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BIOL235 Anatomy & Physiology > Chapter 10: Muscular Tissue > Flashcards

Chapter 10: Muscular Tissue Flashcards

1
Q

What does skeletel muscle do?

A

Move bones or the skeleton mostly. But some attach to and move the skin or other skeletal muscles. It’s striated (alternating light and dark bands) and voluntary. Although most skeletal muscles are controlled subconsciously to some extent.

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2
Q

What is the cardiac muscle?

A

Most of heart wall. Striated but involuntary. Regulated by neurons in the autonomic nervous system and by hormones

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3
Q

What is autorhythmicity?

A

Built in rhythm.

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4
Q

What is smooth muscle tissue?

A

Located in walls of hollow internal structures (blood vessels, airways, and most organs in abdominopelvic cavity) and also skin attached to hair follicles. Non striated, involuntary, some smooth muscle (like one that propel food through GI tract) has autorhythmicity. Regulated by. Neurons part of autonomic nervous system (involuntary) and hormones secreted by endocrine glands

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5
Q

What are the 4 functions of muscular tissue?

A

1) Producing body movements
2) Stabalizing body positions
3) Storing and moving substances in body
4) Generating heat

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6
Q

Muscular tissue contributes to homeostasis. What is electrical excitability?

A

Ability to respond to certain stimuli by prducing electrical signals called ACTION POTENTIALS

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7
Q

What are action potentials and what are the types?

A

Muscle action potentials. Two types: Autorhythmatic electrical signals arising within muscular tissue (like heart’s pacemaker), and chemical stimuli (like nrutransmitters released by hormones, hormones distributed by blood, local changes in pH etc)

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8
Q

Muscle tissue contributes to homeostasis. What is contractibility?

A

Ability of muscular tissue to contract forcebly when stimulated by action potentials. When a skeleton muscle contracts it generates tension while pulling on attachment proteins. Sometimes muscle shortens (like when the tension generated is great enough to overcome the load of the object being moved) and other times it doesn’t shorten (like holding a book in an outstretched hand)

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9
Q

Muscular tissue contributes to homeostasis. What is extensibility?

A

Ability of muscular tissue to stretch without being damaged. Connective tissue within the muscle limits the range of extensibility. Smooth muscle is subject to most stretching like each time the stomach fills with food or when cardiac muscle fills with blood.

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10
Q

Muscular tissue contributes to homeostasis. What is elasticity?

A

Ability of muscular tissue to return to its original length and shape after certain contraction/extension

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11
Q

What are muscle fibres?

A

Cells with elongated shapes

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12
Q

What does connective tissue do?

A

Surrounds and protects muscular tissue.

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13
Q

What is subcutaneous layer of connective tissue?

A

Aka hypodermis. Separates muscle from skin and is composed of areolar connecive tissue and adipose connective tissue. Provides a path for nerves, blood vessels and lymphatic vessels to enter and exit muscles

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14
Q

What is fascia or connective tissue?

A

A dense sheet and broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscle and other organs. Holds muscles with similar functions together, allows free movement of muscles, carries nerves, blood vessels and lyphatic vessels and fills spaces between muscles

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15
Q

3 layers of connective tissue extend form the fascia to protect and strengthen skeletal muscle. What are they?

A

1) Epimysium: Outer layer encircling entire muscles. Dense irregular connective tissue
2) Perimysium: Dense irregular connective tissue. Surrounds groups of 10-100 or more muscle fibres. Separates them into bundles called fascicles. If you t ear a iece of meat it tears along its fascicles
3) Endomysium: Penetrates interior of each fascicle and separates individual muscle fibres. Mostly reticular fibres

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16
Q

What is a tendon’?

A

All 3 connective tissue layers may extend beyond muscle fibres to form a rope-like tendon that attaches a muscle to the periosteum of a bone (ie calcaneal tendon of the gastrocnemius (calf) muscle

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17
Q

What is the aponeurosis of connective tissue?

A

When connective tissue elements extend as a broad, flat sheet it’s called aponeurosis (ie epicranial aponeurosis on top of the skull between the frontal and occipital bellies of the occipitofrontalis muscle)

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18
Q

What are somatic motor neurons?

