Week 6 Ch. 6 Skeletal muscle contraction Flashcards
1
Q
Sarcolemma is
A
the thin membrane enclosing fiber - muscle cell membrane
2
Q
Sarcolemma is made of
A
polysacccharide chains and collagen fibrils
3
Q
Myfibrils are made up of
A
Actin and Myosin
4
Q
Sarcomere
A
point between Z-disks that shorten during muscle contraction
5
Q
Z-disk - function and action
A
provides anchorage for actin
passes from microfibril to microfibril all around muscle fiber
6
Q
Titin: function and location
A
large protein that maintains interaction between actin and Myosin
(tethers myosin to Z-disk0
7
Q
Sarcoplasm
A
instead of cytoplasm in muscles, fills spaces between myofibrils
8
Q
What is in the sarcoplasm
A
K+, magnesium phosphate, protein enzymes, mitochondria
9
Q
Sarcoplasmic reticulum role
A
instead of smooth ER
regulates calcium storage, release and reuptake
10
Q
Action potential for contraction moves from ____ to _____
A
motor nerve to muscle fibers (sarcolemma)
11
Q
Neurotransmitter that is secreted for muscle contraction
A
Acetylcholine (Ach)
12
Q
Acetylcholine binds______ to _____
A
on Ach gated cation channels on sarcolema
open sodium channels
13
Q
Voltage gated sodium channels (role in muscle contraction)
A
open and action potential is initiated (becomes more positive with influx of Na)
14
Q
Action potential begins, muscle membrane is depolarized, and then:
A
SR releases calcium ions
15
Q
Calcium allows
A
actin and myosin to attract and slide, which causes contraction
16
Q
At end of action potential, calcium:
A
goes back in SR
17
Q
Contraction of muscle causes
A
cross-bridges from myosin and actin filaments
18
Q
Myosin is the (heavy or light chain?)
A
heavy
19
Q
Actin is the (heavy or light chain?)
A
light
20
Q
Head of myosin functions as
A
ATPase
21
Q
Tropomyosin (location and function)
A
wraps around actin, lies on top of active sites to block interaction with myosin
22
Q
Troponin (location and function)
A
bound to tropomyosin, attatches to actin and tropomyosin
“staples” tropomyosin to actin
23
Q
Troponin has what binding sites (4)
A
- to actin
2.to tropomyosin - to another troponin
- to calcium
24
Q
In the presence of troponin, tropomyosin
A
blocks actin and myosin binding
25
In the presence of calcium, what happens?
troponin-tropomyosin become inhibited
Calcium causes a conformation change and tropomyosin is pulled away from active sites
26
G actin subunit role
bears active sites for myosin head attachment
27
What is the sliding filament model of contraction?
Shortening occurs when tension generated by cross bridges on thin filaments exceeds forces opposing shortening
thin filaments slide past thick filaments, causing actin and myosin to overlap
28
Contraction ends when crossbridges become
inactive
29
What causes Ca2+ to release into cytosol?
Voltage- sensitive proteins in T tubules change shape (Na+ causes voltage change)
30
Cross bridge cycling steps (once Ca+ is released)
1. Ca+ binds to troponin
2. Troponin changes shape and moves tropomyosin away from myson-binding sites
3.Myosin heads mind to actin, forming crossbridge
4. Cycling initiates, causing sarcormere to shorten and contract
5. Ca+ pumped back into SR and contraction ends
31
What causes a muscle contraction to caese
Nervous stimulation ceases, Ca+ goes pumps back into SR
32
Cross bridge cycling steps
1. Crossbridge forms
2. Working (power stroke)
3. Cross bridge detatchment
4. COcking of myosin head
33
Crossbridge forms:
hi energy myosin head attatches to actin thin filament active site
34
Working (power) stroke:
ADP and Pi are released from myosin head, causing head to pivot and bend, pulling actin filament towards M line
35
Cross bridge detachment:
ATP attatches to myosin head causing cross bridge to detatch
36
Cocking of myosin head:
ATP is hydrolyzed to ADP and Pi, which attatch to myosin head and return it to cocked position
37
Myosin "cocked" position:
Pre-stroke, high energy state
38
Muscle tension definition and cause
cause: contraction
Definition: force exerted on load or object to be moved
39
Isometric contraction
muscle tension increases but does not exceed load
40
Isometric contraction example
You are trying to push down wall but cant (load is greater than max tension can generate)
Muscle cannot change length
41
Isotonic contraction
muscle changes in length and moves load
42
Isotonic contraction example
Lifting weights
43
Two types of isotonic contraction:
1. Concentric
2. Eccentric
44
Concentric contractions: What happens and example
Muscle shortens and does work
ex. picking up weight in bicep curl
45
Eccentric contraction: what happens and example
Muscle lengthens and generates force
ex setting down or lower weight
46
Motor unit definition (s)
nerve-muscle functional unit
motor neuron and all muscle fibers it supplies
47
Muscle twitch is a _______ resulting from______
Muscle fiber's response
a single action potential from motor neuron
48
Myogram
observes and records muscle twitch
49
Latent period of muscle twitch: What is happening and what will you see
Exciting-contraction coupling occuring, no muscle tension seen
(Ach crossing, Ca+ release, myosin binding)
50
Period of contraction muscle twitch: what is happening what will you see?
