MSK Flashcards
Largest type of tissue in human body?
Muscle
Striated muscles? (2)
Skeletal + cardiac
What causes striations?
Myosin + actin
- Myosin = dark thick filaments
- Actin = light thin filaments
Skeletal muscle innervation? Cardiac muscle? Smooth muscle?
- Skeletal muscle = somatic NS
* cardiac + smooth = ANS
Differences between skeletal and cardiac muscle? (4)
Skeletal muscle
- Neurogenic initiation of contraction
- Neuromuscular junction
- No gap junction
- Ca++ entirely from SR
Cardiac
- Myogenic (pacemaker) initiation of contraction
- No neuromuscular junction
- Gap junctions
- Ca++ from ECF and SR (CICR)
What is the neurotransmitter at neuromuscular junction?
Acetylcholine
Skeletal muscle fibres organised into? What is this?
Motor units
* Motor unit = single alpha motor neuron + skeletal muscle fibres it innervates
Number of muscle fibres per motor unit?
- Muscles which serve fine movements (e.g. external eye muscles, facial expression, hand) have fewer fibres per motor unit
- In muscles where power is more important than precision = more muscle fibres
Levels of organisation in skeletal muscle?
- Whole muscle -> muscle fibre (= one muscle cell) -> myofibril -> sarcomere (functional unit)
Myofibril and sarcomeres made up of myocin and actin
How are skeletal muscles attached to skeleton?
Tendons
Functional units of muscle?
Sacromeres
Zones of the sarcomere? (4)
- A-band = thick filaments along with portions of thin filaments that overlap in both ends of thick filaments
- H-Zone = lighter area within middle of A-band where thin filaments don’t reach
- M-Line = extends vertically down middle of A-band within the centre of H-zone
- I-Band = consists of remaining portion of thin filaments that do not project in A-band
What is the definition of a functional unit?
the smallest component capable of performing all the functions of that organ
Where is sacromere found?
Between 2 z-lines
Muscle tension?
Produced by sliding of actin filaments on myocin filaments
Force generation depends on?
ATP-dependent interaction between myosin + actin
ATP only required for muscle contraction? Ca++?
ATP is required for both contraction & relaxation
* Ca++ is required to switch on cross bridge formation
Excitation contraction coupling?
process where surface action potential results in activation of the contractile structures of the muscle fibre
When is Ca++ released in skeletal muscle fibres? What are T-tubules?
In skeletal muscle fibres Ca2+ is released from the lateral sacs of the sarcoplasmic reticulum 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
Explain process of muscle contraction + relaxation
- Acetylcholine released by motor neurone and binds to receptors
- Action potential generated and travels down transverse T-tubules
- AP in T-tubules triggers Ca++ release from SR
- Ca++ binds to troponin-tropomyosin to reveal cross-bridge binding site
- Cross bridge formed between myosin and actin
- Ca++ actively taken up by SR when AP dissipates
- When Ca++ no longer bound to troponin/tropomyosin, binding site is blocked again and myosin detaches from actin
Motor units? Motor unit recruitment? How can muscle fatigue be prevented?
- Motor units = allow simultaneous contraction of muscle fibres
- Motor unit recruitment = stronger contraction achieved by stimulation of more motor units
- Muscle fatigue can be prevented via asynchronus motor unit recruitment during submaximal contractions
What does tension developed by each contracting muscle fibre depend on?
- frequency of stimulation
- length of muscle fibre
- thickness of muscle fibre
How are stronger contractions in skeletal muscle brought about?
If restimulate muscle fibre before it has relaxed, 2nd twitch added on to first twitch resulting in summation
Tetanus contraction? Can this phenomenon occur in cardiac muscle?
Muscle fibre stimulated so rapidly that it does not relax at all between stimuli resulting in MAXIMAL SUSTAINED CONTRACTION
- NO, as long refractory period prevents generation of tetanic contractions
What is the approximate optimal length of skeletal muscle?
In the body the resting length of skeletal muscle is approximately its optimal length (not the same for cardiac muscle)
Contractile component of skeletal muscle? Elastic component skeletal muscle?
- Contractile = sarcomeres
* Elastic = tendon/connective tissue
2 types of skeletal muscle contraction?
