Physiology Flashcards
What two muscle types are striated?
Skeletal and cardiac
What is muscle striation caused by?
Alternating dark bands of myocin (thick filaments) and light bands of actin (thin filaments)
What are skeletal muscle fibres organised into?
Motor units
What is a motor unit?
A single alpha motor neuron and all the skeletal muscle fibres it innervates.
What is the relationship between number of muscle fibres per motor unit and function of muscle?
Muscles which serve fine movements have fewer fibres per motor unit.
Give three examples of fine movement muscles?
- External eye muscles
- Muscles of facial expression
- Intrinsic hand muscles
What makes up myofibrils?
Sacromeres
What type of initiation of contraction is involved in skeletal muscle?
Neurogenic
What type of initiation of contraction is involved in cardiac muscle?
Myogenic
What type of muscle has motor units, no gap junctions but has neuromuscular junctions present?
Skeletal
What type of muscle has no neuromuscular junction but has gap junctions?
Cardiac
In skeletal muscle contraction - where does the calcium come entirely from?
Sarcoplasmic reticulum
In cardiac muscle contraction - where does the calcium come from?
ECF and sarcoplasmic reticulum
What is the process whereby the surface action potential results in activation of the contractile mechanism of the muscle fibre?
Excitation contraction coupling
In skeletal muscle - when is the calcium released from the lateral sacs of the sarcoplasmic reticulum?
When the surface action potential spreads down the transverse T-tubules
What is the transmitter at the neuromuscular junction?
Acetylcholine
What is the functional unit of skeletal muscle?
Sacromeres
What is the smallest component capable of performing all the function of that organ called?
Functional unit
Where is the sacromere found between?
Two Z-lines
What do Z-lines connect?
The thin filaments of 2 adjoining sacromeres
What is the A-band made up from?
Thick filaments along with portions of thin filaments that overlap in both ends of thick filaments
What is the name for the lighter area within middle of A-band where thin filaments do not reach?
H-zone
What line extends vertically down the middle of A-band within centre of H-zone?
M-line
What does the I-band consist of?
Remaining portion of thin filaments that do not project in A-band
How is muscle tension produced?
By sliding of actin filaments on myocin filaments
What is required for both contraction and relaxation of muscle fibres?
ATP
What is required to switch on cross bridge formation?
Calcium
What two primary factors does gradation of skeletal muscle tension depend on?
- Number of muscle fibres contracting within the muscle
2. Tension developed by each contracting muscle fibre
What allows simultaneous contraction of a number of muscle fibres?
Motor units
A stronger contraction could be achieved by stimulation of more motor units - what is this known as?
Motor unit recruitment
During submaximal contractions - what helps prevent muscle fatigue?
A synchronous motor units
What three factors does tension developed by each contracting muscle fibre depend on?
- Frequency of stimulation
- Summation of contractions
- Length of muscle fibres
In skeletal muscle: what is the duration of action potential much shorter than?
Duration of resulting twitch
What does repetitive fast stimulation of skeletal muscle bring about?
Summates twitches to bring about a stronger contraction
If a muscle fibre is restimulated after it has completely relaxed, what length is the is the second twitch?
Same magnitude as first twitch
If a muscle fibre is restimulated before it has completely relaxed, what happens?
Second twitch is added onto the first resulting in summation
What occurs when 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
Can cardiac muscle be tetanised? Explain.
No - the long refractory period prevents generation of tetanic contraction
When can maximal tetanic contraction be achieved?
When muscle is at its optimal length before the onset of contraction.
In teh body the resting length of a skeletal muscle is approximally what?
Its optimal length
What is isotonic contraction used for?
Body movements and for moving objects - muscle tension remains constant as the muscle length changes
What are isometric contractions used for?
Supporting objects in fixed positions and for maintaining body posture - muscle tension develops at constant muscle length.
In both isotonic and isometric contractions muscle tension is transmitted to the bone via what?
Elastic components of muscle
The velocity of muscle shortening decreases as the load what?
Increases
What four things could cause impairment of skeletal muscle function
- Intrinsic disease of muscle
- Disease of NMJ
- Disease of lower motor neurones which supply the muscle
- Disruption of inputs to motor unit
Give 3 examples of genetically determined myopathies that cause intrinsic muscle disease?
