BIOSCI 107 ET: Muscle Flashcards
What are the 3 Types of Muscle?
Skeletal, cardiac, smooth.
Which Muscle Types are Striated?
Skeletal and cardiac.
Which Muscle Types are Under Voluntary Control?
Skeletal.
Where is Cardiac Muscle Located?
Heart.
Where is Smooth Muscle Located?
Wall of internal organs.
How can we Identify Skeletal Muscle Cells?
Sing long cylindrical cells, multiple peripheral nuclei.
How can we Identify Cardiac Muscle Cells?
Branched cells connected via intercalated discs.
How can we Identify Smooth Muscle Cells?
Spindle shaped, with a single nucleus.
What are Skeletal Muscle Cells Composed of?
Fibrils containing contractile filaments.
Where are Thick Filaments Found?
Running the entire length of an A Band.
Where are Thin Filaments Found?
Running the length of the I Band and partway into the A Band.
What is a Z Disc?
Coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another.
What is the H-Zone?
Lighter mid-region where filaments do not overlap.
What is the M Line?
Line of protein myomesin that holds adjacent thick filaments together.
What is the Function of a T-Tubule?
Allows action potentials to be carried deep within the muscle cell.
What is a T-Tubule?
Deep invagination continuous with the sarcolemma, circling each sarcomere at the junctions of A and I Bands.
What is the Sarcoplasma Reticulum?
Calcium storage site.
What are Thick Filaments Composed of?
Myosin.
What is the Structure of Myosin in Thick Filaments?
2 subunits, each has a globular head and a tail, 2 tails intertwine to form a helix.
What is Located in the Globular Heads of Myosin?
A binding site for actin - the head itself is an enzyme that hydrolyses ATP.
What is the Function of Titin in Myosin?
Anchors the thick filament to the Z-line.
What is the Thin Filament Composed of?
Globular actin proteins.
What is the Structure of the Thin Filament?
Double stranded helical actin chain (polymers).
What are Troponin and Tropomyosin?
Regulatory proteins associated with actin.
What is the Sliding Filament Theory of Muscle Contraction?
Sarcomere shortens as thin filaments are pulled over thick filaments - Z line pulled towards M line, I band/H zone become narrower.
Describe the 4 Stages of the Cross Bridge Cycle.
Cross-bridge formation, power stroke, detachment, energization of myosin head.
What are the Requirements for a Cross-Bridge to Form?
Calcium must be present, myosin binding site must be exposed.
What Occurs During Stage 1: Cross-Bridge Formation?
Myosin binds to the actin binding site to form a cross-bridge.
What Occurs During Stage 2: The Power Stroke?
ADP released, myosin head rotates to low energy state, taking thin filament with it, sarcomere is shortened.
What Occurs During Stage 3: Detachment?
New ATP molecule binds to myosin, actin-myosin bind is weakened and myosin detaches.
What Occurs During Stage 4: Energization of Myosin Head?
Myosin head hydrolyses ATP to ADP + Pi, head moves to high energy (cocked) state.
What is the Critical Threshold for Calcium in the Cross-Bridge Cycle?
0.001 - 0.01 mM.
Why is Calcium Important in the Cross-Bridge Cycle?
Calcium ions provide on switch - binding to troponin so tropomyosin exposes myosin binding sites on actin.
How is Calcium Regulated for the Cross-Bridge Cycle?
Calcium channels and active pumps move Ca from cytoplasm back into sarcoplasma reticulum.
What is Isotonic Muscle Activity?
Shortening/lengthening, tension constant, velocity variable.
What is Isometric Muscle Activity?
No shortening, length constant, tension variable.
What Happens during an Isometric Contraction?
At sarcomere level max active force is dependent on the degree of actin and myosin overlap.
What Happens to Active Tension at Lengths <2.0 uM?
Filaments collide and interfere with each other, reducing force developed.
What Happens to Active Tension at Lengths >2.2 uM?
Active forces decline as the extent of overlap between filaments reduce, reducing number of cross bridge.
What is Total Tension?
Active + passive force.
What Happens to Connective Tissue when Muscle is Stretched?
Connective tissue around the muscle cells resists the stretch = passive force.
What is a Motor Unit?
A motor neuron and all the muscle fibres it innervates.
What Happens when ACh is Released into the Neuromuscular Junction?
Action potential travels down motor neuron, Ca channels open, Ca enters axon terminal, ACh vesicles fuse with membrane, ACh released into synpatic cleft.
What Happens when ACh Receptors are Activated?
Binding of ACh to receptors causes opening of ACh gated ion channels, this allows movement of mostly Na into muscle cell - making it less positive.
What Happens when a Muscle Action Potential is Triggered?
Ligand gated channels enable end plate potential to reach threshold, voltage gated Na channels open triggering action potential, this is propagated along sarcolemma.
What Happens when Calcium is Released from the SR?
Action potential is conducted down t tubules, results in voltage gated Ca channels, Ca is released into cytosol.
What Happens when Ca Binds with Troponin?
