Flashcards in Cells and Tissues Deck (88)
What does the force of muscle contraction depend on?
The number of cross bridges- compositions of motor unit, frequency of potentials, length tension relationship
What does and isometric contraction and isotonic contraction mean?
Isometric- same length of sarcomere so elastic elements extend, Isotonic- sarcomere shortens
How are graded muscle contractions achieved?
Changing the number and type of motor units that are activated
What is tetanus?
Sustained contraction with no relaxation due to large number of potentials
Why does length tension affect the force of contraction?
If the sarcomere is too short there is little shortening, if too long there is minimal cross bridge formation
What is energy stored in during rest?
High energy bonds in phosphocreatine- converted to creatine to release ATP
Where does ATP come from during exercise?
Initially the cytoplasm, then creatine, followed by glycolysis then oxidative phosphorylation,
What causes fatigue?
A reduction in sources of ATP
What sort of movement is Glycolytic (white) suited for?
Relies on anaerobic glycolysis so performs fast with high power contractions
What are some features of white muscle fibres?
Colour- little myoglobin, contain few mitochondria, contain glycogen
What exercise is oxidative (red) muscle fibres suited for?
Slow sustained activity
What are some features of red muscle fibres?
High myoglobin, surrounded by capillaries, lots of mitochondria
What is the function of myoglobin and how does it achieve this?
Myoglobin assists aerobic metabolism, by having a greater affinity for oxygen than haemoglobin for the muscle.
Where is smooth muscle found in the body?
GI tract, Uterus, Bladder, Eye, Blood vessels
How is the structure in smooth muscle different to skeletal muscle?
In smooth muscle there is less myosin, and there are no sarcomeres
What are key features of smooth muscle?
Small non-striated, spindle-shaper cells with single nucleus
Why can smooth muscles contract when stretched?
The myosin filaments are longer and covered in heads so can maintain enough overlap for optimal tension
Why are smooth muscles resistant to fatigue?
ATP mostly from oxidative phosphorylation and uses less energy then skeletal
What ion causes contraction in smooth muscle?
How does calcium cause contraction in smooth muscle cells?
Calcium enters the muscle cell and binds to calmodulin activating myosin light chain kinase, which phosphorylates myosin which controls contraction
What causes Ca2+ to rise in smooth muscle?
External entry by voltage and ligand gated ion channels and some from the SR
What does myogenic mean?
No external stimuli needed for contraction, spontaneous
What are the two ways myogenic smooth muscle reaches threshold?
Pacemakers potentials oscillating membrane potentials that regularly reach threshold, or slow cyclic waves which gradually rise until threshold
How do multiunit smooth muscle cells differ?
Multiunit cells each have a terminal ending on every cell for fine control e.g iris
How do single unit cells spread excitation?
Gap junctions between cells
What neurotransmitter do sympathetic nerves release?
How can noradrenaline cause inhibition or excitation in smooth muscle?
Different receptors, alpha receptors cause excitation beta receptors cause inhibition
What causes smooth muscle relaxation?
Decrease in sarcoplasmic calcium using pumps and exchangers
What ions is intracellular high and low in?
High K+, low Na+, v low Ca2-,