Lecture 17 - Muscle structure and function Flashcards
How do the types of muscle divide ?
Striated and non-striated
Striated is Skeletal - myoglobin present, voluntary control, direct nerve muscle communication
or Cardiac - myoglobin present, involuntary control, indirect nerve muscle communication
Non striated is smooth muscle - myoglobin abesnt, involuntary control, No direct nerve muscle communication
Outline the structure of Skeletal Muscle
- Epimysium(deep fascia) -Around muscles, creating muscle compartments
- Perimysium–Around fascicles
- Endomysium–Around individual muscle fibre
blood vessels in between fasicles
muscle compartments - give ya knowledge
limbs divided into compartments by deep fascia
- Trauma to one compartment can lead to compartment syndrome:
- Internal bleeding confined to a single compartment • Build up of pressure
- Compresses blood vessels and nerves, leading to ischaemia and pain
- Treated by fasciotomy–Relieves pressure
what is the role of myoglobin?
what is Rhabdomyolysis ?
Myoglobin is the O2 transport/breif storeage molecule in the striated muscle
Rhabdomyolysis - skeletal muscle necrosis due to a crush injury
myoglobin released into the kidney causes kidney damage
release of intracellular K+ —hyperkalamia
results in potentially fatal cardiac arrhythmias
give some knowledge on skeletal muscle histology
Cells are cylindrical, unbranched and multineucleate
neucli are lined along edges
mitochondria appear as long dark streaks
see stripes along the fibers - rest between the myofibirls
can have transverse and longnitudinal views - cut in different planes of muslce
fibers surrounded by a thin layer of connective tissue with cappilaires and nerves
describe / draw the structure of a Sacromere unit
what contracts the muscle
how does it contract
a sarcomere is Z band to Z band
made of central myosin and peripheral actins
H zone is the myosin only section
M line is the center of the sacromere and myosin unit
I band is the actin only section and Z band
A Band is total length of myosin unit , with Actin crossover
relaxed - larger H zone and I Band
Contract H zone and i band shrinks as actin and myosin come together
A band remains the same as its just myosin length
be able to identify zones on a histogram - check this
Explain the Striated Muscle Contraction and Sliding Filament Theory
- Myosin cross bridge attaches to the actin myofilament
ADP and Pi bound to the myosin head
Myosin head is in the high energy configuration
- Working stroke - myosin head pivots and bends as it pulls the actin filament sliding it toward the M line
ADP and Pi are released
- ATP joins to myosin head - now in low energy configuration - it is not bound to the actin fillament
ATP joining to the myosin head the cross bridge detached from actin
- As ATP hydrolyisis (split) occurs to create ADP and Pi bound to the Myosin Head
the myosin head is Cocked - ready to bind to thin actin filament - go to step 1.
this is triggered by ….
Ca2+ binding to troponin C
Tropomyosin Shifts from Actin, exposing the myosin binding sited
Myosin pulls actin fillaments towards M line via a sliding filament mechanism - this requires ATP hydrolysis
What is the T tubule system ?
Transverse tubules with terminal cisternae of SR (contains Ca2+) either side forms a traid, conntected by the branching cisternae struture
action potiential travels along t tuble and can cause ca2+ to be released into the nerve cell
singal from neurons will induce Ca2+ release over the contracting Sacrolemma
what is Excitation - contraction coupling ?
- Action potential of motor neurone reaches NMJ
- Depolarisation causes voltage-gated Ca2+ions to open, leading to Ca2+ influx and consequent release of ACh from the synaptic knob
- ACh binds to nicotinic AChRs, leading to Na+influx(voltage-gated Na+ channels also open) • Depolarisation spreads locally over sarcolemma and into T tubules
- Voltage-gated Ca2+channels open, causing Ca2+ release into sarcoplasm
- Calcium-induced calcium release (see ICPP)
- Ca2+ binds to troponin C and contraction cycle initiated
what is cardiac muscles structure ?
Histology ?