Ca concentrations reach threshold, myosin binding sites are exposed, cross bridge cycle occurs.
What Happens when the Contraction Ends due to Fallen Ca Levels?
Ca actively pumped into sarcoplasmic reticulum, troponin moves back covering myosin binding sites.
How long can Creatine Phosphate act as an ATP Store?
Less than 15 seconds.
What does Creatine + ADP Make?
Creatine + ATP.
Why is Anaerobic Glycolysis Limited to 30-40s?
Build up of lactic acid and protons.
What is Regulation of Force Dependent on?
Rate of stimulation of individual motor units, number of motor units recruited.
What is a Type 1 Motor Unit?
Slow twitch - units with neurons innervating the slow efficient aerobic cells.
What is a Type 2 Motor Unit?
Fast switch - units with the neurons innervating the large fibres that fatigue rapidly but develop large forces.
What is the ‘Glue’ Preventing Cells from Separating During Contraction?
Desmosomes.
What is a Major Function of Gap Junctions in Cardiac Muscle Cells?
Allow action potentials to be carried from one cell to the next.
How Long does a Ventricular Myocyte Action Potential Last?
Long - >100ms.
Why is there a Plateau Phase for the Ventricular Myocyte Action Potential?
Due to presence of a large sustained Ca ion current.
What are the 3 Major Stages of an Action Potential in a Cardiac Muscle Cell?
Rapid depolarisation, plateau, repolarisation.
Why is there Rapid Depolarisation in the Action Potential of a Cardiac Muscle Cell?
Due to fast voltage-gated Na channel.
Why is there Repolarisation in the Action Potential of a Cardiac Muscle Cell?
Closing of Ca channels and opening of K channels.
What are the 4 Pathways Ca can Utilise to Exit the Cytosol?
SR Ca-ATPase, sarcolemmal Na/Ca exchange, sarcolemmal Ca-ATPase, mitochondrial Ca uniport.
What does a Longer Action Potential For Cardiac Muscle Mean?
Longer contractile phase.
How is Cardiac Output (CO) Calculated?
CO = SV x HR
Stroke volume x heart rate
What is Stroke Volume?
The tension developed by the cardiac muscle fibres in one contraction.
What are the 3 Methods of Increasing Stroke Volume?
Increased stretch of ventricles/rate of firing, certain neurotransmitters.
Which Node Determines the Heart Rate?
SA node in right atrium.
What are the 3 Stages of the Action Potential for Pacemaker Cells?
Pacemaker potential, depolarisation, repolarisation.
Why does the Pacemaker Potential show a Slow Depolarisation?
Due to If current.
Why does is there Depolarisation for the Action Potential of Pacemaker Cells?
At threshold Ca channels open, influx is sustained by slow opening Ca channels.
Why does is there Repolarisation for the Action Potential of Pacemaker Cells?
Ca channels inactivate and K channels open.
What is the Function of the Vagus Nerve?
Decreases heart rate, releases ACh.
What is the Function of Sympathetic Cardiac Nerves?
Increase heart rate and force of contraction.
What is Starlings Law of the Heart?
AS the resting ventricular volume is increased the force of the contraction is increased.
What is the Length Tension Relationship for Cardiac Muscle?
Increased stretch results in more force developed (stroke volume).
What is the Concept of Automaticity?
Increasing heart rate increases contractile force - less time for Ca to be pumped out.
What is Inotropy?
More force developed per given length.
How does Noradrenaline Impact Stroke Volume?
Increased cytosol calcium, increased HR shortening time for extrusion.
What is Multiunitary Organisation in Smooth Muscle?
Bundles of cells which contract independently.
What is Unitary/Visceral Organisation in Smooth Muscle?
Sheets of electrically coupled cells that act in unison.
Do Smooth Muscle Cells have T-Tubules?
No - caveolae instead (increase SA).
How is Actin Anchored to the Sarcolemma in Smooth Muscle Cells?
Dense bodies act like z-lines.
What is the Function of Gap Junctions in Smooth Muscle?
Electrically connect cells together (unitary).
What are Intermediate Filaments in Smooth Muscle Cells?
The cytoskeletal element.
What is the Regulatory Protein of Smooth Muscle Cells?
Calmodulin.
What Impact does the Disorganisation of Smooth Muscle Have?
Greater shortening.
What is the Only Important Part of Initiation of Contraction in Smooth Muscle?
Can be neural, hormonal or spontaneous.
What is the Function of Myosin Light Chain Kinase?
Phosphorylates the light chain in the presence of activated calmodulin.
How is Smooth Muscle Relaxed?
When a myosin light chain phosphatase dephosphoralates the myosin light chain.
What is the Function of Autonomic Nerve Fibres?
Innervate most smooth muscle fibres.
What is the Function of Varicosities?
Release neurotransmitters into a wide synaptic cleft.
What is the Stretch-Relaxation Response of Smooth Muscle?
Initial contraction (resisting stretch), slowly relax (adapting to change in length).
