skeletal muscles

Question 1

in what way do skeletal muscles work, explain it

Answer 1

ANTAGONISTIC PAIRS against an incomprehensible skeleton -(they pull in opposite directions)
example is external and internal intercostal muscles

Question 2

what is a whole muscle made up of

Answer 2

BUNDLE OF MUSCLE FIBERS which is made from MANY SINGLE FIBERS which is made up of multiple SINGLE MICROFIBRIL

Question 3

what are actin, myosin and tropomyosin

Answer 3

proteins

Question 4

what are muscle fibers

Answer 4

the cells that make up skeletal muscles
muscle fibers contain microfibrils- made out of protein
(microfibrils are NOT CELLS)

Question 5

what is the cytoplasm, endoplasmic reticulum and cell-surface membrane of a muscle fiber called

Answer 5

cytoplasm-sarcoplasm
endoplasmic reticulum- sarcoplasmic reticulum
cell-surface membrane-sarcolemma

Question 6

what are the similarities between a normal cholinergic synapse and a neuromuscular junction (5 points)

Answer 6

• both use acetylcholine
• have a neurotransmitter diffusing across the synaptic cleft
• have receptors on the postsynaptic membrane, that binds to the neurotransmitter , which causes an influx of sodium into the postsynaptic cell
• use acetylcholinerase to breakdown acetylcholine
• use sodium ion-potassium ion pump protein to restore resting potential

Question 7

what are the differences between normal cholinergic synapse and neuromuscular junction (2 differences)

Answer 7

NORMAL CHOLINERGIC SYNAPSE

• neurone to neurone
• can be inhibitory or excitatory

NEUROMUSCULAR JUNCTION

• neurone to muscle fiber
• always excitatory

Question 8

describe transmission across a neuromuscular junction

Answer 8

it’s the same as the cholinergic synapse BUT THE POSTSYNAPTIC MEMBRANE IS THE SARCOLEMMA, NOT A NEURONE MEMBRANE

Question 9

explain the sliding filament mechanism

Answer 9

• tropomyosin prevents myosin heads from attaching to the MYOSIN BINDING SITES on ACTIN
• If stimulation of the muscle fiber reaches the neuromuscular junction and reaches the threshold potential, an ACTION POTENTIAL is sent along the SARCOLEMMA of the muscle fiber
• the depolarisation from action potential causes CALCIUM IONS TO BE RELEASED from the SARCOPLASMIC RETICULUM of the muscle fiber cell which DIFFUSE INTO THE MICROFIBRILS
• CALCIUM IONS cause tropomyosin to CHANGE SHAPE and to PULL AWAY from the MYOSIN BINDING SITES on the ACTIN FILAMENTS
• myosin heads can now attach to the myosin binding sites
• creates ‘ACTINOMYOSINE BRIDGES’
• heads of myosin change angle ‘power stroke’- PULLING ACTIN FILAMENT ALONG. ADP +Pi ARE RELEASED FROM THE HEADS
• ATP MOLECULE BINDS TO MYOSIN HEAD -causing it to DETACH from the actin filament
• the HYDROLYSIS OF ATP TO ADP + Pi by ATP HYDROLASE in the myosin heads releases the energy for the myosin heads to RECOCK
• Heads of myosin reattach to binding sites further along the actin filament and the cycle is repeated.

Question 10

What happens at the molecular level when a muscle relaxes?

Answer 10

• impulses to the neuromuscular junction stops
• the CALCIUM IONS get ACTIVELY PUMPED from the cytoplasm into the sarcoplasmic reticulum
• causes troposim to go back to its original shape and therefore block the myosin binding sites
• myosin can no long bind to the myosin binding sites
• so no actinomyosin cross-bridges form.
• Muscle now relaxed and can be freely lengthened by the pull from the other muscle in the antagonistic pair.