skeletal muscle structure and contraction Flashcards
3 muscle types:
- smooth (e.g. contraction and dilation of blood vessels/bronchioles)
- striated (skeletal)
- cardiac
functions of skeletal muscle (5)
- locomotion
- breathing
- postural support
- heat production during cold stress
- largest protein store in body (can tap into if malnourished)
define syncytium
multi nuc. cell
skeletal muscle fibres(cells):
3 general features
- striated (stripy appearance)
- syncytium (multi nucleated cells)
- peripheral nuclei
a bundle of muscle fibres is…?
fascicle
name the 3 types of connective tissue covering in skeletal muscle
EPI-
PERI- -MYSIUM
ENDO-
define epimysium
connective tissue surrounding entire muscle
define perimysium
connective tissue surrounding fascicles (bundles of muscle fibres)
define endomysium
(connective tissue) surrounds individual muscle fibres
2 functions of connective tissue covering in muscles:
- functional: transmit info (load?) from muscle to bone
- protective (stronger than muscle)
the components that make up single muscle fibre: (3 - sub.s within each)
- sarcolemma (membrane)
- myofibrils (tubular structures that pack fibres)
- myofilaments (threadlike strands within myofibrils - ACTIN thin - troponin + tropomyosin, MYOSIN thick)
sarcomeres:
zones and bands - name and say what each has in
I band: actin filaments only
(LIGHT BAND)
A band: actin and myosin filaments (includes I band)
H zone: myosin filaments only *(between M line and Z line)
Z line: boundary between sarcomere
M line/band: transverse line in middle of sarcomere, binds myosin filaments
sliding filament theory: the general idea of what happens (do not need to mention specifics for interactions between filaments) - 3
- formation of cross bridges between actin and myosin fil.s
- movement of thin actin fil. OVER thick myosin fil.
- reduction in dist. between Z-lines
cross bridge formation: 5
- Ca2+ binds to troponin
- troponin undergoes conformational change
- this lifts tropomyosin away from actin filament
- exposing myosin binding sites on actin filament
- myosin heads able to form cross bridge with actin filament
what drives the cross bridge formation?
(hint: movement of myosin head) 5
- myosin heads have sites that bind/hold ATP
- ATPase catalyses hydrolysis of ATP to ADP+Pi
- this releases energy which myosin head uses to tilt and join/form cross bridge with actin filament (via myosin binding sites)
- ADP + Pi leave myosin head, myosin head moves back to original position, dragging thin actin filament over
- thin actin filament dragged closer to M-line, Z-lines of sarcomere closer together
define contrile (in context of ‘contrile property’:
can shorten and generate pulling force
define metabolic (in context of ‘metabolic property’)
involved in metabolic processes e.g. energy release??
muscle differences: compare processes in diff muscle types (2)
- skeletal muscle can fatigue (unlike cardiac)
- some muscles contract more rapidly (e,g, gastrocnemius and soleus, gastrocnemius contracts faster but not as fatigue resistant, soleus - slow to contract but fatigue resistance)
fibre types: 4
FAST: [FAST _____ - blank = type of metabolism that fibre undergoes to get it’s energy)
- TYPE 11a (fast OXIDATIVE)
- TYPE 11b (fast GLYCOLITIC)
- type 11x (intermediate between a + b^)
SLOW:
- TYPE 1 (slow OXIDATIVE)
assessing composition of fibre:
- what makes this possible to assess?
- 2 ways you would do it
- each fibre type has specific myosin (arrangement/composition) isoform
- immunohistochemistry
- histochemistry (ATPase activity)
define muscle fatigue:
decreased maximum contractile force
causes of muscle fatigue: 3
-** reduction/all ATP used up (required for formation of cross bridge)**
- increase inorganic phosphate(builds up after brief strenuous exercise)
- decrease Ca2+
altering fibre-type composition:
- mainly genetically determined/done (e.g. genetic alteration of Belgian Blue = more muscle = ‘more meat production’ xx
name the contractile cells in SMOOTH muscle
leiomyocytes
name the contractile cells in SKELETAL muscle
rhabdomyocytes
(merge to make myofibres)
name the contractile cells in CARDIAC muscle
cardiomyocytes
the organisation of myocytes in skeletal muscle:
they are…
to create…
- grouped into long chains
- myofibres (muscle fibres?)
