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Organ Systems Anatomy and Physiology > Skeletal Muscle > Flashcards

Skeletal Muscle Flashcards

1
Q

3 types of muscles

A

Skeletal, cardiac, smooth

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2
Q

Skeletal Muscle

A

Striated muscle that generates force;
Contracts only when stimulated
Innervated by SOMATIC MOTOR NEURONS

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3
Q

Cardiac Muscle

A

Striated; generates force
Contracts rhythmically
Innervated by AUTONOMIC NERVOUS SYSTEM

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4
Q

Smooth Muscle

A

NON-STRIATED: Used for pressure loads
Maintains Organ Dimensions & Functions
Contracts continuously
Innervated by AUTONOMIC NERVOUS SYSTEM

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5
Q

Endomysium

A

Connective tissue (?) Surrounds individual muscle fibers

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6
Q

Perimysium

A

Connective tissue (?) that surrounds muscle fascicles

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7
Q

Muscle fascicle

A

Functionally discrete bundles of muscle fibers (cells)

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8
Q

Epimysium

A

Surrounds whole muscle (made up of groups of fascicles)

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9
Q

How do nerves and blood vessels interact with muscle fibers

A

Through Connective tissue

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10
Q

Describe a muscle fiber…general overview.

A

Single, multi nucleated cell. Has organelles and contractile structures.

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11
Q

How are muscle cells made in terms of embryology?

1st step

A

Myogenic precursor cells in somites generate myoblasts and satellite cells

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12
Q

What do myoblasts do embyrologically?

A

Several myoblasts fuse to form single muscle fiber

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13
Q

What are satellite cells and what do they do?

Include pre and post natal

A

Stem like cells that survive into adulthood.
Prenatally: divide and fuse with muscle fiber to ensure adequate number of nuclei.
Postnatally: they can replace damaged muscle fibers.

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14
Q

Sarcolemma

A

cell membrane around a single muscle fiber

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15
Q

T-tubules

A

Infoldings of sarcolemma

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16
Q

Sarcoplasmic reticulum

A

Stores and releases Ca ion (2+)…equivalent to endoplasmic reticulum

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17
Q

Regions and function of Sarcoplasmic reticulum

A

Sarcotubules: store Ca 2+ bound to calsequestrin

Terminal cisternae: contact T-tubules

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18
Q

Triads: T-tubule and 2 terminal cisternae

Function?

A

Where action potentials trigger release of Ca 2+ from terminal SR

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19
Q

Myofibrils

A

Organelles of contractile myofilaments segmented into sarcomeres.

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20
Q

What is the structure/ shape of a myofibril?

A

Cylinders that extend the length of the muscle.

Chain of fused Sarcomeres

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21
Q

Sarcomere: shape and structure

A

Cytoskeletally distinct unit containing thick and thin myofilaments: INCLUDING ACTIN and MYOSIN

Joined to each other by Z-lines

Surrounded by SR

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22
Q

What makes a muscle striated”?”

A

Z lines connecting sarcomeres are aligned with each other.

Regularity of sarcomere structures form striations

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23
Q

Titin (connectin) and Nebulin structure and function

A

Together make flexible filamentous network thatsurrounds myofibrils:

Titin: elastic component in muscle that can stretch under tension

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24
Q

Components of Myofilaments

A

THIN: Actin; Tropomyosin; Troponin

THICK: Myosin

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25
Q

Actin

A

Globular protein (G-actin) polymerized into doubled strands (F-actin)

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26
Q

Tropmyosin

A

Covers myosin binding sites

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27
Q

Troponin

A

Regulatory protein bound to tropomyosin

Activated by Ca 2+

28
Q

Myosin structure

A

Tails form tick portion of myofibril

Head and neck form cross bridges that bind to actin

29
Q

How is a sarcomere defined structurally?

this may be poorly worded…think letters

A

Z lines align with each other vertically to form edges

I bands are found on each side of Z band

A bands are found on each side of I band

H zone found in between A bands

M line is in middle of H zone…center of sarcomere

End to end: Z-I-A-H-M-H-A-I-Z

30
Q

What is a motor neuron?

A

Cell body in ventral horn that projects its axon out through ventral root to muscle

Contrasts with 2 cell system for sympathetic system (don’t know what this means so didn’t write a good question for it)

31
Q

What is Neuromuscular Junction?

A

Synapse formed by motor neuron on skeletal muscle

32
Q

How is the Neuromuscular junction formed?

A

Motor neuron axons branch and synapse onto muscle end plates

33
Q

What lines the Junctional folds on a muscle cell?

A

Ach receptors

34
Q

How do the motor neurons communicate with muscle cells?

A

They release Ach onto neuromuscular junctions

35
Q

How does Ach facilitate an action potential?

A

Increases permeability of Na+/K+ channel creating an End Plate Potential

36
Q

What kind of receptors are Ach receptors?

What can block them?

A

Ionotropic nicotine receptors

Botullinum toxin (Botox)

37
Q

What is an end Plate Potential (EPP)

A

Large depolarization similar to an EPSP except greater in amplitude.

