Physiology Flashcards
What are the physiological functions of skeletal muscles?
Maintenance of posture Purposeful movement in relation to external environment Resp movements Heat production Contribution to whole body metabolism
Which muscles are striated?
Skeletal and cardiac
Which muscles are involuntary?
Cardiac muscle
Smooth muscle
What nerves innervate skeletal muscles?
Somatic nervous system
What nerves innervate cardiac and smooth muscle cells?
Autonomic nervous system
How are skeletal muscles initated and propagated for contraction?
Neurogenic intiation of contraction
Motor units
Neuromuscular junction present
NO gap junctions
How are cardiac muscle cells initiated and propagated for contraction?
Myogenic (pacemaker potential)
NO neuromuscular junction
Gap junctions present
What is the neurotransmitter at the neuromuscular junction in skeletal muscle cells?
Acetylcholine
What is a motor unit?
A single alpha motor neuron and all the skeletal muscle fibres it innervates
What determines the number of muscles fibers per motor unit?
Depends on the functions served by the muscle e.g. muscles which serve fine movements such as external eye muscles, muscles of facial expression and intrinsic band muscles have fewer fibres per motor unit
What makes up a sarcomere?
Actin (thin and light)
Myosin (thick and dark)
What is the Z line?
Connection of actin filaments of 2 adjoining sarcomeres
What is the A band?
Myosin filaments along with portions of actin filaments that overlap both ends of myosin filament
What is the H zone?
Lighter area within the middle of the A band where actin filaments dont reach
What is the M line?
Extends vertically down the centre of the H zone
What is the I band?
Consists of remaining portion of actin filaments that do not project into the A band
What is excitation contraction coupling?
Process whereby the surface action potential results in activation of the contractile structures of the muscle fibre
When will calcium be released from the lateral sacs of the SR?
When the surface action potential spreads down the transverse T tubules
What is a T-tubule?
Extensions of the surface membrane that dip into the muscle fibre
What is the action of calcium in muscle contraction?
When relaxed, the cross binding site on actin is covered by the troponin-tropomyosin complex
When Ca binds with troponin, it pulls the troponon-tropomyosin comples aside to expose the cross-bridge binding site
Where is calcium derived from in skeletal muscle contraction?
Sarcoplasmic reticulum
What is ATP needed for in skeletal muscle contraction?
Needed during muscle contraction to power cross bridges
Needed during relaxation to release cross bridges and to pump calcium back into the sarcoplasmic reticulum
What two factors determine the gradation of skeletal muscle tension?
Number of muscles fibres contracting within the muscle
Tension developed by each contracting muscle fibre
What is motor unit recruitment?
A stronger contraction can be achieved by stimulation of more motor units
When is asynchronous motor unit recruitment help utilised?
Sub-maximal contractions to help prevent muscle fatigue
What does tension in contracting muscle fibres determined by?
Frequency of stimulation and summation of contractions
Length of muscle fibre
Thickness of muscle fibre
How can tetanus be achieved in skeletal muscle?
If a skeletal muscle is stimulated rapidly, it does not have time to relax and therefore a maximal sustained contraction occurs
What does muscle fibre length have to do with achieving maximal tetanic contraction?
When the muscle is at optimal length, the cross bridges on myosin filaments overlap with the cross binding sites on actin filaments
When is skeletal muscle at its optimal length?
At rest
What is isotonic contraction in skeletal muscle?
Used for body movements and moving objects
This is when muscle tension remains constant as the muscle length changes
What is isometric contraction?
Used for supporting objects in a fixed position and maintaining body posture
This is when muscle tension develops at a constant muscle length
What are the differentiating factors between different types of skeletal muscle?
Enzymatic pathways for ATP synthesis
Resistance to fatigue - muscle fibres with greater capacity to synthesize ATP are more resistant to fatigue
The activity of myosin ATPase
Will motor units have muscle fibres of the same type?
Yes
Why does muscle contraction require ATP?
During muscle contraction, ATP is split by myosin ATPase to power cross-bridging stroking
During relaxation, ATP is needed to pump Ca2+ back into the SR’s lateral sacs
How can ATP be acquired in skeletal muscle?
Transfer of high-energy phosphate from creatine phosphate to ADP
Oxidative phosphorylation (muscle glycogen stores of glucose and fatty acids in blood)
Anaerobic glycolysis
What are the different types of skeletal muscle fibres?
Slow-oxidative (type 1)
Fast-oxidative (type 2a)
Fast-glycolytic (Type 2x)
When are slow oxidative type 1 muscle fibres used?
Slow twitch fibres
Used for prolonged, low work aerobic activities e.g. maintenance of posture and walking
When are fast oxidative type 2a fibres used?
Used in aerobic and anaerobic metabolism
Useful in prolonged, moderate work activities such as jogging
When are fast glycolytic type 2x fibres used?
Anaerobic metabolism
Useful in short-term high intensity activities such as jumping
What is a reflex?
A stereotyped response to a specific stimulus
What is a stretch reflex?
Negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle
What is the sensory receptor in muscle fibres?
Muscle spindle that is activated via muscle stretch
What will stretching of the muscle spindles cause?
Afferent neurones
Where do afferent neurones synapse?