Cells are cylindrical branched - contract in both directions either side of an intercalated disc, to obtain a 3D contraction
central neucli - 1 or 2 per cell
branching system
no t-tubule system
only one cell - cardiomyocyte that communicate through gap junctions/intercalated disc
intercalated discs - Gap Junctions which couple neighbouring myocytes forming a functional syncytium
use of biochemical markers to do with the heart, what are they ?
• Cardiac troponin I/T -Gold standard for diagnosing MI • Released by necrotic cardiac myocytes
- Creatine kinase (CK) –Can be raised due to: • Myocardial infarction
- Rhabdomyolysis
- Intramuscular injection
- Vigorous physical exercise
what is the structure of smooth muscle
• Cells are spindle-shaped (fusiform) with a single central nucleus
• No sarcomeres or T tubules
Strechy
• Contraction still relies on actin-myosin interactions –More sustained, requires less ATP - via a cross lattice structure in the cell, causing tightening
little dots on histogram are called dense bodies
smooth muscle is in gut and around arterioles/capillaries
what is the basic principle of muscle growth and repair ?
- Striated muscle cells –Cannot divide, but can increase in size (hypertrophy)
- No regenerative capacity
- Smooth muscle cells – Can divide
- Can regenerate
name and define your sarco terminology
Sarcolemma: The outer membrane of a muscle cell
Sarcoplasm: The cytoplasm of a muscle cell
Sarcosome: The mitochondrion
Sarcomere: The contraction unit in striated muscle
Sarcoplasmic reticulum: The smooth endoplasmic
reticulum of a muscle cell
what are the types of muscle fibers
slow, fast and intermediate
explain the differences between the slow and fast and intermediate muscle fibers ?
each fascicle will have at least one of each
Slow twitch - are red - lots of myoglobin, lots of energy production - many mitochondira and cytosomes
Fast twitch are white -quicker to use then stop - eyelid muscles blinking
Slow fibers - smaller diameter , fast fibers thicker diameter
Fast fibers - larger colour , fatigue easily
what are pukunjie fibers ?
Not vital
Purkinje fibres are large cells with:
- abundant glycogen
- sparse myofibrils
- extensive gap junction sites
The Purkinje fibres conduct action potentials rapidly (3-4 m/s, compared to 0.5 m/s for cardiac muscle fibres)
This rapid conduction enables the ventricles to contract in a synchronous manner
differences and similarities of smooth muscle and cardiac
Differences
• Smooth muscle does not contain sarcomeres
• Electrical conduction - specialised cells/routes in cardiac muscle
• No troponins in smooth muscle
In common • Nuclei are central not peripheral • Only one contractile cell type • Act as a syncytium (wave-like function) • Myocytes communicate through g
what is the the thin fillament made of
formed of actin
tropononinc (tnI,TNc(Ca2+ binds), Tnt)
tropomyosin
ca2+ binding to Tnc - conformational change - moves myosin out the way from actin binding site - mysoin head can bind
what is different about the center of the sacromere
myosin is devoid of myosin head,so binding cannot occur
summaries the whole contraction process from ach releas to contraction ?
howd it go ?
what is muscular hypertrophy ?
muscle growth
Overstretching
such that the A and I bands can no longer re-engage
• New muscle fibrils are produced
• New sarcomeres are added in the middle of
existing sarcomeres
• New muscle fibres arise form mesenchymal cells
what is muscular atrophy
muscle loss
Disuse
e.g. bed rest, limb immobilisation, sedentary behaviour, age, etc.
Surgery
e.g. denervation of muscle
Disease
Muscular dystrophies
• Loss of protein, reduced fibre diameter, loss of muscle power
what are the clinical correlates of muscle dysfunction ?
• Duchene muscular dystrophy - mutation to dystrophin - too much Ca2+ enters cells - cell lysis
creatine kinase and myoglobin very high in blood
Muscle cells replaced by adipose tissue
• Rhabdomyolysis
• Myocardial infarction - creatine kinase or TnI is high in blood if this has happened
• Botulism and organophosphate poisoning - sludge and mtwtf