A

The neurons that stimulate muscles to contract. A threadlike axon that extends from the brain or spinal cord to a group of skeletal fibres

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19
Q

What do capillaries do in muscular tissue?

A

Plentiful in muscular tissue. Brings in O2 and nutrients and removes heat and waste products of muscle metabolism. Muscle fibres use and synthesize lots of ATP

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20
Q

What is sarcolemma?

A

Plasma membrane of a muscle cell.

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21
Q

What is Transverse (T) tubules?

A

Thousands of tiny invaginations of the sarcolemma called TRANSVERSE (T) TUBULES, tunnel in from the surface toward the centre f each muscle fibre. Open to outside of fibre, filled with interstitial fluid, muscle action potentials travel along the sarcolemma and through the tubules.

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22
Q

What’s the sarcoplasm?

A

Within the sarcolemma. It is the cytoplasm of muscle fibre. Has lots of glycogen and glycogen can be used for synthesis of ATP. Has red coloured protein called MYOGLOBIN which binds O2 molecules that diffuse into muscle fibres from interstitial fluid. Releases O2 when it’s needed by mitochondria for ATP production

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23
Q

What are myofibrils?

A

Little threads in sarcoplasm. Contractile organelles of skeletal muscle. Extends entire length of muscle fibre. Why skeletal muscle fibre appear striped.

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24
Q

What is the sarcoplasmic reticulum (SR)>

A

Fluid filled system of membranous sacs. Encircles each myofibril. Stores calcium ions (Ca2++). Dilated end sacs of SR called the TERMIONAL CISTERNS. A transverse tubule and the 2 terminal cisterns on either side form a TRIAD. Release of CA 2++ from terminal cisterns of SR triggers muscle contractions

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25
Q

WHat are filaments and what are the two types?

A

Small protein structures within myofibrils. There are thin filaments mainly composed of actin and thick filaments mainly composed of myosin

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26
Q

What are sacromeres?

A

Basic functional units of a myofibril. Compartments

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27
Q

What are z discs?

A

Separate one sacromere from another

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28
Q

What is the M line of the sacromere?

A

Supporting protein that holds the thick filaments together at the centre of the H zone (middle of sacromere)

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29
Q

Myofibrils are built from 3 kinds of proteins. What are these 3 kinds?

A

1) Contractile proteins which generate force during contraction
2) Regulatory proteins which help switch contraction process on/off
3) Structural proteins that keep the thick and thin filaments in proper alignment, give the myofibril elasticity and extensibility, and link myofibrils to the sarcolemma and ECM

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30
Q

What are the 2 contractile proteins?

A

1) Myosin: Main component of thick filament and acts as motor protein (pulls various cell structures to achieve movement by converting chemical energy in ATP to the mechanical energy of motion).
2) Actin: Component of thin filaments that are anchored to Z discs. Individual actin molecules join to form a helix that’s twisted. On each actin is a myosin binding site where the myosin head can attach

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31
Q

What is tropomyosin and troponin?

A

Part of the thin filament. In relaxed muscle myosin is blocked from binding to actin because strands of tropomyosin cover the myosin binding sites. Tropomyosin strands are held in place by troponin molecules

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32
Q

What is titin?

A

The 3rd most pletiful protein in skeletal muscle. Huge size spanning half of sacromere (connects a z disc to M line of sacromere). So therefore helps stabalize the position of the thick filament. Very elastic so accounts for most elasticity and extensibility of myofibrils.

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33
Q

What is the sliding filament mechanism?

A

Skeletal muscle shortens during contraction because the thick and thin filaments slide past one another. Thin filaments slide inward and meet at centre of sacromere. As thin filament slides inward the I band and H zone narrow and eventually disappear when muscle is maximally contracted. When thin filament slides inward the Z discs come closer together and the sarcomere shortens which leads to shortening of whole muscle fibre which leads to shortening of entire muscle

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34
Q

When are the steps of the contraction cycle?

