BL - Muscle Flashcards
What is the prefix used to denote muscle?
“My-“ eg myalgia, myasthenia
What is the prefix used to denote a components of a muscle?
“Sarco-“ eg sarcolemma
What are the three major categories of muscle?
Skeletal (striated), cardiac (striated), smooth (non-striated).
What are the three types of skeletal muscle fibre?
Red, intermediate and white.
Which type of skeletal muscle fibre is the largest?
White, then intermediate, then red is the smallest.
Give some differences between red and white muscle fibres.
Red have rich vascularisation and myoglobin content, numerous mitochondria, slow/weak contraction and fatigue slowly. White is opposite. Intermediate is intermediate.
Which type of skeletal muscle has more neuromuscular junctions?
White
What is the difference in enzyme content between red and white muscles?
Red is rich in oxidative enzymes and poor in ATPase, white is poor in oxidative enzymes but rich in ATP-ase.
What is myoglobin?
Red protein containing haem which functions as an oxygen storing molecule. Structurally similar to haemoglobin subunit.
Which muscle types contain myoglobin?
Skeletal and cardiac - not smooth.
What conditions make haemoglobin more likely to give up oxygen to myoglobin?
Low pH - active muscles produce CO2 which dissolves and lowers pH, causing oxygen to be transferred.
What is a perimysium?
Connective tissue carrying nerves and blood vessels that surrounds a fascicle.
What is the plasmalemma of a muscle cell called?
Plasmalemma
What is it known as when muscles are destroyed?
Atrophy
What is it known as when muscles are remodelled?
Hypertrophy
How and when would disuse atrophy occur?
Loss of protein leads to reduced fibre diameter and loss of power. Occurs due to bed rest, limb immobilisation, sedentary behaviour.
Give two reasons other than disuse for atrophy to occur.
Age and denervation.
How does hypertrophy lead to increase in muscle size?
More contractile proteins, so increase in fibre diameter.
Gove some examples of metabolic changes that occur due to hypertrophy?
Increased enzyme activity for glycolysis, more mitochondria, more stored glycogen, increased blood flow.
True or false - muscle length is increased by frequent stretching?
True, due to addition of sarcomeres. The converse is also true.
What are the thin muscle filaments called?
Actin
What are the thick muscle filaments called?
Myosin
What are skeletal muscles composed of?
Fascicles -> muscle fibres (cells) -> myofibrils -> myofilaments (actin and myosin)
What can a troponin assay be used for?
Can be measured as a marker for cardiac ischaemia, as is released from ischaemic cardiac muscle within an hour. Must measure within 20 hours.
What is creatine kinase?
An enzyme released into the blood by damaged skeletal muscle and brain.
What is the role of calcium in muscle contraction?
Increased amounts of ionic calcium bind to troponin causing a conformational change which moves tropomyosin away from actin’s binding sites, so binding can begin.
Describe the sequence of muscle contraction
- myosin cross bridge attaches to actin myofilament
- myosin head pivots and bends as it pulls the actin filament, sliding it towards the M line
- new ATP attaches to myosin head, cross bridge detaches
- ATP splits to ADP and Pi causing myosin head to cock.
Summarise events leading to contraction of skeletal muscle.
- nerve impulse arrives an NM junction and stimulates release of Ach causing depolarisation
- Na+ enters cell and T tubules are depolarised, causing conformation change.
- Ca2+ enters sarcoplasm from terminal cisternae and binds to TnC subunit of troponin.
- Contraction occurs.
A picture of muscle in LS shows striations, centrally positioned nuclei, intercalated discs and branching. What type of muscle is it?
Cardiac
What is the difference between the tubule placement in skeletal muscle compared with cardiac muscle?
In skeletal muscle they are on the Z bands rather than with the A-I bad junction.
What are the two ways that muscles can increase in size?
Hypertrophy (enlargement of individual cells) or hyperplasia (multiplication of cells)
What is a heart muscle cell also known as?
A cardiomyocyte
What are natriuretic peptides?
Peptide hormones synthesised by the heart, brain and other organs. Their release is often stimulated by heart failure. Their function is to reduce arterial pressure.
How do natriuretic peptides reduce arterial pressure?
Decreasing blood volume and systemic vascular resistance.
When might a patient have elevated levels of ANP?
Hypervolemic states which occur in congestive heart failure.
What can BNP and NT-pro-BNP be used for?
They are sensitive, diagnostic markers for heart failure in patients.
What is the function of Purkinje fibres?
They transmit action potentials to the ventricles from the atrioventricular node.
Give some features of Purkinje fibres.
Large cells with abundant glycogen, sparse myofilaments and extensive gap junction sites
True or false - smooth muscle does not contain T tubules?
True, it also does not contain sarcomeres. It is not striated so no banding is present.
What are myoepithelial cells?
Stellate cells forming a network around secretory units of exocrine glands, where they contract to aid secretion.
What is the function of myofibroblasts?
Produce collagenous matrix at wound healing sites and contract to draw wound together.
Can cardiac muscle be repaired?
No, following damage fibroblasts lay down scar tissue
Can skeletal muscle cells repair themselves?
They cannot divide but tissue can regenerate using mitosis in satellite cells, which can also fuse with existing muscle cells to increase mass.
Can smooth muscle regenerate?
Yes - smooth muscle cells retain their mitotic activity and can form new smooth muscle cells.
Give some examples of diseases caused by smooth muscle dysfunction.
Asthma, irritable bowel syndrome, primary hypertension, detrusor instability
What are the three indicators of muscle injury?
Creatine kinase , myoglobinuria, troponin
What is the significance of “fixed” mottling?
It does not change when pressed, so the change is irreversible
