Muscle Flashcards
What are the 3 types of muscle?
Cardiac muscle.
Smooth muscle.
Skeletal muscle.
Which muscle types are involuntary?
Cardiac and smooth
How are cardiac muscle fibres specialised?
They are myogenic (excitatory and conductive so contract without nervous stimulation)
Intercalated disks containing gap junctions allowing the passage of ions in depolarisation, letting excitation waves spread quickly through cardiac muscle cells.
Does cardiac muscle fatigue?
No
How does the micrograph of cardiac muscle appear?
Branched, striated, intercalated disks visible.
Where is smooth muscle found?
In internal organs and vessels such as arterioles and the bladder.
What shape are smooth muscle cells?
Spindle shaped
Does smooth muscle fatigue?
Yes but not nearly as much as skeletal muscle.
How does smooth muscle appear under a microscope?
Spindle-shaped cells, non-striated.
What is the speed of contraction like in smooth muscle compared to cardiac and skeletal?
Very slow.
What are the defining features of skeletal muscle contraction?
Fast and strong contraction.
What are the defining features of skeletal muscle cells?
They can be multinucleated.
Contain multiple myofibrils made out of actin and myosin filaments.
How does skeletal muscle appear under a microscope?
Tubular shaped cells, all aligned.
Striated cells.
Can be multinucleated
What is the name for the plasma membrane of a muscle fibre (cell)?
The sarcolemma
What is a sarcomere?
A subsection of a myofibril.
The space from one Z-line to the next.
Which muscle fibres are thick and which are thin?
Myosin is thick.
Actin is thin.
What happens to the Z-lines during contraction?
They get closer together.
What happens to the H-band during contraction?
It gets smaller.
What is the A-band?
The dark region of the sarcomere, the length of the thick myosin filaments.
What kind of molecule is myosin?
Fibrous protein
What kind of molecule is actin?
Globular protein
What molecules make up the actin filament?
3 actin chains reinforced by tropomyosin bands with troponin forming the troponin-tropomyosin complex.
What is the role of the troponin-tropomyosin complex?
Tropomyosin reinforces the structure.
The complex prevents myosin heads binding to the actin filaments when the muscle is relaxed.
What happens when an impulse arrives at the neuromuscular junction?
The action potential causes the uptake of calcium ions into the synaptic bulb.
The intake of Ca2+ ions cause vesicles to fuse with the pre-synaptic membrane releasing acetylcholine into the cleft.
What effect does the release of acetylcholine into the cleft of the neuromuscular junction have?
Acetylcholine binds to receptors on the sodium ion channels of the sarcolemma, causing Na+ ions to diffuse into the sarcolemma causing depolarisation.
What happens at the neuromuscular junction once the sarcolemma begins to depolarise?
The wave of depolarisation travels down T-tubules into the muscle fibre, stimulating the release of calcium ions from the sarcoplasmic reticulum into the myofibril.
What effect do the calcium ions have in the myofibril?
Troponin binds to Ca2+, changing the shape of the troponin-tropomyosin complex, unblocking binding sites on the actin filaments.
What happens in the myofibril once the binding sites on actin filaments have been unblocked?
The myosin heads attach forming cross-links and perform a powerstroke, pulling the sarcomere together.
Once the myosin heads have performed a powerstroke, what must happen for the cycle to repeat and the sarcomere to contract further?
ATP is hydrolysed, breaking the myosin-actin cross links and causing the myosin head to detach and reattach further along.
What happens during muscle relaxation?
Nervous stimulation stops.
Ca2+ ions are actively transported back into the sarcoplasmic reticulum.
The troponin-tropomyosin complex blocks binding sites on the actin filaments.
Acetylcholinesterase breaks down acetylcholine in the cleft of the neuromuscular junction.
What is the role of creatine phosphate in muscle contraction?
Creatine phosphate supplies phosphate ions to ADP during muscle contraction, forming ATP.
Creatine phosphate is a quick source of ATP for the muscle, and must be phosphorylated in the mitochondria after contraction.
What is ATP required for in the contraction of skeletal muscle?
ATP is required to break the cross-links between myosin heads and the binding sites on actin filaments.
ATP is required to actively transport Ca2+ ions back into the sarcoplasmic reticulum after muscle contraction has taken place.