- Congenital myopathies
- Muscular dystrophy
- Myotonia
Give a disease which involves chronic degeneration of contractile elements?
Muscular dystrophy
Give a disease which involves abnormalities in muscle membrane ion channels?
Myotonia
Name three subgroups of acquired myopathies which cause intrinsic muscle disease?
- Inflammatory myopathies
- Endocrine myopathies
- Toxic myopathies
Name an inflammatory myopathy?
Polymyosytis
Name an endocrine myopathy?
Cushing syndrome, thyroid disease
Name a toxic myopathy?
Alcohol, statins
What is the simplest monosynaptic spinal reflex?
Stretch reflex
What serves as a negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle?
Stretch reflex
What is the sensory receptor in stretch reflex and what is it activated by
Muscle spindle - activated by muscle stretch
What does stretching the muscle spindle increase?
Firing in the afferent neurons
What do afferent neurons synapse in the spinal cord with?
Alpha motor neurons (efferent limb of the stretch reflex) that innervate the stretched muscle
What is the stretch reflex coordinated by?
Antagonist muscle
Name the spinal segment and peripheral nerve for knee jerk?
L3, L4
Femoral nerve
Name the spinal segment and peripheral nerve for ankle jerk?
S1, S2
Tibial nerve
Name the spinal segment and peripheral nerve for biceps jerk?
C5-C6
Musculocutaneous nerve
Name the spinal segment and peripheral nerve for Brachioradialis jerk?
C5-C6
Radial nerve
Name the spinal segment and peripheral nerve for triceps jerk?
C6-C7
Radial nerve
What are muscle spindles known as?
Intrafusal fibres
What are ordinary muscle fibres referred to as?
Extrafusal fibres
Where are muscle spindles found?
Within the belly of muscles and run parallel to ordinary muscle fibres
What are the sensory nerve endings on muscle spindles known as?
Annulospiral fibres
What has its own efferent (motor) nerve supply
Muscle spindle
What are the efferent neurons that supply muscle spindles called?
Gamma motor neurons
What adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shortens during muscle contraction
Gamma-motor neurones
What three factors cause differences between different types of skeletal muscle fibres?
- The enzymatic pathways for ATP synthesis
- The resistance to fatigue
- The activity of myosin ATPase
What are muscle fibres with greater capacity to synthesise ATP more resistant to?
Fatigue
What does activity of myosin ATPase determine?
Speed of contraction
What are the three metabolic pathways that supply ATP in muscle fibre?
- Transfer of high energy phosphate from creatinine Phosphate to ADP - immediate source
- Oxidative phosphorylation: main source when O2 present
- Glycolysis: main source when O2 not present
What activities are slow oxidative type I fibres used for?
Prolonged relatively low work aerobic activities
What activities are fast oxidative (type IIa) fibres used for?
Prolonged relatively moderate work activities (jogging) - use both aerobic and anaerobic metabolism
What activities are fast glycolytic (type IIx) fibres used for?
Short-term high intensity activities (jumping) - use anaerobic metabolism
What susbtance is released when muscles are damaged?
Creatine kinase
What are the three types of joints?
- Synovial
- Fibrous
- Cartilaginous
What type of joint is bones united by fibrous tissue - they do not allow any movement?
Fibrous (synarthrosis)
What type of joints are bones united by cartilage - they also allow limited movement?
Cartilaginous joint (amphiarthrosis)
Give four examples of cartilaginous joints?
- Intervertebral discs
- Pubic symphsis
- Part of sacroiliac joints
- Costochondral joints
What type of joint has bones seperated by a cavity (containing synovial fluid) and united by a fibrous capsule?
Synovial joint (diarthrosis)
In a synovial joint - what is the inner aspect of fibrous capsule lined with?
Synovial membrane
What - in the synovial joint - is vascular connective tissue with capillary networks and lymphatics?
Synovial membrane
What does the synovial membrane contain which produces synovial fluid?
Synovial cells (fibroblasts)
What is the difference between simple and compound synovial joints?
Simple ones have one pair of articular surfaces, compound have more than one pair of articular surfaces.
Give an example of a simple synovial joint?
Metacarpalphalangeal joint
Give an example of a compound synovial joint?
Elbow joint
Joints have a role of stress distribution - what is the greatest share of loading energy taken up within?
Muscles and tendons crossing each other
What three things provide joint lubrication?
