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L3 Anatomy and Physiology > The Muscular System > Flashcards

The Muscular System Flashcards

1
Q

cardiac muscle

A

involuntary muscle
found in walls of heart
contains some striations but is largely composed of intercalated discs which act as cross bands, separating the opposite ends of the cardiac muscle cell from the next.
these discs help to give cardiac tissue its structural integrity and allow the rapid transmission of electrical pulses to adjacent muscle cells.
cardiac tissue has a lattice like appearance that allows lots of muscle cells to fire and contract simultaneously, as seen with each heartbeat.
cardiac muscle tissue has virtually no anaerobic capacity and therefore relies exclusively on the coronary arteries to deliver a continual supply of oxygenated blood.

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2
Q

Smooth muscle

A

involuntary and non-striated
forms walls of blood vessels and many of body’s organs
cannot contract as fast or forcefully as skeletal muscles
more enduring than other types of muscle tissue - crucial to its continuous activation throughout the lifespan of a person
when it contracts it typically causes constriction - when relaxes causes dilation.

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3
Q

Skeletal muscle

A

forms over one third of total body mass in those with normal body composition
formed by large bundles of fibres that give muscle its striated or striped appearance. so it is also called ‘striated’ muscle tissue
these tiny fibres have the ability to shorten to almost half of their resting length
it is arrangement of these fibres that dictates the speed and force at which muscle fibre can shorten

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4
Q

fibre arrangement

A

skeletal muscles are formed by multiple bundles of muscle fibres known as ‘fascicles’. these vary considerably between muscles in which way their fibres are arranged, which accounts for the different shapes and functional capabilities between muscle groups

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5
Q

fusiform muscle

A

a muscle which packs its fibres parallel to each other in a spindle-like shape is called a ‘fusiform muscle’. This arrangement is thicker in middle and thinner towards end, and is usually found where muscle is required to contract through a larger range and at greater speed.

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6
Q

pennate muscle

A

a muscle which packs its fibres diagonally, or obliquely.
there are three primary types of pennate arrangement = unipennate, bipennate and multipennate
a pennate arrangement packs more fibres into a smaller space than a fusiform muscle, making it considerably stronger and capable of generating much more force. this increased strength does however reduce the speed at which the muscle is able to contract, especially with multipennate fibre.
unipennate = intercostals, tibialis anterior
bipennate = rectus femoris
multipennate = deltoids
fusiform = biceps femoris, bicep brachi

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7
Q

structure of a skeletal muscle

A
  • external wall = epimysium/sheath/fascia = layer of connective tissue
    fascia is made from collagen - binds together at end of muscle to form connections from muscle to bone. here collagen becomes more dense and regular in arrangement.
  • epimysium binds all the fibres together to protect contractile filaments from impact and trauma.
  • large bundles of muscle fibres called fasiculi are bound together within epimysium. Each fasiculus (singular of fasiculi) can hold up to 150 individual muscle fibres.
  • the fasiculi are protected by a thick layer of connective tissue called perimysium.
  • endomysium is a layer of connective tissue protecting each muscle fibre.
  • endomysium binds large groups of smaller fibres together known as myofibrils
  • each myofibril contains contractile units called sarcomere
  • sarcomere is formed by 2 protein filaments = actin and myosin.
  • during a muscle contraction, the myosin heads bind with myosin binding sites along the actin filament to form a cross bridge. these heads then tilt, detach and reattach and tilt again until the sarcomere can shorten no more = how muscles contract
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8
Q

the sliding filament theory (definition)

A
  • describes how muscle contractions occur at a microscopic level as a result of the shortening of individual sarcomeres in sequence
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9
Q

tonic muscles

A
  • sometimes described as antigravity muscles
  • muscles which constantly maintain a certain amount of tone (activation) in order to promote posture and joint stability
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10
Q

tonic muscle examples

A
  • deep neck flexors
  • rectus abdominis
  • external obliques
  • transverse abdominis
  • multifidus
  • mid-lower fibres of trapezius
  • rhomboids
  • serratus anterior
  • gluteus medius (to less extent)
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11
Q

phasic muscles

A

usually found in more peripheral locations and utilise the body’s lever system to a greater extent than tonic muscles

