Lesson 20 The Muscular Tissue

Question 1

what is the purpose of muscles?

Answer 1

to contract and become small!

Question 2

what does the muscular system refer to?

Answer 2

skeletal muscles. NOT cardiac or smooth muscles

Question 3

what characteristics do muscle cells have?

Answer 3

• excitability (responsiveness)
• conductivity
• contractility
• extensibility
• elasticity

Question 4

what is the difference between conductivity and excitability?

Answer 4

excitability is the responsiveness to chemical signals, stretch, and electrical changes across the plasma membrane

conductivity is the local electrical excitation that sets off a wave of excitation that travels along the muscle fiber

Question 5

what are 2 other ways to call skeletal muscle cells?

Answer 5

muscle fibers or myofibers

Question 6

what are the 6 functions of skeletal muscle tissue?

Answer 6

1. produce skeletal movement
2. maintain posture and body position
3. support soft tissues
4. guard entrances and exits
5. maintain body temperature
6. store nutrient reserves

Question 7

what fibrous connective tissues does the skeletal muscle contain (deep to superficial)?

Answer 7

endomysium: surrounds each muscle fiber (thin layer)

perimysium: bundles muscle fibers into fascicles (thick layer)

epimysium: surrounds entire muscle, blends with fascia and deeper connective tissues

Question 8

what is fascia?

Answer 8

a sheet of connective tissue between muscles or muscle groups

Question 9

where does the endomysium, perimysium, and epimysium come together and what does it form?

Answer 9

it comes together at the ends of muscles and forms connective tissue attachment to bone matrix (ex. tendon (bundle) or aponeurosis (sheet))

Question 10

name the components of a muscle fiber

Answer 10

• sarcolemma: plasma membrane of fiber
• sarcoplasm: cytoplasm of fiber
• sarcoplasmic reticulum: smooth ER (stores calcium)
• terminal cisterns: sacs of SR crossing the fiber from one side to another (calcium reservoir)
• transverse tubules: tubular infoldings of sarcolemma; funnels action potentials generated towards terminal cisterns
• myoblasts: stem cells forming the fiber
• myosatellite cells: unspecialized myoblasts remianing between muscle fiber and endomysium

Question 10

why do skeletal muscle cells have multiple nuclei?

Answer 10

myoblasts contribute one nucleus. multiple myoblasts cause for multiple nuclei in the cell.

Question 11

what is inside the sarcoplasm?

Answer 11

• myofibrils: long protein cords (occupy most of sarcoplasm)
• glycogen: carbohydrate stored to provide energy for exercise
• myoglobin: red pigmented protein; storage for oxygen and provides some for muscle activity

Question 12

what are myofibrils composed of?

Answer 12

muscle filaments (myofilaments)

Question 13

what are the 3 kinds of myofilaments?

Answer 13

• thick filaments: made of several hundred myosin molecules
• thin filaments: made of 3 protein types
• elastic filaments: made of huge springy protein called titin

Question 14

what is myosin?

Answer 14

a motor protein

Question 15

what 3 proteins make up thin filaments?

Answer 15

• fibrous (F) actin: 2 intertwined strands of globular (G) actin
• tropomyosin: regulatory protein that blocks the active sites on G actin subunits
• troponin: small, calcium binding protein on each tropomyosin molecule

Question 16

what is a contractile protein and what are 2 examples?

Answer 16

contractile proteins do the work of contraction

myosin and actin are contractile proteins

Question 17

what is a regulatory protein and what are 2 examples?

Answer 17

regulatory proteins act like a switch that determines when the muscle fiber can and cannot contract

tropomyosin and troponin act as regulatory proteins

Question 18

how does contraction occur?

Answer 18

contraction is activated by the release of calcium from the SR into the sarcoplasm, which then binds onto troponin.
troponin changes shape and moves tropomyosin off active sites on actin allowing myosin head to bind onto actin

Question 19

why are there striations on muscles?

Answer 19

myosin and actin are organized in a precise array that account for striations

Question 20

what are striations made up of?

Answer 20

A-bands (dark) and I-bands (light)

Question 21

what is an A-band?

Answer 21

a dark band where thick filaments overlap a hexagonal array of thin filaments.

Question 22

what is the H band and the M line?

Answer 22

the H band is not as dark and is the middle of the A band; thick filaments only

the M line is a dark, transverse protein in the middle of the H band

Question 23

what is the I-band?

Answer 23

a light band; only thin filaments

Question 24

what is the Z disc (Z line)?

Answer 24

a protein complex that provides anchorage for thin filaments and elastic filaments

Question 25

what is a sarcomere?

Answer 25

a segment from Z disc to Z disc; functional contractile unit of muscle fiber

Question 26

how do muscle cells shorten?

Answer 26

they shorten because individual sarcomeres shorten. Z discs are pulled closer together as thick and thin filaments slide past each other

Question 27

do thick and thin filaments change length during shortening?

Answer 27

NO. only the amount of overlap changes as the thin filaments are pulled towards the M line

Question 28

what is the zone of overlap?

Answer 28

the area of the A band minus the H band (where thin and thick filaments overlap) this zone increases during muscle contraction

Question 29

what is denervation atrophy?

Answer 29

shrinkage of paralyzed muscle when nerve remains disconnected. the motor neuron is no longer stimulating the muscle cell

Question 30

how are nerves and muscles related?

Answer 30

skeletal muscles cannot contract unless they're stimulated by a nerve. if nerve connections are severed or poisoned, muscle is paralyzed.

Question 31

what neurons move skeletal muscle cells?

Answer 31

somatic motor neurons. axons of these motor neurons are somatic motor fibers, leading to the skeletal muscle.

Question 32

what is a motor unit?

Answer 32

one nerve fiber and all the muscle fibers innervated by it; they behave as a functional unit

Question 33

how do the muscle fibers of one motor unit act?

Answer 33

they contract in unison and produce weak contraction over a wide area. they provide the ability to sustain long term contraction as the motor units take turns contracting.

Question 34

true or false: effective contraction requires contraction of several motor units at once

Answer 34

TRUE

Question 35

what is the difference between small motor units and large motor units?

Answer 35

small motor units provide a fine degree of control (less muscle fibers) large motor units provide more strength than control (more muscle fibers)

Question 36

what is a synapse?

Answer 36

the point where a nerve fiber meets its target cell

Question 37

what is the synapse called when the target cell is a muscle fiber?

Answer 37

neuromuscular junction (NMJ) or motor end plate