Physiology Flashcards
What are the physiological functions of skeletal muscle?
- Posture
- Movement (delibrate)
- Respiratory movements
- Heat (shivering)
- Metabolism (contribution to whole body metabolism; lots of traffic through muscles)
Skeletal muscle is striated T/F?
TRUE Skeletal muscle is striated
Cardiac muscle is straited T/F?
TRUE Cardiac muscle is striated
Of the three groups of muscle types; which are subject to voluntary control?
Only skeletal muscle is subject to voluntary control. Cardiac and smooth muscle are involuntary muscles.
How is skeletal muscle contraction initiated?
Skeletal muscle contraction is initiated by motor neuron stimulation (neurogenic mechanisms)
How is neurogenic initiation of skeletal muscle contraction different to neurogenic initation of cardiac muscle contraction?
In skeletal muscle there is no continuity of cytoplasm between nerve and skeletal muscle cells :. there’s neurotransmitter (acetylcholine) released at neuromuscular junction
What is a motor unit?
The motor unit is a single alpha motor neuron and all skeletal muscle fibres it innervates.
What is the ratio of muscle fibres per motor unit of a ‘fine movement’ organ/group of muscles compared to that of a ‘power’ organ/group of muscles?
Muscles which serve fine movements have fewer muscle fibres per motor unit. e.g. external eye muscles, muscles of facial expression or intrinsic hand muscles
What is a muscle fibre?
A muscle fibre is considered a single cell. Muscle fibres are made from myofibrils which are made from sarcomeres/ One whole muscle/organ is made up of motor units which is a single alpha motor neuron and all skeletal muscle fibres it innervates
What is a skeletal muscle made up of?
Skeletal muscle consists of parallel muscle fibres bundled by connective tissue
How do skeletal muscles attach to skeleton?
Skeletal muscles are usually attached to the skeleton by means of tendons
What is a myofibril?
A myofibril is a specialised contractile intracellular structure.
What are myofibrils made up of?
Myofibrils have alternating segments of thick and thin protein filaments
Out of actin and myosin which are responsible for darker and lighter appearance in histology slides.
Actin (thin filaments) causes lighter appearance in myofibrils and fibres Myocin (thick filaments) causes the darker appearance
How are actin and myocin arranged?
Within each myofibril: actin and myosin are arranged into sarcomeres- these are the functional units of muscles
What are sarcomeres?
SARCOMERES are the FUNCTIONAL UNITS of MUSCLE
How is a functional unit described?
The functional unit of any organ is the smallest component capable of performing all the functions of that organ e.g. the sarcomere is the functional unit of skeletal muscle
What are the 4 zones of a sarcomere?
- A-Band 2. H-zone 3. M-Line 4. I-Band
Define the A-Band
The A-Band is made up of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments
Define H-Zone
The H-Zone is a lighter area within middle of A-Band where thin filaments don’t reach
Define M-Line
The M-Line extends vertically down middle of A-Band within the centre of H-Zone
Define I-Band
I-Band consists of remaining portion of thin filaments that do not project in A-Band
Define excitation contraction coupling
Excitation contraction coupling is the process whereby the surface action potential results in activation of the contractile structures of the muscle fibre
How does excitation contraction coupling occur in skeletal muscle?
Calcium is released from the lateral sacs of the sarcoplasmic reticulum when the surface action potential spreads down the T-tubules
What are the T-tubules?
T-tubules are extensions of the surface membrane that dip into the muscle fibre
ATP is required for both contraction and relaxation. T/F
TRUE ATP is required for both contraction and relaxation
Why is ATP is needed?
ATP is needed during muscle contraction: - to power cross bridges ATP is needed during relaxed to: - release cross bridges - to pump Ca2+ back into sarcoplasmic reticilum - rigor mortis (a sign of death)
What is the tension developed by a skeletal muscle influenced by?
