Muscle Structure Flashcards
What is the typical vasculature of a muscle like?
Sometimes a single artery enters the muscle belly
Sometimes two or more arteries will enter and join up
Intramuscular arteries expand into capillaries
What is the typical vascularature of a muscle
Some have just one artery running into muscle belly
Some have more than one artery and they meet up
Intramuscular arteries expand into capillaries
What is an anastomosis?
surgical connection between two structures. It usually means a connection that is created between tubular structures, such as blood vessels or loops of intestine.
What is the inervature of the muscle like/
Single nerve branches out into connective tissue
Have motor neurons and sensory neurons
Has neuromuscular junctions
What are synergists/
Muscles that don’t facilitate or oppose a movement, but may effect it
What are fixators?
Muscles that stabilise a joint but doesn’t move it
What is the orgiin
Most proximal POA
What is the insertion?
Most distal POA
Where are skeletal muscles located?
Trachea, arteries
What are the 4 functions of skeletal muscle?
Locomotion and breathing
Posture and support
Heat production during cold stress
Largest protein store in the body
What is the structure of skeletal muscles like
Striated
Synctium (multinucleated)
Peripheral nuclei (at edge)
What are fasicles?
Bundles of muscle fibres
How big is each muscle fibre/
10-100 um in diameter
Up to 30cm in length
What is the epimysium
Surrounds whole muscle
What is the perimysium>
Surrounds bundles of muscle fibres (fascicles)
What is the endomysium
Surrounds individual muscle fibres
What is the sarcolemma?
Muscle cell membrane
What are Myofibrils
Myofibrils are long filaments that run parallel to each other to form muscle (myo) fibers. The myofibrils, and resulting myofibers, may be several centimeters in length. The muscle fibers are single multinucleated cells that combine to form the muscle. Myofibrils are made up of repeating subunits called sarcomere
Tubular structures that pack the fibres
What are myofilamwnts?
Threadlike strands within the myofibrils
Actin and myosin
What is the I band?
Actin alone
What is the A band
Myosin and actin (ambos)
What is Z lime?
End of sarcomere
Defines boundaries
What is H zone
Myosin only
How do muscles contract?
Calcium binds to troponin
Causes tropomyosim to change shape and move away from myosin binding site on actin
Cross bridge bwteeen actin and myosin forms
ATP —> ADP + P breaks cross bridge
What are the three different types of fast fibres
Type IIa
Type IIb
Type 11x
How can you distinguish between different muscle fibre types
Each fibre type has a specific immunohistochemistry
Specific histochemistfy (ATPase activity)
Specific metabolic profiles
What is the following like for type I fibres? (Slow oxidative)
Size of motor unit
Itodhondira
Fatigue resistant
Speed of contraction
Typical functions
Small
Many
High
Low
Posture
What is the following like for type IIa fibres? (Fast oxidative)
Size of motor unit
Itodhondira
Fatigue resistant
Speed of contraction
Typical functions
Intermediate
Many
Intermediate
Moderate
Walk, run
What is the following like for type IIx fibres? (Fast glycolytoc fibres)
Size of motor unit
Itodhondira
Fatigue resistant
Speed of contraction
Typical functions
Large
Moderate
Low
High
Jump, throw
What is the following like for type II b fibres? (Very fast glycolytic fibres)
Size of motor unit
Itodhondira
Fatigue resistant
Speed of contraction
Typical functions
Very large
Few
Very low
Very high
Jump, throw
What is muscle fatigue and what are the causes of it?
Decrease in maximum contractile force
No ATP for formation of cross bridges
Increase in inorganic phosphate
Decrease in Ca2+
What is a motor unit?
Single motor neuron and all of the muscle fibres it innervates
All fibres innervated simulataneously
All same fibre type
How does the neuromuscular junction work?
Action potential at end of neuron stimulates Ca2+ channels to open
Ca2+ channels open and causes vesicles carrying acetylcholine to move to membrane
Acetylcholine moves across synapse and binds to Na+ channels
Na+ enters in membrane of muscle
What breaks down acetylcholine
Acetylcholinesterase
What will happen if drugs act at Ach receptor
Muscle will stay relaxed
What do antiacetylcholineestersse drugs do
Prevent breakdown of acetylcholine so more activation of muscle
What do t tubules do?
