Muscles Pt. 1 Flashcards
What are the characteristics of skeletal muscle?
- Striated.
- Voluntary.
- Moves bones.
What are skeletal muscles controlled by?
Somatic nervous system.
What are the characteristics of smooth muscle?
- Lacks striations.
- Involuntary.
Where are smooth muscles found?
In blood vessels, airways, and lining organs.
What are smooth muscles controlled by?
Autonomic nervous system.
What are the characteristics of cardiac muscle?
- Striated.
- Intercalated discs.
- Involuntary.
What is cardiac muscle controlled by?
Autonomic nervous system.
What are the functions of muscle?
- Produce body movement.
- Stabilize body position.
- Store and move substances w/in the body.
- Generating heat.
How does muscle move the body?
Through tendons that connect them to bones and ligaments that connect them to one another.
What are the muscles called that stabilize body position?
Postural muscles.
What muscles assist with storage and movement of substances in the body?
- Movement of gametes (smooth muscles in vas deferens and uterus).
- Uterus in blood vessel walls.
- Sphincters.
How do muscles generate heat?
They contract, causing shivering.
What are the 4 properties of muscle tissue?
- Contractility.
- Elasticity.
- Electrical Excitability.
- Extensibility.
What does contractility allow for?
The muscular tissue to contract forcefully when stm. by an action potential, allowing for tension generation.
What does electrical excitability allow for?
Responsiveness to action potentials.
What does elasticity allow for?
The muscle to return to its original length and shape after stretching.
What does extensibility allow for?
The muscle to stretch w/o being damaged.
What is the sarcolemma?
Muscle fiber plasma membrane.
What is the transverse tubule/T-tubule?
The sarcolemma extension that carries the action potential to the sarcoplasm.
What is the sarcoplasm?
The cytoplasm of muscle cells.
What is the sarcoplasmic reticulum?
The calcium storage, release, and reuptake unit.
What are terminal cisterns?
End portions of the sarcoplasmic reticulum that contact T-tubules.
What is a triad composed of?
T-tubules + 2 terminal cisterns on either side of the T-tubules.
What is actin?
The thin myofilaments.
What is myosin?
Thick myofilaments.
What is the troponin and tropomyosin complex?
The complex located on the actin filaments that regulate the interaction between actin and myosin. Undergoes a conformation change due to calcium binding.
What is the Z-Disc?
Point of actin attachment.
What is the sarcomere?
The smallest functional unit of a muscle cell. Spans the z-disc.
What is a fasicle?
Bundles of muscle fibers.
What is the motor unit?
A single motor nerve and all the muscle fibers it supplies.
What is a myofibril?
Muscle strand.
What is the rule with a motor unit?
Only one motor nerve innervation per muscle fiber but a motor neuron may innervate more than one muscle fiber.
*How many muscle fibers are innervated is location dependent.
What is the A Band?
Where the myosin is located in the muscle fiber.
What is the I Band?
Where the actin is located in the muscle fiber. Shrinks with contraction.
What is the M Line/Myomesin?
The center of the sarcomere that attaches myosin together.
What portion of the muscle fiber disappears when contraction occurs?
The H-zone.
What is muscle?
Many muscle fibers aligned in parallel.
What is muscle fiber?
Single, multi-nucleated, long cylindrical cells.
What are myofibrils?
Bundles (100’s-1000’s) of contractile filaments within muscle fibers.
What doe the heads on myosin fibers look like?
Bi-lobed.
How do the myosin heads attach to the actin?
In coordination, not unison.
What is the MW of myosin?
480,000
How many polypeptide chains is myosin composed of?
6.
How many heavy chains does myosin contain?
2.
How many light chains does myosin contain?
4.
What do the 2 myosin heavy chains form?
A double helix with a tail and the other end forms bilaterally into a globular bi-lobed head.
How many light chains are connected to each myosin head?
2.
What is the function of myosin light chains?
Controlling the function of the myosin head during contraction.
How many myosin filaments make up a myofilament?
~200.
What are crossbridges?
Protruding arms and heads on the myosin fibers.
At what 2 points do crossbridges flex?
- Where the arm leaves the body.
- Where the head attaches to the arm.
At what angle are crossbridges displaced from one another?
120 degrees.
What does the myosin head contain?
An ATP binding site.
What does ATPase enzyme activity near the ATP binding site cause to occur?
Cleavage of the ATP and utilization of the released energy for contraction.
What are the 3 parts of the actin filament?
- Actin.
- Tropomyosin.
- Troponin.
What is the backbone of the actin filament composed of?
2x-stranded filamentous actin with the addition of globular actin molecules.
What is the MW of actin?
42,000.
Where is ADP found in actin filaments?
Active sites.
What is holding the base of the actin filaments?
Z discs.
What is the MW of tropomyosin?
70,000.
Where is tropomyosin found?
Wrapped spirally around the sides of the F-actin helix.
What does tropomyosin look like in the resting state?
- Lies on top of active sites on actin.
- No attraction of actin and myosin.
Where is troponin found?
Attached intermittently along the sides of tropomyosin.
What 3 protein subunits is troponin composed of?
- Troponin I.
- Troponin T.
- Troponin C.
What is troponin I attached to?
Actin.
What is troponin T attached to?
Tropomyosin.
What is troponin C attached to?
Ca2+.
What is the 3rd most plentiful protein in skeletal muscle?
