6.3 Skeletal muscle Flashcards
Describe the structure of Skeletal muscles
- muscle tissue made up of muscle fibres
- muscle fibres made up of myofibrils - long thin cells that contain many nuclei
- sarcolemma, sarcoplasm and sarcoplasmic reticulum
What is the sarcolemma?
cell membrane of the muscle fibre
What is the role of a tendon?
connects muscle to bone
What are striations?
patterns formed by myofibrils inside each muscle fibre seen under a light microscope
where is the myofibrils located?
in the sarcoplasm of the muscle fibre
What are the 4 myofilaments?
actin
Tropsin
Tropomyosin
myosin
Why does muscle sarcoplasm have lots of mitochondria?
to produce ATP for contraction and resp
What is a sarcomere?
repeat unit of myofibril proteins that have arranged themselves this way
Which myofilament protein is lighter in colour?
actin
Which myofilament protein is the thick filament?
myosin
Which myofilament protein is darker in colour?
myosin
Which myofilament protein is the thinner filament?
actin
what are all the sections to a sarcomere structure?
Z lines
I bands
A band
M line
H zone
What are the Z lines?
mark the boundary of the sarcomere
What is the M line?
marks the middle of the myosin
What is the I band?
where only actin is present
What is the H zone?
where there is only myosin
What is the A band?
where there is both actin and myosin
What are the 2 types of muscle?
slow twitch and fast twitch
What is the use of slow twitch muscle?
endurance
What is the use of fast twitch muscles?
bursts of activity
What are 2 examples of slow twitch muscles?
back muscles and calf muscles
What are 2 examples of fast twitch muscles?
biceps and eye muscles
Describe slow twitch muscle contraction
contract slowly and for longer time
they fatigue slowly
Describe fast twitch muscle contraction
contract and relax rapidly
they contract quickly
fatigued rapidly
Describe slow twitch muscle myofibrils
they low density of myofibrils with many mitochondria
Describe fast twitch muscle myofibrils
high density of myofibrils with fewer mitochondria
What type of respiration occurs in slow twitch muscles?
aerobic
What type of respiration occurs in fast twitch muscles?
anaerobic
Which type of muscle has a higher conc of myoglobin?
slow twitch
Which type of muscle removes lactate quickly?
slow twitch
Which type of muscle has a higher glycogen storage?
fast twitch
What colour is slow twitch muscle?
dark
What colour is fast twitch muscle?
light
What is a neuromuscular junction?
where a motor neurone meets a muscle
Describe how a nervous impulse is transmitted across a neuromuscular junction
- AP arrives at motor neurone axon terminal
- Ca channels open and Ca flood into the presynap neurone
- synaptic vesicles fuse with presynap membrane to release Ach
- Ach diffuses across synaptic cleft to postsynap membrane
- Na gated channels in sarcolemma open and NA diffuse in rapidly
- sarcolemma becomes depolarised - depolarisation passes down the t-tubules that branch through the sarcoplasm
What is troponin structure on an actin filament?
globular protein located at intervals along the actin filament
What is the structure of tropomyosin on the actin filament?
protein that wraps around actin filament by lying in a groove b/w 2 chains of actin molecules
What is the structure of actin molecules in the actin filament?
globular proteins joined in a long chain forming 2 chains that wind around each other forming the actin filament
What are the 2 parts of the myosin molecule structure?
fibrous protein tail
globular protein head
Where is ATPase (hydrolase) located on the myosin molecule?
the globular head
How do myosin molecules arrange to form a myosin filament?
heads at either end of the filament
stack themselves
What happens during muscle contraction according to the sliding filament theory?
thin actin filament slide b/w thick myosin filaments - myosin doesnt move
as a result the sarcomere shortens
What happens to the I band when the sarcomere shortens?
also shortens
What happens to the H zone when the sarcomere shortens?
shortes and may disappear
What happens to the A band when the sarcomere shortens?
stays the same = determined by the length of myosin that doesnt move
What is the role of Ca2+ in the sliding filament theory of muscle contraction?
