Physiology Flashcards
(152 cards)
1
Q
What are the overall physiological functions of skeletal muscle?
A
Maintenance of posture.
Purposeful movement in relation to the external environment.
Respiratory movements.
Heat production.
Contribution to whole body metabolism.
2
Q
What are the 3 types of muscle in the body?
A
Cardiac (striated, involuntary).
Smooth (unstriated, involuntary).
Skeletal (striated, voluntary).
3
Q
What are the three muscle types of the body capable of?
A
Developing tension and producing movement through contraction.
4
Q
How can striation of muscles be visualised under a light microscope?
A
Alternating dark bands (caused by myosin thick filaments) and light bands (caused by actin thin filaments).
5
Q
What is the innervation of skeletal muscle?
A
Skeletal muscles are innervated by the somatic nervous system and are subject to voluntary control.
6
Q
What is the innervation of cardiac and smooth muscle?
A
Cardiac and smooth muscles are innervated by the autonomic nervous system (involuntary).
7
Q
What is the initiation and propagation of contraction of skeletal muscle?
A
Neurogenic initiation of contraction.
Motor units.
Neuromuscular junction present.
No gap junctions.
8
Q
What is the initiation and propagation of contraction of cardiac muscle?
A
Myogenic (pacemaker potential) initiation of contraction.
No neuromuscular junction.
Gap junctions present.
9
Q
What is the excitation-contraction coupling of skeletal muscle?
A
Ca++ entirely from the sarcoplasmic reticulum.
10
Q
What is the excitation-contraction coupling of cardiac muscle?
A
Ca++ from the ECF and sarcoplasmic reticulum (Ca++ induced Ca++ release).
11
Q
What is the gradation of contraction of skeletal muscle?
A
Motor unit recruitment.
Summation of contractions.
12
Q
What is the gradation of contraction of cardiac muscle?
A
Depends on the extent of heart filling with blood (preload) - Frank-Starling mechanism.
13
Q
What is the transmitter at the neuromuscular junction?
A
Acetylcholine.
14
Q
What is a motor unit?
A
A single alpha motor neuron and all the skeletal muscle fibres it innervates.
15
Q
Why do different motor units in different regions of the body have different numbers of muscle fibres within them?
A
The number of muscle fibres per motor unit depends on the functions served by the muscle.
Muscles which serve fine movements (e.g. external eye muscles, muscles of facial expression, and intrinsic hand muscles) have fewer fibres per motor unit that say thigh muscles.
In the hand, precision is more important than power so there are ~10 fibres per motor unit.
In the thigh, power is more important than precision so there are 1000s fibres per motor unit.
16
Q
In brief, what are the levels of organisation in skeletal muscle?
A
Whole muscle.
Muscle fibre (one cell).
Myofibril (specialised contractile intracellular structure).
Sarcomere (functional unit).
Myofibril and sarcomere contain myosin (thick) and actin (thin) filaments.
17
Q
What are myofibrils comprised of?
A
Myofibrils have alternating segments of thick (myosin) and thin (actin) protein filaments.
Within each myofibril, actin and myosin are arranged into sarcomeres which are the functional units of muscle.
18
Q
What are skeletal muscles usually attached to the skeleton by?
A
Tendons.
19
Q
What is a functional unit?
A
The smallest component capable of performing all the functions of that organ.
20
Q
Where is the sarcomere found?
A
Between two Z-lines which connect the thin filaments of 2 adjoining sarcomeres.
21
Q
What are the zones of a sarcomere?
A
A-band.
H-zone.
M-line.
I-band.
22
Q
What is the A-band?
A
Made up of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments.
23
Q
What is the H-zone?
A
Lighter area within the middle of the A-band where thin filaments don’t reach.
24
Q
What is the M-line?
A
Extends vertically down the middle of the A-band within the centre of the H-zone.
25
What is the I-band?
Consists of the remaining portion of thin filaments that do not project in the A-band.
26
How is muscle tension produced?
By sliding actin filaments on myosin filaments.
The sliding filaments theory is the explanation of how muscle shortens and produces force.
27
What does force generation in skeletal muscles depend upon?
It depends upon ATP-dependent interaction between thick (myosin) and thin (actin) filaments.
28
What molecule is required for both contraction and relaxation of muscle?
ATP.
29
What molecule is required to switch on cross-bridge formation?
Ca++.
30
What is excitation-contraction coupling?
The process whereby the surface action potential results in activation of the contractile structure of the muscle fibre.
31
When is Ca++ released from the lateral sacs of the sarcoplasmic reticulum in skeletal muscle?
When the surface action potential spreads down the transverse- (T-) tubules.
