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B5W3 > MUSCLE PHYSIOLOGY > Flashcards

MUSCLE PHYSIOLOGY Flashcards

1
Q

What is skeletal muscle innervated by?

A

somatic motor neurones (has no hormonal influence like cardiac/smooth muscle)

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2
Q

what are the functions of skeletal muscle?

A

to generate force, movement and heat

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3
Q

describe the connective tissue layers of muscle fibres?

A

The entire muscle is surrounded by connective tissue called epimysium
Within the muscles, the cells are collected into fascicles which are surrounded by perimysium
Each singular muscle fibre is surrounded by endomysium `

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4
Q

what are tendons composed of?`

A

dense fibrous connective tissue

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5
Q

what is sarcolemma?

what is sarcoplasm?

A

plasma membrane of muscle fibres

cytoplasm of muscle fibres

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6
Q

what can be found within sarcoplasm?

A 
many nuclei
mitochondria
glycogen granules to make ATP
myoglobin to bind oxygen molecules that diffuse in from interstitial fluid
sarcoplasmic reticulum
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7
Q

what are satellite cells?

A

Satellite cells are precursors to skeletal muscle cells
They are small multipotent cells with very little cytoplasm found in mature muscle-located between the basement membrane and sarcolemma of muscle fibres.

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8
Q

what is a sarcomere?

A

a unit of striated muscle tissue- the repeating unit between 2 Z lines.

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9
Q

describe the structure of sarcomeres?

A

made up of actin and myosin fibres which overlap Titian molecules anchor in to the Z disc and extend to the M-line to act as a spring

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10
Q

what is the Z line of a sarcomere?

A

where the actin filaments are anchored

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11
Q

what is the M line of a sarcomere?

A

where myosin filaments are anchored

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12
Q

what is the I band of a sarcomere?

A

only actin filaments

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13
Q

what is the A band in a sarcomere?

A

the length of myosin filaments which may contain overlapping actin filaments

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14
Q

what is the H zone in a sarcomere?

A

contains only myosin filaments

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15
Q

outline the sliding filament theory?

A

As muscle contracts, the lengths of the H and I bands decrease and can virtually disappear in maximally contracted muscle.
The thin filaments slide on the thick filament to shorten the length of each sarcomere.

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16
Q

what are the thick filaments in a sarcomere made up of?

A

it consist of a tail and 2 myosin heads
it has heavy and light chains. the light chain binds to and regulates the head of the heavy chain
it has a long tail used as a dimerisation domain
several myosin molecules associate to each other to form thick filaments with their heads facing outwards so they can interact with actin filaments.

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17
Q

what are the 3 domains of myosin?

A

The motor domain= interacts with actin and binds to ATP
The neck domain binds light chains
The tail domain= anchors and positions the motor domain so it can interact with actin

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18
Q

what are the thin filaments of the sarcomere made up of?

A

actin, tropomyosin and troponin I,T and C

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19
Q

what is tropomyosin?

A

Regulatory protein that is a component of thin filament. When skeletal muscle fibre is relaxed, tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin.

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20
Q

what is troponin?

A

Regulatory protein that is a component of thin filament. When Ca2+ binds to troponin, it has a conformational change which moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin.

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21
Q

what is the troponin complex made up of?

A

Troponin I – binds to the actin filament.
Troponin T – binds to tropomyosin.
Troponin C – can bind calcium ions

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22
Q

outline cross-bridge cycling?

A

depolarisation is conducted down the t-tubules, causing a huge influx of calcium ions into the sarcoplasm from the sarcoplasmic reticulum.
Calcium binds to troponin C, causing a conformational change that moves tropomyosin away from the myosin head binding sites of the actin filaments.
This allows the myosin head to bind to the actin, forming a cross-link. The power stroke then occurs as the myosin heads pivots in a ‘rowing motion’, moving the actin past the myosin towards the M line. this release ADP and Pi.
ATP then binds to the myosin head, causing it to uncouple from the actin and ADP can be hydrolysed to return the myosin head to its ‘cocked’ position

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23
Q

describe the length-tension relationship for skeletal muscle?

A

it indicates how the forcefulness of muscle contraction depends on the length of sarcomeres within the muscle before contraction begins.
i.e. if sarcomeres are stretched, the zone of overlap shortens so fewer myosin heads can make contact with actin and when sarcomere length is too short, the thick filaments can crumple as they are compressed by Z discs`

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24
Q

how is skeletal muscle length normally held close to the optimum?

A

by firm attachments of skeletal muscle to bone via tendons

25
Q

describe what happens when the action potential reaches the neuromuscular junction?

A

The action potential reaches the axon terminal
The membrane depolarises
which opens Ca2+ channels
synaptic vessels dock to the synaptic membrane and release neurotransmitters into the neuromuscuar junction. Ach binds to nicotinic receptors on the post-synaptic membrane which have ion channels for positively charged ions e.g. Na+ so they can enter the muscle fibre and depolarise the membrane.

26
Q

how does the motor end plate provide a large surface area for ACh?

A

There are junctional folds, deep grooves in the motor end plate

27
Q

how is ACh degraded once it has been used?

A

acetylcholine esterase and the products are uptaken by the axon terminal and are re-used.

28
Q

what are end plate potentials?

A

the voltages which cause depolarization of skeletal muscle fibers caused by neurotransmitters binding to the postsynaptic membrane in the neuromuscular junction. they only cause an action potential when depolarisation reaches threshold potential

29
Q

what are T tubules?

A

invaginations of the sarcolemma that run into the muscle fibre and make close contact with the terminal cisternae. T tubules are filled with interstitial fluid,

30
Q

what are terminal cisternae?

