Muscle and Skin Flashcards
What is muscle?
- A soft tissue which cells are rich of protein filaments actin and myosin that slides past one another
- Process contraction
- Derives from mesoderm
What is the function of muscles?
- To produce force and motion
What are the main functions of the muscle system?
- Maintaining and changing posture
- Locomotion
- Movement of the internal organs; contraction of the heart, movement of food through the digestive system, breathing evolutions of the diaphragm, vasomotions
State the types of muscle tissues.
- Skeletal
- Cardiac
- Smooth
What is synctium?
- A multinucleate cell that can result from multiple cell fusions of uninuclear cells
- May also refer to cells interconnected by specialised membrane with gap junctions which are synchronised electrically
State the structural synctium.
- Skeletal muscle
What are the functional synctium?
- Cardiac muscle
- Smooth muscle
State the skeletal muscles characteristics.
- Most are attached to the bones by tendons
- Cells are multinucleate
- Myofibrils are assembled in myofibers
- Voluntary - subject to the conscious control
- Fibres are surrounded and bundled by connective tissue - develop great force but get tired quickly
State the characteristics of cardiomyocytes.
- Single centrally located nucleus
- branching structure
- Plenty of mitochondria
- abundant reserve of myoglobin (to store oxygen)
- Each cell is in contact with adjacent cells at specialised sites
What is sarcomere?
- A repeating functional unit of a myofibril or cardiomyocyte
Describe the A band of the sarcomere.
Darl band
Full length of thick myosin filament
Describe the I band of the sarcomere.
- Light band
- From Z disks to the ends of thick filaments (thin filaments with NO thick)
Describe the M line of the sarcomere.
- protein to which the thick filaments attach
- centre of sarcomere
Describe the H zone of the sarcomere.
- Thick filaments with NO thin
Describe the Z disk.
- Filamentous network of protein, attaches actin myofilaments
Describe titin filaments of the sarcomere.
- Elastic chains of polypeptides
- Keep thick and thin filaments aligned
Describe the phases of contraction.
a) resting stage; ATP is hydrolysed
b) Ca2+ binds to troponin; myosin binds to actin
c) Powerstroke occurs; the sarcomere contracts; ADP and Pi dissociate from myosin
d) New ATP binds to myosin, causing detachment of myosin from actin; hydrolysis of ATP to ADP and Pi causes recooking of the myosin head
Describe the mechanism of contraction.
- Na+ channels
- L-type Ca2+ channels
- Ca2+ induced Ca2+ release from ryanodine receptors
- Ca2+ stimulates the contractile apparatus
Describe the mechanism of relaxation.
- Ca2+ reuptake into SR
- Withdrawal of Ca2+ to the extracellular media
- Exchange of Ca2+ for 3Na+ with Na+/Ca2+ exchanger; then 3Na+ changed for 2K+ with Na+/K+-ATPase
- Activation of K+ channels
What are the smooth muscles?
Vascular - arteries, veins and lymphatic vessels
Visceral - airways, gastrointestinal tract, urinary system, myometrium, pelvic organs
In the smooth muscle what is the source of Ca2+?
- Cell membrane and supplementary sarcoplasmic reticulum
Describe the mechanisms of vascular smooth muscle contraction.
- Excitation-depolarisation due to opening of voltage-gated L-type Ca2+ channels
- Ca2+-induced Ca2+ release from ER/SR via ryanodine receptor, increase of [Ca2+]
- Ca2+ binds calmodulin (CaM)
- Ca2+-CaM complex activates myosin light chain kinase (MLCK)
- MLCK phosphorylates myosin head group and stimulate contraction
State the importance of calcium (Ca2+).
- Responsible for depolarisation and propagation of excitation
- Responsible for activation of contraction of muscles
- Important signal molecule and second messenger
- It is central to the control of the muscles
Define epithelial tissue.
- Covers external surfaces of body and lining hollow structures
