chap 10

attached to skeletal system, allow movement,composes muscular system,volentary muscle

•Connective tissues •Nerves •Blood vessels

• 1. Exterior collagen layer
• •Connected to deep fascia à separates muscle from surrounding tissues

• 2.Surrounds muscle fiber bundles (fascicles)
• •Contains blood vessel and nerve supply to fascicles

• 3.Surrounds individual muscle cells (muscle fibers)
• •Contains capillaries and nerve fibers contacting muscle cells
• •Contains myosatellite cells (stem cells) that repair damage

• •Endomysium, perimysium, and epimysium come together:
• •At ends of muscles to form connective tissue attachment to bone matrix
• •Tendon (bundle) or aponeurosis (sheet)

• •Are very long (30 cm / 12 in)
• •Develop through fusion of embryonic cells (myoblasts)
• •Become very large
• •Contain hundreds of nuclei

• •The cell membrane of a muscle fiber (cell)
• •Surrounds the sarcoplasm (cytoplasm of muscle fiber)
• •A change in transmembrane potential begins contractions

• •Allow entire muscle fiber to contract simultaneously
• •Have same properties as sarcolemma

• •Made up of bundles of protein filaments (myofilaments)
• •Myofilaments are responsible for muscle contraction
• •Types of myofilaments:

• •A membranous structure surrounding each myofibril
• •Helps transmit action potential to myofibrilSimilar in structure to smooth endoplasmic reticulum
• •Forms chambers (terminal cisternae) attached to T tubules

a triad is made of 1 t-tubule 2 terminal cistenae

release ca2+(via ion pumps) release Ca+ into sarameres 2 begin muscle contraction

• Sarcomeres are the contractile units of muscle (myofibrils surround)
• •Structural units of myofibrils
• •Form visible patterns (stripes, striations) within myofibrils
• •Alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

• m band
• •The center of the A band
• •At midline of sarcomere
• h band
• •Lighter area around the M line
• •Has thick filaments but no thin filaments

•Where thick and thin filaments overlap

• zline
• •The centers of the I bands
• •At two ends of sarcomere
• Titin
• •Are strands of protein
• •Reach from tips of thick filaments to the Z line
• •Stabilize the filaments

f-actin(filamentous),nebulin,tropomysin,troponin

•Controlled by Ca2+

•The active sites of actin bind to myosin

• •Contain about 300 twisted myosin subunits
• •Contain titin strands that recoil after stretching

• The mysosin molecule
• •Tail à binds to other myosin molecules
• •Head à made of two globular protein subunits
• •Reaches the nearest thin filament

what happens•During contraction, myosin heads: •Interact with actin filaments, forming cross-bridges •Pivot, producing motion

• •Troponin–tropomyosin complex changes shape
• •Exposes active site of F-actin

• •Sliding filament theory
• •Thin filaments of sarcomere slide toward M line, alongside thick filaments
• •The width of A zone (dark area of thick filaments) stays the same
• •Z lines move closer together

• •Neural stimulation of sarcolemma
• •Causes excitation–contraction coupling
• •Muscle fiber contraction
• •Interaction of thick and thin filaments
• •Tension production

• •Special intercellular connection between the nervous system and skeletal muscle fiber
• •Controls calcium ion release into the sarcoplasm

• •Action potential reaches a triad
• •Releasing Ca2+
• •Triggering contraction
• •Requires myosin heads to be in “cocked” position
• •Loaded by ATP energy

• •Neural stimulation of sarcolemma
• •Causes excitation–contraction coupling
• •Muscle fiber contraction
• •Interaction of thick and thin filaments
• •Tension production

• 1.contraction cycle begins
• 2.Active-Site Exposure 3.Cross-Bridge Formation 4.Myosin Head Pivoting 5.Cross-Bridge Detachment 6.Myosin Reactivation

adp of myosin head is released when cocked. it needs atp to detach and splits atp to adp releasing energy to recock

• •Duration of neural stimulus
• •Number of free calcium ions in
• sarcoplasm
• Availability of ATP
• relaxation

• •Ca2+
• concentrations fall
• •Ca2+
• detaches from troponin
• •Active
• sites are re-covered by tropomyosin

• •As sarcomeres shorten, muscle pulls
• together, producing tension
• •Muscle shortening can occur at both
• ends of the muscle, or at only one end of the muscle
• •depends on the way the muscle is
• attached at the ends

• •Contraction is an active process
• •SR releases Ca2+ when a motor neuron stimulates the
• muscle fiber
• •Free Ca2+ in the sarcoplasm triggers
• contraction
• •Skeletal muscle fibers shorten as thin
• filaments slide between thick filaments
• •Relaxation and return to resting length
• are passive

• •Length–Tension Relationships
• •Number of pivoting cross-bridges
• depends on:
• •Amount of overlap between thick and
• thin fibers
• •Optimum overlap produces greatest
• amount of tension
• •Too much or too little reduces
• efficiency
• 75-130normal resting of length

• •A single contraction or twitch
• •Which lasts about                                          7–100
• msec.
• sustained muscular contractions
• •Require many repeated
• stimuli

• •The action potential moves through sarcolemma
• •Causing Ca2+ release

• •Calcium ions bind
• •Tension builds to peak

• •Ca2+ levels fall
• •Active sites are covered and tension
• falls to resting levels

repeated stimulus immediatly after relaxion phase frequency <50sec

repeated stimulus before the end of relaxation phase frequency >50sec

rapid stimulation continues muscles not allowed to relax *almost reach max level of tension

stimulation high enough *relaxation stage completely eliminated (producing maximum tension)

internal tension by fibers,number of muscle fibers stimulated. MOTOR units contain hundreds of muscle fibers contracting at same time that r controlled by a single neuron

in whole muscle smoooth motion and increasing tension r produced by slowly increasing number of motor units stimulated. max tension acheived when all motor units reach tetanus,can only be sustained 4 a very short time

less than max tension ,allows motor units to rest in rotation

normal tension of muscle at rest,muscle units maintain body position without motion,increasing muscle tone increases metabolic energy used,even at rest

changes length resulting in motion

if load is less than muscle tension muscle shortens

if muscle tension is less than load (muscle lengthens

skeltetal muscl does not change length,still developing tension

inversly related . the heavier the load. the longer it takes shortening to begin and the less the muscle will shorten

• 1elastic forces (tendons ligaments) expands sarcomeres to resting length.
• 2opposing muscle contractions reverse the direction of the original motion(opposing skeletal muscle pairs
• 3gravity can take the place of opposing muscle contraction to return muscle to its resting state

• atp 2sec 10twitches
• cp 15secs 70 twitches
• glycogen 130secs 670twitches
• aerobic 2400secs 12,000twitches

• stores excess atp
• used to recharge adp to atp usinf enzyme creatine kinase

• (muscles at rest) metabolize fatty acids,store glycogen,build cp reserves
• aerobic metabolism(light activity)34 per glucose molecule
• anarobic 2 per glucose during peak muscular

when muscles can no longer perform a req activity, they r fatigued

depletion of metabolic reserves ,damage to sarcolemma and sacroplasmic reticulum,low ph,muscle exhaustion and pain

the time required after exertion for muscles to return to normal. oxygen becomes available, mitochondrial resumes