Muscle L1: Biomechanics of musculotendinous unit Flashcards
1
Q
What are the 4 types of tissue?
A
- Epithelial tissue
- Muscle tissue
- Nervous tissue
- Connective tissue
2
Q
What are tissues?
A
Tissues are groups of similar cells and their extracellular products, organised to perform a common function.
3
Q
What is epithelial tissue?
A
covers body surfaces, lines cavities & forms glands
4
Q
What is muscle tissue?
A
responsible for movement, interaction with the environment
5
Q
What is nervous tissue?
A
receives, transmits & integrates information to control the activities of the body
6
Q
What is connective tissue?
A
supports the other 3 tissues
7
Q
A muscle (organ) = _____ + ______
A
muscle tissue + connective tissue
8
Q
What is extracellular matrix (ECM)?
A
- A substance produced by the cells of a specific tissue
- Can contain protein, salts, H2O, and dissolved macromolecules
- Located outside of cells
- Respond to physical stresses
- Muscle tissue has very little (if any) ECM – rather, it is surrounded by connective tissue **referred to as ECM in Oatis and some other sources. Connective tissue has a significant ECM
9
Q
Microstructure of muscle belly: Muscle + Connective Tissue influence function
A
I
10
Q
What is endomysium?
A
An array of “tubes” into which muscle fibres insert Image
11
Q
What is perimysium?
A
Thickened area surrounding groups of the muscle fibres Image
12
Q
Muscle is made up of a large number of bundles (_____) of muscle fibres (muscle cells), surrounded by _______ tissue
A
fascicles connective tissue
13
Q
A single muscle fibre (cell) is very long. It runs ____ to other fibres.
A
parallel
14
Q
The fibres is made from a large number of ________, therefore a single muscle fibre has _____ nuclei.
A
fused embryonic cells many
15
Q
Inside each cell is a bundle of _____ (muscle- slender fibre), that lie in parallel
A
myofibrils
16
Q
These are the contractile filaments that convert the electrical signal (action potential) initiated in the nervous system to ______ are within the myofibril
A
muscle force
17
Q
A series of _______make up each myofibrils. The _______is the basic contractile unit of skeletal muscle
A
sacromeres sacromere
18
Q
Thin filaments (actin) attach at the ______.
A
Z line
19
Q
When at rest, actin and myosin overlap _____.
A
partially
20
Q
Whole muscle shortening results as the filaments overlap more, pulling the _____ closer
A
Z line
21
Q
Whole muscle lengthening results as the filaments overlap _____
A
less
22
Q
Contraction can occur during_____ or _____.
A
lengthening or shortening
23
Q
Thick filaments (myosin) anchor at the _____ in the _____ of the sarcomere
A
M line; centre
24
Q
Individual muscle force (N) is influenced by…
A
- Muscle architecture, muscle length
- Muscle fibre length, pennation angle - PCSA
- Specific tension – fibre types
- Number/discharge rate of active motor units i.e. neural drive
- Type of contraction i.e. isometric, concentric, eccentric speed of contraction, force relative to length
- Passive force
- Muscle fatigue and damage
25
Characteristics of muscle architecture
* Different muscles have different force generating capacity.
* Greatest predictor of force is the muscles physiological cross sectional area (PCSA)
* Most common calculation used in the literature:
* PCSA = Muscle volume/ Fiber length
* When also considering pennation angle: PCSA = (Muscle volume x CosΦ)/ Fiber length
* Fiber length and pennation angle [CosΦ] changes with contraction and joint angle… PCSA will change depending on muscle condition when measured
26
What are the characteristics of Muscle volume ?
* Does not change with contraction and joint angle
* Eg. vastus lateralis is larger (in volume) than vastus medialis
27
What are 2 components to make note of when measuring fascicle length?
1. length of a muscle fascicle between the superficial and deep aponeuroses (dashed lines) along the line of collagenous tissue
2. pennation angle (α), defined as the angle between the line of collagenous tissue and the deep aponeurosis.
28
Why does fibre length changes with contraction and joint angle?
* Shorter length during contraction compared to rest
* Due to the sarcomeres (actin and myosin overlap)
29
What is the Muscle-Length-Tension relationship?
* Increases to an optimal point and decreases again
* Vastus medialis has a 30o pennation angle
* Vastus laterialis has a 18o pennation angle
* More force produced
* Larger muscle (volume)
* Smaller pennation angle
30
How does pennation angle changes with contraction and joint angle?
* Muscle force transfer to tendon is reduced when muscle fascicles insert with a greater pennation angle
* Changes in pennation angle during contraction make a small difference to overall force within a muscle.
31
How does force generate capacity of individual muscles?
**PCSA = Muscle volume/ Fiber length**
* Greater force generating capacity from VL than VM
**PCSA = (Muscle volume x CosΦ)/Fiber length**
* Even greater force generating capacity from VL than VM if pennation angle was considered
32
What is specific tension?
Specific tension (Tspe)= the maximum force exerted by the fibers per unit of PCSA
Total muscle force = PCSA x Specific tension
* Type depends on muscle typology, with a higher specific tension associated with Type II muscle fibres.
* Skeletal muscles contain different proportions of Type I, IIA and IIB motor units depending on their function:
* POSTURAL MUSCLES: high proportion Type I (e.g. soleus 86% slow twitch)
* Don’t fatigue, keep using, decreased force
* DYNAMIC MUSCLES: high proportion Type II (e.g. gastrocnemius 56% fast twitch)
* Easily fatigue-able, force
* Most human muscles are mixed (40% - 60% fast twitch)
33
What the 2 fibre types?
