Structure and contraction of skeletal muscles Flashcards
How do muscles work in an antagonistic pairs.
-Work in antagonistic pairs
-one muscle contracts (pull on bone) while other one relaxes
-Attached to bone by tendons
-Ligaments attached from one bone to other
-Skeletal muscle is incompressible so muscles can transmit force to bone
Advantages of skeletal muscles being arranged in antagonistic pairs
Muscles can contract
2nd muscle required to reverse the movement caused by 1st
Helps maintain posture——>contraction of both muscles
gross structure of skeletal muscle
-Muscle made of bundle of muscle fibres packaged together. (muscle–>muscle fibre—> myofibril)
Muscle cell contains
Cell membrane= Sarcolemma
Cytoplasm= sarcoplasm
Myofibrils made up of two proteins, actin and myosin
-shared nuclei
-Lots of endoplasmic reticulum
Ultrastructure of a myofibril
made up of many sarcomeres which are made up of partly overlapping myosin and actin filaments.
Sarcomere consists of:
Z-line- End
M-line=Middle
H zone= around M line which only contains myosin
Myosin filaments=thick
Actin filaments= Thin
This causes a banding pattern to be seen:
I band= light bands containing only thick actin filaments
A bands= dark bands containing thick myosin filaments and some overlapping actin
What happens during Muscle contraction to sarcomere
Myosin head slide actin past myosin causing the sarcomere to contract. Simultaneously contraction of lots of sarcomeres causes myofibrils and muscle fibres to contract.
When the sarcomere contracts:
-H zones shorter
- I band shorter
-A band same
-Z lines closer
Sliding filament theory
-Action potential spreads down T-tubules causing the release of Ca+ ions from sarcoplasmic reticulum which diffuse through the sarcoplasm to the myofibril.
-Ca2+ binds to tropomyosin causing it to move as it changes shape, exposing the myosin binding site on actin.
-So myosin heads (with ADP attached) attach to binding site forming an actinomyosin crossbridge (requires ATP)
-Myosin head bends and this slides actin along myosin (performs a power stroke - needs ATP)
-ATP binds to myosin head causing it to detach from the actin binding site. Breaks the crossbridge.
-The hydrolysis of ATP by ATPase (which is activated by ca2+ release energy for myosin heads to move back to original position
-Myosin reattaches to a different binding site further along actin filament( only repeated as long as Ca2+ present.)
Slow twitch muscles
-Specialised for slow, sustained contractions e.g. endurance activities (maintaining posture)
-Located in muscles that give posture and in leg muscles of long distance runners.
-aerobic respiration produces ATP (oxidative phosphorylation) in muscles for aerobic respiration.
-High levels of myoglobin makes them appear red—-> store large amounts of oxygen in muscle for aerobic respiration.
-Many mitochondria—–> high rate of aerobic respiration
-Many capillaries—> large SA—–> supply high conc. of oxygen/glucose for aerobic respiration and to prevent build up of lactic acid causing muscle fatigue.
Fast twitch
-Specialised for producing rapid, intense contractions of short duration.
-Used for short bursts of speed and power e.g. sprinting
-Located in the legs of sprinters for example
-Anaerobic respiration produces ATP to release energy quickly.
-Low levels of myoglobin makes them a whitish colour—> anaerobic respiration doesn’t need oxygen.
-lots of glycogen—-> hydrolysed to lots of glucose—>used during glycolysis (anaerobic respiration) only yielding 2 ATP per glucose molecules.
-higher conc. of enzymes involved in anaerobic respiration—->higher rate of anaerobic respiration
-Store phosphocreatine which rapidly generates ATP from ADP by providing phosphate
-Muscles can get fatigued quickly because of high amounts of lactate
ROle of phosphocreatine in muscle contraction
-Phosphocreatine stored inside cells
-rapidly makes ATP by phosphorylating ADP by adding phosphate group from PCr.
-PCr runs out after a few seconds so it’s used in short burst of vigorous exercise
