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Anatomy > Structure and function of muscles > Flashcards

Structure and function of muscles Flashcards

1
Q

Muscle functions

A

Move body parts, maintain body posture, adjust the volume of hollow structures, move substances within the body, produce heat

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2
Q

Skeletal muscle

A

attached to the bone, moves the skeleton, forms the bulk of the body’s muscle mass, striated, voluntary control- can b contracted or relaxed at will, contracts quickly and forcefully then relaxes to become ready to contract again, contraction is not maintained for extended periods of tie, fatigues after repeated contraction

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3
Q

smooth muscle

A

found in the walls of hollow organs, involuntary, contracts slowly and may maintain the contraction over an extended period of time, generally does not fatigue, non-striated with a smooth appearance

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4
Q

cardiac muscle

A

found only in the hear, involuntary, contracts quickly and then relaxes but does not fatigue, striated but has shorter cells than skeletal muscle

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5
Q

properties of muscle

A

contractile, excitable, extensible

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6
Q

muscle fibres

A

skeletal muscle cells that are also called myocytes

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7
Q

Sarcolemma

A

the cell membrane surrounding the muscle cell. it acts to contain the muscle fibre’s contents and shield it from the extracellular environment. especially important in muscle contraction. it surrounds the cytoplasms and also tunnels down into the interior of the muscle fibre

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8
Q

t-tubules

A

a network of muscle fibre. the action potentials travel down the t-tubules which enable them to reach every part of the fibre virtually simultaneously to trigger a coordinated muscle contraction

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9
Q

sarcoplasm

A

the cytoplasm of the muscle fibre. It is densely packed with myofibrils, sarcomeres, Sarcoplasmic reticulum (SR), mitochondria , and myoglobin

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10
Q

Myofibrils

A

slender, thread-like organelles accomplish the work of muscle contraction. each myofibril is a bundle of different protein filaments that run the entire length of the muscle fibre

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11
Q

Sarcomeres

A

repeating units found within each myofibril. these are the functional units of muscle that create the striated appearance of skeletal muscle. each sarcomere is composed of two bundles of protein myofilaments- thick filaments and thin filaments. these are responsible for muscle contraction.sarcomere length is shorter when muscle is contracted compared to its resting length

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12
Q

Sarcoplasmic reticulum (SR)

A

Stores calcium ions necessary for muscle contraction. T-tubules are in close contact with the SR

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13
Q

mitochondria

A

these organelles generate the ATP that fuels muscle contraction

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14
Q

myoglobin

A

an iron-containing compound that stores oxygen used to generate energy for muscle contraction

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15
Q

Z discs

A

protein structures that join sarcomeres together at their ends, thin and thick filaments are tethered to the Z discs. thick filaments overlap the thin filaments

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16
Q

somatic motor neuron

A

carries a signal that stimulates contraction in skeletal muscle. the cell bodies of motor neurons are located in the brain or spinal cord and send out axons to communicate with muscle fibres.

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17
Q

visceral motor neuron

A

carries a similar signal to smooth muscle

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18
Q

axon terminals

A

the branches that make contact with several muscle fibres off an axon of a motor neuron

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19
Q

motor units

A

comprises a somatic motor neuron and the skeletal muscle fibres it control.
- when a motor unit is stimulated by an action potential, all of its fibres contract
-many muscles contain motor units of different sizes
-a motor unit consists of a motor neuron and all the muscle fibres it innervates

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20
Q

neuromuscular junction

A

the synapse between a motor neuron and a muscle fibre. an example of a chemical synapse

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21
Q

chemical synapse

A

a synapse is a site where a signal passes from one cell to the next. a chemical synapse uses a neurotransmitter to convey the signal between cells

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22
Q

acetylcholine (ACh)

A

released from the axon terminal of the somatic motor neuron to carry the electrical signal across the synaptic cleft between the motor neuron and the receptors of the muscle fibre

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23
Q

Process leading to a muscle contraction

A

1) an action potential arrives at the axon terminal
2) Synaptic vesicles that contain ACh fuse with the cell membrane and release the ACh molecules into the synaptic cleft
3)ACh diffuses across the synaptic cleft and binds to nicotnic cholinergic receptors on the muscle fibre membrane
4) the bound receptors induce contraction of the muscle

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24
Q

cholinergic receptors

A

bind to acetylcholine. two types: nicotinic and muscarinic.

