CHAPTER 48 ~ Musculoskeletal Systems

Question 1

3 types of vertebrate muscle:

Answer 1

skeletal, cardiac, and smooth

Question 2

Skeletal muscle

Answer 2

“striated” cells are called muscle fibers; large, multinucleated cells formed by fusion of embrionic myoblasts. Each muscle fiber has several myofibrils.
- for mostly voluntary and some involuntary movement.

Question 3

Myofibrils

Answer 3

bundles of actin (thin) and myosin (thick) filaments (contractile proteins)
- consist of repeating units called sarcomeres

Question 4

sarcomeres

Answer 4

overlapping filaments of actin and myosin

Question 5

motor unit

Answer 5

all the muscle fibers activated by one motor neuron

Question 6

Sliding filament mechanism of muscle contraction:

Answer 6

ACh is released by the motor neuron at the neuromuscular junction, opens ion channels in the motor end plate, action potential travels into T-tubules, stimulates release of Ca2+ from sarcoplasmic reticulum, Ca2+ binds to troponin on actin filaments, conformational change pulls tropomyosin off of myosin binding sites on actin = myosin heads bind to actin w/ release of Pi = powerstroke, filaments slide past each other and ADP is released. ATP then binds to myosin, causing it to release actin. ATP is hydrolized, and myosin returns to it’s original position.

Question 7

Cardiac Muscle

Answer 7

also striated, smaller than skeletal, uninucleated; cardiac cells branch and interdigitate = can withstand high pressures.
- arranged in sheets, communicate via gap junctions = allow cytoplasmic continuity.

Question 8

pacemaker and conducting cells

Answer 8

initiate and coordinate heart contractions

Question 9

heartbeat

Answer 9

heartbeat is myogenic = generated by the heart muscle itself, no input from nervous system, although autonomic nervous system CAN modify rate of pacemaker cells.

Question 10

Smooth Muscle

Answer 10

uninucleated, smooth b/c actin and myosin not arranged so regularly; present in most internal organs (i.e. GI tract)

Question 11

twitch

Answer 11

minimum unit of contraction in skeletal muscle; single action potential generates a single twitch

Question 12

if action potentials are close together in time:

Answer 12

the twitches are summed, tension increases. Summed because Ca2+ pumps cannot clear Ca2+ from sarcoplasm before next action potential arrives

Question 13

Tetanus

Answer 13

when action potentials are so frequent that there is a constant presence of Ca2+ in sarcoplasm –> can be maintained as long as there is ATP supply; requires actin and myosin “cycling” to maintain contraction

Question 14

Muscles have 3 systems for obtaining ATP

Answer 14

immediate system, Glycolytic system, & Oxidative System

Question 15

Immediate system

Answer 15

uses pre-formed ATP and creatine phosphate - muscles contain CP which stores energy in a phosphate bond that can transfer to ADP. ==> exhausted within seconds

Question 16

Glycolytic system

Answer 16

metabolizes carbs to pyruvate and lactic acid, ATP available within a few seconds to replace immediate system, but low ATP yield, Anaerobic, and lactic acid accumulates.

Question 17

Oxidative Phosphorylation

Answer 17

becomes active within about a minute; produces large amounts of ATP.

• Aerobic = takes place in mitochondria, so requires O2
• slower than two systems, but can last much longer

Question 18

two types of skeletal muscle fibers:

Answer 18

slow-twitch and fast-twitch

Question 19

Slow-Twitch muscle fibers

Answer 19

contain myoglobin = oxygen binding protein

• oxidative, or ‘red’ muscle
• contain many mitochondria and well supplied with blood vessels
• max tension develops slowly but is highly resistant to fatigue = endurance and aerobic activities
• slow-twitch fibers have fat and glycogen stores, so can produce ATP as long as O2 available

Question 20

Fast-Twitch muscle fibers

Answer 20

• “glycolytic” or “white” muscle
• no myoglobin, few mitochondria and blood vessels
• develop max tension much faster, and max is higher than slow twitch, but fatigues VERY quickly = for sprinters

Question 21

Anaerobic Exercise

Answer 21

increases muscle strength, new actin and myosin filaments form, muscle gets larger

Question 22

Aerobic Activities

Answer 22

increase endurance, oxidative capacity is enhanced by increasing number of mitochondria, blood vessels, myoglobin, and enzymes.

Question 23

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Answer 23

muchas besitos, morgis