Functions of the muscle Flashcards
Functions of the muscle 4
Movement
Control posture
Remove from blood) and
store glucose
Generate heat (temperature regulation)
How is the contractile filament laid out?
http://www.ks.uiuc.edu/Research/telethonin/MuscleL1.jpg
Z line/disc
What are the A band and I band referred to as
A - dArk A Band
I - lIght I Band
What is the name given to repeating unit of the microfilaments
Sarcomere
What is the sarcomere
repeating unit of the microfilaments
What happens to the sarcomere when contraction happens?
I band filament appears to have shortened but is only obscured by the A band whcih pulls it in
Sarcomere shortens
What are the types of contractions
Isotonic
Isometric
What is isometric contraction
Constant length
Taking load at a constant length
Tension increases
What is isotonic contraction
Constant load
Picking something up changing velocity of load
What is tension
Force exerted on an object by a contracting muscle
What is load
Force exerted on muscle by the weight of an object
What are the types of isotonic contraction?
Concentric
Eccentric
What is eccentric contraction
Muscle contracting but lengthening at the same time
What is Concentric contraction
Muscle contracting and shortening
How is a muscle stimulated
Action potential across Motor neuron synapses onto n muscle at motor endplate
Where are the cell bodies of motor neurons located
Ventral horn of spinal cord
What is an action potential
A regenerating depolarization of membrane potential that propagates along an excitable membrane
What does regeneration mean?
uses energy to move along membrane at constant amplitude
What does propagates mean?
Moves along the membrane as an ‘active’ membrane event
What does excitable mean?
capable of generating action potential
What is the name given to the measurement of peripheral nerve conduction
Extracellular/ transmural
How is excitation clinically detected in the body?
Measurement at the body surface
What can record action potentials extracellualrly?
ECG
EMG
EEG
Where does EEG measure action potential
Brain
Where does ECG measure action potential
Heart
Where does EMG measure action potential
Skeletal muscles
How does action potential meter work?
Electrodes place in two areas
Resting:
Positive membrane potential on outside and no action potential means positive whole way through so no potential difference (0V on voltmeter)
Action potential:
When action potential occurs negative membrane potential relative to inside but area of the nerve where action potential has not reached yet will be negative. So electrode 1 positive electrode 2 negative = potential difference across meter (-V of voltmeter
In terms of action potential graph what is depolarisation?
Moving towards 0V x-axis
In terms of action potential graph what is hyperpolarisation?
Moving away 0V x-axis
Why is action potential at a synapse one way?
Neurotransmitter on end of presynaptic cell to receptors on post-synaptic cell
What is a receptor
ligand-gated ion channel / receptor- operated channel
General Synapse- what happens?
AP in pre-synaptic cell causes release of vesicles.
Transmitter diffuses to receptors on post-synaptic cell.
Activation of receptors depolarises (via Na* entry) cell to threshold and initiates an AP in post-synaptic cell.
What does a nerve synpase look like? structure real life photo
Hand like structure of endplate on muscle fibres
If nerve is removed what would the depression be?
Primary synaptic cleft and branching from it secondary synaptic clefts which leaves trophs
What does a post-synaptic neuron have?
Trophs infoldings ‘clefts’
Muscle synapse
Transmitter released from vesicles at ‘active zones’.
- Active zones aligned with infoldings or ‘clefts’ in the post-junctional membrane.
Top of the clefts = nACh receptors
Bottom of clefts = voltage-gated Na+ channels.
What is nACh receptors?
nicotine acetylcholine receptors
Why is it important that nACh receptors are at the top of the celfts?
Minimal distance for diffusion
Why is it important that nACh receptors are at the top of the celfts?
Minimal distance for diffusion
What is important about the Na+ channels being at the bottom of the clefts and not the nACh receptors
Activated by voltage change not transmitter, so distance unimportant
Name muscle relaxants
Botulinum toxin
Curare
Succinylcholine
How does Botulinum toxin prevent contraction of the muscles What does this cause?
Prevents release of ACh-containing vesicles.
Causes paralysis of muscle and inhibition of secretion from exocrine glands normally stimulated by parasymp NS
How does Curare prevent contraction of the muscles What does this cause?
Blocks nAChRs Cause paralysis (used during surgery to prevent muscle spasm)
How does Succinylcholine prevent contraction of the muscles
Short-acting block of nAChR (used during intubation)
What is Succinylcholine also called?
‘suxemethonium’
OneDrive Personal > uni > Brainscape pictures > Capture 2
A- Sarcoplasm B- Sarcolemma (plasmalemma of muscle) .C-Mitochondria D- Triad (SR-T-SR) E- T tubule opening F- Sarcoplasmic reticulum G-Diameter of fibre H-Myofibril
What is the function of sarcoplasmic reticulum
Ca Store
What is the function of T tubules
Conduct quickly muscle action potential into fibres
What is the role of T tubule and sarcoplasmic reticulum in muscle contraction
T-tubules and SR membranes very
T tubule AP stimulates Ca release from SR
Released Ca stimulates contraction
Ca then taken back into SR
What T-tubules
Tubes continuous with the surface membrane roght through the muscle fibres
How calcium is stored and released in the SR?
Leaves through channel
Pumped back in using ATP-driven calcium pumps) from low to high conc
What is a calcium store in the muscle
Sarcoplasmic reticulum
How is action potential used spread through muscle fibres
Action potential moves along the sarcolemma
goes down into the tunnels where these T tubules are
What is the Triad structure
T-tuubule + SR on either side
How is the action potential lead to calcuim release?
Dihydropyridine acts as voltage-sensors on t-tubule membrane
detects voltage change of the action potential and communicate it to -
Ryanodine receptors acts as calcium release channels on SR membrane which when stimulated releases calcium
What triggers malignant hyperthermia
Volatile anaestetics
What causes malignant hyperthermia
Mutation in the ryanodine receptor
What is the effect of malignant hyperthermia
Constant leak of calcium from SR that is matched by increased ATP-dependent calcium pumping
What is the treatment of malignant hyperthermia
Withdrawal of trigger and dantroline (blocks the ryanodine receptor)
Summation
Where action potentials are fired quickly so that force is accumulated before going back down
Myoplasmic Ca falls (initiating relaxation) before muscle makes maximum force
therefore Further stimulation before relaxation complete results adding of force (summation)
What is it called when there is no relaxation between each calcium rise
Fused tetanus or tentanic contraction
When does tetanus contraction occur
In posture
What is in the A band of the microfilament
myosin
What is in the I band of microfilament
actin
Full process of Excitation-Contraction Coupling 1-10
- AP travels across surface of muscle fibre.
- AP moves down T tubules
- DHP receptors sense voltage change and open ryanodine receptors
- Ca2+ ions are released from the SR.
- Ca2+ ions bind troponin causing tropomyosin to move and uncover myosin-binding sites on actin.
- The cross-bridge cycle drives muscle contraction.
- Ca2+ ions are pumped into the SR by the Ca2+-ATPase.
- Ca2+ removal from troponin restores tropomyosin inhibition
- Actin and myosin no longer form bridges
- Muscle relaxes