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25
Q

Stopping the signal.

A

when the signal has been transferred from the neuron to the muscle fibre, then transmission must e stopped, and the acetylcholine recycled

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26
Q

acetylcholinesterase

A

an enzyme found in the synaptic cleft that inactivates and hydrolyzes ACh to cholin and acetate. the choline is taken back into the axon terminal by a choline carrier, where it is recycled into fresh ACh

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27
Q

Muscle fibre after an action potential

A

1) the action potential travels along the sarcolemma
2) Ca2+ is released from the SR into the sarcoplasm, resulting in muscle contraction
3)Ca2+ is pumped back into the SR from the sarcoplasm

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28
Q

The resulting muscle action potential results in initiation of muscle contraction

A

1) local depolarisation of the sarcolemma initiates an action potential that that travels along the sarcolemma and down the t-tubules
2)t-tubules contain many voltage ion channels, including Ca2+ channels
3) the sarcoplasmic reticulum, which stores Ca2+ ions, sits inside the muscle fibre in close association with the t-tubules. Ca2+ relase channels are embedded in the SR membrane.- these open to release Ca2+ into the sarcoplasm in response to an action potential. Increased Ca2+ in the sarcoplasm enables muscle fibres to contract
4)the SR membrane also contains an ATP-fuel pump that moves Ca2+ ions back into the SR. this means that the sacroplasmic concentration of Ca2+ is a balance between the Ca2+ release in response to an action potential and the Ca2+ pumped back into the SR.

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29
Q

Thick filaments

A

bundles of myosin protein. each molecule has two globular heads that protrude from the bundle.
there are two binding sites on each head: one for binding ATP and one for binding thin filaments

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30
Q

crossbridge

A

when a myosin head binds to a thin filament. the connection between thick and thin filaments

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31
Q

thin filaments

A

composed of three proteins.
actin, tropomyosin, and troponin

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32
Q

actins role in thin filaments

A

a small globular protein that is the main constituent. each filament contains two long strands of actin twisted together in a helix. each actin molecules contains a binding site for a myosin head

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33
Q

tropomyosin role in thin filaments

A

prevents myosin from binding to actin until a signal for contraction arrives from the neuron innervating the muscle

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34
Q

troponin role in thin filaments

A

keeps the tropomyosin molecules in place over the binding sites in relaxed muscle, but moves them out of the way for biding to occur

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35
Q

the process of muscle contraction

A

involves myosin repeatedly forming and breaking crossbridges with actin so that actin slides past the myosin and the sarcomere shortens.
the cycle of crossbridge formation and breaking is what generates the force of contraction adnd requires the presence of Ca2+ and energy in the form of ATP

36
Q

muscle in relaxed state

A

myosin cannot interact with actin due to the presence of tropomyosin clocking the actin binding site, no crossbridges can form

37
Q

muscle during contraction

A

-muscle depolarisation results in the release of stored Ca2+ for the SR some of which binds to troponin. this causes a conformational change in troponin and a consequent shift in the troponin-tropomyosin complex. the result is the exposure of the actin binding site
-this allows actin and myosin to form crossbridges. the effect of forming and breaking cross bridges allows actin filaments to slide over myosin so that muscle shortens
-when the electrical impulses t othe msucle stop and Ca2+ is removed by reuptake into the SR, the troponin-tropomyosin complex changes its orientation and once again prevents the interaction of actin with myosin, crossbridges can longer form and the muscle relaxes

