muscle structure and function Flashcards
(12 cards)
connective tissue covering
- layers of dense connective tisse, called fasia, sorround and separate each muscle
- this connective tissue extends beyond the ends of the muscle, and gives rise to tendons that are fused to the periosteum of bones
- somtimes muscles are connected to each other by broad sheets of connective tissues called aponeuroses
- fasia vlends with the epimysium, the layer of connective tissue around each skeletal muscle
- the perimysium extends inward from the epimysium, it surrounds bundles of skeletal muscle fibers called fascicles
- each muscle cell is covered by a connective tissue layer called endomysium
skeletal muscle fibers
- each muslcloe fibre is a single long cylindrical muscle cell which responds to stimulation by contractiong
- the cell membrane of a muscule fiber is the sacolemma
- the cytoplasm of the muscle cell is the sacroplasm containing mitochondria and nuclei
- the sacrocplasm contains parallel myofibrils which are active in muscle contraction
- thick filamnets in myofibrils consist of the protein myosin
- thin filaments in myofibrils constist of the protien actin but also tropin and tropomyosin
- organisation is striations
sarcomeres of the myofibrils
- myofibrils are made up of many units called sarcomeres joined end to end
-a sarcomere extends from one Z line to the next - striations consist of an altering pattern of light and dark bands
- l bands are made up of actin filaments which are ancored to the Z lines
- A bands are made up of overlapping thick and thin filamenys
– in the center of the A band is the H zone which consists of myosin filaments only - the M line in the centre of the H zone
- sarcoplasmic reticulum which is the endoplasmic reticulum of the mucle cell
- the SR is associated with transverse tubules invaginations of the sarcolemma
- each T tubules lies between 2 cisternae of the SR and are open to outiside of the muscle fiber
- the SR and T tubules activate muscle contraction when the fiber is stimulated
neuromusculatar junction
- skeletal muscule fibers contacts only when stimulated by a motor neuron
- each skeletal muscle fiber is functionally connected to the axon of a motor neuron creating a synapse
- the neuron communicates with the muscle fiber by way of chemicals called neurotransmitters released by synapse
- neuromuscular junction - a synapse between a motor neuron and muscle fiber it regultes
- the cytoplasm of the distal end of the motor neurone contains numerous mitocondria and synaptic vesicles storing neurotransmittters
- the motor end plate is where the sacrolemma containg specific receptor for the neurotransmitter
- when an electrical impluse reaches the end of the motor neuron axon the synaptic vesicles release neurotansimitter into the synaptic cleft
- neurtotransimitter diffuses across the cleft vind to the motor end plate and stimulate the muscle fibre to contract
overview of muscle contraction
1.an impulse travels down a motor neuron axon
2. releases ACH
3. ACH binds to receptors in mucle fibres
4. sarcolemma is stimulated and impluse travels over the surface of the muscle fiber and deep into the fiber though transverse tubes
5. impulse reaches the sarcoplasmic reticulum and ca2+ cannels open
6. ca2+ ions diffuse form the sarcoplasmic reticulum into cystol and bind to troponin molecules
7. tropomyosin molecules move and expose specific sites on acitn where myosin heads can bind
8. cross bridges form linking think and thin filaments
9. thin filaments are pulled up towards the center of the sarcomere by pulling of the cross bridges
10. the muscle fibres exert a pulling force on its attatchmenst as a contraction occurs
muscle relaxation
- acetylcholinesterase decomposes ACH and muslce fiber is no longer stimulated
- ca2+ ions are actively transported into sarcoplasmic recticulm
- ATP breaks down cross- bridge linkages between actin and myosin filamenants without the breakdown of ATP itself
- breakdown of ATP cocks the myosin heads
- troponin anf tropomyosin molecules block interaction between myoisn and acin filaments
- the muscle fibre is relaxed until stimulated
threshold stimulus
the minimum strength of stimulus requried to generate an implus through muslce relase of ca2+ ions activate ccross bridges and contract the muscle
latent period
brief delay in between the stimulation and begining of contraction
summation
allows for a greater force of contraction than a single twitch can genertae
- relaxtion time is short called partial tetany
recruitment of motor units
a mucle achieves maximum tension when all of its mortor units have been recruited
smooth muscle
- are elongated with tapered ends, lack striations and have a relatively undevelpoed sarcoplasmic reticulum
- contain thick and thin filaments but randomly arranged
invloves actin and myosin
increase in ca2+
use aRP for energy
diffrences
can be stimukated by Norepenerphine
slower to contract
maintains contraction for longer
cardiac muslce
branching striated cells that interconnect in 3 D network
diffrences:
- sarcoplamic reticulum is not well develpoed not much ca2+
- transerverse tubules supply extra ca2+ from fuild twitches last longer
- self exiting and rhythmic
- intercalated discs transmit force of contraction from one cell to the next
