Muscles Flashcards
Types of Muscles
Cardiac Muscle: Muscles in the heart(involuntary)
Smooth Muscle: Walls of blood vessels and intestines (involuntary)
Skeletal Muscle: attached to skeleton by tendons
Structure of Skeletal Muscle
Muscles cells fused together to form myofibrils. Muscles are made up of bundles of muscle fibres which are made up of myofibrils.
Sarcoplasm: muscle fibres share nuclei and cytoplasm, found around circumference fibres.
Actin and Myosin
Proteins filaments that make up myofibrils.
Actin: thin, two strands wrapped around each other. Wrapped in tropomyosin which covers myosin head binding sites on actin
Myosin: thick, has heads and tails. Myosin joined tail to tail in one sarcomere
Myofibril Structure
See diagram of myofibril.
I band: Only actin, therefore light in colour
A band: Myosin, containing actin overlap (therefore dark) and H zone
H zone: Only myosin region within A band
Z line: Middle of I band
Sarcomere: Region between two adjacent Z lines
Muscle Stimulation
Action potential reaches neuromuscular junction.
Action potential triggered in muscle which travels down T tubules in sarcoplasm and causes the Ca2+ ion channels in the sarcoplasmic reticulum to open
Role of Ca2+ ions in Muscle Contraction
Ca2+ ions diffuse out of sarcoplasmic reticulum into the sarcoplasm
Ca2+ ions bind to troponin on tropomyosin causing a conformational change which exposes the myosin head binding sites on the actin filament.
Ca2+ ions also activate the ATPase
Muscle Contraction Sliding Filament
Myosin head with ADP, initially cocked back, attaches to actin filament forming cross bridge
Power stroke occurs, myosin head changes shape pulling actin filament over it and releasing ADP.
ATP molecule attaches to myosin head and it detaches from the actin filament
ATP hydrolysed by ATPase providing energy for myosin head to change back to original cocked back position
Myosin head next attaches itself further along the actin filament
Myofibril during Muscle Contraction (Evidence for Sliding Filament Theory)
Myofibril shortens as actin filaments are pulled together.
H-zone narrows
I-band narrows
Z-lines get closer together
A-zone remains the same
Muscle Relaxation
Ca2+ ions actively transported back into sarcoplasmic reticulum using energy form hydrolysis of ATP
Tropomyosin blocks myosin head binding sits on actin filaments
Phosphocreatine in Muscle Contraction
PCR phosphorylates ADP into ATP for muscle contraction when oxygen supply and therefore aerobic respiration is limited.
Acts as a supply of phosphate ions.
Slow Twitch Muscle Fibres
Adapted for aerobic respiration
Large store of myoglobin which stores oxygen (gives muscle the red colour)
A rich supply of blood vessels to supply oxygen and glucose
High concentration of mitochondria to produce ATP
Fast Twitch Muscle Fibres
Adapted for short bursts of intense activity.
Thicker an more numerous myosin filaments
High conc. of glycogen
High conc. of enzymes for anaerobic respiration
Store of PCR
