Lecture 1: Skeletal muscle part 1 Flashcards
Are skeletal muscles striated?
yes
Are skeletal muscles under voluntary control?
yes
Shape of skeletal muscle
multiple peripheral cells
Shape of a skeletal muscle?
long, cylindrical cells, single
What are the three main types of muscle?
skeletal
cardiac
smooth
What are skeletal muscles?
attached to bones and is responsible for movement
What are cardiac muscles?
forms the bulk of the heart mass and its contraction ejects blood from the organ
Smooth
mainly lines hollow organs, iris, blood vessels (regulates their dimensions)
Are cardiac muscles under voluntary control?
no
Are cardiac muscles striated?
yes
What are the shape of cardiac muscle cells
branched cells with 1-3 central nuclei
How are cardiac muscles connected?
they are connected by intercalated discs
Where are cardiac muscles located?
in the heart ONLY
What control are smooth muscles under?
involuntary
what is the shape of a smooth muscle?
spindle shaped, uninucleated cells
Are smooth muscle cells striated?
no
Where are smooth muscle cells found?
in the gut, respiratory system, blood vessels
What is a motor unit?
a group of muscle cells which is innervated by a single motor neuron
what are the two major groups of proteins which are responsible for muscle contractions in all 3 muscle types?
actins
myosins
List in order the skeletal muscle is packaged
1.) skeletal muscle is attached to the bone by a tendon
it is wrapped by epimysium
2.) the skeletal muscle contains bunches of fascicles (perimysium surrounded)
3.) fascicles encase bundles of muscle fibres/cells (endomysium)
4.)muscle fibres encase myofibrils
5.) myofibrils encase filaments
What is the structure of a muscle cell?
sarcolemma (plasma membrane)
sarcoplams (like cytoplasm)
t tubule (invaginations of the sarcolemma towards the centre of the myofibril; open to sarcoplasm)
Structure of a myofibril?
surrounded by a sarcoplasmic reticulum (SR); stores Ca2+
triad is formed when 2 terminal cisternae and a T tubule meet
What is the sarcomere?
the smallest unit of contraction
from Z to Z band
Describe cross bridge formation, what are the 4 stages?
Cross bridge formation
power stroke
detachment
energization of myosin head
What happens during cross bridge formation?
the energized myosin head binds to a receptor site on the actin molecule
forming a cross bridge
inorganic phosphate is released
the bond between actin and myosin become stronger
what happens during power stroke?
ADP is released
the inactivated myosin head pivots
sliding the thin myofilament toward the centre of the sarcomere
What happens during cross bridge detachment?
ATP binds to the myosin head
the link between the actin and myosin weakens
the myosin head detaches
What happens during the reactivation of myosin head?
ATP is hydrolyzed to ADP and inorganic phosphate on the myosin heaed
the energy released during hydrolysis
reactivates the myosin head returning it to cocked position
What is the structure of thick filaments?
composed of molecules of myosin mainly
has a tail and a head
the tail is oriented towards the M line
What are thin filaments made of?
double stranded helical actin chain
accesory proteins which regulate them:
troponin
tropomyosin
What is the sliding filament model?
the Z line is pulled to the M line
the I band and the H zone become narrower
as sarcomeres shorten
A bands do not change in length
How does calcium regulate contraction?
as the sarcoplasm is depolarized
Ca2+ channels will open in the SR thus releasing ions into the sarcoplasm, increasing the Ca2+ levels
this will cause more Ca2+ to bind to troponin to enable it to change its conformation, to enable tropomyosin to expose myosin binding sites on actin
What influences the muscle contaction?
the amount of Ca2+ in the cytosol
What is the optimum length of sarcomere for max tension?
- 2 micro metres
2. 0 - 2.2 micrometres
What happens when the length of a sarcomere is less than 2.2 micro metres?
the Z discs will crumple the thick filaments, less myosin head will be able to bind to actin
What happens when the length of a sarcomere is greater than 2.2 micro metres?
there will be either no thin filaments that myosin heads will binds to, or decrease of binding to actin
thus overall, force generated is reduced
