Microstructure and function of human muscle systems Flashcards
- Outline the difference in function of the three main types of human muscle, and explain how their structural differences are related to these functional differences - Explain the functions of the specialised subcellular components seen, including the contractile system, the signalling membrane systems of striated and the intercalated discs of cardiac muscle (24 cards)
What is the function of skeletal muscle?
- Operates skeleton, links bones + tendons, also in diaphragm, upper oesophagus etc.
- Allows movement and respiratory mechanics (diaphragm) and maintaining posture and balance
Is the contraction of skeletal muscle fast or slow?
Fast, but subject to fatigue
What are skeletal muscle fibres formed of?
Thousands of precursor cells in the embryo (myoblasts) fusing together
What is the function of cardiac muscle?
- Producing contractility of the heart, and therefore the pumping action of the heart
- Involuntary control
Is the contraction of cardiac muscle fast or slow?
- Quite rapid, and resists fatigue
- Can contract regularly for 90+ years
How does the structure of cardiac muscle aid its function?
- Branching fibres provide extra strength, curvature (of heart) and resistance to splitting due to high-blood pressure
- Smaller diameter fibres than skeletal muscle, allows for richer blood supply and additional connective tissue for strength
- Numerous mitochondria and rich blood supply allows for aerobic respiration, continuous energy supply, resistance to fatigue
- Intercalated disks- gives very strong attachments and ionic communication between fibres
Where is smooth muscle found?
Internal organs such as gut, lungs, blood vessels, uterus, bladder
Is the contraction of smooth muscle fast or slow?
Slow- but the contraction is very powerful, energy-efficient, and causes little fatigue.
It’s usually involuntary control
What is the epimysium and what is its function?
- Thick, outermost sheath of dense connective tissue
- Prevents friction with other muscles
What is the perimysium and what is its function?
What does it contain?
Supporting connective tissue, carries nerves, blood vessels
Contains elastic fibres and type I collagen, which contribute to its resistance of a muscle to tensile forces
What is the sarcomere?
Contractile unit composed of actin and myosin, each sarcomere is the unit of one Z line to the next
What is the myofibril?
- Bundle of protein filaments actin and myosin, this drives contraction and relaxation
What do T (transverse) tubules do? What muscle category contains T tubules?
T tubules are found in striated muscle, they’re invaginations within the sarcolemma (sarcomere membrane)
T tubules allow for electrical-contraction coupling due to their close association with ryanindine receptors. They can transmit an AP to them, causing them to open (ligand gated), leading to influx of cytosolic calcium ions, which then lead to contraction via striated mechanisms.
They convey stimulus from plasma membrane inside fibres, pass it to SR.
What does the SR (sarcoplamsic reticulum) do
to the signal?
Spreads signal further to myofibrils, initiating contractions via release of calcium
When a motor neurone stimulates a muscle cell, an AP travels along the sarcolemma, down T-tubules, activating RyR1, opens, influx of calcium ions
Describe the features of cardiac muscle
- Striated
- Intercalated disks, strong end-to-end junctions between fibres
- Actin filaments attach to disks
- Many large mitochondria for aerobic respiration
What are purkinje fibres?
Larger, modified cardiac muscle fibres, carry stimulus rapidly to ventricles
Describe the features of smooth muscle
What does the plasma membrane contain?
What is near the membrane?
- No striations
- Involuntary muscle, usually
- Initiation of contraction varies between organ
- No myofibrils
- No complex membrane systems
- Actin + myosin filaments visible
- Junctions between fibres
- Plasma membrane has caveolae, contains many kinds of receptors
- Near membrane is a basic form of SR
What are the 5 tissue types?
- Epithelium
- Connective tissue
- Blood
- Muscle tissues
- Neural tissues
What are fascicles?
- Group of bundled muscle fibres that form one unit
What is muscle surrounded by?
Epimysium
What are fascicles surrounded by?
Perimysium
What is muscle fibre (a muscle cell) surrounded by?
Endomysium and plasma membrane
What causes skeletal muscle to contract?
- AP spreads over fibre’s plasma membrane
- Special intracellular membrane systems carry signal to all parts of cell, diffusion not fast enough
What is the signalling membrane system of cardiac muscle?
How are intercalated disks involved in this?
- Myogenic stimulus- muscle generated - AP starts from pacemaker region in RA, carries wave of contraction across heart, assisted by ion diffusion through gap junctions in intercalated disks
- Purkinje fibres send stimulus to ventricles
