Muscle Contractions Flashcards
(34 cards)
What are muscles?
Muscles are effectors that contract in response to nerve impulses, due to a stimuli
What are the three types of muscles?
Cardiac muscles
smooth muscles
Skeletal muscles
What are cardiac muscles?
Muscles found within the heart, they are myogenic as contractions arise from within the heart itself
What are smooth muscles? Where are they found
Found in the wall of tubular organs
They are involuntary, unscripted and unstriated
Contracts slowly, fatigues slowly
What are skeletal muscles? Where are the found?
Attached to bones via inelastic, connective tissue
Voluntary, striped, striated
Contracts rapidly, fatigues rapidly
What is antagonistic muscle action? In which muscles does it occur?
Where two muscles work in a pairs around an incompressible skeleton/bone. They work to move bones around joints.
As one muscle contracts and shortens, the other relaxes and returns to its normal shape
Describe the gross structure of the skeletal muscles
- tendons attach to either side of the muscle, so attach them to bones
- muscles are made up of bundles of muscle fibres (muscle cells surrounded by a cell plasma membrane) bound by connective tissue
- muscle cells consist of many myofibrils
What would be seen if you were to look at a myofibrils under an electron microscope?
Repeated light and darl bands would be displayed
The light bands (I bands) contains only thin actin filaments
The dark bands (A bands) contains only mainly thick myosin filaments, and some overlapping actin filaments
Sarcomeres are marked by Z lines
What are myofibrils made of?
Repeated functional units called sarcomeres
Contains thin actin filaments and thick myosin filaments
What are sarcomeres?
Repeating functional units found in myofibrils
What is the structure of myosin (in myofibrils)?
Made of a tail and a globular head
The tails are specifically shaped to bind to each other to form a thick filament
The globular heads stick out in all directions, and form actomyosin bridges (cross-links) with adjacent actin filaments
What is the structure of actin (in myofibrils)?
Made of two helical strands of globular actin molecules, that twist round each other
Associated with to regulatory proteins- troponin and tropomyosin
Tropomyosin is a fibrous protein that wraps around the actin filaments
What are the imilaroties between cholinergic synapses and neuromuscular junctions?
Both use neurotransmitters that move by diffusion
Both use Acetylcholine as the neurotransmitter
Both have receptors on the postsynaptic membrane
Both contain sodium and poitrassium ion pumps that cause depolarisation In the post synaptic membrane
What are the differences between neuromuscular junctions and cholinergic synapses?
N can only be excitatory, C can be both excitatory and inhibitory
N only uses motor neurones, and is only between a neurone and effector (muscle)
C uses motor, sensory and relay neurones and can be between two neurones or neurone and effector
Where are motor, relay and sensory neurones found/ used?
Motor neurones are between coordinator and effector
Relay are found in coordinators (CNS)
Sensory neurones are between a stimulus and coordinator
What can be seen on an electron microscope when muscles contract?
The actin filaments (lighter) are pulled over to the myosin filaments (darker)
Sarcomere shortens, so the width will decrease
The M line will remain the same
The H zone will shorten or become non- existent
The overall myosin length stays the same
The actin length shortens
What are the different lines/ zones seen in an electron microscope when viewing muscle fibres
I band- lighter region, only actin
A band- darker region, mostly myosin filaments, darkest bit is where myosin and actin overlap
H zone- contains thick myosin filament only
M line- where myosin filaments are anchored
Z line- where actin filaments are anchored, the distance between two Z lines is the sarcomere
What happens at a neuromuscular junction that leads to the exposure of myosin binding site on actin filaments?
Action potential stimulates Acetyl choline to diffuse across synaptic cleft and bind to receptors on the sarcomere (postsynaptic membrane)
Stimulates an action potential by depolarising the membrane
Action potential moves through the sarcoplasm muscle via a system of T-tubules. T tubules connect the the sarcoplasmic reticulum. Action potential causes Ca2+ channels to open in the sarcoplasmic reticulum membrane, so they rapidly diffuse into the sarcoplsm
Ca2+ binds to troponin on actin, which causes the tropomyosin to move away and expose myosin binding sites on actin filaments
Why do calcium ions diffuse into the sarcoplasmic from the sarcoplasmic reticulum when an action potential reaches it?
Because there is a higher conc. of Ca2+ inside the sarcoplasmic reticulum, because they have been actively transported into the reticulum
Explain the sliding filament theory?
Once they myosin binding site on actin has been exposed, myosin heads, ADP and Pi bind to the actin to form actinmyosin bridges
The myosin heads change angle, and cause the actin filament to be pulled along. This is called the POWER STROKE
ADP and Pi is released and converted into ATP
ATP binds to the myosin head, and the myosin head detaches from the action filament. ACTINMYOSIN BRIDGES ARE BROKEN
ATP hydrolase (found in myosin head) hydrolysis ATP provides energy for the myosin head to return to its normal position
The myosin head, ADP and Pi can now rejoin the actin filament in another position to produce the next power stroke
What happens to make muscles relax?
The nervous impulse in the sarcoplasm ceases, so the calcium ions diffuse back into the sarcoplasmic reticulum
Tropomyosin moves back to its original place, and blocks the myosin minding sites
Myosin heads are unable to bind to the actin filaments, therefore contractions are stopped and the muscles relax
What is rigormortis and why is it caused?
After death, muscles become rigid and remain in their contracted state
This is because cellular respiration is stopped, so ATP is not produced and cannot bind to the myosin heads.
Crossbridges that are already made will remain in the same place, as ATP cannot be used to dissociate myosin heads and Acton filaments
Where does the energy for muscle contractions come from?
ATP hydrolysis
The ATP/ phosphpcreatine system
Glycolysis
Oxidative phosphorylation
What is the ATP/ phosphocreatine system? What is the equation for this?
ADP + PCr <-> ATP + Cr
Phosphocreatine is stored in muscles and acts as a reverse supply of phosphates, so ATP can be reformed from muscle contractions
PCr is split into phosphates and creatine, so phosphates can be used for ATP
The phosphocreatine store is then replenished when the muscles are relaxed
It supplies enough energy for max effort