38
Q

twitch

A

a weak, transient muscle contraction produced by a single action potential in a muscle fibre releasing Ca2+ form the SR. the twitch relaxes when the SR reaccumulates the Ca2+. every twitch produces some degree of tension of the muscle fibre

39
Q

summation of twitches

A

a slightly stronger state of contraction that results if a second action potential occurs before the twitch is finished. thi happened because the pumps in the SR don’t have enough time to pump all the released Ca2+ back into the SR before the muscle fibre is restimulated by another action potential

40
Q

incomplete tetanus

A

a state reached where the muscle fibre only relaxes slightly between subsequent contractions. subsequent action potentials result in progressively greater tension and force until incomplete tetanus is reached.

41
Q

tetanus

A

where action potentials arrive so frequently that the fibre does not relax at all between contractions- there is insufficient time for the SR to reaccumulate Ca2+, so intracellular Ca2+ remains high
(only in maximal contractions like lifting the heaviest weight possible for a single repetition)

42
Q

components of skeletal muscle fibre

A

mitochondria, myofibril, myosin, sarcolemma, sarcomere, sarcoplasm, sarcoplasmic reticulum, t-tubule

43
Q

events of the neuromuscular junction in the order that they occur

A

1) action potential released into the synaptic cleft
2)Ach binds to nicotinic receptors on the sarcolemma
3)depolarisation of sarcolemma
4)Ca2+ ion channels open
5)concentration of intracellular Ca2+ increases 6)Muscle contraction

44
Q

anatomy of muscle- belly

A

the thick central part of muscle that tapers at each end where it is referred to as a head.
at the head the connective tissues surrounding each muscle fibre and groups of muscle fibres become continuous with the dense fibrous connective tissue of the tendon attaching the muscle to the bone. a muscle can have more than one belly inserting at the same point

45
Q

anatomy of muscle- origin

A

the end of the muscle that serves as an anchor for the movement, it does not move when the muscle contracts

46
Q

anatomy of muscle-insertion

A

the end of the muscle that moves a body part. the contraction of muscle pulls the insertion towards the origin.

47
Q

aponeurosis muscles

A

muscle that takes the form of a flat sheet. the tendon is also drawn out into a flat sheet of connective tissue

48
Q

sphincter muscles

A

circular muscles around an orifice, which serves to control the entrance or exit to a structure

49
Q

sesamoid bones

A

small, smooth bones embedded within the tendon or located near joints where tendons pass over bony prominences. protect tendons, enhance mechanical advantage, and reduce friction for tendons

50
Q

bursa

A

fluid filled cushions at sites where the tendon may be at particular risk

51
Q

walls and fluid of the bursae and tendon sheaths

A

resembles similar components of synovial joints. when the tendon moves it is lubricated synovial layers that rub together

51
Q

tendon sheaths

A

if a large part of the tendon is at potential risk from pressure or friction, the fluid-filled cushion wraps around the tendon to enclose it in a tendon sheath

52
Q

muscles of facial expression

A

move the lips, cheeks, nostrils, eyelids, and external ears. they attach to skin or other muscles rather than bone

53
Q

Muscles of mastication

A

the main muscles responsible for chewing
-digastricus
-masseter
-temporalis
-medial and later pterygoids (deep muscles that lie medial to the mandible)

54
Q

muscles of the eye

A

responsible for moving the eye within its bony socket
-dorsal rectus, ventral rectus, lateral rectus, medial rectus: all insert on the sclera (white part of the eye) at the place matching their name
-dorsal oblique and ventral oblique: positioned as their names describe and they act to rotate the eye around its visual axis
-retractor bulbi: forms a cone around the nerve entering the back of the eye, its action is to pull the eye deeper into the socket

55
Q

other muscles of the head

A

-muscle of the tongue
-muscles found in the pharynx, larynx, and soft palate
-extrinsic muscles that attach the head and to the neck and move it in relation to the neck