- Cartilage interstitial fluid
- Synovium-derived hyaluronic acid (mucin) which is a polymer of disaccharides
- Synovium-derived lubrcin - a glycoprotein
What part of a synovial joint supplies the chondrocytes with O2 and nutrients and removes CO2 and waste products?
Synovial fluid
What is the synovial fluid continuously replinished and absorbed by?
The synovial membrane - not a static pool
Why does the synovial fluid have a high viscosity?
Mainly due to presence of hyaluronic acid (mucin) produced by synovial cells
What does the viscosity of synovial fluid vary with?
Joint movement
What is the other consituent of synovial fluid (uric acid) derived by?
Dialysis of blood plasma
Normally the synovial fluid contains few cells, what are they mainly?
Mononuclear leucocytes
What happens to the synovial fluid with rapid movement?
Decreased viscosity and increased elasticity
What condition causes the viscosity and elasticity to become defective?
Osteoarthritis
Describe normal synovial fluid?
Clear and colourless
What is the normal WBC count in synovial fluid?
What does synovial fluid WBC increase in?
Inflammatory and septic arthritis
What does synovial fluid turn red in?
Traumatic synovial tap and in haemorrhagic arthritis
In inflammatory synovial fluid: what is the viscosity, colour, clarity, total WCC and PMN lecuocytes?
Low Straw to yellow Translucent 2000 - 75000 often >50
In septic synovial fluid: what is the viscosity, colour, clarity, total WCC and PMN leucocytes?
Variable Variable Opaque Often > 100 000 Often >75
What are the 4 zones of articular cartilage?
Superficial (10-20%)
Middle (40-60%)
Deep (30%)
Calcified
What is the ECM of articular cartilage made of?
Water (70%) and collagen (20%) - mainly type II contributes most to the elastic behaviour of cartilage and proteoglycans (10%)
In articular cartilage - where os water mostly found?
Near articular surface
What does cartilage water content decrease with?
Age
Where is highest concentration of proteoglycan in cartilage found?
In middle and deep zone
What is proteoglycan found in cartilage mainly composed of?
Glycosaminoglycan e.g. chondroitin suphate
What does chondroitin in cartilage decrease with?
Age
What is proteoglycan in cartilage responsible for in the role of joint?
Compressive properties associated with load baring
What is the water in cartilage responsible for in role of joint?
Resiliency of tissue, nutrition and lubrication
What is the collasgen in cartilage responsible for in joints?
Tensile stiffness and strength
What does cartilage ECM usually constitue of the total cartilage volume?
> 98%
What is the ECM of articular cartilage syntehsised, organised, degraded and maintained by?
Chondrocytes (
The articular cartilage is avascular so where do cartilage ells receive nutrients and O2 from?
Synovial fluid
In the cartilage ECM turnover - what has a negative effect (i.e. breakdown)?
Metalloproteinase proteolytic enzymes e.g. collagenase and stromelysin
What occurs when ECM of cartilage degradation exceeds rate of synthesis?
Joint disease
In cartilage ECM turnover: what does catabolic factors do?
Stimulate proteolytic enzymes and inhibit proteoglycan synthesis
In cartilage ECM turnover: what two immune componenets are involved catabolically?
TNF-alpha
IL-1
In cartilage ECM turnover: what does anabolic factors do?
Stimulate proteoglycan synthesis and counteract effects of IL-1
In cartilage ECM turnover: what two immune components are involved anabolically?
TGF-beta
IGF-1
What do increased levels of serum and synovial keratin sulphate suggest?
Cartilage breakdown - level increases with age and patients with osteoarthritis
What does increased levels of type II colagen in synovial fluid suggest?
Cartilage breakdown - useful in evaluating cartilage erosion in osteoarthritis and rheumatoid arthritis
Cartilage and synovial composition and function deterioate with age and repeated wear and tear giving rise to what?
Osteoarthritis
What does synovial cell proliferation and inflammation cause?
Rheumatoid arthritis
What does deposition of needle shaped salt crystals e.g. uric acid cause?
Gouty arthritis
What does injury and inflammation to periarticular structures cause?
Soft tissue rheumatism e.g. injury to the tendon causes tendonitis
What is subchondral sclerosis and cystic formation found in?
Osteoarthritis
What does deposition of rhomboid shaped calcium pyrophosphate crystals cause?
Pseudo-gout