- Isotonic contraction: used for (1) body movements and for (2) moving objects. Muscle tension remains constant as the muscle length CHANGES
- Isometric contraction: used for (1) supporting objects in fixed positions and for (2) maintaining body posture. Muscle tension develops at CONSTANT muscle length
Differences between different types of skeletal muscle fibres? (3)
- 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 - determines speed at which energy is made available for cross bridge cycling i.e. the speed of contraction
ATP production in skeletal muscle? (3)
- Oxidative phosphorylation (main source when O2 present)
- Transfer of high energy phosphate from creatine Phosphate to ADP
- Glycolysis (main source when O2 is not present)
3 types of skeletal muscle fibre?
- Slow oxidative type I fibres (also known as slow-twitch fibres) - prolonged, low work aerobic activities e.g. maintenance of posture, walking
- Fast oxidative (Type IIa) fibres (also known as intermediate-twitch fibres) - both aerobic and anaerobic metabolism, prolonged moderate work activities e.g. jogging
- Fast glycolytic (Type IIx) fibres (also known as fast-twitch fibers) - anaerobic metabolism, short-term high intensity activities e.g. jumping
Reflex action?
stereotyped response to a specific stimulus - simplest form of coordinated movement
Stretch reflex?
simplest monosynaptic spinal reflex
What kind of mechanism is stretch reflex?
Stretch reflex is negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle
Why is stretch reflex important?
helps maintain posture e.g. while walking
Receptor for stretch reflex? Process?
sensory receptor is the muscle spindle and is activated by muscle stretch
- stretching muscle spindle increases firing in afferent neurons
- afferent neurons synapse in the spinal cord with the alpha motor neurons (efferents) that innervate the stretched muscle
- Contraction of stretched muscle
What is required for stretch reflex other than contraction of affected muscle?
Relaxation of antagonist muscle
Spinal segment and peripheral nerve involved in knee jerk reflex? Ankle jerk? Biceps jerk? Brachioradialis? Triceps jerk?
- Knee jerk (L3, L4) - femoral nerve
- Ankle jerk (S1, S2) - tibial nerve
- Biceps jerk (C5, C6) - musculocutaneous nerve
- Brachioradials (C5, C6) - radial nerve
- Triceps jerk (C6, C7) - radial nerve
What are muscle spindles? Other name? Ordinary muscle fibres?
- Collection of specialised muscle fibres
- Intrafusal fibres
- Ordinary = extrafusal fibres
Where are muscle spindles found? Features?
Found in belly of muscles and run parallel to extrafusal muscle fibres
* Have sensory nerve endings called annulospiral fibres
Efferent supply to muscle spindles? Function?
Gamma motor neurons
* y neurons adjust level of tension in muscle spindles to maintain their sensitivity when muscle contracts
Intrafusal fibres DO NOT contribute to overall strength of contraction!!!
Causes of intrinsic muscle disease? (5)
- Genetic e.g. muscular dystrophy, myotonia, congenital
- Inflammatory e.g. polymyositis
- Non-inflammatory e.g. fibromyalgia
- Endocrine e.g. cushing
- Toxic e.g. alcohol
Ix neuromuscular disease? (5)
- Electromyography (muscular activity via APs)
- nerve conduction studies
- muscle enzymes
- inflammatory markers
- muscle biopsy
Features of skeletal muscle fibres? (3)
- Striated
- Unbranched
- Multinucleate (nuclei are at periphery of fibre)
Muscle fibre arrangement? Connective tissue supporting skeletal muscle tissue?
- Muscle fibres grouped into bundles called fascicles (muscle contains several fascicles)
- connective tissue that surrounds the muscle as a whole is called the epimysium
- connective tissue around a single fascicle is the perimysium
- connetive tissue around a single muscle fibre is the endomysium
What do thousands of sarcomeres placed end-to-end form? How far does a single sarcomere extend?
A myofibril
* sarcomere extends from one Z line to the next
Why are skeletal muscles striated?
Striations are an optical illusion – myofibril dark and light bands held in registry
3 types of skeletal muscle fibres?
- Type I (“RED” fibres): slow contracting fibres that depend on oxidative metabolism -abundant mitochondria and myoglobin, resistant to fatigue and produce less force.
- Type IIA: intermediate - relatively fast contracting, but are also reasonably resistant to fatigue
- Type IIB (WHITE fibres): fast contracting fibres that depend on anaerobic metabolism - few mitochondria and myoglobin, fatigue easily and produce greater force
Features of cartilage? (4)
- Semi-rigid and Deformable
- Permeable
- Avascular
- Cells nourished by diffusion through the extracellular matrix
Features of bone? (3)
- Rigid
- Not Permeable
- Cells within bone must be nourished by blood vessels that pass thru the tissue
Cells found in cartilage? Organisation?
chondrocytes (chondroblasts when immature)
* Chondrocytes held within extracellular matrix called lacuna
Hyaline ECM composed of?
