Muscles Flashcards
What are the 3 types of muscles
- smooth muscle (for contraction and dilation, usuall on vessels)
- cardiac muscle
- striated muscle
What are the functions of skeletal muscle
- locomotion and breathing
- postural support
- heat production during cold stress
- largest protein store in the body (body will use proteins in these muscles in malnourished)
What are the key structural points of skeletal muscle fibres (cells)
- striated
- syncytium (multi nucleated cells)
- peripheral nuclei (nuclei found near the outside of the cell
What is a fasicle
- an bundle of muscle fibres
- multiple fasicles make up a muscle
what is epimysium
CT layer that surrounds the entire muscle
What is perimysium
CT that surrounds each fasicle
Why is CT important for muscles?
Functional (transfer of info) and protective
What is the sarcolemma
muscle cell membrane
what are myofibrils
rod-like structures that pack the filaments together. also known as a muscle fibre
what are myofilaments
what are the different kinds
threadlike strands within myofibrils
- Actin (thin filament) (proponin and propomyosin)
- myosin (thick filament)
what is a sarcomere
an individual unit conatining actin/myosin
Within a sarcomere, what are the different bands/lines called and what are they
- I-bands: actin filaments alone
- A bands: zones containing myosin
- Z line (or disc): defines boundary between sarcomeres
- M-line: transverse line in the middle of the sarcomere that binds the myosin filaments
What is the sliding filament theory
- muscle shortening occurs due to the movement of the actin filament over the myosin filament
- formation of cross-bridges between actin and myosin filaments
- reduction in the distance between Z lines of the sarcomere
What is involved in cross bridge formation and how do they work
- tropomyosin: located along the 2 chains of actin filaments and when calcium is low, blocks the binding of myosin to the actin and the fibre
- troponin: complex that is attached to each tropomyosin
Why is calcium important for muscle function
stimulates muscle contraction
what does troponin do
captures calcium and undergoes a conformational change that lifes tropomyosin away from the actin filament
What are the 3 different fast muscle fibres
- type 2a (fast oxidative)
- tpye 2b (fast glycolytic)
- type 2x (intermediate between a and b)
what are the slow muslce fibres
slow to contract
type 1 fibres (slow oxidative)
how are fibre type compositions within muscles analysed for identification
- immunochemistry (looks for cell markers)
- histochemistry (looks for ATPase activity which is positively correlated to muscle contraction velocity
- fibres have specific metabolic profiles
what is muscle fatigue
decreased maximum contractile force
- ATP is required for formation of cross bridges
- when muscles fatigue, inorganic phosphate increases and calcium decreases
What are the components of the motor unit
- a single alpha motor neuron and all of the corresponding muscle fibres it innervates
what are the key note about a motor unit
- all fibres in a MU innervated simultaneously
- all the same fibre type
- MU size dictates the level of control
- slow MU tend to be smaller and are recruited first during normal exercise
- hennemans size principle (as force increases, more larger MU recruited)
- in ballistic locomotion, faster MU can be recruited initially
label
What is acetylcholine and what is its function
- the chemical intermdiary in the transfer of excitation from nerve to muscle
- releases the synaptic vesicles (calcium triggers the release)
- ACh is then released into the synaptic cleft where it combines with ACh receptors causing depolarisation of the muscle cell and activates the ion channel for Na ions
- it is then rapidly broken down by acetylcholinesterase
what is a t-tubule system
- conducts action potentials from the cell surface to the core of the fibre
- in direct contact with the sarcoplasmic reticulum (SR) surrounding the myofibrils
- the membranes of the SR contain a type of Ca2+ channel called a ryanodine receptor
- voltage-sensitive channels are coupled to RR
- upon depolarisation they change conformation and open RR
how does action potential influence Ca2+ Release
- action potentional in t-tubule
- openes calcium channels in sarcoplasmic reticulum
- calcium released: casues mroe channels to open (calcium induced calcium release) this drives muscle contraction
