muscle contraction and function Flashcards
3 types of muscle tissue in the body
skeletal, smooth and cardiac muscle
each muscle is an organ composed of what ?
skeletal muscle tissue, blood and other connective tissues
what is fascia and its role
layers of dense connective tissue which surround and separate each muscle
fascia extends and give rise to ?
tendons which are fused to the periosteum of bones
what is aponeuroses
when muscles are connected to each other by broad sheets of connective tissues
what is the layer of connective tissue around each skeletal muscle
facia blending with epimysium
does perimysium extend inward
yes it extends inwards from the epimysium
what does perimysium do
surrounds bundles of skeletal muscle fibres called fascicles within each muscle
what is endomysium
each muscle cell fibre covered by a connective tissue layer
Describing muscle fibre
is a single, long, cylindrical muscle cell which responds to stimulation by contracting
the name of the cell membrane of a muscle fibre is ?
sarcolemma
the cytoplasm of a muscle cell is? and what does it contain?
sarcoplasm and it contains many mitochondria and nuclei
sarcoplasm contains what apart from mitochondria and nuclei?
parallel myofibrils, which are active in muscle contraction
what protein thick filaments in myofibrils contain
protein myosin
what protein is contained in think filaments in myofibrils
protein actin, troponin and tropomyosin
what is the name given to organisation of the filaments producing bands
striations
why darker image appears in skeletal muscles striations
it appears darker because actin and myosin overlap A band
I band is lighter
what are myofibrils made up of?
small units Called sarcomere that are joined end to end
sarcomere extends from where?
Z line to the next
what are I bands made up of
I bands are light
made up of actin filaments which are anchored to the Z lines
what are A bands are made up of
A bands appear dark, and there is a overlapping of thick and thin filaments
what zone is in the centre of A band
the centre of A band is H zone and it consists of myosin filaments only
where is the M line
M line is in the centre of the H zone
M line consists of what?
M line consists of proteins that hold the myosin filaments in place
where is sarcoplasmic reticulum
beneath the sarcolemma of a muscle fibre lies a network of membraneous channels
SR Is a what of muscle
endoplasmic reticulum
describe T tubules
lies between 2 cisternae of the SR and are open to the outside of the muscle fibre
how SR and T tubules work together
- by activating muscle contraction when fibre is stimulated
when skeletal muscle fibres contract
only when stimulated by a motor neuron
how synapses are created
each skeletal muscle fibre cell is functionally connected to the axon of a motor neuron
how neurons and muscle fibres communicate
by neurotransmitters which are released at synapse
how neurons communicate with the muscle fibre
neurotransmitters which released at synapses
what do you call a synapse between motor neuron and a muscle fibre which regulates.
neuromuscular junction
The cytoplasm of the distal end of the motor neuron contains what?
it contains numerous mitochondria and synaptic vesicles storing neurotransmitters
motor end plate
it is specialised area in the muscle fibre membrane
where sarcolemma tightly folded ?
in the motor end plate
what motor end plate contains
it contains specific receptors for the neurotransmitter
what happens when an electrical impulse reaches the end of the motor neuron axon?
synaptic vesicles release neurotransmitter into the synaptic cleft
what is synaptic cleft
the gap between the membranes of the neuron and muscle fibre
how muscle fibre contract
the neurotransmitter diffuses across the cleft and bind to the motor end plate and cause stimulation and muscle fibre contract
what are the events involved in muscle contraction?
shortening of sarcomeres and pulling of the muscle against it attachments
where is the pulling force exerted from?
by binding of myosin and actin molecules
shortening of a muscle fibre results from where?
from actin and myosin filaments overlapping as they slide pass each other
shortening of muscle fibres results in what?
it results in shortening of the entire muscle, which pulls on the skeleton to cause movement
describe myosin
consist of two twisted strands, with globular heads projected outward along the strands
how a thick filament is formed
by a group of myosin molecules
what is actin
a globular protein arranged in twisted filaments ( a double helix) , containing myosin binding sites
what are 2 proteins that are associated with the surface of actin molecules?
troponin and tropomyosin and all 3 proteins will form the thin filaments
how cross-bridge is made according to the sliding filament model of muscle contraction?
during a muscle contraction, myosin head attaches to a binding site on the actin filament which forms a cross-bridge
what does the binding between myosin to actin cause
it causes the head to bend, pulling an actin filament and moving it toward the centre of the sarcomere
what happens when filaments increase their overlap?
the sarcomere shortens from both ends
what happens when many sarcomeres shorten
at the same time muscle fibre shortens
what happens when ATP is broken down
it causes the heads to return to the cocked position ready to bind to another actin binding site
what is acetylcholine
is a neurotransmitter for skeletal muscle fibre contraction at the neuromuscular junction
where is acetylcholine produced and stored
it is produced in motor neuron and stored in synaptic vesicles at the distal end of the neuron
what does acetylcholine stimulate
muscle fibre
where is acetylcholine released into
acetylcholine is released into synaptic cleft in the response to an impulse in the motor neuron
what happens after muscle fibre impulse
the sarcoplasmic reticulum releases its stored calcium to the cytosol of the muscle fibre
where the stored calcium released into
released into cytosol of the muscle fibre
the high levels of calcium in the sarcoplasmic reticulum interacts with what?
with the troponin and tropomyosin molecules which move aside exposing the myosin binding sites on the actin filaments
explain the events after nerve impulse stops and lead to relaxation of the muscle
first the enzyme acetylcholinesterase on the motor end plate rapidly decomposes the acetylcholine
secondly, calcium is returned to the sarcoplasmic reticulum, using ATP as an energy source
3rd ATP now binds to the myosin heads breaking the linkages between myosin and actin
finally the actin returns to its original position and the muscle relaxes
what is a myogram
is the recording of an electrically stimulated muscle contraction
definition of latent period
brief delay of between the stimulation and beginning of the contraction
latent period is followed by?
by a period of contraction and a period of relaxation
what is all or none response
when a muscle fibre contracts it contracts to its full extent
muscle consist of a combination of both types:
- fatigue resistant slow twitch fibres
-fatigable fast twitch fibres
describe partial tetany
when exposed to higher frequency of stimulation, relaxation time becomes very short
describe complete tetanic contraction
if the frequency of stimulation is very high and the sustained contraction lacks any relaxation
partial tetany occurs in the body what about complete tetany
no it can only be accomplished in a lab
what is recruitment
an increase in the number of activated motor units within a muscle at higher intensities of stimulation
summation and recruitment together can produce what
sustained contraction of increasing strength
muscle tone is achieved by what?
a continues state of sustained contraction of a few motor units at a time within a muscle
muscle tone is important for?
maintenance of posture
types of smooth muscle cell
- multiunit smooth muscle
-visceral smooth muscle
describe multi smooth muscle
in blood vessels and iris of the eye, fibres occur separately rather than sheets; stimulated by neurons and some hormones
describe visceral smooth muscle
occurs in sheets and is found in the walls of hollow organs; these fibres can stimulate one another and display rhythmicity; these features accomplish peristalsis in tubular organs
name similarities between smooth and skeletal muscle contraction
- both involve reaction between actin and myosin
- both are stimulated by membrane impulses, require an increase in calcium ions in the cells, and use ATP energy
describe differences smooth and skeletal muscle contraction
- both Ach and norepinephrine stimulate and inhibit Smooth muscle contraction while only Ach stimulates skeletal muscle
-hormones can stimulate or inhibit contraction of smooth muscle but not skeletal muscle
- smooth muscle is slower to contract or relax
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