1) 75% water
2) 25% organic material.
* 60% Type II collagen. Type II collagen differs from type I collagen (e.g. tendon) - it is finer and instead of aggregating into linear bundles it forms a 3D meshwork
* 40% proteoglycan aggregates. Proteoglycan aggregates are made up of GAGs (keratan sulfate and chondroitin sulfate) bound to a core protein and hyaluronan
Types of cartilage? (3)
- Hyaline cartilage (blue) - most common form of cartilage
- Elastic cartilage (yellow): very flexible
- Fibrocartilage (white): hybrid between tendon and hyaline cartilage i.e. bands of type I collagen + rows of chondrocytes surrounded by ECM
Sites of hyaline cartilage? (5)
- Articular surfaces
- Tracheal rings
- Costal cartilage
- Epiphyseal growth plates
- Precursor in fetus to many bones
Functions of bone?
- Support
- Levers for movement
- Protection of internal organs
- Calcium store: >95% calcium found in bone + constant exchange of calcium between bone and blood
- Haemopoiesis: only the axial and limb girdle skeleton is involved in blood production
Composition of bone? (4)
- 65% bioapatite (form of calcium phosphate - mostly hydroxyapatite)
- 23% collagen
- 10% water
- 2% non-collaged proteins
Structure of bone? (2)
- outer shell of dense cortical bone makes up the shaft (diaphysis)
- Cancellous/trabecular bone at ends of bone (epiphyses)
How do blood vessels travel through bone?
- Haversian canal + volkman’s canal
Difference in structure of trabecular and cortical bone?
- bone cells and matrix are similar in compact and trabecular bone
- main difference is the presence of spaces (marrow cavities) adjacent to trabecular bone
BOTH TYPEs aRE LAMELLAR!!! (made up of layers)
Cement lines?
lines that are visible surrounding the osteon
What does trabecular bone often lack? Why?
lacks Haversian canals
* the struts are thin so the osteocytes can survive from contact with the marrow spaces
Bone cells? (4)
- Osteoprogenitor cells: reserve cells that can differentiate into osteoblasts
- Osteoblasts: bone forming cells (lots of RER and mitochondria)
- Osteocytes: bone cell trapped within bone matrix
- Osteoclasts: large multinucleated cells - bone resorption
Process of bone remodelling?
CUTTING CONE
- osteoclasts ‘drill’ into the bone forming a tunnel
- a blood vessel will grow into the tunnel bringing osteoblasts which line the tunnel and begin laying down new lamellar bone
- This process continues until only the space of a Haversian canal remains
What is the collection of osteoclasts and osteoblasts that participate in bone remodelling called?
basic multicellular unit or BMU
How do osteoblasts produce bone?
Secrete OSTEOID: collagen, glycosaminoglycans (GAGs), proteoglycans
* this then becomes mineralized over time
What is the mineral of bone made up of?
calcium phosphate crystals, particularly hydroxyapatite
Osteoclast origin and morphology?
- Derived from macrophage line of cells
* Several will fuse to form a single giant cell
Differences between lamellar and woven bone?
During development or following a break, rather than having collagen fibres orientated all in one direction like lamellar bone, the collagen fibres are laid down in a haphazard fashion - WOVEN BONE
Adult osteomyolitis?
Inflammation of bone and medullary cavity, usually in long bones
Places where osteomyolitis is most common?
- Vertebral osteomyolitis
- Diabetic foot infection
- Post-traumatic infection
- Prosthetic joint infection
Most common pathogen in osteomyolitis?
staph aureus
Dx osteomyolitis?
GOLD STANDARD is bone biopsy!
Via percutaneous sample or deep surgical culture
Tx osteomyolitis?
Tx: debridement + antibiotics
Not an emergency, wait for culture results before beginning treatment
Risk factors for osteomyolitis? (6)
- Open fractures
- Diabetes/ Vascular insufficiency
- Haematogeneous osteomyelitis
- Vertebral osteomyelitis
- Prosthetic joint infection
- Specific hosts and pathogens
s/s osteomyolitis?
Rubor, tumor, dolor, functio laesa
How does infection occur in bone?
Bone is highly resistant to infection – infection only occurs with necrosis + high inoculum
How long does osteomyolitis tx take?
6 weeks
Open fractures? Tx? Clinical clues of osteomyolitis with open fracture? Pathogens?