1) Number of muscle fibres (remember they’re organised in a motor unit) contracting 2) Tension developed by each contracting muscle fibre
Describe motor unit recruitment
A stronger contraction can be achieved by stimulation of more motor units
How is muscle fatigue prevented?
Asynchronous motor units recruitment during submaximal contractions help prevent muscle fatigue
What factors affect the tension developed by each contracting muscle fibre?
1) Freq. of stimulation and summation of contractions 2) Length of muscle fibre at onset of contraction 3) Thickness of muscle fibre
What is meant by ‘freq. of stimulation and summation of contractions’ in regards to muscle fibre tension?
It is therefore possible to summate twitches to bring about a stronger contraction through repetitive fast stimulation of skeletal muscle
Define tetanus (in the contest of physiology)
‘a state of sustained contraction of a muscle during which the muslce does not relax to its initial length or tension,induced by a rapid succession of stimuli’
- dictionary.com
Why can tetanus not occur in cardiac muscle?
The refractory period!
Maximum muscle tension develops at optimum muscle length
Maximum muscle tension develops at optimum muscle length
(I know this isn’t a question but just learn it off please)
How is skeletal muscle length tension relationship explained by the sliding filament mechanism?
In the body the resting length of skeletal muscle is approximately its optimal length
How is skeletal muscle tension transferred to bone?
via stretching and tightening of muscle connective tissue and tendon
- the cross bridge cycling of skeletal muscle is the contractile component
- connective tissue and tendon is the elastic component
What are the 2 primary types of skeletal muscle contraction?
- Isotonic contraction
- Isometric contraction
In both isotonic and isometric contractions muscle tension is transmitted to bone via the elastic components of muscle
What decides which type of skeletal muscle contraction is used?
Whether or not the muscle changes length
Describe isotonic contraction
Used for:
- body movements
- moving objects
muscle tension remains constant as the muscle length changes
Describe isometric contraction
used for:
- supporting objects in fixed positions
- maintaing body posture
Muscle tension develops at constant muscle length
‘Muscle tension remains constant as the muscle length changes’
Is this T/F for isotonic contraction?
True
In isotonic contraction muscle tension remains constant as the muscle length changes
‘Muscle tension develops at constant muscle length’
Is this T/F for isometric contraction?
True
In isometric contraction muscle tension develops at constant muscle length
How does load affect the velocity of muscle shortening?
The velocity of muscle shortening decreases as the load increases
Are skeletal muscles fibres all the same?
No they’re not the same
List the main differences between different types of skeletal muscle fibres
- The enzymatic pathways for ATP synthesis
- The resistance to fatigue
- muscle fibres with greater capacity to synthesis ATP are more resistant to fatigue
3. The activity of myosin ATPase - this determines the speed at which energy is made available for cross bridge cycling i.e. the speed of contraction
Each motor unit usually contains one type of muscle fibres
How many different types of skeletal muscle fibres will one motor unit typically have?
Each motor unit usually contains one type of muscle fibre
What are the metabolic pathways that supply ATP in muscle fibre?
- Transfer of high energy phosphate from creatine phosphate to ADP
- immediate source
- Oxidative phosphorylation
- main source when O2 is present
- Glycolysis
- main source when O2 is not present
How many types of skeletal muscle fibres are there?
- Slow-oxidative (Type 1)
- Fast-oxidative (Type IIa)
- Fast- glycolytic (Type IIx)
Describe type 1 skeletal muscle fibres
Slow oxidative type 1 fibres
a.k.a. slow-twitch fibres
mainly for prolonged relatively low work aerobic activity
e.g. maintenance of posture, walking
Describe type IIa skeletal muscle fibres
Fast oxidative (Type IIa) fibres
a.k.a. intermediate twitch fibres
aerobic and anaerobic metabolism
prolonged relatively moderate activities
e.g. jogging
Describe type IIx skeletal muscle fibres
Fast glycolytic (Type IIx) fibres
a. k.a. fast-twitch fibres
* anaerobic* metabolism
* short-term high intensity* activities e.g. jumping
Define the term ‘reflex action’
‘A reflexed action is stereotyped response to a specific stimulus’
- reflex actions are the simplest form of coordinated movement
Describe the stretch reflex
The stretch reflex is the simplest monosynaptic spinal reflex
Why are the neural pathways for reflexes important clinically?
