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
