Muscles Flashcards
What are the functions of muscles?
Produce movement
Stabilise body positions
Store and move substances (myocardium)
Generate heat
What is thermogenesis?
The process of generating heat as a result of muscle contraction
What is the importance of thermogenesis?
Maintain body temperature
What are the key properties of muscle tissue?
Electrical excitability
Contractility
Extensibility
Elasticity
Explain the muscle property of electrical excitability:
Respond to electrical stimuli (action potentials) cause contraction of the muscle
Explain the muscle property of contractility:
The muscles have the ability to shorten creating tension causing movement
Explain the muscle property of extensibility:
Myocardium and smooth muscle can relax and extend when required
Explain the muscle property of elasticity:
Muscles can return to their original position after stretching
What are the different types of muscle tissue?
Cardiac
Smooth
Skeletal
Where is smooth muscle located?
Within the walls of hollow internal organs, e.g. blood vessels, airways and abdominal organs
Smooth muscle is non-striated, what does this mean?
There is no specific tissue pattern
Smooth muscle is non-voluntary, what does this mean?
It is innervated by neurons in the autonomic nervous system so muscle contraction is non voluntary
Compare / Contrast the 3 muscle types in relation to voluntary contraction:
Cardiac = involuntary Smooth = involuntary Skeletal = voluntary
Compare / Contrast the 3 muscle types in relation to striation:
Cardiac = striated Smooth = non-striated Skeletal = striated
Where is cardiac muscle tissue found?
Only in the heart, especially the walls of the heart
Cardiac muscle is striated, what does this mean?
The muscle proteins are formed in well organised bundles (sarcomeres)
Cardiac muscle is involuntary, what does this mean?
The muscle is stimulated by the Sinoatrial node which creates the action potential for contraction to begin
Where are Intercalated discs found and what is their function?
Found in cardiac muscle, they aid in transmitting action potentials through myocardium to increase contraction
Skeletal muscle is striated, what does this mean?
The muscle proteins are formed in an organised fashion, through alternating dark and white bands
Skeletal muscle is voluntary, what does this mean?
Contraction is controlled by neurons as part of the somatic nervous system (although most contractions are subconscious)
Compare / Contrast the 3 muscle types in relation to contraction speed:
Cardiac = moderate Smooth = slow Skeletal = fast
Compare / Contrast the 3 muscle types in relation to size:
Cardiac = Large Smooth = Small Skeletal = Very large
Compare / Contrast the 3 muscle types in relation to regulator proteins for contraction:
Cardiac = Troponin and Tropomyosin Smooth = Calmodulin and Myosin Skeletal = Troponin and Tropomyosin
Compare / Contrast the 3 muscle types in relation to autorhythmicity:
Cardiac = Yes Smooth = Yes Skeletal = No
What is a sarcolemma?
An excitable plasma membrane surrounding a muscle fiber
What is sarcoplasm?
The cytoplasm of the muscle fiber
Where is the sarcoplasm found?
Within the sarcolemma
What substances are found within sarcoplasm which aid muscular contraction?
Glycogen (for ATP)
Myoglobin (O2 receiver)
What is the function of mitochondria in muscle fibers?
They breakdown glycogen into ATP
Many myofibers combine to form a _____:
Muscle fiber
What are sarcomeres?
The smallest component of a myofiber
What are the main contractile proteins of a myofiber?
Myosin (thick filament)
Actin (thin filament)
What is the M line?
The middle of a sarcomere
What is the Z disc?
The end of a sarcomere
What is the A band?
The middle of the sarcomere extending the entire length of the thick filament (myosin), including overlap
What is the H zone?
The area of sarcomere where there is thick filament (myosin) only, so not the overlap area
In relation to M and Z, what happens during muscle contraction?
Z discs are pulled towards the M line, shortening the sarcomere
What is the I band?
The area of sarcomere where there is thin filament (actin) only, so not the overlap area
In a myofiber, what is the name for the protein in the THIN filament?
Actin
Which protein moves the Z disc towards the M line?
Actin (thin filament)
What is the structure of the thick filament?
Myosin tail Myosin head (containing Actin-binding site and ATP-binding site)
What occurs during the second stage of the sliding filament theory?
Attachment of myosin to actin:
Myosin in the high-energy conformation attach to actin’s binding site
Forming a cross bridge
What is the position of tropomyosin during a relaxed state?
It covers the myosin-binding site on the tin filament actin proteins
What causes troponin to become active?
Binding with calcium ions
What are the steps in the sliding filament theory?
ATP hydrolysis
Attachment of myosin to actin
Power stroke
Detachment of myosin from actin
What occurs during the first stage of the sliding filament theory?
ATP hydrolysis:
ATP attached to the ATP-binding site on myosin
ATP -> ADP + Pi (+energy)
Energy is stored in the myosin head
Head cocked into high-energy conformation (90 degrees)
What happens when calcium binds with troponin?
A change in the actin occurs moving the tropomyosin off the myosin-binding site allowing the myosin to bind to the actin
What is the structure of the thin filament?
Two actin strands helically around each other, clumps of troponin, myosin-binding site covered by tropomyosin
In a myofiber, what is the name for the protein in the THICK filament?
Myosin
What occurs during the fourth stage of the sliding filament theory?
Detachment of myosin from actin:
ATP attaches to myosin head
Link between actin and myosin weakens
Cross bridge detaches and actin slides back
What occurs during the third stage of the sliding filament theory?
Power stroke:
Pi is released initiating power stroke
Myosin head pivots and pulls actin towards M line
Then ATP is released
The sliding filament theory is continuous as long as what conditions are present?
There is sufficient ATP in the sarcoplasm and there is stimuli from the nervous system to contract
What are contractile proteins?