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12
Q

phasic muscles examples

A
  • deltoids
  • pectorals
  • latissimus dorsi
  • gluteus maximus
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13
Q

slow twitch motor units

A
  • low firing threshold
  • high fatigue threshold
  • produce lower levels of force/speed
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14
Q

fast twitch motor units

A
  • high firing threshold
  • low fatigue threshold
  • produce higher levels of force/speed
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15
Q

muscle fibre types

A
  • type 1 fibres (Slow Oxidative SO)
  • type 2a fibres (Fast Oxidative Glycolytic FOG)
  • type 2b fibres (Fast Glycolytic FG)
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16
Q

isotonic contractions

A

most commonly used muscle action and involves both shortening and lengthening of the muscle.
this dynamic muscle action may also be referred to as an isointertial action

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17
Q

Type 1 fibres (Slow Oxidative SO)

A

-mostly suited to low-intensity and prolonged exercise
- contain a vast number of aerobic enzymes which enables them to generate lots of energy (ATP)
aerobically within the mitochondria by burning oxygen with glucose, fats and proteins.
- rich capillary network = can deliver large quantities of oxygen to the mitochondria. also remove waste products like carbon dioxide and lactic acid.
- slow contraction speeds and oxidative properties

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18
Q

type 2a fibres (Fast Oxidative Glycolytic FOG)

A
  • ability to act in both an aerobic and anaerobic capacity depending on the intensity and duration of exercise.
  • primary role is to support type 1 and 2b fibres
  • often described as the ‘trainable muscle fibres’ because they are able to adapt themselves to perform the function of either type 1 or 2b fibres.
  • during heavy strength training they would adapt to become 2b fibres but detraining would reverse this process.
  • they are relatively fast to contract and have the ability to use glycogen and oxygen as an energy substrate to release ATP
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19
Q

Type 2b fibres (Fast Glycolytic FG)

A
  • recruited during maximal and explosive activities like sprinting, jumping and heavy resistance training.
  • have incredibly high firing threshold and thus react quickly
  • they are not very enduring and so fatigue easily
  • considerably larger in size than type 1 and 2a which is why they are able to generate more force than others
  • extremely fast to contract but only have the ability to use glycogen as an energy substrate to release ATP
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20
Q

isometric muscle action

A
  • a static muscle contraction
  • length of muscle does not alter
  • distance between origin and insertion remains relatively constant throughout contraction
  • those with high blood pressure should refrain from this
  • many of the key postural muscles working in a ‘tonic’ capacity are recruited isometrically in order to maintain optimum body position
21
Q

the two distinct phases of an isotonic muscle contraction

A

concentric

eccentric

22
Q

concentric phase (isotonic contraction)

A
  • usually first stage of an exercise
  • takes place when muscle becomes shorter and fatter
  • eg the upward phase of a bench press or the extending phase of the leg extension
  • insertion moves towards origin
  • in a few cases the origin can move towards the insertion = eg a crunch (insertion of rectus abdominis moves towards muscle origin at pubis)
23
Q

eccentric phase (isotonic contraction)

A
  • takes place as the muscle lengthens under tension
  • there is still binding between the actin and myosin filaments so should not be confused with relaxation.
  • also called ‘negative phase’
  • eg lower phase of the bench press, squat or bicep curl exercises
  • insertion moves away from the origin
  • muscles are normally up to 40% stronger eccentrically than they are concentrically. this is a factor during strength training and rehab programmes is commonly exploited to improve muscle function and force output.
  • commonly associated with DOMS
24
Q

the motor unit

A
  • ‘functional contractile unit’ of a muscle
  • consists of a nerve and all the muscle fibres under the control of that nerve
  • can be large with lots of muscle fibres per nerve or small with less
  • large motor units are typically found in strong and powerful muscles like the quads, small motor units are found where more precise control is needed such as fingers
  • the number of active motor units in a given muscle effects the muscle’s ability to produce force
  • all muscle fibres within a motor unit are of the same muscle fibre type
  • during periods of prolonged inactivity, the lack of electrical stimulation that causes these motor units to switch off and thus reduces their ability to control muscle fibres
  • the reactivation of these muscle fibres is why there is a large increase of strength observed in novice exercisers
  • also key goal of rehab exercises that seek to restore optimal posture and movement control
25
Q

all or nothing principle

A

‘when a muscle fibre is stimulated by an action potential (electrical signal), every contractile unit within that muscle fibre will contract at the same time’
- this does not mean that every muscle fibre within a muscle is recruited during a contraction. they will recruit the approximate number of fibres needed to produce the desired force output, but when a nerve cell is activated all the muscle fibres under that nerve will contract

26
Q

the sliding filament theory (detail)

