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cardiac muscle

involuntary, striated, intercalated discs, single nucleus

skeletal muscle

striated, multiple nuclei to allow voluntary movement, body mobility

muscle function

movement, posture, protection, thermoregulation, communication

characteristics

excitation, contractability, extensbility, elasticity

development

begins 4th week embryonic stage; mesenchymal cells migrate from mesoderm, differentiate into myoblasts. myoblasts fuse together to form skeletal muscle fiber. satellite cell is an example of an embryonic cell that persist to adulthood, multipotent stem cell limited to muscle line, plays a role in muscle fiber maintence, repair, and remodel

study

tendons

dense regular ct wrappings that extend beyond muscle

aponeuroses

dense regular ct, like tendon but its a sheet

sarcolemma

muscle fiber’s cell membrane, covers muscle fiber. contains invaginations called transverse tubules (t-tubules)

structures of muscle cell

myofibrils - bundles of myofilaments filling up sarcoplasm

sarcoplasmic reticulum - unique to muscle fiber, CONTAINS CALCIUM, wraps around myofibrils

t-tubules - elongated, continuous tube with extracellular space

sarcomere

smallest/functional unit of muscle fiber

• a-band: anisotropic band, contains myosin and overlapping actin

• i-band: isotropic band, contains actin only

• z-line/disc: protein sheet, anchors THIN filaments together and to the sarcolemma

• m-line: formed by small molecules of the protein myomesin that connects in the middle of the sarcomere

• h-band/zone: are of ONLY myosin due to thin filaments not extending into the region

myosin filaments

• thick: contains myosin extending entire length of a-band, connected in middle of sarcomere in m-line

• thin: actin across i-band, partially into a-band. anchored to z-discs

thick filaments

primarily myosin (300), each myosin molecule consists of 6 polypeptide chains; 2 heavy and 4 light. heavy chains twist to form the rodlike tail and have globular head that’s attached to end by flexible hinge region. globular heads with actin binding sites associated with two of light chains tohandle business during contraction.

thin filaments

primarily actin, each actin filament consists of kidney-shaped polypeptide subunites; globular actin/g-actin, has myosin binding sits twisted together into long actin filaments. contain regulatory proteins for muscle contraction (tropomyosin and troponin). tropomyosin is the rodlike protein that spirals about the actin core to help stiffen and stabilize. troponin is a 3 polypeptide subunit that attaches to actin, tropomyosin, and calcium.

Sliding filament theory

1. Cross Bridge Formation: calcium influx, binds to sites on troponin. myosin binding sites exposed by tropomyosin. head attaches to form a cross bridge between myosin head and actin filament.

2. Power Stroke: Myosin head pivots/bends, pulls ACTIN towards M-LINE. ADP and Pi are released from head.

3. Cross Bridge Detachment: ATP binds to myosin causing head to detach from actin. cross bridge is broken

4. Cocking of Myosin Head: Head hydrolyzes to ATP/ADP/Phosphate. Head returns to resting position (high energy).

Acetycholine

Neurotransmitter that motion neurons use to tell skeletal muscle fibers to contract.

Ion channels for skeletal muscle contraction

Chemically gated: Chemical messengers, ion channel creates small local changes in membrane potential

Voltage gated ion channels: Open or close in response to changes in membrane potential

Neuromuscular Junction (occurs before sliding filament theory)

1. AP arrives at axon terminal

2. Voltage gated Ca2+ channels open, enters axon terminal and moves down chemical gradient

3. increased influx of Ca2+ ions causes synaptic vesicles to release Acetylcholine

4. Acetylecholine diffuses across synaptic cleft, bind to its receptors on sarcolemma

5. Binding stimulates opening of chemical ion channels, allows for Na+ to enter and K+ to exit. Causes change in membrane potential

6. Acetylcholinesterase breaks down Acetycholine in synaptic cleft, ion channels close

7. AP causes transient change in membrane potential, interior of sarcolemma becomes more depolarized

*Acetylcholine can be shorted to ACh

Excitation Contraction

1. AP propagtes along sarcolemma down to t-tubulues

2. calcium ions are released, AP causes voltage gatedd Ca channels to open

3. calcium ion influx, binds to troponin removes blocking action of tropomyosin

4. muscle contraction begins where myosin head binds to acting forming bridge

5. after contract, close Ca2+ channels, calcium goes back to SR by active transpor

3 Phases

Latent period - few milliseconds follwing stimulation, cross bridges start to form but no contraction

contraction period - cross bridges active, msucle tension increases. 10ms to 100ms

relaxation - 10 - 100ms due to Ca2+ pumped back into SR. cross bridges declines, muscle tension decreases to 0

tetanus

unfused - degree of temporal summation increases with increase frequency, muscle tension increases with each stimulus. chart looks like teeth

fused - increasing stimuli, muscle tension until maximal tension. no evidence of relaxtion. chart looks like a flat plateau

contractions

concentric - muscle shorten, does work

eccentric - muscle generates force as it lengthens to resting position

these are all isotonic, they change.

isometric - muscle tension develops but the muscle doesn’t shorten. load is greater than force

energy pathways

direct phosphorylation - ATP generated by direct break down of creatine phosphate to creatine using a kinase. kinase transfers phosphate group to a specific molecule. phosphate from creatine is transfered to ADP molecule to make ATP. 2 to 3x more C P stored in muscles than ATP. Intermediate stage

Anerobic - ATP generated by breaking down glucose obtained from book or glycogen stored in muscle. NO OXYGEN. glucose becomes 2 pyruvate molecules releasing 2 ATP. Inefficient, but fast. Glycolytic fibers and lactate fibers have few mitchondria. Fast burst. beginning of sprint

Aerobic - ATP generated by breaking down glucose obtained from body or glycogen stored in muscle. WITH OXYGEN. break down glucose with oxygen leads to aerobix respiration in mitochondria, one glucose yields 32 ATP. Many mitochondria. Endurance.

orbicularis oris

insertion : skin on upper and lower lip

origin : mandible and maxilla