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Anatomy and Physiology > Muscular system > Flashcards

Muscular system Flashcards

1
Q

What are the three types of muscle tissue?

A

skeletal, cardiac, smooth

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2
Q

What are the four major functions of muscle tissue?

A

contractility (shortens)
excitability (responds to a stimulus and produces action potentials)
extensibility (stretches beyond its resting length without damage)
elasticity (returns to its resting length after stretching)

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3
Q

What is the most abundant type of muscle tissue, accounting for around 40-50% of a person’s total body weight?

A

skeletal muscle

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4
Q

What is the structure of skeletal muscle?

A

striated (appears to have light and dark stripes under a microscope)
voluntary muscle

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5
Q

What are the four key functions of skeletal muscle?

A

production of body movements
maintaining body position
storage and movement
generation of heat

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6
Q

How is skeletal muscle involved in the production of body movements?

A

attached to bones of the skeleton

contraction of skeletal muscle pulls the tendons which in turn move the skeleton

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7
Q

How is skeletal muscle involved in maintaining body position?

A

contraction of skeletal muscle stabilises joints

e.g. sustained contraction of neck muscles helps to ensure the neck is maintained upright

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8
Q

How is skeletal muscle involved in storage and movement?

A

stores 80% of the body’s water and stores intracellular ions (e.g. potassium)
contraction of skeletal muscle assists in the flow of lymph fluid and returning blood to the heart

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9
Q

How is skeletal muscle involved in the generation of heat?

A

contraction of skeletal muscle requires the production and use of ATP which is used as energy
three-quarters of this energy is released as heat
involved in thermoregulation
involuntary contraction of skeletal muscle (shivering) increases rate of heat production when we are cold

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10
Q

Each skeletal muscle is an individual unit comprised of which structures?

A

muscle fibres
connective tissue
nerves
blood vessels

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11
Q

What is the structure of the fascia?

A

a layer of dense irregular connective tissue

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12
Q

What are the functions of the fascia?

A

to support and surround the muscle allowing free movement

to provide an entry and exit route for nerves, blood and lymphatic vessels

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13
Q

What are the three layers of connective tissue that extend from the fascia to further strengthen and protect the skeletal muscle?

A

epimysium, perimysium, endomysium

all three layers are continuous with the connective tissue that attaches skeletal muscle to bone and other muscles

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14
Q

What is the structure of the epimysium?

A

outermost layer
consists of dense irregular tissue
surrounds the entire muscle

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15
Q

What is the structure of the perimysium?

A

consists of dense irregular tissue

surrounds bundles of muscle fibres (fascicles)

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16
Q

What is the structure of the endomysium?

A

consists of reticular fibres

separates each individual muscle fibre

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17
Q

What is the structure of a skeletal muscle fibre?

A

a long cylindrical cell
multinucleated at the periphery
mature cell could measure up to 10 cm in length and 10-100 μm in diameter
striated due to the arrangement of the different types of filaments

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18
Q

How is skeletal muscle formed during embryonic development?

A

by the fusion of mesodermal cells called myoblasts

contractile proteins accumulate within the cytoplasm of the myoblasts and are converted to muscle fibres

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19
Q

What are the eight components of skeletal muscle?

A

sarcolemma, transverse (T) tubules, sarcoplasm, myofibrils, sarcoplasmic reticulum (SR), terminal cisterns, myofilaments, sarcomeres

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20
Q

What is the sarcolemma?

A

the plasma membrane of the muscle fibre

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21
Q

What are the T tubules?

A

enter the sarcolemma from the surface and pass towards the centre
open to the outside of the muscle fibre and filled with interstitial fluid

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22
Q

What is the sarcoplasm?

A

the cytoplasm of the muscle fibre
contains large amounts of glycogen used to produce ATP
contains myoglobin (a red-coloured protein found only in muscles and used to bind oxygen)
oxygen is released from myoglobin when needed by mitochondria to produce ATP

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23
Q

What are the myofibrils?

A

small threadlike structures
the contractile organelles of skeletal muscle
extend the entire length of the muscle

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24
Q

What is the SR?

A

a fluid-filled sac enclosing each of the myofibrils

stores calcium ions when the muscle is relaxed

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25
Q

What are the terminal cisterns?

A

open-ended sacs of SR that sit against the sides of the T tubule

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26
Q

What are the myofilaments?