A
  • efferent nerves send an electric impulse from brain to target muscle fibres
  • its transmitted across the muscle wall and triggers the sarcoplasmic reticulum to release calcium into the sarcoplasm
  • greater volumes of calcium are released when a more forceful contraction is required
  • calcium binds with troponin causing it to rise/lift
  • tropomyosin also elevates to reveal the myosin binding sites located along the length of the actin filament
  • myosin head automatically attaches to actin filament = cross bridge
  • myosin heads tilt and pivot causing actin and myosin to slide over each other in opposite directions = power stroke
  • power stroke is fuelled by ATP
  • when myosin head detaches from actin, the cross bridge is broken
  • the process of cross bridging will continue as long as the nerve impulse stimulating the contraction is present and there is sufficient ATP and calcium
  • actin is tethered to structures located on the end of each sarcomere and so any shortening of the length of the actin filament would also result in a shortening of the whole sarcomere, consequently contracting the entire muscle
  • this tilting and sliding action is repeated until the sarcomere cannot shorten anymore and the H-zone within the sarcomere is no longer visible
  • when this process occurs throughout all of the fibres within a muscle, large quantities of force can be produced
  • once the impulse stops, the calcium is pumped back into the sarcoplasmic reticulum and the actin returns to its resting position (causing muscle to lengthen and relax)
27
Q

colour, size and composition of type 1 fibres

A
  • red
  • small diameter
  • rich in capillary density
  • rich in mitochondria
  • rich in myoglobin
  • low ATP levels
  • high levels of aerobic enzymes
  • low levels of anaerobic enzymes
28
Q

colour, size and composition of type 2a fibres

A
  • pink
  • medium diameter
  • moderate capillary density
  • moderate in mitochondria
  • moderate in myoglobin
  • moderate ATP levels
  • moderate levels of aerobic enzymes
  • moderate levels of anaerobic enzymes
29
Q

colour, size and composition of type 2b fibres

A
  • white
  • large diameter
  • low capillary density
  • low in mitochondria
  • low in myoglobin
  • high ATP levels
  • low levels of aerobic enzymes
  • high levels of anaerobic enzymes
30
Q

gradation of force

A

the muscle’s ability to generate force is primarily affected by the following two variables:

  • frequency of activation
  • number of motor units recruited
31
Q

proprioceptors

A
  • specialised sensory receptors located in joints, muscles and tendons, that communicate with the central nervous system about pressure, tension and deformation within that bodily tissue.
  • the information provided to the CNS by proprioceptors is essential in order to perform complex movements in a coordinated manner, and to ensure that muscles maintain an appropriate level of activation, therefore preventing damage.
  • all proprioceptive info is processed at a subconscious level and does not require any thought.
  • the two proprioceptors primarily concerned with musculoskeletal tissues are:
  • muscle spindles
  • golgi tendon organs
32
Q

myoglobin

A
  • iron and oxygen binding protein found in skeletal muscles
  • has a similar structure and function to haemoglobin
  • but only has a single binding site for oxygen to attach whereas haemoglobin has 4
  • serves an oxygen store and transporter within skeletal muscles
  • role in storage is to make sure that any spike in demand for oxygen is met immediately from these stores
  • found in all muscle fibre types but found in greater concentrations in type 1 and 2a as these have greater reliance on oxygen
  • rarely found in smooth and cardiac tissues
33
Q

mitochondria

A
  • powerhouse of the muscle cell/fibre
  • found in the sarcoplasm
  • abundant within type 1 and 2a fibres (rely on aerobic energy pathways)
  • muscles contain highest mitochondria density of any other bodily tissue
  • responsible for production of energy derived from the breakdown of carbs, fats and proteins
  • oxidises glucose, amino acids and fatty acids to generate ATP = aerobic respiration
  • muscular system responds positively to aerobic and endurance activities by increasing number and size of mitochondria in muscle cell
  • the body cannot produce them but can generate more through ‘replication’ (splitting one into two cells)
  • they are constantly dividing, fusing and changing shape
  • their activity is stimulated by energy demand
  • greater size and number of mitochondria means the body can generate ATP from nutrients to fuel muscular contractions = muscle can work at a higher rate and/or for longer
34
Q

muscle spindles

A
  • run parallel to direction of the muscle’s fibres
  • monitor the length and tension within the muscle
  • created by modified muscle fibres called ‘intrafusal fibres’
  • these structures feed information to the nervous system about any fibre length change and the rate at which the change occurs
  • primary purpose is to protect muscles from tears and strains
  • are in constant communication with the spinal cord via sensory neurons
  • stretch reflex is initiated by them
35
Q