Type I Type II
34
What are type I fibres?
Slow twitch, low force, fatigue resistant Lower specific tension
35
What are type II fibres?
Fast twitch, more force, fatigue quickly Higher specific tension
36
Less slow twitch fibres = _____ specific tension
Higher
37
What are characteristics are the number/discharge rate of active motor units (ie. neural drive)
* Each muscle fibre is innervated by a motor neuron (from the spinal cord) at a neuromuscular junction (motor point).
* Motor unit = 1 motoneuron, its motor axon and all of the muscle fibres it innervates
* Motoneuron receives excitatory and inhibitory input from descending pathways, spinal interneurons & afferent fibres
* When sufficient excitatory input to reach firing threshold, an action potential is generated
* Every action potential generated in the motor neuron generates an action potential in the motor units muscle fibres
* actin/myosin cross-bridging
* active force production
* Force is altered by number and discharge rate of single motor units (SMU)
38
What is Henneman's size principle?
* Small motor units (within a motor unit pool) are recruited first
* Same input = increased change in membrane potential in the smaller units \>\> reaches threshold sooner
* Increased drive = increased motor units and bigger motor units
* With increased excitatory input = increased number of motor units and increased size of the recruited motor units
* Assumption: Motor units within the same pool receive the same drive.
* Increased drive = more motor units and bigger motor units
39
What is eupnea?
small motor neurons
40
What is hypercapnea?
recruit larger- more slow twitch
41
What is airway occulution?
60% diaphragm recruited = 50% max. force
42
What is expulsive behaviour?
explosive diaphragm all fast fatigue (fast twitch)
43
What are the 3 types of contractions?
1. Concentric
2. Isometric
3. Eccentric
44
What is a concentric contraction?
During concentric muscle contractions the muscle shortens while contracting
45
What is an isometric contraction?
Neither lengthening or shortening
46
What is an eccentric contraction?
* During eccentric muscle contractions the muscle lengthens while contracting.
Eccentric= higher torque for same motor drive
* Same torque in each condition below
* Motor unit discharge rate lower during eccentric torque matched contractions For each motor unit discharge more torque is produced during eccentric contractions
47
Force opposing the contraction is _____ than the contraction force. Decelerates the movement (absorbing energy)
larger
48
The maximum force that can be produced is dependent on the direction such that: _____ \> _______ \> \_\_\_\_\_\_; and rate of change of muscle length such that the faster you contract concentrically the less force is produced
ECCENTRIC \> ISOMETRIC \> CONCENTRIC
49
An eccentrically contracting muscle can produce _____ force at the same muscle length than a concentrically contracting muscle
more
50
Can hold _____ load than you can lift, and lower _____ load than you can hold steady.
more; more
51
What are some mechanisms for higher muscle force for same neural drive during eccentric contractions?
* Active force is generated through the actin and myosin cross-bridge.
* In eccentric movements actin and myosin ‘hold on’, more stretch of the elastic components (eg titin) \> more force for same energy (# action potentials)
* Decreased rate of cross-bridge detachments \>\> greater force production on the eccentric bout.
52
What is force-velocity relationship?
* The force generated by a muscle is also dependent on its (lengthening/shortening) velocity.
* Mechanisms for higher muscle force at lower shortening speed:
* The force generated by a muscle depends on the total number of actin-myosin cross bridges. • It takes time for cross-bridges to attach.
* As filaments slide past each other faster (i.e. as the muscle shortens with increased velocity), fewer cross bridges are able to attach and generate force.
* As the relative filament velocity decreases, more cross bridges have time to attach and generate force.
* The potential to produce force….. Considering fascicle length, contraction direction and velocity
* Greatest force is produced when the muscle fibres are at optimal length, and the muscle is lengthening
53
Explain Hill’s Mechanical Model and the components. What are the 3 structures that contribute to the 3 components? What makes up the muscle-tendon unit and why are these components important when considering muscle force?
**POSSIBLE EXAM QUESTION**
* Contractile component (CC) – muscle fibers, actin and myosin cross bridges
* Series elastic component (SEC): intracellular titin, tendon
* Parallel elastic component (PEC): connective tissue - epimysium and perimysium,endomysium & passive cross bridge connections
54
What is muscle fatigue?
exercise-induced reduction in ability to produce force peripheral (muscle): failure to produce force appropriate to drive central (brain, spinal cord): failure to drive motoneurons adequately
55
Peripheral (muscle): failure to produce force appropriate to drive Peripheral sites may include?
Peripheral mechanisms will be task dependent, peripheral sites may include:
* neuromuscular junction [reduced release of Ach]
* changes in the muscle cell membrane potential [Na+/K+ pump]
* excitation-contraction coupling due to a change in the calcium release
* accumulation of metabolites [build up of lactate and H+ will change the pH and alter cell membrane]
* depletion of fuels [ATP]
56
Central (brain, spinal cord): failure to drive motoneurons adequately. Central factors include?
Central factors include:
* motivation
* discomfort
* attention
* drugs (e.g. caffeine)
57
How does muscle damage reduce ability to generate force?
58
Force-velocity relationship
TOTAL (purple) muscle force = ACTIVE (blue) + PASSIVE (red) tension
Active Tension = Force produced by active sarcomeres, driven by CNS
Passive Tension = Force produced by stretched connective tissue, cross bridges
