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Physiology > Muscular Basis of Skeletal Muscle Contraction > Flashcards

Muscular Basis of Skeletal Muscle Contraction Flashcards

1
Q

What are the two categories of muscles?

A

Striated and non-striated

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2
Q

What muscle types are striated?

A

Skeletal and cardiac

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3
Q

What muscle types are non-striated

A

smooth

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4
Q

Which muscles have voluntary control?

A

skeletal

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5
Q

Which muscles have involuntary control?

A

cardiac and smooth

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6
Q

Where do you find skeletal muscles

A

attached to bones

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7
Q

Where do you find smooth muscles

A

in hollow organs

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8
Q

Where do you find cardiac muscle?

A

walls of the heart

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9
Q

Describe the gross anatomy of a skeletal muscle?

A
  • made up of bundles of elongated, multinucleated cells
  • separated into bundles by fasciculi by a connective sheath
  • surrounded by a connective tissue sheath
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10
Q

What is the perimysium?

A

a connective sheath that separtes muscle fibers into bundles called fasciculi

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11
Q

What is the epimysium?

A

A connective tissue sheath that surround fasciculi

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12
Q

Describe the microscopic anatomy of a skeletal muscle

A
  • there is a membrane surrounding each fiber
  • each muscle fiber is made up of hundreds to thousands of myofibrils
  • the sarcoplasm lies between the myofibril
  • the endoplasmic reticulum of skeletal muscle fibers is elaborate and highly specialized
  • have alternating light bands (I bands) and dark bands (A bands).
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13
Q

What is the sarcolemma?

A

The membrane surrounding each muscle fiber in a skeletal muscle

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14
Q

What is the sarcoplasm?

A

A skeletal muscle’s cytoplasm

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15
Q

What is the sarcoplasmic reticulum

A

the Endoplasmic reticulum of skeletal muscle fibers

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16
Q

What are I Bands? What else are they called?

A

I bands are regions of thin filaments that are not overlapped with thick filaments.

Aka. Light bands

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17
Q

What are A bands? What are they called?

A

A bands represent thick filaments.

Aka. Dark bands

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18
Q

What is the Z line?

A

it’s a dark line that bisects the I band and divides the myofibril into repeating units. Thin filaments are attached to Z line.

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19
Q

What is a sarcomere?

A

A contractile units composed of thick and thin filaments

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20
Q

What is at the center of the A band?

A

The H Band

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21
Q

What is the H-band?

A

contains only thick filaments and represents the distance between the ends of the thin filaments.

22
Q

What bisects the H band?

A

the M line

23
Q

What is the M line?

A

a dark band of protein that links adjacent thick filaments to one another and maintains their alignment.

24
Q

What makes up thin filaments?

A

Actin, Tropomyosin and troponin

25
Q

What makes up actin?

A

globular proteins (Gactin) that polymerize into a filamentous double stranded helix (F actin)

26
Q

What makes up tropomyosin?

A

Thin filamentous protein that lies along the actin molecule an d prevents interaction of actin with myosin

27
Q

What is troponin?

A

A small molecule that acts as a regulatory protein

28
Q

What makes up thick filaments?

A

Myosin

29
Q

What is the structure of myosin?

A

Two strands which at one end are twisted around each other to form a long tail and at the other form globular heads

30
Q

What forms the thick filaments?

A

the aggregation of the tail regions of many myosin molecules

31
Q

What make up crossbridges?

A

the head regions of myosin that stick out away form the tails on the flexible extension of the myosin molecule

32
Q

What other proteins are associated with the myofilaments?

A

Nebulin and titin

33
Q

What is the form and function of nebulin

A

Form: stretches from the Z line to the end of each thin filament

Function: Regulates the precise length of each thin filament

34
Q

What is the form and function of titin?

A

Form: Spring-like protein connecting the Z line to the center of each thick filament

Function:

  • Maintains the organization and alignment of thick filaments
  • Responsisble for passive elastic properties of muscle and allows muscle to recover after being stretched
  • Also serves as mechanoreceptors which participates in mechanical activity-dependent gene regulation and protein degradation
35
Q

What disorder are defects in titin associated with?

A

muscular dystrophy

36
Q

Myosin crossbridges contain what? that acts as what?

A

an ATP binding site that also act as an ATPase

37
Q

How is chemical energy transduced into mechanical energy via the interaction of actin and myosin and the splitting of ATP?

A
  1. Calcium binds to troponin producing a conformational change which results in the rotation of the tropomyosin molecule, which unveils myosin binding sites on the actin
  2. myosin, which in the resting state is assocated with ADP+P_i, has a high affinity for actin and binds to the actin
  3. The release of P_I from myosin begins the power stroke and the crossbridge rotates fro 90 degrees to 45 degrees causing the sarcomere to shorten. ADP is released at the end of the power stroke.
  4. The ADP-free myosin complex remains bound to actin, until another ATP binds to myosin. The binding of ATP reduces the affinity of the myosin for actin.
  5. Actin and myosin separate and the bound ATP is hydrolyzed
  6. energy from the hydrolysis is used to re-cock the crossbridge from 45 degrees to 90 degrees and the crosbridge ragins its high affinity for actin
  7. Cycle continues until sarcoplasmit Ca2+ levels return to normal
38
Q

What is the attached state in the sliding filament theory?

A

When ADP-free myosin complex remains bound to actin until another ATP binds to myosin

39
Q

What happens to cause rigor?

A

If muscle becomes depleted of ATP, causing myosin to stay in “attached state”

40
Q

What are the two types of contraction?

A

Isometric and isotonic

41
Q

What is an isometric contraction?

A

Contraction at a constant length (no shortening)

42
Q

What is an isotonic contraction?

A

Contraction at a constant load (w/ shortening)

43
Q

True or False: In almost all situations, contractions have both an isometric and isotonic component?

A

True

44
Q

True or False: The heavier the load, the shorter the isometric portion of the contraction?

A

False

45
Q

The force produced by a contraction is dependent to what? is proportional to what?

A

Dependent on the length of the muscle.

Proportional to the amount of overlap of thick and thin filaments in the sarcomeres

46
Q

What does the force needed to stretch a relaxed muscle an indication of?

A

The elastic properties of the connective tissue in the muscle and titin

47
Q

What happens as thick and thin filaments overlap? Describe the progression of force from no overlap of thick and thin to maximum overlap of thick and thin to thin overlap.

A

With no overlap, there is no force. WIth maximum overlap without thin filaments contacting one other, there is maximum force. When thin filaments overlap, force is decreased.

48
Q

What is the relationship between length-tension curve and isotonic contractions?

A

During isotonic contractions, muscle length is changing. The Length tension curve describes the maximum shortening that a contracting muscle can undergo based on the load that it is bearing and the length at which the muscle begins to shorten. If the muscle begins contracting at the same length, it will shortening further bearing a light load than it will bearing a heavier load. If the muscle begins shortening from a reduced length, the amount of shortening will be decreased for the same load

49
Q

Describe the force-velocity curve

A

The relative velocity of a contraction decreases with increased load.

50
Q

The (heavier/lighter) the load, the slower the velocity of contraction

A

heavier

51
Q

When is maximum velocity achieved for a contraction?

A

at zero load (no weight)

52
Q

What does Maximum velocity correspond to?

A

Maximal cross-bridge cycling rate and is determined by the ATPase activity of the myosin present

Physiology (9 decks)

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