A

At the onset of contraction, the SR releases calcium ions into the sarcoplasm where they bind to troponin. Troponin moves tropomyosin away from myosin binding sites on actin. Once binding sites are free contraction cycle can begin. 4 steps:

1) ATP Hydrolosys: Hydrolosys reaction reorients and energizes the myosin head. The products of ATP hydrolysis (ADP and a phosphate group) are still attached to the myosin head
2) Attachment of myosin to actin to form cross-bridges
3) Power Stroke: The site on the cross bridge where ADP is bound opens and the cross bridge rotates and releases ADP. The cross bridge geenrates force as it rotates towards the centre of the sarcomere, sliding thin filament past the thick filament toward the M line
4) Detachment of myosin from actin: When another molecule of ATP binds to the ATP binding site on the myosin head then the myosin head detaches from actin

35
Q

What is the excitation-contraction coupling?

A

The steps that connect excitation (a muscle action potential propogating along the sarcolemma and into the T tubules) to contraction (sliding of filaments)

36
Q

What is the Ca2+ active transport pumps?

A

Contained in the SR. Uses ATP to move Ca2+ constantly from the sarcoplasm into the SR. Calcium ions flow into the sarcoplasm faster than they are transported back by the pumps. After the last action potential has propogated throughout the T tubules, the Ca2+ release channels close. As the pumps move Ca2+ back ito the SR, the concentration of Ca2+ ions in the sarcoplasm quickly decreases

37
Q

What is the length - tension relationship?

A

Length-tension relationship indicates how the forecefulness of muscle contraction depends on length of sarcomeres within a muscle BEFORE contraction begins. Max tension (100%) occurs when the zone of overlap between a thick and thin filament extends from the edge of the H zone to one end of a thick filament.

38
Q

What are somatic neurons?

A

Neurons that stimulate skeletal muscle fibres to contract

39
Q

WHat is the neuromuscular junction (NMJ)?

A

This is where muscle action potentials arise. The synapse between a somatic neuron and skeletal muscle fibre

40
Q

What is the synapse?

A

Region where communication occurs between 2 neurons, or a neuron and target cell (in this case between a somatic neuron and muscle fibre)

41
Q

What is the synatic cleft?

A

Separates the 2 cells

42
Q

What is a neurotransmitter?

A

Because cells don’t touch, the first cell communicates with the second by releasing a chemical messenger called a neurotransmitter

43
Q

What is the axon terminal?

A

The end of the motor neuron that divides into a cluster of SYNAPtIC END BULBS (neural part of the NMJ)

44
Q

What are synaptic vesicles?

A

Hundreds suspended in the cytosol within each synaptic end bulb. Membrane enclosed sac

45
Q

What is acetylcholine (ACh)?

A

Inside each synaptic vesicle and is the neurotransmitter released at the NMJ.

46
Q

What is the neural end plate?

A

Region of the sarcolemma opposite the synaptic end bulbs. Muscle fibre part of the NMJ

47
Q

What is the Acetylcholine receptors?

A

About 30-40 million within each motor end plate. Transmembrane proteins where ACh binds

48
Q

What are junction folds?

A

Deep grooves in the motor end plate that provides a large SA for ACh. INcludes all synaptic end bulbs on one side of synaptic cleft and motor end plate of tje muscle fibre on other side

49
Q

What are the steps in release a muscle action potential?

A

1) Release of ACh
2) Activation of ACh receptors
3) Production of muscle action potential
4) Termination of ACh activity

50
Q

What is acetylcholinesterase (AChE)?

A

Attached to collagen fibres in the ECM of synaptic cleft and breaks down ACh into acetyl and choline (products that can’t activate the ACh receptor).

51
Q

A LOT of ATP is needed to power a contraction cycle to pump Ca2+ into the SR and other metabolic reactions. What are the 3 ways that muscle fibres produce ATP?

A

1) From creatine phosphate (unique to muscle fibres)
2) By anaerobic glycolysis
3) By aerobic respiration

52
Q

What is creatine phosphate / how is it created?

