Muscle Structure Flashcards
In 1929, Lohmann discovered ATP in muscle extracts, and it was soon accepted
that the energy for contraction was provided by _____ ___________, not from Lactic Acid
the conversion of ATP to ADP
+ Pi
Skeletal Muscle
o Cells are cylindrical and between in____length
1 mm – 4 cm
______ cells initially provide myoblasts for muscle growth and ensure
restoration of muscle cells following injury
o Satellite cells maintain their own population by self-renewal, thus are stem cells
Satellite
Cardiac muscle
o Contain
1-3 centrally located nuclei
o Oxidative (~40% cell volume is mitochondria)
o Cells electrically coupled
o AP triggers synchronised Ca2+ release from SR (CICR)
o EC spaces contain collagen
Cardiac muscle Intercalated discs at intercellular junctions, consisting of:
§ Nexus or gap junctions
§ Fascia adherens or intermediate junctions
§ Macula adherens of desmosomes (“spot welds”)
Cardiac Cells have a less extensive SR; diad or a triad system?
diad
1993 Calcium sparks
• Proved that the cell uses spatially defined sub-microscope
signals, rather than the cytoplasm behaving like a single
chemical pool
• Current Ca via ____served to trigger SR release
• This takes the form of ‘calcium sparks’ which summate to make
the whole calcium transient
• The amplitude and number (or frequency of firing) of calcium
sparks determines the ____?
DHPRs
calcium transient amplitude
§ Cardiac Calcium buffered in SR by ______, which takes 35-40 calcium
ions per calsequestrin molecule
calsequestrin
SR membrane contains:
- Calcium release channels (RyRs) abundant in junctional SR
* SERCA (2Ca2:1ATP) regulated by phospholamban
• When SR Ca2+ load is high:
o Increased Ca2+ available for release
o Enhanced fraction of Ca2+ released for any given ICa
trigger (“gain” of EC coupling)
Smooth Muscle
o Two types distinguished:
(i) multi-unit cell: lack electrical coupling, neutrally regulated (as with
skeletal muscle)
§ (ii) single-unit: electrically coupled; syncytial (as with cardiac muscle)
Smooth Muscle
o Found in the walls of hollow organs
o Cells are small what length and diameter?
o Cells contain a single, centrally-located nucleus
o Cells contain both actin and myosin but not in the strict proportions of striated
muscle
o There is no T-tubular system
o There is less extensive SR – rather a limited network of narrow tubules near the
plasmalemmal membrane
100-400 micrometres in length
2-5 um in diameter
Smooth Muscle
o Found in the walls of hollow organs
o Cells are small what length and diameter?
100-400 micrometres in length
2-5 um in diameter
Smooth Muscle
o Cells contain ____nucleus
o Cells contain both actin and myosin but?
a single, centrally-located
not in the strict proportions of striated
muscle
Smooth Muscle
There is _____T-tubular system
o There is less extensive ___– rather a limited network of narrow tubules near the
plasmalemmal membrane
no
SR