T-tubules are extensions of the surface membrane that dip into the muscle fibre and are found in close proximity of the sarcoplasmic reticulum.
32
What is calcium's role in muscle contraction and relaxation?
It is needed to switch on cross-bridge formation.
Muscle fibre becomes excited causing Ca++ to bind with troponin, pulling the tropomyosin complex aside to expose the cross-bridge binding site.
33
Why is ATP need during muscle contraction?
To power the cross bridges.
34
Why is ATP need during muscle relaxation?
To release the cross bridges.
To pump Ca++ back into the sarcoplasmic reticulum.
35
What is a fascicle?
Muscle fibres are grouped into bundles called fascicles.
Muscle typically contains several fascicles.
36
What is the epimysium?
The connective tissue that surrounds the muscle as a whole.
37
What is the perimysium?
The connective tissue around a single fascicle.
38
What is the endomysium?
The connective tissue around a single muscle fibre.
39
What is the tension developed by a skeletal muscle is influenced by?
The number of muscle fibres contracting.
The tension developed by each contracting muscle fibre.
40
What is motor unit recruitment?
A stronger contraction could be achieved by stimulation of more motor units.
41
How is muscle fatigue prevented?
Asynchronous motor units recruitment during submaximal contractions helps prevent muscle fatigue.
42
43
What does the tension developed by each contracting muscle fibre depend on?
Frequency of stimulation.
Summation of contractions.
Length of the muscle fibre at the onset of contraction.
Thickness of muscle fibre.
44
How can a stronger contraction in skeletal muscle be brought about?
In skeletal muscle, the duration of the action potential is much shorter than the duration of resulting twitch.
Therefore, it is possible to summate twitches to bring about a strong contraction through repetitive fast stimulation of skeletal muscle.
45
How does tetanus occur?
If a muscle fibre is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli, a maximal sustained contraction known as tetanus occurs.
46
How does a single twitch occur?
If a muscle fibre is restimulated after it has completely relaxed, the second twitch is the same magnitude as the first twitch.
47
How does twitch summation occur?
If a muscle fibre is restimulated before it has completely relaxed, the second twitch is added on to the first twitch resulting in summation.
48
Which muscle type can be tetanised?
Skeletal muscle.
## Footnote
*Remember cardiac muscle cannot be tetanised as the long refractory period prevents generation of tetanic contraction.*
49
What is an important mechanism for modulating the force of contraction in skeletal muscle?
Increasing the frequency of stimulation.
50
When can maximal tetanic contraction be achieved?
When skeletal muscle is at its optimal length.
51
What is the optimal length of skeletal muscle in the body?
The resting length of a skeletal muscle.
52
What are the two types of skeletal muscle contraction?
Isotonic contraction.
Isometric contraction.
53
What is isotonic contraction?
Used for body movements and for moving objects.
Muscle tension remains constant as the muscle length changes.
54
What is isometric contraction?
Used for supporting objects in fixed positions and for maintaining body posture.
Muscle tension develops at constant muscle length.
55
How is tension transmitted to the bone in isotonic and isometric muscle contractions?
In both isotonic and isometric contractions muscle tension is transmitted to bone via the elastic components of muscle.
56
What are the differences between the types of skeletal muscle fibres?
**Enzymatic pathways for ATP synthesis**.
**Resistance to fatigue** - muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue.
**Activity** **of myosin ATPase** - this determines the speed at which energy is made available for cross-bridge cycling, i.e. the speed of contraction.
57
What are the metabolic pathways that supply ATP in muscle fibres?
**Transfer of high energy phosphate from creatine phosphate to ADP** - immediate source for ATP.
**Oxidative phosphorylation** - main source when O2 is present.
**Glycolysis** - main source when O2 is not present.
58
What are the three main types of skeletal muscle fibre?
Slow-oxidative (type I) - aka slow-twitch fibres.
Fast-oxidative (type IIa) - aka intermediate-twitch fibres.
Fast-glycolytic (type IIx) - fast-twitch fibres.
59
What are type I skeletal muscle fibres used for?
Mainly for prolonged relatively low work aerobic activities e.g. maintenance of posture, walking.
60
What are type IIa skeletal muscle fibres used for?
Both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities e.g. jogging.
61
What are type IIx skeletal muscle fibres used for?
Anaerobic metabolism and are mainly used for short-term high-intensity activities e.g. jumping
62
What is a reflex?
A stereotyped response to a specific stimulus.
63
What is the simplest form of coordinated movement?
Reflex actions.
64
What is the simplest monosynaptic spinal reflex?
The stretch reflex.
65
Why is the stretch reflex important?
It serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of the muscle.
66
What is the mechanism of the stretch reflex?
The sensory receptor is the muscle spindle and is activated by muscle stretch.
Stretching the muscle spindle increases firing in the afferent neuron.
The afferent neurons synapse in the spinal cord with the alpha motor neurons (efferent limb of the stretch reflex) that innervated the stretched muscle.
Activation of the reflex results in contraction of stretched muscle.
67
What is the stretch reflex coordinated by?
Simultaneous relaxation of antagonist muscle.
68
How is the stretch reflex elicited?
By tapping the muscle tendon with a rubber hammer as it rapidly stretches the muscle resulting in its contraction.
E.g. patellar tendon reflex (knee jerk) -\> contraction of the quadriceps femoris.
69
What spinal segment and peripheral nerve are stimulated by the knee jerk reflex?
L3-4.
Femoral nerve.
70
What spinal segment and peripheral nerve are stimulated by the ankle jerk reflex?
S1-2.
Tibial nerve.
71
What spinal segment and peripheral nerve are stimulated by the biceps jerk reflex?
C5-6.
Musculocutaneous nerve.
72
What spinal segment and peripheral nerve are stimulated by the brachioradialis reflex?
C5-6.
Radial nerve.
73
What spinal segment and peripheral nerve are stimulated by the triceps jerk reflex?
C6-7.
Radial nerve.
74
What are muscle spindles?
Sensory receptors for stretch reflex.
Collection of specialised muscle fibres.
Known as intrafusal fibres.
Have sensory nerve endings known as annulospiral fibres.
75
Where are muscle spindles found?
Within the belly of muscles and they run parallel to ordinary muscle fibres (extrafusal fibres).
76
What happens to the discharge from muscle spindles as the muscle is stretched?
The discharge from the muscle spindles sensory endings increases as the muscle (and hence the spindles) is stretched.
77
What is efferent neurons supple muscle spindles?
Gamma motor neurons.
78
What is the purpose of the gamma motor neurons that supply muscle spindles?
They adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shortens during muscle contraction.
79
What can cause impairment of skeletal muscle function?
Intrinsic disease of muscle e.g. genetically determined/acquired myopathies.
Disease of the neuromuscular junction.
Disease of lower motor neurons which supply the muscle.
Disruption of input to motor nerves e.g. upper motor neuron diseases.
80
What are the symptoms of muscle disease?
Muscle weakness/tiredness.
Delayed relaxation after voluntary contraction (myotonia).
Muscle pain (myalgia).
Muscle stiffness.
81
What are examples of genetically determined myopathies?
Congenital myopathies - characteristic of microscopic changes leading to reduced contractile ability of muscles.
Chronic degeneration of contractile elements - muscular dystrophy.
Abnormalities in muscle membrane channels - myotonia.
82
What are examples of acquired myopathies?
Inflammatory myopathies e.g. polyarthritis, inclusion body myositis.
Non-inflammatory myopathies e.g. fibromyalgia.
Endocrine myopathies e.g. Cushing syndrome, thyroid disease.
Toxic myopathies e.g. alcohol, statins.
83
What are useful investigations in neuromuscular disease?
Electromyography (EMG).
Nerve conduction studies.
Muscle enzymes (creatine kinase).
Inflammatory markers (CRP, plasma viscosity).
Muscle biopsy.
84
How does electromyography work?
Electrodes detect the presence of muscular activity.
Records frequency and amplitude of muscle fibres action potentials.
EMG findings are not pathopneumonic of specific disease so they will not provide a definitive diagnosis.
EMG helps differentiate primary muscle disease from muscle weakness caused by neurological disease.
Nerve conduction studies usually done at the same time as an EMG.
85
What is a fibrous joint?
Bones united by fibrous tissues.
Doesn't allow movement.
E.g. skull bone joints.
86
What are synovial joints?
Bones separated by a cavity, containing synovial fluid, and united by a fibrous capsule.
E.g. knee joint, hip joint.
87
What lines the inner aspect of fibrous capsules?
Synovial membrane - vascular connective tissue with capillary networks and lymphatics.
88
What are fibroblasts and where are they found?
Synovial cells found within the synovial membrane that secrete synovial fluid.
89
What covers the articular surfaces of bones within synovial joints?
Cartilage.
90
What classifications of synovial joint are there?
Simple - one pair of articular surfaces, e.g. MCP joint.
Compound - more than one pair of articular surfaces, e.g. elbow.
91
What are the physiological functions of joints?
To serve the functional requirements of the musculoskeletal system:
* Structural support.
* Purposeful motion.
92
What are the roles of joints during purposeful motion?