A

small protein structures contained within the myofibril

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27
Q

What are the two types of myofilaments involved in the contractile process?

A

thin filaments - composed mainly of actin

thick filaments - composed mainly of myosin

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28
Q

Which two other proteins are found in the thin filament?

A

tropomyosin - prevents actin binding to myosin for muscle contraction
troponin - holds tropomyosin in place

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29
Q

What are the sarcomeres?

A

compartments that are the functional unit of the myofibril
separated from each other by Z discs
consist of several distinct bands and zones

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30
Q

What is the A band?

A

extends the entire length of the thick filament

darker middle region of the sarcomere

31
Q

What is the zone of overlap?

A

thick and thin filaments lie side by side near the end of the A band

32
Q

What is the I band?

A

found only in thin filaments

lighter, less dense region

33
Q

What is the H zone?

A

narrow area in the middle of the A band

contains only thick filaments

34
Q

What is the M line?

A

in the middle of the H zone

formed by proteins that hold the thick filaments together

35
Q

What is a neuromuscular junction (NMJ)?

A

the junction between the nervous system and the muscle

36
Q

What is the first stage in the stimulation of muscle contraction?

A

the nerve action potential travels along the motor neuron until it reaches the synaptic vesicles which release ACh into the synaptic cleft

37
Q

What is the second stage in the stimulation of muscle contraction?

A

ACh molecules bind to ACh receptors on the motor end plate and open a sodium ion channel
sodium flows across the membrane

38
Q

What is the third stage in the stimulation of muscle contraction?

A

the flow of sodium into the muscle fibre increases the positive charge and triggers a muscle action potential
this spreads across the sarcolemma and down T Tubules to the cisternae which release calcium into the sarcoplasm to cause muscle contraction

39
Q

What is the fourth stage in the stimulation of muscle contraction?

A

action potential generation stops as ACh is broken down by AChE
AChE breaks ACh into acetyl and choline (which cannot activate ACh receptors)
calcium ion concentration in sarcoplasm declines, returns to resting levels and muscle contraction ends

40
Q

What is the sliding filament hypothesis?

A

during contraction, the light band and the H zone get shorter
Z discs move closer together and the sarcomere gets shorter
this observation led to the sliding filament hypothesis
during contraction, the thick and thin filaments slide past one another

41
Q

What is the first stage in the contraction cycle?

A

when the muscle is stimulated, the action potential passes along the sarcolemma and down the T tubules into the muscle fibre

42
Q

What is the second stage in the contraction cycle?

A

the action potential is carried to the SR, which stores calcium ions, and causes the release of calcium ions into the sarcoplasm

43
Q

What is the third stage in the contraction cycle?

A

the calcium ions bind to the troponin, which alters the shape pulling the tropomyosin aside
this exposes the binding sites on the actin

44
Q

What is the fourth stage in the contraction cycle?

A

myosin head attaches to the actin, forming a cross-bridge

45
Q

What is the fifth stage in the contraction cycle?

A

myosin head tilts backwards, causing actin to slide past myosin (power stroke)
during the power stroke, ADP and Pi are released from the myosin head

46
Q

What is the sixth stage in the contraction cycle?

A

after the power stroke, a new ATP molecule attaches to the myosin head, breaking the cross-bridge
myosin head then returns to its original position (swings forward again) as the ATP is hydrolysed, releasing the energy to make this movement occur
myosin head can now make a new cross-bridge further along the actin filament

47
Q

What happens after contraction?

A

calcium ions are rapidly pumped back into the SR

this allows the muscle to relax

48
Q

What is the role of ATP in muscle contraction?

A

ATP supplies energy for contraction

part of the myosin head acts as ATPase and hydrolyses ATP to ADP and Pi, releasing energy

49
Q

Which three sources produce ATP for muscle contraction?

A

aerobic respiration, anaerobic respiration, creatine phosphate

50
Q

How does aerobic respiration produce ATP for muscle contraction?

A

occurs in mitochondria
Bohr effect helps to release more oxygen from haemoglobin in blood
during intense activity, the rate of ATP production is limited by oxygen delivery to the muscle tissue

51
Q

How does anaerobic respiration produce ATP for muscle contraction?

A

occurs in sarcoplasm
releases a little more ATP from the respiratory substrates but leads to production of lactate which is toxic
only lasts a few seconds before lactate causes fatigue

52
Q

How does creatine phosphate produce ATP for muscle contraction?

