PBL Topic 3 Case 9 Flashcards
1
Q
What is skeletal muscle composed of?
A
- Muscle fibres
2
Q
What is the range of diameters of a muscle fibre?
A
- 10-80 micrometers
3
Q
What is the sarcolemma?
A
- Cell membrane of the muscle fibre
- Composed of a plasma membrane
- And an outer polysaccharide coat containing collagen
4
Q
What is a myofibril?
A
- Contractile threads within muscle fibres
5
Q
Identify two myofibrils. How many of each are located within a muscle fibre?
A
- Myosin (1500)
- Actin (3000)
6
Q
How are the myofibrils arranged in a muscle fibre?
A
- They interlock
- Giving off alternate light and dark bands?
7
Q
What is the sarcomere?
A
- Portion of myofibril between two successive Z lines
8
Q
What happens to the sarcomere during contraction? What is the importance of this?
A
- Shortens 2 micrometers
- Actin and myosin filaments overlap more
- Creating greatest force of contraction
9
Q
What is titin?
A
- Molecule that maintains side-to-side relationship between actin and myosin
10
Q
What is the sarcoplasm and what does it contain?
A
- Space between myofibrils
- Contains large quantities of potassium ions, mitochondria and sarcoplasmic reticulum
11
Q
Outline the structure of a myosin filament
A
- Four light chains and two heavy chains
- Heavy chains wrap spirally around each other into a double helix
- Cross bridges formed by protruding arms and heads
12
Q
Outline the structure of an actin filament
A
- F-actin double helix protein
- Composed of G-actin molecules which functions as active site
- Tropomyosin wraps spirally around F-actin, covering the active sites
- Troponin attaches to tropomyosin
13
Q
Identify the three types of troponin
A
- Troponin I has a strong affinity for actin
- Troponin T has a strong affinity for tropomyosin
- Troponin C has a strong affinity for calcium ions
14
Q
Outline the process that allows myosin to bind with actin
A
- Calcium binds to troponin C
- Troponin is inhibited and moves the tropomyosin deeper into the groove between the actin strands
- This uncovers active sites and allows myosin to bind
15
Q
Outline the walk along theory of contraction
A
- Myosin head binds to active site
- Cross bridge tilts and moves the actin filament along it (power stroke)
- Myosin head breaks away from active site and binds to another active site further along the actin filament
16
Q
How is ATP broken down into ADP and Pi during muscle contraction?
A
- Myosin head possesses ATPase
17
Q
Identify two ways in which ATP influences the myosin head
A
- Energy from breakdown of ATP allows myosin head to tilt and move actin filament along
- Binding of ATP after power stroke causes detachment of myosin head in order to bind to another actin filament
18
Q
Aside from action on the myosin head, identify two other roles of ATP during muscle contraction
A
- Pumping calcium from sarcoplasm into sarcoplasmic reticulum after contraction
- Pumping sodium and potassium across muscle fibre membrane to maintain ionic environment for propagation of action potential
19
Q
How is phosphocreatine able to reconstitute ATP?
A
- Breakdown of phosphocreatine donates a phosphate ion which is able to bind with ADP to form ATP
20
Q
How is glycogen able to reconstitute ATP?
A
- During glycolysis
- Breakdown of glycogen to pyruvic acid and lactic acid liberates energy
- That is used to convert ADP to ATP
21
Q
Identify two advantages of glycogen breakdown during muscle contraction
A
- Can occur in anaerobic conditions
- Rate of ATP formation is 2.5x that from foodstuffs
22
Q
From which source is 95% of energy for muscle contraction derived?
A
- Oxidative metabolism
- In which oxygen reacts with products of glycolysis to liberate ATP
23
Q
What is the efficiency of muscle contraction and why?
A
- 25%
- Much of the energy is lost as heat
24
Q
How is work done calculated?
A
- W = L x D
- Where W is work done
- L is load (force exerted on the muscle by a weight)
- And D is distance of movement against the load
25
What is tension?
- Force exerted on a weight by a muscle
26
What is load?
- Force exerted on a muscle by a weight
27
What is meant by isometric contraction?
