Muscle Structure, Function And Contraction Flashcards
What are the 3 types of muscle tissue?
Cardiac muscle
Skeletal muscle and smooth muscle
Where is cardiac muscle found?
In the heart
Where is smooth muscle found?
In the walls of organs
Which of the 3 muscle types is multi-nucleated?
Skeletal muscle
Which two muscle groups contract involuntary?
Cardiac and smooth muscle
What are the names of the 3 key connective tissues in skeletal muscles?
Epimysium, perimysium, endomysium
What are the relative sizes of the 3 key layers of connective tissue (in comparison to one another)?
Epimysium > perimysium > endomysium
Name 5 functions of muscles
Produces body movements
Stabilises body positions
Regulates organ volumes (sphincters)
Movement of substances within the body
Produces heat (shivering)
Name 5 properties of muscle tissue
Excitability
Conductivity
Contractibility
Extensibility
Elasticity
Why does skeletal muscle have multiple nuclei?
Because during development muscles form from multiple myoblasts fusing together. Each myoblast has its own nucleus therefore when they fuse together you end up with multiple nuclei
Where does skeletal muscle attach to?
Bone, skin or fascia
Maybe via tendons/aponeuroses
What happens to left over myoblasts?
They become satellite cells
What are satellite cells?
Stem cells
When there is some damage to the muscle, the stem cell can divide and assist in repair
Name the 7 functions of skeletal muscle
Produce skeletal movement
Maintain body position
Support soft/hard tissues
Guard body openings
Maintain body temperature
Stores nutrient reserves
Proprioception (knowing where your body is in space)
What is epimysium?
A sheath of connective fascia that surrounds the whole muscle
What is epimysium connected to?
Deep fascia
Which connective tissue separates surrounding muscles from surrounding tissues?
Epimysium
Which connective tissue surrounds muscle fibre bundles (fascicles)?
Perimysium
Which connective tissue in the muscle contains blood vessels and nerve supply to fascicles?
Perimysium
Which connective tissue surrounds individuals muscle cells?
Endomysium
Which connective tissue layer contains satellite cells that repair damage and capillaries and nerve fibres contacting muscle cells?
Endomysium
What do endomysium, perimysium and epimysium come together at the ends of muscle to form?
Connective tissue attachment to bone matrix I.e. tendon (bundle) or aponeurosis (sheet)
Messages from the central nervous system reach the muscle tissue via what nerve?
A peripheral nerve
What is a motor unit?
One motor nerve and the muscle fibres it supplies
What are skeletal muscle cells called?
Fibres
What is the sarcolemma?
The cell membrane of a muscle cell
What is the sarcoplasm?
Cytoplasm of muscle fibre
What do T tubules do?
Carry muscle action potentials down into the cell and allow the entire muscle fibre to contract simultaneously
What is a T tubule?
An invagination of the sarcolemma into the centre of the cell
What is the sarcoplasmic reticulum?
A membranous structure surrounding each myofibril
It is a system of tubular sacs similar to smooth endoplasmic reticulum in non-muscle cells
What does the sarcoplasmic reticulum do?
Helps transmit action potential to the myofibrils
What do terminal cisternae form?
Calcium
What does sarcoplasmic reticulum form at each end?
Chambers (terminal cisternae)
What does sarcoplasmic reticulum do in a relaxed muscle?
Stores calcium ions
How does sarcoplasmic reticulum trigger muscle contraction?
By releasing calcium ions
What is a triad made up of?
1 T-tubule and 2 terminal cisternae
What are myofibrils made up of?
Bundles of protein filaments (myofilaments)
What are myofilaments?
The contractile proteins of muscles
What does the sarcoplasm contain?
Glycogen and fats for energy as well as mitochondria
What does the I band contain?
Only thin filaments (actin)
What does the A band contain?
Thick (myosin) filaments
What is a sarcomere?
The contractile unit of a muscle
What is the importance of titan?
It is thought to be quite important in terms of use of eccentric muscle contraction
Titan attaches the myosin filament to the Z line so prevents the muscle from over stretching and it helps it to recoil back to its normal size
What are thick filaments composed of?
Myosin
What are thick filaments held in place by?
M line proteins
What are thin filaments made up of?
Actin, troponin and tropomyosin
What is the myosin binding site on each actin molecule covered by in a relaxed muscle?
Tropomyosin
What are thin filaments held in place by?
Z lines
What does the M line connect to?
Titan and adjacent thick filaments
What is nebulin?
An in elastic protein that helps align the thin filaments
What does dystrophin do?
Links thin filaments to sarcolemma and transmits the tension generated by the tendon
What type of muscle contraction does the sliding filament mechanism look at specifically?
Concentric isotonic muscle contraction
For contraction to occur there needs to be some sort of stimulation of the muscle, how is it stimulated?
Happens in the form of a nerve impulse or an action potential
Describe the stimulation of muscle contraction
Nerve impulses reaches an axon terminal
Synaptic vessels release acetyl choline
Acetyl choline diffuses to receptors on the sarcolemma
This causes sodium ion channels to open
Sodium ions rush into the cell
A muscle action potential spreads over the sarcolemma and down into the T tubules
Action potential reaches a triad
Terminal cisternae release calcium ions into the sarcoplasm
Calcium ions bind to troponin and causes troponin-tropomyosin complex to move and reval binding sites on actin
Excitation - contraction coupling
Contraction cycle begins
What are the 3 essential components for the contraction cycle to happen?
Neural stimulus
Enough calcium ions
Enough ATP
What are the 6 steps of the contraction cycle of a muscle?
Exposure of active sites on actin
ATP hydrolysis into ADP, Pi and energy
Attachment of myosin to actin to form cross-bridges
Power stroke
Detachment of myosin from actin
Reactivation of myosin
What is the contraction cycle of a muscle ?
Repeating sequence of events that causes the thin filaments to slide between the thick filaments
What is the power stroke?
Pivoting of myosin head, pulling in the thin filament
What are the 9 steps of relaxation of a muscle?
Acetylcholinesterase breaks down acetyl choline within the synaptic cleft
Muscle action potential ceases
Calcium ion channels close
Calcium ions detach from troponin
Active transport pumps calcium ions back into storage in the terminal cisternae of the sarcoplasmic reticulum
Calcium ion concentration falls
Tropomyosin- troponin complex recovers binding site on the actin molecules
Contraction ends
Relaxation occurs, muscle return passively to resting length
What is a neuromuscular junction?
The site of the signal exchange, this is where the synaptic bulb of an axon terminal and muscle fibre connect
What happens when a muscle is above or below optimal length?
Fewer cross bridges exist and less force is produced
What are the 3 sources of ATP production within a muscle?
Creatine phosphate
Anaerobic cellular respiration
Aerobic cellular respiration
What is used to form creatine phosphate?
Excess ATP within the resting muscle
How long does creatine phosphate sustain maximal contraction for?
15 seconds
How many times more plentiful is creatine phosphate in comparison to ATP within the muscle?
3-6 x
How long can glycolysis continue to anaerobically provide ATP for?
30-40 second of maximal activity
How long aerobic respiration provide ATP for?
Any activity lasting over 30 seconds
