B4 MUSCLES

What’re the 3 types of muscles found in the body?

• cardiac

• skeletal

• smooth

What’re features of skeletal muscles?

• function is locomotion

• cells are striated

• contraction is voluntary and conscious

• have regular arrangement so the muscle contracts in one direction

• contraction is rapid

• short length of time contracted

What’re features of cardiac muscle?

• function is pumping blood through the heart

• cells are specialised striated

• contraction is involuntary

• cells branch and interconnect to allow efficient transfer of impulses so brings about simultaneous contraction

• contraction is intermediate

• intermediate length of time contracted

What’re features of smooth muscle?

• function is to line blood vessels, digestive tract and uterus

• cells are unstriated

• contraction is involuntary

• no regular arrangement as different cells can contract in different directions

• contraction is slow

• can remain contracted for a relatively long time

How are skeletal muscles attached to bone?

by tendon

How do skeletal muscles work?

• can only pull

• antagonistic pairs work together

• agonist contracts while antagonist relaxes

What is the structure of the skeletal muscle?

composed of many highly specialised muscle fibres bound by connective tissue

What’re features of muscle fibres?

• surrounded by a thin cell membrane (sarcolemma)

• nuclei is found beneath the sarcolemma

• sarcoplasm contains a large number of mitochondria

• cell contains a large number of myofibrils which run parallel to eachother (surrounded by the sarcoplasmic reticulum)

What’re features of myofibrils?

• made up of myofilaments

• myofilaments are divided into thick (myosin) and thin myofilaments (actin)

• myofilaments are arranged into sarcomeres

What is the structure of a sarcomere?

What happens to the Z lines and the I band when the muscle contracts?

they decrease in length

What happens to the A band when a muscle contracts?

stays the same length

What is the A band, Z line, M line and I band?

• A band- dark region which contains the entire length of myosin

• Z line- boundaries of the sarcomere

• M line- central line of the sarcomere

• I band- light region which contains only actin filaments

What is the structure of an actin filament?

thin filaments in sarcomere which has a binding site for myosin head, when the muscle is relaxed the binding site is covered by tropomyosin

What is the structure of myosin?

thick filaments in sarcomere that have hinged globular heads so they can move back and forth. each myosin has a binding site for actin and a binding site for ATP

What is the role of calcium ions in muscle contraction?

are released from the sarcoplasmic reticulum where they bind to the tropomyosin protein, change its shape and exposes the binding site

What is the role of ATP in muscle contraction?

molecule that releases the energy for muscle contraction. it bindsss to myosin which releases ATP causing the myosin head to bend

What is the role of tropomyosin in muscle contraction?

a protein on actin filament which blocks the actin-myosin binding site at rest

What occurs in the sliding filament theory?

1. calcium ions are released from the sarcoplasmic reticulum

2. calcium ions bind to protein receptors on the tropomyosin, which are complementary to the calcium ions causing the tropomyosin to move

3. this exposes the myosin-head binding sites on the actin filament

4. myosin heads bind to actin binding sites and form cross bridges

5. each myosin head contains ATP which is hydrolysed into ADP and Pi by ATPase, causing a power stroke which pulls the actin filament a short distance

6. a new ATP attaches to myosin head which breaks the cross bridges and separates it from the actin

7. this process repeats moving the actin along a bit more each time

What is the role of ATP in the sliding filament theory?

• hydrolysis of ATP causes myosin heads to bend

• attachment of new ATP molecules causes myosin heads to detach

What is phosphocreatine?

• stored by muscles

• donates a phosphate to ADP to regenerate ATP in the short term

• phosphocreatine can be regenerated utilising ATP when it can be supplied via respiration

What’re the 2 types of muscle fibres which skeletal muscles are made up of?

• slow twitch

• fast twitch

What’re features of slow twitch muscle fibres?

• slow speed of contraction

• found in large proportions in muscles used for posture

• slow rate of fatigue

• good for endurance activities

• energy is released slowly through aerobic respiration so have many mitochondria and are surrounded by capillaries to supply oxygen and glucose

• red due to myoglobin

What’re features of fast twitch muscle fibres?

• faster, stronger speed of contraction

• found in large proportions in muscles used for fast movement

• fast rate of fatigue

• good for short bursts of speed

• energy is released quickly by anaerobic respiration using glycogen, so they have fewer mitochondria and capillaries

• paler in colour due to no myoglobin

How are slow twitch fibres adapted?

• uses aerobic respiration to regenerate ATP, so have many large mitochondria

• high concentration of myoglobin to act as an oxygen store

• very closely associated with a large number of capillaries to provide an oxygen supply

• less extensive sarcoplasmic reticulum as fewer calcium ions required

• less glycogen as glucose is broken down fully

How’re fast twitch fibres adapted?

• use anaerobic respiration (phosphocreatine) to regenerate ATP

• fewer, smaller mitochondria

• low concentration of myoglobin

• fewer capillaries associated with fibres

• extensive sacoplasmic reticulum as more calcium ions are required at one time for rapid intense contraction

• more glycogen as more glucose required as aerobic respiration yields less ATP per glucose