Titin.
*One of the largest protein molecules in the body.
What is the function of titin?
- Helps maintain side-by-side alignment of actin and myosin.
- Myofibril elasticity and extensibility.
How large is a titin protein?
1/2 a sarcomere, Z-disc to M line.
What is the function of myomesin?
- Binds titin to connect adjacent thick filaments to one another.
- Forms M line.
What type of protein is nebulin?
A non-elastic protein.
Where is nebulin found in the myofiber?
Wrapped around the entire length of each actin filament.
What is the function of nebulin?
To help anchor the actin to the Z-disc.
What type of protein is dystrophin?
A cytoskeleton protein.
Where is dystrophin found in the myofiber?
Linking actin of the sarcomere to integral membrane proteins of the sarcolemma.
What is the function of dystrophin?
- Help transmit tension generated.
- To reinforce the the sarcolemma.
What is muscular dystrophy?
An inherited disease that causes the progressive degeneration of skeletal muscle.
What is Duchenne muscular dystrophy (DMD)?
A type of sex-linked (X chromosome) muscular dystrophy caused by a mutation in the gene that codes for dystrophin. This results in the sarcolemma tearing during muscle contraction.
*Most common type.
What is the prevalence of DMD?
1:3500 males.
When are most males with DMD diagnosed? When do most die?
- 2-5 yrs. old.
- 20 years old.
What are the steps of muscle relaxation?
- Ca2+ is pumped into the SR by active transport.
- Ca2+ is released from troponin.
- The troponin slides back into place, covering the myosin binding site.
What is Calsequestrin?
A calcium-binding protein in the SR.
How much higher is the Ca2+ concentration in the SR than in the cytosol?
10,000.
What are the 3 types of muscle action?
- Concentric.
- Eccentric.
- Static.
What is concentric muscle action?
Shortening of the muscle as the actin filaments pull closer together.
*Principle action.
What is eccentric muscle action?
Exerting force while lengthening as the actin filaments are pulled further away from the center of the sarcomere.
What is static muscle action?
Muscle action w/o moving where the muscle length is the same, despite force being generated by the formation and recycling of myosin crossbridges.
*Joint angle does not change
What is isotonic contraction?
Contraction against a constant load, normally when mechanically work is being done.
ex: Locomotion.
What is isometric contraction?
Contraction w/o an appreciable decrease in length of the muscle due to the muscle being unable to overcome the load placed on it.
ex: Posture.
What is the other name for Hyperkalemic Periodic Paralysis (HYPP)?
Impressive Syndrome.
What is the origin of HYPP?
A mutation in the quarter horse stallion Impressive.
What is the mutation that causes HYPP?
A point mutation where a phenylalanine is replaced with a leucine, affecting the function of voltage-gated sodium channels.
What is the heritability pattern of HYPP?
Autosomal dominant with incomplete penetrance.
*H/H horses are more severely affected.
What are the signs of HYPP?
- Dog sitting.
- Loud breathing.
- Muscle fasciculation/tremors.
- Prolapsed third eyelid.
- Sporadic episodes (30-60 min.) of muscle paralysis due to abnormal depolarization of muscle cell membrane.
What is HYPP often confused with?
Tying up.
What is the exact physiological process behind HYPP?
Na+ channels do not close fast enough, causing them to be “leaky”. This results in an inappropriate influx of Na+ followed by K+ efflux, causing hyperkalemia.
What are the downstream effects of the malfunctioning sodium channels?
- Altered membrane permeability to Na+ and K+.
- Altered Na+/K+ pump function.
- Increased K+ in the ECF makes Na+ channels excitable.
- Reduced Ca2+ release from the SR.
What are the treatment options for HYPP?
- Acetazolamide.
- Hydrochlorothiazide.
- Calcium gluconate w/ 5% dextrose solution.
- Karo syrup.
- Low K+ diet.
What is the other name for milk fever?
Parturient Paresis.
When does parturient paresis generally occur?
At/near parturition. Usually w/in 72 hours.
What causes parturient paresis?
The onset of lactation, which depletes the Ca2+ levels in the body (especially in the ECF).
What are signs of stage 1 milk fever?
- Excitability.
- Hypersensitivity.
- Mildly ataxic.
- Mild tremors.
- Restless.
What are signs of stage 2 milk fever?
- Cold extremities.
- Dull demeanor.
- Inappetence.
- Maintenance of sternal recumbency.
- Subnormal temperature.
- Unable to stand.
What are signs of stage 3 milk fever?
- Coma.
- Complete muscle flaccidity.
- Unable to maintain sternal recumbency.
- Unresponsive to stimuli.
*Survives only a few hours in this state.
What is occurring at the nerve during milk fever?
Not enough Ca2+ present to regulate Na+ permeability, leading to increases in resting membrane potential and excitability. However, no neurotransmitters will be released due to no Ca2+ entering near the axon terminal.
What is occurring at the muscle during milk fever?
No action potential from the motor neuron leads to no muscle action potential, no Ca2+ released from SR, and no contraction.
What is the treatment for milk fever?
IV/IP/SQ calcium gluconate.
*Administer slowly to avoid the cardiotoxic effects of Ca2+.
How is milk fever prevented?
- Addition of anionic salts to ration to enhance Ca2+ resorption from bone and absorption from GIT.
*Dietary cation/anion difference (DCAD).
