Tissues 6 Flashcards
What are the 2 parts of the peripheral nervous system?
Sensory - receptors and AFFERENT neurons (to CNS)
Motor - command effector tissues and efferent neurons (from CNS)
What do neuroglia do?
- Support neuronal metabolism
- Maintain ionic balances of interstitial space.
- Some synthesise myelin (e.g. Schwann cells)
Neuroglia more common than neurones
What do dendrites do?
Receive signals from receptors or other neurons
What is the axon hillock?
Where the action potential is initiated
What is the axon terminal?
Where the action potential stops and electrical signal turns into chemical signal at the synapse
What produces myelin?
Oligodendrocytes and Schwann Cells
Where do presynaptic axon terminals lead to?
Dendrites (and neuronal cell bodies)
What is the scale of muscle cells?
Muscle - Muscle Fibres - Myofibrils - proteins (sarcomeres)
Muscle fibres are multi……
Multinucleate.
Cells fused together during development to form fibres
Where are satellite cells?
Outside the myocytes.
Where are muscle stem cells?
Underneath the basal laminae.
Stimulated to differentiate when cell damage occurs.
Where do T-tubules go?
Deep into the myofibrils.
Describe process of muscle activation.
- AP propagates along sarcolemma and into t - tubules
- Dihydropyridine (DHP) receptors in t-tubule recognises change in voltage and change the shape of the protein link to the Ryanodine receptor.
- Ryanodine receptor opened - opens Ca ion channel
- Ca released from sarcoplasmic reticulum to around myofibrils.
- Ca binds to troponin and tropomyosin - changes their conformation to reveal actin binding site.
- Myosin binds to actin - reveals actin-myosin cross bridge.
- Ca actively transported back into SR. Uptake < Release, so Ca conc increases around myofibrils.
Describe the process of muscle relaxation.
- APs stop. No DHP receptors sensing changed voltage. No ryanodine receptors opening.
- Ca still actively transported into SR. So Ca conc decreases.
- Ca dissociates from troponin - causes tropomyosin to reassume original position.
- Actin-myosin cross bridge broken as actin binding site is covered.
What is the unit of contraction?
Sarcomere
What are the 4 proteins involved in a sarcomere?
Actin
Myosin
Troponin
Tropomyosin
Which proteins are responsible for muscle contraction?
Actin and myosin
Name other proteins involved in muscle contraction?
Titin - large spring like filament which anchors myosin to Z line
Nebulin - large filaments associated with actin
CapZ and Tropomodulin - associated with positive and negative ends of actin
Force can only be produced towards the centre of the sarcomere. Why?
Due to the orientation of the myosin heads
What does muscular force production depend on?
- Recruitment - amount of motor units recruited
- Frequency of stimulation - increased frequency of AP means more Ca around filaments, increasing number of cross bridges formed. Increases force
- Filament overlap. More attachable cross bridges means more force
- Velocity of filament sliding. Faster contraction = less force (less change of cross bridge attachment)
Isotonic contraction.
Tension > Load
Muscle contracts and fibres shorten
Isometric contraction
Tension = load
Actin pulled in and out
Muscle does not contract - myosin heads reattach to same point on actin chain
Describe Cardiac muscle.
- Striated Muscle
2. Mechanism of contraction is same as skeletal muscle
Cardiomyocytes have intercalated discs. Describe intercalated discs.
- Specialised discs connecting individual myocytes.
- Have desmosomes and gap junctions.
Desmosomes - hold membrane together
Gap junctions - allow electrical communication between cells
In cardiac muscle, DHP receptors replaced by (Voltage Gated) Ca receptors?
True, BUT NO CONTACT BETWEEN VGCC AND RyR
Does Smooth muscle contain the regular arrangement of actin and myosin?
No
Explain E-C coupling in smooth muscle.
- Depolarisation activates VGCC
- Ca increases, binds to Calmodulin (CaM) and forms complex.
- Myosin Light Chain Kinase (MLCK) activated as a result.
- MLCK phosphorylates Myosin Light Chains (MLC20)
- Cross bridges formed with actin filaments - contraction (leading to vasoconstriction)
