MSK Science Flashcards
What are the three types of muscle?
Skeletal, cardiac and smooth
Which muscles are striated?
Skeletal and cardiac
Which muscles are unstriated?
Smooth
Which muscles are under voluntary control?
Skeletal and cardiac
Which muscles are under autonomic control?
Cardiac and smooth
How are skeletal muscles arranged and innervated?
Arranged into motor units and innervated by a single alpha motor neurone
How many muscle fibres does intrinsic muscles of the hand/extra-ocular muscles have?
Few (10) per motor unit
Innervated by single alpha motor unit
How many muscle fibres does thigh muscles have?
Hundreds to 1,000s
Innervated by single alpha motor unit
What is the difference in initiating contraction between Skeletal muscle and cardiac muscle?
Skeletal: neurogenic initiation of contraction
Cardiac: myogenic
What is the difference in junctions between Skeletal muscle and cardiac muscle?
Skeletal: neuromuscular junction
Cardiac: gap junctions
What is the difference in excitation between Skeletal muscle and cardiac muscle?
Skeletal: Ca is released from lateral sacs of SR when the surface poetical spreads down the transverse T tables
Cardiac: Ca from ECF and SR
What is the neurotransmitter at the skeletal NMJ?
Ach
What is the difference in mediating contraction between Skeletal muscle and cardiac muscle?
Skeletal: motor unit recruitment and summation of contractions
Cardiac: the extent of heart filling with blood
In skeletal muscle, when is Ca released from the SR?
When the surface AP spreads down the transverse T tubules
Sarcomere zone: What is the A band?
Made up of thick filaments along with portions of thin filaments that overlap in both ends of thick filaments
Sarcomere zone: What is the H zone?
Lighter area within middle of A-band where thin filaments don’t reach
Sarcomere zone: What is the M zone?
Extends vertically down middle of A-band within the centre of H-zone
Sarcomere zone: What is the I band?
Consists of remaining portion of thin filaments that do not project in A-band
Can cardiac muscle be tetanised?
No
How is skeletal muscle stimulated to contract?
- Single twitch
- Several twitches fires before the AP has time to relax brings about contraction
- Maximal contraction at optimal length
When is Isotonic contraction used?
- Body movements and moving objects
- Muscle tension remains constant as the muscle length changes
When is Isometric contraction used?
- For supporting objects in fixed position and maintaining body posture
- Muscle tension develops at constant muscle length
Causes of impairment of skeletal muscle function
- Intrinsic muscle disease
- NMJ disease
- Lower motor neurone disease
- Disruption of inputs to motor units
Spinal segment for knee jerk
L3,4
Spinal segment for ankle jerk
S1,2
Spinal segment for Biceps
C5-6
Spinal segment for Brachioradialis
C5,6
Spinal segment for Triceps
C6,7
What are muscle spindles?
- Sensory receptors for stretch reflex
- Collection of specialised muscle fibres
- Within the belly of muscles, running parallel to ordinary muscle fibres
- Sensory nerve endings: annulospiral fibres
How do muscle spindles mediate muscle stretch?
-The discharge from the muscle spindles sensory endings increases as the muscle is stretched
What are the efferent neurones which supply muscle spindles?
Gamma motor neurones
How do Gamma motor neurones work?
Adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shorten during muscle contraction
Are skeletal muscle fibres all the same?
No, each motor unit contains only one type of muscle fibre
What are the three types of skeletal muscle fibres?
- Slow oxidative
- Fast oxidative
- Fast glycolytic
When are type 1 muscle fibres used?
- Slow oxidative
- Aerobic
- Prolonged low work aerobic activities
- Walking
When are type 2a muscle fibres used?
- Intermediate fibres
- Both aerobic and anaerobic
- Prolonged moderate activity
- Jogging
When are type 2x muscle fibres used?
- Fast twitch
- Anaerobic
- High intensity e.g. jumping
Which cells produce synovial fluid?
Fibroblasts
What is the function of synovial fluid and how is it replaced?
