Lecture 7 Flashcards
skeletal muscle characteristics
voluntary movement, transverse striations, nuclei on side, myofibrils regularly arranged -> ring pattern
cardiac muscle characteristics
involuntary, can’t contract continuously (relaxation is needed), initiate their own contraction, transverse striation, intercalated disks, nuclei in middle
smooth muscle characteristics
not consciously controllable -> visceral musculature
how do we call the muscle cell, the cell membrane, the cytoplasm and the endoplasmic reticulum ?
muscle fiber, sarcolemma, sarcoplasm, sarcoplasmic reticulum
describe the composition of a skeletal muscle
connective tissue, blood vessels, nerves, muscle fascicles composed of muscle fibers (cells)
describe the composition of a muscle fiber
multiple nuclei, sarcoplasm, sarcolemma and T-tubules -> linked to the sarcoplasmic reticulum.
In the sarcoplasm : myofibrils, mitochondria, glycogen granules
what is the role of sarcoplasmic reticulum ?
storage of Ca2+
composition of myofibrils (and roles)
1) actin (thin)
2) troponin : ca2+ bindind site
3) tropomyosin : shifts to expose myosin binding site on actin
4) myosin (thick)
5) titin : keeps myosin parallel, prevents overstretching
6) nebulin : keeps actin parallel
Z disks at the border of sarcomere
structure of actin filament
spherical actin molucules (G-actin) aggregate into two bead string-like chains, helically coiled around eachother
structure of myosin filament
schaft and head (all heads on the extremities).
On the head : actin binding site, ATPase with different rates
role of T-tubules ?
bring the action potentials into interior of muscle fiber
contraction cycle
1) Ca2+ concentration increases (due to AP) which releases P from ADP+P
2) myosin head binds to actin
3) ADP is released and myosin head pulls actin inwards
4) ATP binds to head and head detaches
5) ATP is hydrolyzed into ADP+P
what is the motor end plate ?
region of muscle membrane that contains high concentrations of ACh receptors
What is the only neurotransmitter at neuromuscular junctions ? name of the receptor ?
acetyl choline (ACh)
Nicotinic receptor (causes Na+ influx)
property of the AP of motoneurons ?
always generate a subthreshold excitatory postsynaptic potential at the neuromuscular endplate (travels into T-tubules)
what converts AP into Ca2+ release ? what happens with Ca2+ in the end ?
DHP receptor opens RyR release channels in sarcoplasmic reticulum (SR).
Sarcoplasmic Ca2+-ATPase pumps Ca2+ back into SR. Even during relaxation, we consume ATP !
What are the 3 skeletal muscle fiber types and what do they look like ?
1) Red muscle fiber (type I) : slow twitch -> endurance. Red because more mitochondria. The muscle has more type I fibers than IIs.
2) Type IIa intermediate
3) White muscle : type IIx, fast twitch : maximum force (less mitochondria because anaerobic processes).
Force and fatiguability of the three fiber types
Force : type IIx > type IIa > type I
Fatiguability : type IIx > type IIa > type I (never fatigues)
tyo types of muscular contractions
1) isotonic : muscle shortens -> moves the load
2) isometric : muscle does not shorten -> not enough force to move load
two types of smooth muscle
1) single unit smooth muscle cells (small intestine) : cells are connected by gap junctions -> contract as single unit
2) multi-unit smooth muscle cells (eye) : not electronically linked -> each one must be stimulated independently
