009 Muscle function in health and disease Flashcards
1
Q
describe the feedforward/feedback process of controlling movement
A
idea/need/motivation —> plan/intrinsic/extrinsic/posture —> execution/commant to muscles/force/length —> appraisal/sensory feedback/adjust if needed
-prevents movements from being jerky
2
Q
what are the 3 different types of muscle contraction?
A
- concentric
- eccentric
- isometric
3
Q
what is concentric contraction?
A
- when force > load
- the muscle shortens during contraction
4
Q
what is isometric contraction?
A
- when force = load
- muscle stays at the same length during the contraction
5
Q
what is eccentric contraction?
A
- when force < load
- the muscle lengthens during contraction
6
Q
what type of muscle contraction produces the most force?
A
- eccentric
7
Q
what are the neural factors that influence muscle contraction (2)?
A
- descending drive = how drive arrives at the spinal cord and how motor neurone innervates muscle fibre
- motor neurone/motor unit recruitment/coding
8
Q
what are the biomechanical factors that influence muscle contraction (7)?
A
- cross sectional area = direct relationship between CSA and tension produced
- muscle fibre type
- visco elastic properties
- muscle architecture
- length-tension
- load velocity
- contraction time
9
Q
name 3 factors other than neural and biomechanical that influence muscle contraction
A
- temperature
- fatigue
- pre stretching
10
Q
what are the 2 main ways you can alter motor neurons to increase tension produced?
A
- recruit more motor neurones/units to send a larger drive and give a strong stimulus to motor neurone pool
- increase rate of firing of motor unit (summation) = rate coding
11
Q
what is rate coding with motor neurones?
A
- increasing the firing rate of the motor neurone to generate greater force
12
Q
what is the definition of muscle strength?
A
- maximum force or tension output generated by a single muscle or related muscle groups (isometric)
- measured in different ways such as repetition maximum, hand held dyanometer, isokinetics (special training machine that creates different levels of resistance based on the force you give)
- muscle torque = angular motion = the force applied by the muscle through a movement arm of a given length, at given angle to the joint
13
Q
what is the definition of muscle power?
A
- product of force and velocity of muscle action
- power = work/time
- work = force x distance
14
Q
what are the 2 key relationships when talking about muscle functioning?
A
- length-tension relationship
- force-velocity relationship
15
Q
what is the difference between ACSA and PCSA?
A
- ACSA = anatomical cross-sectional area = straight coronal or saggital CSA, only looking at muscle in 1 directon
- PCSA = physiological cross-sectional area = bigger, perpendicular to muscle fibre direction, takes into account all the different layers and directions and angles of muscle fibres
16
Q
describe the length-tension relationship of muscles
A
- tension is proportional to the extent of overlap of actin and myosin filaments, the greater the overlap, the more cross bridges that form
- as the muscle contracts, there is greater tension, and greater overlap of actin and myosin
- if overlapping exceeds a certain point, fewer cross bridges are formed, so tension decreases
- (graph looks like a hill, up, peak then down)
17
Q
describe the force-velocity relationship
A
- graph is a backwards s
- force on y axis, shortening velocity on x axis
- eccentric lengthening = upper left on graph = increasing force, increasing lengthening velocity
-maximum isometric force = where it crosses y axis, when velocity = 0 (as the muscle is neither shortening or lengthening) - concentric shortening = lower right on graph = increase shortening velocity, decreases force
18
Q
describe the power-velocity relationship graph
A
- hill/curve
- as velocity increases, power increases until a maximum and then power decreases
19
Q
what are the 4 types of muscle fibres in animals?
A
- type 1 = slow twitch
- type 2a = fast twitch
- type 2x/d = fast twitch
- type 2b = fast twitch = just animal models
20
Q
what is the fatigue resistance in the different types of muscles fibres?
A
- type 1 = resistant
- type 2a = moderately resistant
- type 2x/d = not resistant, very fatigable
21
Q
what is the myoglobin content in the different types of muscle fibres?
A
- type 1 = high = appears red
- type 2a = moderate
- type 2x/d = low = appears white
22
Q
what is the metabolism of the different muscle fibre types?
A
- type 1 = aerobic oxidative
- type 2a = aerobic, oxidative
- type 2x/d = anaerobic, glycolytic
23
Q
what is the mitochondrial density of the different muscle fibres types?
A
- type 1 = high
- type 2a = high/moderate
- type 2x/d = low
24
Q
what is the glycogen of the different muscle fibre types?
A
- type 1 = low
- type 2a = abundant
- type 2x/d = high
25
what is the myosin ATPase activity in the different muscle fibre types?
- type 1 = low
- type 2a = intermediate
- type 2x/d = high
26
what is the speed of contraction for the different muscle fibre types?