Proteins which generate force during muscle contractions
Myosin, Actin
What are regulatory proteins?
Proteins which help control the muscle contraction process
Tropomyosin, Troponin
What are structural proteins?
Proteins that maintain the alignment of the thick and thin filaments, provide myofibril elasticity and link myofibrils to sarcolemma
(Titin, α-Actinin, Myomesin, Nebulin, Dystrophin)
Where are regulatory proteins Tropomyosin and Troponin found?
On the thin filament (actin)
Explain how regulatory proteins aid muscle contraction:
When calcium ions bind to troponin, it changes shape and subsequently moves tropomyosin away from the myosin-binding site allowing myosin to bind to actin
Where are transverse tubules?
Run from the sarcolemma into the individual muscle fibres
Where are calcium ions located prior to their binding with troponin?
In the terminal cisterns of the sarcoplasmic reticulum
How do calcium ions get into the sarcoplasm from sarcoplasmic reticulum?
Through calcium release channels controlled by voltage
How do calcium ions get into the sarcoplasmic reticulum from the sarcoplasm?
Through the Calcium-ATPase pump
How does an action potential from a neuron trigger the contraction of a muscle?
The action potential travels down the transverse tubule and opens the voltage gated channels to release calcium into the sarcoplasm and sliding filament theory begins
Where does stimulation of the sarcolemma occur?
Neuromuscular junction
What is a neuromuscular junction?
The point where a somatic motor neuron meets a muscle fiber
What neurotransmitter diffuses across the synaptic cleft at the neuromuscular junction?
Acetylcholine (ACh)
Explain the process of synaptic transmission at the neuromuscular junction:
Acetylcholine (ACh) released from vesicle into synaptic cleft
Diffuses across and binds to ACh receptors
Muscle action potential is produced by release of sodium
ACh is broken down
When is Acetylcholine ACh broken down in synaptic transmission?
When there are no longer impulses coming down the axon terminal of the somatic motor neuron
What is a motor neuron consisted of?
A somatic motor neuron plus all of the muscle fibers it stimulates
When Acetylcholine (ACh) binds to the ACh receptors in the junctional fold, which ion is released to begin the muscular contraction?
Sodium / Na+
An action potential down one somatic neuron will stimulate how many muscle fibers?
It varies, averagely around 180 muscle fibers. It will stimulate all muscle fibers supplied by that neuron
How do muscle fibers reduce fatigue and allow recovery of other fibres?
Not all fibers within a muscle belly are contracted at the same time, some contract while others rest
What happens to suitable motor unit recruitment efficiency with age?
We learn how to recruit the fewest fibers to perform a function to allow other fibres to rest as fully as possible
What is wave summation?
When a second action potential occurs before the first muscle fibers have finished with contraction
What is unfused tetanus?
Multiple action potentials are generated, but there is relaxation of muscle fibers between so the contraction force is increased at a jagged rate
What is fused tetanus?
Many consecutive stimuli are sent per second, this produces a steady, sustained force of contraction
What is the relationship between number of action potentials and force of contraction?
More action potentials leads to a greater force of contraction
Explain what is meant by the Muscle Length-Tension Relationship:
The forcefulness of a contraction depends on the zone of overlap between thick and thin filaments
Why would a fully contracted or fully rested sarcomere contract with less force than one partially contracted?
There is less overlap between the thick and thin filaments
What is meant by muscle tone?
The tension in the relaxed muscle
How is muscle tone maintained?
A small number of fibers act in uniform (contract and relax)
When is muscle tone lost and the muscle is considered ‘flaccid’?
When there is injury to the nervous system
What are the different types of muscle contraction?
Isotonic Eccentric
Isotonic Concentric
Isometric
What is the difference between an isotonic and isometric contraction?
Isotonic = Tension remains constant as muscle length decreases or increases Isometric = Tension increases greatly without a change in muscle length
What are the different types of muscle fibers?
Slow oxidative (SO) fibers Fast oxidative-glycolytic (FOG) fibers Fast glycolytic (FG) fibers
Compare the myoglobin content of the different muscle fibers:
SO = many FOG = many FG = few
Compare the mitochondria content of the different muscle fibers:
SO = many FOG = many FG = few
Compare the colour of the different muscle fibers:
SO = red FOG = red-pink FG = white
Compare the capillaries of the different muscle fibers:
SO = many FOG = many FG = few
Compare the ATP generating capacities of the different muscle fibers:
SO = high, by aerobic respiration FOG = intermediate, aerobic respiration and anaerobic glycolysis FG = low, by anaerobic glycolysis
Compare the creatine kinase store of the different muscle fibers:
SO = low FOG = intermediate FG = high
Compare the glycogen store of the different muscle fibers:
SO = low FOG = intermediate FG = high
Compare the contraction velocity (speed) of the different muscle fibers:
SO = slow FOG = fast FG = fast
Compare the fatigue resistance of the different muscle fibers:
SO = high FOG = intermediate FG = low
Compare the rate of ATP hydrolysis of the different muscle fibers:
SO = slow FOG = fast FG = fast
How is ATP generated in slow oxidative (SO) fibers?
Aerobic respiration
What is the order of recruitment of the different muscle fibers?
first = slow oxidative (SO) second = fast oxidative-glycolytic (FOG) third = fast glycolytic (FG)
What is the primary function of slow oxidative (SO) fibers?
Maintaining posture and aerobic endurance
How is ATP generated in fast oxidative-glycolytic (FOG) fibers?
Aerobic respiration and anaerobic glycolysis
What is the primary function of fast oxidative-glycolytic (FOG) fibers?
Walking, sprinting
What is the primary function of fast glycolytic (FG) fibers?
Rapid movements of short durations