In the spinal cord with alpha motor neurones (efferent limb of the stretch reflex) which innervate the stretch muscle
What is the other name for muscle spindles?
Intrafusal fibres
What is the other name for ordinary muscle fibres?
Extrafusal fibres
What are the sensory nerve endings in muscle spindles called?
Annulospiral fibres
What is the efferent neurone that supplies muscle spindles?
Gamma motor neurone
What are some symptoms of muscle disease?
Muscle weakness
Myotonia
Myalgia
Muscle stiffness
What are some useful investigations in regards to neuromuscular disease?
Electromyography Nerve conduction studies Muscle enzymes (CK) Inflammatory markers (CRP, PV) Muscle biopsy
What are some genetic causes of intrinsic muscle disease?
Congenital myopathies
Chronic degeneration (muscular dystrophy)
Myotonia
What are some acquired myopathies?
Inflammatory (polymyositis)
Non-inflammatory (fibromyalgia)
Endocrine myopathies (cushings, thyorid)
Toxic myopathies (alcohol, statins)
What are the different types of joints?
Synovial
Fibrous
Cartilaginous
What is a fibrous joint?
Connects bones by fibrous tissue
Doesn’t allow movement
What is an example of a fibrous joint?
Joint in the skull sutures
What is a catillaginous joint?
Bones united by cartilage
Allows limited movement
What are some examples of cartilaginous joints?
Intervertebral discs
Pubic symphsis
Part of the sacroiliac joints
Costochondral joints
What is a synovial joint?
Bones separated by a cavity and united by a fibrous capsule (and other extra-articular structures e.g. ligaments, tendons and burase)
What is contained within the synovial membrane?
Vascular connective tissue with capillary networks and lymphatics
Contains fibroblasts which produce synovial fluid
What is the physiological function of joints?
Structural support
Purposeful motion
What are the roles of joints during purposeful movement?
Stress distribution
Confer stability
Joint lubrication
How do joints confer stability?
Shape of the articular component
Ligaments provide a second major stabilising influence
Synvovial fluid acts as an adhesive seal that freely permits sliding motion between cartilaginous surfaces
How do joints provide lubrication?
Cartilage interstitial fluid
Synovium derived hyaluronic acid
Synovium dervied lubricin
What are the functions of synovial fluid?
Lubricates joint
Facilitates joint movement
Helps minimise wear-and tear
Aids in nutrition of articular cartilage
Supplies chondrocytes with oxygen and nutrients
What causes synovial fluid to have a high viscosity?
Presence of hyaluronic acid produced by synovial cells
How does the viscosity and elasticity of synovial fluid change during joint movement?
Rapid movement = decreased viscosity and increased elasticity
What will happen to synovial fluid in osetoarthritis?
The elasticity and viscosity of the fluid will not change
What is the WBC count in synovial fluid?
<200 WBC/mm of which polymorphs are usually <25/mm
When will the synovial fluid WBC count increase?
In inflammatory and septic arthritis
What will cause synovial fluid to turn red?
A traumatic synovial tap
Haemorrhagic arthritis
What are the characteristics of normal synovial fluid?
High viscosity Colourless Transparent clarity <200 WCC <25 polymorphs
What are the charcteristics of inflammatory synovial fluid?
Low viscosity Straw/yellow colour Translucent clarity 2000-75,000 WCC >50 polymorphs
What are the characteristics of septic synovial fluid?
Variable viscosity Variable colour Opaque clarity >100,000 WCC >75 polymorphs
What are the different zones to an articular cartilage?
Superficial zone
Middle zone
Deep zone
Calcified zone
What type of cartilage makes up the articular cartilage?
Hyaline cartilage
What makes up the ACM in articular cartilage?
70% water
20% type 2 collagen
GAGs 10%
What is the function of water in hyaline cartilage?
Content decreases with age
Maintains the resilience of the tissue and contributes to the nutrition and lubrication system
What is the function of collagen in hyaline cartilage?
Mainly type 2 which decreases with age
Maintains the cartilage architecture
Provides tensile stiffness and strength
What is the function of proteoglycan in hyaline cartilage?
Highest conc in middle and deep zones
Composed of GAGs
Responsible for the compressive properties associated with load bearing
What synthesises, degrades and organises the ECM of articular cartilage?
Chondrocytes
How do chonrocytes degrate the ECM?
Metalloproteinase proteolytic enzymes - collagnase and stomelysin
What effect do catabolic factors have on cartilage matrix turnover?
Stimulate proteolytic enymes and inhibit proteoglycan synthesis: Produce TNF-alpha and IL-1
What effect do anabolic factors have on cartilage matrix turnover?
Stimulate proteolgycan synthesis and conteract effects of IL-1
Produde tumour growth factor and insulin-like growth factor
What are markers of cartilage degredation?
Serum and synovial keratin sulphate (increased levels = cartilgae breakdown)
Type 2 collagen in synovial fluid (increased levels indicate cartilage breakdown)
What condition is described as synovial cell proliferation and inflammation?
RA
What condition is described as deposition of salt crystals in a joint?
Gouty arthritis
What condition is described as injury and inflammation to periarticular structures?
Tendonitis
What is the difference between gout and pseudogout?
Needle shaped uric acid crystals - gout
Thomboid shaped calcium pyrophosphate crystals - pseudo-gout
