skeletal muscle structure and contraction

Question 1

3 muscle types:

Answer 1

• smooth (e.g. contraction and dilation of blood vessels/bronchioles)
• striated (skeletal)
• cardiac

Question 2

functions of skeletal muscle (5)

Answer 2

• locomotion
• breathing
• postural support
• heat production during cold stress
• largest protein store in body (can tap into if malnourished)

Question 3

define syncytium

Answer 3

multi nuc. cell

Question 4

skeletal muscle fibres(cells):

3 general features

Answer 4

• striated (stripy appearance)
• syncytium (multi nucleated cells)
• peripheral nuclei

Question 5

a bundle of muscle fibres is…?

Answer 5

fascicle

Question 6

name the 3 types of connective tissue covering in skeletal muscle

Answer 6

EPI-

PERI- -MYSIUM

ENDO-

Question 7

define epimysium

Answer 7

connective tissue surrounding entire muscle

Question 8

define perimysium

Answer 8

connective tissue surrounding fascicles (bundles of muscle fibres)

Question 9

define endomysium

Answer 9

(connective tissue) surrounds individual muscle fibres

Question 10

2 functions of connective tissue covering in muscles:

Answer 10

• functional: transmit info (load?) from muscle to bone
• protective (stronger than muscle)

Question 11

the components that make up single muscle fibre: (3 - sub.s within each)

Answer 11

• sarcolemma (membrane)
• myofibrils (tubular structures that pack fibres)
• myofilaments (threadlike strands within myofibrils - ACTIN thin - troponin + tropomyosin, MYOSIN thick)

Question 12

sarcomeres:
zones and bands - name and say what each has in

Answer 12

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

Question 13

sliding filament theory: the general idea of what happens (do not need to mention specifics for interactions between filaments) - 3

Answer 13

• 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

Question 14

cross bridge formation: 5

Answer 14

• 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

Question 14

what drives the cross bridge formation?

(hint: movement of myosin head) 5

Answer 14

• 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

Question 15

define contrile (in context of ‘contrile property’:

Answer 15

can shorten and generate pulling force

Question 16

define metabolic (in context of ‘metabolic property’)

Answer 16

involved in metabolic processes e.g. energy release??

Question 17

muscle differences: compare processes in diff muscle types (2)

Answer 17

• 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)

Question 18

fibre types: 4

Answer 18

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)

Question 19

assessing composition of fibre:

• what makes this possible to assess?
• 2 ways you would do it

Answer 19

• each fibre type has specific myosin (arrangement/composition) isoform
• immunohistochemistry
• histochemistry (ATPase activity)

Question 20

define muscle fatigue:

Answer 20

decreased maximum contractile force

Question 21

causes of muscle fatigue: 3

Answer 21

-** reduction/all ATP used up (required for formation of cross bridge)**

• increase inorganic phosphate(builds up after brief strenuous exercise)
• decrease Ca2+

Question 22

altering fibre-type composition:

Answer 22

• mainly genetically determined/done (e.g. genetic alteration of Belgian Blue = more muscle = ‘more meat production’ xx

Question 23

name the contractile cells in SMOOTH muscle

Answer 23

leiomyocytes

Question 24

name the contractile cells in SKELETAL muscle

Answer 24

rhabdomyocytes

(merge to make myofibres)

Question 25

name the contractile cells in CARDIAC muscle

Answer 25

cardiomyocytes

Question 26

the organisation of myocytes in skeletal muscle:

they are…

to create…

Answer 26

• grouped into long chains
• myofibres (muscle fibres?)