A

found in sarcoplasm
acts as a reserve store of phosphate groups
phosphate can be transferred from creatine phosphate to ADP molecules, creating ATP molecules very rapidly
the enzyme creatine phosphotransferase is involved
the supply of creatine phosphate is sufficient to support muscle contraction for a further 2-4 seconds

53
Q

What is muscle fatigue?

A

the muscle is unable to maintain its force of contraction after a period of prolonged activity

54
Q

What causes muscle fatigue?

A

inadequate calcium released from SR
insufficient oxygen supply
depletion of glycogen
build-up of lactate

55
Q

What is muscle tone?

A

sustained contraction of the muscle fibre maintained by only a few motor neurons
keeps the muscle relaxed but firm and not strong enough for movement

56
Q

What is an isotonic contraction?

A

the force of contraction remains unchanged while the length of muscle changes
this enables body movements and movement of objects

57
Q

What are the two types of isotonic contraction?

A

concentric and eccentric

58
Q

What is a concentric contraction?

A

the force generated overcomes the resistance of the object to be moved
the muscle shortens, pulls on the tendon to decrease the joint angle and produces movement
e.g. the lifting phase of a bicep curl

59
Q

What is an eccentric contraction?

A

when the muscle contracts but the length increases
e.g. after the bicep curl the weight can be smoothly and controllably lowered
more powerful than concentric contractions

60
Q

What is an isometric contraction?

A

the force generated does not overcome the resistance of the object to be moved
there is no change in length of the muscle and no movement, but energy is still used
help stabilise joints and essential in maintaining posture

61
Q

What is the structure of ‘red muscle fibres’?

A

high levels of myoglobin
dark in appearance due to extensive blood supply
high in mitochondria

62
Q

What is the structure of ‘white muscle fibres’?

A

low levels of myoglobin

light in appearance

63
Q

What are the three main groups of skeletal muscle?

A

slow oxidative (SO) fibres, fast oxidative-glycolytic (FOG) fibres, fast glycolytic (FG) fibres

64
Q

What are SO fibres?

A

smallest diameter and least powerful
high in myoglobin and mitochondria
mainly produce ATP by aerobic respiration
the rate at which ATP is used is relatively slow
contraction cycle occurs at a slower pace
less likely to fatigue
essential for posture and useful in endurance activities

65
Q

What are FOG fibres?

A

intermediate diameter
high in myoglobin and have increased blood supply
produce ATP by aerobic and anaerobic respiration
the rate at which ATP is used is three to five times faster than in SO fibres
rate of contraction is faster but duration shorter
moderately resistant to fatigue
used mainly in activities such as walking or sprinting

66
Q

What are FG fibres?

A

largest diameter and contain the largest number of myofibrils
low in myoglobin and mitochondria, relatively few blood capillaries
high in glycogen and produce ATP by glycolysis
hydrolyse ATP quickly
rate of contraction is the fastest and most forceful
fatigue more quickly than SO and FOG fibres
used for anaerobic movements of short duration (e.g. weight-lifting)

67
Q

How does skeletal muscle produce movement?

A

it exerts a force on tendons which pull on bones and other structures
the ends of articulating bones are pulled together but do not move equally in response to the contraction
one tends to remain stationary or close to its original position

68
Q

What is the difference between an origin and insertion?

A

origin - the attachment of a muscle’s tendon to the stationary bones
insertion - the attachment of the other tendon to the movable bone

69
Q

What is the difference between an agonist and antagonist?

A

agonist - mainly responsible for producing the action

antagonist - causes the muscle to move in the opposite direction

70
Q

Skeletal muscles can be grouped into which four areas?

A

head and neck
upper limbs
thorax and abdomen
lower limbs

71
Q

What is bipedalism?

A

the ability to walk upright on two limbs

72
Q

In normal walking, each leg passes through which two stages?

A

support phase - when the foot is on the ground

swing phase - when the foot is off the ground

73
Q

Why are older people at increased risk of falls?

A

tend to walk more slowly
take shorter and variable length steps
have a wider stride (base for balance)
balance is less stable

74
Q

What can nurses do to reduce the risk of falls in older people?

A

promote exercise (e.g. tai chi)

Anatomy and Physiology (13 decks)

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