Cross bridge formation
you will see tension increase
51
Period of relaxation muscle twitch: What is happening and what will you see?
Ca+ reentry into SR
you will see tension decline to zero
52
Different strength and duration of twitches are due to
variations in metabolic properties and enzymes
53
contraction speed and hold
vary between muscles
ex) eye muscles contract rapid and brief, calf muscles contract more slowly and are held longer
54
Graded muscle repsones
varied strength of contraction for different demands
55
Responses of contraction are graded by (2):
1. Changing frequency of stimulation
2. changing strength of stimulation
56
Wave (temporal) summation results if
2 stimuli are received by a muscle in rapid succession
57
In wave (temporal) summation, there is a
summative increase in muscle tension d/t frequency of stimuli
58
Unfused (incomplete) tetanus occurs when
summation reaches near max tension to sustain (quivering)
59
Fused (complete tetanus) occurs when
if stimuli frequency further increases and muscle tension reaches maximum
can lead to muscle fatigue
60
Recruitment is also called
multiple motor unit summation
61
Multiple motor unit summation:
stimulus is sent to more muscle fibers
62
Multiple motor unit summation leads to
more precise control
63
Subthreshold stimulus
no contraction seen
64
threshold stimulus
first observable contraction
65
Maximal stimulus
strongest stimullus that increases max contractile force
66
Stimulus involved in recruitment:
1. sub-threshold
2. threshold
3. maximal
67
Muscle response to changes in stimulus strength method:
recruitment of motor unit works on size principle
68
Recruitment size principle
Motor units are recruited smallest muscle fibers--->largest muscle fibers
69
Motor units in muscles contract asynchronously to
avoid quick fatigue/use of materials
70
ATP is made available for contractions by (3):
1. Direct phosphorylation of ADP by creatine phosphate
2. Anaerobic pathway: glycolysis and lactic acid formation
3. Aerobic respiration - Kreb's cycle
71
Direct phosphorylation of ADP by creatinine phosphate creates ATP by
donates P to ADP, turning it into ATP
72
Anaerobic glycolysis ATP formation
1. glucose is broken down to pyruvic acid (2 ATP)
2. Pyruvic acid is converted into lactic acid for re use
73
Aerobic respiration
1. Glucose is broken down into pyruvic acid
2. pyruvic acid goes through the Kreb's cycle in the mitochondira (32 ATP)
74
Aerobic respiration is used during
aerobic endurance (running)
75
anaerobic threshold
Muscle metabolism converts to anaerobic pathways (HIIT)
76
Force of muscle contraction is dependent on (4):
1. Number of muscle fibers stimulated (recruitment)
2. Relative size of fibers
3. Frequency of stimulation
4. Degree of muscle stretch
77
Number of muscle fibers and force of contraction
More motor units recruited = greater force
78
Relative size of fibers and force of contraction
bulkier muscle, more tension can develop
79
Frequency of stimulation and force of contraction
higher frequency = greater force
80
Degree of muscle stretch and force of contraction: when do sarcomeres generate more force during contraction?
sarcomeres that are 80-%-120% their normal resting length at contraction generate more force
81
How fast a muscle contracts and how long it can stay contracted depends on (3):
1. muscle fiber type
2 load
3. recruitment
82
Speed of contraction is determined by
the speed at which myosin and ATPases split ATP
83
Oxidative fiber use
aerobic pathways
84
Glycolytic fibers use
anaerobic pathways
85
Muscle fiber type is classified according to (2):
1. Speed of contraction
2. Metabolic pathways used for ATP synthesis
86
Skeletal muscles fibers can be classified into 3 types:
1. slow oxidative
2. fast oxidative
3. fast glycolytic
87
Slow oxidative fibers are used in
low intensity endurance activities
i.e. maintaining posture, soleus
88
Fast oxidative fibers are used in
Medium intensity activities
i.e. sprinting or walking
89
Fast glycolytic fibers are used in
short term intense or powerful movements
i.e. HITT exercise
90
Load and recruitment:
muscles contract fastest with no load. increase load = increase contraction time
more motor units contracting = faster and longer
91
Aerobic exercise leads to (3)
1. increased msucle cappilaires
2. increased #mitochonria
3. Increasead myoglobin synthesis
92
Resistance exercise leads to (3)
1. muscle hypertrophy
2. increased mitochondira, myofilaments, glycogen stores, connective tissue
3. increase muscle strength and size
93
Hypertrophy
Increased actin and myosin
94
Hyperplasia
Formation of new muscle cells
95
Lengthening causes
-force generation
-shortening capacity
-imax concentration velocity?
-No change in force generation
-increased shortening capacity
-increased maximum concentration velocity
96
Hypertrophy and hyperplasia cause
-force generation?
-shortening capacity?
-max contraction velocity?
-increased FORCE
-no change in shortening capacity
-no change in max velocity of contraction
