Musculoskeletal Pathophysiology - MUSCLES Flashcards
Approximately, how many human skeletal muscles are there?
~ 600
Approximately, what percentage of our body weight is made of muscles?
~50%
What is the single major purpose of muscles?
Converting the chemical energy in ATP into mechanical energy of motion
What are the main functions of muscles?
- Movement
- Stability
- COntrol of openings/passageways
- Heat production
What are the three types of muscle tissue?
- Skeletal
- Smooth
- Cardiac
Skeletal Muscle: Many skeletal muscles extend b/w _b_ones and cross at least one moveable joint
Define: Contraction, Origin and Insertion
Contraction: One bone moves while the other bone usually remains fixed
Origin: The less movable attatchment of a muscle
Insertion: The more moveable attatchment of the muscle
Muscle fibre ultrastructure
Each muscle fibre has a precise repeating pattern of transverse bands/stripes running along the entire length:
- Light band = I band (end of M-line → connectin)
- Dark band = A band (end of M-line → other end of M line)
- Sacromere = repeating unit within myofibrils (I-A-I)
- Myosin = Thick filaments
- Actin = Thin filaments
- Z disk - Thin fillaments + connectin
- M line - Thick fillaments
What happens to the fillaments and sacromere length during muscle contraction?
Thick & thin filaments slide past each other → sacromere length contracts
Length Tension Relationship
- As sacromere length decreases, active force increases
- until plateu point
- over-decrease in sacromere length does NOT mean more force!
Describe the structure of a thick myofilament
- Each strand has many myosin molecules
- Myosin tail (double twist)
- (double) myosin head
Describe the structure of a thin myofilament
- G actin chains (double twist)
- Tropomyosin “strip” on each chain
- Tropomyosin complex on each tropomyosin strip
Accessory proteins
- Linking proteins (3)
- Dystrrophin (binds to thin filament)
What is Muscular dystrophy?
A hereditary condition marked by progressive weakening & wasting of the muscles
A protein encoded by the Duchenne muscular dystrophy gene called dystrophin has been identified
Dystrophin is absent in muscular dystrophy (it is present in normal cels)
~1:3500 male births; X-linked inheritance in 50% of cases
Muscle-nerve relationship
Muscle fibres are joined to the spinal cord via neuromuxcular junctions attatched to the fibres and the ends at the motor neuron
Nerve-muscle excitation
Arival of nerve signal + Ca2+ → opens voltage gated Ca channels in synaptic knob
Ca stimulates exocytosis of ACh from synaptic vesicle
ACh released into synaptic cleft
Two ACh molecules bind to each receptor protein, opening Na+ and K+ channels
Na+ enters, shifting RMP from -90mV → +75mV
K+ exits, RMP returns to -90mV
Voltage change (EPP) in EP-region opens nearby voltage-gated channels → action potential that spreads over muscle surface
Quick voltage shift is called an end-plate potetntial (EPP)
Define: End-plate potential
A quick volatge shift is called an end-plate potential (EPP)
Excitation-Contraction Coupling in Skeletal Muscle
- Action potetntals propagated down T tubules
- Calcium released from terminal cisternae
- Calcium binds to troponin
- Shifting of tropomyosin; exposure of active sites on actin
What id Myasthenia Gravia?
An autoimmune attack on the ACh receptor at the postsynaptic membrane of the neuromuscular junction
- AcH receptor is damaged/destroyed/insensitive to Ach, disrupts normal neuromuscular transmission
- Predominates in women (20-40)
Symptoms:
Ptosis, diplopia, muscle fatigue after exercise
Ocular muscles affected first in 40% of cases, eventually 85%
Dysarthria (stammering), dysphagia, proximal limb weakness
Severe generalised quadriparesis
Life-threatening respiratory muscle symptoms (myasthenia crisis) ~10%
Treatment:
Anticholinesterases - corticosteroids for semi-chronic cases, NOT useful in a crisis
Define a Tendon
A strip or sheet of tough collagenous connective tissue which attaches a muscle to a bone
Define a Ligament
A strip or sheet of tough collagenous connective tissue that attaches one bone to another
What is the function of tendons and ligaments?
Tendons and ligaments support the bones and joints and either facillitate OR limit motion
- Can be torn/ruptured/separated from bone from their point of attachment
Define a Strain
A tear in a tendon
Define a Sprain
A tear in a ligament
Both tendons and ligaments can be teared/strained/sprained, how yould you treat them?
- they are painfull
- accompanied byt soft tissue swelling
- “RICE” treatment:
- Rest
- Ice
- Compression
- Elevation