Has sufficient amplitude to exceed threshold for action potential initiation

38
Q

How many axon action potentials are needed to initiate a muscle action potential?

A

One (not sure if you can have more than one at times as well)

39
Q

How is Muscle action potential generated?

A

End Plate Potentials depolarize neighboring voltage gated Na+ channels that generate muscle action potential

40
Q

What enzyme breaks down Ach and where is it?

A

acetylcholinesterase…lining of skeletal muscle cell surface

41
Q

what does esterase do?

A

Enhances Neuromuscular junction activity thus enhancing muscle contraction

42
Q

What ion begins muscle excitation?

Where does it come from?

A

Ca 2+ is released from sarcoplasmic reticulum

43
Q

After Ca 2+ is released from SR what happens next?

First couple of steps…

A

Action potential spreads along T tubule….current activates dihydropyridine (DHP) receptors.

44
Q

what is a dihydropyridine (DHP) receptor and what does it do?

Does it work the same in cardiac receptors?

A

L type voltage gated Ca 2+ channel.

When activated, doesn’t allow Ca 2+ flux into cell. Sends voltage to Ryanodine(RCR) receptor.

No…it does permit Ca 2+ into cardiac cells

45
Q

what is a ryanodine receptor (RCR)?

Where is it and what does it do?

A

RCR is attached to the DHP in muscle cell.

It absorbs voltage of action potential directed from T-tubule through DHP.

Releases Ca 2+ from the SR terminal cisternae upon voltage activation

46
Q

Describe Ca 2+ pathway that initiates contraction.

When does it happen in terms of Action Potential?

A

Ca ++ released from terminal cisternae of SR

Ca++ binds to troponin to initiate contraction.

Happens DURING an action potential

47
Q

Describe Ca++ pathway during relaxtion.

When does it happen in terms of Action Potential?

A

Ca++ sequestered into longitudinal sarcotubules of the SR via Ca-ATPase

Ca++ then translocated back to terminal cisernae for subsequent release.

48
Q

What are the two primary cofactors that facilitate contraction?

How?

A

Permission:

  • Ca++ released from SR & binds to troponin.
  • Troponin alters tropomysosin to expose actins binding sites for myosin

Motivation:

  • ATP binds to myosin head & hydrolyzes to ADP and P
  • ADP & P enable myosin head to bind to actin
49
Q

Sliding filament mechanism and contraction:

what are the 4 stages

A
  1. Crossbridge attachment
  2. Working stroke
  3. Detachment
  4. ATP hydrolysis
50
Q

Describe the process fully

A

you are a superstar…tell a friend about how their muscles work :)

Seriously, you got this!

51
Q

What conditions are required for actin to bind to myosin?

A

Ca++ needs to be present.

Actin’s binding site is exposed when tropomyosin is altered by Ca++ bound troponin.

52
Q

What events trigger bending of myosin head?

A

Myosin head bound to ATP. ATP hydolzes into ADP and inorganic P cocking myosin head.

53
Q

What conditions are necessary for muscle to relax?

What is meant by rigor?

A

Ca++ need to return to SR

Rigor is the point at which the myosin head is most tightly bound to the actin after inorganic phosphate is released from myosin.

54
Q

What causes myosin head to restore to its initial position?

A

ADP is released from head causing stroke” part of contraction. Then ATP binds to myosin head causing release from actin.”

55
Q

Discuss difference of 2 headed myosin

Type II vs Type V

Where is each one?

A

Type II: Skeletal muscle- heads bind individually. 2nd head orients and stabilizes structure of motion generating head…generates maximum displacement.

Type V: intracellular organelles- two heads walk along microtubules- think vesicle toting cartoon.

56
Q

What happens during sarcomere contraction?

What is moving and where?

A

net effect of two actin molecules (Z lines) moving toward center of sarcomere…shortens sarcomere.

During continued contraction, come together eventually overlapping.

57
Q

Can contraction occur without any overlapping of actin and myosin?

A

NO!

58
Q

Range of contraction positions?

A

Overextened to severe overlapping

59
Q

The sum of what 2 tensions equal total muscle tension?

A

active and passive

60
Q

Passive tension

A

resistance of CT in muscle tissue (elastic titin fibers)

61
Q

Active tension (isometric)

A

proportional

62
Q

Motor Unit

A

Group of muscle fibers innervated by branches of a single motor neuron

63
Q

Small Motor Units vs. Large Motor Units

A

Small Motor Units adapted for fine and precise motor control…small motor neurons

Large Motor Units: adapted for great force…large motor neurons

64
Q

Twitch

  1. What is it?
  2. How is its duration determined?
  3. Twitches can be summed to generate…?
A
  1. Twitch is a movement of a single motor unit caused by a single action potential
  2. Duration determined by level of myoplasmic Ca++
  3. Tetanus
65
Q

What is spasm (cramp) and how is it generated?

A

Sudden, involuntary contraction generated by continuous CNS activity or muscle dysfunction

Many causes

Organ Systems Anatomy and Physiology (6 decks)

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