Muscle tissue Flashcards
functions of muscle tissue:
movement, stability, storage/movement of substances within body, heat production
properties of muscle tissue:
- electrical excitability (chemical/ electrical stimuli)
- contractility (actin/ myosin sliding)
- extensibility (controlled stretching, protected by ct)
- elasticity (return to og size)
how does motion occur:
conversion of chemical energy (ATP) –> mechanical energy by contractile apparatus of muscle cells
contractile apparatus: made of
proteins actin and myosin
how does the 2 proteins create cellular contraction:
actin/ myosin form myofillaments, arranged parallel to direction of cell contraction
how do muscle cells respond to stimulus?
have excitable cell membrane, responds to stimulus = cellular contraction
muscle tissue term for: cytoplasm
sarcoplasm
muscle tissue term for: plasma membrane
sarcolemma, invaginated by (transverse) t tubules
- can pass action potentials
muscle tissue term for: sER
sarcoplasmic reticulum, stores and releases Calcium ions (key for action potentials)
list types of muscle tissueL
skeletal, cardiac, smooth
brief info/ contraction: skeletal
striated (striped), neatly arranged actin/ myosin
strong, quick discontinuous voluntary contraction
brief info/ contraction: cardiac
striated,
strong, quick continuous involuntary contraction
brief info/ contraction: smooth
not striated, irregular arrangement
weak, slow involuntary contraction
skeletal muscle features:
- very long tubular cells (myofibres/ muscle fibres)
- up of 30cm
- striated; cross striations
- voluntary: innervated (stimulated) by somatic nervous system
brief structure of muscle tissue:
muscle= many fascicles (muscle cell bundles)
surrounded by connective tissues: endomysium, perimysium, epimysium
define fascicle:
consists of myofibres
define myofibre:
consists of many myofibrils
define myofibrils:
bundles of myofilaments thick (myosin), thin (actin)
muscle tissue organisation: small to largest
myofilaments (proteins) -> myofibrils (organelles) -> myofibres (cells) -> muscle fascicle -> muscle
myofibre features: cross section/ structure/ glycogen
cross section: polygon shaped
- developed from myoblasts
- sarcoplasm (cytoplasm) surrounded by sarcolemma (plasma mem.) with 1-2 peripheral nuclei (just underneath sarcolemma)
- substantial glycogen
myofibre features: organelles/ myofilaments
- myoglobin (binds O2)
- mitochondria: rows throughout myofibres
- sarcoplasmic reticulum encircles myofibrils dilated at the end (sarcoplasmic cistern)
- myofilaments myosin (thick), actin (thin)
T tubules: features/ function
transverse tubules
- invagination of plasma membrane (1 T tubule), 2 cisternae of sarcoplasmic reticulum run between myofibrils at A-I junction = TRIAD
- allow electrical impulses to travel to deeper myofilaments
- rapid supply/removal of Calcium ions to myofibrils
define sarcomere (incl):
basic repetitive unit of contractile apparatus (between Z lines) including
- I band
- Z line
- line
- A band
- H band
I band:
actin not overlapping myosin
Z line:
disc in centre of I band, which actin extends from
A band:
all myosin (incl. lil overlapping of actin)
H band:
myosin not overlapping actin
endomysium:
loose connective tissue (reticular fibres) surrounding each muscle fibre
- has smallest capillaries and neuronal branches
perimysium:
dense irregular connective tissue, fat, blood vessels, nerves
- groups fibres into fascicles
epimysium:
dense irregular connective tissue envelopes muscles
- has large vessels and nerves
TENDONS
fascia:
large connective tissue sheet surrounding groups of muscles
list types of skeletal muscle fibres:
Type I: slow oxidative
Type II a: fast oxidative-glycotic
Type II b: fast glycotic
slow oxidative skeletal muscle fibres: features
Type I:
- smallest diameter
- least powerful
- large amount: myoglobin
- numerous capillaries
- uses ATP slowly
- slow contractions, resist fatigue, capable of long prolonged contractions
- aerobic cellular respiration
fast oxidative-glycotic skeletal muscle fibres: features
Type II a:
- medium size
- large amount: myoglobin
- numerous capillaries
- use ATP fast
- fast contractions, both aerobic/anaerobic cellular respiration, moderately resistant to fatigue
fast glycotic skeletal muscle fibres: features
Type II b:
- largest size
- small amount: myoglobin
- few capillaries
- fast, strong contractions, mainly anaerobic cellular respiration, lil resistance to fatigue
nerve supply in muscle tissue: bundle/ junction/ neurotransmitter/ features
neurovascular bundle: nerve and blood vessels usually enter muscle together
neuromuscular junction: synapse btw axon terminals of motor neuron -> sarcolemma
- ends on individual muscle fibres
neurotransmitter: acetylcholine (synaptic vesicles in synaptic end bulbs)
nerve supply: motor unit
neuron and innervated muscle cell
approx how many muscle fibres a single neuron innervates: eg
depending on location, few to many muscle fibres
- eye muscle> 1:3 muscle fibres
- erector spinae> 1:1000s of fibres
tendons features:
- dense regular connective tissue, abundant collagen fibres, few cells, lil ground substance
- densely packed fibres, collagen bundles
eg of neurotransmitter blockers:
botulinum toxin (Botox) curare
muscle-tendon junction:
collagen fibres (tendons) inserted into infoldings of sarcolemma
muscular atrophy and eg.
- disuse atrophy: from not using the muscles enough-> loss of muscle tissue
eg. bedridden, seated jobs - denervation atrophy: sudden atrophy, removal of nerve supply permanent muscular paralysis,
eg. from Guillain-Barre syndrome - hypertrophy: enlargement of muscles
eg. exercise
cardiac muscle: features
- 1 muscle fibre= 1 mononuclear cell, central nucleus and many (larger) mitochondria
- branched columns of cells
- surrounding muscle cells: delicate sheath of endomysial connective tissue -> rich in capillaries (no epimysium)
cardiac muscle: intercalated discs
attachments between muscle fibres (desmosomes-strong attachment and extensive gap junctions- communication)
- allows multiple cells to act together
- and transmission of electrical impulses between cells
cardiac muscle: T tubules
wider, but less abundant
- 1 T tubule with 1 small terminal cisternae of endoplasmic reticulum = diad structure
cardiac muscle: conduction system features
- action potential is created in the heart itself (creates muscle impulse)
SA: sinoatrial node,
AV: atrioventricular node,
atrioventricular bundle of (Hiss), conduction myofibres (Purkinje fibres, fewer myofibrils than surrounding muscle tissue)
- external influence: nervous (parasympathetic and sympathetic), hormonal stimulation = rate of contractions
smooth muscle features:
- surround walls of ducts, hollow organs, blood vessels, GIT etc.
- specialised: slow prolonged contractions
- smaller fusiform (longer rugby ball/ wider in middle) shaped cells, central cigar-shaped nuclei, 2-5 nucleoli
- no T tubules, small SR, only endomysium
smooth muscle: actin, myosin?/ electrical impulses
- diffused actin/myosin-> no striations, can’t differentiate each muscle fibre
- no close association: nerve endings and individual smooth muscle cells
- gap junction allow electrical impulse (action potential) travel between cells
regeneration: cardiac muscle
none beyond early childhood
regeneration: skeletal muscle
limited:
- after injury, satellite cells (skeletal m. precursor) activate, generate new myoblasts –> muscle fibres
- most sever injury repair: fibroblasts -> scar tissue
regeneration: smooth muscle
active regenerative response
steroids: build muscle mass fast