- Contiguous infection
- Tx: debridement, fixation + soft tissue cover
- Clinical clues = non-union + poor wound healing
- Ax: staph aureus + aerobic gram -ve bacteria
Diabetes/venous insufficiency? Dx? Tx?
- Contiguous infection that is often polymicrobial
- Dx: Bone biopsy
- Tx: debridement and antimicrobials
Mild diabetic foot ulcer tx?
Moderate? Severe?
How about patients with penicillin allergy?
MRSA?
- Mild: Fluclox
- Mod: fluclox + metronidazole
- Severe: fluclox, gentamicin + metronidazole
Penicillin allergy
- Mild = doxycycline/co-trimoxazole
- Mod = doxycycline + metronidazole OR co-trimoxazole + metronidazole
- Severe = vancomicin, gentamicin + metronidazole
Tx acute osteomyolitis (i.e. when cannot wait for culture)? What about for patients with penicillin allergy?
Fluclox + gram -ve and anaerobic cover
* allergy = sub fluclox for vanco
Mild MRSA tx? Mod? Severe?
- Mild = Doxycycline or co-trimoxazole
- Mod = vancomycin
- Severe = vancomycin + gram -ve cover
Duration of tx for mild diabetic foot sepsis? Mod? Severe?
Osteomyolitis?
- mild = 7 days
- mod = 7 days
- severe = 7-10 days (14 days if s.aureus bacteraemia)
- osteomyolitis = 6 weeks
Is vancomycin given orally?
NEVER switch a person from IV vancomycin to ORAL vancomycin (unless topical treatment for c.diff) as it is NOT absorbed systemically
Why is oral doxycycline normally given as oral switch from fluclox?
fluclox = big pill 4 x a day
Likely colonisers in culture i.e. not causative organism?
Pseudomonas, klebsiella, epidermidis
Epidemiology haematogenous osteomyolitis? (5)
- Prepubertal children
- PWID
- Central lines
- dialysis
- elderly
Organisms involved in PWID haematogenous osteomyolitis? (2)
- Strep + staph
* unusual pathogens = pseudomonas, candida, eikenella corrodens (needle lickers), mycobacterium
Organisms involved in dilaysis patients with haematogenous osteomyolitis? (2)
- Staph aureus (most common)
* aerobic gram -ve’s
Most common site for haematogenous osteomyolitis?
Unusual sites to be aware of?
- most common = femur
* Unusual sites = osteitis pubis + clavicle
Unusual patients that are prone to haematogenous osteomyolitis?
- Sickle cell
- Gaucher’s disease
- SAPHO and CRMO
Pathogens involved in sickle cell osteomyolitis? Where does it commonly affect?
- Salmonella + staph aureus
* Long bones
Gaucher’s disease? Most commonly affects? Pathogens involved?
- Lysosomal storage disorder (can mimic bone crisis)
- Often affects tibia
- Staph aureus
S/s SAPHO (adults) + CRMO (kids)? (3) Most common sites? Dx?
- Fever, weight loss, malaise
- Chest wall, pelvis + spine
- Dx = lytic lesions seen on x-ray + raised inflammatory markers
Vertebral osteomyolitis? Most common pathogen?
Vertebral osteomyolitis = spondylodiscitis (disc space infection)
* staph aureus
Risk factors vertebral osteomyolitis? (6)
Mostly haematogenous
- Epidural abscess/psoas abscess
- PWID
- IV infection
- GU infection
- Skin infection
- post-operative
s/s vertebral osteomyolitis? (5)
Dx? (2)
- <50% have fever, <50% have raised WCC, insidious pain, neurological signs, infammatory markers
- Dx: Can have someone with vertebral osteomyolitis who has no fever, normal WCC – so MRI important!! Also biopsy
Biopsy for vertebral osteomyolitis? Why is biopsy carried out?
- First biopsy = 40% yield
- Second biopsy = 80% sensitivity
Important as empiric antibiotics should be avoided
Tx vertebral osteo? (2)
When is MRI repeated in vertebral osteo? (3)
- Drainage of large psoas/epidural abscesses
- Antimicrobials for 6 weeks minimum
MRI repeated only if
- Unexplained increase in inflammatory markers
- Increasing pain
- New signs/ symptoms
Vertebral TB also known as? S/s? Why does epidemiology matter?
= Pott’s disease
* often NO systemic symptoms i.e. no cough
Epidemiology MATTERS
- In kids, check reduced receptors for IFN-gamma, IL 12
- In adults over HIV test
Risk factors for prosthetic joint infection? (4)
What is a common indication of infection in prosthetic joints?