A

Relaxed muscle fibres produce more ATP than is needed for resting metabolism. Most excess ATP is used to synthesize creatine phosphate. Creatine kinase (CK) catalyzes the transfer of one of the high energy phosphate groups from ATP to creatine, forming phophate and ADP. When a contraction starts and ADP levels rise, CK catalyzes the transfer of a high energy phosphate group from creatine phosphate back to ADP. This direct phophorylation reaction quickly generates new ATP molecules. Occurs rapidly so phosphate is first source of energy when muscle contraction begins

53
Q

WHat is anaerobic glycolysis?

A

When creatine phosphate is depleted, glucose is catabolized to generate ATP. Glucose passes from blood into contracting muscle fibres via facilitated diffusion but can also be produced by breakdown of glycogen within muscle fibres. Glycolysis is reactions that break down each glucose molecule into 2 molecules of pyrovic acid. Under the anaerobic conditions, the pyrovic acid generated from glycolysis is converted to LACTIC ACID –> this is called anaerobic glycolysis. Produces 2 molecules of ATP and 2 of lactic acid.

54
Q

What is aerobic respiration?

A

With O2. Pyruvic acid formed by glycolysis enters the mitochondria where it undergoes aerobic respiration. Produces ATP, CO2, water and heat. Slower than anaerobic but yields more ATP per glucose molecule (30-32).

55
Q

Muscular tissue has 2 sources of O2. What are these sources?

A

1) Oxygen that diffuses into muscle fibres from the blood and 2) O2 released by myoglobin within muscle fibres

56
Q

What is muscle fatigue?

A

Inability of a muscle to maintain force of contraction after prolonged activity

57
Q

What is central fatigue?

A

Caused by changes in central nervous system. Before muscle fatigue occurs a person may feel tired and want to stop activity (may be protective mechanism to protect from muscle damage)

58
Q

What are some factors that may possibly contribute to muscle fatigue?

A

1) Inadequate release of calcium ions from SR resulting in decline of Ca2+ in sarcoplasm
2) Depletion of creatine phosphate
3) Insufficient O2
4) Depletion of glycogen and other nutrients
5) Buildup of lactic acid and ADP
6) Failure of action potentials to release enough ACh

59
Q

What is Oxygen dept?

A

The added O2, over and above the resting oxygen consumption, that’s taken into the body after exercise.

60
Q

The extra O2 is used to pay back/restore metabolic conditions to the resting level in 3 ways:

A

1) Convert lactic acid back into glycogen stores in the liver
2) Resynthesize creatine phosphate and ATP in muscle fibres
3) Replace the O2 removed from myoglobin

61
Q

What is recovery oxygen uptake?

A

Better term than oxygen dept due to elevated use of oxygen after exercise:

1) Elevated body temp after workout increases rate of chemical reactions which use ATP faster so more O2 needed to produce ATP
2) Heart and muscles of breathing must work harder and so consumes more ATP
3) Tissue repair process occuring at increased rate

62
Q

What is a motor unit?

A

A somatic motor neuron plus all of the skeletal muscle fibres it stimulates. A single somatic motor neuron makes contact with about 150 skeletal muscle fibres and all of the muscle fibres in one motor unit contract in unison. Muscle fibres of a motor unit are dispersed through muscle rather than clustered.

63
Q

What does the strength of a muscle contraction depend on ?

A

Size of motor units and number that are activated

64
Q

What is a twitch contraction?

A

Brief contraction of all muscle fibres in a motor unit in response to a single action potential in its motor neuron

65
Q

What are the phases of a twitch contraction?

A

1) Latent phase: Delay occurs between application of stimulus and beginning of contraction. Muscle AP sweeps over the carcolemma and calcium ions are released from the SR
2) Contraction period: Calcium ions bind to troponin and cross-bridges form. Peak tension develops in the muscle fibre
3) Relaxation period: Ca2+ is actively transported back into SR, myosin binding sites are covered my tropomyosin, myosin heads detach from actin and tension in muscle fibre decreases

66
Q

What is the refractory period of a muscle contraction?

A

When a muscle fibre receives enough stimulation to contract it temporarily loses its excitability and can’t respond for a time. The period of lost excitability is called refractory period

67
Q

What is wave summation?

A

When a 2nd stimulus occurs after the refractory period of the 1st stimulus is over but before the muscle fibre has relaxed, the 2nd contraction will be stronger than the first

68
Q

What is unfused (incomplete) tetanus?