- Contraction that does not involve lengthening or shortening of a muscle
28
What is meant by isotonic contraction?
-Contraction that does involve lengthening or shortening of a muscle
29
What is concentric contraction?
- Isotonic contraction that involves shortening of a muscle
30
What is eccentric contraction?
- Isotonic contraction that involves lengthening of a muscle
31
What is a type I fibre?
- Slow oxidative fibre
- That combines low myosin ATPase activity
- With high oxidative energy
32
What is a type IIb fibre?
- Fast glycolytic fibre
- That combines high myosin ATPase activity
- With high glycolytic activity
33
What is a type Ib fibre?
- Fast-oxidative-glycolytic activity
- That combines high myosin ATPase activity
- With high oxidative capacity
- And intermediate glycolytic activity
34
How does blood supply differ in slow and fast fibres?
- More extensive in slow fibres for oxygen for oxidative phosphorlylation
35
What is myoglobin and how does the presence of myoglobin differ in slow and fast fibres
- More extensive in slow fibres for storage of oxygen, giving slow fibres a red appearance
- Less extensive in fast fibres, giving fast fibres a white appearance
36
Which type of fibre possesses a more extensive sarcoplasmic reticulum?
- Fast fibres
37
Which type of fibre possesses a more glycolytic enzymes?
- Fast fibres
38
Which type of fibre possesses a more mitochondria?
- Slow fibres
39
What is a motor unit?
- All the muscle fibres innervated by a single nerve fibre
40
The average motor unit possesses how many muscle fibre?
- 80 to 100
41
What is spatial summation?
- Intensity of muscle contraction can be increased by increasing the number of motor units
- Size principle
42
What is temporal summation?
- Intensity of muscle contraction can be increased by increasing the frequency of contraction
43
What is tetanisation?
- As frequency increases, successive contractions fuse together, giving appearance of smooth and continuous contraction
44
What is the maximum contractile strength of a muscle?
- 3-4kg per cubic centimetre
45
How is muscle tone maintained?
- Low rate of nerve impulses from spinal cord
46
What is muscle fatigue proportional to?
- Rate of depletion of glycogen
47
What is meant by coactivation of antagonist muscles?
- All movements are caused by simultaneous contraction of agonist and antagonist muscles
- Position of limb is determined by relative degrees of contraction of agonist and antagonist muscles
48
Identify 4 processes that can occur in muscle remodelling
- Increase in number of myofibrils (fibre hypertrophy)
- Addition of sarcomeres to ends of muscle fibres (sarcomere hypertrophy)
- Increase in number of muscle fibres (hyperplasia)
- Destruction of muscle fibres (denervation atrophy)
49
What is rigor mortis?
- After death, muscles become rigid
- Due to loss of ATP
- Which causes separation of cross bridges from actin filaments
- Lasts 24 hours
50
Describe the physiological anatomy of a neuromuscular junction
- Large myelinated nerve fibre branch and invaginate into muscle fibre
- Invaginated space known as synaptic trough
- Synaptic trough separated from nerve fibre by synaptic cleft
- Subneural clefts located at bottom of trough
51
Explain the role of Ca2+ ions on the secretion of ACh from the presynaptic nerve fibre
- Binds to synaptotagmins
- Causing a change in the SNARE complex
- Allowing fusion of ACh vesicles with neural membrane
- Followed by exocytosis
52
Explain the effect of ACh on the postsynaptic muscle fibre membrane
- Two molecules of ACh bind to ACh receptor
- (Which is composed of two alpha, a beta, a delta and a gamma protein)
- Allowing entry of positive sodium ions into the muscle fibre
53
Explain why negative ions do not enter the postsynaptic muscle fibre
- Opening possesses a negative field which repels negative ions
54
What is the end plate potential and what is its value?
- Local potential caused by influx of sodium ions into the end plate
- 50 to 75 millivolts
55
What are T-tubules and what is their purpose?
