L6 - muscle cells Flashcards
does connective tissue separate smooth muscle cells?
yes
what happens to the nucleus of contracted muscle cells
they become stretched out and can possible see indentations
what is epimysium
sheath of fibrous elastic tissue surrounding a muscle
describe features of skeletal muscle
striated
peripheral nuclei
multinucleated cells
what surrounds myofibrils
sarcolemma
how can t tubules be identified
they run transversely
invaginations of the sarcolemma that indentate into muscle cells
function of T tubules
contain many voltage gated channels that carry on the depolarisation
what is the sarcoplasmic reticulum
Ca2+ store that surrounds myofibrils
describe smooth muscle structure
uninucleate
no striations
spindle shapes
why does connective tissue surround smooth muscle cells
allow nerve tracts and blood vessels
define phasic contractions and give an example
periodic contractions
eg oesophagus, SI only contracts when food enters
define tonic contraction
constant contraction, relax to open
eg sphincters
what are single unit smooth muscle cells
cells connected by gap junctions and contract as a single unit
what are multi unit smooth muscle cells
cells are not electrically linked and can be stimulated individually
describe appearance of cardiac muscle
uninucleate
striated
branched
contain intercalated disks
what are intercalated disks?
desmosomes and gap junctions
where are cardiac muscle cell nuclei located
centrally
explain process of contraction in skeletal muscle
- ACh binds to receptors on post S membrane allowing Na entry
- membrane depolarises and this depolarisation travels down the T tubules
- alters conformation of DHP receptor which is directly coupled to Ryr receptor
- leads to Ca2+ release from sarcoplasmic reticulum
- Ca2+ binds to troponin on actin
- causes tropomyosin to move exposing myosin binding site
- power stroke
does each muscle fibre need to be innervated separately for contraction?
yes
explain process of power stroke
- myosin head bends, sliding actin filament along , ADP and Pi released
- new ATP binding to myosin head breaks cross bridge
explain arrangement of actin and myosin in smooth muscle
- dense bodies (connected to sarcolemma) throughout cell anchor actin filaments (like Z line)
- myosin is surrounded by actin
what connects dense bodies in smooth muscle
Intermediate filaments
explain mechanism of smooth muscle contraction
- Ca2+ enters cytoplasm from ECF and SR
- Ca2+ binds to calmodulin (CaM)
- Ca-CaM activates myosin light chain kinase
- MLCK phosphorylates myosin heads and increases myosin ATPase activity
- ADP + Pi will now be bound to myosin (increased ATPase activity)
- cross bridge to actin can form sliding actin along
explain mechanism of smooth muscle relaxation
- Ca2+ pumped out of cell / into SR
- Ca2+ unbinds from CaM
- MLCK activity drops
- myosin ATPase activity drops
- cross bridges dont form
- relaxation
explain mechanism of cardiac muscle contraction
- auto rhythmic cells fire APs
- depolarisation spreads through gap junctions
- Ca2+ enters cell
- leads to Ca2+ release from sarcoplasmic reticulum
- Ca2+ binds to troponin on actin
- causes tropomyosin to move exposing myosin binding site
- power stroke
how is Ca2+ removed for relaxation of cardiac muscle
- Na / Ca2+ antiport
what anchors myosin filaments to Z line in striated muscle
titin