- proteins in the t-tubules stimulate the Ca2+ channel proteins in the sarcoplasmic reticulum to open
- Ca2+ diffuse out of the sarcoplasmic reticulum into the myofibrils - actin filaments in the sarcomere
- Ca2+ binds to troponin molecules on the actin filament
- troponin changes shape –> dislodging the tropomyosim
- myosin binding sites on the actin filamet are exposed
Describe the process of the sliding filament theory
- myosin heads attach to actin binding sites, forming an actinmyosin cross bridge, ADP and Pi attach to myosin heads
- ADP and Pi are released, changing the angle of the myosin head, pulling actin over the myosin = POWER STROKE
- attachment of ATP to myosin head causes myosin heads to detach from actin sites, cross bridge broken
- ATP is hydrolysed by ATP(hydrol)ase, releasing energy to extend the myosin head ready to bind to actin again = RECOVERY STROKE
What is the power stroke of the sliding filament theory?
the myosin is pulling on the actin filament and causes it to slide over the myosin filament
What is the recovery stroke of the silding filament theory?
the movement of the myosin heads back to its original position after a power stroke to repeat the process of muscle contraction
What are antagonistic muscles?
a pair of muscles working in opposition against an incompressible skeleton
What does the muscle do to the bone and a joint when the muscle is contracted?
when muscle contracts it exerts a force to pull on a bone and flex a joint
What causes a muscle to relax?
a lack of stimulation of the motor end plate = no Ca2+ released = binding sites are covered
What does a flexor do and what is its opposing muscle action?
it bends limbs
opposition = extensor - straightens limb
What does an abductor do and what is its opposition muscle action?
moves limbs laterally away from the body
opposition = adductor = moves limbs laterally towards the body
What does a Protractor do and what is its opposition muscle action?
moves limb forward
opposition = retractor = moves limb backwards
What are 2 examples of antagonistic pairs?
biceps and triceps
hamstring and quadriceps
How is ATP produced from phosphatecreatine?
ADP is phosphorylated by phosphatecreatine and ATP and creatine is produced
Where is phosphatecreatine stored in the muscle fibre?
in the sarcoplasm
What is the role of phosphatecreatine?
a rapid source of ATP
What is used to produce ATP for muscle contraction when all creatine has been used up?
triose phosphate
How is lactate produced from triose phosphate?
- triose phosphate phosphorylates ADP to ATP, and it is oxidised to reduce NAD
- pyruvate is produced
- Pyruvate is reduced from NADH2 to NAD
- lactate produced
What are the disadvantages of sourcing ATP from triose phosphate?
only 2 ATP per 1 glucose
build up of lactate - acidic conds, lowers the pH and causes cramps
What type of neurones (inhibitory or excitatory) are at a cholinergic synapse?
both
What type of neurones (inhibitory or excitatory) are at a neuromuscular junction?
excitatory only
What do pre-synaptic neurones link to at a cholinergic synapse?
links neurons to other neurones or to other effector organs
What do pre-synaptic neurones link to at a neuromuscular junction?
links motor neurones to muscle fibres
What type of neurones does a cholinergic synapse include?
sensory, relay and motor
What happens in terms of action potentials at a cholinergic synapse?
an action potential may be produced in the post-synaptic neurone
What happens in terms of action potentials at a neuromuscular junction?
action potential ends here
Where does Ach bind to at a cholinergic synapse?
to receptors on post-synaptic membrane
Where does Ach bind to at a neuromuscular junction?
receptors on the motor end plate
What is the role of the sarcolemma?
contains the t-tubules
What is the role of the sarcoplasm?
stores phosphocreatine
lots of mitochondria for ATP
What is the role of ATP in muscle contraction?
provides energy for the movement of filaments by changing the angle of the myosin head
causes the formation and detachment of cross-bridges
Why do fast fibres have a high conc of gycogen?
glycogen converted into glucose for glycolysis to produce ATP for rapid muscle contraction
Why do fast fibres fatigue more rapidly than slow fibres?
they anaerobically respire = produces lactic acid and it produces less ATP than aerobic resp
Why can damage to the myelin sheath cause muscular paralysis?
disruption to salatatory conduction
slower impulses along the neurone
slower to reach the neuromuscular junction
