Muscles Flashcards
(15 cards)
Types of Muscle
Skeletal
Cardiac
Smooth
Skeletal Muscle
Fibres are multinucleate with distinct striations
Attached by tendons to bones
Mvmnt of parts of body and locomotion
Strong contractions but not long lasting
Cardiac Muscle
Cells are striated and branched - form a linked network - intercalated discs between cells
Found only in wall of heart
Pumping of heart maintains blood circulation
Cardiac muscle will contract through life
Smooth Muscle
Spindle-shaped cells with a single nucleus and no striations
Present in iris and ciliary body and walls of tubular organs
Mvmnt of materials within body
Peristalsis in gut can continue for long periods
Structure Skeletal Muscle
Nuclei lie just beneath sarcolemma (surface membrane)
Packed myofibrils each surrounded by sarcoplasmic reticulum and joined transversely by T tubules - mitochondria between which
Structure myofibril
Overlapping arrays of thick and thin filaments of proteins myosin and actin
M Line
Line middle of myosin
Z line
Line in middle of actin
Sarcomere
From z line to z line
I band
Just actin
H zone
Just myosin
A band
All of myosin
Incl bits of actin linked
Muscle Contraction
Sliding Filament Theory
Shortening of myofibrils causes muscle contraction
Sequence myofibril shortening
•AP arrives via motor neurone at synapse with sarcolemma
•AP propagated through T-tubules along sarcoplasmic reticulum - Ca2+ to be released into sarcoplasm
•Ca2+ cause ancillary proteins - normally cover binding sites on actin - to be displaced - uncover binding sites
•Heads of myosin mol next to uncovered binding sites attach to actin filaments - form acto-myosin bridges
•Myosin heads rotate - pull thin actin over thick myosin
•ATO binds with myosin heads - energy released from hydrolysis causes m-heads to detach
•detached heads regain og position and attach to another exposed BS on actin - cycle repeated
•process continues as long as AP propagated through muscle fibre
