17,18-skeletal muscle Flashcards
What are the 4 tissue types ?
- Nervous
- Muscle
- Connective
- Epithelial
What are the functions of skeletal muscle ?
- Produce heat:help genererate heat during contraction->helps maintain normal body temp
- Movement of body : responsible for all locomotion and manipulation
- Stabilise joints:help strenghen & stabilise joints of skelaton
- Maintain posture & bidy position:working continuosly
What are general functions of musclesc ?
- Excitability =reieve and respond to stimulas by changing memebrane potential
- Contractility =ability to shorten forcibly when stimulated
- Extensibility :ability to stretch/extend muscle fibres shorten when contracting ;conversly can be stretched when relaxed even beyond resting length
- Elasticity: ability of muscle cell to spring back-recoil
Organisational levels of skeletal muscles ?
Muscle fascile
muscle fibre
myofibril
arrangements of myofilaments
actin & myosin
Organisation of sarcomeres ?
A band =dark regions
I band =light regions
middle of I band=Z band
Actin ?
Made of 3 proteins: globular (G) actin, tropomyosin & troponin.
o Chain of 200 G actin subunits form a strand: fibrous (F) actin.
o Each G actin subunit has a myosin myofilament active site
→ myosin head can bind at this site (as during contraction).
o When a muscle is relaxed, tropomyosin (long, fibrous protein)
covers/blocks the active sites on G actin subunits:
o For a muscle to contract, tropomyosin must move.
o Troponin consists of 3 subunits:
(1) a subunit anchors troponin to
actin;
(2) a subunit prevents tropomyosin from uncovering the
active sites in relaxed muscle;
(3) a subunit that binds Ca2+ ions
Myosin ?
Thick filament
Composed of many myosin molecules (shaped like golf clubs).
o Each molecule is made of 2 myosin heavy chains, wound together to form a rod portion; note: 2 myosin heads.
o 4 light myosin chains are attached to the heads of each
myosin molecule.
What is dystrophin ?
links the thin actin myofilaments to
integral proteins of the sarcolemma (i.e. plasma membrane of the muscle fibre):
o Loss of dystrophin → muscle fibres damage
more easily; compromises the sarcolemma.
In DMD its mutated -x linked
Symptoms fo DMD ?
muslce weakness
muscle atrophy
contractures
What is the sliding filament theory ?
changes in banding pattern -myofilaments slide past each other
Cross bridges –>each actin molecule chain is able to bind to 1 myosin head region
Sliding filament model :myofilaments ?
Thick & thin filaments slide past each other without shortening
Ca2+ions are key for muscle contraction
Action potentials cause release of Ca2+ from SR –>in at the sarcoplasm ,Ca2+ binds troponin –>causes tropomyosin to move –>exposes the active binding on actin myofilaments —> myosin heads can now bind to these sites to form cross-bridges
Muscles contract when cross-bridges move (→ mechanical component of muscle contraction: rapid sequence of events, cause sarcomeres to shorten)
What is step 1 cross bridge cycle ?
Before each cycle, myosin head is in its resting position:
o Myosin stores chemical energy from ATP breakdown that occurred during
the previous cycle; appropriate stimulus causes release of Ca2+ from SR…
Cross bridge cycle step 2 ?
Myosin head remains in its resting position until muscle fibre is stimulated by incoming action potentials (originating from a motor neuron):
o Excitation-contraction is initiated: Ca2+ binds → active sites exposed →
myosin heads bind → cross-bridges are formed.
Cross bridge cycle step 3 ?
Cross-bridge formation triggers rapid movement of myosin heads at their
hinged position:
o Power stroke: movement of the myosin heads → this causes the actin
myofilament to be ‘pulled’ past the myosin myofilament (towards H zone).
Cross bridge cycel step 4 ?
Binding of ATP to the myosin head causes it to detach from actin myofilament
