Muscles Flashcards
(32 cards)
muscle properties
[hint: C triple E]
Contractility:
Ability of muscle to shorten with a force
Requires energy
Relaxes passively
Excitability:
Capacity of muscle to respond to stimulation (nerves)
Electrical stimulation (heart)
Extensibility:
Muscle can be stretched to its normal resting length and beyond to a limited degree
Stomach/bladder expand as fill
Elastic:
Our muscles return or recoil to resting position when relaxed
muscle types, descriptions, and their locations
skeletal (voluntary). has parallel cells with connective tissue between to form fascicles. has cytoplasmic striations (repeating patterns of light and dark bands), has multiple nuclei
cardiac (myocardium, involuntary). has spindle shaped cells without striations and a single central nucleus
smooth (involuntary). Located in the tissues (walls of hollow organs). Responsible for controlling diameter of structures and peristalsis (movement of food through the digestive system)
skeletal muscle fibre structure
[hint: sarcomere]
sarcomeres made up of alternating actin and myosin filaments which provide striations on muscle cells in longitudinal direction
actin description
[hint: think “tin” = thin, Z is at the end of the alphabet]
Actin = thin myofilament with 6nm diameter, 1μm long
Anchored to Z lines
myosin description
[hint: think M for myosin and middle]
Myosin = thick myofilament with 15nm diameter, 1.5ųm long
Anchored at M lines
Pulls actin along its length (sliding filament mechanism of muscle contraction)
does actin or myosin pull?
[hint: think thin people get pulled more]
myosin
skeletal muscle contraction
- ATP is bound to myosin head in the relaxed position
- When ATP is dephosphorylated to ADP+Pi, it is positioned to form a cross bridge by binding to the actin. However, tropomyosin inhibits/blocks binding sites on actin and prevents this cross-bridge formation
- Electrical excitation of the muscle cell releases calcium from the sarcoplasmic reticulum. Calcium binds to troponin and moves the tropomyosin out of the way to allow cross bridge formation
- Power stroke: release of phosphate bound to myosin head – myosin head moves along the actin filament, dragging it
- At end of excitation, calcium pumps back into sarcoplasmic reticulum, allowing tropomyosin to block myosin binding again and ATP (ADP + Pi) is bound again
muscle contraction speed cause
The speed of ATP use and replacement determines how quickly muscle cells contract
what does tropomyosin do?
[hint: think tropomyosin “trips” up the binding]
takes up the actin binding site so myosin heads cannot form a cross-bridge
latent period
prior to crossbridge formation
what causes calcium release
nervous signal (electrical excitation of muscle cell)
where is calcium released from
sarcoplasmic reticulum
what does troponin do?
[hint: what else starts with “trop”]
when calcium binds to it, TROPonin moves the TROPomyosin out of the way to allow crossbridge formation
contraction period
crossbridge formation + power stroke (dragging of actin along the length of myosin
relaxation period
back to original: calcium pumps back into sarcoplasmic reticulum, allowing tropomyosin to block myosin binding again and ATP (ADP + Pi) is bound again
cardiac muscle contraction
same as skeletal
skeletal muscle type 1 description
Type I /slow twitch /red:
Contracts slowly
Slow to fatigue
Supplied by nerves that activate to contract
Use aerobic (slower) metabolism to generate large amounts of ATP – adapted to deliver O2 to mitochondria using myoglobin
Fibers are red due to myoglobin content which transports O2
skeletal muscle type 2 description
Type II /fast twitch /white
Contract quickly
Fast to fatigue
Use anaerobic (faster) metabolism to generate less ATP – NOT adapted to deliver O2 to mitochondria
smooth muscle contraction types
[hint: think phases are quick, tonic takes a long time to drink]
Phasic – rapid
Tonic – slower maintain tension longer
difference between skeletal and smooth muscle contraction
[hint: think CALM down, CALModulin lets smooth muscle function]
Smooth:
- Ca2+ binds calmodulin (already in the cell) in sarcoplasm rather than troponin.
- Ca-Calmodulin complex activates MLCK (needed for smooth but not skeletal contraction, as skeletal muscle already has ATP) which drives phosphorylation of myosin head (ATP) to enable crossbridge formation.
- Nitric oxide influx from extracellular space -
Drives MLCK to cause relaxation - The Ca2+ concentration determines the force of contraction. The higher the Ca2+ influx, the more force is generated.
- 100-1k x slower so tonic contraction can occur with minimal O2 and ATP usage
- Stimulus for smooth muscle contraction can be varied
motor unit definition
one motor neuron which supplies a group of muscle cells
motor unit types (4) and descriptions
small (red), large (white), slow (red), fast (white)
small motor unit description
Small motor units (red, fewer fibres – mostly type 1)
Higher myoglobin content
Innervate less muscle fibers
Generate less tension
Enable fine control
Fatigue resistant
large motor unit description
Large motor units (white, more fibres – mostly type 2)
Lower myoglobin content
Generate more tension
Fatigue more quickly
Innervate more muscle fibres
