Ch.6 Muscle Physiology Flashcards
1
Q
muscle type/classification
A
- skeletal, smooth, cardiac
- smooth, striated (other 2)
2
Q
functions of skeletal muscle
A
- body movement
- maintenance of posture
- respiration (diaphragm and intercostal contractions)
3
Q
functions of smooth muscle
A
- constriction of viscera (peristalsis of gastrointestinal tract)
- constriction of blood vessels
4
Q
functions of cardiac muscle
A
heart beat
5
Q
organization of skeletal muscle
A
one myofibril –> one muscle fiber –> fascicle of muscle fibers (100s) –> bundles of muscle fibres
6
Q
investments of skeletal muscle
A
- epimysium: dense collagenous connecti ve tissue that surrounds entire muscle
- perimysium: collagenous connective tissue that surrounds bundles of muscle fibers called fascicles
- endomysium: fine sheath of connective tissue composed of reticular fibers that surrounds individual muscle fibers
epimysium (outside), perimysium (middle - around fascicle), endomysium (inner - surrounds fiber which contains lots of myofibrils)
7
Q
myotendinous junction
A
finger-like extensions of the muscle fibers insert into the connective tissue of the tendon
8
Q
basal lamina
A
external lamina - contains glycoproteins and collagen
9
Q
binding of basal lamina to the skeletal myofiber
A
- cross talk between inside and outside of cell
- basal lamina binds the myofiber via the dystroglycan-containing complex
10
Q
organization of a fascicle of myofibers
A
- long, cylindrical and striated
- multinucleated with nuclei located at the periphery (why? and how do they have so many nuclei?)
11
Q
myofibrils
A
- aligned in parallel
- separated by mitochondria (important for providing energy to skeletal muscle movement) and the sarcoplasmic reticulum
- composed of filaments called myofilaments
12
Q
sarcoplasmic reticulum (SR)
A
- a smooth endoplasmic reticulum
- forms an interconnected network of tubules
- runs longitudinally to the myofibril
- surrounds individual myofibrils with its complex tubule network
- forms chambers called terminal cisternae on either side of the T-tubules
- stores Ca+ when muscle is at rest
- releases Ca+ in the sarcoplasm when muscle is stimulated
13
Q
the triad junction, t-tubules, and voltage gated channel
A
- a single T-tubule and two terminal cisternae
- T-tubules are deep invaginations of the sarcolemma that run perpendicular to the length of the myofiber (think T has perpendicular lines, so adding T to tubule is the one that runs perpendicularly)
- T-tubule has dihydropyridine receptors that fit with Ca2+ release channels on the foot proteins of the cisterna –> when they are bound together in the triad junction they form a voltage-gated Ca2+ channel
- cycle of contraction and relaxation so that Ca2+ is pumped back for another contraction to take place
14
Q
composition of a contractile unit of myofibrils
A
- the sarcomere is the contractile unit
- check slide (pg.19) for picture
- composed of myosin (thick) filament, actin (thin) filament, and elastic (titin) filaments
15
Q
myosin (thick) filament
A
- two head/tail molecules wrapped around each other
- each head has one actin binding site and one myosin ATPase site (ATP will bind and be hydrolyzed)
16
Q
actin (thin) myofilament
A
- two actin strands wrapped around each other
- troponin complexes within strand
- tropomyosin strands (2) also wrapped around with actin filaments
17
Q
binding of myosin head to actin
A
- at low Ca2+ concentration, the myosin binding sites on actin are masked by the tropomyosin
- at high Ca2+ concentration, the tropomyosin no longer masks the binding sites and myosin can bind actin
steps:
1. sarcoplasmic reticulum releases Ca2+
2. Ca2+ binds on top of troponin causing a change of its conformation
3. along with this change, tropomyosin shifts position
4. this shift exposes the binding site on myosin
5. now actin can bind to myosin
18
Q
skeletal muscle contraction
A
- myosin head attaches to the actin myofilament, forming a cross bridge
- power stroke: myosin head bends backwards and pulls on the actin filament, dragging it towards the centre of the sarcomere
- new ATP attaches to the myosin head, and the cross bridge detaches
- ATP hydrolysis into ADP and Pi leads to the cocking of the myosin head, returning to its original position
19
Q
what leads to shortening of sarcomere?
A
- pulling of the actin filaments from the myosin heads that are bound to actin
- actin and myosin filaments overlap slightly for relaxed muscles, and then actin filaments on opposite sides end up overlapping when muscle is fully contracted
- NOT caused by actual shortening of either actin of myosin strands, just sliding against each other
20
Q
motor unit
A
a motor neuron and all the muscle fibers in innervates
21
Q
motor endplate
A
- a specialized domain of the sarcolemma
- highly excitable
- responsible for initiating the action potential that propagates across the myofiber, causing the muscle contraction
22
Q
excitation-contraction coupling
A
- action potential generated is propagated along the sarcolemma and down the T tubules
- action potential triggers Ca2+ release from terminal cisternae of SR
- calcium ions bind to troponin - exposes actin active site
- contraction of myosin fiber, and release of ATP
- Ca2+ is removed by active transport into the SR
- tropomyosin blockage restored, muscle fibers relax
23
Q
neuromuscular junction (NMJ)
A
- junction between the axon terminal of a motor neuron and the motor end plate
