11: Muscular System

Question 1

what is excitability?

Answer 1

the ability to receive and respond to a stimulus

Question 2

what is contractability?

Answer 2

the ability to shorten and exert a pull on other structures

Question 3

what is extensibility?

Answer 3

the ability to be stretched without damage

Question 4

what is elasticity?

Answer 4

the ability to return to the original shape after being stretched

Question 5

what are 4 basic properties (abilities) of muscle tissues?

Answer 5

excitability, contractability, extensibility, elasticity

Question 6

describe the structure of a skeletal muscle

Answer 6

multinucleated.
includes bundled muscle fascicles surrounded epimysium.
each cell in skeletal muscle tissue is a single muscle fibre, surrounded by a perimysium.

Question 7

what are myofibrils responsible for?

Answer 7

skeletal muscle contraction

Question 8

how does skeletal muscle contraction work?

Answer 8

following a nerve impulse, the A band and I band move closer together, increasing the zone of overlap and decreasing muscle length, causing a contracted muscle

Question 9

how are multinucleated skeletal muscle fibres formed?

Answer 9

fusion of myoblasts

Question 10

what are 3 functions of skeletal muscles

Answer 10

• skeletal movement
• posture and body position
• support
• control of entries and exits
• body temp
• nutrient reserve

Question 11

explain how skeletal muscles aid skeletal movement

Answer 11

they pull on tendons and move the bones

Question 12

explain how skeletal muscles improve posture and body position

Answer 12

tension in skeletal muscles maintain body posture

Question 13

explain how skeletal muscles support organs

Answer 13

muscle layers in abdominal wall and pelvic floor support organs and shield from injury

Question 14

explain how skeletal muscles control exits and entries

Answer 14

by encircling openings of digestive and urinary tracts, muscles provide voluntary control over swallowing, defecation and urination

Question 15

explain how skeletal muscles controls body temperature

Answer 15

contractions produce heat to maintain body temp in normal functioning range

Question 16

explain how skeletal muscles provide nutrient reserves

Answer 16

during undernutrition the contractile proteins in skeletal muscles break down and their amino acids are released into circulation to provide energy

Question 17

when do muscle cells regenerate?

Answer 17

normally mitotically quiescent (inactive), initiate proliferation in response to stress induced by injury to mediate regeneration

Question 18

what is hypertrophy?

Answer 18

an increase in individual muscle fibre size

Question 19

what is hyperplasia?

Answer 19

an increase in number of muscle fibres

Question 20

what is atrophy?

Answer 20

decrease in size of muscle

Question 21

describe the structure of cardiac muscle

Answer 21

single nucleus cells, branches and connected by intercalated discs.
smaller cells that possess less sarcomeres than skeletal muscle cells.

Question 22

explain how the control mechanism of cardiac muscles is involuntary

Answer 22

cardiac muscles do not rely on nerve activity to start a contraction.
specialised pacemakers establish a regular rate of contraction.
nervous system can alter pacemaker activity, but does not provide voluntary control over individual cells.
pacemakers can respond to hormones that modulate heart rate to control blood pressure

Question 23

can cardiac muscle cells regenerate?

Answer 23

no, because there is no counterpart to myosatellite cells of skeletal muscle. if myocardial cells die, they’re replaced by fibrous non-contractile scar tissue.

Question 24

describe the structure of smooth muscle

Answer 24

single nucleus, small and spindle shaped, no organised sarcomeres

Question 25

how do smooth muscles receive nerve signals?

Answer 25

autonomic nerve fibres branch diffusely on top of smooth muscle cells. instead of making direct contact, multiple varicosities are distributed along nerve fibre w vesicles containing neurotransmitters

Question 26

what are functions of smooth muscles?

Answer 26

- regulate movement of food, urine and reproductive tract secretions - control diameter of respiratory pathways - regulate diameter of blood vessels

Question 27

explain how control of smooth muscles is involuntary

Answer 27

contraction of some smooth muscle tissue can be controlled by nervous system but contractile activity is not voluntary a pacesetter cell can trigger action potentials and contractions in smooth muscle

Question 28

what are triggers of smooth muscle contraction?

Answer 28

hormones, neural stimulation, local factors like stretching

Question 29

can smooth muscle cells regenerate?

Answer 29

yes, they can divide

Question 30

how is the calcium signal for muscle contraction created?

Answer 30

-an action potential arrives at the neuromuscular junctions - ACh is released, opens sodium ion channels -> action potential depolarizes sarcolemma - this triggers release of calcium ions from sarcoplasmic reticulum storage - Ca++ initiates contraction, sustained by ATP

Question 31

how does the calcium signal initiate skeletal muscle contraction?

Answer 31

- binding sites for myosin on actin are partially blocked by tropomyosin, so myosin is only weakly bound to actin - calcium ions bind to tropomyosin, pulling it away from myosin-binding site - myosin head attaches to actin at binding site, creating the cross-bridge - hydrolysis of ATP to ADP + P causes myosin head to move actin (aka power stroke) - ATP binds to myosin and reconfigures the complexes to their relaxed states - multiple power strokes = contraction!!

Question 32

when and how does muscle contraction stop?

Answer 32

signalling from motor neuron ends - repolarises sarcolemma and t-tubules - closes voltage gated calcium channels, Ca++ pumped back into SR muscle can also stop contracting when it runs out of ATP = becomes fatigued

Question 33

describe the action potentials of skeletal muscles, cardiac muscles and neurons

Answer 33

skeletal: 0, depolarization, repolarization, 0 cardiac: 0, depolarization, drop the plateau, repolarization, 0 neuron: 0, depolarization, repolarization, 0, hypperpolarization, 0