- calcium pumped back into sarcoplasmic reticulum, relaxing muscle
whata re the receptors in the muscle
- muscle spindle
- golgi tendon organ
what are muscle spindles receptive to and what are they
- sensitive to stretch
- provide information on muscle length
- modified muscle fibres (intrafusal fibres, ONLY stretch and send data, do not take load)
what are the golgi tendon organ receptors receptive to
- monitor tension developed in muscle
- prevents damage during excessive force generation
- excessive stimulation results in reflex relaxation of muscle
what is hypertrophy
cells increasing in size
in mucscles cells: increase in myofibrils and myofilaments to enlarge the muscle cells
this is how we get growth of muscles
what is hyperplasia
increasing number of cells
What is Atrophy
a reduction in muscle volume or mass which may be generalised or limited to certain muscles
what factors cause hypertrophy and atrophy
- anabolic factors (building the muscle with mechanical load or steroid)
- catabolic factors (breaking down the muscle via disuse, denervation, disease, malnutrition)
how does mechanical stimulus produce an increase in fibre size
- IGF-1 (insulin like growth factor)
what are the 4 types of muscle pathology
- injury
- nerve damage
- disease
- aging
what is necrosis and how is it triggered in muscular injury
cell death
- in muscle injury when sarcolemma is torn or damaged there is an influx of calcium whihc triggers the nectrotic mechanisms
what cells are responisble for repairing injured muscle cells and how do they work to repair damaged muscle
satellite cells
- activated following damage
- proliferate and differentaite to form muscle cells and daughter cells
they sit btwn the sarcolemma and endomysium
what are the steps of nerve damage pathology in the muscles
- motor nerve gets damaged
- muscle lacks innervation
- muscle uncergoes atrophy
what is stringhalt disease
- onset of excessive felxion in 1 or both hindlimbs
- in severe cases causes muscle tetanises
- muscle atrophy
how do you detect muscle damage
myoglobinuria
- O2 binding protein in the muscle
- excessive amounts of myoglobin in the urine
- too much can cause kidney damage
creatine kinase
- enzyme used by muscles
- increased levels can indicate muscle damage or wasting (be careful with this one though as it can also be present shortly after moderate exercise)
what are the 2 noted inflammatory muscle diseases
- polymyositis
- masicatory muscle myositis (MMM)
what is polymyositis
- generalized inflamatory myopthay
- muscle damage is thought to be the result of cell-mediated immunity (immune system start to attack own muscles)
what is masticatory muscle myositis
- focal inflammatory myopathy that selectively affects the muscles of the mastication (chewing muscles)
- clinical signs include lock jaw, fox like contour to the head and prominence of the zygomatic arch
what is duchenne muscular dystrophy
- occurs in humans dogs and mice
- congenital and inherited disease
- mutation of the gene coding for the membrane protein dystrophin (x-linked recessive disorder)
- leads to degeneration/regeneration resulting eventually in the failure of the respiratory muscles
what are the 2 noted hypothyroidism
- hypothyroidism
- cushings disease (hyperadrenocorticism)
what is the effect of hypothyroidism to the muscles
- problems with carbohydrate metabolism which interferes with glycolitic metabolism
- muscle biopsies show atrophy type 2 fibres
- clinical signs include weakness, stiffness, reluctance to move and decreased exercise tolerance and muscle wastage
what is the effect of cushings diseas on the muscle
- selective atrophy of type 2 fibres
- breakdown of muscle proteins and inhibition of muscle protein synthesis
- clinical signs include weakness, stiff gait, muscle atrophy an inability to walk in dogs
what is an example of a nutrition myopathy
selenium and vitamin E deficiency
- clinical signs include still birth and weak calf (stiffness and inability to stand
- affects calves, lambs, swine and foals
- doesnt often affect carnivores
- can be treated with supplements over a course of 3 months but this is costly
what is sarcopenia
atrophy associated with aging
- loss of motor axons
- denervation
- degeneration/regeneration
- loss of motor fibres
- motor-unit size
- fibrosis
- IGF-1