The neural pathways for reflexes are importatn for localising lesions in the motor system
List examples of tendon reflexes that can be elicited y rubber hammer
- Knee jerk
- Ankle jerk
- Biceps jerk
- Brachioradialis
- Triceps jerk
What spinal segment and peripheral nerve is the knee jerk testing?
knee jerk:
L3, L4
Femoral nerve
What spinal segment and peripheral nerve does the ankle jerk test?
Ankle jerk:
S1, S2
Tibial Nerve
What spinal segment and peripheral nerve does the biceps jerk test?
Biceps jerk:
C5, C6
Musculocutaenous nerve
What spinal segment and peripheral nerve does the brachioradialis test?
Brachioradialis:
C5, C6
radial nerve
What spinal segment and peripheral nerve does the triceps jerk test?
Triceps jerk:
C6, C7
Radial nerve
Define and describe muscle spindles
Muscle spindles are the sensory receptors for stretch reflex
- muscle spindles are collection of specialised muscle fibres
- a.k.a. intrafusal fibres
- ordinary muscle fibres= extrafusal fibres
- muscle spindles have sensory nerve endings known as annulospiral fibres
Where are muscle spindles found?
Muscle spindles are found within the belly of muscles and run parallel to ordinary muscle fibres (extrafusal fibres)
The contraction of intrafusal fibres contributes to the overal strength of muscle contraction
T/F?
FALSE
The contraction of intrafusal fibres does NOT contribute to the overall strength of muscle contraction
What could cause impairment of muscle function?
- Intrinsic disease of muscle
- Disease of NMJ
- Disease of lower motor neurons which supply the muscle
- Disruption of input to motor nerves (e.g. upper motor neuron disease
neuromuscular and neurological diseases will be covered during the neurology course in Y3
What are two main groups of diseases that cause intrinsic muscle disease?
- genetically determined myopathies
- acquired myopathies
List some genetically determined myopathies
- Congenital myopathies: characeristic microscopic changes leading to reduced contractile ability of muscles
- Chronic degeneration of contractile elements- muscular dystrophy
- Abnormalities in muscle membrane ion channels e.g. myotonia
List some acquired myopathies
- Inflammatory myopathies e.g. polymyositis, inclusion body myositis
- Non-inflammatory myopathies e.g. fibromyalgia
- Endocrine myopathies e.g. Cushing syndrome, thyroid disease
- Toxic myopathies e.g. alcohol, statins
List some symptoms of muscle disease:
- muscle weakness/ tiredness
- delayed relaxation after voluntary contraction (myotonia)
- muscle pain (myalgia)
- muscle stiffness
Discuss EMG; a useful investigation in neuromuscular disease
- Electromyography (EMG)
- electrodes detect the presence of muscular activity
- records freq. and amplitude of muscle fibres action potentials
- EMG findings not pathognomonic of specific diseasse- will not provide the 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
List some useful investigations in neuromuscular disease
- EMG
- Nerve conduction studies; determine the functional integrity of peripheral nerves
- Muscle enzymes; creatine kinase
- inflammatory markers; C-reactive protein (CRP), plasma viscosity (PV)
- Muscle biopsy
Define the 3 main types of joints in the human skeleton and give examples
- Synovial
- bones separated by cavity containing synovial fluid and united by a fibrous capsule (& other extra-articular structures e.g. ligaments, tendons, and bursae)
- synovial membrane is vascular connective tissue with capillary networks & lymphatics. contains synovial cells which produces synovial fluid
- articular surfaces of bones covered with cartilage
- Fibrous
- no movement
- skull
- Cartilaginous
- limited movement
- intervertebral discs
- pubic symphsis
- part of sacroiliac joints
- costochondral joints
What are the 2 subtypes of synovial joints?