- Dihydropyridine voltage gated calcium channel
- That penetrates all the way through the muscle fibre
- Allowing the action potential to penetrate deep enough to the myofibrils to cause maximum muscle contraction
56
Describe the process of excitation-contraction coupling
- Calcium ions enter the sarcoplasm through the T-tubules
- Which binds to ryanodine receptors on the sarcoplasmic reticulum
- Causing release of many more calcium ions into the sarcoplasm and into the myofibrils
- To bind to troponin C, to relax its inhibitory grip on tropomyosin to allow myosin to bind to actin active sites
57
What happens to calcium ions following muscle contraction?
- Pumped out of muscle fibres by sodium calcium exchanger
| - Into sarcoplasmic reticulum (regulated by phospholambin) and T-tubule extracellular fluid
58
Outline the effects of training on muscle hypertrophy
- Increase in number of myofibrils, mitochondrial enzymes, ATP, phosphocreatine and glycogen and triglycerides
59
What is AMPK and its role?
- Adenosine Monophosphate-Activated Kinase
- Increases cellular energy
- By inhibiting anabolic energy consuming pathways and stimulating energy producing catabolic pathways
60
What is gait?
- Cyclical pattern of musculoskeletal motion that carries the body forward
61
Identify the two phases of gait and their relative proportions
- Stance occupying 60% of the cycle
| - Swing occupies 40% of the cycle
62
Describe the features of antalgic gait and identify its cause
- 'Dot-dash' movement
| - Caused by pain
63
Describe the feature of a gait with limb-length discrepancy
- Tiptoe on shorter side
| - Hip and knee flexion on longer side
64
Describe the features of apraxic gait and identify its cause
- Small shuffling steps (marche a petit pas)
| - Caused by frontal lobe damage e.g. hydrocephalus, infarction
65
Describe the features of myopathic / waddling gait and identify its cause
- Patient bends pelvis forward and walks with a waddle
| - Caused by muscle or hip disease
66
Describe the features of diplegic / scissoring gait and identify its cause
- Patient walks stiffly on the toes and has problems turning
| - Bilateral upper neuron lesion causing bilateral spasticity
67
Describe the features of a Parkinsonian gait and identify its cause
- Stooped posture
- Slow, shuffling gait
- Unilateral arm swing
- Resting tremor
- Caused by basal ganglia dysfunction
68
Describe the features of a hemiplegic gait and identify its cause
- Flexed upper limbs on affected side
- Extended lower limbs on affected side
- With circumduction of leg
- Unilateral upper motor neurone lesion
69
Describe the features of ataxic gait and identify its cause
- Broad-based gate
- Poor tandem gait
- Side-swinging
- Caused by a cerebellar lesion, problem with spinocerebellum since there is overshooting of movements hence side-swinging
70
Describe the features of sensory ataxia and identify its cause
- Slaps the foot down on walking
- Gait is high stepping to allow clearance of weak foot
- Caused by damage to common fibular nerve
71
What is a stress fracture?
- One caused by recurrent episodes of minor trauma
- Typically in long bones
- Heals after rest
72
What is a pathological fracture?
- One caused by a disease such as osteoporosis, osteomalacia, rickets, Paget's disease, malignant tumours
73
What is a compound fracture?
- One in which broken bone pierces the skin
74
What is a comminuted fracture?
- One in which bone is broken into more than two fragments
75
Outline the process of fracture healing
- Blood vessel rupture results in haematoma
- Which is replaced by granulation tissue
- Chondroblasts deposit hyaline over the granulation tissue to form a provisional callus
- Osteoprogenitor cells deposit a layer of woven bone over the provisional callus forming a bony callus
- Bony union achieved when fracture site is completely bridged by woven bone.
76
Identify four causes of delayed fracture healing
- Excessive movement during healing process
- Poor intrinsic blood supply or interruption of blood supply
- Infection in a compound fracture
- Necrosis in a comminuted fracture
77
What is the A band composed of, how does it appear?
- Consists of myosin filaments as well as the actin filaments that overlap it
- Appears dark because it is anisotropic to light
78
What is the I band composed of, how does it appear?
- Consists of actin filaments only on either side of the A band
- Appears light because it is isotropic to light
79
What is the Z line?