Stress distribution - *NB greatest share of loading energy is undertaken by muscles and tendons crossing each joint.*
Confer stability.
Joint lubrication.
93
What features of a joint confer stability?
**Shape** **of the** **articular** **component.**
**Ligaments** - provide a second major stabilising influence.
**Synovial fluid** - acts as an adhesive seal that freely permits sliding motions between cartilaginous surfaces.
94
How are joints lubricated?
Cartilage interstitial fluid.
Synovium-derived hyaluronic acid (mucin) - polymer of disaccharides.
Synovium-derived lubrcin (glycoprotein).
95
What are the function of synovial fluid?
Lubricates joint.
Facilitates joint movements - reduces friction.
Helps minimise wear-and-tear of joints through efficient lubrication.
Aids in the nutrition of cartilage.
Supplies the chondrocytes with oxygen and nutrients and removes CO2 and waste products.
96
Why does synovial fluid have a high viscosity?
Mainly due to the presence of hyaluronic acid (mucin) produced by the synovial cells.
97
What cells are normally found in synovial fluid?
Few mononuclear leucocytes.
98
What viscosity and elasticity of synovial fluid is associated with rapid joint movement?
Rapid movement is associated with decreased viscosity and increased elasticity.
99
Which disease causes viscosity and elasticity of synovial fluid to become defective in an affected joint?
Osteoarthritis.
100
What does synovial fluid look like?
Clear and colourless.
101
What findings of synovial fluid would indicate an inflammatory or septic arthritis?
Increased WBC count in the synovial fluid.
102
When would synovial fluid appear red?
In a traumatic synovial tap and haemorrhagic arthritis.
103
What does it indicate if synovial viscosity is high, colourless, transparent with a total WCC of \<200/mm3 and \<25/mm3 PMN leucocytes?
Normal synovial fluid.
104
What does it indicate if synovial viscosity is low, straw to yellow, translucent with a total WCC of 2000-75000/mm3 and \>50/mm3 PMN leucocytes?
Inflammatory synovial fluid.
105
What does it indicate if synovial viscosity is variable, colour is variable, opaque with a total WCC of \>100000/mm3 and \>75/mm3 PMN leucocytes?
Septic synovial fluid.
106
Label the types of synovial fluid.
A - normal as it is viscous and clear.
B - joint with mild synovial inflammation.
C - joint with mild synovial inflammation and the blood stain is caused by trauma.
D - severely inflamed joint as the fluid is thin and opaque due to a very high polymorph count.
107
What are the main functions of articular cartilage?
Provides a low friction lubricated gliding surface - helps prevent wear-and-tear of joints.
Distributes contact pressure to subchondral bone.
Composition of the cartilage ECM and the interaction between the fluid and solid phase of cartilage plays a significant role in determining the mechanical properties of cartilage.
108
What is articular cartilage composed of?
Hyaline - elastic and sponge-like properties.
109
What is the ECM of articular cartilage composed of?
Water (70%).
Type II collagen (20%) - elastic behaviour of cartilage.
Proteoglycans (10%).
110
What mechanical properties of the major cartilage joints does water contribute to?
Maintains the resiliency of the tissue and contributes to the nutrition and lubrication system.
Unevenly distributed - higher near the articular surface.
Cartilage water content decreases with age.
111
What mechanical properties of the major cartilage joints does collagen contribute to?
Provides tensile stiffness.
Maintains cartilage architecture.
Mainly type II collagen which decreases with age.
112
What mechanical properties of the major cartilage joints does proteoglycan contribute to?
Responsible for the compressive properties associated with load bearing.
Highest concentration is found in the middle and deep zones.
113
What cell synthesises, organises and degrades the ECM of cartilage?
Chondrocytes.
114
Since articular cartilage is avascular, how does it receive nutrients and oxygen?
Via the synovial fluid.
115
What would happen if the rate of ECM degradation exceeds the rate of synthesis or changes in the relative amounts of the major components of cartilage occur?
Joint disease would occur - osteoarthritis.
There would be changes in the mechanical properties of cartilage.
116
How do catabolic factors cause cartilage matrix turnover?
Stimulate proteolytic enzymes and inhibit proteoglycan synthesis via TNF-alpha and IL-1.
117
How do anabolic factors cause cartilage matrix turnover?
Stimulate proteoglycan synthesis and counteract the effects of IL-1 via TGF-beta and insulin-like growth factor 1.
118
What are markers of cartilage degradation?
**Serum and synovial keratin sulphate** - increased levels indicate breakdown; level increases with age and patients with osteoarthritis.
