of the muscle fiber. Membrane has ion
pumps that continually transport Calcium ions inward from the
sarcoplasm Allow electrical impulses traveling along the sarcolemma
to move deeper into the cell.
Slide 19
Triad A T-tubule sandwiched between 2 sacs of SR. Allows an
electrical impulse traveling along T- tubule to stimulate the
release of Ca++ causing a contraction of the mm cell.
Slide 20
Myofilaments Each myofibril contains thousands of thick and
thin myofilaments Four different proteins make up these
myofilaments Myosin Makes up THICK filaments Heads are chemically
attracted to actin molecules Myosin heads are known as cross
bridges when attached to actin. Actin- globular protein that forms
two fibrous strands twisted around each other to form the bulk of
the THIN filament. Tropomyosin- protein that blocks the active
sites on the actin molecules Troponin- protein that holds
tropomyosin molecules in place
Slide 21
Slide 22
Sliding Filament Theory The sliding filament theory states that
when signaled the actin filament within each sarcomere slides
toward one another, shortening the sarcomere in each fiber causing
muscle contraction.
Slide 23
Mechanism of contraction When a motor neuron sends and impulse
to the muscle cell The neurotransmitter ACETYLCHOLINE is released
and stimulates the T tubules and the impulse travels inward causing
release of Ca++. Ca++ binds to troponin, causing the tropomyosin to
shift and expose active sites on the actin.
Slide 24
Relaxation of Muscle Immediately after Ca ions are released the
SR begins pumping them back into the sacs. Ca++ ions are removed
from the troponin and it shuts down the contraction. ATP is the
energy source Muscle cells continually re-synthesize ATP from the
breakdown of CREATINE PHOSPHATE Aerobic respiration- adequate
levels of ATP because Oxygen is available. Anaerobic respiration-
inadequate O2 levels in cell respiration result in lactic acid
fermentation. See ACTIN-MYOSIN ppt
Slide 25
The Motor Unit= Neuromuscular junctions (nerve meets
muscle)
Slide 26
Muscle fiber types Red-slow twitch fibers (dark meat) Thin,
slow acting ATPases, red in color due to myoglobin Fat metabolism,
fatigue resistant- aerobic pathways High endurance, not much power
White-fast twitch (white meat) Little myoglobin, thicker, fast
acting ATPases Large glycogen reserves, anaerobic, fatigable fibers
Short term, rapid, intense movements Intermediate-fast twitch
fibers Fast acting, fast acting myosin, oxygen dependent, less
fatigable,
Slide 27
Muscle fibers cont Muscles contain a mixture of muscle fibers
Sprinting- white fast twitch Marathon- red slow twitch Posture- red
slow twitch Weight lifters- balance between red and white.
Slide 28
Physiology of Skeletal Muscle Contraction Energy Sources
Breakdown of ATP ATP ADP + O2 + energy Energy comes from CELLULAR
RESPIRATION Results depend on AMOUNT OF OXYGEN AVAILABLE Moderate
activity- adequate amounts of oxygen Strenuous activity- not enough
oxygen causing Pyruvic Acid (from the first step of Cell
respiration) to be converted to LACTIC ACID OXYGEN DEBT-extra
oxygen that must be taken in by the body for restorative process.
Difference between the amount of oxygen needed for totally aerobic
respiration during muscle activity and the amount actually
used.
Slide 29
Muscle tone Steady partial contraction present at all times
State of tension when awake Enable muscle to react immediately Does
not produce active movement Loss of muscle tone in paralysis, coma,
atrophy, prolonged immobilization.
Slide 30
Muscle fatigue Muscle unable to contract Tension drops
Inability to generate enough ATP to power contraction Excessive
accumulation of lactic acid and ionic imbalance Spasm- sudden
involuntary contraction Clonic- alternating spasm with relaxation
Tonic- sustained Tetanus-smooth sustained contraction Tetany-result
of low calcium, increases excitability of neurons, convulsions may
follow.
Slide 31
Twitch Contraction A quick jerk of a muscle that is produced as
a result of a single, brief threshold stimulus. 3 phases Latent: AP
reaches sarcolemma; SR releases Ca 2+ ; 2ms Contraction:
Cross-bridge formation; Ca 2+, troponin; 15ms Relaxation: Ca 2 +
uptake; tropomyosin covers actin; 25ms All or None response- Once
the muscle fiber has been stimulated to contract the muscle fiber
will contract to its fullest extent.
Slide 32
Twitch Contraction
Slide 33
Twitch to full contraction How do twitches achieve whole muscle
contraction? By building tension 1. Multiple motor units are
stimulated (recruited) 2. Stimulus from nerve arrives more
frequently
Slide 34
Types of Muscle contraction- myography Single twitch
contraction- seen in above slide Treppe Staircase phenomenon-
strength of contraction builds after it has contracted a few times
(stronger when you get warmed up) Tetanus Results from the
coordinated contractions of different motor units within the muscle
organ. These motor units fire in an overlapping time sequence to
produces a relay team effect that results in a sustained
contraction. This is the kind of contraction exhibited by normal
skeletal muscle organs most of the time. (incomplete and complete
tetanus)
Slide 35
Muscle contraction cont Muscle tone Tonic contraction is a
continual, partial contraction in a muscle organ. At any one moment
a small number of the muscle fibers in a muscle contract, producing
a tautness of the muscle rather than a recognizable contraction.
Muscle tone. Allows muscle to always be ready to respond when
stimulated immediately. Muscles with less tone than normal are
FLACCID Muscles with excess tone are called SPASTIC. GRADED
STRENGTH PRINCIPLE- basically the number of muscle fibers
contracting are in response to the task. Ie. Heavy object, more
myofibrils contract
Slide 36
Isotonic vs. Isometric contraction Isotonic contraction is a
contraction in which the tone or tension within a muscle remains
the same as the length of the muscle changes. (P 328) There is
actually movement- lifting weights Isometric contraction is a
contraction where the length of the muscle stays the same while the
muscle tension increases. Ie. Pulling up on an immovable
object.
Slide 37
Slide 38
Points of Interest Muscle fatigue- simply muscle exhaustion.
Muscle runs out of ATP rendering myosin heads incapable of
producing the force required for continued contraction Exercise
effects on muscle: Disuse causes atrophy (wasting away). Overuse
causes hypertrophy (overgrowth) Strength training- increases the
number of myofilaments in each muscle fibers, increasing muscle
mass. (muscle fibers stay the same myofilaments can increase.)
Endurance training- lean muscle not hypertrophy. This increases the
number of blood vessels to the tissue, increasing oxygen
availability and efficiency along with increase in mitochondria for
higher ATP production.
Slide 39
Cardiac muscle Heart muscle Cells directly connected via
intercalated discs (pores through which ions pass) Allows all
connected cells to contract as one Cardiac muscle is autorhythmic
(spontaneous generation of AP) Involuntary (influenced by hormones)
Metabolism is always aerobic
Slide 40
Smooth muscle Less actin & myosin, no sarcomeres Contracts
slowly No O 2 debt Autorhythmic Involuntary control