Simple Synovial Joint
- one pair of articular surfaces
- metacarpophalangeal joint
Compound Synovial Joint
- more than one pair of articular surfaces
- elbow joint
What are the physiological functions of joints?
To serve the functional requirements of the MSK system
- structural support
- purposeful motion
List the role of joints during purposeful motion
- Stress distribution
- Confer stability
- Joint lubrication
Discuss how joints confer stabiltiy during purposeful motion
- shape of the articular component e.g. hip joint
- ligaments provide a second major stabilising influence
- synovial fluid acts as an adhesive seal that freeely permits sliding motion between cartilaginous surfaces
Discuss how joint lubrication is provided during purposeful motion
Joint lubrication is provided by:
- cartilage interstitial fluid
- synovium- derived hyaluronic acid (mucin)- a polymer of disaccharides
- synovium- derived lubrcin- a glycoprotein
What are the functions of synovial fluid?
- Lubricates the joint
- Facilities joint movements- reduces fricion
- Helps minimise wear-and-tear of joints through efficient lubrication
- Aids in the nutrition of articular cartilage
- Supplies the chondrocytes (cartilage cells) with O2 and nutrients and remove CO2 and waste products
What are the characteristics of the synovial fluid?
- fills joint cavity (<3.5ml in adult knee)
- continuously replenished and absorbed by the synovial membrane i.e. not a static poole
- high viscosity
- mainly due to hyaluronic acid (mucin) produced by the synovial cells
- viscosity of the synovial fluid varies with joint movement
- other constituents (e.g. uric acid) are derviedby dialysis of blood plasma
- contains few cells (mainly mononuclear leucocytes)
Discuss changes in elasticity and viscosity of synovial fluid during joint movement
- viscosity and elasticity of synovial CHANGE during joint movement
RAPID movement is associated DECREASED VISCOSITY and INCREASED ELASTICITY
- these properties of synovial fluid become defective in a diseased joint e.g. osteoarthritis
Describe appearance and cell count of normal synovial fluid
- clear and colourless
- <200 WBC/mm3 of which polymorphs are usually <25mm3
Describe appearance and cell count of inflammatory synovial fluid
- straw to yellow
- translucent
- WBC/mm3 = 2,000-75,000 of which polymorphs are <25/mm3
Describe the appearance and WBC of septic synovial fluid
- variable viscosity and colour
- opaque
- WBC often >100,000/mm3 of which polymorphs are >75/mm3
Explain the main functions of articular cartilage
- provides a low friction lubricated gliding surface which helps prevent wear-and-tear of joints
- distributes contact pressure to subchodral bone
- the composition of the cartilage ECM and the interaction between the fluid and solid phase of the cartilage plays a significant role in determining the mechanical properties of cartilage
Describe the structure of articular cartilage
Discuss articular cartilage
- usually hyaline
- elastic and sponge-like property
- covers articular surfaces
- special extracellular matrix made of:
- predominantly of water (70%),
- collagen (20%)- mainly type II contributes most to elastic behaviour of cartilage,
- and proteoglycans (10%)
Discuss the mechanical properties of water as a major cartilage component
WATER
- accounts for 70% of the cartilage wet weight
- unevenly distributed, highest (80%) near the articular surface
- cartilage water content decreases with age
- maintain the resiliency of the tissue and contributes to the nutrition and lubrication system
Discuss the mechanical properties of collagen as a component of cartilage
COLLAGEN
- accounts for 20% of the cartilage wet weight
- mainly type II which decreases with age
- maintain cartilage architecture
- provides tensile stiffness and strength
Discuss the mechanical properties of proteoglycan as a component of cartilage
PROTEOGLYCAN
- accounts for 10% of cartilage wet weight
- highest conc. is found in the middle and deep zone
- composed mainly of glycosaminoglycan e.g. chondroitin sulphate
- composition of cartilage proteoglycan changes with age e.g. chondrodroitin decreases with age
- responsible for the compressive properties associated with load bearing
How much of total cartilage volume is taken up by extracellular matrix and chondrocytes?