56
Q

brachiocephalicus

A

a large straplike muscle that runs from the proximal region of the forelimb up to the base of the skull-when on the ground flexes the neck laterally, when non weight bering it draws the forelimb forward (protracts the forelimb)

57
Q

sternocephalicus

A

a smaller, straplike muscle that extends from the sternum to the base of the skull and acts to flex or lower the head and neck

58
Q

Cutaneous muscles

A

thin, broad, superficial muscles that tense and twitch the skin

59
Q

Trapezius

A

a triangular sheet of muscle that originates from the dorsal midline and inserts on the spine of the scapula- draws the leg forward

60
Q

pectoral muscles

A

run from the rib and sternum and insert on the humerus- adduct the limb and hold it against the body wall

61
Q

latissimus dorsi

A

large, fan-shaped muscle that originates on the thoracic spine and inserts on the humerus -retracts the forelimb

62
Q

extrinsic muscles of the forelimb

A

attach the forelimb to the trunk and move the limb relative to the body
-trapezius
-pectoral muscles
-latissimus dorsi
-brachiocephalicus

63
Q

intrinsic muscles of the forelimb

A

originate and insert on the forelimb. they act on the joints of the limb, but don’t move the limb relative to the body

64
Q

triceps brachii

A

has four heads with separate origins. three heads originate from the proximal humerus and the fourth from the scapula. they all insert on the olecranon of the ulna- extends the elbow joint

65
Q

biceps brachii

A

originates from the scapula and inserts on the radius and ulna -flexes the elbow joint

66
Q

two carpal extensors

A

originate from the humerus and insert on the carpal bones, running in front of the lower limb and foot

67
Q

two digital extensors

A

originate from the humerus and insert on the third phalanx, running in front of the lower limb and foot

68
Q

two carpal flexors

A

run behind the carpus and foot

69
Q

two digital flexors

A

-superficial digital flexor insert on the second phalanx
-deep digital flexor inserts on the third phalanx

70
Q

intrinsic muscles of the hindlimb

A

all insert on the hindlimb itself or on the pelvic girdle

71
Q

Iliopsoas muscle

A

originates from the lumbar spine and inserts on the femur- flexes the hip joint

72
Q

gluteals

A

forms the curve of the rump- extends the hip joint and abduct the thigh

73
Q

hamstrings

A

forming the caudal aspect of the thigh- extends the hip, flexes the stifle, and extends the hock

74
Q

biceps femoris

A

the most lateral muscle of the hamstring group, runs over the femur to the tibia and inserting on the calcaneus of the hock

75
Q

semitendinosus

A

in the hanmstring group. muscle that runs from the pelvis and inserts on the tibia and calcaneus-extends the hip, flexes the stifle and extends the hock

76
Q

semimembranosus

A

in the hamstring group, most medial muscle of the group, running from the pelvis to the femur and tibia- extends the hip and flexes the stifle

77
Q

quadriceps

A

forming the cranial aspect of the thigh

78
Q

quadriceps femoris

A

large muscle running down the cranial aspect of the thigh, consisting of four parts, all insert on the tibial tuberosity or crest. the tendon of this muscle contains the patella, which articulate with the femur at the stifle joint -extends the stifle joint

79
Q

adductor muscles

A

forming the medial aspect of the thigh

80
Q

pectineus

A

adductor muscle that runs from the pubis to the distal femur-adducts the limb

81
Q

gastrocnemius

A

originates from the caudodistal femur ad inserts on the calcaneus of the tarsus- extends the hock and flexes the stifle

82
Q

tibialis cranialis

A

originates from the tibia and inserts onto the tarsal bones- flexes the hock and rotates the paw medially

83
Q

three digital extensors

A

run cranially- extends the digits

84
Q

superficial digital flexor of the hind limb

A

runs from the femur to the phalanges and is one of the components of the common calcaneal tendon- extends the tarsus and flexes the digits

85
Q

deep digital flexor

A

inserts on the distal phalanges- extends the tarsus and flexes the digits

86
Q
A

Anatomy (11 decks)

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