A

dilated end sacs of sarcoplasmic reticulum

31
Q

what is a triad?

A

a transverse tubule and the 2 terminal cisternae either side

32
Q

what is the function of T tubules?

A

T-tubules bring the sarcolemma very close to the sarcoplasmic reticulum at all regions throughout the cell to allow for synchronised Ca2+ release

33
Q

what is excitation-contraction coupling?

A

the action potential travels down T tubules and this depolarisation opens L-type Ca2+ channels. mechanical coupling between these channels and the Ca2+ release channels in the terminal cisternae cause Ca2+ release channels to open and allow Ca2+ stored in the sarcoplasmic reticulum to migrate into the sarcoplasm.

34
Q

what is rigor mortis?

A

a state of muscular rigidity that begins 3-4 hours after death and lasts about 24 hours.

35
Q

what causes rigor mortis?

A

After death, Ca2+ ions diffuse out of the Sarcoplasmic reticulum and allow myosin heads to bind to actin.
Since ATP synthesis has ceased, cross-bridges cannot detach from active sites, so skeletal muscles throughout the body become locked in the contracted position.
It lasts until proteolytic lysosomal enzymes released by autolysis begin to digest the decomposing cells.

36
Q

what do muscles require energy for?

A

cross-bridge movement and myosin release during contraction
to pump Ca2+ back into the sarcoplasmic reticulum during relaxation
to restore the membrane potential

37
Q

what are the 3 sources of ATP in muscles? which is most efficient?

A

creatine phosphate
anaerobic respiration
aerobic respiration (most efficient- lasts longest)

38
Q

how do we get ATP from creatine phosphate?

A

creatine phosphate transfers a high-energy phosphate to ADP. The products of this reaction are ATP and creatine.

39
Q

why is creatine kinase an important marker of muscle damage?

A

in muscle degeneration, mescal cells break open and their contents enter the bloodstream. most creatine kinase exists in muscle so a concentration rise in the blood indicates muscle damage

40
Q

when do muscle twitches occur?

A

when one muscle fibre contracts in response to a command (stimulus) by the nervous system

41
Q

what is the lag phase of a muscle twitch?

A

The time between the activation of a motor neuron until the muscle contraction occurs

42
Q

what are the 3 types of muscle fibre?

A

Type 1 fibres: slow twitch oxidative fibres
Type 2a fibred: fast twitch oxidative-glycolytic fibres
Type 2b fibres: fast twitch glycolytic fibres

43
Q

how can the proportions of our muscle fibres change?

A

with training, age, atrophy or denervation

44
Q

what is tetanus?

A

a sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate.

45
Q

what is a motor unit?

A

made up of a motor neuron and the skeletal muscle fibers innervated by that motor neuron’s axonal terminals.

46
Q

how can muscles produce contractions of variable force and duration if action potentials are ‘all or nothing’ responses?

A

motor unit recruitment: the process by which different motor units are activated to produce a given level and type of muscle contraction.

47
Q

what is Henneman’s size principle?

A

as more force is needed, motor units are recruited in a precise order according to the magnitude of their force output, with small units being recruited first, thus exhibiting task-appropriate recruitment.

48
Q

what is asynchronous recruitment?

A

-When the nervous system modulates the firing rates of the motor so that different motor units take turns maintaining muscle tension. -The alteration of active motor units allows some of the motor units to rest between contractions and prevents fatigue.

49
Q

describe how the level of stimulation from low, medium and to high affect which motor neurones control the muscle fibres?

A

at low level of stimulation, we have small motor neurones controlling small diameter, slow pitch muscle fibres
at higher levels of stimulation strength, we have larger motor neurone controlling larger diameter , ox-glyc fast twitch muscle fibres
at maximum stimulation strength we have large motor neurones controlling larger-diameter, glyc fast twitch muscle fibres.

50
Q

what is an isometric contraction?

give an example

A

when muscle creates tension without moving a lot/length of muscle doesn’t change
e.g. doing a plank/holding weight keeping it stationary

51
Q

what is isotopic contraction?

give an example

A

when muscle creates tension and moves a lot/muscle shortens

e.g. bicep curl

52
Q

in isotopic contraction, when will muscles begin to shorten?

A

when force=load (when tension is a max)

53
Q

describe the relationship between load and velocity of muscles shortening?

A

as load increases, the velocity of muscle shortening decreases
at max load= muscle can’t move (isometric)
at min load= velocity of muscle length change is maximal

54
Q

what are the advantages of the musculoskeletal system being considered as a lever and fulcrum system?

A

it means the muscle operates at an optimum length-tension relationship
it maximises the distance and speed at which the load is moved

55
Q

what are the disadvantages of the musculoskeletal system being considered as a lever and fulcrum system?

A

compared to other systems it requires more force to moved requires more force to resist a load

56
Q

what is the hypodermis?

A

a connective tissue/adipose tissue layer directly below the dermis and serves to connect the skin to the underlying fascia of the bones and muscles.
It provides a pathway for nerves, blood vessels, and lymphatic vessels to enter and exit muscles.

57
Q

what is the function of the adipose layer of the hypodermis/subcutaneous layer?

A

tores most of the body’s triglycerides, serves as an insulating layer that reduces heat loss, and protects muscles from physical trauma

58
Q

what is fascia?

A

a dense sheet of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body.

59
Q

what is the function of fascia?

A

It holds muscles with similar functions together, it allows free movement of muscles, carries nerves, blood vessels, and lymphatic vessels, and fills spaces between muscles.

B5W3 (9 decks)

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