Muscle microstructure and contraction Flashcards
What are the 3 main types of muscle?
briefly describe there nervous control?
Smooth-under INVOLUNTARY CONTROL from the AUTONOMIC NERVOUS SYSTEM
Cardiac- heart, controlled by AUTONOMIC NERVOUS SYSTEM and circulating chemicals
Skeletal-VOLUNTARY control from the SOMATIC nervous system, usually attached to bones
Where is smooth muscle found?
In the walls of airways
What is the difference between a lower and upper motor neuron?
Lower-goes to the muscles
Upper-comes from the brain
What are the different ways that muscle fibres can be arranged and what does this impact?
- Parallel
- Fusiform
- Triangular
- Multipennate
- Bipennate
- Unipennate
- Pennate the muscle fibres an be attached in different orientations with respect to other things they attach to e.g. ligaments and this impacts their function
What is the structure of skeletal muscles from macro to micro?
bone->tendon->muscle->FASICLES(bundles of muscle fibres)->MYOFIBRE(muscle fibre)->MYOFIBRIL->MYOFILAMENTS(myosin and actin)
What connective tissue is in skeletal muscle?
EPIMYSIUM-outer tissue surrounding muscle(group of fasicles)
PERIMYSIUM- surrounds individual muscle fascicles
ENDOMYSIUM-surrounds a single muscle fibre(myofibre)
What are muscle fibres formed from?
Lots of different MYOBLAST cells
What is a Sarcolemma?
PLASMA MEMBRANE that covers a MYOFIBRE(muscle fibre)
What are the 4 structures in a myofibre?
T-TUBULES-channels that tunnel into the centre of the muscle fibre to allow contraction of inner muscle
SARCOPLASMIC RETICULUM- network of fluid filled tubules
SARCOPLASM- cytoplasm containing MYOGLOBIN and MITOCHONDRIA
MYOFIBRILS-make it up
What is the structure of myofibrils?
SARCOMERE- repeated muscle units
Each muscle unit consists of:
H-ZONE-only myosin
Z-DISC-marks the end of a sarcomere
I-BAND-only actin
A-BAND-overlap of actin and myosin
M-LINE-Middle of sarcomere
Light and dark bands give the muscle STRIATED appearance
Dark bands=Thick bands = MYOSIN
Light bands =Thin bands=ACTIN
What is the structure of Myosin?
- TWO globular heads
- Single tail formed from 2 alpha helices
- tails of several hundred molecules form one filament
What is the structure of actin?
- molecule twisted into a HELIX
- each molecule has a MYOSIN binding site
- on the filament there are TROPOMYOSIN stands which have myosin binding sites on them but when the muscle is not contracting these binding sites are blocked by TROPONIN COMPLEXES
What is the sliding filament theory?
Theory that the myosin and actin filaments slide over eachother to cause muscle contraction
Describe what happens to zones when contraction occurs?
I-band-becomes shorter
A-band-SAME LENGTH
H-Zone- becomes narrowed or disappeared Z-bands get closer together
What initiates muscle contraction?
1-Action potential propagates along the surface membrane of the muscles fibre and into the T-TUBULES
2-DIHYDROPYRIDINE RECEPTOR in t-tubule membrane senses change in voltage and changes shape of the protein linked to the RYANODINE RECEPTOR
3-This causes the ryanodine receptor (calcium channel) in the SARCOPLASMIC RETICULUM to open
4-Ca2+ is released fro the SR into the space around the filaments
5-Calcium binds to TROPONIN and TROPOMYOSIN moves allowing CROSSBRIDGE formation between myosin and actin filaments
6-Calcium is actively transported (via an ATP driven pump) while action potentials continue