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LQB388 > Muscle > Flashcards

Muscle Flashcards

1
Q

Three Major Function of Muscles

A
  1. movement of body
  2. movement of materials throughout the body
  3. maintenance of body temp through heat production (homeostasis)
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2
Q

Three different Types of Muscle:

A
  1. Skeletal: attaches to skeleton
  2. cardiac: heart
  3. smooth: walls of hollow structures
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3
Q

Structure of skeletal muscle fiber:

A
  • elongated cylindrical shape
  • multi-nucleated
  • 10-100 microns in diameter
  • up to 20cm long
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4
Q

What is the plasma membrane in muscle cells called

A

Sarcolemma

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5
Q

What is the cytoplasm of skeletal muscle Fibers called

A

Sarcoplasm

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6
Q

Contents of Sarcoplasm of Skeletal Muscle Fibers

A
  • high conc. glycogen for energy for contraction
  • myoglobin: high O2 levels that can be used for energy production
  • myofibrils
  • sarcoplasmic reticulum
  • T-Tubules
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7
Q

Myofibrils in Skeletal Muscle Cells:

A
  • cylindrical bundles of filaments
  • 1-2 microns
  • 80% vol of sarcoplasm
  • contain myofilaments which comprise contractile elements of muscle fibre
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8
Q

Sarcoplasmic Reticulum in Skeletal Muscle Fibers:

A
  • interconnected series of segments that surround microfibrils
  • has lateral sacs
    high conc of Ca2+ essential for muscle contraction
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9
Q

Transverse (or T-) Tubules in Skeletal Muscle Fibers:

A
  • continuous with extracellular space
  • runs across thickness of muscle fiber
  • closely associated with lateral sacs of sarcoplasmic reticulum
  • initiate muscle contraction by conducting electrical signals from sarcolemma into muscle fiber
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10
Q

What subdivision of the nervous system are motor-neurons apart of?

A

Somatic Nervous System (of the Efferent (motor) division

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11
Q

Structural Features of Motor-neurons:

A
  • nerves cells whose axons innervate skeletal muscle fiber
  • cell bodies (somata) located in brain-steam or anterior horns of spinal cord
  • large myelinated axon (rapid conduction)
  • axon branches to innervate multiple muscle fibers
  • each muscle fiber on innervated by one motor-neuron
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12
Q

Structural Features of Motor Unit:

A

a motor-neuron + muscle fiber it innervates.
unit size determine muscle function:
muscles producing large forces = large motor unit
muscles producing small forces = small motor unit

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13
Q

Structural Significance of motor-neurons having myelinated axons

A

Allows conducting electrical signals (APs) at high velocities from CNS to skeletal muscle fibers, with minimum delay

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14
Q

Structural Components of Neuromuscular Junction:

A
  • Axon Terminals

- Motor Endplate

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15
Q

Function of Neuromuscular Junction

A

Synaptic site for the transmission of action potential from nerve to the muscle

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16
Q

Axon Terminal of Neuromuscular Junction:

A
  • loose myelinsheath as they approach muscle fiber but Schwan cells maintain insulation.
  • terminals contain ACh (neurotransmitter) & mitochondria
  • membrane of terminal has large no. of voltage-gated ca2+ channels
  • terminal is separated from sarcolemma * contains enzymes (acetylcholinesterase) responsible for degradation of ACh
  • choline molecules released are transported back to terminal & reused to form ACh. choline recycling allows neuromuscular transmission of reaction potentials to continue
17
Q

Motor Endplate of Neuromuscular Junction:

A
  • is opposite axon terminal
  • highly folded to increase SA
  • large no. of nicotinic acetylcholine receptors
  • acetylcholinesterase enzyme metabolises acetylcholine
18
Q

Effect of ACh is limited by Two Mechanisms:

A
  1. diffusion of ACh from endplate

2. ACh degradation by acetylcholinesterase in cleft

19
Q

Describe the mechanism of excitation-contraction coupling

A

efers to AP produced at the end-plate which travels along through muscle fibre length in both directions causing contraction

20
Q

Muscle Fiber Contraction:

A
  • AP travels along muscle fiber -> meets T-Tubule -> flows down T-Tubule in middle of fiber
  • presence of AP in T-Tubule triggers opening of Ca2+ channels is sarcoplasmic reticulum
  • Ca2+ runs down conc gradient in sarcoplasm
  • increases sarcoplasmic Ca2+ triggers myofibrils to shorten -> contraction of whole muscle fiber
21
Q

Relaxation of Muscle Fiber:

A
  • when AP stops flowing down T-Tubule, Ca2+ is pumped out of sarcoplasm back to sarcoplasmic reticulum
  • ca2+ conc in sarcoplasmic reticulum returns to resting levels & myofibrils return to normal length - relaxation
22
Q

Structure of Thin Myofilaments:

A 
5-8nm in diameter & 1 micron long
has three constituent proteins:
1. actin
2. tropomyosin
3. troponin complex
23
Q

Myofilaments - Actin Structure:

A
  • two chain globular protein molecules twisted around each other forming double helix
  • high affinity binding site for myosin
  • forms backbone of thin myofilaments
24
Q

Myofilaments - Tropomyosin Structure:

A
  • 2 chains wrapped around actin helix. positioned on top so that myosin binding sites are blocked
25
Q

Myofilaments - Troponin Complex Structure:

A
  • 3 polypeptides with high binding affinity
  • 1st polypeptide: holds tropomyosin threads over myosin binding sits of actin
  • 2nd polypeptide: binds to actin
  • 3rd polypeptide: binds to ca2+, triggering contraction of myofibrils
26
Q

Structure of Thick Myofilaments:

A
  • 12-18nm diameter
  • 1.6 microns long
  • made up of ~200 myosin molecules
  • 1 end of myosin is made up of 2 folded protein strands
  • heads form cross-bridges each have an actin binding site and an ATPase
27
Q

Thick & Thin Myofilament Arrangement:

A
  • highly ordered
  • striated appearance
  • thick located in between thin & overlap
  • thick surrounded by 6 thin in hexagonal arrangement
28
Q

What is a Sarcomere?

A

Contractile unit of a muscle fiber.

represented by distance between Z-lines

29
Q

how the sarcomere length changes during muscle contraction and relaxation

A

changes in sarcomere reflect changes in whole myofibril

30
Q

What is Rigor Mortis

A
  • stiffness of skeletal muscles (starts 4hrs after death)
  • reaches peak after 12 hrs
  • subsides after 2-3 days
  • stiffness due to leakage of Ca2+ into sarcoplasm from extracellular fluid & sarcoplasmic reticulum
  • cells die & are unable to maintain large ion conc
  • Some of this calcium binds to troponin & displaces troponin filament. Allows binding of some cross-bridges and initiates power stroke. Results in muscle fiber shortening
  • There is no ATP available to detach the cross-bridges
    Muscle fibers remain contracted until filaments decompose after one’s death
31
Q

Isotonic Contraction of Skeletal Muscles:

A

tension of muscles remain constant as muscle shortens. Results in movement.
E.g. Length of biceps brachii muscle fibers decreases

32
Q

Isometric Contraction of Skeletal Muscles:

A

Tension of muscle increases, but no change in muscle length.
E.g. Maintenance of posture

33
Q

Motor Unit Recruitments:

A
  • weak contraction -> less motor units recruited
  • strong contraction -> more motor units recruited
  • sustained contraction -> different motor neurons recruited
  • coordinated by CNS
34
Q

Action Potential Frequency:

A

increased AP freq -> increases force generated

35
Q

Twitch Contraction:

A

smallest contractile response to a single electrical stimulus

36
Q

Tetanic Contraction

A

largest contractile response to a single electrical stimulus

37
Q

Slow Twitch (Type I) Fibers:

A
  • develop at slow rate
  • small in diameter
  • rich capillary network
  • high conc of myoglobin in sarcoplasm
  • suited to movements that require low force but sustained contractions
    e. g. distance running
38
Q

Electromyography:

A
  • recording of electrical activity in skeletal muscle during contraction
  • recorded by two electrodes on skin surface
  • connected to voltmeter & measures potential difference
    Plot: changes in potential diff over time
39
Q

electromyography in sport and clinical sciences.

A
  • used to analyse muscle dysfunction in athletes, detects inappropriate muscle activation patters, assists in establishing & assessing treatment outcomes in conditions

LQB388 (15 decks)

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