- type 1 = slow, 15mm/s
- type 2a = fast, 40-50mm/s
- type 2x/d = fastest 50-60mm/s
27
what is the motor unit size of the different muscle types?
- type 1 = small
- type 2a = intermediate
- type 2x/d = large
28
what are the muscle fibre diameters of the different muscle fibre types?
- type 1 = small
- type 2a = intermediate
- type 2x/d = large
29
what muscle fibre types do we have most common and least common in the human body?
most common = type 2x/d
least common = type 1
30
what type of muscle fibre is best for long distance running?
- type 1 = slow twitch = less quickly fatigued
31
what type of muscle fibre is best for sprinting?
- type 2 = fast twitch = quickly fatigued but produce stronger contractions
32
on a normal force/power and velocity graph, where is the Fmax, Pmax and Vmax?
- Force curve = downwards slope from y axis, Fmax = y intercept at top
- power curve = positive hill curve, Pmax is the top of the curve/peak
- Vmax = x axis intercept, greatest velocity
33
what happens to the power and the velocity if the sarcomeres are in parallel or series?
- same power produced (Pmax), but different optimal velocities (Vmax)
- parallel has a lower Vmax than series
34
how does the cross-sectional areas of a muscle affect its strength?
- increased CSA = increased muscle strength
- due to:
- improved activation via neural system
- decreased drive to antagonist via the neural system
- changes in pennation angle (angle between the longitudinal axis of the entire muscle and its fibres)
- loss of intramuscular fat
- hypertrophy of individual muscles
35
what are the neural factors involved in muscle strength?
- activation of motor units (frequency and number)
- involvement of afferent and efferent pathways
- synchronisation (muscles are activated more efficiently if at the same time)
36
what are the 4 main principles of strength training?
- overload = muscle worked at load > than normal, at least 65% of repetitive maximum load
- specificity = adaptations occur based on training type
- individuality = variability from person-person (genetics, metabolism...)
- reversibility = training effects will reverse if stopped
37
name 7 ways to increase muscle force and strength
- progressive resistance weight training
- isometric training (static)
- isokinetic training (dynamic)
- use of weight bearing exercise (body weight as resistance)
- repetition
- circuit training
- strength training combined with task training
38
what is the difference between the force and muscle CSA for men and women?
- women have a lower MCSA and lower force than men, but the strength per MCSA is the same in women as men (proportional)
39
what is muscle plasticity?
- the potential to increase muscle size and contractile protein composition (fibre type)
40
how can muscle fibres change type?
- fibre type depends on neural innervation and fuel
-the stimulus must be consistent, or the fibre type will return to original
- type 1 ---> type 2a ---> type 2x/d
- type 2x/d ---> type 2a (increase fatigue resistance) but cannot change to type 1 (only by not training/reversing, you cannot create more type 1 than you already have)
41
how does ageing affect our muscles(6)?
- neural activation decreases (decreased motor recruitment and rate coding)
- muscle CSA decreases (atrophy, turns into fat)
- muscle architecture (decreased angle of pennation)
- muscle fibre type (greater loss of type 2)
- length-tension relationship ( loss of elasticity)
- agonist/antagonist coactivation (ineffective)
42
what are UMN/LMN lesions?
- neurological disease of either upper motor neurone/lower motor neurone
43
what part of the nervous system is UMN lesions?
CNS
44
what part of the nervous system is LMN lesions?
PNS or CNS
45
give some examples of UMN lesions diseases
- stroke, cerebral palsy, trauma
46
give some examples of LMN lesions diseases
- polio, trauma
47
what kind of paralysis is UMN lesions diseases?
- spasticity (contracted/tight)
48
what kind of paralysis is LMN lesion diseases?
- flaccid paralysis
49
what happens to the muscle tone in UMN lesions?
- increased muscle tone
50
what happens to muscle tone in LMN lesions?
- decreased muscle tone
51
what happens to muscle reflexes in UMN lesions?
- hyper-reflexia
52
what happens to muscle reflexes in LMN lesions?
- absent or very reduced
53
describe how cerebral palsy develops
- UMN lesion
- leads to loss of inhibition of lower motor neurons, which gives positive UMN features, e.g. spasticity. hyper-reflexia
-loss of connection to lower motor neurons, which gives negative UMN features e.g. weakness, fatigability, poor balance
- leads to musculoskeletal pathology = muscle shortening, bony torsion, joint instability, degenerative arthritis
54
how does a health disorder affect muscle adaptability?
- neural activation = decreased recruitment of motor units and rate coding
- CSA = decreased
- muscle architecture altered = sarcomeres stiffer and longer, angle of pennation reduced
- muscle fibre type = mostly type 1
- length-tension relationship altered
- muscle tone change
- inappropriate agonist and agonist coordination, e.g. both at same time = ineffective