A

When a skeletal muscle fibre is stimulated at a rate of 20-30 times/second, it can only partially relax between stimulations. Sustained and wavering contraction

69
Q

What is fused (complete) tetanus?

A

When a skeletal muscle fiber is stimulated at a higher rate of 80-100 times a second it does not relax at all. Sustained contraction where individual twitches cannot be detected

70
Q

When does wave summation and both kinds of tetanus occur?

A

When additional Ca2+ is released from the SR while levels of Ca2+ in the sarcoplasm is still elevated

71
Q

What is the motor unit recruitment process?

A

It is a process where the number of active motor units increases. Usually the motor neurons of an entire muscle don’t contract in unision –> while some are contracting others are relaxed and this pattern delays fatigue and allows contraction f an entire muscle to be sustained for long periods. Weakest motor units recruites first and then progressively stronger motor neurons added if task requires more force.This recruitment is responsible for producing smooth movements rather than a series of jerks.

72
Q

What is muscle tone?

A

A small amount of tautness or tension in the muscle due to weak involuntary contractions of motor neurons

73
Q

How is muscle tone established? What is flaccid?

A

By enruons in the brain and spinal cord that excite the muscle’s motor neurons. When the motor nuerons serving the skeletal muscle are damaged or cut the muscle becomes FLACCID, which is a state of limpless where the muscle tone is lost

74
Q

How is muscle tone sustained?

A

Small groups of motor neurons are alternatively active and inactive in a constantly shifting pattern

75
Q

WHat is the function of muscle tone?

A

Muscle tone keeps skeletal muscles firm (ie., keeping our head upright).

76
Q

What are the two types of muscle contractions?

A

Isotonic and isometric

77
Q

What happens during an isotonic contraction?

A

The tension developned in the muscle remains almost constant while the muscle changes its length. Used for body movements and moving objects. 2 types Concentric and eccentric

78
Q

WHat is concentric isotonic contraction?

A

Tension is greate enough to overcome the resistance of the object being moved. The muscle shortens and pulls on another structure, like a tendon, tp produce movement and reduce angle of joint. Like picking up a book is a concentric isotonic contraction of the biceps brachii muscle in arm

79
Q

What is an eccentric isotonic contraction?

A

Like lowering or putting down a book. Tension exerted by the myosin cross-bridges resists movement of a load (ie the book) and slows the lengthening process. Repeated eccentric isotonic contraction produce more muscle damane and more delayed onset muscl soreness than concentric iso cont

80
Q

What is isometric contraction?

A

The tension generated is not enough to exceed the resistance of the objects to be moved and the muscle does not change length. Ie holding a book steady using an outstretched arm, Energy still expended. Important because maintains posture, supports objects in fixed position and stabalizes some joints that are moved

81
Q

What are the 3 types of SKELETAL muscle fibres?

A

Slow oxidase fibres, Fast oxidase-glycolytuc fibres and fast glycolytic fibres

82
Q

What are slow oxidative fibres?

A

Dark red because lots of myoglobin and blood capillaries. Large mitochondria. Generates ATP by aerobic resp. Slow contraction. Longer to reach peak tension. Resistant to fatigue and capable of prolonged sustained contractions for many hours. Function: Maintaining posture and for aerobic endurance-type activities like running a marathon

83
Q

What is fast oxidative-glycolitic fibres?

A

Largest fibres. Lots of myoglobin and blood capillaries so dark red. Generates ATP by anaerobic AND aerobic respiration and resistant to fatigue. Produces ATP (and speed of contraction) faster than SO fibres. Function: activity like walking and sprinting. Reaches peak tension here

84
Q

What are fast glycolytic fibres?

A

Low myoglobin content, few blood capillaries and few mitochondria. Appears white. ATP generated by glycolysis because lots of glycogen. FG fibres contract strongest and fast. Function: Adapted for intense anaerobic movements of short duration (ie weight lifting or throwing a ball). Fatigue quickly. Larger in a weight lifter than sedentary person

BIOL235 Anatomy & Physiology (10 decks)

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