Muscles Flashcards
Skeletal muscles
- muscle on bone
– Striated muscle attached to bones of the skeleton
– Control body movement
– Voluntary control; responds to somatic motor neurons
cardiac muscle
– Striated muscle found only in the heart w/ intercalated disks
– Moves blood through the circulatory system
– Involuntary control; responds to autonomic innervation, spontaneous contraction, modulated by the endocrine system
smooth muscle
- in arteries and veins, stomach intestines, lining of esophagus, etc.
- lacks striations
– Primary muscle of the internal organs and tubes
– Influence the movement of material into, out of and within the body
– Involuntary control; responds to autonomic innervation, spontaneous
contraction, modulated by the endocrine system
origin and insertion of skeletal muscles
– Origin: closest to the trunk or to more stationary bone ( more proximal and doesn’t move)
– Insertion: more distal or more mobile attachment (moves and more distal)
flexor and extensor skeletal muscles
- Flexor: brings bones together (majority = anterior side of body. Ex: biceps)
- Extensor: moves bones away (posterior side of body. Ex: triceps)
Flexor-extensor pairs form antagonistic muscle groups
- antagonistic = does the opposite
- ex: bicep is flexed so tricep is antagonistic
antagonistic muscles
- antagonistic muscle groups move bones in opposite directions
- muscle contraction can pull on a bone but cannot push a bone away
what are muscle cells called?
- muscle fibers
- long and cylindrical
- fused cells with many nuclei
satellite cells (stem cells)
- in charge of repair
- differentiate into muscle for growth or repair
fascicles
- fibers bundled into fascicles surrounded by connective tissue sheath
- blanket around muscle fiber and glues tendon to bon
connective tissue surrounds entire muscle
– Continuous with connective tissue sheath
– Holds muscle to bone with tendon
sarcolemma
cell membrane of muscle fiber
sarcoplasm
cytoplasm of muscle fibers
sarcoplasmic reticulum
- endoplasmic reticulum
- wraps around myofibrils like a lace
▪ Longitudinal tubes with enlarged ends called terminal cisternae
▪ Concentrates and sequesters - stores calcium
myofibrils
- accessory proteins associated w/ muscle fibers
- bundles of contractile and elastic proteins that help with contraction
- ex: myosin, actin, etc
transverse (t) tubules
- Continuous with the sarcolemma
- T-tubule + 2 flanking terminal cisternae = triad
- Allow action potentials to penetrate nearer to the internal structures of the fiber
thin filament
- actin
thick filament
- myosin: isoform. small changes
- heavy chains: motor domain; myosin ATPase
- light chains: regulatory fxn
regulatory proteins
- tropomyosin: covering actin binding sites
- troponin: on top of tropomyosin as gatekeeper. won’t come off unless it interacts w/ Ca2+
slow-twitch fibers (ST or type I)
- swimming
- rely primarily on oxidative phosphorylation
- looks red
- aerobic
fast-twitch fibers
- sprinting, 100 m dash, quick bursts of energy
– Develop tension faster
▪ Split ATP more rapidly
– Pump Ca2+ into sarcoplasmic reticulum more rapidly - Fast-twitch oxidative-glycolytic fiber (FOG or type IIA)
- Use oxidative and glycolytic metabolism
- Fast-twitch glycolytic fibers (FG or type IIB/X)
- Rely primarily on anaerobic glycolysis
isotonic contractions
- looking if it moves or produce force
- concentric action is a shortening action –> picking up table (biceps = shortening)
- eccentric action is a lengthening action –> lowering it (bicep = lengthening)
- promotes strength
isometric contractions
- contraction that produces force and nothing moves
- not strong enough or not putting enough force
- series elastic elements
- sarcomeres shorten while elastic elements stretch, resulting in little change in overall length
motor unit
- consists of one motor neuron and all the muscle fibers it innervates
- a muscle may have many motor units of diff types
sliding filament theory of contraction
– Overlapping actin and myosin myofibrils
– Fibrils are fixed length
– Slide past each other in energy-dependent
- tropomyosin covers actin binding sites
- troponin acts as the gatekeeper and it opens the gate once Ca2+ binds to it
- once calcium binds troponin, myosin heads can bind to the actin and contraction can happen
- upon contraction the actin (thin) and myosin (thick) glide past each other
- ATP molecules bind to myosin heads thus severing the bonds btw myosin and actin (Myosin ATPase)
- energy is stored in the myosin heads ready to be used for the next movement cycle
Events at the neuromuscular junction
- Acetylcholine (ACh) is released from the somatic motor neuron
- ACh initiates an action potential in the muscle fiber
- ACh binds to receptors on the sarcolemma
- Na+ enters the cell and K+ ions exit the cell
- Depolarization → end-plate potential (EPP) → muscle action potential
- The muscle action potential triggers calcium release from the sarcoplasmic reticulum
- L-type calcium channel dihydropyridine (DHP) receptor on t-tubule
- Ryanodine receptors (RyR) on sarcoplasmic reticulum
- Calcium combines with troponin to initiate contraction
calcium pump
- pumps the calcium back into the sarcoplasmic reticulum
lever
- rigid bar that pivots around a point called a fulcrum
- bones form levers
what forms fulcrums?
- flexible joints
Class III
- most common lever
- spine, hip, knee, elbow, shoulder
class II
- doing plantar flexion
- calf muscle
class I
- neck flexion
- cervical flexion and extension
- fulcrum = middle
phasic smooth muscles
- contract we have movement go thru
- swallow food –> esophagus contracts and moves food down
- usually relaxed and upon contraction we have movement
tonic smooth muscles
- relaxation movement will go thru
- esophageal and urinary bladder sphincters
- holding pee till you can go
- usually contracted and upon relaxation we have movement
what is smooth muscle controlled by?
- autonomic nervous system
for smooth muscles where does Ca2+ come from for contractions?
- comes from extracellular fluid and sarcoplasmic reticulum
true or false. smooth muscles can sustain contractions for extended periods without fatiguing
true. we wanna make sure its all going in one direction
what does smooth muscle lack?
- troponin
- uses calmodulin instead
calcium in smooth muscles
- utilize it from the blood from the ECF
- skeletal gets calcium from SR
myosin phosphorylation controls contraction
- sarcoplasmic reticulum and ECF releases Ca+
- Ca+ binds to calmodulin
- Calmodulin activates myosin light chain kinase
- myosin light chain kinase phosphorylates myosin light chains
- this increases mason ATPase activity (we break down more ATP that is attached to myosin)
- myosin light chain phosphorylase dephosphorylates myosin ATP
- this causes relaxation of the muscle
calcium initiates smooth muscle contraction
- Contraction caused by electrical signaling is
electromechanical coupling - Contraction caused by chemical signaling is
pharmacomechanical coupling - Sarcoplasmic Ca2+ release
- Ryanodine receptor (RyR) calcium release channel
- IP3-receptor channel
- Calcium-induced calcium release (CICR)
- Store-operated Ca2+ channels
cell membrane calcium entry
- Voltage-grated Ca2+ channels
- Ligand-grated Ca2+ channels, or receptor operated calcium channels (ROCC)
- Stretch-activated calcium channels
- Open when pressure or other force distorts cell membrane
- Myogenic contraction
- Some smooth muscles have unstable membrane potentials
- Slow-wave potentials
- Pacemaker potentials