- Rheumatoid arthritis
- Diabetes
- Malnutrition
- Obesity
Dehiscing of wound
Difference between planktonic and sessile bacteria? Pathogens in prosthetic joint infection? (6)
Planktonic = bacteraemia Sessile = biofilm * Staph aureus, epidermidis, propionibacterium (rarely strep + entero) * Gram -ve i.e. E.coli * Fungi * Mycobacterium
Tx PVL-producing staph aureus?(3)
Fluclox, clindamycin, linezolid etc
Dx prosthetic joint infections? (4)
- Culture - tissue sample
- Blood culture
- CRP
- Radiology
Prosthetic joint infection tx? (3)
- removal of prosthesis and cement
- antibiotics at least 6 weeks
- re-implantation of joint after aggressive antibiotic therapy
Tx staph epidermidis in prostehtic joint infection?
Vancomycin
Septic arthritis?
Ax septic arthritis? (4)
Inflammation of the joint space caused by infection
- Wound
- Haematogenous
- Spread from osteomyolitis in adjacent bone
- Infection in adjacent soft tissues i.e. cellulitis
Bacteria involved in septic arthritis? (5)
- Staph aureus
- Strep
- Coag neg staph - if prosthetic joints
- Neisseria gonorrheae - if sexually active
- Haemophilus influenzae - in young children
s/s septic arthritis? Dx?
* Severe pain, red, hot, swollen, pus, limited movement Dx: * Culture joint fluid * Blood culture if fever * exclude crystals (microscopy)
Septic arthritis tx?
- Presumptive tx to cover staph aureus = fluclox
- If <5 y/o add ceftriaxone for H.influenzae
(adjust when organisms confirmed)
Viral arthritis?
- Hep B, alphavirus, rubella, parvovirus
Pyomyositis? Ax? (3)
Muscle inflamamtion caused by infection
- Staph aureus!! most common
- Immunosuppressed = psuedomonas, strep, enterococcus
- Clostridial infection contaminated wounds
Tetanus? Pathogen?
Toxin-mediated illness caused by clostridium tetani
* Gram +ve strictly anaerobic rods = produce SPORES that live in soil etc
s/s tetanus? Incubation peroid?
Neurotoxin causes spastic paralysis, lock jaw, sadonic smile
* 4 days - weeks
Tx tetanus? (5)
- Surgical debridement
- Anti-toxin
- Supportive measures.
- Penicillin/Metronidazole
- Booster vaccination
Ix fresh tissue lesions?
- Cytogenetic studies - karyotyping, FISH
* Molecular genetic studies
Karyotype? Advantages and disadvantages?
Karyotype = culture cells then arrest during cell division
- adv = overview of chromosome structure
- dis = will NOT detect small lesions, issue with quality of cells
FISH use?
Useful for known translocations
Immunohistochemistry process?
place pigment on antibody with specific target protein - any pigment staining means the protein is present
Benign connective tissue lesions? (5)
- common = ganglion cyst, giant cell tumour, fibromatosis
* rare = fibrous cortical defect, fibrous dysplasia
Ganglion cyst? Common site?
Histo?
Not a true cyst (no epithelial lining), causes degenerative change within connective tissue
- Common site = wrist (found near joint capsule or tendon)
- Histo = space with myxoid (mucous) material, inflammatory changes
Superficial fibromatoses e.g.? (4)
- Dupuytren’s
- Knuckle pads
- Plantar
- Penile - peyronie’s
Dupuytren’s epidemiology? Ax?
- Older males
* Idiopathic but associated with alcohol
Deep fibromatosis? E.g? Ax?
Different than superifcial fibromatosis
- Mesenteric or pelvic DESMOID tumours
- Associated with Gardner’s syndrome (FAP)
Giant cell tumour e.g.? (3)
- Pigmented villonodular synovitis – large joints
- Giant cell tumour of tendon sheath – digits
- Giant cell tumour of bone
Tx giant cell lesions? (2)
- GC tendon sheath = small nodules that are easily excised (rarely recur)
- PVNS - more destructive and diffuse, more difficult to excise and often recur
Angiolipoma? s/s?
- Vascular lipomas
* Unlike other lipomas they are painful, usually multiple and peripheral
benign mesenteric tumours? (5)
ANGEL
- Angiolipoma
- Neuroma (pinched nerve)
- Glomus tumour (nail beds)
- Eccrine spiradenoma (skin adnexal tumour)
- cutaneous leiomyoma (of erector pilae)