- cartilage ECM >98% of total cartilage vol.
- chondrocytes <2%
What is the role of chondrocytes regarding the ECM?
The ECM is synthesized, organised, degraded and maintained by chondrocytes
The rate of ECM degradation doesn’t exceed the rate at which it is replaced
‘The articular cartilage is avascular’
T/F?
True
How do chondrocytes receive nutrients and O2?
Chondrocytes receive O2 and nutrients via the synovial fluid
State 2 ways disease could occur in cartilage of a joint
Changes in the relative amounts of the three major components of cartilage (i.e. wayer, collagen, and proteoglycans) would change the mechanical properties of cartilage
Joint disease would also occur if the rate of ECM degradation exceeds the rate of its synthesis
Discuss catabolic and anabolic factors of cartilage matrix turnover
- Catabolic factors
- stimulate proteolytic enzymes and inhibit proteoglycan synthesis
- tumour necrosis factor (TNFalpha)
- interleukin (IL-1)
- stimulate proteolytic enzymes and inhibit proteoglycan synthesis
- Anabolic factors
- stimulate proteoglycan synthesis and counteract effects of IL-1
- tumour growth factor (TGFbeta)
- insulin-like growth factor (IGF-1)
- stimulate proteoglycan synthesis and counteract effects of IL-1
What are the markers of cartilage degradation
- serum and synovial keratin sulphate
- increased levels indicate cartilage breakdown
- level increases with age and patients with osteoarthritis
- type II collagen in synovial fluid
- increased levels indicaate cartilage breakdown
- useful in evaluation cartilage erosion e.g. in oesteoarthritis and rheumatoid arthritis
List some of the things that can go wrong in a joint
- cartilage and synovial composition and function deteriorate with age and repeated wear and tear giving rise to osteoarthritis
- synovial cell proliferation and inflammation cause rheumatoid arthritis
- deposition of salt crystals e.g. uric acid can cause gouty arthritis
- injury and inflammation to periarticular structures causes soft tissue rheumatism e.g. injury to the tendon causes tendonitis
What are the effects on the subchondral bone following cartilage wear and tear?
cyst formation
sclerosis in subchondral bone
osteophyte formation
Can you recognise synovial proliferation and inflammation in rheumatoid arthritis in histology
Can you recognise synovial proliferation and inflammation in rheumatoid arthritis in arthroscope?
What’s the difference between gout and pseudo-gout?
- deposition of needle shaped uric acid crystals causes gouty arthritis
- deposition of rhomboid shaped calcium pyrophosphate crystals causes pseudo-gout
Define pain
The International Association for the Study of Pain defines pain as:
‘An unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage’
Define transduction
transduction is the translation of noxius stimulus into electrical activity at the peripheral nociceptor
Define transmission
Transmission is the propagation of pain sugnal as nerve impulses through the nervous system
Define modulation
Modulation is the modificaiton/hindering of pain transmission in the nervous system e.g. by inhibitory neurotransmitters like endogenous opioids
Define perception
Perception is the conscious experience of pain. Causes physiological and behavioural responses
Define nociceptors
Nociceptors are specific primary sensory afferent neurones normally activated by intense noxious stimuli (e.g. mechanical, thermal or chemical)
- nociceptors are first order neurones that relay information to second order neurones in the CNS by chemical synaptic transmission
Describe the nociceptive pathway
Second order neurones ascend the spinal cord in the anterolateral system (terminate in the thalamus) comprising mainly of the spinothalamic tract and spinoreticular tract
From the thalamus, sensory information is relayed (third order neurones) to the primary sensory cortex
What is the role of the spinothalamic tract?