golgi tendon organs

A
  • perform similar role to muscle spindles
  • located at the junction between the muscle and the tendon
  • primary role is to monitor tension and deformation in and around the tendinous area and provide feedback to CNS via sensory neurons
  • when tension is considered dangerously high, the spinal cord instructs the muscle to cease the stretch reflex contraction.
  • this inhibitory process is known as the inverse stretch reflex or the autogenic inhibition
  • their activity always overrides that of muscle spindles because the tendinous area is less vascular and does not have the same rich blood supply as muscle tissue
  • in injury and tissue damage, tendinous tissue would take longer to repair than muscle tissue because its supply of oxygen and nutrients is much less
36
Q

frequency of activation

A
  • skeletal muscles are stimulated by an action potential that is delivered to the muscle fibres via a motor neuron
  • each action potential results in brief muscle activation = twitch
  • twitch alone is not enough to create a muscle contraction so multiple must be generated to create muscle movement
  • reducing the time between twitches increases the level of activation that a motor unit can exert and results in stronger contractions
37
Q

tetanus

A

the maximum amount of force that a motor unit can generate - occurs when twitches are delivered at so high a frequency that they fuse into a single and continuous level of muscle activation

38
Q

motor unit recruitment

A
  • the total number of motor units recruited within a muscle will dictate the volume of force that can be produced from that muscle contraction
  • the sequence in which these fibres are recruited will inevitably result in a tiny delay between the point of muscle activation and the time taken to reach a muscle’s maximum force output
  • can decrease this time by increasing efficiency of neuromuscular system
  • low threshold motor units are activated first = type 1 fibres are first to be recruited. if these do not produce desired force, type 2a and 2b will be recruited in accordance to their size (smallest to largest)
  • motor units high in the recruitment order are largely used for strength, speed and power activities
39
Q

size principle

A

all motor units are recruited in a particular order based on their size

40
Q

action potential

neuromuscular anatomy 1

A
  • motor neurons are nerves that transmit nervous impulses from the brain or spinal cord towards a skeletal muscles or gland. this nervous impulse is called an action potential
  • in skeletal muscles this impulse would create a stimulatory effect that causes the affected muscle to contract
41
Q

the neuromuscular junction

neuromuscular anatomy 2

A

the point at which the axon of the motor neuron transmitting the impulse interacts with the muscle fibre
created by the interaction of the motor end plate and muscle fibre

42
Q

motor end plates

neuromuscular anatomy 3

A
  • towards the terminal end, axons divide into fine filaments that terminate at minute pads called motor end plates
  • each plate interacts with a sensitive area of the muscle fibre to create a structure similar to a synapse
43
Q

synaptic cleft

neuromuscular anatomy 4

A

the space between the motor end plate where the nervous impulse is transmitted across. it is transmitted with the release of the neurotransmitter ‘acetylcholine’

44
Q

acetylcholine

neuromuscular anatomy 5

A
  • interacts with the muscle fibre side of the synaptic cleft
  • causes sodium to go into the muscle fibre and potassium to go into the synaptic cleft
  • this rapid exchange of sodium and potassium creates an electrical charge on the muscle fibre membrane that spreads across the muscle fibre as an action potential. this action potential then stimulates the muscle to contract in accordance with the principles of the sliding filament theory
45
Q

the nervous impulse

A

starts off electrical, becomes chemical at neuromuscular junction and becomes electrical again at muscle cell

46
Q

the number of muscle fibres

A

the number of muscle fibres contained within a skeletal muscle cannot be increased through exercise or physical activity because it is pre-determined by genetic factors.
Although they do not increase in number, diet and exercise can increase their size. this is largely result of new protein tissue being added along the existing muscle fibre = hypertrophy

47
Q

the composition of a skeletal muscle fibre

A

in respect to muscle fibre types in skeletal muscles, the composition of them are is largely pre determined by genetic factors and cannot be changed by exercise

48
Q

types of muscle fibre in skeletal muscle

A
  • all 3 muscle fibre types can be found within a skeletal muscle with the dominance of a particular fibre being responsible for the genetic advantages that some people have over others in terms of athletic abilities
  • muscle fibre type distribution is not universal throughout the entire musculoskeletal system and so some muscle groups will contain more or less of a specific muscle fibre than others
  • some muscle groups are more likely to contain a greater proportion of a specific muscle fibre type than others based on their location and functional role within the body.
  • eg key postural muscles like transverse abdominis typically have higher proportion of type 1 fibres because they are needed to produce relatively low levels of force over long periods of time
  • eg large locomotor muscle groups like quads, pecs and glutes contain a mixture of type 1 and 2 fibres because need to be both enduring and strong

L3 Anatomy and Physiology (13 decks)

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