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121 > L13. Muscles > Flashcards

L13. Muscles Flashcards

1
Q

Three types of muscle tissue

A

SMOOTH MUSCLE- in the walls of organs, moves the contents of organs
CARDIAC MUSCLE- contractile component of the heart
SKELETAL MUSCLE- attaches and moves the skeleton

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2
Q

Characteristics of muscle tissue

A

RESPONSIVENESS- when stimulated, muscle cells will respond with electrical changes across the plasma membrane
CONDUCTIVITY- stimulation of a muscle fibre will trigger a wave of excitation which travels along the fibre
CONTRACTILITY- ability to shorten when stimulated
EXTENSIBILITY- ability to stretch out again between contractions
ELASTICITY- ability to recoil to original length when tension is released

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3
Q

Skeletal muscle

A
  • voluntary
  • appears striated (striped) under microscope
  • muscle cells/ fibres are long, thin and cylindrical
  • multinucleated
  • moves the skeleton
  • produces heat
  • attaches to bone via tendon
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4
Q

Function of skeletal muscle

A
  • produces movement (shortens > levers bones > movement)
  • maintain posture
  • stabilises joints
  • generates heat
  • protects viscera
  • storage of glycogen
  • guards body entrances and exits
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5
Q

Smooth muscle

A
  • involuntary
  • lacks striation
  • muscle fibres are relatively short
  • single nucleated
  • “fusiform” or spindle shaped
  • form layers in the walls of hollow organs (digestive, respiratory, urinary tracts, blood vessels, uterus, etc)
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6
Q

Function of smooth muscle

A
  • moves contents of organs*
  • churning and mixing action of the stomach
  • propulsion of food along the GIT
  • contraction of the uterus during childbirth
  • vasodilation/ constriction of blood vessels, etc
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7
Q

Cardiac muscle

A
  • specialised muscle tissue that has properties of both smooth muscle and skeletal muscle
  • involuntary
  • striated and branched
  • cells called myocytes; short and thick
  • single nucleated
  • localised to the heart
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8
Q

Single skeletal muscle organisation

A

MUSCLE FIBRE (CELL)- bunch of myofibrils wrapped in endomysium
MUSCLE FASCICLE- bunch of muscle fibres wrapped in perimysium
MUSCLE- bunch of fascicles wrapped in epimysium

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9
Q

Components of muscle cell

A
  • myofibrils
  • sarcolemma (plasma membrane)
  • sarcoplasm (cytoplasm)
  • sarcoplasmic reticulum (sacs containing calcium)
  • Transverse tubules
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10
Q

Myofibrils

A
  • each muscle fibre contains myofibrils arranged lengthways
  • each myofibril contains myofilaments:
    > myosin (thick)
    > actin (thin)
    > titin (elastic)
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11
Q

Sarcomere

A
  • repeating unit that occurs the length of a myofibril
  • the patterning gives striated appearance in skeletal muscle
  • a sarcomere extends from one z-line to the next z-line
  • actin and myosin overlap each other in the sacomere
  • titan don’t allow overstretch
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12
Q

Transverse tubules

A
  • narrow tubes which extend from the surface of the sarcolemma deep into the sarcoplasm
  • conduct action potentials
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13
Q

Sarcoplasmic reticulum

A
  • similar to endoplasmic reticulum
  • membranous sacs filled with calcium
  • surrounds myofibrils
  • bound to T-tubules
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14
Q

4 steps in muscle contraction

A
  • excitation
  • excitation/ contraction coupling
  • contraction
  • relaxation
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15
Q

Neuromuscular junction

A
  • where the nerve meets the muscle (synaptic cleft)
  • SYNAPTIC KNOB (axon terminal) of neuron meets with the motor end plate of the muscle
  • synaptic knobs release neurotransmitter (ACh)
  • ACh diffuses across the synaptic cleft
  • ACh receptors located in junctional folds on motor end plate bind with ACh
  • Impulse is passed onto the muscle, stimulating it to contract
  • ACh is then broken down by AChE, stops impulses
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16
Q

Excitation

A
  1. nerve impulses arrives
  2. causing calcium channels to open
  3. calcium moves into the neuron causing the vesicles to fuse with the plasma membrane to release neurotransmitter
  4. neurotransmiter binds to receptor
  5. receptors open, allowing more sodium in and potassium out
  6. restart another action potential on the muscle
17
Q

Excitation/ Contraction Coupling

A
  1. The AP spreads from the motor end plate to all over the muscle fibre
  2. When the AP reaches a T-tubule, it continues down into the sarcoplasm, reaching the sarcoplasmic reticulum
  3. this triggers the sarcoplasmic reticulum to release calcium
  4. calcium release exposes the binding site on actin
  5. this allows myosin heads to bind to actin
18
Q

Contraction

A
  1. myosin binds to an ATP molecule and hydrolyses it to ADP > release energy which is used to “spring load” the myosin head
  2. The “loaded” myosin heads then bind to the exposed actin filaments, forming cross-bridges
  3. myosin pulls along the actin, releasing the ADP- “power stroke”
  4. myosin will bind to another ATP molecule, detach from actin, “re-load” (recovery stroke) the head, attach to new active site on actin and repeat the cycle> sarcomere shorten= contraction
19
Q

Relaxation

A
  1. Nerve impulses stop arriving at the NMJ so no more ACh is released by the synaptic knob
  2. ACh dissociates with its receptors and is broken down by AChE
  3. calcium in the cytosol is now actively pumped back into the SR for storage
  4. calcium dissociates from actin
  5. binding site is no longer exposed so no more cross bridge with myosin
  6. relaxation occurs due to elastic recoil as well as action of the antagonist muscle

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