Muscle Tissue (Function and Dysfunction) Flashcards
Cardiac vs smooth muscle
similarities
-central nuclei
-only one contractile cell type (no fast/slow twitch)
-wave like function, act as syncytium
-myocytes communicate through gap junctions(small molecules pass between adjacent cells
differences
-cardiac can be multinucleated
-cardiac is branched
-connexins in smooth muscle
-no sarcomeres in smooth muscle
-electrical conduction- specialised cells in cardiac muscle
-no troponin in smooth muscle as no sarcomere
-cardiomyocytes have intercalated discs
DHP
dihydropyridine
RyR
ryanodine receptor
neuromuscular junction
neuromuscular junction
point of contact between a motor neuron and a skeletal muscle cell
properties of neuromuscular junction
-small terminal swellings of the axon
-contains vesicles of acetylcholine
Innervation of skeletal muscle (neuromuscular junction)
- Initiation: nerve impulse along motor neuron axon arrives at neuromuscular junction
- Impulse prompts release of ACh into synaptic cleft causing local depolarisation of the sarcolemma
- Voltage gated Na+ channels open, Na+ ions enter cell
- General depolarisation spreads over sarcolemma into T tubules
- Voltage sensor proteins of T tubule membrane change their conformation
- Gated Ca2+ ion-release channels of adjacent terminal cisternas activated
- Ca2+ rapidly released into sarcoplasm
- Ca2+ binds to TnC subunit of troponin and contraction cycle initiated
- Ca2+ ions returned to terminal cisternas of sarcoplasmic reticulum
What’s a neuromuscular junction formed of?
Neurone and muscle
how does the average fibres per motor unit affect fine control and power?
Lower fibres per unit - more fine control
higher fibres per unit - more power
Kranocyte
a connective tissue cells that resides over the terminal Schwann cell - anchors nerve to muscle cell
T Tubes and sarcoplasmic reticulum of skeletal muscle structure
Look at lecture 12 pg 12
- Sacrolemma
- T
myasthenia gravis
*autoimmune disease
*antibodies block Ach receptor, and 30% reduction in receptor number is enough for symptoms
*endplate invaginations reduced and reduced synaptic transmission
-muscle weakness
Explain the histological appearance of myasthenia gravis
2 axons, round not crescent moon shape
More mitochondria for ATP
no invaginations for ACh receptor gene
Leads to non functioning muscle cell
Sliding filament theory
- Ca2+ binds to TnC of troponin, and conformational change moves tropomyosin away from actin’s binding sites
- Myosin cross bridge attached to actin myofilament
- Myosin head pivots and bends as it pulls on actin filament, sliding it towards the M line. ADP and Pi released
- As the new ATP attached to the myosin head, cross bridge detaches
- As ATP is hydrolysed into ADP and Pi by ATPase, cocking of myosin head occurs
myosin molecule
Tail: binds to other myosin molecules
Head: made of 2 globular protein subunits and reaches the nearest thin filament
what are the two protein components of actin?
F - actin fibres
G - actin globules
what part of the sarcomere is devoid of myosin heads?
the centre of the sarcomere (M line)
when does the myosin head cock?
when ATP that was bound to it is hydrolysed
When muscle contracts, do actin and myosin filaments shorten? Does sarcomere shorten?
No, Actin and myosin dont shorten
Yes, The sarcomere does shorten
What’s the points of origin?
Bone, typically proximal, greater mass and more stable during contraction than insertion point
What’s the point of insertion?
Structure the muscle attaches to
Tends to be moved by contraction
Tends to be distal (part that moves)
Could be bone, tendon, connective tissue
Usually tendon to bone
Greater motion than origin during contraction
what are the 5 different muscle roles in movement?
-agonists- prime movers
-antagonists - oppose prime movers
-synergists - assist prime movers (alone they can’t perform movement, but their angle of pull assists)
-neutralisers- prevent unwanted actions that an agonist can perform
-fixators- act to hold a body part immobile whilst another part is moving. Stabilise a joint
what are the three different levers in biomechanics?
-first class (see saw)
-second class (wheelbarrow)
-third class (fishing rod)
First class lever system
fulcrum between load and effort
E.g. extension/flexion of head
second class lever system
load between fulcrum and effort
E.g. plantar flexion of foot