- Supplies the chondrocyte with oxygen, nutrients and removes CO2 and waste products
- It is continuously replenished and reabsorbed by synovial membrane
How does synovial joint viscosity vary with movement?
Rapid movement: decreased viscosity and increased elasticity of synovial fluid
What contributes to the viscosity of synovial fluid?
Hyaluronic acid (mucin) produced by synovial cells
How does synovial fluid change in:
- Trauma
- Inflammatory
- Septic arthritis
Trauma: red on aspiration
Inflammatory: straw to yellow colour, translucent, leukocytes, WCC
Septic arthritis: v.high WCC and leukocytes
What is the composition of articular cartilage?
- Usually hyaline
- Has a special ECM made of:
- water (70%)- nutrition and lubrication
- type 2 collagen (20%)- architecture
- proteoglycans (10%)- load bearing
How does the mechanical properties of cartilage components change with age?
- Water content (70%) decreases with age
- Collagen (20%, architecture) decreases with age
- Proteoglycan (10%, load bearing decreases with age)
How is cartilage turnover mediated?
- Catabolic factors: Stimulate proteolytic enzymes and inhibit proteoglycan synthesis
- Anabolic factors: Stimulate proteoglycan synthesis and counteract effects of IL-1
What is the prophylaxis in Orthopaedic surgery?
- Co-amoxiclav pre and post op
- Min 6 wks pre-op
What are the likely organisms in an acute BJI?
Streptococci and Staph Aureus
What are the likely organisms in an chronic BJI?
CoNS, proprionibacteria
How many bone and tissue samples in a BJI?
Min 3 bone/tissue samples
What is the neurotransmitter at the NMJ?
Ach
What is the post synaptic receptor where Ach binds to?
Nicotinic receptor
What is the structure of the Nicotinic receptor?
- Pentameric
- 2 alpha
- Beta
- Sigma
- Gamma
Summarise what happens at the pre-synaptic phase of the NMJ
- Acetate + choline= Acetylcholine
- Ach is concentrated in vesicles by vesicular Ach transporter
- AP at terminal causes depolarisation and opening of Ca gated channels and Ca enters terminal
- Ca causes vesicles to fuse with pre-synaptic membrane and exocytosis whereby Ach diffuses into the synaptic clef occurs
- Ach activates post synaptic nicotinic receptors on end plate
Summarise what happens at the post-synaptic phase of the NMJ
- Ach activates Nicotinic receptor
- When Na influx>K efflux through receptor, mini end plate potential is generated
- Many mini end plate potential summate to an end plate potential
- End plate potential generated through Na channel and enters through transverse tubule
- AP at transvers tubule triggers Ca release from SR, interacts with troponin and mediates contraction
How is the action of Ach at the end plate of the NMJ terminated?
By the enzyme Acetylcholinesterase at the NMJ
Features of Myasthenia Gravis
- Weakness of eye and eye lid muscles
- Autoimmune
- Antibodies against nicotinic Ach receptors in end plate
- Decreased function
- Decreased e.p.p
Radiolucent nidus in cortex of bone, dull pain, worse at night, relieved by NSAIDs
Osteoid Osteoma (benign)
Cartilage capped bony projection, in 20s
Osteochrondroma (benign)
Benign cartilage tumour, 20s, “chicken wire calcification”, well defined osteolytic foci
Chondroblastoma (benign)
V.rare bone tumour from notochord remnants, older adults
Chordoma (benign but locally invasive)
Malignant osteoblasts forming osteoid, rapid growth, ends of long bones, young people
Osteosarcoma
Malignant chondrocytes bone tumour
Chondrosarcoma
Peripheral primitive neuroectodermal tumour, irregular tan to brown tumour mass, “small round blue cell” on histology
Ewing’s sarcoma
Malignant proliferation of plasma cells in bone marrow, old age, causes renal failure, “spike” on protein electrophoresis, Bence Jones Protein
Multiple Myeloma
