Muscles I Flashcards
What type of muscle is not striated?
Smooth
What types of muscle are striated?
Skeletal and Cardiac
What are some characteristic of Skeletal muscles?
- Large fibres
- Multinucleate
- Repeating sarcomeres
What are some characteristic of Cardiac muscles?
- Medium-sized fibers
- Single nucleus
- Repeating sarcomeres
- Intercalated disks
What are some characteristic of Smooth muscles?
- Small spindle-shaped fibres
- Single nucleus
- Contractile fibres not arranged as repeating sarcomeres
What is the only muscle type that is NOT directly influenced by endocrine system?
Skeletal
What is the cell in muscles?
Muscle fiber
Is a myofibril a cell?
No
What is the myofibril made out of ?
Bundles of contractile proteins
What is the plasma membrane of muscle fibres?
Sarcolemma
What are t-tubules?
They are extensions of pm that help spreading action potential by regulating concentration of calcium ions
What are the components of a sarcomere?
Myosin thick filament
actin thin filament
Z disk
M line
What are the different areas in a sarcomere?
A band = area of the myosin filaments
H zone = are between actin filaments and m-line
I band = area between a group of myosin filaments of one sarcomere and the other
What does the sarcoplasmic reticulum do?
It wraps around myofibril. Similar to ER. Stores calcium ions
What is the role of nebulin?
It helps to align actin
What does titin do ?
functions as a molecular spring which is responsible for the passive elasticity of muscle in addition to keeping myosin molecules in place.
What is myosin composed of?
2 heavy chains
4 light chains (regulatory LC, essential LC)
Where does Calcium bind on actin filament?
To the troponin complex
What wraps around actin ?
Tropomyosin
What is the troponin complex made out of?
Troponin T: binds tropomyosin
Troponin I : binds actin
Troponin C : binds Ca++
What is the role of tropomyosin?
To cover actin filament and prevent binding. of myosin heads to it (and therefore muscle contraction)
Is sarcoplasmic reticulum Smoot or rough?
Smooth (no ribosomes)
What happens to the bands during muscle contraction?
Z disks get closer
H zone and I band shorten
A band remains constant
What is the receptor that is affected by action potential?
DHR
What happens to DHR upon action potential?
It changes conformation and it opens RyR Ca2+ release channels in sarcoplasmic reticulum
How does ACh cause action potential in muscle fibre?
It opens up ACh receptor channel that allow exchange of ions, especially entry of Na+ that depolarises the cell creating END PLATE POTENTIAL (EPP)
What happens after released calcium causes muscle contraction?
Calcium ions are pumped back in the sarcoplasmic reticulum by Ca2+-ATPase
In what position is myosin usually found in living muscles?
In the cocked position.
What is cocked position?
Myosins have just finished hydrolysing ATP, so they have ADP and Pi still bound to them and are ready to do the power stroke. This cross bridge is quite weak since tropomyosin covers most of binding site, however it helps in creating potential energy.
What happens during power stroke?
Calcium binds to troponin, leading to movement of tropomyosin.
The myosins cross bridges transform into strong bonds.
Myosin releases Pi.
This allows myosin to swivel, swinging the actin filament towards M line.
What happens at the end of a power stroke’
Myosins release ADP
What is the rigor state?
When myosins don’t have ATP nor ADP bound to them so they bind really strongly to myosin heads. Does not happen often in living muscles because plenty of ATP can bind to the heads. Happens in dead muscles as no more ATP is produced (rigor mortis); however stops after a few days when enzymes released start the decay of the muscle
What happens when ATP binds to myosin head?
Myosin releases actin, however the ATP is quickly hydrolysed so the myosin head can rotate and locks itself in the cocked position
What is phospocreatine
A quick source of ATP
What enzyme makes Atp from Adp and phosphocreatine?
Creatine kinase
Where is ATP needed in the ec cycle?
1) Myosin ATPase (contraction)
2) Ca2+-ATPase (relaxation)
3) Na+-K+-ATPase (restores ions that cross cell membrane during action potential)
What is tension?
Force generated by contraction
What is a twitch?
A single contraction/relaxation cycle in a muscle fibre
What does force generation depend upon?
#sarcomeres #myofibrils #muscle fibres
What is a motor unit?
A unit made up of the motor neuron and its corresponding muscle fibre(s).
Can a single motor neuron innervate more than one muscle fibres?
Yes
What does maximum tension depend on?
- Sarcomere length at beginning of contraction
2. Frequency of action potentials
Duration of contraction depends on:
- resistance to fatigue
2. Speed of Calcium pumping back into the SR
Speed of contraction activation depends on:
Myosin isoform present in the muscle
How many isoforms of myosins?
12
What are the three types of muscle fibres?
Type I : slow-twitch red
Type IIa: fast-twitch red
Type IIb: fast-twitch white
What type of muscle fibre is the most fatigue resistant?
Type I : slow-twitch red
Are slow-twitch fibres smaller or bigger in diameter?
Smaller
What is kinesthesia?
The awareness of how the body is moving in space
What is proprioreception?
The awareness of where the different parts of the body are in space
What are the three types of proprioreceptors?
1) Muscle spindles (stretch)
2) Golgi tendon organs (tension)
3) Joint capsule receptors ( position)
Which proprioreceptor responds to stretch?
Muscle spindle
Which proprioreceptor responds to tension?
Golgi tendon
Where do the sensory neurons lie in skeletal muscle ?
In the intrafusal fibres
Where do motorneurons end in the skeletal muscle?
Alpha- extrafusal fibres
Gamma- intrafusal fibres
Does the sensory neuron coming from muscle spindle synapse directly with motor neuron in spinal chord?
Yes
Does the sensory neuron coming from gold tendon synapse directly with motor neuron in spinal chord?
No
