Muscles Flashcards
What are the three types of muscle tissue?
- Skeletal
- Cardiac
- Smooth
Define:
Excitability
Plasma membranes can change electrical states and send action potential along membrane length
What are the three properties of muscle tissue?
- Elasticity
- Extensibility
- Contractility
Define:
Elasticity
Allows muscle to return to original length when relaxed due to elastic fibers
Define:
Extensibility
Muscle tissue can stretch or extend
Define:
Contractility
Allows muscle tissue to pull on its attachment points and shorten with force
Define:
Epimysium
Outer sheath of dense, irregular connective tissue covering muscle
Define:
Fascicle
Bundles of muscle fibers
Define:
Sarcomere
Functional unit of skeletal muscle
What are the two key proteins that make up contractile machinery?
Actin and myosin
What happens to sarcomere structure when muscle contracts?
- A band stays the same.
- I band becomes smaller.
- Z-discs come closer together.
Define:
Myosin
- Thick filament
- Composed of globular head and long tail
Define:
Actin
- Thin filament
- Double helix, “string of pearls”
Define:
Troponin
Globular molecule attached at regular intervals to tropomyosin
Define:
Tropomyosin
Long polypeptide chain that lies in grooves between actin helices
What is the force generated by actin-myosin interaction proportional to?
The number of myosin heads that can interact with thin filament
What is the excitation portion of “excitation-contraction coupling”?
Propagation of action potential along sarcolemma
Where does the action potential travel from the sarcolemma to reach the sarcoplasmic reticulum?
The transverse-tubules (T-tubules)
What ion initiates muscle fiber contraction?
Calcium
What are the steps involved in cross-bridge cycling?
- ATP binds with myosin head, forming ADP and Pi with calcium binding to troponin.
- Myosin binds with exposed actin binding site, generating force.
- ADP and Pi released from myosin head.
- Another ATP binds to myosin.
How does muscle relaxation occur?
- Signaling from motor neuron ends and sarcolemma repolarizes
- Muscle runs out of ATP and becomes fatigued
Define:
Sliding filament theory of muscle contraction
Shortening of sarcomere results from relative movement of actin and myosin filaments past each other while each filament retains original length
Define:
Creatine phosphate
Created when resting muscle transfers energy from excess ATP to creatine to produce ADP and creatine phosphate
What are the three types of muscle contraction?
- Isotonic
- Isometric
- Isokinetic
Define:
Isotonic contraction
Tension in muscle stays constant and load is moved while length of muscle changes
Define:
Concentric contraction
Muscle shortens to move load
Define:
Eccentric contraction
Muscle lengthens while resisting load
Define:
Isometric contraction
Muscle produces tension without changing length and not moving load
Define:
Isokinetic contraction
Muscle contraction and resulting change in joint angle at constant speed
How is the number of muscle fibers in a motor unit determined?
By degree of control required by muscle
Fine movement muscles have fewer muscle fibers per unit while coarse movement muscles have many muscle fibers per unit.
Define:
Myogram
Measures muscle activation and contraction
What are the three phases of a twitch?
- Latent period
- Contraction period
- Relaxation phase
Define:
Latent period
When action potential is propagated along sarcolemma and calcium ions released from sarcoplasmic reticulum
Define:
Contraction phase
- Calcium ions bind to troponin
- Tropomyosin moves away from actin bindinng sites, causing cross-bridges to form
Define:
Relaxation phase
Tension decreases as contraction stops with calcium ions pumped out of sarcoplasm into sarcoplasmic reticulum
Define:
Muscle tone
Small amount of contraction in skeletal muscles
Define:
Hypotonia
Absence of low-level contractions that cause muscle tone
Define:
Hypertonia
Excessive muscle tone and excessive reflex responses (hyperreflexia)
Define:
Slow oxidative, type I muscle fiber
- Contract relatively slowly and use aerobic respiration to produce ATP
Define:
Fast oxidative, type IIa muscle fiber
Have fast contractions and primarly use aerobic respiration but can also use anaerobic respiration
Define:
Fast glycolytic, type IIb muscle fiber
Have relatively fast contractions and use glycolysis to produce ATP
Define:
Gap junction
Forms channels between adjacent fibers allowing depolarizing current from cations to flow from one muscle cell to next
What is the function of electric coupling
Quick transmission of action potentials and coordinate heart contractions
Define:
Syncytium
Functional unit of contraction created by network of electrically connected cardiac muscle cells
Define:
Desmosomes
Cell structure anchoring ends of cardiac muscle fibers together
What is the function of pacemaker cells?
Control heart contractions in response to signals from autonomic nervous system to speed up/slow down heart rate
Define:
Autorhythmicity
The ability to depolarize and fire action potentials independently
Where is smooth muscle most commonly found?
- Walls of hollow organs
- Bloood vessels
- Respiratory/urinary system
- Eyes
- Skin
What is the equivalent of Z-discs found in smooth muscle?
Dense bodies
Define:
Calveoli
Membrane indentations that supply calcium ions via the sarcoplasmic reticulum
What is cross-bridge formation regulated by in smooth muscle cells?
Calmodulin
What is the stress-relaxation response in visceral smooth muscle?
Mechanical stress from stretching muscle triggers contraction followed by relaxation.
What is the function of somites?
Give rise to myoblasts
Define:
Myoblast
Muscle stem cell
Define:
Fibrosis
Scar tissue
What is the function of satellite cells?
Help repair skeletal muscle cells
How is smooth muscle regenerated?
From pericytes