Help spread single from motor neuron throughout muscle
What channel does sarcoplasmic reticulum contain?
Ryanodine receptor for Ca2+
How do t tubules help muscle contraction
Action potential in t tubules
Opens Ca2+ in sarcoplasmic reticulum
Ca2+ releases indices more Ca2+ to be released
Them Ca2+ pumped back into SR
What are the two types of receptors in muscles/
Muscle spindles
Golgi tendon organ
What are muscle spindle fibres
Provide information on length of muscle and how quickly it is changing (velocity)
Sensory neurons in fibres to detect this
Uensitive to stretch
What are Golgi tendon organs?
Monitor tension developed in muscle
Prevents damage during excessive force generation
What is an aponeurosis
A flat sheet of muscle with flat tendons
What is the structure of a smooth muscle like?
Single centrally located nucleus
No striations
Where would you find smooth muscle
In viscera (internal organs)
Blood vessels
Uterus wall
What controls each type of muscle
Skeletal- somatic
Cardiac/ smooth- autonomic
What can stimulate smooth muscle to contract
Hormones
Neuronal communication
What is the structure of skeletal muscle like?
40cm in length
100um in diameter
Multinucleated at periphery
Striations
What are the two types of skeletal muscles
Slow twitch
Fast twitch
What is the structure of cardiac muscle like?
Up to 90um in length
Up to 15um in diameter
One or two nuclei in centre of cell
Show striations
Cardiomyocytes are often branched for cell to cell connectiin
What happens to muscle structure is immobilised?
Sarcomeres deleted
What is hypertrophy and hyperplasia?
Hypertrophy- cells increasing in size
Hyperplasia- increasing number of cells
How do muscles grow?
Due to hypertrophy
Muscle fibre increases in size, increase in myofibrils and myofilaments
What factors can cause hypertrophy in muscles?
Building up the muscle
Anabolic steroids
What factors cause atrophy (breakdown of muscles)
Disuse
Denervation
Disease
Malnutrition
How does a mechanical stimukus increase muscle size?
IGF 1 causes:
satellite cell profilerstiom
Protein synthesis (myosin and actin)
What is the problem with IGF 1?
Cause cause too much cell proliferation, so results in tumour production
Why does necrosis of muscle cells occur?
Torn/ damaged sarcolemma
Influx of Ca2+, which triggers necrotic mechanisms
What is the function of satellite cells and where are they?
Activated following damage
Profilerste and differentiate to form muscle cells and daughter cells
In between sarcolemma and endomysium
What is stringhalt?
Onset of excessive Flexion in one or both hind limbs
Causes severe muscle spasms (tetanises)
Muscle atrophy
Most likely by nerve damage, and muscles stay fully contracted
What is neuropathy of the laryngeal muscles?
Only affects left muscles, as left recurrent laryngeal nerve goes round aorta so more likely to get damaged
Affects ability to open glottis (opens into windpipe)
Turbulent air flow, so causes roaring
How can you detect muscle damage?
Myoglobinuria —>check urine for myoglobin (like heamoglobin in muscle, binds to O2), too much can indicate muscle damage and could cause kidney damage
Creatine kinase —> enzyme used by muscles, but not specific. Increase levels can indicate muscle damage or wasted
What is polymyosistois?
Generalised inflammatory myopathy
Due to over active immune response, from cell mediated
What is masticating muscle myositis?
Focal inflammatory myopathy, only affects muscles in jaw for chewing
Lock jaw
Prominence of zygomatic arch (cheekbone)
What is Duchenne Muscular dystrophy?
Congenital/ inherited myopathy
Occurs in dog, humans and mice
Mutation in the gene coding for membrane protein dystrophin
Links to degeneration of respiratory muscles
What are the two examples of endocrine myopathies
Hypothyroidism —> stiffness, weakness, muscle wastage, atrophy of type II fibres
Cushing disease —> muscle weakness, stiff gait, muscle atrophy and inability to walk in dogs. Atrophy of type II Fibres, inhibition of muscle protein synthesis
What is selenium/ vitamin D deficiency
Still birth/ weak calf
Doesn’t usually affect carnivores
What is sarcopenia
Atrophy associated with ageing
Due to loss of motor neurons
Degeneration
Loss of motor fibres
Fibrosis—> build up of connective tissue
