Muscles 1 Flashcards
What are the three types of muscle that exist in the body?
Skeletal and cardiac (striated)
Smooth (blood vessels, airways, uterus, GI tract)
How are skeletal muscle fibres formed?
Groups of cells make a large chain which fuses to form a multinucleated fibre.
Formed by mononucleate myoblasts before birth
What surrounds muscle?
Groups of fibres encased in a connective tissue sheath
What is the function of satellite cells?
They replace damaged cells after injury, they then differentiate to form new muscle fibres
What is the Z line?
The border between sarcomeres
What does do the prefixes myo and sarco mean?
Muscle and flesh respectively
What is a myofibril?
The muscle strand that makes up a muscle cell
What are the thick and thin types of filament?
Thick Myosin and thin actin
What are the names given to the accessory proteins that cover actin?
Troponin and tropomyosin
What does troponin do to tropomyosin?
Holds the tropomyosin in a blocking position on actin
What is the effect of calcium on troponin?
Pulls away tropomyosin revealing binding sits on actin for crossheads.
Where are calcium ions released from?
The sarcoplasmic reticulum, which is studded with calcium pumps and surrounds each sarcomere
What is the function of the transverse tubules?
Conducts electrical signals and allows them to travel deep into the muscle fibre, ensuring the entirety of the muscle fibre receives the command to contract.
What causes the cross head to adopt a high energy configuration?
When it hydrolyses an ATP molecule
What causes the cross head to flip?
When it attaches to the actin and releases its ADP + Pi
What is the state of rigor?
When the cross head is in its low energy conformation whilst it is attached to the actin
What causes cross bridge dissociation?
ATP binding to the cross head (relaxation)
What is a motor unit?
Muscle fibres + motor neurone
Why do several motor neurones enter a large muscle group instead of one branched neurone?
Prevents paralysis of the large muscle group if the branched motor neurone becomes damaged. Allows small contraction, instead of every muscle fibre being innervated by the single branched neurone
What is tension?
The force exerted by a muscle
What is the load?
The force exerted on a muscle
What is the result of too much overlap?
The filaments interfere with one another
What does the A band measure?
The length of the myosin filament (remains unchanged during contraction)
What does the H band measure?
The distance between the actin filaments (reduced on contraction)
What does the I band measure?
The distance between the two myosin filaments
What is referred to as contraction with constant length?
Isometric
What is referred to as contraction with shortening length?
Isotonic
What is referred to as contraction with increasing length?
Lenghtening
What is a twitch?
The contraction of a single muscle fibre
What is the latent period?
The time between AP and start of contraction
What does contraction time depend on?
Calcium ion concentration
What happens to contraction velocity and the distance shortened by a muscle as the load increases?
Contraction velocity decreases and the distance shortened decreases
What is fused tetanus?
Constant stimulation by action potentials, no relaxation in the muscle
Why is tetanic tension greater than twitch tension (in a single fibre)?
Calcium concentration never gets the chance to decrease and allow troponin/tropomyosin to re-block myosin binding sites due to summation of APs keeping channels open
What is the optimal length of a muscle?
Muscle length for greatest isometric tension.
What is each fascicle encased in?
Connective tissue (epimysium)
Which fibre do you find cross-heads?
Myosin
How does AP in neuro-muscular junction lead to muscle contraction?
Electrical signal travels through transverse tubules, opens voltage-gated calcium channels allowing outflow of calcium, calcium changes shape of troponin opening binding site for cross bridge allowing sliding contraction
How does exercise change muscles?
Regular muscle usage results and more contractile protein in sarcomere –> increase in muscle size and contraction strength (as well as duration)
What is hypertrophy and when does it occur in muscles?
Hypertrophy - rapid enlargement of organ, skin or muscle
Occurs after Muscle damage (permenant) by increasing fibril size to support and compensate for damaged muscle