The spinothalamic tract is involved in pain perception
(location, intensity)
What is the role of the spinoreticular tract?
The spinoreticular tract is involved in autonomic responses to pain, arousal, emotional responses, fear of pain
What are the 2 subtypes of nociceptors?
A-gamma fibres
and
C-fibres
Describe the A-gamma fibres
A-gamma fibres are mechanical/thermal nociceptors that are thinly myelinated (conduction velocity 6-30ms-1)
Responds to noxious mechanical and thermal stimuli
Describe C-fibres
C-fibres are nociceptors that are myelinated (conduction velocity of 0.5-2.0ms-1) collectively they respond to all noxius stimuli (e.g. they are polymodal)
Mediate ‘second’, or slow, pain
Compare A-gamma fibres and C-fibres
- A-gamma causes first pain sensation which feels lancinating, stabbing, pricking sensations
- C-fibres causes the second ‘wave’ of pain which feels like burning, throbbing, cramping, aching sensations
*
How can pain be classified?
- Mechanisms (pain mechanisms may overlap): e.g. nociceptive, inflammatory, pathological (neuropathic or dysfunctional)
- Time course: e.g. acute, chronic, breakthrough pain
- Severity: e.g. mild, moderate, severe
- Source of origin: e.g. somatic or visceral
Discuss nociceptive pain
This represents normal response to injury of tissues by damaging stimuli
- only provoked by intense stimulation of nociceptors by noxius stimuli e.g. mechanical, chemical and thermal
- functions as early warning physiological protective system to detect and avoid noxious stimuli
Discuss inflammatory pain
Caused by activation of the immune system by tissue injury or infection
- pain is activated by a variety of mediators released at the site of inflammation by leucocytes, vascular endothelium and tissue resident mast cells
- discourages physical contact (with the affected part) and also discourages movement (e.g. of a joint)
What does inflammatory pain cause for a person?
(other than pain)
- Causes heightened pain sensitivity to noxious stimuli (hyperalgesia)
- Causes pain sensitivity to innocuous stimuli (allodynia)
If inflammation is pathological, why is inflammatory pain different to pathological pain?
The way this classification is done is that inflammation serves a purpose and is :. different to pathological pain
It is part of the fighting off and recovery process
Discuss pathological pain; neuropathic
Neuropathic pain is caused by damage to neural tissue
Examples include:
- compression neuropathies
- peripheral neuropathies
- central pain (following stroke or spinal injury)
- postherpetic neuralgia
- trigeminal neuralgia
- phantom limb
How may neuropathic pathological pain be described?
- burning
- shooting
- numbness
- pins
- needles
May be less localised
Discuss pathological pain; dysfunctional
In dysfunctional pain there is no identifiable damage or inflammation
e.g:
- fibromyalgia
- irritable bowel syndrome
- tension headache
- temperomandibular joint disease
- interstitial cystitis
Pain cannot be attributed to inflammation or nerve damage or any other cause really. We’re clueless
How is pathological pain treated?
Simple analgesics usually not very effective in pathological pain (neuropathic or dysfunctional)
Sometimes treated with drugs not orginally developed for pain (e.g. antidepressatns or anti-epileptics)
What is referred pain?
Pain developed in one part of the body felt in another structure away from the place of its development
Where does referred pain usually actually come from?
Pain originating in superficial structures is usually not referred
Deep or visceral pain can be felt as referred pain
What causes referred pain?
Referred pain is caused by convergence of nociceptive visceral and skin afferents upon the same spinothalamic neurons at the same spinal level
This leads to the feeling of the pain in an area of the skin which is distant from the internal organ where the pain originates
List some sites of referred pain
Skeletal muscle fibres usually extend the entire length of muscle. T/F?
True Skeletal muscle fibres usually extend the entire length of muscle.
