Muscle Flashcards
What are the characteristics of skeletal muscle?
Voluntary control
Striated
Single long cylindrical cells
Multiple peripheral nuclei
What are the characteristics of caridac muscle?
Only in heart Striated Branched with 1 - 3 central nuclei (variable) Connected via intercalated discs Involuntary control
What are the characteristics of smooth muscle?
Involuntary Found the wall of internal organs Spindle shaped (fat middle, thin ends) Uni-nucleated Not striated
What is the structure of skeletal muscle?
Attached to bones via tendons The fibres can be long (up to 35cm) Reasonably wide (.1mm) Composed of fibrils containing highly organised contractile filaments
What are the components of a sarcomere (myofibril)?
Thin actin filaments
Thick myosin filaments
Z discs (anchoring point)
What are the areas of a sarcomere?
H zone (Exclusively thick filaments) M line (Thick filaments are joined) A band (thick and thin filaments) I band (thin filaments)
What is the T tubule?
Tunnels continuous with the sarcolemma into the cell at A and I bands, full of extracellular fluid, exposing the fibres to APs etc.
What is the Sarcoplasma Reticulum?
Calcium storage site, the terminal cisternae lie close to the T tubules.
What is the Sarcolemma?
Surrounds the cell, has holes for T tubules
Structure of thick filaments?
Myosin
Made out of two subunits
Has a head and a tail, the two tails form a helix
Heads having a binding site for actin
The head is an enzyme that hydrolyses ATP
Thin filaments
Primarily globular actin proteins
Filaments are a double stranded helical actin chain
Troponin and tropomyosin are regulatory proteins associated with actin in cardiac and skeletal muscle
What is the sliding filament theory?
The sarcomere shortens as the thin filaments are pulled over the thick filaments.
Z-line is pulled towards the M-line
The I band and the H zone become narrower
Which areas don’t change in contraction?
M line and A band
Which areas change during contraction?
Z discs and I band
What are the steps of the cross bridge cycle?
- Cross-bridge formation (Actin-Myosin)
- Power stroke (ADP and Pi released)
- Detachement (New ATP)
- Energisation of mysoin head (ATP to ADP + Pi)
Why must calcium be present?
It binds with troponin to move tropomyosin allowing access to myosin binding sites on the actin.
What happens during the power stroke?
Both Pi and ADP released
Mysoin rotates to low energy state (45 degrees to actin).
Pulls the thin filaments
What happens during detachment?
New ATP binds to myosin head and it detaches from actin.
What happens during energisation of myosin head?
Hydrolysis of ATP to ADP and Pi
Myosin head cocks to it’s high energy confirmation
(90 degrees to actin)
Why is calcium important?
Calcium ions provide the “on” switch for the cross cycle
The cycle will continue as long as Ca levels remain above the critical threshold. (.001 - .01 mM).
How is calcium regulated?
Calcium channels in the SR open and calcium flows into cytosol/t tubules
Active Ca ATPase pumps are constantly moving calcium back into the SR.
What is isometric contraction?
No shortening
Length constant
Tension variable
What is Isotonic contraction?
Shortening
Tension constant
Velocity variable
Why determines the the maximum force in isometric contraction?
The degree of myosin and actin overlap
2.2 um is optimum
At what stage do the filaments start overlapping too much?
At what length does the force start decreasing due to stretch?
> 2.2um
What are the steps of a motor neuron action potential?
- ACh released into neurotransmitter junction
- Activation of ACh receptors
- A muscle AP is triggered
- Calcium is released from the SR
- Calcium binds with troponin
- Cross bridge formation
- Power stroke
- De tatchment
- Re-energisation
- Contracation ends when Ca levels fall
What happens when an Action potenital hits the end plate?
Ca+ enters axon terminal, which trigggers the ACh vesicles fusing with membrane
What does the binding of ACh allow?
The movement of Na+ into the muscle cell (end plate potential)
What is ACh broken down by?
Acytelcholieesterase
What happens when enough ligand gated channels open?
Voltage gated channels open and propagate down the sacrolemma
What is the typical resting potential for motor neurons?
-90 mV
What is the excitation-contraction coupling?
Action potentials run down the sarcolemma and the t tubules.
AP reaches the voltage sensitive protein which then releases the voltage gated channel in the sarcoplasmic reticulum into the sarcoplasm.
What does creatine phophate do?
It can hold a phosphate and donate it to an ADP. (under 15 seconds only)
Anaerobic process
What are the charateristics of anaerobic glycolysis?
Fast but efficient.
Leads to a build uo of lactic acid and H+ limits duration to 30-40s
What are the characterisics of aerobic metabolism?
Efficient but slow
Only about 300 W
Cna run for a long time
What are type one muscle fibres?
Slow oxidative
What are type IIB muscle fibres?
Fast glycolyitc
What are type IIA muscles?
Fast oxidative (not in humans)
What regulates force?
- Rate of stimulation of individual motor unit
2. The number of motor units used.
What muscle fibres do we usually recruit first?
Type I
What is another name for involuntary movement?
Myogenic
What is another name for voluntary movement?
Neurogenic
Is cardiac muscle electrically isolated like skeletal?
No
What’s the difference in T tubules between skeletal an cardia?
The T-tubules are at the Z disks in cardiac and there is only one per sarcomere instead of 2 at the …
What are the two types of cardiac action potential?
Ventricular myocyte
Sinoatrial node
In Ventricular myocyte AP, what ion flows do we have?
Out:
Na+
Ca2+
In:
K+
How long is a vetricular monocyte AP?
300 - 400 ms
What are the steps of calcium-induced calcium release?
- Excittion
- Opeing of voltage-sensative plasma membrane
- Flow of C into cell
- Stimulation of CA from SR
- Cytosolic concentration inrease
- Contraction
What is a DHPR channel?
L type Calcium channel
How do we increase the CO?
Increased stretch of ventricles
Increased rate of firing
Certain hormones
What is the cardiac output equation?
Cardiac output = Stroke volume * Heart rate
Why does the heart beat spontaneously?
Because the SA node is spontaneously depolarizing
What is the ion flow in Sinoatrial Node APs?
In:
CaL
CaT
If(funny)
Out:
K
What is the spontaneous depolarisation commonly called?
Pacemaker potential
What are ways to control thr heart rate?
- Decrease the threrhold
- Making the maximum diastolic potential more postive (less hyperpolarised)
- Increasing the rate of spontaneous deploarisation
What does the Vagus nerve do?
It is part of the parasympathetic system
Activates SA node
DereaSes heart rate
Release Acetyl Choline
What does the Sympathetic nerve do?
Increases heart rate
Releases noradrenaline
Activates AV Node
What is intrinsic heart rate?
100-110 bpm
