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Principles of Human Structure & Function > Week 10 Muscle Contraction II > Flashcards

Week 10 Muscle Contraction II Flashcards

1
Q

what is a motor unit

A

the motor neuron and all muscle fibers it supplies

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2
Q

What are the three phases of muscle twitch

A

latent period, period of contraction, period of relaxation

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3
Q

what is the latent period

A

events of excitation-contraction coupling; no muscle tension

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4
Q

what is the period of contraction

A

cross-bridge formation; tension increases

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5
Q

what is the period of relaxation?

A

Ca2+ re-enters into the sarcoplasmic reticulum; tension declines to zero

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6
Q

what is a muscle twitch

A

is a response of a motor unit to a single action potential of its motor neuron

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7
Q

what is a graded muscle response

A

skeletal muscle can alter the strength of contraction for different demands by changing the frequency or strength of stimulation.

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8
Q

what is graded muscle response 2

A

Changing the stimulus strength by increasing nerve stimulus to activate more motor units

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9
Q

what is graded muscle response by size principle

A
  1. muscle fibers with smallest muscle fibers recruited first
  2. motor units with larger muscle fibers are recruited as intensity increase
  3. largest motor units activated for most powerful contractions (50 x contractile force of smaller fibers)
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10
Q

what is an example of graded muscle response by size

A

the same arm can lightly pick up a pen but deliver a mighty punch to a boxing bag

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11
Q

can motor units be recruited simultaneously

A

yes. e.g., weightlifting

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12
Q

What are isotonic contractions

A

muscle changes in length and moves the load

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13
Q

What does the isotonic contraction concentric mean?

A

that the muscle is shorted

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14
Q

what does the isotonic contraction eccentric mean

A

that the muscle is lengthened

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15
Q

what are isometric contractions

A

Tension increases to muscle’s capacity, but muscle neither shortens nor lengthens

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16
Q

what are the types of muscle fibers

A

speed of contraction and major pathway for ATP generation

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17
Q

What is slow speed contraction

A

myosin ATPases hydrolyze ATP slowly

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18
Q

what is fast speed contraction

A

myosin ATPase hydrolyse ATP fast

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19
Q

what is oxidative

A

use aerobic pathways for making ATP

20
Q

what is glycolytic

A

use mainly anaerobic pathways

21
Q

what are slow oxidative fibers

A

contract slowly
require oxygen
fatigue resistant
endurance activities

22
Q

what are fast oxidative fibers

A

contract quickly
require oxygen
fatigue slowly
intermediate activities walking running

23
Q

what are fast glycolytic fibers

A

contract quickly
don’t require oxygen
fatigue quickly
short term, intense movements

24
Q

are all fibers in one motor unit the same

A

yes

25
Q

what is muscle fatigue

A

physiological inability to contract

26
Q

what causes muscle fatigue

A
  1. Ionic imbalance
  2. Increased inorganic phosphate
  3. A potential relative deficit in ATP as muscles use up their stores
  4. Decrease glycogen
  5. interference in calcium regulation and release
27
Q

what is interference in calcium regulation and release?

A

Potassium is lost from the muscle cells as action potentials keep firing. This causes K+ accumulation in the T-tubules, disturbing the membrane potential of the muscle and halts Ca2+ release from the sarcoplasmic reticulum.

28
Q

what is oxygen debt

A
  • occurs during anaerobic activity

- extra O2 is needed to replenish glycogen, creatine phosphate stores and to convert lactic acid to pyruvate

29
Q

what are the smooth muscle organs

A

blood vessels, gastrointestinal & urinary tract, respiratory tract, and reproductive system

30
Q

what is the function of blood vessels

A

regulate blood flow and pressure and regulate filtration in kidneys

31
Q

what is the function of the gastrointestinal and urinary tracts

A

regulate movement along internal passages

32
Q

what is the function of the respiratory tract

A

alters diameter of airways

33
Q

what is the function of the reproductive system

A

movement of sperm , oocytes, and delivery of fetus

34
Q

What is the structure of smooth muscle

A 
small spindle-shaped cells
single central nucleus 
no striations 
smaller than skeletal muscle cells 
less developed sarcoplasmic reticulum 
no sarcomeres, myofibrils, or T tubules
the plasma membrane has alveoli which allow rapid entry of Ca2+ from the extracellular fluid
35
Q

what are the layers in smooth muscle

A

Circular muscle layer

Longitudinal muscle layer

36
Q

what is a circular muscle

A
  • cells run circumferentially around an organ

- contractions reduce diameter if lumen of organ

37
Q

what is longitudinal muscle

A
  • cells run in the longitudinal axis of an organ

- contractions reduce the length of the organ

38
Q

what is the nerve supply of smooth muscle

A
  • no neuromuscular junctions
  • innervated by autonomic NS
  • axons of nerves innervating
    smooth muscle have swellings
    (varicosities) that contain
    neurotransmitters
39
Q

what are the mechanisms of contraction for smooth muscle

A
  1. Ca2+ (mainly from ECF) binds to and activates calmodulin
  2. Activated calmodulin activates myosin (light chain) kinase (MLCK)
  3. MLCK phosphorylates and activates myosin
  4. Cross bridges interact with actin
  5. When intracellular Ca2+ levels drop - relaxation
40
Q

what is the regulation of smooth muscle contraction

A

By nerves, hormones, and local chemical changes

41
Q

What is neural regulation

A
  • Neurotransmitter binding causes an increase in [Ca2+] in sarcoplasm; either graded potential or action potential
  • The response depends on neurotransmitter and type of receptor molecules (G-Protein coupled receptors)
42
Q

How do hormones regulate smooth muscle contraction

A
  • Some smooth muscle cells have no nerve supply
  • Depolarise in response to chemical stimuli that bind to G protein-linked receptors
  • Chemical factors include hormones, CO2, pH
43
Q

what are the special features of smooth muscle contraction

A
  • active relaxation
  • stress-relaxation response
  • hyperplasia
44
Q

what is active relaxation

A

Nerve or chemical stimuli can contract or relax because myosin heads are orientated in one direction on one side and a different on the other side

45
Q

what is a stress-relaxation response

A
  • Responds to stretch only briefly, then adapts to the new length
  • Retains ability to contract on demand
  • Enables organs such as the stomach and bladder to temporarily store contents
46
Q

What is hyperplasia

A

smooth muscle can divide and increase numbers

Principles of Human Structure & Function (5 decks)

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