**Type II collagen in synovial fluid** - increased levels indicate cartilage breakdown; useful in evaluating cartilage erosion in osteoarthritis and rheumatoid arthritis.
119
What is pain?
An unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage.
120
What are the distinct processes in the physiology of pain?
Transduction.
Transmission.
Modulation.
Perception.
121
What is transduction?
Translation of noxious stimulus into electrical activity at the peripheral nociceptor.
122
What is transmission?
Propagation of pain signals as nerve impulses through the nervous system.
123
What is modulation?
Modification/hindering of pain transmission in the nervous system, e.g. by inhibitory neurotransmitters like endogenous opioids.
124
What is perception?
Conscious experience of pain.
Causes the physiological and behavioural responses.
125
What are nociceptors?
Specific primary sensory afferent neurons normally activated by intense noxious stimuli e.g. mechanical, thermal or chemical.
First-order neurons that relay information to second-order neurons in the CNS by chemical synaptic transmission.
126
127
What neurotransmitters are released by first-order nociceptive neurons and where does this occur?
Glutamate, substance P, neurokinin A.
Dorsal horn of the spinal cord.
128
Where do first-order nociceptive neurons synapse with second-order neurons?
Dorsal horn of the spinal cord.
129
What is the spinothalamic tract involved in?
Pain perception (location and intensity).
130
What is the spinoreticular tract involved in?
Autonomic responses to pain, arousal, emotional responses and fear of pain.
131
What is the path of second-order neurons in the nociceptive pathway?
Second-order neurons ascend the spinal cord in the anterolateral system and terminate in the thalamus.
132
What is the course of third order neurons in the nociceptive pathway?
Originate in the thalamus and relay sensory information to the primary sensory cortex.
133
What fibres are nociceptors comprised of?
Adelta myelinated and C unmyelinated fibres.
134
What information do Adelta fibres transmit?
Mechanical and thermal nociceptive information as they respond to noxious mechanical and thermal stimuli.
135
What information fo C fibres transmit?
C fibres respond to all noxious stimuli.
136
What neural fibre mediates fast pain and why?
Adelta because it is thinly myelinated and can transmit information faster than unmyelinated C fibres.
137
What neural fibre mediates slow pain and why?
C fibres because they transmit information slower the myelinated Adelta fibres.
138
What are the characteristics of first or fast-mediated pain?
139
What are the characteristics of second or slow-mediated pain?
140
How can pain be classified?
**Mechanisms** - nociceptive, inflammatory, pathological (neuropathic/dysfunctional).
**Time course** - acute, chronic, breakthrough pain.
**Severity** - mild, moderate, severe.
**Source of origin** - somatic, visceral.
141
What is nociceptive pain?
Normal response to injury of tissues by noxious stimuli.
Adaptive.
Functions as an early warning physiological protective system to detect and avoid noxious stimuli.
142
What can provoke nociceptive pain?
Intense stimulation of nociceptors by noxious stimuli e.g. mechanical, chemical, thermal.
143
What is inflammatory pain?
Caused by activation of the immune system by tissue injury/infection.
Adaptive - promotes repair until healing occurs.
Discourages physical contract with the affected part and also discourages movement e.g. of a joint.
144
What activates inflammatory pain?
Pain is activated by a variety of mediates released at the site of inflammation by leucocytes, vascular endothelium and tissue-resident mast cells.
145
What is hyperalgesia?
Causes heightened pain sensitive to noxious stimuli.
146
What is allodynia?
Pain sensitivity to innocuous stimuli (stimuli that don't normally cause pain sensation).
147
What is neuropathic pain?
Caused by damage to neural tissue.
Examples include compression neuropathies, peripheral neuropathies, central pain (following stroke or spinal injury), post-herpetic neuralgia, trigeminal neuralgia, phantom limb.
Can be perceived as burning, shooting, numbness, pins and needles - may be less localised.
148
What is dysfunctional pathological pain?
No identifiable damage or inflammation.
E.g. fibromyalgia, IBS, tension headache, TMJ joint disease, interstitial cystitis.
Not a protective pain but maladaptive.
149
What medication does dysfunctional pathological pain respond to?
Anti-depressants, anti-epileptics (drugs not originally developed for pain).
*Doesn't respond to simple analgesia.*
150
What is referred pain?
Pain developed in one part of the body felt in another structure away from the place of its development.
## Footnote
*Deep/visceral pain can be felt as referred pain.*
151
What causes referred pain?
Convergence of nociceptive visceral and skin afferents upon the same spinothalamic neurons at the same spinal level.
Leads to the feeling of the pain in an area of skin which is distant from the internal organ where the pain originates.
152
What are common sites of referred pain?