- The lateral part of each actin filament is anchored to a network of interconnecting proteins known as the Z line
80
What is the H zone?
- Consists of myosin filaments only in the centre of the A band
- Does not contain overlapping actin filaments
81
What is the M line?
- Dark band composed of proteins that link together the central region of the thick filament
82
What is meant by fibre hypertrophy?
- Increase in size of muscle fibre
| - Due to increased number of myofibrils due to increase use
83
What is meant by sarcomere hypertrophy?
- Increase in size of muscle fibre
- Due to increased stretching of a muscle
- And increased number of sarcomeres at each end where they attach to muscles
84
What is meant by fibre hyperplasia?
- Increase in number of muscle fibres
| - Rare
85
What is meant by denervation atrophy?
- As a result of impaired nerve supply to a muscle
- Decrease in size of muscle fibre
- And replacement with fibrous fatty tissue
- Which continues to shorten resulting in contracture
86
Identify the four stages of stance phase
- Heal strike
- Loading response
- Midstance
- Heal off
87
Which muscles are used during heel strike? (2)
- Tibialis anterior
| - Gluteus maximus
88
Which muscles are used during loading response? (1)
- Quadriceps femoris
89
Which muscles are used during midstance? (2)
- Gastrocnemius
| - Soleus
90
Which muscles are performed during terminal stance? (2)
- Gastrocnemius
| - Soleus
91
Identify the three stages of swing phase
- Pre-swing
- Mid-swing
- Terminal swing
92
Which muscles are used during pre-swing ? (1)
- Rectus femoris
93
Which muscles are used during mid-swing? (1)
- Iliopsoas
| - Rectus femoris
94
Which muscles are used during terminal swing?
- Hamstrings
- Tibialis anterior
- Ankle dorsiflexors
95
What is a placebo?
- Inert substance that causes symptom relief
96
Identify three non-interactive theories of placebo
- Individual trait theories e.g. personality
- Treatment characteristics e.g. size of drug
- Characteristics of health professional
97
Identify six factors involved in the interactive theory of placebo
- Experimenter bias
- Patient's expectations
- Reporting error
- Conditioning effects
- Anxiety reduction
- Endorphins
98
Outline Cognitive Dissonance Theory with relation to placebo
- For a placebo to work they must involve investment
- For someone to invest they must see themselves as rational, in control and be able to justify their behaviour
- If these factors align the person experiences low dissonance resulting in less distress
99
How does the placebo effect relate to health beliefs?
- Individual needs to believe the intervention is effective
100
How does the placebo effect relate to illness cognitions?
- Individual needs to believe that the illness can be overcome
101
How does the placebo effect relate to health related behaviour
- Individuals believe intervention promotes good health
| - So take health promoting measures in other areas of their lifestyle
102
How does the placebo effects relate to stress?
- Reduces stress since the individual believes that they have taken control of their illness
103
How does the placebo effect relate to pain reduction?
- Related to opiate release or by anxiety reduction by taking intervention
104
What is Shared Decision Making
- Process in which clinicians and patients work together
- To select tests, treatments, management or support packages
- Based on both clinical evidence and the patients informed preference
105
What is the importance of Shared Decision Making
- Ethical imperative by professional regulatory bodies
| - Patients want to be more involved than they currently are in making decisions about their own health and health care.
106
What does patient driven decision making involve?
- Physician presents all options
- Physician makes no recommendation
- Patient makes their own choice
107
What does physician recommendation decision making involve?
- Physician presents all options
- Physician makes a recommendation
- Based on patient's values and perspective
108
What is meant by equal partners decision making involve?
- Physician presents all options
- Physicians and patients work together to reach a mutual decision
- Based on patients values and perspectives
109
What is meant by informed non-dissent decision making?
- Physician determines best course of action
- Based on patients values and perspectives
- Patient has a right to veto a decision
- Silent is construed as tacit consent
110
What is meant by physician driven decision making
- Only applies to value neutral decisions
- Care must be taken as they do not necessarily know what a patient deems as value neutral
- Physicians should be aware of possible patient perspectives
